WO2000009307A9

WO2000009307A9 - A mold for making a three-dimensional complex structure, said mold comprising at least three mold portions, method of making said mold, and use of said mold for making three-dimensional complex structures

Info

Publication number: WO2000009307A9
Application number: PCT/US1999/018209
Authority: WO
Inventors: Donald E Ingber; David E Butz; Eric R Roberts; Dale Clifford; John J Kummailil
Original assignee: Molecular Geodesics Inc; Donald E Ingber; David E Butz; Eric R Roberts; Dale Clifford; John J Kummailil
Priority date: 1998-08-11
Filing date: 1999-08-11
Publication date: 2000-08-03
Also published as: WO2000009307A2; WO2000009307A3; AU5554499A

Abstract

Molds, methods of forming the molds, and methods of using the molds to form complex unitary three-dimensional structures are provided. The complex unitary three-dimensional structures and its complement have a high degree of interlocking. The molds include at least three mold portions constructed and arranged to include a complement of complex three-dimensional unitary structure when in an assembled configuration, and a portion of the complement when in an unassembled configuration. The structure is not removable from the mold portions without destroying at least a portion of the mold. The method involves providing a mold that includes a complement of the complex unitary three-dimensional structure, introducing a fluid material into the mold, and removing the complex unitary three-dimensional structure from the mold.

Description

A MOLD FOR MAKING A THREE-DIMENSIONAL COMPLEX STRUCTURE, SAID MOLD

COMPRISING AT LEAST THREE MOLD PORTIONS, METHOD OF MAKING SAID MOLD,

AND USE OF SAID MOLD FOR MAKING THREE-DIMENSIONAL COMPLEX STRUCTURES

Background Of The Invention Field Of The Invention

The present invention is directed to methods of making molds for complex unitary three-dimensional structures the molds formed thereby, and methods of forming the complex unitary three-dimensional structures, in particular, complex unitary foams, lattices, trusses, scaffolds, and biomimetic structures.

Related Applications

This application claims priority under 35 U.S.C. §119(e) to commonly assigned, co- pending U.S. provisional Application Serial Nos. 60/108,694, filed on 1 1/17/98; and under 35 U.S.C. §120 to commonly assigned, co-pending U.S. non-provisional Application Serial No. 09/132,646, filed on 8/11/98.

Related Art

Extensive complex unitary three-dimensional structures are desired in many areas of industry and medicine, but have been, in some instances, difficult to manufacture economically. Due to the tortuous geometry of extensive complex unitary three-dimensional structures, such structures cannot be made by simple molding or conventional investment casting techniques, because the positive mold cannot be removed from the permanent master mold. For example, the tensegrity trusses described in co-pending and commonly assigned U.S.S.N. 08/964,497, filed November 5, 1997, and the tetrakaidecahedral lattice structures described in co-pending and commonly assigned U.S.S.N. 08/997.574, filed December 24, 1997 cannot be made using conventional techniques.

Possibly the oldest method of molding shapes of complex geometry is the lost-core or investment casting method, which is known to have been used as early as 4000 B.C. in China. The investment casting process has been found to be an inexpensive method of producing such parts, which require minimal or no finishing after casting. In a typical modern investment casting process, a master mold of the desired structure is used to cast a positive mold of the structure part from wax, a thermoplastic polymer, or another material removable by melting, leaching, or other processes such as sublimation or vibration. The positive mold is then coated with a ceramic slurry and dried. The wax is melted out. leaving a ceramic negative mold, or complementary mold, which can be fired and then filled with molten metal.

Finally, the ceramic mold is broken away from the metal casting.

The geometries which can be produced by the investment casting method are limited by the requirement that the wax positive mold be removable from the master mold. If the geometries of the positive and complementary molds are interlocking, this may require the master mold to have many pieces (increasing the expense of the method), or may render the part unmanufacturable by investment casting.

There are several difficulties with the lost-core approach for the production of complex unitary three-dimensional structures. One is related to the number of steps required, as well as the complexity of accomplishing some of the steps for certain materials of choice.

In addition, due to the number of steps required, poor surface quality and poor reproduction of detail are typical, as the final structure is molded against surfaces which have been molded against the original pattern of the sacrificial master, with loss of detail at each stage. The greatest difficulty, however, is the production of the original sacrificial master. Since the sacrificial master is a duplicate of the final structure, it is just as difficult to produce by any low cost casting or molding technique.

One method that is available for producing extensive complex three-dimensional structures is solid free-form fabrication, which includes, but is not limited to, three- dimensional printing, selective laser sintering, and stereolithography. Solid free-form fabrication techniques provide a direct method for creating structures with complex geometries, eliminating the need for a sacrificial master mold. However, such techniques are generally relatively expensive and have relatively slow build rates. Furthermore, the surface quality produced by such techniques is inherently poor relative to what is desirable and possible using direct machining or permanent molds. As a result, such methods are generally reserved for rapid prototyping rather than mass production.

International Publication WO 98/19843 discloses an integrally formed three- dimensional truss structure, and molds and methods for production of the structure.

Accordingly, a need exists for improved methods of forming extensive complex unitary three-dimensional structures. Summary

The present invention is directed to a method of forming complex unitary three- dimensional structures in which the structure and its complement have a high degree of interlocking. In one embodiment, the invention is directed to a mold that includes at least three mold portions constructed and arranged to include a complement of a complex three- dimensional unitary structure when in an assembled configuration, and a portion of the complement when in an unassembled configuration. In one embodiment, the mold portions each include at least two surfaces. In another embodiment, the mold portions each include at least two surfaces, and each surface corresponds to a periodic plane of the complex three- dimensional unitary structure.

Another embodiment is directed to a mold that includes a plurality of mold portions positioned adjacently and in direct contact with one another and an at least partially solidified material having the shape of a complex unitary three dimensional structure. The structure is not removable from the mold portions without destroying at least a portion of the mold.

Another aspect of the invention is directed to a method of forming a mold for a complex unitary three-dimensional structure. The method involves providing at least three mold preforms, and forming a mold portion from each of the at least three mold preforms. Each of the preforms includes a portion of a complement of the complex unitary three- dimensional structure. The mold portions are assembled adjacently and in direct contact with each other to provide the mold.

Another embodiment of the method involves providing a mold that includes a complement of the complex unitary three-dimensional structure, introducing a fluid material into the mold, and removing the complex unitary three-dimensional structure from the mold.

Another embodiment of the method involves forming a plurality of mold portions. Each mold portion includes at least a portion of a complement of a complex unitary three dimensional structure. A mold is formed from the plurality of mold portions by positioning the plurality of mold portions adjacently and in direct contact with each other, such that the portions of the complement combine to form the complement. A fluid material is introduced into the mold and allowed to solidify such that the structure is not removable from the mold without breaking the mold, and the mold is not removable from the structure without breaking the structure.

Another embodiment of the invention is a method of producing a regular truss. The method involves forming a plurality of mold portions. The mold portions comprise (usually solid, but possibly hollow) polyhedra, which have grooves along at least some edges of the polyhedra mold portions are assembled into a mold by fitting the polyhedra together, for example in a tessellated arrangement. The grooves at the edges of the polyhedra combine to form channels, where the channels define the truss structure. The mold is then filled with a liquid composition, filling the channels. The liquid composition is then hardened, for example by cooling, to form a solid truss, which is interlocked with the mold. After the truss has solidified, the mold is removed without destroying the truss. This may be accomplished, for example, by melting, dissolution, sublimation, vibration, or enzymatic degradation. When the mold has been removed, the truss remains, and may be subjected to sintering or other finishing steps. The disposable mold portions are preferably of a shape that can be formed by casting or molding processes, but are assembled into a mold shape that cannot be directly formed by simple casting or molding, because of a high degree of interlocking of the mold and the truss produced therefrom.

Some of the advantages of the present invention include a reduction in time and cost for the formation of the structures, improved surface quality, and the elimination of the formation of a sacrificial master. Other advantages of the methods and molds of the present invention include the formation of complex structures without the need for assembling individual components. Further advantages of the present methods and molds of the invention are the facilitation of using materials that require minimal assembly and that may be used in a variety of different applications including lightweight materials, filtration, foam, insulation, etc. Other applications include, but are not limited to, thermal insulation; applications where light weight is a critical issue, such as aerospace applications; applications where low pressure drop is a critical issue, such as filtration and catalysis; applications where high strength porous materials are desired, such as biomedical devices for tissue repair or reconstruction, and spinal fusion cages or scaffold for bone repair; biomimetic industrial materials; and medical devices.

DEFINITIONS "Complex unitary three-dimensional structure," as used herein, means any structure having an interlocking or tortuous geometry that precludes manufacturing using conventional molding or fabrication techniques, including microfabrication techniques. Such structures include, but are not limited to, complex unitary highly porous materials, including foams, lattices, trusses, scaffolds, cylinders, microcages, and biomimetic materials. "Complement," or "complementary space," as used herein, means the space occupied by the negative of any complex unitary three-dimensional structure such as, but not limited to, a cubic lattice, an octet truss, a tetrakaidecahedral truss, geometrically simpler structures such as regular trusses, lattices, and foams, or lattice structures with regular, irregular or functionally adapted architecture. "Complement," as applied to a physical body, represents the locus of space which lies within or near the body, but which the body does not occupy. Thus, a negative mold and the positive casting produced therefrom are complements of one another if the casting fills all the spaces of the mold.

As it is used herein, the terms "regular lattice" or "regular truss" refer to an array of struts disposed at the edges of a set of tessellated polyhedra. The struts may be of uniform cross-section or of differing cross-sections. The set of tessellated polyhedra preferably comprises a number of identical polyhedra. The set preferably comprises no more than four distinct shapes, and more preferably comprises only one or two distinct shapes. The edges of the polyhedra may be straight or curved. A regular lattice or regular truss may also include members disposed at faces of some of the polyhedra.

The terms "structural member," "member," and "strut" are used interchangeably herein, referring to the individual elements that make up the interconnected framework of the complex unitary three-dimensional structures, including, but not limited to, struts, geodesic elements, extensible elements, and non-compressible elements. "Module," as used herein, means a plurality of integrally connected structural members that delineate the edges of at least a portion of a polyhedron.

"Integrally connected," as used herein, means a single composition or structure made up of a plurality of elements to form a single unitary body. The structure does not have discrete connectors or additional bonding or adhesive materials. "Fluid," as used herein, means any flowable material, not limited to liquids, that may be used to fill a tortuous mold. That is, any material that will flow from one point to another under the influence of, for example, gravity or a pressure differential, including, for example, gases and particulate materials.

"Functionally graded," as used herein, means that the material properties of the structure may vary along its length or depth. "Functionally adapted," as used herein, means that the microarchitecture of the structures may vary in density and geometric arrangement locally from place to place within the larger unitary structure so as to provide various physical properties and functional utility as needed in different locations within the structure. For example, in one area the structure may be optimized for physical strength, in another for energy absorption, and in another for passage of fluid or heat removal.

"Groove," as used herein with reference to a mold or mold portions, means any depression formed in a parting surface, having any cross-sectional area. The term groove includes, but is not limited to, half-round, -square, and -vee shaped cross-sections in a surface, and the like. In addition, the term "groove" is also meant to include less than half - round, -square, and -vee shaped cross-sections in a surface, and the like.

"Channel," as used herein with reference to a mold or mold portions, means the complementary space that is formed by corresponding grooves when mold portions are assembled, or that is formed directly in a mold or mold portions, for example, by drilling. "Assembled," as used herein with reference to a mold or mold portions, means that the parting surfaces of the plurality of mold portions are positioned adjacently and in direct contact with each other, such that the grooves formed in the parting surfaces of the mold portions, or the edges formed at the intersection of the parting surfaces of the mold portions, form channels for receiving a fluid to be introduced into the mold. This may be accomplished, in a variety of ways including, but not limited to, aligning the mold portions and pressing them between several plates.

"Unassembled," as used herein with reference to a mold or mold portions, means that the parting surfaces of the plurality of mold portions are not positioned adjacently and in direct contact with each other. "Wall," as used herein, means a layer of solidified molding material disposed between two tiers of complex unitary three-dimensional structures. The walls may be separate from or integrally connected to the tiers.

"Skin," as used herein, means a layer of solidified molding material disposed on the exterior of a complex unitary three-dimensional structure. The skin may be spaced apart from or integrally connected to the structure. "Scaffold," as used herein, means a material having an extended repeating structure, which forms a framework or skeleton onto which and into which additional components may be introduced to impart additional features to the material.

"Geodesic element," as used herein, means a geometric element which defines the shortest distance between two points on the surface of a solid. For example, a line is the shortest distance between two vertices on a surface of a polyhedron, a path along a great circle is the shortest distance (and hence, a geodesic element) for a sphere, and a spiral is a geodesic element on the surface of a cylinder. A triangle is geodesic because it represents the shortest, most economical path between three vertices on the surface of a polyhedron. "Tensegrity structure," as used herein, means an arrangement of interconnected structural members that self-stabilizes through transmission of continuous tension and discontinuous compression. Tensegrity elements may be composed of members that selectively resist tension or compression locally or of all non-compressible members that may resist either tension or compression depending on their location and the path of force transmission. A triangle composed of all non-compressible struts is an example of the latter type of self-stabilizing tensegrity structure, as described in co-pending and commonly assigned U.S.S.N. 08/964,497, filed November 5, 1997, incorporated herein by reference.

"Extensible element," as used herein, means an element that is capable of extension or an increase in the length of the member within a given range of movement in response to application of a tensile force to one or both ends of the member.

"Non-compressible element," as used herein, means an element that is incapable of shortening along its length when compressive forces are applied to one or both ends of the member. However, the non-compressible member may be able to buckle under compression, without shortening its length. A noncompressible member may or may not be able to extend in length when external tensile forces are applied to its ends. Such an extensible, non- compressible member would be able to withstand compression, but not tension.

"Regular lattice" or "regular truss" refer to an array of struts disposed at the edges of a set of tessellated polyhedra. The struts may be of uniform cross-section or of differing cross- sections. The set of tessellated polyhedra preferably comprises a number of identical polyhedra. The set preferably comprises no more than four distinct shapes, and more preferably comprises only one or two distinct shapes. The edges of the polyhedra may be straight or curved. A regular lattice or regular truss may also include members disposed at faces of some of the polyhedra.

"Tetrakaidecahedral truss" refers to an array of struts which define the edges of a set of tessellated tetrakaidecahedra. The tetrakaidecahedra may be orthic, Kelvin, or other space- filling identical tetrakaidecahedra. Examples of tetrakaidecahedral trusses are given in co- pending and commonly assigned U.S.S.N. 08/997,574, which is incorporated herein by reference.

"Octet truss" refers to an array of struts which define the edges of a set of tessellated octahedra and tetrahedra, as described in U.S. Patent No. 2,986,241, to R. Buckminster Fuller. "Biomimetic material," as used herein, means a material that mimics the microstructural organization, mechanical responsiveness, functionally adapted microarchitecture or catalytic activities of living cells and tissue. Biomimetic materials exhibit the strength, flexibility, and porosity of living tissues, and their elements rearrange, rather than deform or break locally, when mechanically stressed.

Brief Description Of The Drawings

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings in which: FIG. 1 is a perspective view of a variety of complex unitary three-dimensional structures having parallel members that can be bisected by parallel planes;

FIG. 2 includes side and bottom views of a complex unitary three-dimensional structure that does not have parallel members;

FIG. 3 is a flow-chart of one method according to the invention for directly forming the molds of the present invention;

FIG. 4 is a perspective view of a complex unitary cubic lattice structure;

FIG. 5 is a perspective view of a mold in an assembled configuration according to one embodiment of the present invention, for forming a unitary cubic lattice structure;

FIG. 6 is an exploded perspective view of the mold of FIG. 5; FIG. 7 is a perspective view of an end plate mold portion of the mold of FIG. 5;

FIG. 8 is a perspective view of a mid plate mold portion of the mold of FIG. 5;

FIG. 9 is a perspective view of a cross-section of the assembled mold of FIG. 5 along plane A- A;. FIG. 10 is a perspective view of a cross-section of the assembled mold of FIG. 5 along plane B-B;

FIG. 11 is a perspective view of a complex unitary octet structure;

FIG. 12 is a perspective view of a mold in an assembled configuration, according to another embodiment of the present invention, for forming a unitary octet truss structure; FIG. 13 is an exploded perspective view of the mold of FIG. 12;

FIG. 14 is a perspective view of an mid-plate mold portion of the mold of FIG. 12;

FIG. 15 is an expanded perspective view of a portion of the mid-plate mold portion of FIG. 14;

FIG. 16 is a perspective view of an end-plate mold portion of the mold of FIG. 12; FIG. 17 is a perspective view of a cross-section of the assembled mold of FIG. 12 along plane C-C;

FIG. 18 is a perspective view of a cross-section of the assembled mold of FIG. 12 along plane D-D;

FIG. 19 is a perspective view of a mold in an assembled configuration, according to another embodiment of the present invention, for forming a complex unitary octet truss structure;

FIG. 20 is a cross-sectional view of a mold portion used to form the mold of FIG. 19;

FIG. 21 is a side view of the mold portion of FIG. 19;

FIG. 22 is a top view of the mold portion of FIG. 19; FIG. 23 is a perspective view of an orthic tetrakaidecahedral regular truss;

FIG. 23A shows a single orthic tetrakaidecahedral mold portion having registration structures at the square faces;

FIG. 24 illustrates a perspective view of a master mold for forming a plurality of mold portions of FIG. 23 A; FIG. 25 illustrates a perspective cut-away view of the mold of FIG. 24;

FIG. 26 illustrates a perspective view of single layer of a plurality of adjacently placed mold portions shown in FIG. 23A;

FIG. 27 illustrates a perspective cut-away view of two layers of a plurality of adjacently placed mold portions of FIG. 23 A;

FIG. 28 illustrates a cut-away perspective view of the mold shown in FIG. 26;

FIG. 29 illustrates a perspective cut-away view of the mold of FIG. 27;

FIGS. 30 and 31 illustrate ridge configurations for the master mold of FIGS. 24 and 25; FIG. 32 is a perspective view of a unitary cylindrical octet truss structure with integrally connected walls and skins;

FIG. 33 is a perspective view of the mold portions used to form the cylindrical octet truss of FIG. 32;

FIG. 34 is a perspective cut away view of a complex unitary functionally adapted truss structure including skins;

FIG. 35 is cross-section of the structure of FIG. 34 through plane E-E;

FIG. 36 is a cross-section of another embodiment of the structure of FIG. 34;

FIG. 37 is a cross-section of a mold in an assembled configuration that is useful for forming the structure of FIG. 34, including several tiers of trusses; FIG. 38 is a cross-section of a mold in an assembled configuration that is useful for forming the structure of FIG. 34;

FIG. 39 is a schematic illustration of an extrusion die and embossing assembly used to form the mold portions of FIG. 20-22;

FIG. 40 is a perspective view of the extrusion die of the embossing assembly of FIG. 37;

FIG. 41 is an expanded perspective view of the embossing assembly of FIG. 39;

FIG. 42 is an expanded perspective view of the embossing assembly of FIG. 39, showing extrusion of the mold portions of FIGS. 20-22; FIG. 43 is a schematic illustration of a mold portion adapted to receive cables and struts;

FIG. 44 is a perspective view of a mold assembly including removable pins used to produce rhomboidal mold portions; FIG. 45 is a schematic illustration of a method of forming single crystal unitary structures; and

FIG. 46 is a flow-chart of a method according to the invention for forming porous foams.

Detailed Description

The present invention is directed to methods of making molds for forming complex unitary three-dimensional structures, and the molds formed thereby, that have proven costly, difficult, or impossible to form using existing techniques. The present invention is also directed to methods of using the molds to form such complex unitary three-dimensional structures. In contrast to other methods, the present invention provides molds for and methods of making complex unitary three-dimensional structures of relatively large extent.

One aspect of the invention is the provision of the molds and mold portions for use in conjunction with the methods of the invention, which are described in greater detail below, to form complex unitary three-dimensional structures. The shape of the molds of the invention is dictated, in part, by the shape of the desired complex unitary three-dimensional structures. The structures formed using the molds of the invention may have regular or irregular shapes. The structures may also include skins on the exterior, as well as walls on the interior separating or sub-dividing the structure. The walls and skins may be separate from or integrally connected to the structures, and may be formed concurrently with or after forming the structure. The design of the structures may be functionally graded and may include functionally adapted microarchitecture. The size and extent of the structures that may be provided using the methods and molds of the invention is limited only by practical considerations. Structures with varying density may be provided by varying the spacing between the members, or by forming multi-tiered structures in which each tier has a different spacing between its members. Additional structures that may be provided include those with predetermined microarchitecture, including geodesic lattices, as well as lattices that are both regular or irregular in form, tensegrity lattices containing isolated compression struts interconnected by an integral series of tensile cables, as well as curved structures. The structures may be simple arrangements of identical struts along the edges of a set of identical tessellated polyhedra, in which case they will be expected to have isotropic properties. Alternatively, the cross-section of the struts may be varied in different regions of the structure by using mold portions having variable sizes and shapes of grooves. The properties of the structure would then be expected to be anisotropic. For example, the structure might be stiffer in a region having thicker struts. Such embodiments might have utility, for example, in the construction of sneaker soles. Currently, such soles are constructed from a number of different polymers in order to obtain differing stiffnesses at the heel, arch, ball, and toe of the shoe. By varying strut size of a lattice incorporated into a sneaker sole, these stiffnesses could be precisely engineered for a sole constructed from a single material.

In general, a mold according to the present invention includes at least three mold portions. The at least three mold portions may be assembled to form a mold. When in an assembled configuration, the interior of the mold includes a complement of a complex unitary three-dimensional structure. When in an unassembled configuration, the mold portions include at least a portion of the complement. Any number of additional mold portions may be used, limited only by practical considerations of the technology and material used to form the complex unitary three-dimensional structure, which are discussed in greater detail below. The number of mold portions required to form a mold for the desired structure may be related to the periodicity of the desired structure. For example, a mold for a simple lattice structure may include as few as three mold portions, whereas a mold for more complex structures such as an octet truss or orthic tetrakaidecahedral truss may include many times that number, depending upon the ease of subdivision. Each mold portion preferably includes at least two surfaces that are spaced apart. In one embodiment, the surfaces are parallel and equidistant. In another embodiment, the surfaces are equidistant and not parallel. In yet another embodiment, the surfaces are not parallel, and the distance between the surfaces varies. Preferably, at least one of the surfaces is a parting surface of the mold, including a plurality of fluidly connected grooves formed in the parting surface and a plurality of channels fluidly connected to at least one groove. The channels may extend partially or completely through the mold portion. For ease of illustration, the grooves are represented in the FIGS, as half round cross-sections, which form channels having circular cross-sections when the mold is in an assembled configuration. Those skilled in the art will recognize that the geometric cross-section of the grooves is dictated, in part, by the desired cross-section of the members of the complex unitary structure of interest. When the mold is in an assembled configuration, the parting surfaces of the mold portions are preferably positioned adjacent to and in direct contact with each other. The assembled mold portions may extend in any direction, depending on the geometry of the desired structure. When the mold is in an assembled configuration, it includes channels corresponding to the grooves on the mold portions. The channels may be complements of the members of the desired complex unitary three-dimensional structure. The length, orientation, and cross-sectional dimensions of the channels is dictated, in part, by the design of the structure and its intended application.

Preferably, the structural members have a cross-section that may range from about 1 micron to about 1 meter, more preferably from 1 centimeter to about 1 meter. In a particularly preferred embodiment, the structural members have a cross-section in a range from about 1 micron to about 1 centimeter. Thus, the channels according to any of the embodiments described herein preferably have cross-sections ranging from about 1 micron to about 1 meter, and more preferably from about 1 centimeter to about 1 meter and, in a preferred embodiment, from about 1 micron to about 1 centimeter. The assembled molds also include apertures for receiving a fluid material, and risers for releasing air and excess fluid during the molding process, both of which are well known in the art. The apertures and risers may be any shape or size, and are preferably positioned so as to allow the fluid material to be introduced and distributed into the assembled mold in a substantially uniform manner. In preferred embodiments, the mold portions include registration guides for aligning the parting surfaces, which are preferably interlocking for ease of use. The registration guides may be any shape or size, and may be positioned at any location on the mold or mold portions. These may take, for example, the form of cones or frustrums of cones and their complements, which interlock when the mold portions are joined. A mold portion having the shape of a single tetrakaidecahedron with such registration structures is shown in FIG. 31. The mold portions may be held together mechanically, or they may be physically joined by a variety of methods including heat, friction, or solvent welding. One embodiment of the invention is the provision of molds and mold portions that are particularly advantageous for forming complex unitary three-dimensional structures that may be stratified along parallel planes that bisect parallel horizontal members of the structures. In general, many complex three-dimensional structures, such as lattices, foams, and trusses, include periodic, repeating, space-filling patterns. Several examples of such structures are illustrated in FIG. 1, each of which may be stratified along parallel horizontal planes that bisect parallel horizontal members of the structure. By way of example, a cubic lattice structure may be stratified into rectilinear portions by bisecting two sets of parallel horizontal members. Similarly, an octet truss structure may be stratified into rectilinear portions by bisecting three sets of parallel horizontal members. Thus, one aspect of the invention is to advantageously exploit such periodic properties, allowing the direct formation of molds and mold portions from which such structures may be easily formed as a unitary body, without the need for additional fasteners or connectors, as in other methods.

For ease of illustration in the FIGS., the following reference characters have been used in conjunction with the reference numerals as follows: "m" designates a structural member of a complex unitary three-dimensional structure; "c" designates a channel in a mold or mold portion that is a complement of structural member "m"; and "g" designates a groove that combines with another groove in an adjacent component to form a channel "c" when in an assembled mold configuration. By way of illustration, 200m designates a structural member of a complex unitary three-dimensional structure; 200c designates a channel that is a complement of structural member 200m; and 200g designates one of the two grooves from which channel 200c is formed.

The stratified mold portions may have a wide range of thicknesses, depending upon the material from which they are formed, as well as the desired complex three-dimensional structure. One embodiment useful for forming very thin stratified mold portion involves casting thin, flat layers of material and creating a master pattern on each layer that corresponds to the desired structure. After etching the layers, the masking material is removed. The layers are then assembled, preferably by stacking, and compressed tightly together using, for example, a conventional hydraulic press. Thus, the assembled layers will include a complement of the desired complex unitary three-dimensional structure.

FIG. 4 is an illustration of an exemplary cubic lattice structure 12, which includes two sets of intersecting parallel members 26m and 28m that are mutually perpendicular, and a third set of parallel members 30m disposed orthogonally to members 26m and 28m, preferably at the intersections of members 26m and 28m. In the embodiment, the outermost members 32m of the cubic lattice structure are larger in diameter than the interior members, which may provide increased strength and ease of handling. A mold 10 for forming the cubic lattice structure 12 is illustrated in an assembled configuration in FIG. 5, and in an unassembled configuration in FIG. 6. In the present embodiment, mold 10 is preferably rectangular, and is useful for making a complex unitary cubic lattice structure similar to the complex unitary cubic lattice structure 12, when used in conjunction with the methods described above. Those of ordinary skill in the art will recognize that the rectangular shape of mold 10 is for illustrative purposes only. In addition, the mold portions and the molds may be any size or shape, and any number of mold portions may be assembled to increase the extent of the mold, and thereby the structure, limited only by practical considerations. In the present embodiment, mold 10 includes five rectangular mold portions: end-plates 14a and 14b, and three mid-plates 16. Those of skill in the art will also recognize that any number of mid-plates may be disposed between the end-plates, limited only by practical considerations. For example, the assembled mold 10 illustrated in FIG. 6 will provide a cubic lattice structure with four tiers whereas the structure illustrated in FIG. 3 has five tiers. In the present embodiment, the mid-plate mold portions are symmetrical in construction, allowing the mid-plates to be used interchangeably. Similarly, in the present embodiment, the end-plate mold portions are symmetrical in construction, and are also interchangeable.

A plurality of apertures 20c for receiving a fluid material and a plurality of risers 21c for allowing the release of air and excess fluid during the molding process are disposed at one end of the assembled mold 10. Mold 10 also preferably includes registration guides 18c for aligning mold portions 14a, 14b and 16. For ease of illustration, the same reference numerals have been used throughout the FIGS, to designate the apertures, risers, and registration guides.

FIG. 7 is an expanded schematic illustration of a mid-plate 16, which includes two opposing planar parting surfaces 22a and 22b (which may be seen more easily in FIG. 6). Planar parting surfaces 22a and 22b are symmetrical in construction and include two sets of fluidly connected intersecting parallel grooves 26g and 28g that are mutually perpendicular, representing at least a portion of a complement of a complex unitary cubic lattice structure. Channels 30c extend through each mid-plate 16 and are fluidly connected to and orthogonally disposed to grooves 26g and 28g. In the present embodiment, channels 30c are preferably disposed at each intersection of grooves 26g and 28g. Depending on the application, it may be desirable to include additional channels between the intersection points of the grooves 26g and 28g, or to include fewer channels 30c. This may be useful, for example, when structures with varying density are desired. Each mid-plate 16 also includes a groove 32g fluidly connected to and extending around grooves 26g and 28g, for receiving and distributing the fluid material from which the cubic lattice structure may be formed, as described in more detail below. Groove 32g is also fluidly connected to riser grooves 21g. FIG. 8 is a schematic illustration of end-plate 14a, which is symmetrical in construction to end-plate 14b. End-plate 14a includes a planar parting surface 34a and an exterior surface 34b. Similarly, end-plate 14b (See Fig. 5) includes a planar parting surface 36a and an exterior surface 36b. Planar parting surfaces 34a and 36a each include two sets of fluidly connected intersecting parallel grooves 26g and 28g that are mutually perpendicular, and a groove 32g fluidly connected to and extending around grooves 26g and 28g, as discussed above with reference to planar parting surfaces 22a and 22b of mid-plate 16. As in the mid-plate, groove 32g is also fluidly connected to riser grooves 21g.

FIGS. 9 and 10 are perspective views of mold 10, in an assembled configuration, showing perspective cut-away views along planes A-A and B-B, respectively. As can be seen when viewing FIGS. 9 and 10 together, when in an assembled configuration, channels 26c and 28c are disposed orthogonally to mid-plate channels 30c. Channels 26c and 28c correspond to the interior volume of grooves 26g and 28g of parting surfaces 22a, 22b, 34a and 36b. Channels 30c of each mid-plate are fluidly connected to and extend substantially through each mid-plate 16, and are fluidly connected to parallel channels 26c, 28c, and 32c, terminating at planar parting surfaces 34a and 36a. Similarly, registration channels 18c are fluidly connected parallel to mid-plate channels 30c extending completely through each mid- plate 16, terminating at exterior surfaces 34b and 36b of end-plates 14a and 14b. Channel 32c, corresponding to the interior volume of groove 32g of parting surfaces 22a, 22b, and 34a,b, is disposed orthogonally to mid-plate channels 30c and registration channels 18c, and is fluidly connected to channels 26c, 28c, 30c and 32c and to the atmosphere via channel 20c. Thus, the interior space of mold 10, when in an assembled configuration, includes a complement of a complex unitary cubic lattice structure. FIG. 11 is an illustration of an exemplary octet truss structure 38 formed using the method of the invention. The octet truss structure 38 includes three sets of intersecting parallel members at mutual 60° angles, and three sets of members disposed at an angle to the parallel members of the structure, preferably disposed at the intersection of the three intersecting parallel members.

Another embodiment of the present invention is directed to a mold 40 for forming a complex unitary octet truss structure. Mold 40 is schematically illustrated in an assembled configuration in FIG. 12 and in an unassembled configuration in FIG. 13, and is similar in construction to mold 10 to the extent that the mold portions may be assembled by stacking. In the present embodiment, mold 40 includes five rectangular mold portions: end-plates 42a and 42b, and three mid-plates 44. As in the previous embodiment, those of ordinary skill in the art will recognize that the rectangular shape of the mold is for illustrative purposes only.

Mid-plate 44 is illustrated schematically in FIG. 14, and in an expanded view in FIG. 15. In the present embodiment, mid-plate 44 includes two opposing planar parting surfaces 46a and 46b. Each mid-plate 44 includes three sets of fluidly connected intersecting parallel grooves 48g, 50g, and 52g, at mutual 60 degree angles, disposed on the opposing parting surfaces 46a and 46b. Relative to parting surface 46a, parting surface 46b has grooves offset such that intersection points 54 are positioned immediately above the centers of the triangular spaces 56 on the opposing parting surface. Therefore, the opposing planar parting surfaces 46a and 46b represent planes containing coplanar members of a unitary octet truss structure. Each mid-plate 44 also includes three sets of fluidly connected intersecting channels 58c, 60c, and 62c fluidly connected to grooves 48g, 50g, and 52g at intersection points 54. In the present embodiment, the extent of the mold may be increased only by adding additional mid- plates in sets of three, due to the offset of the grooves with respect to the triangular spaces of the opposing parting surfaces. Due to the offset, the mid-plate and end-plate mold portions are not symmetrical in construction, and are not completely interchangeable. Each mid-plate 44 also includes a groove 32g fluidly connected to and extending around grooves 48g, 50g, and 52g, for receiving and distributing the fluid material from which the complex unitary octet truss structure may be formed. FIG. 16 is a schematic illustration of end-plate 42a, which includes a planar parting surface 64a and an exterior surface 64b. Similarly, end-plate 42b includes a planar parting surface 66a and an exterior surface 66b. Each of planar parting surface 64a, 66a includes three sets of fluidly connected intersecting parallel grooves 48g, 50g, and 52g at mutual 60 degree angles to each other.

FIGS. 17 and 18 are perspective views of cross-sections of assembled mold 40 along planes C-C and D-D. As seen in FIGS. 17 and 18, when in an assembled configuration, channels 58c, 60c and 62c extend through nodes 54, terminate at parting surfaces 64a and 66a, and are disposed at a 60 degree angle to mid-plate channels 48c, 50c, and 52c, and to each other. Channels 58c, 60c and 62c are fluidly connected to all other channels via nodes 54.

Thus, one aspect of the invention is the provision of molds and mold portions that are particularly advantageous for forming complex unitary three-dimensional structures that may be stratified along parallel planes that bisect parallel horizontal members of the structures.

Another embodiment of the invention is the provision of molds and mold portions for forming complex unitary three-dimensional structures for which stratification is not practically feasible. That is, the present invention also encompasses regularly and irregularly shaped structures that do not have parallel horizontal members that may be stratified along parallel horizontal planes, as shown in FIG. 2, which illustrates side and bottom views of such a structure. For example, the previously described octet truss structure may be subdivided into regular parallel planes, as described above. Alternatively, the previously described octet truss structure may be subdivided into triangular prisms, or rhomboidal prisms with twice the cross-sectional area of a triangular prism, as described below.

FIG. 19 is a schematic illustration of another embodiment of a mold 70 that may be used to form a complex unitary octet truss structure. Mold 70 includes a plurality of prismatic mold portions 72. As shown in cross-section in FIG. 20, each mold portion 72 is symmetrical in construction, and includes three planar parting surfaces 73, 74, and 75, and grooves 76g at each intersection of two parting surfaces.

FIGS. 21 and 22 are side and top views of mold portion 72, respectively. Planar parting surfaces 73 and 74 each include two sets of fluidly connected intersecting parallel grooves 78g and 80g positioned at mutual 60 degree angles, representing at least a portion of a complement of an octet truss lattice structure. The remaining planar parting surface 75 includes parallel grooves 75g that are perpendicular to grooves 76g. When in an assembled configuration, mold 70 includes a plurality of "layers" of mold portions 72. Each layer is formed by a first plurality of mold portions 72 positioned adjacently such that the grooves 76g are positioned in direct contact with each other, followed by a second plurality of mold portions 72 inverted between the first, such that the parting surfaces 74 are positioned adjacently and in direct in contact with each other. Therefore, when in an assembled configuration, as shown in FIG. 19, grooves 76g form channels 76c for receiving a fluid to be introduced into the mold 70. In like manner, several "layers" may be stacked above the first layer to increase the extent of the mold.

Another embodiment of the invention is for making the orthic tetrakaidecahedral lattice structure shown in FIG. 23, for which stratification is not practically feasible. A number of mold portions, shown in FIG. 23 A, can be placed adjacently and in direct contact with one another, and then stacked to form a highly interlocking mold for the desired lattice structure. By way of example, a permanent mold may be created which has the shape of the complement of a single layer of tessellated solid tetrakaidecahedra. One half of such a mold is shown in FIG. 24; the other half is identical. FIG. 25 shows a cutaway view of the same mold.

One half of a permanent mold having the shape of the complement of a single layer of adjacently placed tessellated solid tetrakaidecahedra is shown in FIG. 26, while the adjacently placed and stacked layers of mold portions which form the mold are shown in FIG. 27. FIGS. 28 and 29 show cutaway views of FIGS. 26 and 27, respectively. For the production of a regular truss, which has struts disposed along edges of an arrangement of tessellated polyhedra, the basic shape of the permanent mold will preferably be the complement of a set of one or more of the mold portions, or polyhedra. Such a mold is illustrated in FIG. 24. The edges of the inverse polyhedral cavities of the mold comprise ridges, which will correspond to grooves in the disposable mold portion(s); such a mold portion is shown in FIG. 26. The ridges of the permanent mold, which will correspond to the grooves of the mold portions, can be more clearly seen in the cutaway view of FIG. 25. The ridges should be designed in such a way that it is possible to remove the mold portions from the mold after forming without destroying either mold portion or mold. Cross-sections of two molds, and the corresponding mold portions produced, are shown in FIGS. 30 and 31. The mold in FIG. 30 is improperly designed for casting a rigid mold portion, in that the mold portion cannot be removed, while the mold in FIG. 31 can be separated from the mold portion as shown by arrows. The mold shown in FIG. 30 would be suitable for casting a mold portion from a material sufficiently flexible that the mold portion could be removed from the mold.

Once the disposable mold portions have been formed, they are assembled to form the mold, as shown in FIG. 27. In preferred embodiments, the mold portions are polyhedra or groups of polyhedra which fit together so that identical faces of polyhedra on different mold portions are sealed in contact. The grooves at the edges of the mold portions then combine to form channels, as shown in FIG. 28. It is not necessary that every edge of each polyhedron be grooved; only the grooves necessary to form the desired struts need be included. If desired, certain polyhedra may be shaped so that their faces are not brought into contact when the mold portions are joined; the final truss will then contain planar members at these faces. In other embodiments, certain polyhedra may be eliminated from the mold assembly entirely; the final truss will then contain solid polyhedral members at corresponding locations. In all these embodiments, the lattice formed must be open-cell, i.e., it must be possible to remove the mold portion material without breaking the lattice. One method for making the molds and mold portions according to the present invention is shown in the flow-chart illustrated in FIG. 3. The methods of the invention typically involve generating designs for the complex unitary three-dimensional structures using computer-aided design (CAD) techniques, or other suitable design techniques. A CAD complement of the desired complex unitary three-dimensional structure is generated and subdivided into portions. The structure may be subdivided into rectilinear portions by, for example, stratification. Alternatively, the structure may be subdivided into a variety of non- rectilinear modular portions. The complementary portions may be used as templates or patterns for forming the mold portions by conventional manufacturing techniques, as described below in greater detail. One embodiment of the method involves selecting a suitable material for the mold and subdividing the material into preforms for the mold portions. The material may be subdivided, for example, by stratification. After subdividing the preform, grooves, channels, and/or perforations are formed on the surface of, or extending partially or completely through the preforms in order to form the mold portion. Preferably, the grooves and channels are directly molded into the surface of the mold portions, but they may also be machined directly into the mold portions. Formation of the grooves and channels in the preforms may take place in any sequence for ease of manufacturing. The molds and/or mold portions may be formed directly or, alternatively, machined to produce both regular and irregular shapes.

Techniques suitable for forming the grooves on the surface of the preforms and/or channels that extend partially or completely through the preforms include, but are not limited to, embossing, cutting (including laser cutting), drilling (including laser drilling, ion-beam microdrilling, irradiation-based microdrilling, high speed drilling and other ablation techniques), etching (including laser etching, microetching, ion-beam etching, and irradiation-based etching), microcontact printing and etching, micromolding, self-assembly techniques, water-jet machining, laser ablation, or ballistic penetration with spherical or cylindrical projectiles, and any combination thereof. In a preferred embodiment, high speed drilling is used when channels are needed at oblique angles to a planar surface, or when tensegrity structures, including biomimetic tensegrity structures, are desired. Where very fine structures are desired, self-assembly techniques may be used.

In the present embodiment, because the mold portions are formed directly, rather than by lost core or other processes, they have a relatively higher quality surface finish than is typically achieved using other methods, and the relatively higher quality surface finish is duplicated in the complex unitary three-dimensional structure. Thus, the methods of the present invention provide a greater degree of resolution/accuracy than may be achieved using other methods. In some instances, it may be desirable or even necessary to use conventional techniques to form the mold portions. When this is desired, conventional techniques for molding, which are well known in the art, may be used to form a two-piece permanent mold from which each mold portion may be formed. Such a permanent mold may be used repeatedly to produce a plurality of the same mold portions using less costly material and methods, such as, for example, by injection molding a polymeric material into the permanent mold. Such a method is particularly advantageous, for example, for forming the mid-plate or interior modular mold portions, which are described in greater detail below, and which are typically destructively removed after solidification of the fluid material in the mold. Since only a few permanent molds need be created, expensive processes such as, for example, stereolithography or electron discharge machining, can be used to create precision molds, that will then be used in lower-cost bulk production methods. Of course, inexpensive methods, such as conventional machining, casting, and other known methods, may also be used to produce the permanent molds.

The shape of the permanent mold is, of course, dictated in part by the shape of the desired complex three-dimensional structure. A number of casting-type techniques can be used to form the disposable mold portion(s) from the permanent mold, including casting, die casting, injection molding, reaction injection molding, rotational molding (to form hollow mold portions), and casting into thermoformed cavities. It will be apparent to those skilled in the art that the most appropriate technique will depend on the materials and geometries of both mold and mold portions, as well as the degree of precision required in the casting, and skilled artisans will understand how to select a suitable method for forming the mold portions. Thus, one advantage of certain embodiments of the invention is that a permanent mold may be used to create a large number of identical disposable mold portions, which may be assembled to form a mold for the final structure. It should be noted that while the mold used in the first step is conventionally described as the "permanent" or "master" mold, it may be found advantageous in certain applications to use a disposable mold in this step. Such embodiments are encompassed within the scope of the present invention. Those of ordinary skill in the art will recognize that while the Figures and Example illustrate the production of an orthic tetrakaidecahedral truss, any other complex unitary three-dimensional structure may be produced by the same methods. Suitable materials for the molds and mold portions according to any of the embodiments disclosed herein are limited only by the condition that the mold may be destroyed without damaging the complex unitary three-dimensional structure. For example, the molds may be formed from materials that melt, sublime, degrade enzymatically, or that disintegrate with vibration, impact, or chemical dissolution. Structures formed from eutectic or other low-melting-point metals may be removed by melting; such metals are preferably chosen to have a melting point low enough that the solidified structure is able to maintain its structural integrity during the process. This technique is also suitable for removing molds made from thermoplastic polymers and other organic and inorganic compositions capable of melting. When the mold portions are formed, for example, from camphor, phosphorus, sulfur, or other materials capable of subliming, the molds may be removed by heating to the sublimation temperature. Material may be expeditiously removed even below the sublimation temperature by holding at a temperature where the mold portions have a significant vapor pressure, and pulling a vacuum or blowing gas through the system. In yet another embodiment, the mold or mold portions may be formed from a lightly sintered powder, nano- or micro-beads, crystals or the like, which can be disintegrated by mechanical action, for example, by vibration, impact, or by chemical dissolution. Impact may also be used to disintegrate lightly bound crystals, such as slightly moistened salt crystals. In a further embodiment, the mold portions may be formed from a protein such as collagen, starch, or another material removable by enzymatic degradation.

Another aspect of the invention that may be used in conjunction with any of the previously described embodiments is directed to molds for forming complex unitary three- dimensional structures that include walls, or walls and skins. The walls and skins may be separate from or integrally connected to the structure, and may be located on the outer surface, the inner surface, and between interior members. Because the structures of the invention exhibit very high structural efficiency, a minimal amount of material is required to support the walls and skins. The walls and skins are preferably formed concurrently with the complex structures but, if desired, they may be added after forming the structure, for example, by wrapping a flexible material around a structure (e.g. by fixing, adhering, welding, and the like). Advantages of such structures may include enhanced mechanical properties, such as the stiffness of the structure. Laminated truss structures may be used as parts (e.g. wings, exhaust pipes, inflow jets, the hull or fuselage, missile bay doors, and the like) in aircraft, spacecraft, watercraft (e.g. surface ships, submersibles, and the like), as well as land craft (e.g. trucks, automobiles, buses, trains, tractors, cranes, and the like). Furthermore, laminated truss structures may be used as high impact material coverings to protect any of the above- described crafts or buildings against damage from impacts, such as damage from exploding projectiles.

Another aspect of the invention is directed to molds for, and methods of forming molds for, functionally adapted complex unitary three-dimensional structures having regular curves. One preferred embodiment of such a functionally adapted complex three-dimensional structure is illustrated in FIG. 32, which is a cylindrical structure 81 including a cylindrical octet truss 85 integrally connected to equidistant skins 82 and 83. The cylindrical octet truss structure is functionally adapted for many uses. For example, the laminated covering on the truss limits or prevents the permeability of liquid or gas in a radial direction. The cylindrical structure may be used as a radiator and/or insulator by allowing a coolant to flow through the structure. In another example, the cylindrical structure may be used to provide counter current fluid flow, with a first fluid traveling in one direction through the interior of the cylinder and a second fluid, which may be the same or different from the first fluid, traveling in an opposite direction through the truss structure. In another example, the laminated cylindrical structure may be used as a load-bearing strut, such as a supporting pole. As shown in FIG. 42, the mold for forming the cylindrical structure 81 includes a plurality of mold portions 84 positioned adjacently and in direct contact with one another, and centered within a cylindrical preform 86. The plurality of mold portions 84 are spaced apart from the cylindrical preform 86 to provide a space 88 into which a fluid may be introduced. In the present embodiment, if an integral skin is desired, channels 90 are included to fluidly connect the space between the mold portions 84 and cylindrical mold 86. Thus, in the present embodiment, a wall is formed in space 88 that is integrally connected to the members of the geodesic octet structure. If it is desired that the wall is not integrally connected to the members, channels 90 may be omitted.

Another aspect of the invention is directed to molds for and methods of forming molds for functionally adapted complex unitary three-dimensional structures with irregular curves. One preferred embodiment illustrated in cut-away view in FIG. 43 is an irregularly curved structure 92 including a truss 94 integrally connected to skins 96 and 98. FIG. 35 illustrates a cross-section of structure 92 through plane "E-E". In contrast to previous embodiments, such an irregularly curved structure cannot be subdivided into parallel planes bisecting parallel members of the truss. Moreover, the skins are not equidistant. The curved cylindrical structure is specifically adapted to function as a jet nozzle based on its light weight, high strength, and high interior volume capacity, relative to other jet nozzles. The structures of the present embodiment may also be designed such that as the contours of the structure vary, so does the spacing between the two external skins. An alternative arrangement that may be used in conjunction with regularly and irregularly curved structures includes additional tiers of trusses positioned between skins, with walls positioned between the tiers of trusses. As in previous embodiments, the walls and skins may be spaced apart from or integrally connected to the trusses. Such an arrangement may be used to vary the density of a structure, as shown in FIG. 36, which shows the cross- sectional structure of FIG. 35 with two additional tiers of trusses 104 and 106 integrally connected to skins 96 and 102, and to walls 98 and 100. The spacing between the members of the truss in each tier varies. Thus, the density of a structure may be varied by changing the spacing between truss members of each tier.

A cross-section of a mold that may be used to form curved structures, both regularly and irregularly shaped, is shown in FIG. 37. Mold 110 includes two symmetrical mold portions 112 and 114 positioned adjacently and in direct contact with one another, and centered within a preform 134. As in the previous embodiment, the plurality of mold portions are spaced apart from the preform to provide a space into which a fluid may be introduced to form a skin surrounding the mold portions. The mold portions are spaced apart from the preform using spacers, which is well known in the art, and which are not illustrated herein. A channel 118 is fluidly connected to the complementary space of the mold to receive and introduce a fluid therein.

Similarly, a cross-section of a mold that may be used to form tiered structures, both regularly and irregularly shaped, is shown in FIG. 38. Mold 120 includes a plurality of mold portions 122, 124, 126, 128, 130, and 132, centered within preform 134. As in the previous embodiment, the plurality of mold portions are spaced apart from the preform using spacers, to provide a space into which a fluid may be introduced to form a skin surrounding the mold portions, and a channel 118 is fluidly connected to the complementary space of the mold to receive and introduce a fluid therein.

Another embodiment of the method involves using an extrusion die and embossing assembly to form a mold portion. The assemblies may be adapted for connection to any type of polymer forming equipment, including, but not limited to, extrusion, injection molding, reaction injection molding, and the like. Assembly 140 illustrated in FIG. 39 is adapted for use with a polymer extrusion apparatus to form the previously described octet truss mold portion 72. Assembly 140 includes an extrusion die 142 and three embossing rollers 144, 146, and 148. Although illustrated herein with reference to an octet truss mold portion, those of skill in the art will recognize that such assemblies may be designed to form a variety of mold portions.

As shown in FIG. 40, extrusion die 142 is substantially triangular in cross-section, and includes three protrusions 150 positioned at each of the vertices of the triangle, extending toward the center of the die. As shown in FIG. 41, embossing rollers 144, 146, and 148 are adapted to connect to the extrusion die 142 at mutual 60 degree angles. Each embossing roller includes an outer surface 152 on which a raised repeating pattern is disposed. Embossing rollers 144 and 146 include raised repeating patterns of two parallel sets of lines 154 and 156 extending across the outer surface of the rollers, intersecting at an angle of 60 degrees. Embossing roller 148 includes a raised repeating pattern of a single line 158 extending perpendicularly across the outer surface of the roller.

In practice, as illustrated in FIG. 42, the extrusion die and embossing assembly 140 is connected to, for example, the outlet of a polymer extrusion apparatus, which is generally known in the art. A fluid polymeric material is formed from a polymeric precursor and extruded through the outlet of the extruder and through the extrusion die 142. As the fluid polymeric material exits extrusion die, the three protrusions 150 extending into the die form grooves 76 at the triangular vertices of the extruded polymeric material, and the raised repeating pattern on the outer surface of the three embossing rollers form grooves 160 on the surfaces of the extruded polymeric material immediately after extrusion from the die, while the extruded material is still formable. As in previous embodiments, additional perforations or channels may be formed in each mold portion using any of the methods described above.

The method of the present embodiment is particularly useful for forming mold portions for structures with or without definable planar separation planes. Mold portions formed in this manner may be made to any desired length or cross-section, limited only by the equipment and material capabilities. The mold portions may then be assembled as described above with reference to the previous embodiments to form a mold containing a complement of the desired complex unitary structure.

Anisotropic properties can also be achieved by constructing the mold portions so that certain adjacent polyhedron faces do not come into contact when the mold is assembled. The truss formed will then comprise planar members at these faces, as well as struts along the edges of the polyhedra. Such embodiments may, for example, have anisotropic resistance to air flow, making them useful for filtration applications.

Another aspect of the invention is directed to a method of using the previously described molds and mold portions to form complex unitary three-dimensional structures. The method involves assembling the mold portions described above to form a mold that includes a complement of the desired complex unitary three-dimensional structure. Once the mold portions have been assembled, the mold may be filled with a fluid material, which may be at least partially solidified to form the desired complex unitary three-dimensional structure. Due to the complexity of the channels, it will often be desirable to fill the mold channels with the assistance of a pressure gradient.

In a prefeπed embodiment, a master mold, preferably a permanent mold, is used to create a set of disposable mold portions. Each mold portion includes at least one polyhedron with grooved edges. The disposable mold portions are assembled to create a mold for a lattice structure such that the grooved edges of adjacent mold portions combine to form channels corresponding to the members of the desired structure. The assembled mold is used to form the desired structure, and the mold is removed.

Materials for investment casting and similar techniques requiring a disposable mold are well known in the art, as are their methods of removal. For example, mold portions formed from a eutectic or other low-melting- metal may be melted out of the structure. The metal should be chosen to have a melting point low enough that the solidified truss can maintain its structural integrity during melting of the mold. This technique is also suitable for removing mold portions formed from thermoplastic polymers and other organic and inorganic compositions capable of melting.

The assembled mold is used to form the regular truss using any of a number of known techniques, such as casting, die casting, injection molding, reaction injection molding, and powder injection molding. These techniques have the common feature that the mold is filled with a fluid material which is then transformed into a solid structure.

In order to provide a smooth surface finish on the assembled mold, a sealing coat may be injected into the interior of the assembled mold, as well as applied to the exterior of the mold, to seal any spaces. A fluid material, preferably a metal, may then be introduced into the assembled mold to form the complex three-dimensional structure. Thereafter, the mold is destructively removed in order to access the structure. In the present embodiment, the conventional casting material may include calcium carbonate, bone meal, biologicals, and sprayed enzymes. The etching of the mold or cast may be accomplished using known techniques such as photolithography and etching. The exposed surface of the layer may be etched, preferably by chemical etching, UV light, or other methods disclosed. The most suitable technique for any given application will depend on the materials and geometry used. Trusses can be manufactured from a wide variety of materials, including epoxies, thermoplastic polymers, thermosetting polymers, elastomers, metals, metal alloys, ceramics, biological materials, carbon, calcium, metalloids, and combinations thereof. In many embodiments, it may be desirable to coat the mold with a release agent, which may be done either before or after assembly of the disposable mold portions into the mold. Due to the tortuosity of the mold, it will often be desirable to fill the mold with the assistance of a pressure gradient. This may be accomplished by vacuum filling or by pressure casting, for example. The truss may be formed as a green preform at this stage, which will be transformed into the final truss after removal of the disposable mold.

While these steps are described separately below, it will be understood by those skilled in the art that these steps may be combined in certain embodiments of the invention. For example, the formation and assembly of disposable mold portions may take place as a single step, or as a series of formation and assembly substeps. Solidification of the material may be accomplished in a variety of ways, which is dependent on the choice of material introduced into the mold. For example, simple cooling may be used, as in classical injection molding and casting. Alternatively, solidification may be accomplished by polymerization or other chemical reactions as in reaction injection molding (RIM), or by heating and sintering. After the material has been solidified, at least to a point where it is capable of maintaining its own structural integrity, the mold may be removed. Typically, at least a portion of the mold must be removed destructively. The exact method of removal will depend upon the material from which the mold was formed, as well as the material from which the complex unitary structure was formed. Once the mold portions have been removed, what remains is the desired solidified complex unitary structure. This may be the final structure, or may be subjected to further processing, including sintering or surface treatments. Thus, one aspect of the present invention is that it provides a method of inexpensively producing complex unitary structures, which have not previously been made by casting or molding processes without the use of fasteners, connectors, or welding. Another aspect of the invention is that it eliminates the necessity to form what is known in the art as the "sacrificial master" of the desired structure, which is required in investment or shell casting. Suitable materials for the complex imitary structures according to any embodiment disclosed herein are limited only by the condition that the material be sufficiently fluid to flow through the channels of the molds, and by the condition that the material must be able to withstand any destructive process used to remove some of the mold portions. Thus, suitable materials include, but are not limited to metals, metal alloys, polymers, glasses, ceramics, and elastomers. In preferred embodiments that are functionally adapted to filtration and detoxification applications, preferred materials include high UV light transmitting polymers, such as, for example, ACLAR™ (available from Allied Signal Engineering Plastics).

Where channels of the molds have very narrow cross-sections, for example, less than about 1000 microns, it may be advantageous to use a monomeric material, which has a relatively low viscosity in comparison to polymeric materials. In this manner, very narrow structural members may be formed, for example, on the order of less than about 1000 microns, more preferably in the range of about 500 microns to about 1 microns. In preferred embodiments, monomers that are curable at room temperature are prefeπed, including, but not limited to, acrylates, methacrylates, cyanoacrylates, isoprene, vinyl esters and butadienes. Any monomeric material may be used in the present embodiment, limited only by the ability to polymerize the material while in the mold, and the ability of the mold to withstand relatively higher temperature polymerization reactions.

Another embodiment of the method of forming the complex unitary three-dimensional structures is illustrated in FIG. 43. According to the method, prefabricated structural members 164 are inserted into the channels 166 of a mold portion 168, before introducing the fluid material into the assembled mold. The fluid material is introduced into the assembled mold, solidified, and the mold is removed. A structure 162 thus formed will include isolated rigid members interconnected by a unitary network of cables in the form of the desired complex unitary three-dimensional structure. The prefabricated structural members may be pins, including hollow pins. In embodiments that may require additional strength, the prefabricated structural members may be metals, such as copper and aluminum. Where flexibility is desired, such as when the structural members are extensible, the prefabricated structural members may be elongated members and/or planar members, and may include an elastomer. Such a method is useful for forming tensegrity structures, which structures may be prestressed, for example, by using polymers that shrink during the casting procedure or when exposed to specific conditions, such as heat. In other embodiments, the structural members may be carbon. In other embodiments, the structural members may be ceramics, such as silica crystals, or glass. In still other embodiments the members may be any of proteins, carbohydrates, nucleic acid, or lipids.

Another embodiment of the invention is directed to a method for directly molding a mold portion. According to the method, prefabricated pins are inserted into an assembled mold before introducing a fluid material into the assembled mold. FIG. 35 illustrates a mold 172 for forming a rhomboidal mold portion that may be used to form an octet truss, as discussed previously. In the present embodiment, a plurality of pins 174 corresponding to the members of the octet truss structure are inserted into the mold 172. The pins 174 are left in place as a fluid material is introduced into the mold and the fluid material is allowed to flow around the pins. Once the fluid material has solidified, the pins are removed. Thus, the area occupied by an individual pin forms a groove or channel through or between the mold portions.

In another embodiment of the method, illustrated in FIG. 36, any of the molds described herein may be used to guide and limit the formation of single crystals and thus, to create single crystal unitary structures, such as metals having complex or simple porous geometries. According to this method, a mold is assembled, and a crystallizable material is introduced into the mold. The assembled mold, including the crystallizable material, is then made to pass through a transitional heating zone, a crystal growth zone, and a cooling zone in order to effect crystal growth, in a manner similar to conventional silicon crystal growth. Advantages of such a method are the provision of single crystal metal parts, which have higher resiliency. Suitable materials for use with the present method include, but are not limited to metals, alloys. One prefeπed material is a titanium alloy.

One of ordinary skill in the art will recognize that the methods and molds of the present invention may be used to produce complex unitary structures of relatively large extent by varying the size and or quantity of mold portions assembled. Accordingly, another aspect of the invention involves combining several complex unitary structures to form structures of even greater extent than is possible for using a particular molding material and method. Both techniques provide the advantage of eliminating the requirement of connecting the structural members at each nodal intersection, as in other methods. Yet another aspect of the present invention is directed to a manufacturing method for providing regular microfoams at lower cost and higher throughput than is cuπently available. Such foams preferably have a relatively high degree of regularity (containing similar repeating modular cells) on a smaller scale. According to the method, a plurality of particles are allowed to self-assemble, thus forming a close packed structure with voids between the particles. The particles may have any shape or size in order to create foams with different properties. Such foams may be particularly adapted to industrial applications, and biomedical applications, such as foams for space filling and orthodontic applications. In a preferred embodiment, the particles are spherical beads. The particles may be allowed to self-assemble on any surface, or in a mold of any shape or size, which may be chosen based on the desired shape of the final foam. In one embodiment, the particles are compressed in order to flatten the contact between the particles. In another embodiment, the beads may be sintered together. A fluid material is then introduced into the voids between the particles, which may be performed under the influence of pressure. The fluid material is then allowed to solidify. The particles are then removed from the solidified material using any of the methods described above with regard to the previous embodiments. That is, the particles are removed destructively in order to obtain a foam, which is preferably tetrakaidecahedral (on average).

In another embodiment, the particles may be electrically conducting, for example, metal particles. In the present embodiment, the fluid material is preferably a liquid electroplating solution. The method involves introducing the electroplating solution into the voids between the electrically conducting particles. A voltage is then applied to the interconnected electrically conducting particles to promote electroplating of a material onto the surface of the interconnected particles. When the electroplating is complete, the metal particles are dissolved, for example, by heating or melting. Thus, a metal microfoam structure is obtained. The resulting metal microfoam may be electroplated repeatedly in order to increase its mass and strength. In a preferred embodiment, gold particles of a few nanometers in diameter are used to create a nanofoam. Such gold particles are typically made from colloidal gold, and are available from Jansen Biomedical Products. In another embodiment of the method, the particles may also be magnetic, which allows the packing of the particles to be performed in the presence of a magnetic field. Such a process will allow the formation of anisotropic foams, with a predetermined alignment of cells. Working Example

The method of the invention has been used to produce an orthic tetrakaidecahedral truss composed of silicone rubber. The method used was as follows:

The master mold was formed of DuPont SOMOS 7110 epoxy resin, and was produced by stereolithography using IDEAS MASTER SERIES™ computer-aided design software by Structural Dynamic Research Corporation. Each half of the mold was of the shape shown in FIG. la. The other side of the mold in this case was a flat plate, so that the mold formed a layer of 10-sided structures, each of which was half of an orthic tetrakaidecahedron.

The disposable mold portions were each in the form of a single layer of half- These mold portions were injection molded using the master mold, and were formed from

MetSpec™ 174, from MCP, Inc., an alloy of bismuth (57%), tin (17%), and indium (26%), which has a melting point of 78°C. Mold portions were stacked flat sides together to form layers of tetrakaidecahedra as shown in FIG. 2a; these layers were then stacked in the arrangement of FIG. 3 a. Ten mold portions were stacked together to form the mold.

The assembled mold was compressed and filled under vacuum with a liquid silicone rubber precursor. The precursor was allowed to cross-link in the mold in an autoclave under pressure at room temperature, and then the assembly was heated to melt the mold. The final product was a silicone rubber orthic tetrakaidecahedral lattice having a strut length of about 7 mm and a strut thickness of about 1 mm. Some adhesion of silicone to the metal mold was observed using this procedure. Such adhesion can be eliminated by coating the metal mold pieces with wax or another release agent prior to filling the mold, or by using a mold material that is inherently unreactive to the strut material.

Further modifications and equivalents of the invention herein disclosed will occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the spirit and scope of the invention as defined by the following claims.

What is claimed is:

Claims

1. A mold, comprising: at least three mold portions constructed and aπanged to include a complement of a complex three-dimensional unitary structure when in an assembled configuration and to include a portion of the complement when in an unassembled configuration.

2. The mold according to claim 1 , wherein the mold portions each include at least two surfaces.

3. The mold according to claim 2, wherein the at least two surfaces are equidistant.

4. The mold according to claim 3, wherein the at least two surfaces are parallel.

5. The mold according to claims 2, wherein at least one of the surfaces is a parting surface, and each parting surface includes a plurality of fluidly connected grooves formed in the parting surface.

6. The mold according to claim 5, further comprising a plurality of channels extending from the parting surface and at least partially through the mold portion, and wherein each channel is fluidly connected to at least one groove.

7. The mold of claim 6, wherein the grooves combine to form a plurality of channels in the mold when the mold is in an assembled configuration, and each channel has a cross- section and a length.

8. The mold of claim 7, wherein the cross-section of at least one of the plurality of channels varies along the length of the channel.

9. The mold of claim 7, wherein the cross-section of the plurality of channels is substantially identical along the length of the channel.

10. The mold of claim 8, wherein the cross-section and length of the plurality of channels are substantially identical.

11. The mold of claim 8, wherein the cross-section and length of the plurality of channels varies.

12. The mold of claim 9, wherein the cross-section and length of the plurality of channels are substantially identical.

13. The mold of claim 9, wherein the cross-section and length of the plurality of channels varies.

14. The mold of claim 8, wherein the plurality of channels are spaced apart uniformly when the mold is in an assembled configuration.

15. The mold of claim 9, wherein the plurality of channels are spaced apart uniformly when the mold is in an assembled configuration.

16. The mold of claim 8, wherein the plurality of channels are spaced apart non-uniformly when the mold is in an assembled configuration.

17. The mold of claim 9, wherein the plurality of channels are spaced apart non-uniformly when the mold is in an assembled configuration.

18. The mold according to claim 8, further comprising an outer shell spaced apart from the at least three mold portions.

19. The mold according to claim 9, further comprising an outer shell spaced apart from the at least three mold portions.

20. The mold according to claim 18, further comprising at least one channel fluidly connected to the mold and to the outer shell.

21. The mold according to claim 19, further comprising at least one channel fluidly connected to the mold and to the outer shell.

22. The mold according to claim 18, wherein the complex unitary structure includes a skin.

23. The mold according to claim 19, wherein the complex unitary structure includes a skin.

24. The mold according to claim 22, wherein the skin is integral to the complex unitary structure.

25. The mold according to claim 23, wherein the skin is integral to the complex unitary structure.

26. The mold according to claim 20, wherein the channels have a cross-section in a range from about 1 micron to about 1 meter.

27. The mold of claim 21 , wherein the channels have a cross-section in a range from about 1 micron to about 1 meter.

28. The mold of claim 20, wherein the channels have a cross-section in a range from about 1 centimeter to about 1 meter.

29. The mold of claim 21 , wherein the channels have a cross-section in a range from about 1 centimeter to about 1 meter.

30. The mold of claim 20, wherein the channels have a cross-section in a range from about 1 micron to about 1 centimeter.

31. The mold of claim 21 , wherein the channels have a cross-section in a range from about 1 micron to about 1 centimeter.

32. A mold, comprising: at least three mold portions constructed and aπanged to include a complement of a complex three-dimensional unitary structure when in an assembled configuration and to include a portion of the complement when in an unassembled configuration; wherein the mold portions each include at least two surfaces.

33. A mold, comprising: at least three mold portions constructed and aπanged to include a complement of a complex three-dimensional unitary structure when in an assembled configuration and to include a portion of the complement when in an unassembled configuration; wherein the mold portions each include at least two surfaces, and each surface coπesponds to parallel plane of the complex three-dimensional unitary structure.

34. A method of forming a mold for a complex unitary three-dimensional structure, comprising: providing at least three mold preforms; forming a mold portion from each of the at least three mold preforms, each of the preforms including a portion of a complement of the complex unitary three-dimensional structure; and assembling the mold portions adjacently and in direct contact with each other to provide the mold.

35. The method of claim 34, wherein the complex unitary three-dimensional structure includes a plurality of periodic parallel planes.

36. The method of claim 35, wherein each mold portion includes at least two mold surfaces, and each mold surface coπesponds to a periodic parallel plane of the complex unitary three-dimensional structure.

37. The method of claim 35, wherein positioning the mold portions adjacently and in direct contact with each other involves stacking the mold portions.

38. The method of claim 35 , further comprising : forming at least two layers of the adjacently positioned mold portions; and stacking the layers.

39. The method of claim 35, wherein the at least three mold portions have substantially identical shapes.

40. The method of claims 34, further comprising forming registration structures on the at least three mold portions.

41. The method of claim 40, further comprising forming the mold portions from a material selected from the group consisting of epoxies, polymers, metals, metal alloys, metalloids, ceramics, biological materials, carbon, calcium, glass, silica, and combinations thereof.

42. The method of claim 40, further comprising forming the mold portions from a material selected from the group consisting of metals, metal alloys, polymers, polymer blends, and wax.

43. The method of claim 40, further comprising forming the mold portions from a material selected from the group consisting of solvent soluble polymers, starch, sugar, wax, and bound powder.

44. The method of claim 40, further comprising forming the mold portions from a material selected from the group consisting of camphor, sulfur, phosphorous, and sublimation dyes.

45. The method of claim 40, further comprising forming the mold portions from a material selected from the group consisting of proteins, carbohydrates, lipids, and nucleic acids.

46. The method of claim 40, further comprising forming the mold portions from a material selected from the group consisting of collagen, albumin, agarose, alginate, and starch.

47. The method of claim 40, further comprising assembling at least three mold portions by a process selected from the group consisting of welding, friction-assisted welding, solvent welding, and mechanical pressure.

48. The method of claim 40, further comprising providing the mold portions by forming the mold portions using a process selected from the group consisting of casting, molding, micromachining, self-assembly, solid free form fabrication, injection molding, reaction injection molding, rotational molding, and casting into thermoformed cavities.

49. The method of claim 35, further comprising: forming a master of at least one of the mold portions before the step of assembling the mold.

50. The method of claim 49, further comprising: forming a plurality of sacrificial mold portions from the master, and assembling the mold using at least one of the sacrificial mold portions.

51. The method of claim 35, wherein the complement includes grooves formed in the at least three mold portions.

52. The method of claim 35, wherein the complement includes channels formed in the at least three mold portions.

53. The method of claim 51 , further comprising forming the grooves using a method selected from the group consisting of embossing, cutting, drilling, etching, laser cutting, laser etching, laser drilling, microetching, ion-beam drilling, iπadiation-based microdrilling, iπadiation-based etching, and combinations thereof.

54. The method of claim 52, further comprising forming the channels using a method selected from the group consisting of water-jet machining, laser ablation, etching, ballistic penetration, drilling, laser drilling, high speed drilling, and combinations thereof.

55. A method of forming a complex unitary three-dimensional structure, comprising:

providing a mold that includes a complement of the complex unitary three-dimensional structure; introducing a fluid material into the mold; and removing the complex unitary three-dimensional structure from the mold.

56. The method of claim 55, wherein the fluid material is selected from the group consisting of epoxies, thermoplastic polymers, thermosetting polymers, metals, metal alloys, ceramics, biological materials, carbon, calcium, metalloids, crystallizable materials, and combinations thereof.

57. The method of claim 56, further comprising introducing the fluid material into the mold at ambient pressure.

58. The method of claim 56, further comprising introducing the fluid material into the mold under a pressure gradient.

59. The method of claim 57, further comprising allowing the fluid material to at least partially solidify in the mold.

60. The method of claim 58, further comprising allowing the fluid material to at least partially solidify in the mold.

61. The method of claim 55, further comprising forming the mold using a process selected from the group consisting of a solid free form fabrication, casting, die casting, injection molding, reaction injection molding, rotational molding, and casting into thermoformed cavities.

62. The method of claim 55, wherein removing the structure from the mold involves destroying at least a portion of the mold.

63. The method of claim 62, wherein the destroying step involves changing the temperature of the mold.

64. The method of claim 62, wherein the destroying step is leaching.

65. The method of claim 62, wherein the destroying step is sublimation.

66. The method of claim 62, wherein the destroying step is vibration.

67. The method of claim 62, wherein the destroying step is impact.

68. The method of claim 62, wherein the destroying step is enzymatic degradation.

69. The method of claim 55, further comprising assembling a plurality of complex unitary three-dimensional structures using a process selected from the group consisting of welding, friction-assisted welding, and solvent welding.

70. The method of claim 34, wherein the complex unitary three dimensional structure includes a plurality of periodic parallel planes.

71. A method, comprising: forming a plurality of mold portions, each mold portion including at least a portion of a complement of a complex unitary three dimensional structure; forming a mold from the plurality of mold portions by positioning the plurality of mold portions adjacently and in direct contact with each other, such that the portions of the complement combine to form the complement; and introducing a fluid material into the mold and allowing the fluid material to solidify, such that the structure is not removable from the mold without breaking the mold, and the mold is not removable from the structure without breaking the structure.

72. A mold, comprising: a plurality of mold portions positioned adjacently and in direct contact with one another; and an at least partially solidified material having the shape of a complex unitary three dimensional structure, wherein the structure is not removable from the mold portions without destroying at least a portion of the mold.

73. A method of forming a regular truss, comprising: forming a plurality of disposable mold portions, each mold portion comprising at least one polyhedron having grooved edges, wherein the plurality of disposable mold portions comprises at least two substantially identical polyhedra; assembling the mold portions into a solid mold, wherein at least a portion of the grooved edges of the polyhedra combine to form channels in the solid mold; filling said solid mold with a fluid, wherein the channels are filled with the fluid; transforming the fluid into a solid truss, wherein said filled channels become struts of the truss, the truss being interlocked with the solid mold; and removing the solid mold.

74. The method of claim 73, wherein the solid mold is removed by melting.

75. The method of claim 74, wherein the mold portions are formed from at least one of the group consisting of metals, metal alloys, polymers, polymer blends, and wax.

76. The method of claim 73, wherein the solid mold is removed by leaching.

77. The method of claim 76, wherein the mold portions are formed from a material selected from the group consisting of solvent soluble polymers, starch, sugar, and waxes.

78. The method of claim 73, wherein the solid mold is removed by sublimation.

79. The method of claim 78, wherein the mold portions are formed from at least one of camphor, sulphur, phosphorus, and sublimation dyes.

80. The method of claim 73, wherein the solid mold is removed by vibration.

81. The method of claim 80, wherein the mold portions are formed from a bound powder, and where the vibration includes a component substantially at a resonant frequency of the bound powder.

82. The method of claim 73, wherein the solid mold is removed by enzymatic degradation.

83. The method of claim 82, wherein the mold portions comprise a material selected from the group consisting of proteins, carbohydrates, lipids, and nucleic acids.

84. The method of claim 83, wherein the mold portions comprises a material selected from the group consisting of collagen, albumin, agarose, and starch.

85. The method of claim 73, wherein the mold portions each consist of a single polyhedron.

86. The method of claim 73, wherein the mold portions each consist of a single layer of polyhedra.

87. The method of claim 73, wherein the mold portions are substantially identical.

88. The method of claim 73, wherein the mold portions include registration structures which align the mold portions to assemble the solid mold.

89. The method of claim 73, wherein assembling includes bonding mold portions together by a process selected from the group consisting of welding, friction-assisted welding, and solvent welding.

90. The method of claim 73, wherein the mold portions are formed by a process selected from the group consisting of casting, die casting, injection molding, reaction injection molding, rotational molding, and casting into thermoformed cavities.

91. The method of claim 73, wherein filling is accomplished at atmospheric pressure.

92. The method of claim 73, wherein filling is accomplished using a pressure differential.

93. The method of claim 73, wherein transforming the fluid into the solid truss comprises polymerizing the fluid.

94. The method of claim 73, wherein transforming the fluid into the solid truss comprises cooling and solidifying the fluid.

95. The method of claim 73, wherein the solid truss is formed from a material selected from the group consisting of epoxies, thermoplastic polymers, thermosetting polymers, metals, metal alloys, ceramics, biological materials, carbon, calcium, metalloids, and combinations thereof.

96. The method of claim 73, wherein the solid truss is a tetrakaidecahedral truss.

97. The method of claim 73, wherein the solid truss is an octet truss.

98. The method of claim 73, wherein the solid truss includes tensegrity elements.

99. The method of claim 73, wherein the struts of the truss are all of substantially identical cross-section.

100. The method of claim 73, wherein the truss includes at least two struts having differing cross-sections.

101. The method of claim 73, wherein the truss includes a planar member.

102. The method of claim 73, wherein the truss includes a solid polyhedral member.