WO2009045176A1

WO2009045176A1 - Method of making a scaffold for tissue and bone applications

Info

Publication number: WO2009045176A1
Application number: PCT/SG2008/000380
Authority: WO
Inventors: Chandrasekaran Margam; Wan Kheng Victor Lee; Yong Chiah Vincent Lee; Boon Hon Yeo; Ramanath Sathyanarayana Hassan
Original assignee: Bio-Scaffold International Pte Ltd
Priority date: 2007-10-03
Filing date: 2008-10-03
Publication date: 2009-04-09

Abstract

A method of making a scaffold for tissue regeneration and/or bone growth includes providing a polymer, providing a scaffold structure using the polymer, wherein the scaffold structure includes the polymer and pores, exposing the scaffold structure to an organic solvent, and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure by increasing a chemical bond strength of the polymer. Advantageously, the scaffold has high strength, high porosity and a well-controlled pore structure.

Description

Method of Making a Scaffold for Tissue and Bone Applications

Cross-Reference to Related Applications

This application claims priority to U.S. provisional application serial no. 60/960,558, filed October 3, 2007, which is incorporated herein by reference.

Field of the Invention The present invention generally relates to a scaffold, and more particularly to a method of making a scaffold for tissue regeneration and/or bone growth.

Background of the Invention In dental tissue engineering, a scaffold plays a pivotal role in preventing resorption of alveolar bone thereby preserving the bone height and volume after a tooth extraction. When a tooth is extracted, a blood clot develops in the socket which leads to formation of new-bone. However, this healing process does not allow ad integrum restitution of the initial alveolar bone volume because physiological resorption decreases the height and width of the alveolar ridge. The resulting alveolar bone loss affects long-term stability of conventional or implant-borne prosthetic restoration for partially or totally toothless patients. Moreover, this can also result in non-uniformity of the ridge.

Various techniques exist to limit alveolar bone loss, such as atraumatic extraction, immediate postextraction of a removable prosthesis, immediate placement of a dental implant, and immediate bone filling of an extraction socket. Filling materials to prevent alveolar crest resorption such as allografts and xenografts generate supply problems and risk cross contamination. Synthetic bone substitutes to overcome these limitations include biphasic calcium phosphates (BCP), associations of hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP), collagen fibres of porcine origin and synthetic biopolymers of polylactic acid. Biphasic calcium phosphates have been used for bone regeneration since their structure and chemical composition is close to the biological apatite of bone tissues. However, biphasic calcium phosphates have yet to achieve satisfactory results.

With synthetic polymers, poly L-lactide foam has been used for dry sockets (alveolar osteitis). However, poly L-lactide foam is relatively weak. As a result, stronger and porous synthetic polymers have been developed. Biodegradable polymers are attractive candidates for scaffolds because they degrade as the new tissue forms and eventually disappear from the patient. Thus, biodegradable polymer scaffolds (bioscaffolds) show great promise for tissue engineering. However, biodegradable polymer scaffolds that provide a suitable substitute for an alveolar socket and prevent resorption and promote post extraction bone remodeling still present a challenge. Biodegradable polymer scaffolds are not well understood and have much room for improvement.

Biodegradable polymer scaffolds for tissue engineering are expected to have the following characteristics: (i) three-dimensional and highly porous with a three-dimensional interconnected pore network for cell/tissue growth and flow transport of nutrients and metabolic waste; (ii) biodegradable or bioresorbable with a controllable degradation and resorption rate to match cell/tissue growth in vitro and/or in vivo (this calls for graded porosity); (iii) surface chemistry conducive for cell attachment, proliferation and differentiation; (iv) adequate mechanical properties to match those of the tissues at the site of implantation; and (v) convenient and cost-effective manufacture in a wide variety of shapes and sizes. Furthermore, biodegradable polymer scaffolds should provide guided bone regeneration which requires large space with high strength across the pore network.

Biodegradable polymer scaffold manufacturing has severe limitations. For instance, stereolithography requires a photocurable polymer which has insufficient strength. Three- dimensional printing depends on chemical bonds between the polymer and the binder (rather than the polymer alone) which have insufficient strength. Gas foaming and solvent leaching to obtain the pores in the scaffold lack sufficient control over the pore size and connectivity. In addition, solvent leaching provides little or no strength increase (perhaps 15 percent) of the polymer. Accordingly, a need exists for a method of making a biodegradable polymer scaffold that has high strength, high porosity and a well-controlled pore structure. Summary of the Invention

The present invention provides a method of making a scaffold for tissue regeneration and/or bone growth that includes providing a polymer, providing a scaffold structure using the polymer, wherein the scaffold structure includes the polymer and pores, exposing the scaffold structure to an organic solvent, and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure by increasing a chemical bond strength of the polymer.

The polymer can be provided as polymer particles with a size of 20 to 200 microns and selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL- lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof, and the polymer particles can be provided using a cryogenic mill.

The scaffold structure can be provided using three-dimensional printing and consist of the polymer and a binder, or alternatively, using fused deposition modeling and consist of the polymer. The scaffold structure can be exposed to the organic solvent while the organic solvent is a vapour, or alternatively, while the organic solvent is a liquid. The scaffold structure can be exposed to the organic solvent at an elevated vapour pressure. For instance, the scaffold structure can be exposed to the organic solvent at a pressure that increases from zero vapour pressure to the elevated vapour pressure and then is maintained at the elevated vapour pressure for a predetermined time period. Furthermore, the scaffold structure can be exposed to the organic solvent without agitation.

The scaffold structure strength can increase by at least 200 percent, for instance by 200 to 2500 percent, due to the organic solvent exposure and removal.

The organic solvent can be selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

Preferably, the organic solvent does not remove material from the scaffold structure, does not change a shape of the scaffold structure and does not change a shape of the pores.

Removing the organic solvent can include drying the scaffold structure and then annealing the scaffold structure. For instance, exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure can include exposing the scaffold structure to the organic solvent a single time, then drying the scaffold structure and then annealing the scaffold structure, or alternatively, exposing the scaffold structure to the organic solvent a first time, then drying the scaffold structure a first time, then exposing the scaffold structure to the organic solvent a second time, then drying the scaffold structure a second time and then annealing the scaffold structure. The drying can occur at a temperature of 25⁰C for 15 minutes, and the annealing can occur at a temperature of 110 to 15O⁰C for 1 to 15 hours. Removing the organic solvent can also shrink the scaffold structure, for instance by 25 to 50 percent.

The scaffold can have a porosity of 60 to 80 percent due to the pores. The pores can include macropores and micropores in which the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity. Furthermore, the macropores can have a size that is at least 500 percent that of the micropores. For instance, the macropores can have a size of 600 to 1500 microns and the micropores can have a size of 20 to 150 microns.

The scaffold can include a biodegradable biocompatible polymer and provide a dental alveolar socket. In addition, the scaffold can have the same shape and pore structure as the scaffold structure. For instance, the polymer can be a biodegradable polymer, the scaffold structure can consist essentially of the biodegradable polymer, and the scaffold can consist essentially of the biodegradable polymer, have the same shape, porosity and composition as the scaffold structure, have greater strength than the scaffold structure and have a smaller scale than the scaffold structure. Accordingly, the organic solvent exposure and removal can convert the scaffold structure into a far stronger scaffold without altering its shape or composition.

Advantageously, the scaffold has high strength, high porosity and a well-controlled pore structure.

These and other objects, features and advantages of the present invention will become more apparent in view of the detailed description that follows.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be more fully described, with reference to the drawings in which:

Fig. 1 is a process diagram of a method of making a scaffold in accordance with a first embodiment of the present invention;

Fig. 2 is a process diagram of a method of making a scaffold in accordance with a second embodiment of the present invention; Fig. 3 is a process diagram of a method of making a scaffold in accordance with a third embodiment of the present invention; and

Fig. 4 is a scaffold manufactured in accordance with the present invention.

Detailed Description of the Invention

In the following description, the preferred embodiments of the present invention are described. It shall be apparent to those skilled in the art, however, that the present invention may be practiced without such details. Some of the details are not be described at length so as not to obscure the present invention. Fig. 1 shows a process diagram of method 100 of making a scaffold in accordance with a first embodiment of the present invention. The scaffold is a biodegradable, biocompatible, dental alveolar socket that promotes the preservation of bone height and volume after tooth extraction.

In step 110, polymer particles with a particle size varying from 20 to 200 microns are provided from polymer pellets using a cryogenic mill. The polymer is a biodegradable, biocompatible polymer such as polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof. For instance, the polymer is polyglycolide, poly L-lactide and poly co-glycolide in the desired ratio. Furthermore, the polymer is not photocurable. In step 120, the polymer particles are mixed with binder particles to provide a polymer blend. The polymer particles provide 80 to 95 percent of the polymer blend and the binder particles provide 5 to 20 percent of the polymer blend (by atomic weight). For instance, the polymer particles provide 90 percent of he polymer blend and the binder particles provide 10 percent of the polymer bend. In addition, the binder particles are polyvinyl alcohol and have the same size as the polymer particles.

In step 130, a scaffold structure is provided using three-dimensional printing of the polymer blend. The scaffold structure consists essentially of the polymer (and thus the biodegradable, biocompatible polymer from the polymer particles) with the remainder the binder (and thus the polyvinyl alcohol from the binder particles). The scaffold structure has a cylindrical shape with an axial bore therethrough and four identical axially-centered radially- distributed macropores (channels) in the sidewalls that extend to the bore and are spaced from the axial ends of the bore, a height (in the axial direction) of 4 to 15 millimeters and a diameter (in the radial direction) of 3 to 15 millimeters. For instance, the scaffold structure has a height of 6.5 millimeters and a diameter of 5.8 millimeters. The scaffold structure includes a pore structure in a predetermined three-dimensional interconnected pore network that has a porosity of 60 to 80 percent due to the pores between the polymer and binder particles. The pores include macropores and micropores. The macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

Furthermore, the macropores have a size of 600 to 1500 microns and the micropores have a size of 20 to 150 microns. For instance, the macropores have a size of 1500 microns and the micropores have a size of 150 microns.

In step 140, the scaffold structure is exposed to an organic solvent. The organic solvent can be acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof. Furthermore, the organic solvent can be vapour or liquid. For instance, the organic solvent is acetone vapour. The scaffold structure is initially exposed to the organic solvent at 25⁰C (room temperature) and 0 bar (vapour pressure). Thereafter, the temperature of the organic solvent is linearly increased to 7O⁰C (elevated temperature) and as a result the pressure of the organic solvent vapour is linearly increased to 1 bar (elevated pressure) over 10 minutes, and then the temperature is maintained at 70⁰C and as a result the elevated pressure is maintained at 1 bar for 1 minute. Furthermore, the organic solvent exposure is performed without agitation. That is, the scaffold structure and the organic solvent remain stationary and no vibration is applied. The organic solvent converts the polymer at and slightly beneath the exposed surfaces of the scaffold structure from the loose polymer particles held together by the binder particles into a softened, semi-liquid (gel-like) state and "cold welds" the adjoining polymer particles together, thereby increasing a chemical bond strength of the polymer at these polymer particles and increasing the strength of the scaffold structure. However, the organic solvent does not reach me polymer located at deeper internal regions of the scaffold structure. For instance, the organic solvent penetrates 20 percent of the scaffold structure without reaching the remaining 80 percent of the scaffold structure. As a result, the organic solvent partially strengthens the scaffold structure at its external shell.

In step 150, the scaffold structure is dried. For instance, the scaffold structure is dried at 25⁰C (room temperature) and 1 bar (atmospheric pressure) for 15 minutes.

In step 160, the scaffold structure is exposed to the organic solvent a second time. The scaffold structure is initially exposed to the organic solvent at 25⁰C (room temperature) and 0 bar (vapour pressure). Thereafter, the temperature of the organic solvent is linearly increased to 7O⁰C (elevated temperature) and as a result the pressure of the organic solvent vapour is linearly increased to 1 bar (elevated pressure) over 10 minutes, and then the temperature is maintained at 70⁰C and as a result the elevated pressure is maintained at 1 bar for 30 minutes (rather than 1 minute). Furthermore, the organic solvent exposure is performed without agitation. That is, the scaffold structure and the organic solvent remain stationary and no vibration is applied.

The organic solvent converts the polymer at the deeper internal regions of the scaffold structure from the loose polymer particles held together by the binder particles into a softened, semi-liquid (gel-like) state and "cold welds" the adjoining polymer particles together, thereby further a chemical bond strength of the polymer at these polymer particles and further increasing the strength of the scaffold structure. Thus, the organic solvent reaches the remaining polymer in the scaffold structure that was not reached by the organic solvent during the shorter exposure in step 140. For instance, the organic solvent penetrates the remaining 80 percent of the scaffold structure. As a result, the organic solvent further strengthens the scaffold structure at its interior beneath its external shell.

In step 170, the scaffold structure is dried a second time. For instance, the scaffold structure is dried at 25⁰C and 1 bar for 15 minutes. hi step 180, the scaffold structure is annealed at 110 to 15O⁰C for 1 to 15 hours to provide the scaffold. For instance, the scaffold structure is annealed at 140⁰C for 4 hours. The anneal drives out any remaining solvent in the scaffold structure and hardens the polymer. In this manner, the drying and anneal remove the organic solvent from the scaffold structure. Moreover, the anneal further increases the strength of the scaffold structure, for instance by 10 to 15 percent, although by far less than the organic solvent exposure and drying. The organic solvent exposure and removal increases the strength of scaffold structure by 200 to 2500 percent, for instance by 2000 percent. As another example, the organic solvent exposure and removal increases the scaffold structure strength by 0.1 to 4.5 megapascals. However, the drying and the enneal anneal do not remove material from the scaffold structure, do not change the shape of the scaffold structure and do not change the shape of the pores. Furthermore, the drying and the anneal reduce the scale of the scaffold structure, for instance by 25 to 50 percent. For example, the drying reduces the scale of the scaffold structure by 33 percent, and the anneal further reduces the scale of the scaffold structure by 10 percent. However, the drying and the anneal do not change the shape of the scaffold structure and do not change the shape of the pores. Instead, the scaffold retains the same shape, porosity and composition as the scaffold structure but is far stronger than and has a smaller scale than the scaffold structure. In other words, the scaffold is essentially identical to the scaffold structure except that the scaffold is much stronger than and shrunk relative to the scaffold structure. Thus, the scaffold retains the three-dimensional patterning provided in step 130 on a stronger and smaller scale.

The scaffold consists essentially of the polymer, consists of the polymer and the binder and has the same shape, porosity and composition as the scaffold structure but is far stronger than and is somewhat smaller than the scaffold structure due to secondary processing of the scaffold structure in steps 140 to 180 after solid free forming the scaffold structure in step 130. Advantageously, the scaffold has exceptionally high strength and high porosity to provide the necessary support and space for successful alveolar bone preservation and remodeling. Furthermore, the scaffold retains its high strength for 8 weeks or more to permit osteoclasts and remodeled bone to attain sufficient strength. Fig. 2 shows a process diagram of method 200 of making a scaffold in accordance with a second embodiment of the present invention. In the second embodiment, the organic solvent exposure and drying steps are performed once (rather than twice). For purposes of brevity, any description in the first embodiment is incorporated in the second embodiment insofar as applicable and need not be repeated, and process steps of the second embodiment similar to those in the first embodiment have corresponding reference numerals indexed at two-hundred rather than one-hundred. For instance, step 210 corresponds to step 110, etc. In step 210, polymer particles are provided.

In step 220, the polymer particles are mixed with binder particles to provide a polymer blend. In step 230, a scaffold structure is provided using three-dimensional printing of the polymer blend.

In step 260, the scaffold structure is exposed to an organic solvent, hi step 270, the scaffold structure is dried.

In step 280, the scaffold structure is annealed, thereby removing any remaining solvent from the scaffold structure and hardening the polymer to provide the scaffold.

Fig.3 shows a process diagram of method 300 of making a scaffold in accordance with a third embodiment of the present invention. In the third embodiment, the scaffold structure is provided using fused deposition modeling (rather than three-dimensional printing) of the polymer (rather than the polymer and the binder). For purposes of brevity, any description in the first embodiment is incorporated in the third embodiment insofar as applicable and need not be repeated, and process steps of the third embodiment similar to those in the first embodiment have corresponding reference numerals indexed at three- hundred rather than one-hundred. For instance, step 310 corresponds to step 110, etc. In step 310, polymer particles are provided.

In step 320, the polymer particles are converted into polymer filaments by melting the polymer particles into a polymer fluid, extruding the polymer fluid through openings in a plate and then hardening the extruded polymer fluid. For instance, the polymer filaments have a diameter of 1.78 millimeters. hi step 330, the scaffold structure is provided using fused deposition modeling (rather than three-dimensional printing) of the polymer filaments (rather than the polymer particles and the binder particles). The scaffold structure consists of the polymer (rather than the polymer and the binder). In step 360, the scaffold structure is exposed to an organic solvent.

In step 370, the scaffold structure is dried. hi step 380, the scaffold structure is annealed, thereby removing any remaining solvent from the scaffold structure and hardening the polymer to provide the scaffold. The scaffold structure consists of the polymer (rather than the polymer and the binder). Fig.4 shows scaffold 400 manufactured in accordance with method 100 of the present invention. Scaffold 400 (like the scaffold structure) has a cylindrical shape with axial bore 410 therethrough and four identical axially-centered radially-distributed macropores 420a, 420b, 420c and 42Od in the sidewalls that extend to bore 410 and are spaced from the axial ends of bore 410. Scaffold samples manufactured in accordance with method 100 of the present invention were tested for strength and degradation. The samples included cylindrical samples with a height of 6.5 millimeters and a diameter of 5.8 millimeters, and rectangular samples with a height of 9.54 millimeters, a length of 6.5 millimeters and a width of 1.67 millimeters.

Phosphate buffered solution with 1OX concentration obtained from Sigma Aldrich was diluted with deionized water to obtain 20 ml of the solution. Deionized water was filled in individual containers. The solution was also filled in other individual containers and the volume was calculated based on the ratio provided in ISO standard 13781:1997 (E), i.e., 30:1. Some samples were unsoaked, other samples were delicately placed in the containers with deionized water and soaked in the deionized water, and other samples were delicately placed in the containers with the solution and soaked in the solution and the containers were sealed. The solution pH was tested and adjusted to be 7.2 to 7.6 and was continuously monitored. The solution was replaced on alternate days to maintain the pH at 7.2 to 7.6. The containers with the samples immersed in the solution were immersed in a constant temperature water bath at 36.5 to 37.5⁰C.

The initial samples for 0 week testing included the unsoaked samples and the samples soaked in deionized water in the containers for 1 hour and then removed from the containers for vacuum desiccation. The initial samples were evaluated with mechanical tests, differential scanning calorimetry and other tests. The remaining samples were soaked in the solution in the containers and then removed from the containers at intervals of 4, 8 and 12 weeks for mechanical tests.

The initial samples were tested under dry conditions to ascertain the dry strength/ maximum load under dry conditions. The remaining samples were then tested using an Instron 4505 universal test machine at a 1 mm/min compression rate at which a linear relationship between the load and displacement cancelled other influences on the tests. The test temperature was 23°C.

The storage modulus of the samples was tested using a single cantilever beam in a dynamic mechanical analyzer with three samples tested per batch to ensure repeatability, multifrequency mode, cantilever beam frequency at 1 Hz, amplitude at 20 microns, equilibrate at 25°C, ramping at 5°C/min to 150⁰C and an air bearing.

The samples removed after 4 and 8 weeks were dried in a vacuum dessiccator for 2 weeks for differential scanning calorimetry tests and mass change determination per ISO standard 13781:1997 (E) section 5.1.4, whereas the mechanical tests were performed under wet conditions per ISO standard 13781 : 1997 (E) section 6.1. The maximum load sustained at 0 weeks was approximately 60 Newtons when the samples ware immersed in deionized water for an hour before testing. However, when the unsoaked samples were tested, the maximum load sustained was 170 to 250 Newtons. The load reduction was likely caused by softening of the polymer due to water intake and simultaneous hydration of the samples. The maximum load dropped to 20 Newtons after 4 weeks, 5 Newtons after 8 weeks and 4

Newtons after 12 weeks of immersion in the solution. The storage modulus also dropped from 250 megapascals at 0 weeks to 200 megapascals after 4 weeks. Three samples were tested under each condition and the average load and modulus were calculated. The maximum load sustained by the samples in the dry condition was approximately 170 Newtons. The strain at break varied with different compression rates. The samples revealed a fairly high strain before fracture except the sample tested at 3 mm/min. The premature failure might have been due to mishandling during processing or experiments, or alternatively, to imperfections in the sample.

The samples tended to fail faster with higher compression rate. This was likely due to the short time given for the polymeric chains to align with a faster rate of compression. The samples also failed faster with lower strain. Conversely, when the polymeric chains were strained slowly, the molecular alignment could allow higher strains to be withstood. With about 170 Newtons of load at failure and a surface area of about 15 square millimeters (after shrinkage), a calculated compressive strength of about 12 to 15 megapascals was achieved with samples which possessed pores only in the vertical direction.

The storage modulus dropped from 250 megapascals to 7 megapascals with immersion in the solution over 12 weeks. The storage modulus drop was not significant over the first 4 weeks and a steep reduction in the storage modulus occurred for 8 weeks and longer. Thus, the samples sustained high strength during the initial 4 weeks of immersion in the solution which was critical for early phase bone remodelling in dental sockets.

Following the storage modulus, the compressive load sustained also decreased with immersion in the solution but the initial reduction for the first 4 weeks of immersion in the solution was higher, losing about 66% strength. For the next 8 weeks the load dropped by about 85% compared to the first 4 weeks. However, the load drop between 8 and 12 weeks was less significant than between 0 and 4 weeks and between 4 and 8 weeks.

Since there was a drop in load carrying capacity, the samples tested in- vitro and in- vivo were compared at 4 weeks by harvesting a sample from a rabbit and testing for maximum load carrying capacity.

Three samples harvested from in-vivo were tested for compressive loads — sample 1 as harvested, sample 2 harvested and air dried for 1 hour, and sample 3 harvested and air dried for 1 day before vacuum packing for testing. Sample 1 showed similar results to in- vitro samples where the pre-conditions were similar, i.e. immersion in the solution followed by mechanical tests, whereas for air drying the maximum load increased to approximately 80 to 100 Newtons which was about 40% of the original load sustained under dry conditions without any immersion in the solution. This indicated that the samples were intact and mechanical strength was retained for 4 weeks of in-vivo tests. The first 4 weeks were critical as the loss of maximum load sustainable was considerable in magnitude though the loss was not as significant as for the 8 and 12 weeks as compared with the earlier 4 and 8 weeks respectively.

The relative crystallinity of the samples did not change significantly between 0 and 4 weeks which indicated good scaffold integrity for 4 weeks. However, the 8 weeks data could not be confirmed due to suspected contamination in the desiccated samples.

The embodiments set forth above are illustrative. Numerous other embodiments are contemplated. For instance, the scaffold structure can be formed by three-dimensional printing, fused deposition modeling, compression molding, injection molding, and direct and indirect rapid prototyping. Thus, the scaffold structure can be formed with the desired shape and size in a highly flexible manner with the most convenient and cost-effective approach. The scaffold structure and the scaffold can include, consist essentially of or consist of the polymer. Likewise, the polymer can be various biocompatible and biodegradable polymers (biopolymers) approved by the Federal Drug Administration (FDA) for pharmaceuticals and tissue engineering. The scaffold is well-suited for a wide variety of medical applications such as dental, maxillofacial and cranial tissue regeneration and bone growth in humans and animals.

It is understood that in the context of the present invention, the scaffold structure and the scaffold have the "same" shape, porosity and/or composition at the macroscopic level rather than the microscopic level. That is, the scaffold structure and the scaffold physical appearance are essentially identical except that the scaffold has a smaller scale than the scaffold structure at the macroscopic level. Thus, the scaffold structure and the scaffold have no appreciable differences in shape, porosity and/or composition. Microscopic and similar slight differences and trivial variations between the scaffold structure and the scaffold shape, porosity and/or composition would be expected, as is clear to those skilled in the art.

However, the scaffold structure and the scaffold have appreciable differences in strength and scale. That is, the scaffold is appreciably stronger and smaller than the scaffold structure. Moreover, the scaffold structure and the scaffold can have different shape, porosity and/or composition at the macroscopic level in various embodiments. It is understood that in the context of the present invention, the organic solvent is

"removed" from the scaffold structure at the macroscopic level rather than the microscopic level. Microscopic and similar slight traces and trivial remnants of the organic solvent in the scaffold would be expected, as is clear to those skilled in the art Likewise, the organic solvent need not be removed in a single step, and instead can be removed in multiple steps (such as drying and annealing) that are consecutive or interspersed with the organic solvent exposure or other treatment steps.

The above description and examples illustrate the preferred embodiments of the present invention, and it will be appreciated that various modifications and improvements can be made without departing from the scope of the present invention.

Claims

1. A method of making a scaffold for tissue regeneration and/or bone growth, the method comprising: providing a polymer; providing a scaffold structure using the polymer, wherein the scaffold structure includes the polymer and pores; exposing the scaffold structure to an organic solvent; and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure by increasing a chemical bond strength of the polymer.

2. The method of claim 1 , wherein the polymer is provided as polymer particles with a size of 20 to 200 microns.

3. The method of claim 1 , wherein the polymer is provided as polymer particles using a cryogenic mill.

4. The method of claim 1 , wherein the polymer is selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof.

5. The method of claim 1 , wherein the scaffold structure is provided using three- dimensional printing.

6. The method of claim 1 , wherein the scaffold structure is provided using fused deposition modeling.

7. The method of claim 1 , wherein the scaffold structure consists of the polymer and a binder.

8. The method of claim 1, wherein the scaffold structure consists of the polymer.

9. The method of claim 1, wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a vapour.

10. The method of claim 1 , wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a liquid.

11. The method of claim 1 , wherein the scaffold structure is exposed to the organic solvent at an elevated vapour pressure.

12. The method of claim 11 , wherein the scaffold structure is exposed to the organic solvent at a pressure that increases from zero vapour pressure to the elevated vapour pressure and then is maintained at the elevated vapour pressure for a predetermined time period.

13. The method of claim 1 , wherein the scaffold structure is exposed to the organic solvent without agitation.

14. The method of claim 1 , wherein the organic solvent is selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

IS. The method of claim 1, wherein the organic solvent does not remove material from the scaffold structure.

16. The method of claim 1 , wherein the organic solvent does not change a shape of the scaffold structure.

17. The method of claim 1 , wherein the organic solvent does not change the pores.

18. The method of claim 1 , wherein removing the organic solvent decreases a scale of the scaffold structure.

19. The method of claim 18, wherein removing the organic solvent decreases the scale of the scaffold structure by 25 to 50 percent.

20. The method of claim 1 , wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases the strength of the scaffold structure by at least 200 percent.

21. The method of claim 20, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases the strength of the scaffold structure by 200 to 2500 percent.

22. The method of claim 1 , wherein removing the organic solvent from the scaffold structure includes drying the scaffold structure and then annealing the scaffold structure.

23. The method of claim 22, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure includes: exposing the scaffold structure to the organic solvent a single time; then drying the scaffold structure; and then annealing the scaffold structure.

24. The method of claim 22, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure includes: exposing the scaffold structure to the organic solvent a first time; then drying the scaffold structure a first time; then exposing the scaffold structure to the organic solvent a second time; then drying the scaffold structure a second time; and then annealing the scaffold structure.

25. The method of claim 22, wherein exposing the scaffold structure to the organic solvent and drying the scaffold structure increases the strength of the scaffold structure by a first amount, annealing the scaffold structure increases the strength of the scaffold structure by a second amount, and the first amount is at least 1000 percent the second amount.

26. The method of claim 1 , wherein the scaffold has a porosity of 60 to 80 percent due to the pores.

27. The method of claim 26 wherein the pores include macropores and micropores, the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

28. The method of claim 1 , wherein the scaffold structure and the scaffold have the same shape and pore structure.

29. The method of claim 1 , wherein the scaffold consists essentially of the polymer and the polymer is a biodegradable biocompatible polymer.

30. The method of claim 1 , wherein the scaffold is a dental alveolar socket.

31. A method of making a scaffold for tissue regeneration and/or bone growth, the method comprising: providing polymer particles that are a biodegradable polymer; providing a scaffold structure using the polymer particles, wherein the scaffold structure consists essentially of the biodegradable polymer and includes pores; then exposing the scaffold structure to an organic solvent; and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure by increasing a chemical bond strength of the polymer and the scaffold consists essentially of the biodegradable polymer.

32. The method of claim 31 , wherein the polymer is selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof.

33. The method of claim 31, wherein the scaffold structure is provided using three-dimensional printing and consists of the polymer and a binder.

34. The method of claim 31 , wherein the scaffold structure is provided using fused deposition modeling and consists of the polymer.

35. The method of claim 31 , wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a vapour at elevated pressure.

36. The method of claim 31 , wherein the scaffold structure strength increases by 200 to 2500 percent due to the organic solvent exposure and removal.

37. The method of claim 31 , wherein the organic solvent is selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

38. The method of claim 31 , wherein the organic solvent does not remove material from the scaffold structure, does not change a shape of the scaffold structure and does not change a shape of the pores.

39. The method of claim 31 , wherein the scaffold has a porosity of 60 to 80 percent due to the pores, the pores include macropores and micropores, the macropores have a size that is at least 200 percent that of the micropores, the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

40. The method of claim 31 , wherein the scaffold is a biodegradable dental alveolar socket.

41. A method of making a scaffold for tissue regeneration and/or bone growth, the method comprising: providing polymer particles; providing a scaffold structure using the polymer particles, wherein the scaffold structure includes the polymer and pores; then exposing the scaffold structure to an organic solvent without agitation; and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure by increasing a chemical bond strength of the polymer.

42. The method of claim 41, wherein the polymer is selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof.

43. The method of claim 41 , wherein the scaffold structure is provided using three-dimensional printing and consists of the polymer and a binder.

44. The method of claim 41 , wherein the scaffold structure is provided using fused deposition modeling and consists of the polymer.

45. The method of claim 41 , wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a vapour at elevated pressure.

46. The method of claim 41 , wherein the scaffold structure strength increases by 200 to 2500 percent due to the organic solvent exposure and removal.

47. The method of claim 41 , wherein the organic solvent is selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

48. The method of claim 41, wherein the organic solvent does not remove material from the scaffold structure, does not change a shape of the scaffold structure and does not change a shape of the pores.

49. The method of claim 41 , wherein the scaffold has a porosity of 60 to 80 percent due to the pores, the pores include macropores and micropores, the macropores have a size that is at least 200 percent that of the micropores, the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

50. The method of claim 41 , wherein the scaffold is a biodegradable dental alveolar socket.

51. A method of making a scaffold for tissue regeneration and/or bone growth, the method comprising: providing polymer particles; providing a scaffold structure using the polymer particles, wherein the scaffold structure includes the polymer and pores; then exposing the scaffold structure to an organic solvent, thereby increasing a strength of the scaffold structure by increasing a chemical bond strength of the polymer; and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure at least 200 percent by increasing a chemical bond strength of the polymer.

52. The method of claim 51 , wherein the polymer is selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof.

53. The method of claim 51 , wherein the scaffold structure is provided using three-dimensional printing and consists of the polymer and a binder.

54. The method of claim 51 , wherein the scaffold structure is provided using fused deposition modeling and consists of the polymer.

55. The method of claim 51 , wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a vapour at elevated pressure.

56. The method of claim 51 , wherein the scaffold structure strength increases by 200 to 2500 percent due to the organic solvent exposure and removal.

57. The method of claim 51 , wherein the organic solvent is selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

58. The method of claim 51 , wherein the organic solvent does not remove material from the scaffold structure, does not change a shape of the scaffold structure and does not change a shape of the pores.

59. The method of claim 51 , wherein the scaffold has a porosity of 60 to 80 percent due to the pores, the pores include macropores and micropores, the macropores have a size that is at least 200 percent that of the micropores, the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

60. The method of claim 51 , wherein the scaffold is a biodegradable dental alveolar socket.

61. A method of making a scaffold for tissue regeneration and/or bone growth, the method comprising: providing polymer particles; providing a scaffold structure using the polymer particles, wherein the scaffold structure includes the polymer and pores; then exposing the scaffold structure to an organic solvent; and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure by increasing a chemical bond strength of the polymer, the scaffold structure and the scaffold have the same shape, porosity and composition and the scaffold structure has a larger scale than the scaffold.

62. The method of claim 61 , wherein the polymer is selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof.

63. The method of claim 61, wherein the scaffold structure is provided using three-dimensional printing and consists of the polymer and a binder.

64. The method of claim 61 , wherein the scaffold structure is provided using fused deposition modeling and consists of the polymer.

65. The method of claim 61, wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a vapour at elevated pressure.

66. The method of claim 61 , wherein the scaffold structure strength increases by 200 to 2500 percent due to the organic solvent exposure and removal.

67. The method of claim 61 , wherein the organic solvent is selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

68. The method of claim 61 , wherein the organic solvent does not remove material from the scaffold structure, does not change a shape of the scaffold structure and does not change a shape of the pores.

69. The method of claim 61 , wherein the scaffold has a porosity of 60 to 80 percent due to the pores, the pores include macropores and micropores, the macropores have a size that is at least 500 percent that of the micropores, the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

70. The method of claim 61 , wherein the scaffold is a biodegradable dental alveolar socket.

71. A method of making a scaffold for tissue regeneration and/or bone growth, the method comprising: providing polymer particles that are a biodegradable polymer; providing a scaffold structure using the polymer particles, wherein the scaffold structure consists essentially of the biodegradable polymer and includes pores; then exposing the scaffold structure to an organic solvent without agitation; and removing the organic solvent from the scaffold structure to provide the scaffold, wherein exposing the scaffold structure to the organic solvent and removing the organic solvent from the scaffold structure increases a strength of the scaffold structure at least 200 percent by increasing a chemical bond strength of the polymer, and the scaffold consists essentially of the biodegradable polymer and has the same shape, porosity and composition as and is at least 200 percent stronger than and is at least 25 percent smaller than the scaffold structure.

72. The method of claim 71 , wherein the polymer is selected from the group consisting of polyglycolide, polyactide, poly L-lactide, poly DL-lactide, poly co-glycolide, polycaprlactone, polyhydroxybutrate and combinations thereof.

73. The method of claim 71 , wherein the scaffold structure is provided using three-dimensional printing and consists of the polymer and a binder.

74. The method of claim 71 , wherein the scaffold structure is provided using fused deposition modeling and consists of the polymer.

75. The method of claim 71, wherein the scaffold structure is exposed to the organic solvent while the organic solvent is a vapour at elevated pressure.

76. The method of claim 71 , wherein the scaffold structure strength increases by 200 to 2500 percent due to the organic solvent exposure and removal.

77. The method of claim 71 , wherein the organic solvent is selected from the group consisting of acetone, dichloromethane, hex-fluoroisopropanol, chloroform, alcohol and combinations thereof.

78. The method of claim 71 , wherein the organic solvent does not remove material irom the scaffold structure, does not change a shape of the scaffold structure and does not change a shape of the pores.

79. The method of claim 71 , wherein the scaffold has a porosity of 60 to 80 percent due to the pores, the pores include macropores and micropores, the macropores have a size that is at least 200 percent that of the micropores, the macropores provide 50 to 70 percent of the porosity and the micropores provide 30 to 50 percent of the porosity.

80. The method of claim 71 , wherein the scaffold is a biodegradable dental alveolar socket.