Composite fibrous biomaterials for tissue engineering obtained using a supercritical CO2 antisolvent process

Several techniques have been proposed for producing porous structures or scaffolds for tissue engineering but, as yet, with no optimal solution. With regard to this topic, this paper focuses on the preparation of biocompatible nanometric filler–polymer composites organized in a network of fibers. Titanium dioxide (TiO₂) or hydroxyapatite (HAP) nanopowders as the guest particles and poly(lactic acid) (L-PLA) or the blend poly(methylmethacrylate)/poly(ε-caprolactone) (PMMA/PCL) as the polymer carrier were selected as model systems for this purpose. A supercritical antisolvent technique was used to produce the composites. In the process developed, the non-soluble particulate filler was suspended in a polymer solution, and both components were sprayed simultaneously into supercritical carbon dioxide (scCO₂). Using this technique, polymeric matrices were loaded with ～10–20 wt.% of inorganic phase distributed throughout the composite. Two different hybrid materials were prepared: a PMMA/PCL + TiO₂ system where either fibers or microparticles were prepared by varying the molecular weight of the used PMMA; and fibers in the case of L-PLA + HAP system. After further post-processing in a three-dimensional network, these nanofibers can potentially be used as scaffolds for tissue engineering.     

Preconditioned 70S30C bioactive glass foams promote osteogenesis in vivo

Bioactive glass scaffolds (70S30C; 70% SiO₂ and 30% CaO) produced by a sol–gel foaming process are thought to be suitable matrices for bone tissue regeneration. Previous in vitro data showed bone matrix production and active remodelling in the presence of osteogenic cells. Here we report their ability to act as scaffolds for in vivo bone regeneration in a rat tibial defect model, but only when preconditioned. Pretreatment methods (dry, pre-wetted or preconditioned without blood) for the 70S30C scaffolds were compared against commercial synthetic bone grafts (NovaBone® and Actifuse®). Poor bone ingrowth was found for both dry and wetted sol–gel foams, associated with rapid increase in pH within the scaffolds. Bone ingrowth was quantified through histology and novel micro-CT image analysis. The percentage bone ingrowth into dry, wetted and preconditioned 70S30C scaffolds at 11 weeks were 10 ± 1%, 21 ± 2% and 39 ± 4%, respectively. Only the preconditioned sample showed above 60% material–bone contact, which was similar to that in NovaBone and Actifuse. Unlike the commercial products, preconditioned 70S30C scaffolds degraded and were replaced with new bone. The results suggest that bioactive glass compositions should be redesigned if sol–gel scaffolds are to be used without preconditioning to avoid excess calcium release.     

Novel silk sericin/gelatin 3-D scaffolds and 2-D films: Fabrication and characterization for potential tissue engineering applications

In this study, we report for the first time the fabrication of novel 3-D sericin/gelatin scaffolds and 2-D films using non-mulberry Antheraea mylitta silk cocoon sericin protein. The matrices were fabricated, biophysically characterized and optimized for cell culture applications. Blended sericin/gelatin 3-D scaffolds were highly porous with an optimum pore size of 170 ± 20 μm. The scaffolds were robust with enhanced mechanical strength and showed high compressibility. Swelling studies showed high swellability along with complete degradation in the presence of phosphate-buffered saline. Cytocompatibility of the matrices was evaluated using feline fibroblasts showing normal spreading and proliferation as assessed by fluorescence microscopy. Cell cycle analysis showed cytocompatibility without any cell cycle arrests. Low immunogenicity of the matrices as observed through tumor necrosis factor α release reveal its potential as future biopolymeric graft material. The results of this novel study lay the foundation for the use of the silk cocoon protein sericin as a biocompatible biopolymer for tissue engineering applications.     

Mechanical properties and dual drug delivery application of poly(lactic-co-glycolic acid) scaffolds fabricated with a poly(β-amino ester) porogen

Polymeric scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. Scaffolds can be further enhanced by enabling the release of one or more drugs to stimulate regeneration or for the treatment of a specific disease or condition. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres were mixed with poly(β-amino ester) (PBAE) particles to create novel hybrid scaffolds capable of dual release of drug and growth factor. Fast-degrading PBAE particles loaded with the drug ketoprofen acted as porogens that provided a rapid 12 h release. The PLGA microspheres were loaded with a growth factor, bone morphogenetic protein 2, and fused together around the porogens to create a slow-degrading matrix that provided sustained release lasting 70 days. Drug release was further tailored by varying the amount of porogen added to the scaffold. Bioactivity measurements demonstrated that the scaffold fabrication technique did not damage the drug or protein. The compressive modulus was affected by the amount of porogen added, extending from 50 to 111 MPa for loadings from 60 to 40% PBAE, and after 5 days of degradation, it decreased to 0.6 to 1.1 kPa when the porogen was gone. PLGA containing a quick-degrading porogen can be used to release two drugs while developing a porous microarchitecture for cell ingrowth with in a matrix capable of maintaining a compressive modulus applicable for soft tissue implants.     

A facile method to fabricate poly(l-lactide) nano-fibrous morphologies by phase inversion

Scaffolds with a nano-fibrous morphology are favored for certain tissue engineering applications as this morphology mimics the tissue’s natural extracellular matrix secreted by the cells, which consists of mainly collagen fibers with diameters ranging from 50 to 400 nm. Porous poly(l-lactide) (PLLA) scaffolds obtained by phase inversion methods generally have a solid-wall pore morphology. In contrast, this work presents a facile method to fabricate highly porous and highly interconnected nano-fibrous scaffold sheets by phase inversion using PLLA of very high molecular weight (5.7 × 10⁵ g mol^–1). The scaffold sheets consist of nano-fibers within the desired range of 50–500 nm. When applying phase separation micromolding as a fabrication method besides the porous nano-fibrous morphology, an additional topography can be introduced into these sheets. Culturing of C2C12 pre-myoblasts on these nano-fibrous sheets reveals very good cell adhesion, morphology and proliferation. Excellent alignment of the cells is induced by fabrication of 25 μm wide microchannels in these sheets. These results warrant further evaluation of these sheets as tissue engineering scaffolds.     

Fabrication of porous polysaccharide-based scaffolds using a combined freeze-drying/cross-linking process

Biocompatible three-dimensional (3-D) porous scaffolds are of great interest for tissue engineering applications. We here present a novel combined freeze-drying/cross-linking process to prepare porous polysaccharide-based scaffolds. This process does not require an organic solvent or porogen agent. We unexpectedly found that cross-linking of biomacromolecules such as pullulan and dextran with sodium trimetaphosphate could be performed during freeze-drying. We have demonstrated that the freeze-drying pressure modulates the degree of porosity. High freeze-drying pressure scaffolds presented pores with a mean diameter of 55 ± 4 μm and a porosity of 33 ± 12%, whereas low freeze-drying pressure scaffolds contained larger pores with a mean diameter of 243 ± 14 μm and a porosity of 68 ± 3%. Porous scaffolds of the desired shape could be easily obtained and were stable in culture medium for weeks. In vitro viable mesenchymal stem cells were found associated with porous scaffolds in higher proportions than with non-porous scaffolds. Moreover, cells penetrated deeper into scaffolds with larger pores. This novel combined freeze-drying/cross-linking processing of polysaccharides enabled the fabrication of biocompatible scaffolds with controlled porosity and architectures suitable for 3-D in vitro culture and biomedical applications.     

Mesenchymal stem cell proliferation and differentiation on load-bearing trabecular Nitinol scaffolds

Bone tissue regeneration in load-bearing regions of the body requires high-strength porous scaffolds capable of supporting angiogenesis and osteogenesis. 70% porous Nitinol (NiTi) scaffolds with a regular 3-D architecture resembling trabecular bone were produced from Ni foams using an original reactive vapor infiltration technique. The “trabecular Nitinol” scaffolds possessed a high compressive strength of 79 MPa and high permeability of 6.9 × 10^?6 cm². The scaffolds were further modified to produce a near Ni-free surface layer and evaluated in terms of Ni ion release and human mesenchymal stem cell (hMSC) proliferation (AlamarBlue), differentiation (alkaline phosphatase activity, ALP) and mineralization (Alizarin Red S staining). Scanning electron microscopy was employed to qualitatively corroborate the results. hMSCs were able to adhere and proliferate on both as-produced and surface-modified trabecular NiTi scaffolds, to acquire an osteoblastic phenotype and produce a mineralized extracellular matrix. Both ALP activity and mineralization were increased on porous scaffolds compared to control polystyrene plates. Experiments in a model coculture system of microvascular endothelial cells and hMSCs demonstrated the formation of prevascular structures in trabecular NiTi scaffolds. These data suggest that load-bearing trabecular Nitinol scaffolds could be effective in regenerating damaged or lost bone tissue.     

A biaxial rotating bioreactor for the culture of fetal mesenchymal stem cells for bone tissue engineering

The generation of effective tissue engineered bone grafts requires efficient exchange of nutrients and mechanical stimulus. Bioreactors provide a manner in which this can be achieved. We have recently developed a biaxial rotating bioreactor with efficient fluidics through in-silico modeling. Here we investigated its performance for generation of highly osteogenic bone graft using polycaprolactone–tricalcium phosphate (PCL–TCP) scaffolds seeded with human fetal mesenchymal stem cell (hfMSC). hfMSC scaffolds were cultured in either bioreactor or static cultures, with assessment of cellular viability, proliferation and osteogenic differentiation in vitro and also after transplantation into immunodeficient mice. Compared to static culture, bioreactor-cultured hfMSC scaffolds reached cellular confluence earlier (day 7 vs. day 28), with greater cellularity (2×, p < 0.01), and maintained high cellular viability in the core, which was 2000 μm from the surface. In addition, bioreactor culture was associated with greater osteogenic induction, ALP expression (1.5× p < 0.01), calcium deposition (5.5×, p < 0.001) and bony nodule formation on SEM, and in-vivo ectopic bone formation in immunodeficient mice (3.2×, p < 0.001) compared with static-cultured scaffolds. The use of biaxial bioreactor here allowed the maintenance of cellular viability beyond the limits of conventional diffusion, with increased proliferation and osteogenic differentiation both in vitro and in vivo, suggesting its utility for bone tissue engineering applications.     

Bone regeneration in rat calvarial defects implanted with fibrous scaffolds composed of a mixture of silicate and borate bioactive glasses

Previous studies have evaluated the capacity of porous scaffolds composed of a single bioactive glass to regenerate bone. In the present study, scaffolds composed of a mixture of two different bioactive glasses (silicate 13-93 and borate 13-93B3) were created and evaluated for their response to osteogenic MLO-A5 cells in vitro and their capacity to regenerate bone in rat calvarial defects in vivo. The scaffolds, which have similar microstructures (porosity = 58?67%) and contain 0, 25, 50 and 100 wt.% 13-93B3 glass, were fabricated by thermally bonding randomly oriented short fibers. The silicate 13-93 scaffolds showed a better capacity to support cell proliferation and alkaline phosphatase activity than the scaffolds containing borate 13-93B3 fibers. The amount of new bone formed in the defects implanted with the 13-93 scaffolds at 12 weeks was 31%, compared to values of 25, 17 and 20%, respectively, for the scaffolds containing 25, 50 and 100% 13-93B3 glass. The amount of new bone formed in the 13-93 scaffolds was significantly higher than in the scaffolds containing 50 and 100% 13-93B3 glass. While the 13-93 fibers were only partially converted to hydroxyapatite at 12 weeks, the 13-93B3 fibers were fully converted and formed a tubular morphology. Scaffolds composed of an optimized mixture of silicate and borate bioactive glasses could provide the requisite architecture to guide bone regeneration combined with a controllable degradation rate that could be beneficial for bone and tissue healing.     

Calcium alginate beads embedded in silk fibroin as 3D dual drug releasing scaffolds

3D scaffolds based on embedding drug loaded calcium alginate beads within silk fibroin protein were fabricated for investigating controlled dual drug release. The 3D matrices were evaluated for in vitro release using two different molecular weight model compounds, bovine serum albumin (66 kDa) and FITC–Inulin (3.9 kDa). The model compound release profiles revealed dependence on molecular weight of encapsulated model drugs for sustained release. Further, silk fibroin protein blended calcium alginate beads resulted in prolonged drug release without initial bursts for 35 days as compared to calcium alginate beads without silk fibroin as control. The release kinetics were further tested as a function of wt% silk content for scaffold fabrication suggesting their possible role in restricting initial burst and leading to sustainable release of compounds for prolong time. Silk coatings on calcium alginate beads provided mechanically stable shells as well as a diffusion barrier to the encapsulated protein drugs thus controlling their release. Scanning electron microscopic observations were carried out to assess cellular viability and biocompatibility of bead embedded-silk 3D scaffolds using fibroblast cells. The results highlight the versatile and tunable properties of calcium alginate embedded fibroin 3D scaffolds making them exciting candidate for the controlled release of a wide spectrum of bioactive molecules from a single delivery vehicle.     

Substrate stiffness and contractile behaviour modulate the functional maturation of osteoblasts on a collagen–GAG scaffold

Anchorage-dependent cells respond to the mechanical and physical properties of biomaterials. One such cue is the mechanical stiffness of a material. We compared the osteogenic potential of collagen–glycosaminoglycan (CG) scaffolds with varying stiffness for up to 6 weeks in culture. The mechanical stiffness of CG scaffolds were varied by cross-linking by physical (dehydrothermal (DHT)) and chemical (1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDAC) and glutaraldehyde (GLUT)) methods. The results showed that all CG substrates allowed cellular attachment, infiltration and osteogenic differentiation. CG scaffolds treated with EDAC and GLUT were mechanically stiffer, retained their original scaffold structure and resisted cellular contraction. Consequently, they facilitated a 2-fold greater cell number, probably due to the pore architecture being maintained, allowing improved diffusion of nutrients. On the other hand, the less stiff substrates cross-linked with DHT allowed increased cell-mediated scaffold contraction, contracting by 70% following 6 weeks (P < 0.01) of culture. This reduction in scaffold area resulted in cells reaching the centre of the scaffold quicker up to 4 weeks; however, at 6 weeks all scaffolds showed similar levels of cellular infiltration, with higher cell numbers found on the stiffer EDAC- and GLUT-treated scaffolds. Analysis of osteogenesis showed that scaffolds cross-linked with DHT expressed higher levels of the late stage bone formation markers osteopontin and osteocalcin (P < 0.01) and increased levels of mineralisation. In conclusion, the more compliant CG scaffolds allowed cell-mediated contraction and supported a greater level of osteogenic maturation of MC3T3 cells, while the stiffer, non-contractible scaffolds resulted in lower levels of cell maturation, but higher cell numbers on the scaffold. Therefore, we found scaffold stiffness had different effects on differentiation and cell number whereby the increased cell-mediated contraction facilitated by the less stiff scaffolds positively modulated osteoblast differentiation while reducing cell numbers.     

Injectable and porous PLGA microspheres that form highly porous scaffolds at body temperature

Injectable scaffolds are of interest in the field of regenerative medicine because of their minimally invasive mode of delivery. For tissue repair applications, it is essential that such scaffolds have the mechanical properties, porosity and pore diameter to support the formation of new tissue. In the current study, porous poly(dl-lactic acid-co-glycolic acid) (PLGA) microspheres were fabricated with an average size of 84 ± 24 μm for use as injectable cell carriers. Treatment with ethanolic sodium hydroxide for 2 min was observed to increase surface porosity without causing the microsphere structure to disintegrate. This surface treatment also enabled the microspheres to fuse together at 37 °C to form scaffold structures. The average compressive strength of the scaffolds after 24 h at 37 °C was 0.9 ± 0.1 MPa, and the average Young’s modulus was 9.4 ± 1.2 MPa. Scaffold porosity levels were 81.6% on average, with a mean pore diameter of 54 ± 38 μm. This study demonstrates a method for fabricating porous PLGA microspheres that form solid porous scaffolds at body temperature, creating an injectable system capable of supporting NIH-3T3 cell attachment and proliferation in vitro.     

Enhanced bone regeneration in rat calvarial defects implanted with surface-modified and BMP-loaded bioactive glass (13-93) scaffolds

The repair of large bone defects, such as segmental defects in the long bones of the limbs, is a challenging clinical problem. Our recent work has shown the ability to create porous scaffolds of silicate 13-93 bioactive glass by robocasting which have compressive strengths comparable to human cortical bone. The objective of this study was to evaluate the capacity of those strong porous scaffolds with a grid-like microstructure (porosity = 50%; filament width = 330 μm; pore width = 300 μm) to regenerate bone in a rat calvarial defect model. Six weeks post-implantation, the amount of new bone formed within the implants was evaluated using histomorphometric analysis. The amount of new bone formed in implants composed of the as-fabricated scaffolds was 32% of the available pore space (area). Pretreating the as-fabricated scaffolds in an aqueous phosphate solution for 1, 3 and 6 days to convert a surface layer to hydroxyapatite prior to implantation enhanced new bone formation to 46%, 57% and 45%, respectively. New bone formation in scaffolds pretreated for 1, 3 and 6 days and loaded with bone morphogenetic protein-2 (BMP-2) (1 μg per defect) was 65%, 61% and 64%, respectively. The results show that converting a surface layer of the glass to hydroxyapatite or loading the surface-treated scaffolds with BMP-2 can significantly improve the capacity of 13-93 bioactive glass scaffolds to regenerate bone in an osseous defect. Based on their mechanical properties evaluated previously and their capacity to regenerate bone found in this study, these 13-93 bioactive glass scaffolds, pretreated or loaded with BMP-2, are promising in structural bone repair.     

Mechanical properties of bioactive glass (13-93) scaffolds fabricated by robotic deposition for structural bone repair

There is a need to develop synthetic scaffolds to repair large defects in load-bearing bones. Bioactive glasses have attractive properties as a scaffold material for bone repair, but data on their mechanical properties are limited. The objective of the present study was to comprehensively evaluate the mechanical properties of strong porous scaffolds of silicate 13-93 bioactive glass fabricated by robocasting. As-fabricated scaffolds with a grid-like microstructure (porosity 47%, filament diameter 330 μm, pore width 300 μm) were tested in compressive and flexural loading to determine their strength, elastic modulus, Weibull modulus, fatigue resistance, and fracture toughness. Scaffolds were also tested in compression after they were immersed in simulated body fluid (SBF) in vitro or implanted in a rat subcutaneous model in vivo. As fabricated, the scaffolds had a strength of 86 ± 9 MPa, elastic modulus of 13 ± 2 GPa, and a Weibull modulus of 12 when tested in compression. In flexural loading the strength, elastic modulus, and Weibull modulus were 11 ± 3 MPa, 13 ± 2 GPa, and 6, respectively. In compression, the as-fabricated scaffolds had a mean fatigue life of ～10⁶ cycles when tested in air at room temperature or in phosphate-buffered saline at 37 °C under cyclic stresses of 1–10 or 2–20 MPa. The compressive strength of the scaffolds decreased markedly during the first 2 weeks of immersion in SBF or implantation in vivo, but more slowly thereafter. The brittle mechanical response of the scaffolds in vitro changed to an elasto-plastic response after implantation for longer than 2–4 weeks in vivo. In addition to providing critically needed data for designing bioactive glass scaffolds, the results are promising for the application of these strong porous scaffolds in loaded bone repair.     

Multi-functional P(3HB) microsphere/45S5 Bioglass®-based composite scaffolds for bone tissue engineering

Novel multi-functional P(3HB) microsphere/45S5 Bioglass®-based composite scaffolds exhibiting potential for drug delivery were developed for bone tissue engineering. 45S5 Bioglass®-based glass–ceramic scaffolds of high interconnected porosity produced using the foam-replication technique were coated with biodegradable microspheres (size < 2 μm) made from poly(3-hydroxybutyrate), P(3HB), produced using Bacillus cereus SPV. A solid-in-oil-in-water emulsion solvent extraction/evaporation technique was used to produce these P(3HB) microspheres. A simple slurry-dipping method, using a 1 wt.% suspension of P(3HB) microspheres in water, dispersed by an ultrasonic bath, was used to coat the scaffold, producing a uniform microsphere coating throughout the three-dimensional scaffold structure. Compressive strength tests confirmed that the microsphere coating slightly enhanced the scaffold mechanical strength. It was also confirmed that the microsphere coating did not inhibit the bioactivity of the scaffold when immersed in simulated body fluid (SBF) for up to 4 weeks. The hydroxyapatite (HA) growth rate on P(3HB) microsphere-coated 45S5 Bioglass® composite scaffolds was very similar to that on the uncoated control sample, qualitatively indicating similar bioactivity. However, the surface topography of the HA surface layer was affected as shown by results obtained from white light interferometry. The roughness of the surface was much higher for the P(3HB) microsphere-coated scaffolds than for the uncoated samples, after 7 days in SBF. This feature would facilitate cell attachment and proliferation. Finally, gentamycin was successfully encapsulated into the P(3HB) microspheres to demonstrate the drug delivery capability of the scaffolds. Gentamycin release kinetics was determined using liquid chromatography–mass spectrometry. The release of the drug from the coated composite scaffolds was slow and controlled when compared to the observed fast and relatively uncontrolled drug release from the bone scaffold (without microsphere coating). Thus, this unique multifunctional bioactive composite scaffold has the potential to enhance cell attachment and to provide controlled delivery of relevant drugs for bone tissue engineering.     

Unique microstructural design of ceramic scaffolds for bone regeneration under load

During the past two decades, research on ceramic scaffolds for bone regeneration has progressed rapidly; however, currently available porous scaffolds remain unsuitable for load-bearing applications. The key to success is to apply microstructural design strategies to develop ceramic scaffolds with mechanical properties approaching those of bone. Here we report on the development of a unique microstructurally designed ceramic scaffold, strontium–hardystonite–gahnite (Sr–HT–gahnite), with 85% porosity, 500 μm pore size, a competitive compressive strength of 4.1 ± 0.3 MPa and a compressive modulus of 170 ± 20 MPa. The in vitro biocompatibility of the scaffolds was studied using primary human bone-derived cells. The ability of Sr–HT–gahnite scaffolds to repair critical-sized bone defects was also investigated in a rabbit radius under normal load, with β-tricalcium phosphate/hydroxyapatite scaffolds used in the control group. Studies with primary human osteoblast cultures confirmed the bioactivity of these scaffolds, and regeneration of rabbit radial critical defects demonstrated that this material induces new bone defect bridging, with clear evidence of regeneration of original radial architecture and bone marrow environment.     

Repairing a critical-sized bone defect with highly porous modified and unmodified baghdadite scaffolds

This is the first reported study to prepare highly porous baghdadite (Ca₃ZrSi₂O₉) scaffolds with and without surface modification and investigate their ability to repair critical-sized bone defects in a rabbit radius under normal load. The modification was carried out to improve the mechanical properties of the baghdadite scaffolds (particularly to address their brittleness) by coating their surfaces with a thin layer (～400 nm) of polycaprolactone (PCL)/bioactive glass nanoparticles (nBGs). The β-tricalcium phosphate/hydroxyapatite (TCP/HA) scaffolds with and without modification were used as the control groups. All of the tested scaffolds had an open and interconnected porous structure with a porosity of ～85% and average pore size of 500 μm. The scaffolds (six per scaffold type and size of 4 mm × 4 mm × 15 mm) were implanted (press-fit) into the rabbit radial segmental defects for 12 weeks. Micro-computed tomography and histological evaluations were used to determine bone ingrowth, bone quality, and implant integration after 12 weeks of healing. Extensive new bone formation with complete bridging of the radial defect was evident with the baghdadite scaffolds (modified/unmodified) at the periphery and in close proximity to the ceramics within the pores, in contrast to TCP/HA scaffolds (modified/unmodified), where bone tended to grow between the ulna adjacent to the implant edge. Although the modification of the baghdadite scaffolds significantly improved their mechanical properties, it did not show any significant effect on in vivo bone formation. Our findings suggest that baghdadite scaffolds with and without modification can serve as a potential material to repair critical sized bone defects.     

Mechanical and microstructural properties of polycaprolactone scaffolds with one-dimensional,two-dimensional,and three-dimensional orthogonally oriented porous architectures produced by selective laser sintering

This article reports on the experimental determination and finite element modeling of tensile and compressive mechanical properties of solid polycaprolactone (PCL) and of porous PCL scaffolds with one-dimensional, two-dimensional and three-dimensional orthogonal, periodic porous architectures produced by selective laser sintering (SLS). PCL scaffolds were built using optimum processing parameters, ensuring scaffolds with nearly full density (>95%) in the designed solid regions and with excellent geometric and dimensional control (within 3–8% of design). The tensile strength of bulk PCL ranged from 10.5 to 16.1 MPa, its modulus ranged from 343.9 to 364.3 MPa, and the tensile yield strength ranged from 8.2 to 10.1 MPa. These values are consistent with reported literature values for PCL processed through various manufacturing methods. Across porosity ranged from 56.87% to 83.3%, the tensile strength ranged from 4.5 to 1.1 MPa, the tensile modulus ranged from 140.5 to 35.5 MPa, and the yield strength ranged from 3.2 to 0.76 MPa. The compressive strength of bulk PCL was 38.7 MPa, the compressive modulus ranged from 297.8 to 317.1 MPa, and the compressive yield strength ranged from 10.3 to 12.5 MPa. Across porosity ranged from 51.1% to 80.9%, the compressive strength ranged from 10.0 to 0.6 MPa, the compressive modulus ranged from 14.9 to 12.1 MPa, and the compressive yield strength ranged from 4.25 to 0.42 MPa. These values, while being in the lower range of reported values for trabecular bone, are the highest reported for PCL scaffolds produced by SLS and are among the highest reported for similar PCL scaffolds produced through other layered manufacturing techniques. Finite element analysis showed good agreement between experimental and computed effective tensile and compressive moduli. Thus, the construction of bone tissue engineering scaffolds endowed with oriented porous architectures and with predictable mechanical properties through SLS is demonstrated.     

Evaluation of bone regeneration in implants composed of hollow HA microspheres loaded with transforming growth factor β1 in a rat calvarial defect model

Implants that serve simultaneously as an osteoconductive matrix and as a device for local growth factor delivery may be required for optimal bone regeneration in some applications. In the present study, hollow hydroxyapatite (HA) microspheres (106–150 μm) in the form of three-dimensional (3-D) scaffolds or individual (loose) microspheres were created using a glass conversion process. The capacity of the implants, with or without transforming growth factor β1 (TGF-β1), to regenerate bone in a rat calvarial defect model was compared. The 3-D scaffolds supported the proliferation and alkaline phosphatase activity of osteogenic MLO-A5 cells in vitro, showing their cytocompatibility. Release of TGF-β1 from the 3-D scaffolds into phosphate-buffered saline ceased after 2–3 days when ～30% of the growth factor was released. Bone regeneration in the 3-D scaffolds and the individual microspheres increased with time from 6 to 12 weeks, but it was significantly higher (23%) in the individual microspheres than in the 3-D scaffolds (15%) after 12 weeks. Loading with TGF-β1 (5 μg per defect) enhanced bone regeneration in the 3-D scaffolds and individual microspheres after 6 weeks, but had little effect after 12 weeks. 3-D scaffolds and individual microspheres with larger HA diameter (150–250 μm) showed better ability to regenerate bone. Based on these results, implants composed of hollow HA microspheres show promising potential as an osteoconductive matrix for local growth factor delivery in bone regeneration.