WO2023141468A2

WO2023141468A2 - Compositions for forming three-dimensional objects and methods thereof

Info

Publication number: WO2023141468A2
Application number: PCT/US2023/060843
Authority: WO
Inventors: Hany Basam Eitouni; Katrina Irene PATERSON; Scott Allen MULLIN
Original assignee: Holo, Inc.
Priority date: 2022-01-19
Filing date: 2023-01-18
Publication date: 2023-07-27
Also published as: WO2023141468A3

Abstract

The present disclosure provides mixtures and methods thereof for forming a three-dimensional (3D) object. In an aspect, the mixture can comprise one or more polymeric precursors configured to form a polymeric material. The mixture can further comprise one or more metal particles. The mixture can further comprise one or more hollow particles.

Description

COMPOSITIONS FOR FORMING THREE-DIMENSIONAL OBJECTS AND

METHODS THEREOF

CROSS-REFERENCE

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/300,915, filed January 19, 2022, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Three-dimensional (3D) printing techniques have been rapidly adopted for many different applications, such as rapid prototyping and fabrication of specialty components. Some 3D printing technologies print with metal or ceramic particles mixed with organic compounds (e.g., polymers) to create green parts that are in the shape of a 3D object. These green parts may undergo a de-binding process, e.g., through thermal decomposition in an open furnace, to selectively remove the organic compounds while holding in place the metal or ceramic particles in a desired shape, and then a sintering operation to fuse the metal or ceramic particles together to form the 3D object.

SUMMARY

[0003] The present disclosure provides mixtures for forming a three-dimensional (3D) object, methods thereof, and systems for using such mixtures for forming the 3D object. The 3D object formed from the mixtures of the present disclosure can comprise a polymer and a hollow particle.

[0004] In an aspect, the present disclosure provides a mixture for forming a three- dimensional (3D) object, the mixture comprising: one or more polymeric precursors configured to form a polymeric material; one or more metal particles; and one or more hollow particles. [0005] In some embodiments of any one of the mixtures disclosed herein, the one or more hollow particles comprise a plurality of porous particles. In some embodiments of any one of the mixtures disclosed herein, an average porosity of the one or more hollow particles is at least about 10%. In some embodiments of any one of the mixtures disclosed herein, an average porosity of the one or more hollow particles is at least about 20%. In some embodiments of any one of the mixtures disclosed herein, an average porosity of the one or more hollow particles is at least about 40%.

[0006] In some embodiments of any one of the mixtures disclosed herein, the one or more metal particles (Pl) and the one or more hollow particles (P2) are present in the mixture in a volume ratio (P1 :P2) of at least about 0.1. In some embodiments of any one of the mixtures disclosed herein, the volume ratio (P1 :P2) is at most about 60. In some embodiments of any one of the mixtures disclosed herein, the volume ratio (Pl :P2) is between about 0.4 and about 50. In some embodiments of any one of the mixtures disclosed herein, the volume ratio (Pl :P2) is between about 0.5 and about 40. In some embodiments of any one of the mixtures disclosed herein, the volume ratio (P1 :P2) is between about 1 and about 10.

[0007] In some embodiments of any one of the mixtures disclosed herein, the Pl is present at an amount of between about 10% and about 60% by volume of the mixture.

[0008] In some embodiments of any one of the mixtures disclosed herein, the Pl is present at an amount of between about 20% and about 50% by volume of the mixture.

[0009] In some embodiments of any one of the mixtures disclosed herein, the P2 is present at an amount of between about 1% and about 50% by volume of the mixture.

[0010] In some embodiments of any one of the mixtures disclosed herein, the P2 is present at an amount of between about 2% and about 40% by volume of the mixture.

[0011] In some embodiments of any one of the mixtures disclosed herein, the one or more metal particles (Pl) and the one or more hollow particles (P2) in the mixture have an average particle size ratio (P1 :P2) of at least about 0.1. In some embodiments of any one of the mixtures disclosed herein, the average particle size ratio (P1 :P2) is at most about 60. In some embodiments, the average particle size ratio (P1 :P2) is between about 0.2 and about 30.

[0012] In some embodiments of any one of the mixtures disclosed herein, the Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

[0013] In some embodiments of any one of the mixtures disclosed herein, the Pl has an average particle size of between about 2 micrometer to about 100 micrometers.

[0014] In some embodiments of any one of the mixtures disclosed herein, the P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

[0015] In some embodiments of any one of the mixtures disclosed herein, the P2 has an average particle size of between about 10 micrometers and about 200 micrometers.

[0016] In some embodiments of any one of the mixtures disclosed herein, the one or more metal particles (Pl) and the one or more hollow particles (P2) are present, in combination, at an amount of greater than about 15% by weight of the mixture.

[0017] In some embodiments of any one of the mixtures disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 20% by weight of the mixture.

[0018] In some embodiments of any one of the mixtures disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 40% by weight of the mixture.

[0019] In some embodiments of any one of the mixtures disclosed herein, the amount of the P1 and the P2, in combination, is greater than about 60% by weight of the mixture.

[0020] In some embodiments of any one of the mixtures disclosed herein, the Pl is present in an amount of between about 65% and about 95% by weight of the mixture.

[0021] In some embodiments of any one of the mixtures disclosed herein, the Pl is present in an amount of between about 70% and about 90% by weight of the mixture.

[0022] In some embodiments of any one of the mixtures disclosed herein, the P2 is present in an amount of less than about 1% by weight of the mixture.

[0023] In some embodiments of any one of the mixtures disclosed herein, the P2 is present in an amount of less than about 0.5% by weight of the mixture.

[0024] In some embodiments of any one of the mixtures disclosed herein, the mixture further comprises at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors.

[0025] In some embodiments of any one of the mixtures disclosed herein, the mixture further comprises at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0026] In some embodiments of any one of the mixtures disclosed herein, the hollow particle is a polymeric hollow particle.

[0027] In another aspect, the present disclosure provides a method for forming a three- dimensional (3D) object, the method comprising: (a) providing a mixture comprising: one or more polymeric precursors configured to form a polymeric material; one or more metal particles (Pl); and one or more hollow particles (P2); (b) exposing the mixture to a stimulus to cause the one or more polymeric precursors to form the polymeric material that at least partially encapsulates the metal particles and the hollow particles, thereby to form a green part corresponding to at least a portion of the 3D object.

[0028] In some embodiments of any one of the methods disclosed herein, the one or more hollow particles comprise a plurality of porous particles. In some embodiments of any one of the methods disclosed herein, an average porosity of the one or more hollow particles is at least about 10%. In some embodiments of any one of the methods disclosed herein, an average porosity of the one or more hollow particles is at least about 20%. In some embodiments of any one of the methods disclosed herein, an average porosity of the one or more hollow particles is at least about 40%.

[0029] In some embodiments of any one of the methods disclosed herein, the mixture is provided adjacent to a print window.

[0030] In some embodiments of any one of the methods disclosed herein, the stimulus comprises a light, and the method further comprises directing the light through the print window and towards the mixture.

[0031] In some embodiments of any one of the methods disclosed herein, the mixture is provided to a mold corresponding to at least a portion of the 3D object. In some embodiments of any one of the methods disclosed herein, the method further comprises subjecting the green part to a first temperature to form a brown part corresponding to at least the portion of the 3D object, wherein the polymeric material and the P2 are configured to decompose at the first temperature.

[0032] In some embodiments of any one of the methods disclosed herein, the method further comprises subjecting the brown part to a second temperature to sinter the Pl, wherein the second temperature is higher than the first temperature.

[0033] In some embodiments of any one of the methods disclosed herein, the hollow particle is a polymeric hollow particle.

[0034] In some embodiments of any one of the methods disclosed herein, the one or more metal particles (Pl) and the one or more hollow particles (P2) are present in the mixture in a volume ratio (Pl :P2) of at least about 0.1.

[0035] In some embodiments of any one of the methods disclosed herein, the volume ratio (Pl :P2) is at most about 60. In some embodiments, the volume ratio (Pl :P2) is between about 0.4 and about 50. In some embodiments, the volume ratio (P1 :P2) is between about 0.5 and about 40. In some embodiments, the volume ratio (P1 :P2) is between about 1 and about 10.

[0036] In some embodiments of any one of the methods disclosed herein, the Pl is present at an amount of between about 10% and about 60% by volume of the mixture.

[0037] In some embodiments of any one of the methods disclosed herein, the Pl is present at an amount of between about 20% and about 50% by volume of the mixture.

[0038] In some embodiments of any one of the methods disclosed herein, the P2 is present at an amount of between about 1% and about 50% by volume of the mixture.

[0039] In some embodiments of any one of the methods disclosed herein, the P2 is present at an amount of between about 2% and about 40% by volume of the mixture.

[0040] In some embodiments of any one of the methods disclosed herein, the one or more metal particles (Pl) and the one or more hollow particles (P2) in the mixture have an average particle size ratio (Pl :P2) of at least about 0.1.

[0041] In some embodiments of any one of the methods disclosed herein, the average particle size ratio (P1 :P2) is at most about 60. In some embodiments, the average particle size ratio (Pl :P2) is between about 0.2 and about 30. [0042] In some embodiments of any one of the methods disclosed herein, the Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

[0043] In some embodiments of any one of the methods disclosed herein, the Pl has an average particle size of between about 2 micrometer to about 100 micrometers.

[0044] In some embodiments of any one of the methods disclosed herein, the P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

[0045] In some embodiments of any one of the methods disclosed herein, the P2 has an average particle size of between about 10 micrometers and about 200 micrometers.

[0046] In some embodiments of any one of the methods disclosed herein, the one or more metal particles (Pl) and the one or more hollow particles (P2) are present, in combination, at an amount of greater than about 15% by weight of the mixture.

[0047] In some embodiments of any one of the methods disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 20% by weight of the mixture. In some embodiments, the amount of the Pl and the P2, in combination, is greater than about 40% by weight of the mixture. In some embodiments of any one of the methods disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 60% by weight of the mixture.

[0048] In some embodiments of any one of the methods disclosed herein, the Pl is present in an amount of between about 65% and about 95% by weight of the mixture.

[0049] In some embodiments of any one of the methods disclosed herein, the Pl is present in an amount of between about 70% and about 90% by weight of the mixture.

[0050] In some embodiments of any one of the methods disclosed herein, the P2 is present in an amount of less than about 1% by weight of the mixture.

[0051] In some embodiments of any one of the methods disclosed herein, the P2 is present in an amount of less than about 0.5% by weight of the mixture.

[0052] In some embodiments of any one of the methods disclosed herein, the mixture further comprises at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors.

[0053] In some embodiments of any one of the methods disclosed herein, the mixture further comprises at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0054] In another aspect, the present disclosure provides a mixture for forming a three- dimensional (3D) object, the mixture comprising one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a hollow particle, wherein the mixture is characterized by one or more members selected from the group consisting of: (i) the Pl and the P2 are present in the mixture in a volume ratio (Pl :P2) of at least about 0.1; (ii) the Pl and the P2 in the mixture have an average particle size ratio (P1 :P2) of at least about 0.1; and (iii) the Pl and the P2 are present, in combination, at an amount of greater than about 15% by weight of the mixture.

[0055] In some embodiments of any one of the mixtures disclosed herein, hollow particle comprises a porous particle. In some embodiments of any one of the mixtures disclosed herein, an average porosity of the hollow particle is at least about 10%. In some embodiments of any one of the mixtures disclosed herein, an average porosity of the hollow particle is at least about 20%. In some embodiments of any one of the mixtures disclosed herein, an average porosity of the hollow particle is at least about 40%.

[0056] In some embodiments of any one of the mixtures disclosed herein, the hollow particle is a polymeric hollow particle.

[0057] In some embodiments of any one of the mixtures disclosed herein, the Pl comprises the metal particle.

[0058] In some embodiments of any one of the mixtures disclosed herein, the Pl comprises the ceramic particle.

[0059] In some embodiments, of any one of the mixtures disclosed herein the mixture is characterized by two or more members selected from the group consisting of (i), (ii), and (iii). [0060] In some embodiments of any one of the mixtures disclosed herein, the mixture is characterized by (i), (ii), and (iii).

[0061] In some embodiments of any one of the mixtures disclosed herein, in (i), the volume ratio (Pl :P2) is at most about 60.

[0062] In some embodiments of any one of the mixtures disclosed herein, in (i), the volume ratio (Pl :P2) is between about 0.4 and about 50.

[0063] In some embodiments of any one of the mixtures disclosed herein, in (i), the volume ratio (Pl :P2) is between about 0.5 and about 40.

[0064] In some embodiments of any one of the mixtures disclosed herein, in (i), the volume ratio (P1 :P2) is between about 1 and about 10.

[0065] In some embodiments of any one of the mixtures disclosed herein, the Pl is present at an amount of between about 10% and about 60% by volume of the mixture.

[0066] In some embodiments of any one of the mixtures disclosed herein, the Pl is present at an amount of between about 20% and about 50% by volume of the mixture. [0067] In some embodiments of any one of the mixtures disclosed herein, the P2 is present at an amount of between about 1% and about 50% by volume of the mixture.

[0068] In some embodiments of any one of the mixtures disclosed herein, the P2 is present at an amount of between about 2% and about 40% by volume of the mixture.

[0069] In some embodiments of any one of the mixtures disclosed herein, the average particle size ratio (Pl :P2) is at most about 60.

[0070] In some embodiments of any one of the mixtures disclosed herein, the average particle size ratio (P1 :P2) is between about 0.2 and about 30.

[0071] In some embodiments of any one of the mixtures disclosed herein, the Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

[0072] In some embodiments of any one of the mixtures disclosed herein, the Pl has an average particle size of between about 2 micrometer to about 100 micrometers.

[0073] In some embodiments of any one of the mixtures disclosed herein, the P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

[0074] In some embodiments of any one of the mixtures disclosed herein, the P2 has an average particle size of between about 10 micrometers and about 200 micrometers.

[0075] In some embodiments of any one of the mixtures disclosed herein, in (iii), the amount of the Pl and the P2, in combination, is greater than about 20% by weight of the mixture.

[0076] In some embodiments of any one of the mixtures disclosed herein, in (iii), the amount of the Pl and the P2, in combination, is greater than about 40% by weight of the mixture.

[0077] In some embodiments of any one of the mixtures disclosed herein, in (iii), the amount of the Pl and the P2, in combination, is greater than about 60% by weight of the mixture.

[0078] In some embodiments of any one of the mixtures disclosed herein, the Pl is present in an amount of between about 65% and about 95% by weight of the mixture.

[0079] In some embodiments of any one of the mixtures disclosed herein, the Pl is present in an amount of between about 70% and about 90% by weight of the mixture.

[0080] In some embodiments of any one of the mixtures disclosed herein, the P2 is present in an amount of less than about 1% by weight of the mixture.

[0081] In some embodiments of any one of the mixtures disclosed herein, the P2 is present in an amount of less than about 0.5% by weight of the mixture.

[0082] In some embodiments of any one of the mixtures disclosed herein, the mixture further comprises at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors.

[0083] In some embodiments of any one of the mixtures disclosed herein, the mixture further comprises at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0084] In another aspect, the present disclosure provides a method for forming a three- dimensional (3D) object, the method comprising: (a) providing a mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a hollow particle, wherein the mixture is characterized by one or more members selected from the group consisting of: (i) the Pl and the P2 are present in the mixture in a volume ratio (P1 :P2) of at least about 0.1; (ii) the Pl and the P2 in the mixture have an average particle size ratio (Pl :P2) of at least about 0.1; and (iii) the Pl and the P2 are present, in combination, at an amount of greater than about 15% by weight of the mixture; (b) exposing the mixture to a stimulus to cause the one or more polymeric precursors to form the polymeric material that at least partially encapsulates the Pl and the P2, thereby to form a green part corresponding to at least a portion of the 3D object.

[0085] In some embodiments of any one of the methods disclosed herein, the hollow particle comprises a porous particle. In some embodiments of any one of the methods disclosed herein, an average porosity of the hollow particle is at least about 10%. In some embodiments of any one of the methods disclosed herein, an average porosity of the hollow particle is at least about 20%. In some embodiments of any one of the methods disclosed herein, an average porosity of the hollow particle is at least about 40%.

[0086] In some embodiments of any one of the methods disclosed herein, in (a), the mixture is provided adjacent to a print window.

[0087] In some embodiments of any one of the methods disclosed herein, the stimulus comprises a light, and wherein the method further comprising directing the light through the print window and towards the mixture.

[0088] In some embodiments of any one of the methods disclosed herein, in (a), the mixture is provided to a mold corresponding to at least a portion of the 3D object.

[0089] In some embodiments of any one of the methods disclosed herein, the method further comprises subjecting the green part to a first temperature to form a brown part corresponding to at least the portion of the 3D object, wherein the polymeric material and the P2 are configured to decompose at the first temperature. [0090] In some embodiments of any one of the methods disclosed herein, the method further comprises subjecting the brown part to second temperature to sinter the Pl, wherein the second temperature is higher than the first temperature.

[0091] In some embodiments of any one of the methods disclosed herein, the hollow particle is a polymeric hollow particle.

[0092] In some embodiments of any one of the methods disclosed herein, the Pl comprises the metal particle.

[0093] In some embodiments of any one of the methods disclosed herein, the Pl comprises the ceramic particle.

[0094] In some embodiments of any one of the methods disclosed herein, the mixture is characterized by two or more members selected from the group consisting of (i), (ii), and (iii).

[0095] In some embodiments of any one of the methods disclosed herein, the mixture is characterized by (i), (ii), and (iii).

[0096] In some embodiments of any one of the methods disclosed herein, the volume ratio (Pl :P2) is at most about 60.

[0097] In some embodiments of any one of the methods disclosed herein, the volume ratio (Pl :P2) is between about 0.4 and about 50.

[0098] In some embodiments of any one of the methods disclosed herein, the volume ratio (Pl :P2) is between about 0.5 and about 40.

[0099] In some embodiments of any one of the methods disclosed herein, the volume ratio (P1 :P2) is between about 1 and about 10.

[0100] In some embodiments of any one of the methods disclosed herein, the Pl is present at an amount of between about 10% and about 60% by volume of the mixture.

[0101] In some embodiments of any one of the methods disclosed herein, the Pl is present at an amount of between about 20% and about 50% by volume of the mixture.

[0102] In some embodiments of any one of the methods disclosed herein, the P2 is present at an amount of between about 1% and about 50% by volume of the mixture.

[0103] In some embodiments of any one of the methods disclosed herein, the P2 is present at an amount of between about 2% and about 40% by volume of the mixture.

[0104] In some embodiments of any one of the methods disclosed herein, the average particle size ratio (Pl :P2) is at most about 60.

[0105] In some embodiments of any one of the methods disclosed herein, the average particle size ratio (P1 :P2) is between about 0.2 and about 30.

[0106] In some embodiments of any one of the methods disclosed herein, the Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

[0107] In some embodiments of any one of the methods disclosed herein, the Pl has an average particle size of between about 2 micrometer to about 100 micrometers.

[0108] In some embodiments of any one of the methods disclosed herein, the P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

[0109] In some embodiments of any one of the methods disclosed herein, the P2 has an average particle size of between about 10 micrometers and about 200 micrometers.

[0110] In some embodiments of any one of the methods disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 20% by weight of the mixture.

[oni] In some embodiments of any one of the methods disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 40% by weight of the mixture.

[0112] In some embodiments of any one of the methods disclosed herein, the amount of the Pl and the P2, in combination, is greater than about 60% by weight of the mixture.

[0113] In some embodiments of any one of the methods disclosed herein, the Pl is present in an amount of between about 65% and about 95% by weight of the mixture.

[0114] In some embodiments of any one of the methods disclosed herein, the Pl is present in an amount of between about 70% and about 90% by weight of the mixture.

[0115] In some embodiments of any one of the methods disclosed herein, the P2 is present in an amount of less than about 1% by weight of the mixture.

[0116] In some embodiments of any one of the methods disclosed herein, the P2 is present in an amount of less than about 0.5% by weight of the mixture.

[0117] In some embodiments of any one of the methods disclosed herein, the mixture further comprises at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors.

[0118] In some embodiments of any one of the methods disclosed herein, the mixture further comprises at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0119] In another aspect, the present disclosure provides a mixture for forming a three- dimensional (3D) object, the mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a particle exhibiting an interior density of a material, wherein, upon exposure to a stimulus, the particle is capable of transforming into an additional particle exhibiting an additional interior density of the material that is lower than the interior density of the material of the particle. [0120] In some embodiments of any one of the mixtures disclosed herein, the additional particle is a hollow particle.

[0121] In some embodiments of any one of the mixtures disclosed herein, the hollow particle is a polymeric hollow particle.

[0122] In some embodiments of any one of the mixtures disclosed herein, a size of the additional particle is greater than that a size of the particle.

[0123] In some embodiments of any one of the mixtures disclosed herein, the size of the additional particle is greater than that a size of the particle by at least about 10%. In some embodiments, the size of the additional particle is greater than that a size of the particle by at least about 50%. In some embodiments, the size of the additional particle is greater than that a size of the particle by at least about 100%.

[0124] In some embodiments of any one of the mixtures disclosed herein, the Pl and the P2 are present in the mixture in a volume ratio (Pl :P2) of at least about 0.1.

[0125] In some embodiments of any one of the mixtures disclosed herein, the Pl is present at an amount of between about 10% and about 60% by volume of the mixture.

[0126] In some embodiments of any one of the mixtures disclosed herein, the P2 is present at an amount of between about 1% and about 50% by volume of the mixture.

[0127] In some embodiments of any one of the mixtures disclosed herein, the Pl and the P2 in the mixture have an average particle size ratio (Pl :P2) of at least about 0.1.

[0128] In some embodiments of any one of the mixtures disclosed herein, the Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

[0129] In some embodiments of any one of the mixtures disclosed herein, the P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

[0130] In some embodiments of any one of the mixtures disclosed herein, the Pl and the P2 are present, in combination, at an amount of greater than about 15% by weight of the mixture. [0131] In some embodiments of any one of the mixtures disclosed herein, the Pl is present in an amount of between about 65% and about 95% by weight of the mixture.

[0132] In some embodiments of any one of the mixtures disclosed herein, the P2 is present in an amount of less than about 1% by weight of the mixture.

[0133] In some embodiments of any one of the mixtures disclosed herein, the mixture further comprises at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors.

[0134] In some embodiments of any one of the mixtures disclosed herein, the mixture further comprises at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0135] In some embodiments of any one of the mixtures disclosed herein, the stimulus comprises a thermal treatment.

[0136] In another aspect, the present disclosure provides a method for forming a three- dimensional (3D) object, the method comprising: (a) providing a mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a particle exhibiting an interior density of a material; and (b) exposing the mixture to a stimulus to cause the particle to transform into an additional particle exhibiting an additional interior density of the material that is lower than the interior density of the material of the particle.

[0137] In some embodiments of any one of the methods disclosed herein, the exposing further causes the one or more polymeric precursors to form the polymeric material, which polymeric material at least partially encapsulates the Pl.

[0138] In some embodiments of any one of the methods disclosed herein, the additional particle is a hollow particle.

[0139] In some embodiments of any one of the methods disclosed herein, the hollow particle is a polymeric hollow particle.

[0140] In some embodiments of any one of the methods disclosed herein, a size of the additional particle is greater than a size of the particle.

[0141] In some embodiments of any one of the methods disclosed herein, the size of the additional particle is greater than the size of the particle by at least about 10%. In some embodiments, the size of the additional particle is greater than the size of the particle by at least about 50%. In some embodiments, the size of the additional particle is greater than the size of the particle by at least about 100%.

[0142] In some embodiments of any one of the methods disclosed herein, the Pl and the P2 are present in the mixture in a volume ratio (Pl :P2) of at least about 0.1.

[0143] In some embodiments of any one of the methods disclosed herein, the Pl is present at an amount of between about 10% and about 60% by volume of the mixture.

[0144] In some embodiments of any one of the methods disclosed herein, the P2 is present at an amount of between about 1% and about 50% by volume of the mixture.

[0145] In some embodiments of any one of the methods disclosed herein, the Pl and the P2 in the mixture have an average particle size ratio (Pl :P2) of at least about 0.1.

[0146] In some embodiments of any one of the methods disclosed herein, the Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

[0147] In some embodiments of any one of the methods disclosed herein, the P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

[0148] In some embodiments of any one of the methods disclosed herein, the Pl and the P2 are present, in combination, at an amount that is greater than about 15% by weight of the mixture.

[0149] In some embodiments of any one of the methods disclosed herein, the Pl is present in an amount of between about 65% and about 95% by weight of the mixture.

[0150] In some embodiments of any one of the methods disclosed herein, the P2 is present in an amount of less than about 1% by weight of the mixture.

[0151] In some embodiments, the method further comprises at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors.

[0152] In some embodiments, the method further comprises at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0153] In some embodiments, the stimulus comprises a thermal treatment.

[0154] Another aspect of the present disclosure provides a non-transitory computer readable medium comprising machine executable code that, upon execution by one or more computer processors, implements any of the methods above or elsewhere herein.

[0155] Another aspect of the present disclosure provides a system comprising one or more computer processors and computer memory coupled thereto. The computer memory comprises machine executable code that, upon execution by the one or more computer processors, implements any of the methods above or elsewhere herein.

[0156] Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only illustrative embodiments of the present disclosure are shown and described. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

INCORPORATION BY REFERENCE

[0157] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. To the extent publications and patents or patent applications incorporated by reference contradict the disclosure contained in the specification, the specification is intended to supersede and/or take precedence over any such contradictory material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0158] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings (also “Figure” and “FIG.” herein), of which:

[0159] FIG. 1 schematically illustrates an example composition for three-dimensional (3D) printing.

[0160] FIG. 2 schematically illustrates another example composition for 3D printing.

[0161] FIG. 3 shows an example of a 3D printing system.

[0162] FIGs. 4 and 5 show another example of a 3D printing system.

[0163] FIG. 6 shows a computer system that is programmed or otherwise configured to implement methods provided herein.

[0164] FIG. 7 schematically illustrates trapping of a polymer of a breakdown product thereof within a three-dimensional object during treatment by a stimulus, such as heat.

[0165] FIG. 8 shows a scanning-electron microscopy (SEM) image of hollow polymeric particles.

[0166] FIG. 9 schematically illustrates debinding of polymeric binder and/or hollow particles within a three-dimensional object.

[0167] FIG. 10 illustrates an increase in debinding wall thickness prior to cracking upon an increase in an amount of hollow particles (“u-sphere”) in a mixture for printing each wall.

[0168] FIG. 11 shows example images of a 3D-printed object comprising a substantially non-cracked wall and another 3D-printed object comprising a cracked wall.

[0169] FIG. 12 shows an example external image (left and an example cross-sectional image (right) of a porous particle.

[0170] FIG. 13 shows a debindable wall thickness of a 3D-printed object that is printed in absence of porous microparticle fillers (baseline) as compared to a debindable wall thickness of a 3D-printed object that is printed with porous microparticle fillers (baseline with 10 volume % porous filler). DETAILED DESCRIPTION

[0171] While various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.

[0172] The term “hollow particle” as disclosed herein generally refers to a structurally non- homogeneous particle having an interior density that is lower than an exterior density. A hollow particle can comprise an unfilled space or hollowed-out space within at least a portion of the hollow particle. A hollow particle can comprise a core-shell structure, wherein a density of a first material in the core (e.g., an amount of a polymeric material per volume) is lower than a density of a second material in the shell (e.g., an amount of the same polymeric material or a different polymeric material per volume). A thickness of the shell of such hollow particle can be uniform. Alternatively, the thickness of the shell may not be uniform. The first material and the second material can be the same. Alternatively, the first material and the second material can be different. For example, the hollow particle can comprise a substantially void interior, which void interior is filled with gas. In another example, the hollow particle can comprise a first material having a first density and a second material having a second density that is lower than the first density, wherein the first material at least partially encompasses the second material. The hollow particle can comprise one or mor materials, such as, for example, polymers.

[0173] A hollow particle can comprise a porous particle (e.g., a microporous particle or a nanoporous particle) comprising one or more voids, such as one or more pores. A pore of the one or more pores can be substantially contained within an interior of the porous particle, such that an inner surface of the pore is not in fluid communication with an exterior surface of the porous particle. Alternatively or in addition to, at least a portion of a pore of the one or more pores can be exposed to the exterior surface of the porous particle, such that at least a portion of the inner surface of the pore is in fluid communication with the exterior surface of the porous particle.

[0174] The term “three-dimensional object” (also “3D object”), as used herein, generally refers to an object or a part of an object that is printed by three-dimensional (3D) printing. The 3D object may be at least a portion of a larger 3D object or an entirety of the 3D object. The 3D object may be fabricated (e.g., printed) in accordance with a computer model of the 3D object. [0175] The term “mixture,” as used herein, generally refers to a material that is usable to print a 3D object. The mixture may be referred to as a feedstock, liquid, or resin (e.g., a photoactive resin). In some cases, the mixture may be held inside a vat. A layer of the mixture to be subjected to the light may be confined between a bottom of the vat (e.g., a window) and the build head. The bottom of the vat may be a build surface. Alternatively, a layer of the mixture to be subjected to the light may be confined between the build head and the surface of the mixture. The surface of the mixture may be a build surface. In some cases, the mixture may be deposited on or adjacent to an open platform. A layer of the mixture to be subjected to the light may be defined by pressing the mixture (e.g., by a blade or a build head) into a film of the mixture. The open platform may be a build surface. In the embodiments described herein, a thickness of the layer of the mixture may be adjustable. In some cases, the mixture may comprise one or more members from polymeric precursors, photoinitiators, photoinhibitors, coinitiators for curing, other light absorbers (e.g., ultraviolet (UV) light absorbers), radical inhibitors, organic and/or inorganic particulate materials, solvent, fillers (e.g., inert fillers), etc.).

[0176] The mixture may include a photoactive resin. The photoactive resin may include a polymerizable and/or cross-linkable component (e.g., a polymeric precursor) and a photoinitiator that activates curing of the polymerizable and/or cross-linkable component, to thereby subject the polymerizable and/or cross-linkable component to polymerization and/or cross-linking. Such polymerization and/or cross-linking of the polymerizable and/or crosslinkable component, respectively, may form a polymeric material. The photoactive resin may include a photoinhibitor that inhibits curing of the polymerizable and/or cross-linkable component. The 3D printing may be performed with greater than or equal to about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more mixtures. As an alternative, the 3D printing may be performed with less than or equal to about 10, 9, 8, 7, 6, 5, 4, 3, 2 mixtures, or no mixture (e.g., a single component). A plurality of mixtures may be used for printing a multi-material 3D object. [0177] The polymeric precursor in the mixture may comprise monomers to be polymerized into the polymeric material, oligomers to be cross-linked into the polymeric material, or both. The monomers may be of the same or different types. An oligomer may comprise two or more monomers that are covalently linked to each other. The oligomer may be of any length, such as at least 2 (dimer), 3 (trimer), 4 (tetramer), 5 (pentamer), 6 (hexamer), 7, 8, 9, 10, 20, 30, 40, 50, 100, 200, 300, 400, 500, or more monomers. Alternatively or in addition to, the polymeric precursor may include a dendritic precursor (monodisperse or polydisperse). The dendritic precursor may be a first generation (Gl), second generation (G2), third generation (G3), fourth generation (G4), or higher with functional groups remaining on the surface of the dendritic precursor. The resulting polymeric material may comprise a homopolymer and/or a copolymer. The copolymer may be a linear copolymer or a branched copolymer. The copolymer may be an alternating copolymer, periodic copolymer, statistical copolymer, random copolymer, and/or block copolymer.

[0178] Examples of monomers include one or more of hydroxy ethyl methacrylate; n-Lauryl acrylate; tetrahydrofurfuryl methacrylate; 2 , 2, 2 - trifluoroethyl methacrylate; isobornyl methacrylate; polypropylene glycol monomethacrylates, aliphatic urethane acrylate (i.e., Rahn Genomer 1122); hydroxy ethyl acrylate; n-Lauryl methacrylate; tetrahydrofurfuryl acrylate; 2 , 2, 2 - trifluoroethyl acrylate; isobornyl acrylate; polypropylene glycol monoacrylates; trimethylpropane triacrylate; trimethylpropane trimethacrylate; pentaerythritol tetraacrylate; pentaerythritol tetraacrylate; triethyleneglycol diacrylate; triethylene glycol dimethacrylate; tetrathyleneglycol diacrylate; tetrathylene glycol dimethacrylate; neopentyldimethacrylate; neopentylacrylate; hexane dioldimethacylate; hexane diol diacrylate; polyethylene glycol 400 dimethacrylate; polyethylene glycol 400 diacrylate; diethylglycol diacrylate; diethylene glycol dimethacrylate; ethyleneglycol diacrylate; ethylene glycol dimethacrylate; ethoxylated bis phenol A dimethacrylate; ethoxylated bis phenol A diacrylate; bisphenol A glycidyl methacrylate; bisphenol A glycidyl acrylate; ditrimethylolpropane tetraacrylate; and ditrimethylolpropane tetraacrylate.

[0179] Polymeric precursors may be present in an amount ranging between about 3 weight % (wt%) to about 90 wt% in the mixture. The polymeric precursors may be present in an amount of at least about 3 wt%, 4 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%,

90 wt%, or more in the mixture. The polymeric precursors may be present in an amount of at most about 90 wt%, 85 wt%, 80 wt%, 75 wt%, 70 wt%, 65 wt%, 60 wt%, 55 wt%, 50 wt%, 45 wt%, 40 wt%, 35 wt%, 30 wt%, 25 wt%, 20 wt%, 15 wt%, 10 wt%, 5 wt%, 4 wt%, 3 wt%, or less in the mixture.

[0180] In some cases, the mixture may include a plurality of particles (e.g., metal, non- metal, or a combination thereof). The mixture may be a slurry or a paste. The plurality of particles may be solids or semi-solids (e.g., gels). The plurality of particles may be suspended throughout the mixture in a monodisperse distribution or a polydisperse distribution.

[0181] A resin may be a raw material usable for a digital light processing (DLP)-based 3D printing process or stereolithography (SLA)-based 3D printing process. In some cases, the resin may not comprise pre-polymerized and/or cross-linked polymers. Alternatively, the resin may comprise pre-polymerized and/or cross-linked polymers. In some cases, the resin may comprise other components such as photoinhibitors, UV absorbers, and inert fillers. The term “composite resin” may generally refer to a resin that comprises (i) metal, ceramic, or other suspended particles and/or (ii) a plurality of precursor compounds thereof, as provided herein. [0182] The term “polymeric material” as used herein, generally refer to compositions based on polymers, oligomers, or monomers, which can be selectively polymerized and/or crosslinked upon exposure to a stimulus. In some cases, the stimulus may be electromagnetic radiation (light or actinic radiation), and the polymeric material may be referred to a photopolymer. [0183] In some cases, the stimulus to form a polymeric material from a plurality of polymeric precursors may be one or more lights. One or more lights (e.g., from one or more light sources) may be used to initiate (activate) curing of a portion of the film, thereby to print at least a portion of the 3D object. In some cases, one or more lights (e.g., from one or more light sources) may be used to inhibit (prevent) curing of a portion of the film adjacent to a surface of the film (e.g., a surface adjacent to one or more sides of the vat or a surface of the open platform). In some cases, one or more lights (e.g., from one or more light sources) may be used by one or more sensors to determine a profile and/or quality of the film.

[0184] The 3D printing may be performed with one wavelength. The 3D printing may be performed with at least about 2, 3, 4, 5, 6, 7, 8, 9, 10 or more wavelengths that are different. The 3D printing may be performed with at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more lights. The 3D printing may be performed with at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more light sources, and it may be desirable to prevent curing of a portion of the film adjacent to the surface of the film.

[0185] The one or more lights may comprise electromagnetic radiation. The term “electromagnetic radiation,” as used herein, generally refers to one or more wavelengths from the electromagnetic spectrum including, but not limited to x-rays (about 0.1 nanometers (nm) to about 10.0 nm; or about 10¹⁸ Hertz (Hz) to about 10¹⁶ Hz), UV rays (about 10.0 nm to about 380 nm; or about 8* 10¹⁶ Hz to about 10¹⁵ Hz), visible light (about 380 nm to about 750 nm; or about 8* 10¹⁴ Hz to about 4* 10¹⁴ Hz), infrared (IR) light (about 750 nm to about 0.1 centimeters (cm); or about 4* 10¹⁴ Hz to about 5x l0ⁿ Hz), and microwaves (about 0.1 cm to about 100 cm; or about 10⁸ Hz to about 5* 10¹¹ Hz).

[0186] The one or more light sources may comprise an electromagnetic radiation source. The term “electromagnetic radiation source,” as used herein, generally refers to a source that emits electromagnetic radiation. The electromagnetic radiation source may emit one or more wavelengths from the electromagnetic spectrum. [0187] In some cases, the mixture may include a plurality of particles (e.g., metal, non- metal, or a combination thereof). The mixture may be a slurry or a paste. The plurality of particles may be solids or semi-solids (e.g., gels). The plurality of particles may be suspended throughout the mixture in a monodisperse distribution or a polydisperse distribution.

[0188] The term “particles,” as used herein, generally refers to any particulate material. In some cases, the particles may be melted or sintered (e.g., not completely melted). The particulate material may be in powder form. The particles may be inorganic materials. The inorganic materials may be metallic (e.g., aluminum or titanium), intermetallic (e.g., steel alloys), ceramic (e.g., metal oxides) materials, or any combination thereof. In some cases, the term “metal” or “metallic” may refer to both metallic and intermetallic materials. The metallic materials may include ferromagnetic metals (e.g., iron and/or nickel). In some cases, the particles may be treated by heat to be substantially removed (e.g., subject to debinding). For example, the particles can be organic particles (e.g., polymeric hollow particles as disclosed herein) that can be substantially removed during sintering of a 3D printed object, e.g., to form a metal and/or ceramic 3D object.

[0189] The particles as disclosed herein may have various shapes and sizes. For example, a particle may be in the shape of a sphere, cuboid, or disc, or any partial shape or combination of shapes thereof. The particle may have a cross-section that is circular, triangular, square, rectangular, pentagonal, hexagonal, or any partial shape or combination of shapes thereof. Upon heating, the particles may sinter (or coalesce) into a solid or porous object that may be at least a portion of a larger 3D object or an entirety of the 3D object. The 3D printing may be performed with at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more types of particles. As an alternative, the 3D printing may be performed with less than or equal to about 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 particle, or no particles. A particle may be a nanoparticle. A particle may be a microparticle.

[0190] The metallic materials for the particles may include one or more of aluminum, calcium, magnesium, barium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, niobium, molybdenum, ruthenium, rhodium, silver, cadmium, actinium, and gold. The particles may comprise a rare earth element. The rare earth element may include one or more of scandium, yttrium, and elements of the lanthanide series having atomic numbers from 57-71.

[0191] The intermetallic materials for the particles may be a solid-state compound exhibiting metallic bonding, defined stoichiometry and ordered crystal structure (i.e., alloys). The intermetallic materials may be in pre-alloyed powder form. Examples of such pre-alloyed powders may include, but are not limited to, brass (copper and zinc), bronze (copper and tin), duralumin (aluminum, copper, manganese, and/or magnesium), gold alloys (gold and copper), rose-gold alloys (gold, copper, and zinc), nichrome (nickel and chromium), and stainless steel (iron, carbon, and additional elements including manganese, nickel, chromium, molybdenum, boron, titanium, silicon, vanadium, tungsten, cobalt, and/or niobium). The pre-alloyed powders may include superalloys. The superalloys may be based on elements including iron, nickel, cobalt, chromium, tungsten, molybdenum, tantalum, niobium, titanium, and/or aluminum. [0192] The ceramic materials for the particles may comprise metal (e.g., aluminum, titanium, etc.), non-metal (e.g., oxygen, nitrogen, etc.), and/or metalloid (e.g., germanium, silicon, etc.) atoms primarily held in ionic and covalent bonds. Examples of the ceramic materials include, but are not limited to, an aluminide, boride, beryllia, carbide, chromium oxide, hydroxide, sulfide, nitride, mullite, kyanite, ferrite, titania zirconia, yttria, and magnesia. [0193] The term “particle size,” as used herein, generally refers to a mean or median particle size of a population of particles. The particle size may be obtained from a direct measurement or an indirect measurement. The particle size may be measured by obtaining visualization (e.g., images, pictures, micrographs such as scanning electron microscopy (SEM) image, transmission electron microscopy (TEM) image, atomic force microscopy (AFM) image, etc.), and calculating the mean or median particle size of a population of particles shown in such visualization. The particle size may be measured by dynamic light scattering (DLS) measurements. In some cases, the particle size may be obtained by a model that transforms (e.g., in an abstract way) a real particle shape into a simple and standardized shape (e.g., a mathematical shape, such as a sphere). In some cases, a spherical shape may be used when a size parameter such as diameter makes sense. A population of particles maybe monodisperse with substantially the same particle dimension (or size). In some cases, a population of particles may be polydisperse with different dimensions (or sizes), and the term “particle size distribution,” as used herein, may reflect such polydispersity. In some cases, a particle size of a collection of particles may generally refer to a dso of the particles, which is the diameter for which 50% of the particles have a smaller diameter and 50% percent have a larger diameter. The dso can also be referred to as the median diameter for the collection of particles.

[0194] The term “photoinitiation,” as used herein, generally refers to a process of subjecting a portion of a mixture to a light to cure (or gel) a photoactive resin in the portion of the mixture. The light (photoinitiation light) may have a wavelength that activates a photoinitiator that initiates curing of a polymerizable and/or cross-linkable component in the photoactive resin. [0195] The term “photoinhibition,” as used herein, generally refers to a process of subjecting a portion of a mixture to a light to inhibit curing of a photoactive resin in the portion of the mixture. The light (photoinhibition light) may have a wavelength that activates a photoinhibitor that inhibit curing of a polymerizable and/or cross-linkable component in the photoactive resin. The wavelength of the photoinhibition light and another wavelength of a photoinitiation light may be different wavelengths. In some examples, the photoinhibition light and the photoinitiation light may be projected from the same optical source. In some examples, the photoinhibition light and the photoinitiation light may be projected from different optical sources.

[0196] The terms “photoinitiation light” and “first light” may be used synonymously herein. The terms “photoinhibition light” and “second light” may be used synonymously herein.

[0197] The terms “energy,” as used herein, generally refers to an electromagnetic (e.g., ultraviolet ray or visible light) exposure per unit area (e.g., millijoule per square centimeter; mJ/cm²). The term “intensity,” as used herein, generally refers to the energy (as described above) per time (e.g., milliwatt per square centimeter; mW/cm²).

[0198] The term “vat,” as used herein, generally refers to a structure (e.g., a container, holder, reservoir, etc.) that holds a mixture during 3D printing. The mixture may be usable for 3D printing. One or more sides of the vat (e.g., a bottom or side surface) may include an optically transparent or semi-transparent window (e.g., glass or a polymer) to direct light through the window and to the mixture. In some cases, the window may be precluded. In such a scenario, light may be provided to the mixture from above the vat, and it may be desirable to prevent curing of a portion of the mixture adjacent to the surface of the mixture.

[0199] The term “open platform,” as used herein, generally refers to a structure that supports a mixture or a film of the mixture during 3D printing. The mixture may have a viscosity that is sufficient to permit the mixture to remain on or adjacent to the open platform during 3D printing. The open platform may be flat. The open platform may include an optically transparent or semi-transparent print window (e.g., glass or a polymer) to direct light through the window and to the mixture or the film of the mixture. In some cases, the window may be precluded. In such a scenario, light may be provided to the mixture of the film of the mixture from above the open platform, such as directly above or from a side of the open platform.

[0200] The term “window,” as used herein, generally refers to a structure that is part of a vat or a container. In some cases, the window may be in contact with the mixture. In some cases, the window may not be in contact with the mixture. The window may be transparent or semitransparent (translucent). The window may be comprised of an optical window material, such as, for example, glass or a polymeric material (e.g., polymethylmethacrylate (PMMA)). In some cases, the window may be comprised of polydimethylsiloxane (PDMS) or other polymeric materials that are permeable to oxygen. During printing, the oxygen dissolved in the window may (i) diffuse into a contact surface between the window and the mixture comprising the photoactive resin (the window-mixture interface) and (ii) inhibit curing of the photoactive resin at the contact surface. The window may be positioned above an optical source for photopolymer-based 3D printing using bottom-up illumination. As an alternative, the window may be positioned below the optical source. As another alternative, the window may be positioned between a first optical source and a second optical source.

[0201] The term “build head,” as used herein, generally refers to a structure that supports and/or holds at least a portion (e.g., a layer) of a 3D object. The build head may be configured to move along a direction away from a bottom of a vat or an open platform. Such movement may be relative movement, and thus the moving piece may be (i) the build head, (ii) the vat or the open platform, or (iii) both. The moving piece may comprise a mechanical gantry capable of motion in one or more axes of control (e.g., one or more of the XYZ planes) via one or more actuators during 3D printing.

[0202] The term “green body,” as used herein, generally refers to a 3D object that includes a polymeric material matrix in which a plurality of particles (e.g., metal, ceramic, cermet, inorganic carbon, or a combination thereof) is encapsulated. The particles may be configured for sintering or melting. The green body may be self-supporting. The green body may be heated in a heater (e.g., a furnace) to burn off at least a portion of the polymeric material. Some of the metal, ceramic, and/or cermet particles may begin to coalesce during this process.

[0203] The term “brown body,” as used herein, generally refers to a green body that has been treated (e.g., solvent treatment, heat treatment, pressure treatment, etc.) to remove at least a portion (e.g., at least about 20 percent (%), at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or more; at most about 100%, at most about 95%, at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 40%, at most about 30%, at most about 20%, or less) of the polymeric material within the green body. The brown body may comprise the plurality of particles of the green body. The plurality of particles may be capable of sintering or melting. The brown body may be self-supporting. The brown body may be heated in a heater (e.g., in a furnace) to bum off at least a portion of any remaining polymeric material and coalesce the plurality of particles into at least a portion of a larger 3D object or an entirety of the 3D object. In some cases, subjecting a green body to such treatment to remove at least a portion of the binder (e.g., polymeric material, hollow particles, etc.) may increase density of a plurality of particles (e.g., metal and/or ceramic particles), and this process may be referred to as a brown body (or brown part) densification.

[0204] All ranges disclosed herein are meant to include all ranges subsumed therein unless specifically stated otherwise. As used herein, “any range subsumed therein” means any range that is within the stated range.

[0205] Three-dimensional (3D) printing techniques can be used to print 3D objects. Mixtures usable for such 3D printing can comprise metal or ceramic particles, to print green parts. These green parts can be treated (e.g., thermal treatment) to remove (e.g., de-bind) polymeric materials within the green parts and sinter the metal or ceramic particles, to form a metal or ceramic 3D object.

[0206] In some cases, upon treatment (e.g., thermal treatment) of a green part, at least a portion of the polymeric material (or organic material) that is encapsulating the metal or ceramic particles can remain. Such presence of the remaining polymeric or organic materials can lead to various problems and limitations of 3D printing, e.g., incomplete sintering, sintered objects with one or more cracks, limitation in printing thickness and/or quality, etc. Thus, there is an unmet need for a composition (or mixture) and methods thereof for forming metal or ceramic 3D objects (e.g., via 3D printing, injection molding, etc.) with a reduced amount of residual organic materials (e.g., substantially free of the residual organic material).

Compositions for forming a 3D object and methods thereof

[0207] In an aspect, the present disclosure provides a mixture for forming a 3D object (e.g., 3D printing, injection molding, etc.). The mixture can comprise one or more polymeric precursors configured to form a polymeric material. The mixture can further comprise a first plurality of particles (Pl) comprising a metal particle and/or a ceramic particle. The mixture can further comprise a second plurality of particles (P2) comprising a hollow particle.

[0208] Alternatively, or in addition to, the P2 can comprise a particle exhibiting an interior density of a material, wherein, upon exposure to a stimulus (e.g., thermal energy, light, pressure, etc.), the particle can be capable of transforming into an additional particle exhibiting an additional interior density of the material that is lower than the interior density of the particle. For example, the particle can be a substantially non-hollow particle (e.g., a non-hollow polymeric particle) and the additional particle can be a hollow particle (e.g., a hollow polymeric particle). In some cases, the additional interior density of the material in the additional particle can be lower than the interior density of the material in the particle by at least about 0.01%, at least about 1%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 100%, at least about 120%, at least about 150%, at least about 200%, at least about 300%, at least about 400%, at least about 500%, at least about 1,000%, or more. The additional interior density of the material in the additional particle can be lower than the interior density of the material in the particle by at most about 1,000%, at most about 500%, at most about 400%, at most about 300%, at most about 200%, at most about 150%, at most about 120%, at most about 100%, at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 45%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 1%, at most about 0.01%, or less. In some cases, a dimension (e.g., a diameter) of the additional particle can be greater than a dimension (e.g., a diameter) of the particle by at least about 0.01%, at least about 1%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 100%, at least about 120%, at least about 150%, at least about 200%, or more. The dimension of the additional particle can be greater than the dimension of the particle by at most about 200%, at most about 150%, at most about 120%, at most about 100%, at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 45%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 1%, at most about 0.01%, or less.

[0209] In some embodiments, the hollow particle as disclosed herein can comprise a coreshell particle. In some cases, the hollow particle can comprise one or more polymers (e.g., a polymeric hollow particle). The shell of the hollow particle can comprise a polymeric material at a first density. The first density of the polymeric material within the shell of the hollow particle can be greater than a second density of the polymeric material within the core of the hollow particle by at least about 0.1, at least about 0.2, at least about 0.3, at least about 0.4, at least about 0.5, at least about 1, at least about 2, at least about 3, at least about 4, at least about 5, at least about 6, at least about 7, at least about 8, at least about 9, at least about 10, at least about 15, at least about 20, at least about 30, at least about 40, at least about 50, at least about 60, at least about 70, at least about 80, at least about 90, at least about 100, at least about 200, at least about 500, at least about 1000, or more. The first density of the polymeric material within the shell of the hollow particle can be greater than a second density of the polymeric material within the core of the hollow particle by at most about 1000, at most about 5000, at most about 200, at most about 100, at most about 90, at most about 80, at most about 70, at most about 60, at most about 50, at most about 40, at most about 30, at most about 20, at most about 15, at most about 10, at most about 9, at most about 8, at most about 7, at most about 6, at most about 5, at most about 4, at most about 3, at most about 2, at most about 1, at most about 0.5, at most about 0.4, at most about 0.3, at most about 0.2, at most about 0.1, or less. For example, the core of the hollow particle (e.g., expandable microsphere) can be substantially free of the polymeric material. In another example, the core of the hollow particle can be substantially free of any solid material, such as a polymeric material, a metal material, a ceramic material, etc. The core of such hollow particle may be filled with gas (e.g., air, oxygen, nitrogen, argon, helium, etc.). The pressure of gas in the hollow particle can be below atmospheric pressure, equal to atmospheric pressure, or above atmospheric pressure, or the space in the hollow particle may be substantially under vacuum. The core of such hollow particle may be completely or partially filled with solvent (e.g., butane, isobutane, pentane, isopentane, hexane, hexanes, heptane, decane, 2-methylpropane, 2-methylbutane, 2,2,4-trimethylpentane, other hydrocarbons, or other solvents).

[0210] In some embodiments, the hollow particles (e.g., expandable microspheres) can be filled with hydrocarbon solvent at a volumetric percentage of 5% to 30%.

[0211] In some embodiments, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be at least about 0%, about 0.1%, at least about 1%, at least about 2%, at least about 4%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 99%, or more. Alternatively, or in addition to, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be about 100%, at most about 99%, at most about 95%, at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 4%, at most about 2%, at most about 1%, at most about 0.1%, or less. [0212] In some cases, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be about 1 % to about 99 %. In some cases, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be at least about 1 %. In some cases, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be at most about 99 %. In some cases, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be about 1 % to about 4 %, about 1 % to about 5 %, about 1 % to about 10 %, about 1 % to about 15 %, about 1 % to about 22 %, about 1 % to about 30 %, about 1 % to about 35 %, about 1 % to about 40 %, about 1 % to about 60 %, about 1 % to about 80 %, about 1 % to about 99 %, about 4 % to about 5 %, about 4 % to about 10 %, about 4 % to about 15 %, about 4 % to about 22 %, about 4 % to about 30 %, about 4 % to about 35 %, about 4 % to about 40 %, about 4 % to about 60 %, about 4 % to about 80 %, about 4 % to about 99 %, about 5 % to about 10 %, about 5 % to about 15 %, about 5 % to about 22 %, about 5 % to about 30 %, about 5 % to about 35 %, about 5 % to about 40 %, about 5 % to about 60 %, about 5 % to about 80 %, about 5 % to about 99 %, about 10 % to about 15 %, about 10 % to about 22 %, about 10 % to about 30 %, about 10 % to about 35 %, about 10 % to about 40 %, about 10 % to about 60 %, about 10 % to about 80 %, about 10 % to about 99 %, about 15 % to about 22 %, about 15 % to about 30 %, about 15 % to about 35 %, about 15 % to about 40 %, about 15 % to about 60 %, about 15 % to about 80 %, about 15 % to about 99 %, about 22 % to about 30 %, about 22 % to about 35 %, about 22 % to about 40 %, about 22 % to about 60 %, about 22 % to about 80 %, about 22 % to about 99 %, about 30 % to about 35 %, about 30 % to about 40 %, about 30 % to about 60 %, about 30 % to about 80 %, about 30 % to about 99 %, about 35 % to about 40 %, about 35 % to about 60 %, about 35 % to about 80 %, about 35 % to about 99 %, about 40 % to about 60 %, about 40 % to about 80 %, about 40 % to about 99 %, about 60 % to about 80 %, about 60 % to about 99 %, or about 80 % to about 99 %. In some cases, the volumetric percentage of the hydrocarbon solvent filling the hollow particles can be about 1 %, about 4 %, about 5 %, about 10 %, about 15 %, about 22 %, about 30 %, about 35 %, about 40 %, about 60 %, about 80 %, or about 99 %.

[0213] In some embodiments, an average dimension (e.g., diameter) of the hollow particle as disclosed herein (e.g., a porous particle, a core-shell particle, etc.) can be at least about 100 nanometers (nm), at least about 200 nm, at least about 300 nm, at least about 400 nm, at least about 500 nm, at least about 600 nm, at least about 700 nm, at least about 800 nm, at least about 900 nm, at least about 1 micrometer (pm), at least about 5 pm, at least about 10 pm, at least about 20 pm, at least about 30 pm, at least about 40 pm, at least about 50 pm, at least about 60 pm, at least about 70 pm, at least about 80 pm, at least about 90 pm, at least about 100 pm, at least about 200 pm, at least about 300 pm, at least about 400 pm, at least about 500 pm, at least about 600 pm, at least about 700 pm, at least about 800 pm, at least about 900 pm, or more.

The average dimension of the hollow particle can be at most about 900 pm, at most about 800 pm, at most about 700 pm, at most about 600 pm, at most about 500 pm, at most about 400 pm, at most about 300 pm, at most about 200 pm, at most about 100 pm, at most about 90 pm, at most about 80 pm, at most about 70 pm, at most about 60 pm, at most about 50 pm, at most about 40 pm, at most about 30 pm, at most about 20 pm, at most about 10 pm, at most about 5 pm, at most about 1 pm, at most about 900 nm, at most about 800 nm, at most about 700 nm, at most about 600 nm, at most about 500 nm, at most about 400 nm, at most about 300 nm, at most about 200 nm, at most about 100 nm, or less.

[0214] In some embodiments, the hollow particle as disclosed herein (e.g., a porous particle, a core-shell particle, etc.) can be characterized by exhibiting a degradation temperature, as ascertained by therm ogravimetric (TG) analysis. For example, the degradation temperature can be a peak value of a first derivative (e.g., a local maximum value of first peak, a local maximum value of a second peak, etc., in an ascending order of temperature) of the weight change of the hollow particle with respect to a change (e.g., an increase) in temperature. The hollow particle can lose a portion of its mass when heated to the degradation temperature, e.g., via vaporization and/or burning of compounds derived from at least one polymeric material of the hollow particle. Such portion of the mass of the hollow particle can be at least or up to about 1%, at least or up to about 5%, at least or up to about 10%, at least or up to about 20%, at least or up to about 30%, at least or up to about 40%, at least or up to about 50%, at least or up to about 60%, at least or up to about 70%, at least or up to about 80%, or at least or up to about 90%. The degradation temperature of the hollow particle can be at least or up to about 200 degrees Celsius (°C), at least or up to about 210°C, at least or up to about 220°C, at least or up to about 230°C, at least or up to about 240°C, at least or up to about 250°C, at least or up to about 260°C, at least or up to about 270°C, at least or up to about 280°C, at least or up to about 290°C, at least or up to about 300°C, at least or up to about 310°C, at least or up to about 320°C, at least or up to about 330°C, at least or up to about 340°C, at least or up to about 350°C, at least or up to about 360°C, at least or up to about 370°C, at least or up to about 380°C, at least or up to about 390°C, at least or up to about 400°C. The degradation temperature of the hollow particle can range between about 200°C and about 400°C, between about 200°C and about 380°C, between about 200°C and about 360°C, between about 200°C and about 350°C, between about 200°C and about 340°C, between about 200°C and about 330°C, between about 200°C and about 320°C, between about 200°C and about 310°C, between about 200°C and about 300°C, between about 210°C and about 300°C, between about 220°C and about 300°C, between about 230°C and about 300°C, between about 240°C and about 300°C, or between about 250°C and about 300°C. [0215] In some embodiments, the hollow particle as disclosed herein (e.g., a porous particle, a core-shell particle, etc.) can be characterized by exhibiting reduced (e.g., suppressed) heat generation during thermal decomposition, e.g., as ascertained by deferential thermal analysis (DTA). Heat generated by thermal decomposition of the hollow particle can be lower than that heat generated by thermal decomposition of a control particle (e.g., a substantially solid particle, such as solid polymeric particle, e.g., a solid acrylic microsphere) by at least about 1%, at least about 2%, at least about 3%, at least about 4%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90%, at least about 95%, or more. The heat generated by thermal decomposition of the hollow particle can be lower than that the heat generated by thermal decomposition of the control particle by at most about 95%, at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 40%, at most about 30%, at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 4%, at most about 3%, at most about 2%, at most about 1%, or less. For example, the heat generated by thermal decomposition of the hollow particle as a temperature (e.g., a temperature around the degradation temperature of the hollow particle) can be at least or up to about 0.1 microvolt (p V), at least or up to about 0.2 pV, at least or up to about 0.3 pV, at least or up to about 0.4 pV, at least or up to about 0.5 pV, at least or up to about 0.6 pV, at least or up to about 0.7 pV, at least or up to about 0.8 pV, at least or up to about 0.9 pV, at least or up to about 1 pV, at least or up to about 1.1 pV, at least or up to about 1.2 pV, at least or up to about 1.3 pV, at least or up to about 1.4 pV, at least or up to about 1.5 pV, at least or up to about 1.6 pV, at least or up to about 1.7 pV, at least or up to about 1.8 pV, at least or up to about 1.9 pV, at least or up to about 2 pV, at least or up to about 3 pV, at least or up to about 4 pV, or at least or up to about 5 pV.

[0216] In some embodiments, the hollow particle as disclosed herein can comprise a porous particle comprising one or more pores. The hollow particle can be made of at least one material (e.g., at least one polymeric material) and the one or more pores of the porous particle can be substantially free of the at least one polymeric material. A pore of the one or more pores of the porous particle can be filled with the hydrocarbon solvent as disclosed herein, e.g., at any of the volumetric percentage of the hydrocarbon solvent as disclosed herein. Alternatively, the pore of the one or more pores of the porous particle may not be filled with the hydrocarbon solvent, e.g., may be filled with a gas, such as air.

[0217] The hollow particle (e.g., a porous particle) can comprise at least 1 about pore, at least about 5 pores, at least about 10 pores, at least about 15 pores, at least about 20 pores, at least about 30 pores, at least about 40 pores, at least about 50 pores, at least about 60 pores, at least about 70 pores, at least about 80 pores, at least about 90 pores, at least about 100 pores, at least about 200 pores, at least about 300 pores, at least about 400 pores, at least about 500 pores, or more. The porous particle can comprise at most about 500 pores, at most about 400 pores, at most about 300 pores, at most about 200 pores, at most about 100 pores, at most about 90 pores, at most about 80 pores, at most about 70 pores, at most about 60 pores, at most about

50 pores, at most about 40 pores, at most about 30 pores, at most about 20 pores, at most about

15 pores, at most about 10 pores, at most about 5 pores, or at most about 1 pore.

[0218] An average dimension (e.g., diameter) of the pore(s) of the hollow particle (e.g., a porous particle) can be at least about 10 nm, at least about 50 nm, at least about 100 nm, at least about 200 nm, at least about 300 nm, at least about 400 nm, at least about 500 nm, at least about 600 nm, at least about 700 nm, at least about 800 nm, at least about 900 nm, at least about 1 pm, at least about 5 pm, at least about 10 pm, at least about 20 pm, at least about 30 pm, at least about 40 pm, at least about 50 pm, at least about 60 pm, at least about 70 pm, at least about 80 pm, at least about 90 pm, at least about 100 pm, at least about 200 pm, at least about 300 pm, at least about 400 pm, at least about 500 pm, at least about 600 pm, at least about 700 pm, at least about 800 pm, at least about 900 pm, or more. The average dimension of the pore(s) of the hollow particle (e.g., a porous particle) can be at most about 900 pm, at most about 800 pm, at most about 700 pm, at most about 600 pm, at most about 500 pm, at most about 400 pm, at most about 300 pm, at most about 200 pm, at most about 100 pm, at most about 90 pm, at most about 80 pm, at most about 70 pm, at most about 60 pm, at most about 50 pm, at most about 40 pm, at most about 30 pm, at most about 20 pm, at most about 10 pm, at most about 5 pm, at most about 1 pm, at most about 900 nm, at most about 800 nm, at most about 700 nm, at most about 600 nm, at most about 500 nm, at most about 400 nm, at most about 300 nm, at most about 200 nm, at most about 100 nm, at most about 50 nm, at most about 10 nm, or less.

[0219] An average porosity of the hollow particle (e.g., a porous particle) can be at least about 1%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or more. The average porosity of the hollow particle (e.g., a porous particle) can be at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 40%, at most about 30%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 1%, or less. For example, the average porosity of the hollow particle can be about 50%.

[0220] The hollow particle (e.g., a porous particle) can comprise at least one polymeric material. For example, the hollow particle can comprise a solid region comprising the at least one polymeric material, and a porous region comprising one or more pores. The solid region can surround at least a portion of the porous region. A density (e.g., a true specific gravity) of the hollow particle (e.g., a quantity of mass of the solid region per unit volume of the hollow particle as a whole) can be at least about 10 milligrams per cubic centimeter (mg/cm³), at least about 20 mg/cm³, at least about 30 mg/cm³, at least about 40 mg/cm³, at least about 50 mg/cm³, at least about 60 mg/cm³, at least about 70 mg/cm³, at least about 80 mg/cm³, at least about 90 mg/cm³, at least about 0.1 grams per cubic centimeter (g/cm³), at least about 0.2 g/cm³, at least about 0.3 g/cm³, at least about 0.4 g/cm³, at least about 0.5 g/cm³, at least about 0.6 g/cm³, at least about 0.7 g/cm³, at least about 0.8 g/cm³, at least about 0.9 g/cm³, at least about 1 g/cm³, at least about 2 g/cm³, at least about 3 g/cm³, at least about 4 g/cm³, at least about 5 g/cm³, at least about 6 g/cm³, at least about 7 g/cm³, at least about 8 g/cm³, at least about 9 g/cm³, at least about 10 g/cm³, at least about 20 g/cm³, at least about 30 g/cm³, at least about 40 g/cm³, at least about 50 g/cm³, or more. The density (e.g., a true specific gravity) of the hollow particle can be at most about 50 g/cm³, at most about 40 g/cm³, at most about 30 g/cm³, at most about 20 g/cm³, at most about 10 g/cm³, at most about 9 g/cm³, at most about 8 g/cm³, at most about 7 g/cm³, at most about 6 g/cm³, at most about 5 g/cm³, at most about 4 g/cm³, at most about 3 g/cm³, at most about 2 g/cm³, at most about 1 g/cm³, at most about 0.9 g/cm³, at most about 0.8 g/cm³, at most about 0.7 g/cm³, at most about 0.6 g/cm³, at most about 0.5 g/cm³, at most about 0.4 g/cm³, at most about 0.3 g/cm³, at most about 0.2 g/cm³, at most about 0.1 g/cm³, at most about 90 mg/cm³, at most about 80 mg/cm³, at most about 70 mg/cm³, at most about 60 mg/cm³, at most about 50 mg/cm³, at most about 40 mg/cm³, at most about 30 mg/cm³, at most about 20 mg/cm³, at most about 10 mg/cm³, or less.

[0221] In some embodiments, an amount of hollow particles (e.g., porous particles) in a mixture or the resulting 3D-printed object can be at least or up to about 1 volume % (lvol%), at least or up to about 2vol%, at least or up to about 3 vol%, at least or up to about 4 vol%, at least or up to about 5 vol%, at least or up to about 6 vol%, at least or up to about 7 vol%, at least or up to about 8 vol%, at least or up to about 9 vol%, at least or up to about 10 vol%, at least or up to about 11 vol%, at least or up to about 12 vol%, at least or up to about 13 vol%, at least or up to about 14 vol%, at least or up to about 15 vol%, at least or up to about 20 vol%, at least or up to about 30 vol%, at least or up to about 40 vol%, pr at least or up to about 50 vol%.

[0222] Without wishing to be bound by theory, 3D objects printed with the hollow particles (e.g., core-shell particles, porous particles, etc.) as disclosed herein can increase a postprocessing (e.g., post-debinding and/or post-sintering) maximum wall thickness (i.e., achievable wall thickness) that is substantially free of cracking, as compared to 3D objects printed without the hollow particles, by at least or up to about 1%, at least or up to about 5%, at least or up to about 10%, at least or up to about 15%, at least or up to about 20%, at least or up to about 30%, at least or up to about 40%, at least or up to about 50%, at least or up to about 60%, at least or up to about 70%, at least or up to about 80%, at least or up to about 90%, at least or up to about 100%, at least or up to about 120%, at least or up to about 140%, at least or up to about 150%, at least or up to about 160%, at least or up to about 180%, at least or up to about 200%, at least or up to about 250%, or at least or up to about 300%.

[0223] In some embodiments, the first plurality of particles (Pl) can comprise one or more metal particles. In some embodiments, the first plurality of particles (Pl) can comprise one or more ceramic particles. In some embodiments, the first plurality of particles (Pl) can comprise one or more metal particles and one or more ceramic particles.

[0224] In some embodiments, the mixture as disclosed herein can be characterized by one or more members selected from the group consisting of (i) the Pl and the P2 can be present in the mixture in a volume ratio (P 1 :P2) of at least about 0.1; (ii) the P 1 and the P2 in the mixture can have an average particle size ratio (Pl :P2) of at least about 0.1; and (iii) the Pl and the P2 can be present, in combination, at an amount greater than about 15% by weight of the mixture. In some cases, the mixture can be characterized by two or more of (i), (ii), and (iii). In some cases, the mixture can be characterized by all of (i), (ii), and (iii).

[0225] In some cases, the Pl and the P2 can be present in the mixture as disclosed herein in a volume ratio (Pl :P2) of at least about 0.1. The volume ratio (Pl :P2) can be at least about 0.01, at least about 0.05, at least about 0.1, at least about 0.2, at least about 0.3, at least about 0.4, at least about 0.5, at least about 1, at least about 2, at least about 3, at least about 4, at least about 5, at least about 6, at least about 7, at least about 8, at least about 9, at least about 10, at least about 15, at least about 20, at least about 30, at least about 40, at least about 50, at least about 60, at least about 70, at least about 80, at least about 90, at least about 100, at least about 200, or more. Alternatively, or in addition to, the volume ratio (Pl :P2) can be at most about 200, at most about 100, at most about 90, at most about 80, at most about 70, at most about 60, at most about 50, at most about 40, at most about 30, at most about 20, at most about 15, at most about 10, at most about 9, at most about 8, at most about 7, at most about 6, at most about 5, at most about 4, at most about 3, at most about 2, at most about 1, at most about 0.5, at most about 0.4, at most about 0.3, at most about 0.2, at most about 0.1, at most about 0.05, at most about 0.01, or less.

[0226] The volume ratio (Pl :P2) can be about 0.1 to about 100. The volume ratio (Pl :P2) can be at least about 0.1. The volume ratio (Pl :P2) can be at most about 100. The volume ratio (Pl :P2) can be about 0.1 to about 0.2, about 0.1 to about 0.5, about 0.1 to about 1, about 0.1 to about 2, about 0.1 to about 5, about 0.1 to about 6, about 0.1 to about 8, about 0.1 to about 10, about 0.1 to about 20, about 0.1 to about 50, about 0.1 to about 100, about 0.2 to about 0.5, about 0.2 to about 1, about 0.2 to about 2, about 0.2 to about 5, about 0.2 to about 6, about 0.2 to about 8, about 0.2 to about 10, about 0.2 to about 20, about 0.2 to about 50, about 0.2 to about 100, about 0.5 to about 1, about 0.5 to about 2, about 0.5 to about 5, about 0.5 to about 6, about 0.5 to about 8, about 0.5 to about 10, about 0.5 to about 20, about 0.5 to about 50, about 0.5 to about 100, about 1 to about 2, about 1 to about 5, about 1 to about 6, about 1 to about 8, about 1 to about 10, about 1 to about 20, about 1 to about 50, about 1 to about 100, about 2 to about 5, about 2 to about 6, about 2 to about 8, about 2 to about 10, about 2 to about 20, about 2 to about 50, about 2 to about 100, about 5 to about 6, about 5 to about 8, about 5 to about 10, about 5 to about 20, about 5 to about 50, about 5 to about 100, about 6 to about 8, about 6 to about 10, about 6 to about 20, about 6 to about 50, about 6 to about 100, about 8 to about 10, about 8 to about 20, about 8 to about 50, about 8 to about 100, about 10 to about 20, about 10 to about 50, about 10 to about 100, about 20 to about 50, about 20 to about 100, or about 50 to about 100. The volume ratio (P1 :P2) can be about 0.1, about 0.2, about 0.5, about 1, about 2, about 5, about 6, about 8, about 10, about 20, about 50, or about 100.

[0227] In some cases, the percentage of the Pl (e.g., comprising metal particles, such as particles comprising copper) by volume in the mixture as disclosed herein can be at least about 0.01%, at least about 1%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or more. Alternatively, or in addition to, the percentage of Pl by volume in the mixture as disclosed herein can be at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 45%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 1%, at most about 0.01%, or less. The percentage of the Pl by volume in the mixture as disclosed herein can be about 1 % to about 90 %. The percentage of the Pl by volume can be at least about 1 %. The percentage of the Pl by volume can be at most about 90 %. The percentage of the Pl by volume can be about 1 % to about 10 %, about 1 % to about 20 %, about 1 % to about 30 %, about 1 % to about 35 %, about 1 % to about 40 %, about 1 % to about 45 %, about 1 % to about 50 %, about 1 % to about 60 %, about 1 % to about 70 %, about 1 % to about 80 %, about 1 % to about 90 %, about 10 % to about 20 %, about 10 % to about 30 %, about 10 % to about 35 %, about 10 % to about 40 %, about 10 % to about 45 %, about 10 % to about 50 %, about 10 % to about 60 %, about 10 % to about 70 %, about 10 % to about 80 %, about 10 % to about 90 %, about 20 % to about 30 %, about 20 % to about 35 %, about 20 % to about 40 %, about 20 % to about 45 %, about 20 % to about 50 %, about 20 % to about 60 %, about 20 % to about 70 %, about 20 % to about 80 %, about 20 % to about 90 %, about 30 % to about 35 %, about 30 % to about 40 %, about 30 % to about 45 %, about 30 % to about 50 %, about 30 % to about 60 %, about 30 % to about 70 %, about 30 % to about 80 %, about 30 % to about 90 %, about 35 % to about 40 %, about 35 % to about 45 %, about 35 % to about 50 %, about 35 % to about 60 %, about 35 % to about 70 %, about 35 % to about 80 %, about 35 % to about 90 %, about 40 % to about 45 %, about 40 % to about 50 %, about 40 % to about 60 %, about 40 % to about 70 %, about 40 % to about 80 %, about 40 % to about 90 %, about 45 % to about 50 %, about 45 % to about 60 %, about 45 % to about 70 %, about 45 % to about 80 %, about 45 % to about 90 %, about 50 % to about 60 %, about 50 % to about 70 %, about 50 % to about 80 %, about 50 % to about 90 %, about 60 % to about 70 %, about 60 % to about 80 %, about 60 % to about 90 %, about 70 % to about 80 %, about 70 % to about 90 %, or about 80 % to about 90 %. The percentage of the Pl by volume can be about 1 %, about 10 %, about 20 %, about 30 %, about 35 %, about 40 %, about 45 %, about 50 %, about 60 %, about 70 %, about 80 %, or about 90 %.In some cases, the percentage of the P2 by volume in the mixture as disclosed herein can be at least about 0.01%, at least about 1%, at least about 5%, at least about 10%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or more. Alternatively, or in addition to, the percentage of the P2 by volume in the mixture as disclosed herein can be at most about 90%, at most about 80%, at most about 70%, at most about 60%, at most about 50%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%, at most about 10%, at most about 5%, at most about 1%, at most about 0.01%, or less.

[0228] The percentage of the P2 by volume in the mixture as disclosed herein can be about 1 % to about 90 %. The percentage of the P2 by volume in the mixture as disclosed herein can be at least about 1 %. The percentage of the P2 by volume in the mixture as disclosed herein can be at most about 90 %. The percentage of the P2 by volume in the mixture as disclosed herein can be about 1 % to about 5 %, about 1 % to about 10 %, about 1 % to about 20 %, about 1 % to about 25 %, about 1 % to about 30 %, about 1 % to about 35 %, about 1 % to about 40 %, about 1 % to about 50 %, about 1 % to about 60 %, about 1 % to about 75 %, about 1 % to about 90 %, about 5 % to about 10 %, about 5 % to about 20 %, about 5 % to about 25 %, about 5 % to about 30 %, about 5 % to about 35 %, about 5 % to about 40 %, about 5 % to about 50 %, about 5 % to about 60 %, about 5 % to about 75 %, about 5 % to about 90 %, about 10 % to about 20 %, about 10 % to about 25 %, about 10 % to about 30 %, about 10 % to about 35 %, about 10 % to about 40 %, about 10 % to about 50 %, about 10 % to about 60 %, about 10 % to about 75 %, about 10 % to about 90 %, about 20 % to about 25 %, about 20 % to about 30 %, about 20 % to about 35 %, about 20 % to about 40 %, about 20 % to about 50 %, about 20 % to about 60 %, about 20 % to about 75 %, about 20 % to about 90 %, about 25 % to about 30 %, about 25 % to about 35 %, about 25 % to about 40 %, about 25 % to about 50 %, about 25 % to about 60 %, about 25 % to about 75 %, about 25 % to about 90 %, about 30 % to about 35 %, about 30 % to about 40 %, about 30 % to about 50 %, about 30 % to about 60 %, about 30 % to about 75 %, about 30 % to about 90 %, about 35 % to about 40 %, about 35 % to about 50 %, about 35 % to about 60 %, about 35 % to about 75 %, about 35 % to about 90 %, about 40 % to about 50 %, about 40 % to about 60 %, about 40 % to about 75 %, about 40 % to about 90 %, about 50 % to about 60 %, about 50 % to about 75 %, about 50 % to about 90 %, about 60 % to about 75 %, about 60 % to about 90 %, or about 75 % to about 90 %. The percentage of the P2 by volume in the mixture as disclosed herein can be about 1 %, about 5 %, about 10 %, about 20 %, about 25 %, about 30 %, about 35 %, about 40 %, about 50 %, about 60 %, about 75 %, or about 90 %.

[0229] In some cases, the Pl and the P2 can be present in the mixture as disclosed herein in an average particle-size ratio (Pl :P2) of at least about 0.1. The average particle-size ratio can be at least about 0.001, at least about 0.01, at least about 0.1, at least about 0.15, at least about 0.2, at least about 0.3, at least about 0.4, at least about 1, at least about 2, at least about 4, at least about 5, at least about 10, at least about 20, at least about 30, at least about 40, at least about 50, at least about 60, at least about 70, at least about 100, or more. Alternatively, or in addition to, the average particle-size ratio (Pl :P2) can be at most about 100, at most about 70, at most about 60, at most about 50, at most about 40, at most about 30, at most about 20, at most about 10, at most about 5, at most about 4, at most about 3, at most about 2, at most about 1, at most about 0.4, at most about 0.3, at most about 0.2, at most about 0.15, at most about 0.1, at most about 0.01, at most about 0.001, or less.

[0230] The average particle-size ratio (P1 :P2) can be about 0.01 to about 100. The average particle-size ratio (P1 :P2) can be at least about 0.01. The average particle-size ratio (P1 :P2) can be at most about 100. The average particle-size ratio (P1 :P2) can be about 0.01 to about 0.2, about 0.01 to about 0.5, about 0.01 to about 1, about 0.01 to about 2, about 0.01 to about 5, about 0.01 to about 10, about 0.01 to about 15, about 0.01 to about 30, about 0.01 to about 50, about 0.01 to about 60, about 0.01 to about 100, about 0.2 to about 0.5, about 0.2 to about 1, about 0.2 to about 2, about 0.2 to about 5, about 0.2 to about 10, about 0.2 to about 15, about 0.2 to about 30, about 0.2 to about 50, about 0.2 to about 60, about 0.2 to about 100, about 0.5 to about 1, about 0.5 to about 2, about 0.5 to about 5, about 0.5 to about 10, about 0.5 to about 15, about 0.5 to about 30, about 0.5 to about 50, about 0.5 to about 60, about 0.5 to about 100, about 1 to about 2, about 1 to about 5, about 1 to about 10, about 1 to about 15, about 1 to about 30, about 1 to about 50, about 1 to about 60, about 1 to about 100, about 2 to about 5, about 2 to about 10, about 2 to about 15, about 2 to about 30, about 2 to about 50, about 2 to about 60, about 2 to about 100, about 5 to about 10, about 5 to about 15, about 5 to about 30, about 5 to about 50, about 5 to about 60, about 5 to about 100, about 10 to about 15, about 10 to about 30, about 10 to about 50, about 10 to about 60, about 10 to about 100, about 15 to about 30, about 15 to about 50, about 15 to about 60, about 15 to about 100, about 30 to about 50, about 30 to about 60, about 30 to about 100, about 50 to about 60, about 50 to about 100, or about 60 to about 100. The average particle-size ratio (P1 :P2) can be about 0.01, about 0.2, about 0.5, about 1, about 2, about 5, about 10, about 15, about 30, about 50, about 60, or about 100.

[0231] In some cases, the average particle size of the Pl can be at least about 0.1 micrometers, at least about 1 micrometer, at least about 4 micrometers, at least about 6 micrometers, at least about 8 micrometers, at least about 10 micrometers, at least about 20 micrometers, at least about 30 micrometers, at least about 40 micrometers, at least about 50 micrometers, at least about 60 micrometers, at least about 75 micrometers, at least about 100 micrometers, at least about 125 micrometers, at least about 150 micrometers, at least about 175 micrometers, at least about 200 micrometers, at least about 300 micrometers, or more. Alternatively, or in addition to, the average particle size of Pl can be at most about 300 micrometers, at most about 200 micrometers, at most about 175 micrometers, at most about 150 micrometers, at most about 125 micrometers, at most about 100 micrometers, at most about 75 micrometers, at most about 60 micrometers, at most about 50 micrometers, at most about 40 micrometers, at most about 30 micrometers, at most about 20 micrometers, at most about 10 micrometers, at most about 8 micrometers, at most about 650 micrometers, at most about 4 micrometers, at most about 1 micrometer, at most about 0.1 micrometers, or less.

[0232] The average particle size of the Pl can be about 0.1 micrometers to about 300 micrometers. The average particle size of the Pl can be at least about 0.1 micrometers. The average particle size of the Pl can be at most about 300 micrometers. The average particle size of the Pl can be about 0.1 micrometers to about 1 micrometer, about 0.1 micrometers to about 4 micrometers, about 0.1 micrometers to about 8 micrometers, about 0.1 micrometers to about 20 micrometers, about 0.1 micrometers to about 30 micrometers, about 0.1 micrometers to about 40 micrometers, about 0.1 micrometers to about 50 micrometers, about 0.1 micrometers to about 60 micrometers, about 0.1 micrometers to about 75 micrometers, about 0.1 micrometers to about 150 micrometers, about 0.1 micrometers to about 300 micrometers, about 1 micrometer to about 4 micrometers, about 1 micrometer to about 8 micrometers, about 1 micrometer to about 20 micrometers, about 1 micrometer to about 30 micrometers, about 1 micrometer to about 40 micrometers, about 1 micrometer to about 50 micrometers, about 1 micrometer to about 60 micrometers, about 1 micrometer to about 75 micrometers, about 1 micrometer to about 150 micrometers, about 1 micrometer to about 300 micrometers, about 4 micrometers to about 8 micrometers, about 4 micrometers to about 20 micrometers, about 4 micrometers to about 30 micrometers, about 4 micrometers to about 40 micrometers, about 4 micrometers to about 50 micrometers, about 4 micrometers to about 60 micrometers, about 4 micrometers to about 75 micrometers, about 4 micrometers to about 150 micrometers, about 4 micrometers to about 300 micrometers, about 8 micrometers to about 20 micrometers, about 8 micrometers to about 30 micrometers, about 8 micrometers to about 40 micrometers, about 8 micrometers to about 50 micrometers, about 8 micrometers to about 60 micrometers, about 8 micrometers to about 75 micrometers, about 8 micrometers to about 150 micrometers, about 8 micrometers to about 300 micrometers, about 20 micrometers to about 30 micrometers, about 20 micrometers to about 40 micrometers, about 20 micrometers to about 50 micrometers, about 20 micrometers to about 60 micrometers, about 20 micrometers to about 75 micrometers, about 20 micrometers to about 150 micrometers, about 20 micrometers to about 300 micrometers, about 30 micrometers to about 40 micrometers, about 30 micrometers to about 50 micrometers, about 30 micrometers to about 60 micrometers, about 30 micrometers to about 75 micrometers, about 30 micrometers to about 150 micrometers, about 30 micrometers to about 300 micrometers, about 40 micrometers to about 50 micrometers, about 40 micrometers to about 60 micrometers, about 40 micrometers to about 75 micrometers, about 40 micrometers to about 150 micrometers, about 40 micrometers to about 300 micrometers, about 50 micrometers to about 60 micrometers, about 50 micrometers to about 75 micrometers, about 50 micrometers to about 150 micrometers, about 50 micrometers to about 300 micrometers, about 60 micrometers to about 75 micrometers, about 60 micrometers to about 150 micrometers, about 60 micrometers to about 300 micrometers, about 75 micrometers to about 150 micrometers, about 75 micrometers to about 300 micrometers, or about 150 micrometers to about 300 micrometers. The average particle size of the Pl can be about 0.1 micrometers, about 1 micrometer, about 4 micrometers, about 8 micrometers, about 20 micrometers, about 30 micrometers, about 40 micrometers, about 50 micrometers, about 60 micrometers, about 75 micrometers, about 150 micrometers, or about 300 micrometers.

[0233] In some cases, the average particle size of the P2 can be at least about 0.1 micrometers, at least about 1 micrometer, at least about 10 micrometers, at least about 15 micrometers, at least about 20 micrometers, at least about 30 micrometers, at least about 50 micrometers, at least about 70 micrometers, at least about 80 micrometers, at least about at least about 100 micrometers, at least about 120 micrometers, at least about 150 micrometers, at least about 200 micrometers, at least about 250 micrometers, at least about 300 micrometers, at least about 350 micrometers, at least about 400 micrometers, at least about 450 micrometers, at least about 500 micrometers, at least about 600 micrometers, at least about 1000 micrometers, or more. Alternatively, or in addition to, the average particle size of Pl can be at most about 1000 micrometers, at most about 600 micrometers, at most about 500 micrometers, at most about 450 micrometers, at most about 400 micrometers, at most about 350 micrometers, at most about 300 micrometers, at most about 250 micrometers, at most about 200 micrometers, at most about 150 micrometers, at most about 120 micrometers, at most about 100 micrometers, at most about 80 micrometers, at most about 70 micrometers, at most about 50 micrometers, at most about 30 micrometers, at most about 20 micrometers, at most about 15 micrometers, at most about 10 micrometers, at most about 1 micrometer, at most about 0.1 micrometers, or less.

[0234] The average particle size of the P2 can be about 0.1 micrometers to about 1,000 micrometers. The average particle size of the P2 can be at least about 0.1 micrometers. The average particle size of the P2 can be at most about 1,000 micrometers. The average particle size of the P2 can be about 0.1 micrometers to about 1 micrometer, about 0.1 micrometers to about 15 micrometers, about 0.1 micrometers to about 20 micrometers, about 0.1 micrometers to about 50 micrometers, about 0.1 micrometers to about 75 micrometers, about 0.1 micrometers to about 100 micrometers, about 0.1 micrometers to about 120 micrometers, about 0.1 micrometers to about 125 micrometers, about 0.1 micrometers to about 150 micrometers, about 0.1 micrometers to about 300 micrometers, about 0.1 micrometers to about 1,000 micrometers, about 1 micrometer to about 15 micrometers, about 1 micrometer to about 20 micrometers, about 1 micrometer to about 50 micrometers, about 1 micrometer to about 75 micrometers, about 1 micrometer to about 100 micrometers, about 1 micrometer to about 120 micrometers, about 1 micrometer to about 125 micrometers, about 1 micrometer to about 150 micrometers, about 1 micrometer to about 300 micrometers, about 1 micrometer to about 1,000 micrometers, about 15 micrometers to about 20 micrometers, about 15 micrometers to about 50 micrometers, about 15 micrometers to about 75 micrometers, about 15 micrometers to about 100 micrometers, about 15 micrometers to about 120 micrometers, about 15 micrometers to about 125 micrometers, about 15 micrometers to about 150 micrometers, about 15 micrometers to about 300 micrometers, about 15 micrometers to about 1,000 micrometers, about 20 micrometers to about 50 micrometers, about 20 micrometers to about 75 micrometers, about 20 micrometers to about 100 micrometers, about 20 micrometers to about 120 micrometers, about 20 micrometers to about 125 micrometers, about 20 micrometers to about 150 micrometers, about 20 micrometers to about 300 micrometers, about 20 micrometers to about 1,000 micrometers, about 50 micrometers to about 75 micrometers, about 50 micrometers to about 100 micrometers, about 50 micrometers to about 120 micrometers, about 50 micrometers to about 125 micrometers, about 50 micrometers to about 150 micrometers, about 50 micrometers to about 300 micrometers, about 50 micrometers to about 1,000 micrometers, about 75 micrometers to about 100 micrometers, about 75 micrometers to about 120 micrometers, about 75 micrometers to about 125 micrometers, about 75 micrometers to about 150 micrometers, about 75 micrometers to about 300 micrometers, about 75 micrometers to about 1,000 micrometers, about 100 micrometers to about 120 micrometers, about 100 micrometers to about 125 micrometers, about 100 micrometers to about 150 micrometers, about 100 micrometers to about 300 micrometers, about 100 micrometers to about 1,000 micrometers, about 120 micrometers to about 125 micrometers, about 120 micrometers to about 150 micrometers, about 120 micrometers to about 300 micrometers, about 120 micrometers to about 1,000 micrometers, about 125 micrometers to about 150 micrometers, about 125 micrometers to about 300 micrometers, about 125 micrometers to about 1,000 micrometers, about 150 micrometers to about 300 micrometers, about 150 micrometers to about 1,000 micrometers, or about 300 micrometers to about 1,000 micrometers. The average particle size of the P2 can be about 0.1 micrometers, about 1 micrometer, about 15 micrometers, about 20 micrometers, about 50 micrometers, about 75 micrometers, about 100 micrometers, about 120 micrometers, about 125 micrometers, about 150 micrometers, about 300 micrometers, or about 1,000 micrometers. [0235] In some cases, the combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be at least 0.1%. The combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be at least 1%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 75%, at least 85%, at least 95%, or more. Alternatively or in addition to, the combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be at most 95%, at most 85%, at most 75%, at most 65%, at most 60%, at most 55%, at most 50%, at most 45%, at most 40%, at most 35%, at most 30%, at most 25%, at most 20%, at most 15%, at most 10%, at most 5%, at most 1%, or less.

[0236] The combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be about 1 % to about 95 %. The combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be at least about 1 %. The combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be at most about 95 %. The combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be about 1 % to about 10 %, about 1 % to about 15 %, about 1 % to about 20 %, about 1 % to about 30 %, about 1 % to about 40 %, about 1 % to about 50 %, about 1 % to about 60 %, about 1 % to about 65 %, about 1 % to about 75 %, about 1 % to about 85 %, about 1 % to about 95 %, about 10 % to about 15 %, about 10 % to about 20 %, about 10 % to about 30 %, about 10 % to about 40 %, about 10 % to about 50 %, about 10 % to about 60 %, about 10 % to about 65 %, about 10 % to about 75 %, about 10 % to about 85 %, about 10 % to about 95 %, about 15 % to about 20 %, about 15 % to about 30 %, about 15 % to about 40 %, about 15 % to about 50 %, about 15 % to about 60 %, about 15 % to about 65 %, about 15 % to about 75 %, about 15 % to about 85 %, about 15 % to about 95 %, about 20 % to about 30 %, about 20 % to about 40 %, about 20 % to about 50 %, about 20 % to about 60 %, about 20 % to about 65 %, about 20 % to about 75 %, about 20 % to about 85 %, about 20 % to about 95 %, about 30 % to about 40 %, about 30 % to about 50 %, about 30 % to about 60 %, about 30 % to about 65 %, about 30 % to about 75 %, about 30 % to about 85 %, about 30 % to about 95 %, about 40 % to about 50 %, about 40 % to about 60 %, about 40 % to about 65 %, about 40 % to about 75 %, about 40 % to about 85 %, about 40 % to about 95 %, about 50 % to about 60 %, about 50 % to about 65 %, about 50 % to about 75 %, about 50 % to about 85 %, about 50 % to about 95 %, about 60 % to about 65 %, about 60 % to about 75 %, about 60 % to about 85 %, about 60 % to about 95 %, about 65 % to about 75 %, about 65 % to about 85 %, about 65 % to about 95 %, about 75 % to about 85 %, about 75 % to about 95 %, or about 85 % to about 95 %. The combined percentages by weight of the Pl and the P2 in the mixture as disclosed herein can be about 1 %, about 10 %, about 15 %, about 20 %, about 30 %, about 40 %, about 50 %, about 60 %, about 65 %, about 75 %, about 85 %, or about 95 %.

[0237] In some cases, the percentage by weight of the Pl in the mixture as disclosed herein can be at least 1%. The percentage by weight of the Pl in the mixture as disclosed herein can be at least 1%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or more. Alternatively, or in addition to, the percentage by weight of the Pl in the mixture as disclosed herein can be at most 95%, at most 90%, at most 85%, at most 80%, at most 75%, at most 70%, at most 65%, at most 60%, at most 50%, at most 40%, at most 30%, at most 20%, at most 10%, at most 5%, at most 1%, or less.

[0238] The percentage by weight of the Pl in the mixture as disclosed herein can be about 1 % to about 95 %. The percentage by weight of the Pl in the mixture as disclosed herein can be at least about 1 %. The percentage by weight of the Pl in the mixture as disclosed herein can be at most about 95 %. The percentage by weight of the Pl in the mixture as disclosed herein can be about 1 % to about 10 %, about 1 % to about 25 %, about 1 % to about 50 %, about 1 % to about 60 %, about 1 % to about 65 %, about 1 % to about 70 %, about 1 % to about 75 %, about 1 % to about 80 %, about 1 % to about 85 %, about 1 % to about 90 %, about 1 % to about 95 %, about 10 % to about 25 %, about 10 % to about 50 %, about 10 % to about 60 %, about 10 % to about 65 %, about 10 % to about 70 %, about 10 % to about 75 %, about 10 % to about 80 %, about 10 % to about 85 %, about 10 % to about 90 %, about 10 % to about 95 %, about 25 % to about 50 %, about 25 % to about 60 %, about 25 % to about 65 %, about 25 % to about 70 %, about 25 % to about 75 %, about 25 % to about 80 %, about 25 % to about 85 %, about 25 % to about 90 %, about 25 % to about 95 %, about 50 % to about 60 %, about 50 % to about 65 %, about 50 % to about 70 %, about 50 % to about 75 %, about 50 % to about 80 %, about 50 % to about 85 %, about 50 % to about 90 %, about 50 % to about 95 %, about 60 % to about 65 %, about 60 % to about 70 %, about 60 % to about 75 %, about 60 % to about 80 %, about 60 % to about 85 %, about 60 % to about 90 %, about 60 % to about 95 %, about 65 % to about 70 %, about 65 % to about 75 %, about 65 % to about 80 %, about 65 % to about 85 %, about 65 % to about 90 %, about 65 % to about 95 %, about 70 % to about 75 %, about 70 % to about 80 %, about 70 % to about 85 %, about 70 % to about 90 %, about 70 % to about 95 %, about 75 % to about 80 %, about 75 % to about 85 %, about 75 % to about 90 %, about 75 % to about 95 %, about 80 % to about 85 %, about 80 % to about 90 %, about 80 % to about 95 %, about 85 % to about 90 %, about 85 % to about 95 %, or about 90 % to about 95 %. The percentage by weight of the Pl in the mixture as disclosed herein can be about 1 %, about 10 %, about 25 %, about 50 %, about 60 %, about 65 %, about 70 %, about 75 %, about 80 %, about 85 %, about 90 %, or about 95 %.

[0239] In some cases, the percentage by weight of the P2 in the mixture as disclosed herein can be at least 0.01%. The percentage by weight of the P2 in the mixture as disclosed herein can be at least 0.01%, at least 0.025%, at least 0.05%, at least 0.075%, at least 0.1%, at least 0.2%, at least 0.3%, at least 0.4%, at least 0.5%, at least 0.6%, at least 0.7%, at least 0.8%, at least 0.9%, at least 1%, at least 2%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, or more. Alternatively, or in addition to, the percentage by weight of the P2 in the mixture as disclosed herein can be at most 50%, at most 40%, at most 30%, at most 20%, at most 10%, at most 5%, at most 2%, at most 1%, at most 0.9%, at most 0.8%, at most 0.7%, at most 0.6%, at most 0.5%, at most 0.4%, at most 0.3%, at most 0.2%, at most 0.1%, at most 0.075%, at most 0.5%, at most 0.025%, at most 0.01%, or less.

[0240] The percentage by weight of the P2 in the mixture as disclosed herein can be about 0.01 % to about 50 %. The percentage by weight of the P2 in the mixture as disclosed herein can be at least about 0.01 %. The percentage by weight of the P2 in the mixture as disclosed herein can be at most about 50 %. The percentage by weight of the P2 in the mixture as disclosed herein can be about 0.01 % to about 0.05 %, about 0.01 % to about 0.1 %, about 0.01 % to about 0.2 %, about 0.01 % to about 0.5 %, about 0.01 % to about 0.7 %, about 0.01 % to about 0.9 %, about 0.01 % to about 1 %, about 0.01 % to about 2 %, about 0.01 % to about 5 %, about 0.01 % to about 25 %, about 0.01 % to about 50 %, about 0.05 % to about 0.1 %, about 0.05 % to about 0.2 %, about 0.05 % to about 0.5 %, about 0.05 % to about 0.7 %, about 0.05 % to about 0.9 %, about 0.05 % to about 1 %, about 0.05 % to about 2 %, about 0.05 % to about 5 %, about 0.05 % to about 25 %, about 0.05 % to about 50 %, about 0.1 % to about 0.2 %, about 0.1 % to about 0.5 %, about 0.1 % to about 0.7 %, about 0.1 % to about 0.9 %, about 0.1 % to about 1 %, about 0.1 % to about 2 %, about 0.1 % to about 5 %, about 0.1 % to about 25 %, about 0.1 % to about 50 %, about 0.2 % to about 0.5 %, about 0.2 % to about 0.7 %, about 0.2 % to about 0.9 %, about 0.2 % to about 1 %, about 0.2 % to about 2 %, about 0.2 % to about 5 %, about 0.2 % to about 25 %, about 0.2 % to about 50 %, about 0.5 % to about 0.7 %, about 0.5 % to about 0.9 %, about 0.5 % to about 1 %, about 0.5 % to about 2 %, about 0.5 % to about 5 %, about 0.5 % to about 25 %, about 0.5 % to about 50 %, about 0.7 % to about 0.9 %, about 0.7 % to about 1 %, about 0.7 % to about 2 %, about 0.7 % to about 5 %, about 0.7 % to about 25 %, about 0.7 % to about 50 %, about 0.9 % to about 1 %, about 0.9 % to about 2 %, about 0.9 % to about 5 %, about 0.9 % to about 25 %, about 0.9 % to about 50 %, about 1 % to about 2 %, about 1 % to about 5 %, about 1 % to about 25 %, about 1 % to about 50 %, about 2 % to about 5 %, about 2 % to about 25 %, about 2 % to about 50 %, about 5 % to about 25 %, about 5 % to about 50 %, or about 25 % to about 50 %. The percentage by weight of the P2 in the mixture as disclosed herein can be about 0.01 %, about 0.05 %, about 0.1 %, about 0.2 %, about 0.5 %, about 0.7 %, about 0.9 %, about 1 %, about 2 %, about 5 %, about 25 %, or about 50 %. [0241] In some embodiments, the Pl of the mixture as disclosed herein can comprise metal particles. For example, the Pl of the mixture can comprise copper particles. In another example, the Pl of the mixture can comprise metal particles (e.g., copper particles) and can be substantially free of ceramic particles. In some embodiments, the Pl of the mixture as disclosed herein can comprise ceramic particles. For example, the Pl of the mixture can comprise ceramic particles and can be substantially free of metal particles. In some embodiments, the Pl of the mixture as disclosed herein can comprise metal particles and ceramic particles.

[0242] Using the mixture comprising the hollow particles as disclosed herein can enhance resolution of the formation of the 3D object (e.g., 3D printing resolution, such as a thickness of a print layer or print feature that is substantially free of cracks) by at least about 1%, at least about 2%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 100%, or more, as compared to that of a 3D object formed by a mixture that does not comprise the hollow particles.

[0243] FIG. 1 shows an example of a mixture 100 as disclosed herein. The mixture 100 comprises one or more polymeric precursors 110 configured to form a polymeric material. The mixture 100 further comprises a first plurality of particles (Pl) 120 comprising a metal particle or a ceramic particle. The mixture 100 further comprises a second plurality of particles (P2) 130 comprising a hollow particle. The mixture 100 is characterized by one or more members selected from the group consisting of: (i) the Pl and the P2 are present in the mixture in a volume ratio (P1 :P2) of at least about 0.1; (ii) the Pl and the P2 in the mixture have an average particle size ratio (Pl :P2) of at least about 0.1; and (iii) the Pl and the P2 are present, in combination, at an amount of greater than about 15% by weight in the mixture.

[0244] FIG. 2 shows an example of a mixture 200 as disclosed herein. The mixture 200 comprises one or more polymeric precursors 210 configured to form a polymeric material. The mixture 200 further comprises one or more metal particles 220. The mixture 200 further comprises one or more hollow particles 230.

[0245] In some embodiments, the mixture as disclosed herein can further comprise additional components usable for forming the 3D object. The mixture can comprise at least one photoinitiator configured to initiate formation of the polymeric material from the plurality of polymeric precursors. The mixture can comprise at least one photoinhibitor configured to inhibit formation of the polymeric material from the plurality of polymeric precursors.

[0246] In another aspect, the present disclosure provides a method for forming a 3D object (e.g., 3D printing, injection molding, etc.). The method can utilize any one of the mixtures disclosed herein. For example, the mixture can comprise the one or more polymeric precursors configured to form the polymeric material. The mixture can further comprise the first plurality of particles (Pl) comprising the metal particle and/or the ceramic particle. The mixture can further comprise the second plurality of particles (P2) comprising the hollow particle. Alternatively, or in addition to, the P2 can comprise a particle exhibiting an interior density of a material, wherein, upon exposure to a stimulus, the particle can be capable of transforming into an additional particle exhibiting an additional interior density of the material that is lower than the interior density of the particle (e.g., a hollow particle).

[0247] In some embodiments, the mixture can be utilized in an injection molding process to form the 3D object. In some cases, the 3D object printed from the mixture as disclosed herein comprises an injection mold. In some cases, the mixture as disclosed herein can be provided (e.g., infused, injected, deposited, etc.) into an existing mold to form at least a portion of a 3D object. For example, the mixture as disclosed herein can be provided (e.g., deposited) onto the existing mold at a temperature above the melting point of the mixture as disclosed herein and cooled to form a solid 3D object.

[0248] In some embodiments, the mixture as disclosed herein can be utilized in various 3D printing systems and methods (e.g., stereolithography) to form the 3D object. In some embodiments, the method, as disclosed herein, for forming a three-dimensional object can comprise providing any one of the mixtures as disclosed herein and exposing the provided mixture to a stimulus to cause the one or more polymeric precursors to form the polymeric material that at least partially encapsulates the metal particles and the hollow particles, thereby to form a green part corresponding to at least a portion of the 3D object. In some cases, the method, as disclosed herein, for forming a three-dimensional object can further comprise providing the mixture adjacent to a print window (e.g., for stereolithography). In some cases, the stimulus can comprise a light, and the method can further comprise directing the light through the print window and towards the mixture. In some cases, the method can further comprise providing the mixture to a mold corresponding to at least a portion of the 3D object (e.g., for metal injection molding). In some cases, the method can further comprise subjecting the green part to a first temperature to form a brown part corresponding to at least the portion of the 3D object, wherein the polymeric material and the P2 are configured to decompose at the first temperature. In some cases, the method can further comprise subjecting the brown part to a second temperature to sinter the Pl, wherein the second temperature is higher than the first temperature. In some cases, the hollow particle used in the method as disclosed herein can be a polymeric hollow particle. Additional aspects for 3D printing

[0249] FIG. 3 shows an example of a 3D printing system 600. The system 600 includes a vat 602 to hold a mixture 604, which includes a polymeric precursor. The vat 602 includes a window 606 in its bottom through which illumination is transmitted to cure a 3D printed structure 608. The 3D printed structure 608 is shown in FIG. 3 as a block, however, in practice a wide variety of complicated shapes can be 3D printed. In some cases, the 3D printed structure 608 includes entirely solid structures, hollow core prints, lattice core prints and generative design geometries. Additionally, a 3D printed structure 608 can be partially cured such that the 3D printed structure 608 has a gel-like or viscous mixture characteristic.

[0250] The 3D printed structure 608 is 3D printed on a build head 610, which is connected by a rod 612 to one or more 3D printing mechanisms 614. The 3D printing mechanisms 614 can include various mechanical structures for moving the build head 610 within and above the vat 602. This movement is a relative movement, and thus moving pieces can be the build head 610, the vat 602, or both, in various cases. In some cases, the 3D printing mechanisms 614 include Cartesian (xyz) type 3D printer motion systems or delta type 3D printer motion systems. In some cases, the 3D printing mechanisms 614 include one or more controllers 616 which can be implemented using integrated circuit technology, such as an integrated circuit board with embedded processors and firmware. Such controllers 616 can be in communication with a computer or computer systems 618. In some cases, the 3D printing system 600 includes a computer 618 that connects to the 3D printing mechanisms 614 and operates as a controller for the 3D printing system 600.

[0251] A computer 618 can include one or more hardware (or computer) processors 620 and a memory 622. For example, a 3D printing program 624 can be stored in the memory 622 and run on the one or more processors 620 to implement the techniques described herein. The controller 618, including the one or more hardware processors 620, may be individually or collectively programmed to implement methods of the present disclosure.

[0252] Multiple devices emitting various wavelengths and/or intensities of light, including a light projection device 626 and light sources 628, can be positioned below the window 606 and in communication to the computer 618 (or other controller). In some cases, the multiple devices include the light projection device 626 and the light sources 628. The light sources 628 can include greater than or equal to about 2, 3, 4, 5, 6, 7, 8, 9, 10, or more light sources. As an alternative, the light sources 628 may include less than or equal to about 10, 9, 8 7, 6, 5, 4, 3, 2 or fewer light sources. As an alternative to the light sources 628, a single light source may be used. The light projection device 626 directs a first light having a first wavelength into the mixture 604 within the vat 602 through window 606. The first wavelength emitted by the light projection device 626 is selected to produce photoinitiation and is used to create the 3D printed structure 608 on the build head 610 by curing the photoactive resin in the mixture 604 within a photoinitiation layer 60630. In some cases, the light projection device 626 is utilized in combination with one or more projection optics 62632 (e.g. a projection lens for a digital light processing (DLP) device), such that the light output from the light projection device 626 passes through one or more projection optics 62632 prior to illuminating the mixture 604 within the vat 602.

[0253] In some cases, the light projection device 626 is a DLP device including a digital micro-mirror device (DMD) for producing patterned light that can selectively illuminate and cure 3D printed structures 608. The light projection device 626, in communication with the computer 618, can receive instructions from the 3D printing program 624 defining a pattern of illumination to be projected from the light projection device 626 into the photoinitiation layer 60630 to cure a layer of the photoactive resin onto the 3D printed structure 608.

[0254] In some cases, the light projection device 626 and projection optics 632 are a laser and a scanning mirror system, respectively (e.g., stereolithography apparatus). Additionally, in some cases, the light source includes a second laser and a second scanning mirror system. Such light source may emit a beam of a second light having a second wavelength. The second wavelength may be different from the first wavelength. This may permit photoinhibition to be separately controlled from photoinitiation. Additionally, in some cases, the platform 638 is separately supported on adjustable axis rails 640 from the projection optics 632 such that the platform 638 and the projection optics 632 can be moved independently.

[0255] The relative position (e.g., vertical position) of the platform 638 and the vat 602 may be adjusted. In some examples, the platform 638 is moved and the vat 602 is kept stationary. As an alternative, the platform 638 is kept stationary and the vat 602 is moved. As another alternative, both the platform 638 and the vat 602 are moved.

[0256] The light sources 628 direct a second light having a second wavelength into the mixture 604 in the vat 602. The second light may be provided as multiple beams from the light sources 628 into the build area simultaneously. As an alternative, the second light may be generated from the light sources 628 and provided as a single beam (e.g., uniform beam) into the beam area. The second wavelength emitted by the light sources 628 is selected to produce photoinhibition in the photoactive resin in the mixture 604 and is used to create a photoinhibition layer 634 within the mixture 604 directly adjacent to the window 606. The light sources 628 can produce a flood light to create the photoinhibition layer 634, the flood light being a non-pattemed, high-intensity light. In some cases, the light sources 628 are light emitting diodes (LEDs) 336. The light sources 628 can be arranged on a platform 638. The platform 638 is mounted on adjustable axis rails 640. The adjustable axis rails 640 allow for movement of the platform 638 along an axis. In some cases, the platform 638 additionally acts as a heat-sink for at least the light sources 628 arranged on the platform 638.

[0257] The respective thicknesses of the photoinitiation layer 630 and the photoinhibition layer 634 can be adjusted by computer 618 (or other controller). In some cases, this change in layer thickness(es) is performed for each new 3D printed layer, depending on the desired thickness of the 3D printed layer, and/or the type of 3D printing process being performed. The thickness(es) of the photoinitiation layer 630 and the photoinhibition layer 634 can be changed, for example, by changing the intensity of the respective light emitting devices, exposure times for the respective light emitting devices, the photoactive species in the mixture 604, or a combination thereof. In some cases, by controlling relative rates of reactions between the photoactive species (e.g., by changing relative or absolute amounts of photoactive species in the mixture, or by adjusting light intensities of the first and/or second wavelength), the overall rate of polymerization can be controlled. This process can thus be used to prevent polymerization from occurring at the resin-window interface and control the rate at which polymerization takes place in the direction normal to the resin-window interface.

[0258] For example, in some cases, an intensity of the light sources 628 emitting a photoinhibiting wavelength to create a photoinhibition layer 634 is altered in order to change a thickness of the photoinhibition layer 634. Altering the intensity of the light sources 628 can include increasing the intensity or decreasing the intensity of the light sources 628. Increasing the intensity of the light sources 628 (e.g., LEDs) can be achieved by increasing a power input to the light sources 628 by controllers 616 and/or computer 618. Decreasing the intensity of the light sources 628 (e.g., LEDs) can be achieved by decreasing a power input to the light sources 628 by controllers 616 and/or computer 618. In some cases, increasing the intensity of the light sources 628, and thereby increasing the thickness of the photoinhibition layer 634, will result in a decrease in thickness of the photoinitiation layer 630. A decreased photoinitiation layer thickness can result in a thinner 3D printed layer on the 3D printed structure 608.

[0259] In some cases, the intensities of all of the light sources 628 are altered equally (e.g., decreased by a same level by reducing power input to all the light sources by an equal amount). The intensities of the light sources 628 can also be altered where each light source of a set of light sources 628 produces a different intensity. For example, for a set of four LEDs generating a photoinhibition layer 634, two of the four LEDs can be decreased in intensity by 10% (by reducing power input to the LEDs) while the other two of the four LEDs can be increased in intensity by 10% (by increasing power input to the LEDs). Setting different intensities for a set of light sources 628 can produce a gradient of thickness in a cured layer of the 3D printed structure or other desirable effects.

[0260] In some cases, the computer 618 (in combination with controllers 616) adjusts an amount of a photoinitiator species and/or a photoinhibitor species in the mixture 604. The photoinitiator and photoinhibitor species can be delivered to the vat 602 via an inlet 646 and evacuated from the vat 602 via an outlet 648. In general, one aspect of the photoinhibitor species is to prevent curing (e.g., suppress cross-linking of the polymers) of the photoactive resin in the mixture 604. In general, one aspect of the photoinitiation species is to promote curing (e.g., enhance cross-linking of the polymers) of the photoactive resin in the mixture 604. In some cases, the 3D printing system 600 includes multiple containment units to hold input/output flow from the vat 602.

[0261] In some cases, the intensities of the light sources 628 are altered based in part on an amount (e.g., volumetric or weight fraction) of the one or more photoinhibitor species in the mixture and/or an amount (e.g., volumetric or weight fraction) of the one or more photoinitiator species in the mixture. Additionally, the intensities of the light sources 628 are altered based in part on a type (e.g., a particular reactive chemistry, brand, composition) of the one or more photoinhibitor species in the mixture and/or a type (e.g., a particular reactive chemistry, brand, composition) of the one or more photoinitiator species in the mixture. For example, an intensity of the light sources 628 for a mixture 604 including a first photoinhibitor species of a high sensitivity (e.g., a high reactivity or conversion ratio to a wavelength of the light sources 628) can be reduced when compared to the intensity of the light sources 628 for a mixture 604 including a second photoinhibitor species of a low sensitivity (e.g., a low reactivity or conversion ratio to a wavelength of the light sources 628).

[0262] In some cases, the changes to layer thickness(es) is performed during the creation of the 3D printed structure 608 based on one or more details of the 3D printed structure 608 at one or more points in the 3D printing process. For example, the respective layer thickness(es) can be adjusted to improve resolution of the 3D printed structure 608 in the dimension that is the direction of the movement of the build head 610 relative to the vat 602 (e.g., z-axis) in the layers that require it.

[0263] Though the 3D printing system 600 is described in FIG. 3 as a bottom-up system where the light projection device 626 and the light sources 628 are located below the vat 602 and build head 610, other configurations can be utilized. For example, a top-down system, where the light projection device 626 and the light sources 628 are located above the vat 602 and build head 610, can also be employed.

[0264] FIGs. 4 and 5 show additional examples of a 3D printing system. Referring to FIG. 4, the system 700 includes a platform 701 comprising an area (i.e., a print surface, such as a film 770) configured to hold the mixture 704 or a film of the mixture 704, which includes a photoactive resin. The mixture 704 may include a plurality of particles (e.g., metal, intermetallic, and/or ceramic particles). The platform 701 comprises a print window 703. The system 700 further comprises a film transfer unit 772 that is configured to hold the film 770. The film transfer unit is operatively coupled to one or more actuators to dispose the film 770 onto the print window 703.

[0265] The platform 701 comprises a plurality of first coupling units 750. The platform 701 is an open platform, wherein the mixture 704 is self-supporting on or adjacent to the film 770 without requiring support or being supported by any wall. The plurality of first coupling units 750 are not in contact with the mixture 704 during 3D printing. The system 700 includes a build head 710 configured to move relative to the platform 701. The build head 710 is movable by an actuator 712 (e.g., a linear actuator) operatively coupled to the build head 710. Alternatively, or in addition to, the platform 701 may comprise one or more actuators to move the platform 701 relative to the build head 710. The build head 710 comprises a surface 711 configured to hold at least a portion of a 3D object 708a (e.g., a previously printed portion of the 3D object) or a different object onto which the at least the portion of the 3D object is to be printed. The surface 711 of the build head 710 may be a portion of a surface of the build head 710. Alternatively, or in addition to, the surface 711 may be a surface of an object (e.g., a film or a slab) that is disposed on or adjacent to a surface of the build head 710. The build head 710 comprises a plurality of second coupling units 760. One of the plurality of second coupling units 760 of the build head 710 is configured to couple to one of the plurality of the first coupling units 750 of the platform 701 to provide an alignment of film 770 relative to the surface 711 of the build head 710 during 3D printing. In some examples, the plurality of first coupling units 750 (e.g., three first coupling units) and the plurality of second coupling units 760 (e.g., three second coupling units) may couple to generate a kinematic coupling between the build head 710 and the film 770, to provide an alignment between the build head 710 and the film 770. The relative movement between the build head and the platform may continue until each of the plurality of first coupling units 750 is coupled to its respective second coupling unit from the plurality of second coupling units 760 (or vice versa). [0266] One or more of the plurality of first coupling units 750 of the platform 701 may comprise one or more sensors 752. Alternatively, or in addition to, one or more of the plurality of second coupling units 760 of the build head 710 may comprise one or more sensors 762. The one or more sensors 752 and/or the one or more sensors 762 may be configured to at least detect coupling of the first coupling unit(s) 750 and the second coupling unit(s) 760.

[0267] The plurality of first coupling units 750 of the platform 701 may be operatively coupled to one or more actuators 754 (e.g., one or more z-axis telescopic actuators) configured to adjust a height (or protrusion) of the plurality of first coupling units 750 relative to the platform 701 (or relative to a surface of the film 770 disposed adjacent to the platform 701). The one or more actuators 754 may comprise one or more fasteners 756 (e.g., one or more shaft clamps) configured to fasten, hold on to, or stabilize a movement of the plurality of first coupling units 750 relative to the actuators 754.

[0268] The plurality of second coupling units 760 of the build head 710 may be operatively coupled to one or more actuators (e.g., one or more z-axis telescopic actuators) configured to adjust a height (or protrusion) of the plurality of second coupling units 760 relative to a surface 711 of the build head 710 (or relative to a surface of the object 708a disposed on the build head 710). The one or more actuators may comprise one or more fasteners (e.g., one or more shaft clamps) configured to fasten, hold on to, or stabilize a movement of the plurality of second coupling units 760 relative to the actuators.

[0269] One or more optical sources 726 directs one or more lights to the mixture 704 to cure the photoactive resin in the at least the portion of the mixture 704, thereby to print at least a portion of the 3D object on the surface of the build head 710 or a surface of the object 708a disposed on the surface of the build head 710. The optical source(s) 726 may direct the light(s) through the print surface 702 of the platform 701 and to the at least the portion of the mixture for 3D printing.

[0270] Referring to FIG. 5, the 3D printing system 800 comprises a mixture deposition zone 810 and a printing zone 820 that are (i) connected to a same platform 701 or (ii) coupled to the same platform 701. The system 800 further comprises a deposition head 705 configured to deposit a mixture 704 to the platform 701, print window 703, and/or film 770 configured to hold a mixture. In this example, the deposition head is configured to deposit the mixture 704 onto the film 770. The deposition head 705 comprises a nozzle 707 that is in fluid communication with a source of the mixture 704 and at least one wiper 706 configured to (i) reduce or inhibit flow the mixture 704 out of the deposition head 705, (ii) flatten the mixture 704 into a film or layer of the mixture 704, and/or (iii) remove any excess of the 704 from the film 770. The system 800 further comprises a mixture sensor 830 (e.g., a camera, a densitometer, etc.) configured to detect one or more qualities of the mixture 704 that is deposited onto the film 770. The mixture sensor comprises a mixture sensor light source 832 and a mixture sensor detector 834. The mixture sensor light source 832 is disposed beneath the film 770, and the mixture sensor detector 834 is disposed above the film 770. Alternatively, or in addition to, the mixture sensor light source 832 and the mixture sensor detector 834 may be disposed inversely or on the same side of the film 770. Subsequent to depositing a layer of the mixture 704 on the film 770, the mixture sensor light source 832 may emit a sensor light (e.g., infrared light) through at least the film 770 and towards the layer of mixture 704 on or adjacent to the film 770, and the mixture sensor detector 834 may capture or detect any of the infrared light that is transmitted through the layer of the mixture 704. Measurements by the mixture sensor 830 can help determine whether a quality of the layer of the mixture 704 is sufficient to proceed with printing at least a portion of the 3D object. The printing zone 820 can comprise one or more components of the 3D printing system 700 provided in FIG. 4.

[0271] Referring to FIG. 5, the film 770 is coupled to a film transfer unit 772. The film transfer unit 772 is configured to move 860 at least between and/or over the mixture deposition zone 810 and the printing zone 820.

[0272] Other features any of the 3D printing systems and methods may be as described in, for example, U.S. Patent Publication No. 2016/0067921 (“THREE DIMENSIONAL PRINTING ADHESION REDUCTION USING PHOTOINHIBITION”), U.S. Patent Publication No. 2018/0348646 (“MULTI WAVELENGTH STEREOLITHOGRAPHY HARDWARE CONFIGURATIONS”), U.S. Patent Publication No. 2018/0333911 (“VISCOUS FILM THREE-DIMENSIONAL PRINTING SYSTEMS AND METHODS”), International Application No. PCT/US2019/068413 (“SENSORS FOR THREE-DIMENSIONAL PRINTING SYSTEMS AND METHODS”), and International Application No. PCT/US2020/033279 (“STEREOLITHOGRAPHY THREE-DIMENSIONAL PRINTING SYSTEMS AND METHODS”), each of which is entirely incorporated herein by reference.

Computer systems

[0273] The present disclosure provides computer systems that are programmed to implement methods of the disclosure. FIG. 6 shows a computer system 1101 that is programmed or otherwise configured to operate the 3D printer of the present disclosure. The computer system 1101 can regulate various aspects of the present disclosure, such as, for example, using any one of the mixtures disclosed herein to print a 3D object, and/or subjecting the 3D object to a stimulus (e.g., thermal treatment) to debind at least a portion of hollow particles in the 3D object. The computer system 1101 can be an electronic device of a user or a computer system that is remotely located with respect to the electronic device. The electronic device can be a mobile electronic device.

[0274] The computer system 1101 includes a central processing unit (CPU, also “processor” and “computer processor” herein) 1105, which can be a single core or multi core processor, or a plurality of processors for parallel processing. The computer system 1101 also includes memory or memory location 1110 (e.g., random-access memory, read-only memory, flash memory), electronic storage unit 1115 (e.g., hard disk), communication interface 1120 (e.g., network adapter) for communicating with one or more other systems, and peripheral devices 1125, such as cache, other memory, data storage and/or electronic display adapters. The memory 1110, storage unit 1115, interface 1120 and peripheral devices 1125 are in communication with the CPU 1105 through a communication bus (solid lines), such as a motherboard. The storage unit 1115 can be a data storage unit (or data repository) for storing data. The computer system 1101 can be operatively coupled to a computer network (“network”) 1130 with the aid of the communication interface 1120. The network 1130 can be the Internet, an internet and/or extranet, or an intranet and/or extranet that is in communication with the Internet. The network 1130 in some cases is a telecommunication and/or data network. The network 1130 can include one or more computer servers, which can enable distributed computing, such as cloud computing. The network 1130, in some cases with the aid of the computer system 1101, can implement a peer-to-peer network, which may enable devices coupled to the computer system 1101 to behave as a client or a server.

[0275] The CPU 1105 can execute a sequence of machine-readable instructions, which can be embodied in a program or software. The instructions may be stored in a memory location, such as the memory 1110. The instructions can be directed to the CPU 1105, which can subsequently program or otherwise configure the CPU 1105 to implement methods of the present disclosure. Examples of operations performed by the CPU 1105 can include fetch, decode, execute, and writeback.

[0276] The CPU 1105 can be part of a circuit, such as an integrated circuit. One or more other components of the system 1101 can be included in the circuit. In some cases, the circuit is an application specific integrated circuit (ASIC).

[0277] The storage unit 1115 can store files, such as drivers, libraries and saved programs. The storage unit 1115 can store user data, e.g., user preferences and user programs. The computer system 1101 in some cases can include one or more additional data storage units that are external to the computer system 1101, such as located on a remote server that is in communication with the computer system 1101 through an intranet or the Internet.

[0278] The computer system 1101 can communicate with one or more remote computer systems through the network 1130. For instance, the computer system 1101 can communicate with a remote computer system of a user. Examples of remote computer systems include personal computers (e.g., portable PC), slate or tablet PC’s (e.g., Apple® iPad, Samsung® Galaxy Tab), telephones, Smart phones (e.g., Apple® iPhone, Android-enabled device, Blackberry®), or personal digital assistants. The user can access the computer system 1101 via the network 1130.

[0279] Methods as described herein can be implemented by way of machine (e.g., computer processor) executable code stored on an electronic storage location of the computer system 1101, such as, for example, on the memory 1110 or electronic storage unit 1115. The machine executable or machine readable code can be provided in the form of software. During use, the code can be executed by the processor 1105. In some cases, the code can be retrieved from the storage unit 1115 and stored on the memory 1110 for ready access by the processor 1105. In some situations, the electronic storage unit 1115 can be precluded, and machine-executable instructions are stored on memory 1110.

[0280] The code can be pre-compiled and configured for use with a machine having a processer adapted to execute the code, or can be compiled during runtime. The code can be supplied in a programming language that can be selected to enable the code to execute in a precompiled or as-compiled fashion.

[0281] Aspects of the systems and methods provided herein, such as the computer system 1101, can be embodied in programming. Various aspects of the technology may be thought of as “products” or “articles of manufacture” typically in the form of machine (or processor) executable code and/or associated data that is carried on or embodied in a type of machine readable medium. Machine-executable code can be stored on an electronic storage unit, such as memory (e.g., read-only memory, random-access memory, flash memory) or a hard disk. “Storage” type media can include any or all of the tangible memory of the computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives and the like, which may provide non-transitory storage at any time for the software programming. All or portions of the software may at times be communicated through the Internet or various other telecommunication networks. Such communications, for example, may enable loading of the software from one computer or processor into another, for example, from a management server or host computer into the computer platform of an application server. Thus, another type of media that may bear the software elements includes optical, electrical and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links or the like, also may be considered as media bearing the software. As used herein, unless restricted to non-transitory, tangible “storage” media, terms such as computer or machine “readable medium” refer to any medium that participates in providing instructions to a processor for execution.

[0282] Hence, a machine readable medium, such as computer-executable code, may take many forms, including but not limited to, a tangible storage medium, a carrier wave medium or physical transmission medium. Non-volatile storage media include, for example, optical or magnetic disks, such as any of the storage devices in any computer(s) or the like, such as may be used to implement the databases, etc. shown in the drawings. Volatile storage media include dynamic memory, such as main memory of such a computer platform. Tangible transmission media include coaxial cables; copper wire and fiber optics, including the wires that comprise a bus within a computer system. Carrier-wave transmission media may take the form of electric or electromagnetic signals, or acoustic or light waves such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media therefore include for example: a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD or DVD-ROM, any other optical medium, punch cards paper tape, any other physical storage medium with patterns of holes, a RAM, a ROM, a PROM and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave transporting data or instructions, cables or links transporting such a carrier wave, or any other medium from which a computer may read programming code and/or data. Many of these forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution.

[0283] The computer system 1101 can include or be in communication with an electronic display 1135 that comprises a user interface (LT) 1140 for providing, for example, a window displaying a plurality of mixtures that the user can select to use for 3D printing. Examples of UI’s include, without limitation, a graphical user interface (GUI) and web-based user interface. [0284] Methods and systems of the present disclosure can be implemented by way of one or more algorithms. An algorithm can be implemented by way of software upon execution by the central processing unit 1105. The algorithm can, for example, determine appropriate intensity and exposure time of (i) the photoinitiation light and/or (ii) the photoinitiation light during the 3D printing. EXAMPLES

Example 1: Limitations of three-dimensional (3D) printing

[0285] During brown part densification of a three-dimensional (3D) object comprising (i) a binder and (ii) a plurality of particles (e.g., metal and/or ceramic particles), at least a portion of the binder can be removed prior to sintering, as shown in FIG. 7. In some cases, at least a portion of the binder may not be removed and may remain within the brown part prior to sintering of the plurality of particles (e.g., particle coalescence), as shown across the stages 1 through 4 in FIG. 7. In some cases, such trapped binder can result in blistering and/or cracking of the 3D object during sintering at higher temperatures. In some cases, when the binder breakdown products do not diffuse to the edge of the 3D object, the breakdown products can end up trapped within the part. Trapping of the binder and/or the breakdown products thereof within the 3D object can limit 3D print quality (e.g., cracks), physical properties (e.g., strength, brittleness, etc.) of such 3D print, and/or 3D print resolution. In some cases, the maximum wall thickness of a 3D printed object can be limited by binder removal efficiency. For example, a binder (e.g., lacking hollow particles) can have a maximum wall thickness of about 2.5 millimeters (mm) to avoid cracks.

[0286] For 3D printing via binder jetting, a powder bed can be packed (e.g., at about 55% by volume) and a binder can be added (e.g., to about 10% by volume) to glue particles together. The remaining volume (e.g., about 35%) can be void space, which during debinding can facilitate a pathway for breakdown gasses of the binder to escape. In contrast, for other methods of forming a 3D object (e.g., 3D printing via stereolithography, injection molding, etc.), a liquid or viscous mixture is provided to a substrate (e.g., a print surface for stereolithography, a molding for injection molding, etc.), and there may not be any voids within the liquid or viscous mixture. Thus, to enhance debinding, e.g., in a more uniform fashion and/or to reduce print resolution limitation (e.g., wall thickness limitation), the liquid or viscous mixture can be modified to exhibit a greater degree of porosity. For example, porosity can be achieved in such mixture by addition of hollow particles (e.g., hollow polymer micro-spheres) that can collapse to form a porous network during debinding.

Example 2: A mixture comprising hollow particles (e.g., hollow microspheres) and methods thereof

[0287] A mixture for forming a 3D object, as disclosed herein, can comprise a plurality of hollow particles (e.g., polymeric/plastic hollow microspheres). In some cases, the hollow plastic particles can be substantially the same size or smaller than other particles in the mixture (e.g., metal and/or ceramic particles). For example, a mixture can comprise a plurality of particles having an average particle size (e.g., diameter) between about 8 micrometers and about 50 micrometers, and the mixture can comprise polymeric hollow particles that have an average particle size (e.g., diameter) in the same size range. The hollow particles can collapse and burn (e.g., pyrolyze) in the furnace during thermal debinding. The hollow particles can be substantially removed during the debinding process, so that the resulting sintered part can be a substantially pure metal and/or ceramic material with substantially no ash. For example, Expancel from Nouryon can be used as the hollow polymeric particles (e.g., having an average diameter between about 20 micrometers and about 120 micrometers), as shown by the scanning electron microscopy (SEM) image in FIG. 8. Alternatively or in addition to, other spherical and/or non-spherical hollow particles can be used. The hollow particles may not pyrolyze, such that they may not contribute appreciable ash as a contaminant to the sintered part.

[0288] For example, as demonstrated in FIG. 9, a printed 3D object can comprise a binder that is encapsulating a plurality of metal particles. The binder can comprise photopolymer binder (e.g., polymers polymerized from polymeric precursors during printing of the 3D object) and a plurality of hollow microspheres. During an initial treatment (e.g., initial thermal debinding), the hollow microspheres can be collapsed, to leave a porous pathway. During a subsequent treatment (e.g., subsequent thermal debinding), the binder and the remainder of the hollow microspheres and/or breakdown products thereof can be fully removed (e.g., burnt into gaseous phase), thereby to leave behind a substantially fully de-bound 3D object. Any remainder of the binder in the resulting 3D object (e.g., if any) may be less than that of a control 3D object formed without any hollow particles and subjected to similar thermal treatments. [0289] For example, a mixture was prepared by having a plurality of hollow polymeric particles (e.g., at about 15% by volume of the mixture) and a plurality of copper particles (e.g., at about 35% by volume of the mixture). A maximum thickness of a 3D printed feature (e.g., a maximum wall thickness) that is substantially free of cracking (e.g., as referred to as a white state) was increased by increasing the volume percentage of the hollow polymeric particles (e.g., 10 volume % microsphere, 15 volume % microsphere), as shown in FIG. 10. FIG. 11 shows an example image of a sintered copper object that is substantially free of cracked walls (left) and a sintered copper object that comprises a plurality of cracked walls (right). Example 3: A mixture comprising hollow particles (e.g., porous microparticles) and methods thereof

Table 1. Characteristics of a population of porous microparticles used for printing a 3D object.

[0290] A printed 3D object can comprise a binder that is encapsulating a plurality of metal particles. The binder can comprise photopolymer binder (e.g., polymers polymerized from polymeric precursors during printing of the 3D object) and a plurality of hollow particles, such as a population of porous microspheres as shown in Table 1. During an initial treatment (e.g., initial thermal debinding), the porous microspheres can be collapsed, to leave a porous pathway. During a subsequent treatment (e.g., subsequent thermal debinding), the binder and the remainder of the porous microspheres and/or breakdown products thereof can be fully removed (e.g., burnt into gaseous phase), thereby to leave behind a substantially fully de-bound 3D object. Any remainder of the binder in the resulting 3D object (e.g., if any) may be less than that of a control 3D object formed without any porous particles and subjected to similar thermal treatments.

[0291] For example, a mixture was prepared by having a plurality of polymeric porous particles (e.g., at about 10% by volume of the mixture) and a plurality of stainless steel particles (e.g., at about 35% by volume of the mixture). A series of 3D printed objects were prepared with different wall thicknesses. These 3D printed objects were subjected to thermal debinding and sintering in a furnace and observed for cracking. A maximum thickness of a 3D printed feature (e.g., a maximum wall thickness) that is substantially free of cracking (e.g., as referred to as a white state) was increased by about 135%, by increasing the volume percentage of the porous polymeric particles (e.g., 0% to 10 volume % microsphere), as shown in FIG. 13.

[0292] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. It is not intended that the invention be limited by the specific examples provided within the specification. While the invention has been described with reference to the aforementioned specification, the descriptions and illustrations of the embodiments herein are not meant to be construed in a limiting sense. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Furthermore, it shall be understood that all aspects of the invention are not limited to the specific depictions, configurations or relative proportions set forth herein which depend upon a variety of conditions and variables. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is therefore contemplated that the invention shall also cover any such alternatives, modifications, variations or equivalents. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A mixture for forming a three-dimensional (3D) object, the mixture comprising: one or more polymeric precursors configured to form a polymeric material; one or more metal particles; and one or more hollow particles.

2. The mixture of claim 1, wherein the one or more hollow particles comprise a plurality of porous particles.

3. The mixture of claim 1, wherein an average porosity of the one or more hollow particles is at least about 10%.

4. The mixture of claim 1, wherein an average porosity of the one or more hollow particles is at least about 20%.

5. The mixture of claim 1, wherein an average porosity of the one or more hollow particles is at least about 40%.

6. The mixture of claim 1, wherein said one or more metal particles (Pl) and said one or more hollow particles (P2) are present in said mixture in a volume ratio (Pl :P2) of at least about 0.1.

7. The mixture of claim 6, wherein said volume ratio (Pl :P2) is at most about 60.

8. The mixture of claim 6, wherein said volume ratio (Pl :P2) is between about 0.4 and about 50.

9. The mixture of claim 6, wherein said volume ratio (Pl :P2) is between about 0.5 and about 40.

10. The mixture of claim 6, wherein said volume ratio (Pl :P2) is between about 1 and about

10.

11. The mixture of claim 1, wherein said Pl is present at an amount of between about 10% and about 60% by volume of said mixture.

12. The mixture of claim 1, wherein said Pl is present at an amount of between about 20% and about 50% by volume of said mixture.

13. The mixture of claim 1, wherein said P2 is present at an amount of between about 1% and about 50% by volume of said mixture.

14. The mixture of claim 1, wherein said P2 is present at an amount of between about 2% and about 40% by volume of said mixture.

15. The mixture of claim 1, wherein said one or more metal particles (Pl) and said one or more hollow particles (P2) in said mixture have an average particle size ratio (Pl :P2) of at least about 0.1.

16. The mixture of claim 15, wherein said average particle size ratio (Pl :P2) is at most about 60.

17. The mixture of claim 15, wherein said average particle size ratio (Pl :P2) is between about 0.2 and about 30.

18. The mixture of claim 1, wherein said Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

19. The mixture of claim 1, wherein said Pl has an average particle size of between about 2 micrometer to about 100 micrometers.

20. The mixture of claim 1, wherein said P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

21. The mixture of claim 1, wherein said P2 has an average particle size of between about 10 micrometers and about 200 micrometers.

22. The mixture of claim 1, wherein said one or more metal particles (Pl) and said one or more hollow particles (P2) are present, in combination, at an amount of greater than about 15% by weight of said mixture.

23. The mixture of claim 22 wherein said amount of said Pl and said P2, in combination, is greater than about 20% by weight of said mixture.

24. The mixture of claim 22, wherein said amount of said Pl and said P2, in combination, is greater than about 40% by weight of said mixture.

25. The mixture of claim 22, wherein said amount of said Pl and said P2, in combination, is greater than about 60% by weight of said mixture.

26. The mixture of claim 1, wherein said Pl is present in an amount of between about 65% and about 95% by weight of said mixture.

27. The mixture of claim 1, wherein said Pl is present in an amount of between about 70% and about 90% by weight of said mixture.

28. The mixture of claim 1, wherein said P2 is present in an amount of less than about 1% by weight of said mixture.

29. The mixture of claim 1, wherein said P2 is present in an amount of less than about 0.5% by weight of said mixture.

30. The mixture of claim 1, further comprising at least one photoinitiator configured to initiate formation of the polymeric material from said plurality of polymeric precursors.

31. The mixture of claim 1, further comprising at least one photoinhibitor configured to inhibit formation of the polymeric material from said plurality of polymeric precursors.

32. The method of claim 1, wherein said hollow particle is a polymeric hollow particle.

33. A method for forming a three-dimensional (3D) object, the method comprising:

(a) providing a mixture comprising: one or more polymeric precursors configured to form a polymeric material; one or more metal particles (Pl); and one or more hollow particles (P2);

(b) exposing said mixture to a stimulus to cause said one or more polymeric precursors to form said polymeric material that at least partially encapsulates said metal particles and said hollow particles, thereby to form a green part corresponding to at least a portion of said 3D object.

34. A mixture for forming a three-dimensional (3D) object, the mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a hollow particle, wherein said mixture is characterized by one or more members selected from the group consisting of:

(i) said Pl and said P2 are present in said mixture in a volume ratio (Pl :P2) of at least about 0.1;

(ii) said Pl and said P2 in said mixture have an average particle size ratio

(Pl :P2) of at least about 0.1; and

(iii) said Pl and said P2 are present, in combination, at an amount of greater than about 15% by weight of said mixture.

35. The mixture of claim 34, wherein the hollow particle comprises a porous particle.

36. The mixture of claim 34, wherein an average porosity of the hollow particle is at least about 10%.

37. The mixture of claim 34, wherein an average porosity of the hollow particle is at least about 20%.

38. The mixture of claim 34, wherein an average porosity of the hollow particle is at least about 40%.

39. The mixture of claim 34 wherein said hollow particle is a polymeric hollow particle.

40. The mixture of claim 34, wherein said Pl comprises said metal particle.

41. The mixture of claim 34, wherein said Pl comprises said ceramic particle.

42. The mixture of claim 34, wherein said mixture is characterized by two or more members selected from the group consisting of (i), (ii), and (iii).

43. The mixture of claim 34, wherein said mixture is characterized by (i), (ii), and (iii).

44. The mixture of claim 34, wherein, in (i), said volume ratio (Pl :P2) is at most about 60.

45. The mixture of claim 34, wherein, in (i), said volume ratio (Pl :P2) is between about 0.4 and about 50.

46. The mixture of claim 34, wherein, in (i), said volume ratio (Pl :P2) is between about 0.5 and about 40.

47. The mixture of claim 34, wherein, in (i), said volume ratio (Pl :P2) is between about 1 and about 10.

48. The mixture of claim 34, wherein said Pl is present at an amount of between about 10% and about 60% by volume of said mixture.

49. The mixture of claim 34, wherein said Pl is present at an amount of between about 20% and about 50% by volume of said mixture.

50. The mixture of claim 34, wherein said P2 is present at an amount of between about 1% and about 50% by volume of said mixture.

51. The mixture of claim 34, wherein said P2 is present at an amount of between about 2% and about 40% by volume of said mixture.

52. The mixture of claim 34, wherein, in (ii), said average particle size ratio (Pl :P2) is at most about 60.

53. The mixture of claim 34, wherein, in (ii), said average particle size ratio (Pl :P2) is between about 0.2 and about 30.

54. The mixture of claim 34, wherein said Pl has an average particle size of between about

1 micrometer to about 200 micrometers.

55. The mixture of claim 34, wherein said Pl has an average particle size of between about

2 micrometers to about 100 micrometers.

56. The mixture of claim 34, wherein said P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

57. The mixture of claim 34, wherein said P2 has an average particle size of between about 10 micrometers and about 200 micrometers.

58. The mixture of claim 34, wherein, in (iii), said amount of said Pl and said P2, in combination, is greater than about 20% by weight of said mixture.

59. The mixture of claim 34, wherein, in (iii), said amount of said Pl and said P2, in combination, is greater than about 40% by weight of said mixture.

60. The mixture of claim 34, wherein, in (iii), said amount of said Pl and said P2, in combination, is greater than about 60% by weight of said mixture.

61. The mixture of claim 34, wherein said Pl is present in an amount of between about 65% and about 95% by weight of said mixture.

62. The mixture of claim 34, wherein said Pl is present in an amount of between about 70% and about 90% by weight of said mixture.

63. The mixture of claim 34, wherein said P2 is present in an amount of less than about 1% by weight of said mixture.

64. The mixture of claim 34, wherein said P2 is present in an amount of less than about 0.5% by weight of said mixture.

65. The mixture of claim 34, further comprising at least one photoinitiator configured to initiate formation of the polymeric material from said plurality of polymeric precursors.

66. The mixture of claim 34, further comprising at least one photoinhibitor configured to inhibit formation of the polymeric material from said plurality of polymeric precursors.

67. A method for forming a three-dimensional (3D) object, the method comprising:

(a) providing a mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a hollow particle, wherein said mixture is characterized by one or more members selected from the group consisting of:

(ii) said Pl and said P2 in said mixture have an average particle size ratio (Pl :P2) of at least about 0.1; and

(iii) said Pl and said P2 are present, in combination, at an amount of greater than about 15% by weight of said mixture;

(b) exposing said mixture to a stimulus to cause said one or more polymeric precursors to form said polymeric material that at least partially encapsulates said Pl and said P2, thereby to form a green part corresponding to at least a portion of said 3D object.

68. A mixture for forming a three-dimensional (3D) object, the mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a particle exhibiting an interior density of a material, wherein, upon exposure to a stimulus, the particle is capable of transforming into an additional particle exhibiting an additional interior density of the material that is lower than the interior density of the material of the particle.

69. The mixture of claim 68, wherein the additional particle is a hollow particle.

70. The mixture of claim 69, wherein the hollow particle is a polymeric hollow particle.

71. The mixture of claim 68, wherein a size of the additional particle is greater than that a size of the particle.

72. The mixture of claim 71, wherein the size of the additional particle is greater than that a size of the particle by at least about 10%.

73. The mixture of claim 71, wherein the size of the additional particle is greater than that a size of the particle by at least about 50%.

74. The mixture of claim 71, wherein the size of the additional particle is greater than that a size of the particle by at least about 100%.

75. The mixture of claim 68, wherein said Pl and said P2 are present in said mixture in a volume ratio (Pl :P2) of at least about 0.1.

76. The mixture of claim 68, wherein said Pl is present at an amount of between about 10% and about 60% by volume of said mixture.

77. The mixture of claim 68, wherein said P2 is present at an amount of between about 1% and about 50% by volume of said mixture.

78. The mixture of claim 68, wherein said Pl and said P2 in said mixture have an average particle size ratio (Pl :P2) of at least about 0.1.

79. The mixture of claim 68, wherein said Pl has an average particle size of between about 1 micrometer to about 200 micrometers.

80. The mixture of claim 68, wherein said P2 has an average particle size of between about 5 micrometers and about 500 micrometers.

81. The mixture of claim 68, wherein said Pl and said P2 are present, in combination, at an amount of greater than about 15% by weight of said mixture.

82. The mixture of claim 68, wherein said Pl is present in an amount of between about 65% and about 95% by weight of said mixture.

83. The mixture of claim 68, wherein said P2 is present in an amount of less than about 1% by weight of said mixture.

84. The mixture of claim 68, further comprising at least one photoinitiator configured to initiate formation of the polymeric material from said plurality of polymeric precursors.

85. The mixture of claim 68, further comprising at least one photoinhibitor configured to inhibit formation of the polymeric material from said plurality of polymeric precursors.

86. The mixture of claim 68, wherein said stimulus comprises a thermal treatment.

87. A method for forming a three-dimensional (3D) object, the method comprising:

(a) providing a mixture comprising: one or more polymeric precursors configured to form a polymeric material; a first plurality of particles (Pl) comprising a metal particle or a ceramic particle; and a second plurality of particles (P2) comprising a particle exhibiting an interior density of a material; and

(b) exposing said mixture to a stimulus to cause said particle to transform into an additional particle exhibiting an additional interior density of the material that is lower than the interior density of the material of the particle.