CN117858729A

CN117858729A - Nucleation method for producing polycaprolactone powder

Info

Publication number: CN117858729A
Application number: CN202280055338.XA
Authority: CN
Inventors: 托马斯·乔治·加德纳; 维多利亚·汉娜·派尔; 特拉维斯·李·希斯洛普
Original assignee: Jabil Circuit Inc
Current assignee: Jabil Inc
Priority date: 2021-08-19
Filing date: 2022-08-17
Publication date: 2024-04-09
Also published as: CN117858699A

Abstract

The present invention discloses a method for preparing a polycaprolactone powder having properties that make it well suited for powder bed fusion 3D printing processes. The polycaprolactone powders disclosed herein have a melting enthalpy between 80J/g and 140J/g. The polycaprolactone powders described herein have a D between 20 microns and 150 microns ₉₀ . The polycaprolactone powders described herein contain a detectable amount of biocompatible solvents, bioabsorbable solvents, and/or ethyl lactate.

Description

Nucleation method for producing polycaprolactone powder

Cross-reference to related patent applications

The present patent application claims priority from U.S. provisional patent application No. 63/234,812, filed on day 2021, 8, and 19, and U.S. provisional patent application No. 63/265,641, filed on day 2021, 12, and 17, the contents of which are incorporated herein by reference in their entirety.

Technical Field

The present disclosure relates to the production of polycaprolactone (also known as PCL) powder. The disclosed polycaprolactone powders can be used as build materials for producing three-dimensional articles by 3D printing or other known manufacturing methods such as molding. The disclosed polycaprolactone powders may be suitable for producing implantable articles by Selective Laser Sintering (SLS).

Background

Biocompatible and bioabsorbable polymers can be used to make medical implants that are non-toxic to humans.

The 3D printer creates a solid three-dimensional object by joining adjacent materials together, for example by melting and/or sintering the adjacent materials such that they solidify together upon cooling. The 3D printer typically builds the object layer by layer following the instructions of a Computer Aided Design (CAD) model. 3D printing is one type of additive manufacturing. Additive manufacturing may include material extrusion, powder bed melting, adhesive spraying (binder jetting), photo curing, sheet lamination, directed energy deposition, and material spraying.

Selective Laser Sintering (SLS) is a type of 3D printing technique that can be used to manufacture medical implants and the like. SLS machines may require that the printing/build material be in powder form with a particular particle size distribution and other characteristics. The machine may also require that the printing material have a certain amount of fluidity. Fluidity may allow the printing material to spread evenly over each layer of new build material before electromagnetic energy (typically in the form of laser energy) is applied to sinter the predefined areas.

The 3D printing application may include: selective Laser Sintering (SLS), multi-jet fusion (MJF), high-speed sintering (HSS), and electrophotography.

A glidant may be added to improve the flowability of the SLS printing material. However, it may not be necessary to add certain glidants to a medical implant, as their addition may adversely affect the patient's body. Thus, when producing SLS powder for use in manufacturing medical implants, it may be desirable in some instances to have good particle sphericity to minimize or eliminate the need for glidants.

The present disclosure relates to a solvent precipitation process for producing partially crystalline polycaprolactone powders that may be suitable for use in SLS machines.

Disclosure of Invention

Various variations within the scope of the claims may include processes involving the preparation of PCL powder, compositions and articles of manufacture and their use in additive manufacturing processes (including PBF processes).

At least one variation may include a powder comprising polycaprolactone particles. The powder has greater than 90 volume percent of particles having a particle size between 20 microns and 150 microns. The powder has a detectable amount of solvent and a detectable amount of nucleating agent, wherein the solvent is a biocompatible solvent or a bioabsorbable solvent. In some variations, the solvent is ethyl lactate. In some variations, the nucleating agent is hydroxyapatite. In some variations, greater than 90 volume percent of the polycaprolactone particles have sphericity greater than 0.75. In another variation, greater than 90 volume percent of the polycaprolactone particles have sphericity greater than 0.80. In some variations, the volume percent of polycaprolactone particles having a particle size less than 20 microns is zero or undetectable. In some variations, the powder has a peak melting temperature of about 55 ℃ to about 65 ℃ and a melting enthalpy of about 90J/g to about 120J/g. In some variations, the powder has a recrystallization peak from about 15 ℃ to about 35 ℃. In some variations, the powder has a degradation temperature of about 250 ℃ to about 425 ℃. In some variations, greater than 96% of the number percent polycaprolactone particles have a particle size less than 125 microns. In some variations, the moisture content of the polycaprolactone particles is adjusted and maintained between 0.5% w/w and 5% w/w.

At least one variation may include a method of preparing a PCL powder, which may include combining polycaprolactone in a polar organic solvent, dissolving the polycaprolactone in the polar organic solvent to form a solution, and cooling the solution to a temperature that causes precipitation of at least a portion of the dissolved polycaprolactone. A nucleating agent may be added to the solution to promote precipitation. Separating the powder from the solution, leaving a second more diluted PCL solution, and contaminants from the raw PCL; such as residual catalyst, initiator, polymerization solvent, monomers and oligomers. The separated powder may then be washed and dried. In some variations, the method further comprises heating the combined polycaprolactone and polar organic solvent. In some variations, the method further comprises a separation step that separates the dried polycaprolactone particles having a particle size less than 150 microns from the larger dried polycaprolactone particles to form polycaprolactone of a particular size. In some variations, the percentage of nucleating agent in the combined polycaprolactone/nucleating agent mixture is between about 0.5 mass% and 10 mass%. In some variations, the nucleating agent is hydroxyapatite. In some variations, the polar organic solvent is selected from the group consisting of: ethyl acetate, ethyl lactate, gamma valerolactone, N-Dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), dichloromethane (DCM), chloroform, acetone and dimethyl sulfoxide (DMSO).

At least one variation may include a method of producing a powder comprising polycaprolactone particles, the method comprising combining polycaprolactone and a polar organic solvent, and dissolving the polycaprolactone in the polar organic solvent along with at least one nucleating agent. The solution is then cooled to a lower temperature, causing at least a portion of the dissolved polycaprolactone to precipitate in the solution. The precipitated polycaprolactone is separated from the solution, washed and dried. In some variations, the method includes heating the solution.

At least one variation may include a method of additive manufacturing that includes selectively melting or sintering adjacent polycaprolactone particles. More than 95% by number of the polycaprolactone particles have a particle size of less than 125 microns, and more than 90% by volume of the polycaprolactone particles have a sphericity of greater than 0.75. The polycaprolactone particles contain a detectable amount of ethyl lactate and a detectable amount of hydroxyapatite. In some variations, the moisture content of the polycaprolactone particles is adjusted and maintained between 0.5% -5% w/w.

At least one variation may include an article comprising polycaprolactone particles. More than 90 volume percent of the polycaprolactone particles have a particle size of 20 microns to 150 microns. The polycaprolactone particles contain a detectable amount of nucleating agent. The polycaprolactone particles comprise a detectable amount of solvent comprising at least one of a biocompatible solvent or a bioabsorbable solvent.

At least one variation may include a medical product comprising polycaprolactone particles. More than 90 volume percent of the polycaprolactone particles have a particle size of 20 microns to 150 microns. The polycaprolactone particles contain a detectable amount of nucleating agent. The polycaprolactone particles comprise a detectable amount of solvent comprising at least one of a biocompatible solvent or a bioabsorbable solvent.

Powder compositions for use in the PBF process are provided, which include PCL powder prepared by such a process. The article may be prepared by using such PCL powder in a PBF process to form the article.

Exemplary variations of the disclosed devices, systems, and methods provide PCL powders with suitable properties and characteristics for SLS, MJF, HSS and electrophotographic 3D printing applications. One embodiment of the present disclosure may provide a precipitated PCL powder formed by precipitating a polymer from a solvent and then using the precipitated powdered polymer in a powder-based 3D printing process.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure or claims.

Variations may include powders comprising polycaprolactone particles. In at least one variation, greater than 90 volume percent of the polycaprolactone particles have a particle size of 20 microns to 150 microns.

Drawings

Fig. 1 is a flow chart illustrating a method of producing polycaprolactone powder according to at least one variation.

Fig. 2 is a graph showing the results of thermogravimetric analysis (TGA) of a polycaprolactone sample produced according to at least one variation.

Fig. 3 is a graph showing a Differential Scanning Calorimetric (DSC) curve of polycaprolactone precipitated according to at least one variation.

Fig. 4 is a graph showing particle size volume distribution of SLS-grade powder produced according to at least one variation.

Fig. 5 is a graph showing particle size number distribution of SLS-grade powder produced according to at least one modification.

Fig. 6 is a table showing powder data for polycaprolactone powders prepared according to at least one variation.

Fig. 7 is a photograph of a strip printed with SLS using polycaprolactone comprising 4% w/w (weight/weight) hydroxyapatite (also referred to as HA) according to at least one variant.

FIG. 8A is a graph showing the tensile curve generated by stretching a polycaprolactone (with 4% w/w hydroxyapatite) tensile bar produced by SLS.

Fig. 8B is a table showing a summary of material properties obtained from the tensile test in fig. 8A.

Fig. 9 is a graph showing a DSC curve of a hydroxyapatite nucleated polycaprolactone powder obtained according to at least one variation.

Fig. 10 is a graph showing a particle number size distribution according to at least one variation.

Fig. 11 is a graph showing a particle number size distribution according to at least one variation.

Fig. 12A and 12B show a comparison between (12A) a polycaprolactone powder nucleated with 4% w/w hydroxyapatite and (12B) a polycaprolactone powder dry blended with 4% w/w hydroxyapatite and left for more than 24 hours according to at least one variation.

Fig. 13 is a table showing a comparison of particle size distribution between individually precipitated polycaprolactone and polycaprolactone precipitated with hydroxyapatite as a nucleating agent according to at least one variation.

Fig. 14A to 14G show polycaprolactone discs prepared by various methods.

Fig. 15 is a graph showing a DSC profile of a polycaprolactone powder reprecipitated in ethyl lactate according to at least one variation.

FIG. 16 is a graph showing DSC curves of a polycaprolactone powder reprecipitated in the presence of 4% w/w hydroxyapatite as a nucleating agent according to at least one variation.

Detailed Description

The following description is merely illustrative in nature of the subject matter, manufacture, and use of one or more inventions and is not intended to limit the scope, application, or uses of any particular invention or applications of the invention claimed in this application, or the scope, application, or uses of the patent claims which may be filed claiming priority to the present application. With respect to the disclosed methods, the order of the steps presented is illustrative in nature, and thus, in various embodiments, the order of the steps may be different. As used herein, "a" and "an" mean that "at least one" item is present; where possible, a plurality of such items may be present. Unless explicitly indicated otherwise, all numerical values in this specification should be understood to be modified by the word "about" and all geometric and spatial descriptors should be understood to be modified by the word "substantially" in describing the broadest scope of the present technology. When applied to a value, the term "about" means that the calculation or measurement allows some slight imprecision in the value (with some approach to making the value accurate; approximating or reasonably approaching the value; nearly). If, for some reason, the imprecision provided by "about" and/or "substantially" is not otherwise understood in the art with this ordinary meaning, then "about" and/or "substantially" as used herein is intended to at least refer to variations that may result from the ordinary methods of measuring or using these parameters.

Although the open-ended terms "comprising" are used herein to describe and claim embodiments as synonyms for non-limiting terms such as including, containing, or having, embodiments may alternatively be described using more limiting terms such as "consisting of … …" or "consisting essentially of … …. Thus, for any given embodiment of a recited material, component, or process step, the present technology also specifically includes embodiments consisting of or consisting essentially of such material, component, or process step, without the inclusion of additional material, component, or process (for consisting of … …), and without the inclusion of additional material, component, or process (for consisting essentially of … …) that affects the important properties of the embodiment, even if such additional material, component, or process is not explicitly recited in the present application. For example, recitation of a composition or method of recitation of elements A, B and C specifically contemplates embodiments consisting of A, B and C or consisting essentially of A, B and C, excluding element D as may be recited in the art even though element D is not explicitly recited herein as being excluded.

The term "or" as used herein with respect to a list of two or more items, elements, components, or materials does not denote a complete separation, such that the listed items, elements, components, or materials are mutually exclusive. For example, "X, Y or Z" does not mean that each of X, Y, Z are mutually exclusive of each other. Two or more of X, Y, Z may partially or fully overlap each other, or at least one of X, Y or Z may be included in at least one other of X, Y or Z, or be a subgenera of at least one other of X, Y or Z. As another example, "cells can grow on a monolayer, three-dimensional, or bead" does not mean that cells grown on a bead do not include cells grown in three-dimensions. As another example, "at least one biocompatible solvent, bioabsorbable solvent, or ethyl lactate" does not mean that ethyl lactate or a solvent comprising ethyl lactate is neither a biocompatible solvent nor a bioabsorbable solvent; nor does it mean that the biocompatible or bioabsorbable solvent cannot be or include ethyl lactate.

As described herein, unless otherwise indicated, the ranges disclosed include endpoints, and include all different values and further divided ranges within the entire range. Thus, for example, a range of "from A to B" or "from about A to about B" includes A and B. The disclosure of values and ranges of values for specific parameters (such as amounts, weight percentages, etc.) does not preclude the use of other values and ranges of values herein. It is envisioned that two or more specific example values of a given parameter may define the endpoints of a range of values for the parameter that may be claimed. For example, if parameter X is exemplified herein as having a value a and is also exemplified as having a value Z, it is envisioned that parameter X may have a range of values from about a to about Z. Similarly, it is contemplated that disclosure of two or more ranges of parameter values (whether such ranges are nested, overlapping, or different) falls within all possible combinations of ranges of values that can be claimed using endpoints of the disclosed ranges. For example, if parameter X is exemplified herein as having a value in the range of 1-10, or 2-9, or 3-8, it is also contemplated that parameter X may have other value ranges including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, 3-9, and so forth.

When an element or layer is referred to as being "on," "engaged to," "connected to" or "coupled to" another element or layer, it can be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to" or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a similar fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. The terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as "inner," "outer," "lower," "under … …," "lower," "above … …," "upper," and the like, may be used herein for ease of description to describe one element or component's relationship to another element or component as illustrated in the figures. In addition to the orientations shown in the drawings, the spatially relative terms are intended to encompass different orientations of the device in use or operation. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or components would then be oriented "above" the other elements or components. Thus, the exemplary term "below" may include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions) and the spatially relative descriptors used herein interpreted accordingly.

The particle size of the PCL polymer may affect its use in additive manufacturing processes. As used herein, D ₅₀ (known as "volume median diameter" or "volume average particle diameter") refers to the particle diameter of the powder, wherein 50% by volume of the particles in the total distribution of the reference sample have the particle diameter Or smaller particle diameter. Similarly, D ₁₀ Refers to the particle diameter of the powder, wherein 10% by volume of the particles in the total distribution of the reference sample have the particle diameter or less; d (D) ₉₀ Refers to the particle diameter of the powder, wherein 90% by volume of the particles in the total distribution of the reference sample have the particle diameter or less. Particle size may be measured by any suitable method known in the art to measure particle size by diameter. Semi-crystalline polymer powders provided herein may have a D of less than 150 μm ₉₀ Particle size.

As used herein, "layer" is a convenient term that includes any shape, regular or irregular, having at least a predetermined thickness. In particular embodiments, the size and configuration of the two dimensions are predetermined, and in particular embodiments, the size and shape of all three dimensions of the layer are predetermined. The thickness of each layer may vary widely depending on the additive manufacturing method. In particular implementations, the thickness of each layer formed may be different from the previous or subsequent layers. In particular embodiments, the thickness of each layer may be the same. In particular embodiments, each layer formed may have a thickness of 0.5 millimeters (mm) to 5mm.

A particular variation may include forming the plurality of layers in a preset pattern by an additive manufacturing process. In many variations, additive manufacturing may produce two or more layers, or 20 or more layers. The maximum number of layers may vary widely, for example by taking into account factors such as the size of the article being manufactured, the technology used, the capacity and capabilities of the equipment used, and the level of detail desired in the final article. For example, 5 to 100,000 layers may be formed, or 20 to 50,000 layers may be formed, or 50 to 50,000 layers may be formed.

The term "powder bed melting" or "powder bed melting" is used herein to refer to a process in which a polymer is selectively sintered layer by layer or melted and melted to provide a 3-D article. Sintering may produce an article having a density of less than about 90% of the density of the solid powder composition, while melting may provide an article having a density of 90% -100% of the solid powder composition. With the semi-crystalline polymers provided herein, melting may be facilitated such that the resulting density may be close to that obtained by injection molding methods.

Powder bed melting or powder bed melting also includes all laser sintering and all selective laser sintering processes and other powder bed melting techniques as defined by ASTM F2792-12 a. For example, sintering of the powder composition may be accomplished by application of electromagnetic radiation rather than laser-generated electromagnetic radiation, where the selectivity of sintering is accomplished, for example, by selective application of inhibitors, absorbers, susceptors, or electromagnetic radiation (e.g., by using a mask or directed laser beam). Any other suitable electromagnetic radiation source may be used including, for example, an infrared radiation source, a microwave generator, a laser, a radiant heater, a bulb, or a combination thereof. In particular embodiments, selective mask sintering ("SMS") techniques may be used to create three-dimensional articles. For further discussion of the SMS process, see, for example, U.S. patent No. 6,531,086, the entire contents of which are incorporated herein by reference, an SMS machine is described in which a protective mask is used to selectively block infrared radiation, resulting in selective irradiation of a portion of the powder layer. If the SMS process is used to produce articles from the powder compositions of the present technology, it may be desirable to include one or more materials in the powder composition that enhance the infrared absorption properties of the powder composition. For example, the powder composition may include one or more heat absorbing bodies (e.g., glass fibers or glass beads) or dark colored materials (e.g., carbon black, carbon nanotubes, or carbon fibers).

Also included herein are all three-dimensional articles prepared by powder bed fusion of a composition comprising the semi-crystalline polymer powder described herein. After the article is manufactured layer by layer, the article may exhibit excellent resolution, durability, and strength. Such articles may include various manufactured articles having a variety of uses, including use as prototypes, end products, and molds for end products.

The article may be formed from a pre-set pattern that may be determined from a three-dimensional digital representation of the desired article, as is known in the art and described herein. The materials may be connected or cured under computer control (e.g., operating in accordance with a Computer Aided Design (CAD) model) to create a three-dimensional article.

In particular, any suitable powder bed melting process, including a laser sintering process, may be used to produce a powder bed melted (e.g., laser sintered) article from a composition comprising PCL powder. The articles may include a plurality of overlying and adhered sintered layers that include a polymer matrix, which in some embodiments may have reinforcing particles dispersed throughout the polymer matrix. Laser sintering processes are known and are based on the selective sintering of polymer particles, wherein a layer of polymer particles is briefly exposed to laser energy and the polymer particles exposed to laser energy are thus bonded to each other. Continuous sintering of the polymer particle layer produces a three-dimensional article. Details concerning the selective laser sintering process can be found, for example, in U.S. Pat. No. 6,136,948 and WO 96/06881, the entire contents of each of which are incorporated herein by reference. However, the semi-crystalline polymer powders described herein may also be used in other rapid prototyping or rapid manufacturing processes of the prior art, particularly those described above. For example, semi-crystalline polymer powders may be particularly useful for producing moulds from powders by SLS (selective laser sintering) process, as described in U.S. Pat. No. 6,136,948 or WO 96/06881, the contents of each of which are incorporated herein by reference in their entirety, by SIB process (selective inhibition bonding of powders) as described in WO 01/380561, by 3D printing as described in EP 0431924, or by microwave process as described in DE 10311438.

The molten layer of the powder bed fusion article may have any thickness suitable for the selective laser sintering process. The average thickness of each monolayer is at least 50 μm, at least 80 μm, or at least 100 μm. In many variations, the average thickness of each of the plurality of sintered layers is less than 500 μm, less than 300 μm, or less than 200 μm. Thus, the monolayers of some embodiments may be 50 to 500 μm, 80 to 300 μm, or 100 to 200 μm thick. Three-dimensional articles produced from the powder compositions of the present technology using a layer-by-layer powder bed fusion process other than selective laser sintering may have the same or different layer thicknesses as described above.

Many variations may provide methods of making and using PCL powders with suitable characteristics for Selective Laser Sintering (SLS), multi-jet fusion (MJF), high-speed sintering (HSS), and Electrophotographic (EPG) 3D printing. At least one variation may provide a precipitated PCL powder formed by precipitating a polymer from a saturated solution of PCL in a polar organic solvent, forming the polymer into crystallites, and then using the precipitated polymer powder in a PBF 3D printing process. Many variations of PCL powder can exhibit optimized characteristics for the PBF process, including its optimized particle size and dispersity, shape and crystallinity, while using a dispersant-free single solvent process in its manufacture.

A method of preparing PCL powder may include dissolving bulk PCL in ethyl lactate at an elevated temperature to form a solution; the solution was cooled to room temperature to form D ₉₀ PCL powder in precipitated form with a value of less than 150 microns (micrometers or μm); d (D) ₅₀ A value of less than or equal to 100 μm, or D ₅₀ PCL powder in precipitated form with a value between 0 and 100 μm. The method can also produce a product in which the particles can exhibit a specific size (average diameter of about 30 μm to about 40 μm), low dispersibility, spherical shape, and crystallization characteristics suitable for the above-described printing method, as compared with the results of the foregoing method. The reprecipitation effect was also used for purifying PCL.

In a particular embodiment, a method of preparing PCL powder is provided, the method comprising dissolving bulk PCL in a polar solvent, such as an ester; for example ethyl lactate, to form a first solution of dissolved polymer at a first temperature. The first solution is then cooled to a second temperature, wherein the second temperature is lower than the first temperature. A portion of the dissolved PCL precipitates as a powder from the first solution on the way to or upon reaching the second temperature, leaving behind a second more diluted PCL solution. The precipitated PCL powder may be separated from the residue of the second solution by, for example, gravity filtration, vacuum filtration or centrifugation. The isolated PCL powder may also be washed with water or an organic solvent, provided that the washing solvent is miscible with the solvent used for reprecipitation, and the washing solvent does not dissolve the polymer powder to a detrimental extent (e.g., unacceptable excessive material loss and/or unacceptable excessive particle size reduction), and may not be a solvent for the polymer powder product at all. The isolated PCL powder may also be dried after any washing procedure (if applied). In particular embodiments, the polar solvent may include ethyl lactate. In other embodiments, the polar solvent may consist essentially of ethyl lactate. In still further embodiments, the polar solvent may consist of ethyl lactate.

Various solvent temperatures can be used in the process for preparing PCL powder by reprecipitation. The dissolving step may include heating the PCL in a polar solvent to form a first solution of dissolved PCL at a first temperature, wherein the first temperature is greater than room temperature. The cooling step may include cooling the first solution to a second temperature, wherein the second temperature is below the precipitation temperature of the polymer solution, and may be at ambient temperature ("room temperature") or less. Ambient ("indoor") temperature is understood to be about 20-25 ℃ (68-77°f).

Various embodiments of the PCL may exhibit the following physical properties. The PCL powder may have a D of less than about 150 μm ₉₀ Particle size. In particular embodiments, the PCL powder may have a D of less than about 100 μm ₅₀ . The PCL powder may also have a D of about 1 micrometer to about 100 micrometers ₅₀ Values. Particular embodiments include those wherein the PCL powder has a D of about 30 μm to about 40 μm ₅₀ Values. The PCL powder may be in the form of spherical particles.

The melting point and enthalpy of fusion of the polymer powder can be determined using Differential Scanning Calorimetry (DSC); for example, a TA instruments Discovery series DSC 250, which scans at a rate of 20 ℃/min.

The percent crystallinity of the polymer can be determined by the ratio of the enthalpy of fusion measured by DSC to the theoretical 100% crystalline polymer, with the enthalpy of fusion of PCL reported to have a value of 139.5J/g (Gupta and Geeta, j.appl.polym. sci.2012,123 (4), 1944-1950). The percent crystallinity can also be determined by powder x-ray crystallography and correlated in a direct linear relationship with melting enthalpy.

Powder flow of the polymer powder can be measured using ASTM D1895, method a, and determined using a cone with a 10mm nozzle diameter.

In some embodiments, the particle size of the polymer powder is determined by laser diffraction as known in the art. For example, a laser diffractometer such as Microtrac S3500 may be used to determine particle size.

In a particular embodiment, a powder composition for a PBF 3D printing process is provided, wherein such powder composition comprises PCL powder prepared according to the methods provided herein. For example, a powder composition for a PBF process can include a composition having a D of less than about 150 μm ₉₀ Particle size and D of about 30 μm to about 40 μm ₅₀ PCL powder of value. Such powder compositions may include a mixture of PCL powder having different physical properties with the additives and other components described herein.

In certain embodiments, the reprecipitated PCL powder prepared by the methods disclosed herein is used in a PBF 3D printing process to form an article. A particular method of making an article includes providing D ₉₀ Particle size of less than about 150 μm, D ₅₀ PCL powder having a value of about 30 μm to about 40 μm. The PCL powder is then used in a PBF process to form the article.

In certain embodiments, one or more articles prepared by an additive manufacturing process are provided. These methods may include providing PCL powder prepared according to one or more of the methods described herein. The PCL powder is then used in a PBF process to form one or more articles.

Particular embodiments may include methods of powder bed fusion to form a three-dimensional object using a powder composition comprising PCL powder. Due to the good flowability of the reprecipitated PCL powder, a smooth and dense powder bed can be formed, thus achieving optimal precision and density of the sintered article.

In certain embodiments, the method of preparing PCL powder comprises dissolving bulk PCL in a polar solvent such as ethyl lactate at a temperature above room temperature. Ambient ("indoor") temperature is understood to be about 20-25 ℃ (68-77°f); thus, PCL can be dissolved in ethyl lactate at above ambient temperature. PCL is soluble in ethyl lactate solvent and thus forms a PCL solution. In general, solutions can be prepared at temperatures above room temperature such that the amount of dissolved PCL is greater than the amount of solvent that can remain in solution at ambient temperature. The mixing of PCL with ethyl lactate solvent can be performed on-line or in batch. The process can be easily performed on a manufacturing scale. Upon cooling to room temperature (e.g., about 20 ℃), the dissolved PCL begins to crystallize and precipitate out of the ethyl lactate solvent, resulting in precipitation of PCL precipitate.

After precipitation, the ethyl lactate solvent is removed, for example by filtration or centrifugation. The PCL powder can then be washed with a solvent (e.g., water) that is miscible with the reprecipitation solvent and moderately volatile, filtered to remove the washing solvent, and dried with or without heating and with or without vacuum. More advantageously, a washing solvent is used in which PCL is rarely or not dissolved.

As provided herein, PCL is dissolved in a polar organic solvent. For example, PCL may be dissolved in a solvent under conditions that produce a saturated solution of PCL, wherein changing the conditions (e.g., lowering the temperature of the solution) results in precipitation of PCL powder therefrom. In particular embodiments, the solvent may include ethyl lactate and one or more other esters or one or more other polar organic solvents. In particular embodiments, the solvent may consist essentially of ethyl lactate, wherein no other components are present that substantially affect PCL crystallization. In particular embodiments, the solvent may be substantially 100% ethyl lactate. It is also noted that upon precipitation of PCL powder from a solution of PCL in ethyl lactate, a portion of the dissolved PCL may remain in solution. In particular embodiments, a second solvent that is miscible with the reprecipitation solvent but does not support dissolution of PCL may be added to the PCL/solvent solution to induce precipitation. In particular embodiments, the use of a nucleating agent in powder form may be used to induce precipitation and may help control particle size and dispersion of particle size and may help improve the overall spherical shape of the powder particles. Thus, the precipitated PCL powder was separated from the remainder of the solution, leaving an ethyl lactate solution and a portion of the dissolved PCL.

Ethyl lactate is a useful solvent for this process because it dissolves PCL well; shown herein as being used to produce powders with characteristics well suited for PBF 3D printing processes; having a boiling point that is completely separated from ambient temperature, allowing a wide cooling range during precipitation; is miscible with commonly available and effective wash solvents (e.g., water or low molecular weight alcohols); exhibit relative non-toxicity in mammals (as demonstrated in their use as food additives); and can be decomposed into ethanol and lactic acid in vivo.

In particular embodiments, the precipitated PCL powder has a D of less than 150 μm ₈₅ Particle size; specifically, the D90 particle size is less than 150 μm. Particular embodiments include wherein the PCL powder has a D of less than 150 μm ₉₀ Particle size. PCL powder in which 100% of the particles have a size of less than 150 μm can also be prepared by this method. The PCL powder may also have a D of less than or equal to 100 μm ₅₀ Values. Specifically, the PCL powder may have a D of 10 μm to 100 μm ₅₀ Values. The average particle diameter of the PCL powder may also be less than or equal to 100 μm, or the PCL powder may include a D of between 0 and 100 μm ₅₀ Values.

In certain embodiments, a method of making an article includes providing a powder composition comprising PCL powder and using a powder bed fusion process with the powder composition to form a three-dimensional article. At least one PCL powder may have a D of less than 150 μm in diameter ₅₀ Particle size, and prepared by the method described above. Embodiments include wherein the PCL powder has a D of less than 150 μm ₉₀ D having a particle diameter of 100 μm or less ₅₀ Value, or D of 0-100 μm ₅₀ Values.

PCL powder can be used as the sole component in the powder composition and applied directly during the powder bed melting step. Alternatively, the PCL powder may be first mixed with other polymer powders, for example, another crystalline polymer or an amorphous polymer, or a combination of a semi-crystalline polymer and an amorphous polymer. The powder composition for powder bed fusion may comprise 50 to 100 wt% PCL powder, based on the total weight of all polymeric materials in the powder composition.

PCL powder may also be combined with one or more additives/components to produce a powder that can be used in a powder bed fusion process. These optional components may be present in sufficient amounts to perform a particular function without adversely affecting the performance of the powder composition in the powder bed melt or the articles made therefrom. The optional components may have a D falling within the average particle diameter of the PCL powder or optional leveling agent ₅₀ Values. If desired, each optional component may be milled to a desired particle size and/or particle size distribution, which may be substantially similar to PCL powder. Optional components may be particulate materials and include organic and inorganic materials such as fillers, leveling agents, and colorants. Other additional optional components may also include, for example, toners, fillers, colorants (e.g., pigments and dyes), lubricants, preservatives, thixotropic agents, dispersants, antioxidants, adhesion promoters, light stabilizers, organic solvents, surfactants, flame retardants, antistatic agents, plasticizers, and combinations comprising at least one of the foregoing. Another optional component may also be a second polymer that alters the properties of the PCL powder. In particular embodiments, each optional component, if present, may be present in the powder composition in an amount of from 0.01 wt% to 30 wt% based on the total weight of the powder composition. The total amount of all optional components in the powder composition may be 0 to 30 wt% based on the total weight of the powder composition. Such additives may also enhance the conversion of IR laser energy into thermal energy in the powder bed.

In a powder bed fusion process, such as a laser sintering process, each optional component need not be melted. However, to form a strong and durable article, each optional component may be selected to be uniformly compatible with the PCL polymer. For example, the optional component may be a reinforcing agent that imparts additional strength to the formed article. Examples of reinforcing agents include one or more types of glass fibers, carbon fibers, talc, clay, wollastonite, glass beads, and combinations thereof. Such additives may also enhance the conversion of IR laser energy into thermal energy in the powder bed.

The powder composition may optionally contain a leveling agent. In particular, the powder composition may comprise particulate levelling agents in an amount of 0.01 to 5 wt%, specifically 0.05 to 1 wt%, based on the total weight of the powder composition. In a particular embodiment, the powder composition comprises the particulate leveling agent in an amount of 0.1 to 0.25 weight percent, based on the total weight of the powder composition. The leveling agent included in the powder composition may be a particulate inorganic material having a median particle diameter of 10 μm or less, and may be selected from the group consisting of hydrated silica, amorphous alumina, vitreous silica, vitreous phosphate, vitreous borate, vitreous oxide, titanium dioxide, talc, mica, fumed silica, kaolin, attapulgite, calcium silicate, alumina, magnesium silicate, and combinations thereof. The leveling agent may be present in an amount sufficient to allow the semi-crystalline polymer powder to flow and level on the build surface of a powder bed fusion device (e.g., a laser sintering device). Such additives may also enhance the conversion of IR laser energy into thermal energy in the powder bed.

The powder composition may optionally contain an infrared absorber to facilitate the conversion of laser energy to thermal energy in the SLS process. The IR absorber may be one or more of a variety of inorganic or organic substances, such as at the wavelength of the IR laser (typically 10.6 μm, corresponding to 943cm ^-1 ) Metal oxides (e.g., titanium dioxide, silicon dioxide, glass, tungsten (VI) oxide), metal nanoparticles (e.g., gold nanorods), or organic compounds that are strongly absorbed.

Another optional component is a colorant, such as a pigment or dye, such as carbon black, to impart a desired color to the article. The colorant is not limited as long as the colorant does not adversely affect the composition or the article made therefrom, and wherein the colorant is stable enough to maintain its color under the conditions of the powder bed fusion process and exposure to heat and/or electromagnetic radiation (e.g., a laser used in a sintering process). Such additives may also enhance the conversion of IR laser energy into thermal energy in the powder bed.

Other additives include, for example, toners, fillers, lubricants, preservatives, thixotropic agents, dispersants, antioxidants, adhesion promoters, light stabilizers, organic solvents, surfactants, flame retardants, antistatic agents, plasticizers, and combinations thereof. Such additives may also enhance the conversion of IR laser energy into thermal energy in the powder bed.

Another optional component may also be a second polymer that improves the properties of the PCL powder.

The powder composition is a meltable powder composition and may be used in a powder bed melting process, such as selective laser sintering. Examples of selective laser sintering systems for manufacturing components from fusible powder compositions, particularly from fusible PCL powders disclosed herein, can be described as follows. A thin layer of the powder composition comprising PCL powder was spread over the sintering chamber. The laser beam traces a computer-controlled pattern corresponding to a cross-sectional slice of the CAD model to selectively melt the powder, which has been preheated to a temperature slightly below its melting temperature. After sintering of one layer of powder, the powder bed piston is lowered in predetermined increments (typically 100 μm) and another layer of powder is spread over the previous sintered layer by rollers. Then, as the laser melts and fuses each successive layer to the previous layer, the process is repeated until the entire article is completed. Thus, three-dimensional articles comprising multiple fused layers can be fabricated using the PCL powders described herein.

One or more variations may be constructed and arranged to provide one or more advantages, which may include, but are not limited to, the use of a single solvent in the preparation of PCL powder, which facilitates solvent recovery and reuse thereof. In many variations, PCL powder produced by at least one of the disclosed methods provides improved PBF performance. Thus, additive manufacturing processes using powder bed fusion, including Selective Laser Sintering (SLS), multi-jet fusion (MJF), high-speed sintering (HSS), and electrophotographic 3D printing, may benefit from the formation and use of PCL powder produced as described herein. In particular, 3D printing of implantable, bioabsorbable medical devices would benefit from the PCL powder materials described herein.

In many variations, the reprecipitation process can be used to purify PCL material, removing residual catalyst, initiator, monomer, and other contaminants. By dissolving the PCL, the contaminants trapped in the solid space are released into the resulting PCL solution. When PCL is reprecipitated, the amount of contaminants re-intercalated in the solid is significantly reduced due to the lower probability of intercalation and the property of forming crystallites to exclude contaminants. The reprecipitation process can be repeated with fresh, uncontaminated solvent to further reduce the contamination level. A common contaminant to be removed from PCL is tin compounds that remain as tin catalysts commonly used in epsilon-caprolactone polymerization processes.

Various variations may include a method of producing a powder suitable for additive manufacturing, the method comprising: mixing a suitable polymeric material with a solvent; dissolving a polymeric material suitable for additive manufacturing into a solvent to form a solution; cooling the solution to a temperature at which at least a portion of the dissolved polymeric material suitable for additive manufacturing precipitates out of the solution; separating the precipitated polymeric material from the solution; washing the separated, precipitated polymeric material to form a washed polymeric material; and drying the washed polymeric material to form a dried polymeric material suitable for additive manufacturing.

In at least one variation, the polycaprolactone powder can be formed by dissolving polycaprolactone in a heated solvent. Alternatively, the solvent may not require heating. The solvent may be a non-toxic, biocompatible solvent. In at least one variation, the solvent can be ethyl lactate. A single solvent may be used. Reprecipitation solvents such as gamma valerolactone and ethyl acetate may be used. Reprecipitation systems such as xylene and petroleum ether, tetrahydrofuran and methanol, or methylene chloride and water can be used. Dispersants such as polyvinylpyrrolidone may also be used in certain variations.

Examples

Reprecipitation of polycaprolactone powders

Fig. 1 shows a method for producing polycaprolactone powder according to at least one variant. For example, as shown in step 101, polycaprolactone can be combined with a solvent. Polycaprolactone tablets of any size may be used. The solvent may be one or more of the solvents described above. A single solvent may be used. The polycaprolactone may be heated prior to addition to the solvent to prevent the temperature of the solvent from decreasing upon addition of the polycaprolactone. The solvent may be heated. Optionally, the solvent may not require heating. In at least one variation, the polycaprolactone can be heated to a temperature above the melting point of the polycaprolactone and then added to the solvent. The temperature of the solvent may also be higher than the melting point of polycaprolactone. The polycaprolactone/solvent combination may be mixed, for example by stirring. A stirring rate of 200 to 800 revolutions per minute may be used. In at least one variation, a 600 to 700rpm agitation rate may be used. The concentration of polycaprolactone can be in the range of 1% w/v to 20% w/v, where the concentration of polycaprolactone is calculated by dividing the mass of polycaprolactone (in grams, g) by the volume of solvent (in milliliters, ml). In some variations, the concentration of polycaprolactone can be (a) 13% w/v to 15% w/v or (b) 8% w/v to 10% w/v. Fresh or recycled (previously used to reprecipitate polycaprolactone) solvent may be used. At step 102, the temperature of the solvent/polycaprolactone combination may be controlled to a set point temperature. In one variation, the set point temperature may be between 60 degrees celsius and 145 degrees celsius (inclusive of the endpoints of the range). In at least one variation, the set point temperature can be in the range of 80 to 110 degrees celsius (inclusive of the endpoints of the range). The setpoint temperature may be a temperature very close (e.g., within about 5 degrees celsius) to the boiling point of the solvent. The boiling point of the ethyl lactate solvent may be about 154 degrees celsius. The temperature of the solvent may be equal to the set point temperature. As shown in step 102, polycaprolactone can be dissolved into a solvent to form a solution. Step 102 may continue until all of the polycaprolactone is dissolved. When all of the polycaprolactone is dissolved, the solution may appear completely transparent and there may be little or no visible solids.

In step 103, the temperature of the polycaprolactone solution may be reduced. The cooling step may reduce the temperature to and below the saturation point of the solution, which may result in precipitation of the dissolved polycaprolactone from the solution. In one variation, the temperature of the polycaprolactone/solvent solution may be reduced to room temperature. In step 104, the precipitated polycaprolactone may be separated from the solution. Separation may be accomplished, for example, by vacuum filtration or by other separation techniques such as screening, centrifugation, cyclone separation, air separation, drying, and the like. After the polycaprolactone is separated from the solution in step 104, the polycaprolactone may be washed in a washing step 105. Residual solvents can be displaced and/or extracted from polycaprolactone using a miscible wash such as water. The wash liquor may be combined with polycaprolactone and the composition may be stirred. Alternatively, a wash solution may be sprayed onto the polycaprolactone solid on top of the mesh or screen to displace and/or extract the solvent and wash it out of the polycaprolactone. Other liquid displacement or extraction methods may also be used in step 105. After washing the polycaprolactone, it can be dried. Polycaprolactone can be dried by heating to a temperature from ambient temperature (e.g., 20 degrees celsius) to 50 degrees celsius. Polycaprolactone can be stationary in that hot air (or other gas, such as nitrogen) is passed through it to carry away water vapor. Alternatively, the polycaprolactone can be tumbled or otherwise moved to improve the mass transfer of the wash liquid from the polycaprolactone to the surrounding environment during the drying step. The vacuum system can be used to reduce the pressure to which the polycaprolactone is exposed during the drying step to reduce the energy required for drying and/or to achieve more complete drying.

The dried polycaprolactone particles can be separated by size in step 107. Size separation polycaprolactone particles with particle diameters in the range of 30 μm to 150 μm, 20 μm to 150 μm or 1 μm to 150 μm can be isolated/isolated. Size separation polycaprolactone particles having a particle diameter within a specific range required for end uses such as SLS printing can be isolated. Size separation may be accomplished by sieving, cyclone separation, air classifier, etc. Finally, polycaprolactone or a specific sized fraction of polycaprolactone can be used as a build material for the article of manufacture. For example, polycaprolactone of a particular size fraction can be used as a build material in an SLS printer to produce 3D printed articles. In at least one variation, the size separation step is not included and the powder is used for end use applications (e.g., SLS printing) without the size separation step.

Powder characterization

The properties of the polycaprolactone powder precipitated according to the variant are shown in fig. 2 to 5. FIG. 2 shows the results of thermogravimetric analysis (TGA) of a polycaprolactone sample produced according to at least one variation. TGA analysis heats the sample and measures its weight as the temperature increases. The presence of residual solvents and thermal decomposition temperatures can be determined by TGA results, as they may manifest as a change in weight loss rate. The second curve (line) on the TGA plot is the derivative of the TGA plot and shows the rate of change of weight. As shown in fig. 2, degradation of at least one variant begins at 358 ℃, resulting in a weight loss of 3% due to moisture.

Fig. 3 shows a Differential Scanning Calorimetry (DSC) curve of polycaprolactone precipitated according to at least one variant. As shown in the variant of FIG. 3, the first melting peak has an onset temperature of 49.81 ℃and a peak temperature of 58.39 ℃and an enthalpy of 101.86J/g. The recrystallization peak in FIG. 3 had an initial temperature of 25.87℃and a peak temperature of 21.02℃and enthalpy of 66.219J/g. The second melting peak in FIG. 3 had an onset temperature of 45.68℃and an enthalpy of 55.090J/g.

In many variants, the use of ethyl lactate solvent may result in a polycaprolactone powder having at least one of the following properties: (a) a degradation onset temperature of about 287 ℃ to about 420 ℃, (b) a TGA mass loss of about 0 mass% to about 3 mass%, (c) a first melting onset temperature of about 49 ℃ to about 58 ℃, (D) a first melting peak temperature of about 58 ℃ to about 65 ℃, (e) a first melting peak enthalpy of about 97J/g to about 111J/g, (f) a recrystallization onset temperature of about 25 ℃ to about 34 ℃, (g) a recrystallization peak temperature of about 21 ℃ to about 28 ℃, (h) a recrystallization enthalpy of about 56J/g to about 67J/g, (i) a second melting onset melting temperature of about 45 ℃ to about 54 ℃, (J) a second melting peak temperature of about 51 ℃ to about 58 ℃, (k) a second melting enthalpy of about 26J/g to about 58J/g, (l) D when determined in volume percent ₁₀ Between about 32 μm and about 517 μm, (m) when used in the form ofWhen the volume percentage is determined, D ₅₀ Between about 50 μm and about 944 μm, (n) D, when determined in volume percent ₉₀ Between about 83 and about 1297 μm, (o) between about 0 and about 100 volume percent of particles having a diameter greater than 150 μm, (p) between 0 and 1 volume percent of particles having a diameter less than 20 μm, (q) D when determined by the number percent ₁₀ Between about 14 μm and about 245 μm, (r) D when measured in percent by number ₅₀ Between 24 μm and 359 μm,(s) D when measured in percent by number ₉₀ Between 48 μm and 876 μm, (t) a number percentage of particles greater than 150 μm in diameter is between about 0 and about 100% or (u) a number percentage of particles less than 20 μm in diameter is between about 0 and about 35%.

When specifying data, D of y μm _x Meaning that x percent of the particles in the sample have a particle size of less than y μm. For example, 100 μm D ₅₀ (when determined by volume percent) means that 50% (by volume) of the particles in the sample have a particle size of less than 100 μm.

In a variation using ethyl lactate solvent, the method may produce a polycaprolactone powder containing particles, wherein about 70 volume percent to about 100 volume percent of the particles have a particle diameter between 20 μm and 150 μm. Variations may produce polycaprolactone powders comprising particles, wherein greater than 80 volume percent, greater than 90 volume percent, greater than 95 volume percent, greater than 98 volume percent, or even greater than 99 volume percent of the particles have a particle diameter of 20 μm to 150 μm.

In a variation using ethyl lactate solvent, the method may produce a polycaprolactone powder containing particles, wherein about 70% to about 100% by number of the particles have a particle diameter between 20 μm and 150 μm. Variations may produce polycaprolactone powders comprising particles wherein greater than 80%, greater than 90%, greater than 95%, greater than 98%, or even greater than 99% of the particles have a particle diameter between 20 μm and 150 μm. When the disclosed reprecipitation method is carried out to produce polycaprolactone powder, analytical methods such as NMR (nuclear magnetic resonance spectroscopy), GC (gas chromatography), TGA (thermogravimetric analysis), etc. can be used to detect trace amounts of residual solvents in the polycaprolactone powder.

The use of ethyl acetate solvents can result in polycaprolactone powders having at least one of the following characteristics: (a) a degradation onset temperature of about 329 degrees celsius to about 475 degrees celsius, (b) a TGA mass loss of between about 0 and about 0.5 mass percent, (c) a first melting onset temperature of between about 52 degrees celsius and about 57 degrees celsius, (D) a first melting peak temperature of between about 64 degrees celsius and about 67 degrees celsius, (e) a first melting peak enthalpy of between about 96J/g and about 105J/g, (f) a recrystallization onset temperature of between about 27 degrees celsius and about 31 degrees celsius, (g) a recrystallization peak temperature of between about 22 degrees celsius and about 26 degrees celsius, (h) a recrystallization peak temperature of between about 48J/g and about 63J/g, (i) a second melting peak temperature of between about 50 degrees celsius and about 60 degrees celsius, (J) a second melting peak temperature of between about 56 degrees celsius and about 59 degrees celsius, (k) a second melting enthalpy of between about 50J/g and about 55J/g, (l) when determined by volume percent, D ₁₀ About 28 μm, (m) D, when determined by volume percent ₅₀ About 1066 μm, (n) D when determined by volume percent ₉₀ About 1283 μm, (o) about 67 volume percent of particles having a diameter greater than 150 μm, (p) about 1 volume percent of particles having a diameter less than 20 μm, (q) D when determined by volume percent ₁₀ About 46 μm, (r) D, when determined by volume percent ₅₀ About 25 μm,(s) D, when determined by volume percent ₉₀ About 3 μm, (t) a number percentage of particles greater than 150 μm in diameter is about 0% or (u) a number percentage of particles less than 20 μm in diameter is about 33% by number.

Polycaprolactone produced according to at least one variation can have an intrinsic viscosity (inclusive of the endpoints of the range) of 0.3 to 3.0 deciliters per gram (dl/gm), as measured in chloroform at 25 ℃. Polycaprolactone produced according to at least one variation can have an intrinsic viscosity (inclusive of the endpoints of the range) of 1.1 to 1.4 deciliters per gram (dl/gm), as measured in chloroform at 25 ℃. Polycaprolactone can have a weight average molecular weight of 5,000 daltons to 200,000 daltons, specifically 100,000 daltons to 150,000 daltons, as measured by Gel Permeation Chromatography (GPC) using a crosslinked styrene-divinylbenzene column and calibrated to polystyrene references. GPC samples were prepared at a concentration of 1mg (mg/mL) per mL, and eluted at a flow rate of 1.5 mL/min.

Fig. 4 shows the particle size volume distribution of SLS-grade powder produced according to at least one variation. According to at least one variation, such as the variation shown in FIG. 4, the distribution may be nearly Gaussian, where D ₁₀ 62.14 μm, D ₅₀ 102.2 μm, D ₉₀ 156.6 μm.

Fig. 5 shows the particle size number distribution of SLS grade powder produced according to at least one variation. The distribution may be relatively controlled, with a drop in the order of 100 μm; 31.23 μm D ₁₀ D of 59.88 μm ₅₀ And a D of 105.0 μm ₉₀ 。

Fig. 6 shows powder data for polycaprolactone powders prepared according to at least one variant. Fig. 6 shows that at least one variant polycaprolactone powder has a melting peak temperature of 58.4 ℃. The figure also shows that the polycaprolactone produced according to at least one variant is free of fine particles (defined as particles with a diameter of less than 20 μm). This may be beneficial in certain applications because fine particles may impede the flow ability of the powder. The sphericity of the particles produced according to at least one variant was also tested. The 90.54% v/v (volume/volume or "volume percent") polycaprolactone particles have sphericity greater than 0.75. The polycaprolactone particles of 80.64% v/v have sphericity greater than 0.80. Calculating sphericity value by equation 1, wherein D _a Defined in equation 2, D _p Defined in equation 3. Higher sphericity values are associated with better flow capacity. In at least one variation, a polycaprolactone powder having a Hausner ratio, defined as the ratio of tap density to bulk density, of less than 1.25 may be prepared.

SLS test

Polycaprolactone produced according to at least one variation may be mixed with one or more other biocompatible components, such as hydroxyapatite. In at least one variant, the hydroxyapatite may be added to the polycaprolactone in an amount between 0.5% w/w and 10% w/w of the mass of the polycaprolactone. Hydroxyapatite is a mineral that is present in enamel and bone for bone tissue engineering. In a variant, other components may be added to the polycaprolactone. Other components may include one or more types of glass fibers, carbon fibers, talc, clay, wollastonite, glass beads, or combinations thereof.

Polycaprolactone produced according to at least one variation is blended with 4% w/w hydroxyapatite (the mass of hydroxyapatite is 4% of the mass of polycaprolactone) and used in an SLS printer to produce tensile bars. Seven tensile bars were formed using a 40W dual laser scan with a scan pitch of 0.18mm at a part temperature of 56.5 ℃ and a feed temperature of 40 ℃. The tensile bars were then stretched using the ASTM D638-4 type stretching method. The stretching rate was 5.00mm/min. FIG. 7 shows a photograph of a bar printed with SLS using polycaprolactone comprising 4% w/w Hydroxyapatite (HA). FIG. 8A shows the tensile curve generated by stretching a polycaprolactone (with 4% w/w hydroxyapatite) tensile bar produced by SLS. Fig. 8B shows a summary of material properties obtained from the tensile test in fig. 8A.

According to at least one variant, the moisture content of the polycaprolactone/hydroxyapatite powder can be adjusted before the powder is used in the SLS machine. Water may facilitate the melting process by acting as an endothermic agent. Hydroxyapatite may hinder the melting process by acting as a desiccant. Hydroxyapatite can promote melting of polycaprolactone powder due to its infrared absorbing properties. Researchers have found that the amount of moisture (water) in polycaprolactone/hydroxyapatite powder can affect the quality of SLS printed components made with this material. The low moisture content of polycaprolactone/hydroxyapatite may be detrimental to part quality. To ensure good printed part quality, water may be added to the modified polycaprolactone powder or polycaprolactone/hydroxyapatite mixture. For example, the moisture content of the polycaprolactone powder or polycaprolactone/hydroxyapatite blend may be adjusted such that the powder has an increased or decreased moisture content. For example, the water content may be adjusted by adding water to the powder or by placing the powder in a humidity-controlled atmosphere. The water content in the polycaprolactone powder or the polycaprolactone/hydroxyapatite powder blend may be adjusted such that the water content of the powder is between 0.5w/w and 5% w/w. In at least one variation, the powder may contain about 3% w/w water (moisture).

Nucleating agents such as hydroxyapatite

In at least one variation, the solvent/polycaprolactone mixture can further comprise a nucleating agent. In at least one variation, the solvent/polycaprolactone mixture can further comprise hydroxyapatite as a nucleating agent.

Examples

The steps are as follows:

a250 mL Erlenmeyer flask was charged with ethyl lactate (100 mL) and heated to 80 ℃. Once the set temperature is reached, polycaprolactone and hydroxyapatite are added, wherein the loading of polycaprolactone in solvent is 12% w/v (g/mL) and the hydroxyapatite is 4% w/w of polycaprolactone. The mixture was stirred until the polymer was completely dissolved, then heat was removed and reprecipitation was performed. Once the mixture had precipitated out such that the stirring bar was not movable, it was filtered to recover the solvent, washed in RT DI water for 3 hours, filtered, and air dried in an evaporation dish for 72 hours.

Observation results:

after dissolution of the polycaprolactone, the solution remained opaque, probably due to the fact that the hydroxyapatite particles were insoluble in ethyl lactate.

The mixture precipitated within 2 hours after heat removal. On a 250ml scale, this is twice the speed of a polycaprolactone solution without nucleating agent. 43.5% of ethyl lactate was recovered.

Powder analysis:

fig. 9 shows a DSC profile of the resulting polycaprolactone powder nucleated by hydroxyapatite according to at least one variant. The first melting curve had a peak at 62.42℃and enthalpy of 101.68J/g. The recrystallization curve exhibited a peak at 26.62℃and an enthalpy of 59.38J/g. The second melting curve had a peak at 57.80℃and an enthalpy of 45.78J/g.

FIG. 10 shows a particle number size distribution according to at least one variation, where D ₁₀ 19.14 μm, D ₅₀ 30.58 μm, D ₉₀ 53.13 μm. Only 12.74% of all particles are outside the desired SLS range (where the desired SLS range is a particle diameter range between 20 μm and 150 μm), 99.95% of all particles are less than 150 μm, and 12.69% of particles are less than 20 μm.

FIG. 11 shows a particle number size distribution, D, according to at least one variation ₁₀ 31.47 μm, D ₅₀ 61.25 μm, D ₉₀ 120.6 μm. Only 4.04% of the particles are outside the desired SLS range (the desired SLS range may be 20 μm-150 μm), 96.87% of all particles are less than 150 μm, and 0.91% of the particles are less than 20 μm.

Compared to the powder without nucleating agent:

FIGS. 12A and 12B show a comparison between (12A) a polycaprolactone powder nucleated with 4% w/w hydroxyapatite and (12B) a polycaprolactone powder dry blended with 4% w/w hydroxyapatite and allowed to stand for more than 24 hours. Figures (figures 12A and 12B) compare discs prepared by melting about 8g of polycaprolactone/hydroxyapatite blend. Sample "(12A)" was added with 4% w/w hydroxyapatite prior to reprecipitation, allowing it to act as a nucleating agent. Sample "(12B)" had 4% w/w of hydroxyapatite added as a dry blend after sieving of the powder.

In a variant in which hydroxyapatite is added as a nucleating agent, it may be added during the polycaprolactone precipitation step to form a solution comprising hydroxyapatite, polycaprolactone and solvent. In at least one variant, an amount of hydroxyapatite may be added to the solvent/solution such that the hydroxyapatite is present in an amount between 0.5% w/w and 10% w/w of the mass of polycaprolactone. The polycaprolactone may then be precipitated from the solution to form a precipitated polycaprolactone powder comprising hydroxyapatite. The method may be used to prepare a wafer, such as the wafer "(12A)" shown in fig. 12A. The wafer preparation method may include melting a polycaprolactone-containing material, and then allowing the material to cool and solidify.

In a dry-blended version of hydroxyapatite and polycaprolactone, the polycaprolactone may be precipitated from the solvent and dried. The dried polycaprolactone can then be mixed with a specific amount of hydroxyapatite to form a powder comprising polycaprolactone and hydroxyapatite. The method may be used to prepare a wafer, such as the wafer "(12B)" shown in fig. 12B. The wafer preparation method may include melting a polycaprolactone-containing material, and then allowing the material to cool and solidify.

Fig. 13 shows a comparison of particle size distribution between polycaprolactone precipitated alone and polycaprolactone precipitated with hydroxyapatite as a nucleating agent. As shown in FIG. 13, the addition of hydroxyapatite as a nucleating agent in the reprecipitation step improves the particle size distribution and can produce more polycaprolactone particles falling within the range of 20 μm to 150 μm.

The volume and number distribution is considered when determining whether the powder is suitable for SLS. In an ideal case, the volume and number distribution would be the same, D ₅₀ Is 60 μm and is distributed between 30 μm and 150 μm, the smallest powder being outside this range. However, in reality, this is unlikely to occur. Thus, the volume distribution is checked to determine if the powder is suitable for SLS and the quantity distribution is checked to determine if there are any potential problems that may occur. For example, too many particles smaller than 30 μm or smaller than 20 μm may cause flow problems, while too many particles larger than 150 μm may cause resolution (resolution) problems.

Fig. 13 shows a comparison between particle size distribution of polycaprolactone precipitated with and without hydroxyapatite as a nucleating agent. Viewing ofObserving the volume distribution, both powders had a relatively gaussian distribution, but polycaprolactone precipitated with hydroxyapatite had nearly ideal D ₅₀ . Furthermore, polycaprolactone precipitated with hydroxyapatite has a smaller volume percentage of particles outside the desired range (where the desired range may be a particle diameter size range between 20 μm and 150 μm diameter, inclusive of the end of the range). From the number distribution, 12.7% more polycaprolactone precipitated with hydroxyapatite than without nucleating agent had particles smaller than 20 μm. However, polycaprolactone powders with nucleating agents may be preferred because of their close to ideal volume distribution.

Fig. 14A shows a wafer prepared by melting virgin (virgin) polycaprolactone (at ambient humidity) in a convection oven. Fig. 14A shows two opposite sides (top and bottom) of a single wafer, as shown in fig. 14B-14G. Fig. 14B shows a wafer prepared by melting the original polycaprolactone (at ambient humidity) under IR (infrared). Fig. 14C shows a wafer prepared by dry blending the newly produced polycaprolactone with 4% w/w hydroxyapatite and subsequent melting in a convection oven. FIG. 14D shows a disc prepared by dry blending the newly produced polycaprolactone with 4% w/w hydroxyapatite and subsequent melting under IR. Fig. 14E shows a wafer prepared by the following method: 4% w/w hydroxyapatite was dry blended with polycaprolactone, the blend aged at ambient conditions for 24 hours, and the aged blend was subsequently melted in a convection oven. FIG. 14F shows a wafer prepared by dry blending 4% w/w hydroxyapatite with polycaprolactone, aging the blend for 24 hours at ambient conditions, and then melting the aged blend at IR. Fig. 14G shows a wafer prepared by melting polycaprolactone in a convection oven, wherein the polycaprolactone is formed by a powder precipitation process comprising 4% w/w hydroxyapatite as a nucleating agent (i.e. the hydroxyapatite is added to the solvent during precipitation to form a solution comprising the hydroxyapatite, the polycaprolactone and the solvent). As shown in fig. 14G, the addition of hydroxyapatite as a nucleating agent to ethyl lactate during precipitation of polycaprolactone produced a wafer of uniform appearance. In other words, without being bound by theory, the use of hydroxyapatite as a nucleating agent during precipitation appears to produce a molten mass that can be thoroughly mixed with uniform concentrations of hydroxyapatite and polycaprolactone throughout the molten mass.

Figure 15 shows the DSC profile of the polycaprolactone powder reprecipitated in ethyl lactate. As shown, the polycaprolactone was first heated to 100 ℃ at a rate of 20 ℃ per minute. The first melting peak temperature was 58.39 ℃and the melting enthalpy was 99.928J/g. The polycaprolactone sample was then cooled to-10 ℃ at a cooling rate of 20 ℃ per minute. The recrystallization peak temperature was 21.02℃and enthalpy was 62.261J/g. The polycaprolactone sample was then heated a second time to 100 c (as shown by the bottom dashed line in fig. 15) at a rate of 20 c/min. The second heating cycle showed a melting peak temperature of 51.22℃and a melting enthalpy of 52.677J/g.

FIG. 16 shows DSC curves of polycaprolactone powders reprecipitated (in ethyl lactate) in the presence of 4% w/w hydroxyapatite as nucleating agent, wherein 4% w/w hydroxyapatite is calculated by dividing the mass of hydroxyapatite added to ethyl lactate by the mass of polycaprolactone added to ethyl lactate. The DSC protocol used to generate the data in FIG. 16 was the same as the DSC protocol used to generate the data in FIG. 15-first, the sample was heated to 100deg.C at a ramp rate of 20deg.C/min, then cooled to-10deg.C at a rate of 20deg.C/min, and then heated again to 100deg.C at a ramp rate of 20deg.C/min. As shown in FIG. 16, the first melting peak temperature of the sample of polycaprolactone reprecipitated in the presence of hydroxyapatite as a nucleating agent was 62.42℃and enthalpy was 101.68J/g. The sample had a recrystallization peak temperature of 26.62℃and enthalpy of 59.376J/g. Finally, the second peak melting temperature of the sample was 57.80℃and enthalpy was 45.775J/g.

Claims

1. A powder comprising polycaprolactone particles, wherein greater than 90 volume percent of the polycaprolactone particles have a particle size between 20 microns and 150 microns, wherein the polycaprolactone particles contain a detectable amount of nucleating agent, and wherein the polycaprolactone particles contain a detectable amount of solvent, the solvent comprising at least one of a biocompatible solvent or a bioabsorbable solvent.

2. The powder of claim 1, wherein the solvent comprises ethyl lactate.

3. The powder of claim 1, wherein the nucleating agent is hydroxyapatite.

4. The powder of claim 1, wherein greater than 90 volume percent of the polycaprolactone particles have a sphericity greater than 0.75.

5. The powder of claim 1, wherein greater than 80 volume percent of the polycaprolactone particles have a sphericity greater than 0.80.

6. The powder of claim 1, wherein the volume percent of polycaprolactone particles having a particle size of less than 20 microns is zero or undetectable.

7. The powder of claim 1, wherein the powder has a melting enthalpy of about 90J/g to about 120J/g.

8. A powder comprising polycaprolactone particles, a detectable amount of ethyl lactate, and a detectable amount of a nucleating agent; wherein the powder has a peak melting temperature of about 55 ℃ to about 65 ℃ and a melting enthalpy of about 90J/g to about 120J/g.

9. The powder of claim 8, wherein the nucleating agent is hydroxyapatite.

10. The powder of claim 8, wherein the powder has a recrystallization peak from about 15 ℃ to about 35 ℃.

11. The powder of claim 8, wherein the powder has an onset degradation temperature of about 250 ℃ to about 425 ℃.

12. The powder of claim 8, wherein greater than 96% by number of the polycaprolactone particles have a particle size of less than 125 microns.

13. The powder of claim 8, wherein greater than 90 volume percent of the polycaprolactone particles have a sphericity greater than 0.75.

14. A powder comprising polycaprolactone particles having a detectable amount of ethyl lactate and a detectable amount of nucleating agent, wherein greater than 96% by number of the polycaprolactone particles have a particle size of less than 125 microns, and wherein greater than 90 volume percent of the polycaprolactone particles have sphericity greater than 0.75, and wherein the polycaprolactone particles have a moisture content adjusted to and maintained between 0.5% w/w and 5% w/w.

15. The powder of claim 14, wherein the nucleating agent is hydroxyapatite.

16. A method of producing the powder of claim 1, the method comprising:

combining polycaprolactone and a polar organic solvent;

dissolving the polycaprolactone in the polar organic solvent to form a solution;

cooling the solution to a temperature at which at least a portion of the dissolved polycaprolactone precipitates out of the solution;

adding a nucleating agent to the solution;

separating precipitated polycaprolactone from the solution;

washing the isolated, precipitated polycaprolactone to form washed polycaprolactone; and

drying the washed polycaprolactone to form dried polycaprolactone.

17. The method of claim 16, further comprising heating the polycaprolactone and the polar organic solvent in combination.

18. The method of claim 16, further comprising a separation step of separating dried polycaprolactone particles having a particle size of less than 150 microns from larger dried polycaprolactone particles to form polycaprolactone of a particular size.

19. The method of claim 18, wherein the percentage of nucleating agent in the combined polycaprolactone/nucleating agent mixture is between about 0.5 mass% and 10 mass%.

20. The method of claim 16, wherein the nucleating agent is hydroxyapatite.

21. The method of claim 16, wherein greater than 90 volume percent of the polycaprolactone particles of the particular size have a sphericity greater than 0.75.

22. The method of claim 16, wherein greater than 80 volume percent of the polycaprolactone particles of the particular size have a sphericity greater than 0.80.

23. The method of claim 16, wherein the polar organic solvent is selected from the group consisting of: ethyl acetate, ethyl lactate, gamma valerolactone, N-Dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), dichloromethane (DCM), chloroform, acetone and dimethyl sulfoxide (DMSO).

24. The method of claim 23, wherein the polar organic solvent is ethyl lactate.

25. A method of producing the powder of claim 1, the method comprising:

combining polycaprolactone and ethyl lactate;

dissolving the polycaprolactone and at least one nucleating agent in the ethyl lactate to form a solution;

cooling the solution to a temperature at which at least a portion of the dissolved polycaprolactone precipitates out of solution;

Separating precipitated polycaprolactone from the solution;

drying the washed polycaprolactone to form dried polycaprolactone.

26. The method of claim 25, wherein the at least one nucleating agent comprises hydroxyapatite.

27. The method of claim 25, wherein the solution is heated.

28. A method of additive manufacturing, the method comprising:

selectively melting or sintering adjacent polycaprolactone particles,

wherein greater than 96% by number of the polycaprolactone particles have a particle size of less than 125 microns, and wherein greater than 90 volume percent of the polycaprolactone particles have a sphericity of greater than 0.75,

wherein the polycaprolactone particles comprise a detectable amount of hydroxyapatite and

wherein the polycaprolactone particles contain a detectable amount of ethyl lactate.

29. The method of claim 28, wherein the polycaprolactone particles have a moisture content adjusted to and maintained between 0.5% w/w and 5% w/w.

30. An article comprising the powder of claim 1.

31. A medical product comprising the powder of claim 1.