A decellularized nerve matrix scaffold inhibits neuroma formation in the stumps of transected peripheral nerve after peripheral nerve injury.

Traumatic painful neuroma is an intractable clinical disease characterized by improper extracellular matrix (ECM) deposition around the injury site. Studies have shown that the microstructure of natural nerves provides a suitable microenvironment for the nerve end to avoid abnormal hyperplasia and neuroma formation. In this study, we used a decellularized nerve matrix scaffold (DNM-S) to prevent against the formation of painful neuroma after sciatic nerve transection in rats. Our results showed that the DNM-S effectively reduced abnormal deposition of ECM, guided the regeneration and orderly arrangement of axon, and decreased the density of regenerated axons. The epineurium-perilemma barrier prevented the invasion of vascular muscular scar tissue, greatly reduced the invasion of α-smooth muscle actin-positive myofibroblasts into nerve stumps, effectively inhibited scar formation, which guided nerve stumps to gradually transform into a benign tissue and reduced pain and autotomy behaviors in animals. These findings suggest that DNM-S-optimized neuroma microenvironment by ECM remodeling may be a promising strategy to prevent painful traumatic neuromas.

Nerve bundle formation during the promotion of peripheral nerve regeneration: collagen VI-neural cell adhesion molecule 1 interaction.

The formation of nerve bundles, which is partially regulated by neural cell adhesion molecule 1 (NCAM1), is important for neural network organization during peripheral nerve regeneration. However, little is known about how the extracellular matrix (ECM) microenvironment affects this process. Here, we seeded dorsal root ganglion tissue blocks on different ECM substrates of peripheral nerve ECM-derived matrix-gel, Matrigel, laminin 521, collagen I, and collagen IV, and observed well-aligned axon bundles growing in the peripheral nerve ECM-derived environment. We confirmed that NCAM1 is necessary but not sufficient to trigger this phenomenon. A protein interaction assay identified collagen VI as an extracellular partner of NCAM1 in the regulation of axonal fasciculation. Collagen VI interacted with NCAM1 by directly binding to the FNIII domain, thereby increasing the stability of NCAM1 at the axolemma. Our in vivo experiments on a rat sciatic nerve defect model also demonstrated orderly nerve bundle regeneration with improved projection accuracy and functional recovery after treatment with 10 mg/mL Matrigel and 20 µg/mL collagen VI. These findings suggest that the collagen VI-NCAM1 pathway plays a regulatory role in nerve bundle formation. This study was approved by the Animal Ethics Committee of Guangzhou Medical University (approval No. GY2019048) on April 30, 2019.

The effect of a nanofiber-hydrogel composite on neural tissue repair and regeneration in the contused spinal cord.

An injury to the spinal cord causes long-lasting loss of nervous tissue because endogenous nervous tissue repair and regeneration at the site of injury is limited. We engineered an injectable nanofiber-hydrogel composite (NHC) with interfacial bonding to provide mechanical strength and porosity and examined its effect on repair and neural tissue regeneration in an adult rat model of spinal cord contusion. At 28 days after treatment with NHC, the width of the contused spinal cord segment was 2-fold larger than in controls. With NHC treatment, tissue in the injury had a 2-fold higher M2/M1 macrophage ratio, 5-fold higher blood vessel density, 2.6-fold higher immature neuron presence, 2.4-fold higher axon density, and a similar glial scar presence compared with controls. Spared nervous tissue volume in the contused segment and hind limb function was similar between groups. Our findings indicated that NHC provided mechanical support to the contused spinal cord and supported pro-regenerative macrophage polarization, angiogenesis, axon growth, and neurogenesis in the injured tissue without any exogenous factors or cells. These results motivate further optimization of the NHC and delivery protocol to fully translate the potential of the unique properties of the NHC for treating spinal cord injury.

Tissue engineering for the repair of peripheral nerve injury.

Peripheral nerve injury is a common clinical problem and affects the quality of life of patients. Traditional restoration methods are not satisfactory. Researchers increasingly focus on the field of tissue engineering. The three key points in establishing a tissue engineering material are the biological scaffold material, the seed cells and various growth factors. Understanding the type of nerve injury, the construction of scaffold and the process of repair are necessary to solve peripheral nerve injury and promote its regeneration. This review describes the categories of peripheral nerve injury, fundamental research of peripheral nervous tissue engineering and clinical research on peripheral nerve scaffold material, and paves a way for related research and the use of conduits in clinical practice.

Spatial distribution affects the role of CSPGs in nerve regeneration via the actin filament-mediated pathway.

CSPGs are components of the extracellular matrix in the nervous system, where they serve as cues for axon guidance during development. After a peripheral nerve injury, CSPGs switch roles and become axon inhibitors and become diffusely distributed at the injury site. To investigate whether the spatial distribution of CSPGs affects their role, we combined in vitro DRG cultures with CSPG stripe or coverage assays to simulate the effect of a patterned substrate or dispersive distribution of CSPGs on growing neurites. We observed neurite steering at linear CSPG interfaces and neurite inhibition when diffused CSPGs covered the distal but not the proximal segment of the neurite. The repellent and inhibitory effects of CSPGs on neurite outgrowth were associated with the disappearance of focal actin filaments on growth cones. The application of an actin polymerization inducer, jasplakinolide, allowed neurites to break through the CSPG boundary and grow on CSPG-coated surfaces. The results of our study collectively reveal a novel mechanism that explains how the spatial distribution of CSPGs determines whether they act as a cue for axon guidance or as an axon-inhibiting factor. Increasing our understanding of this issue may promote the development of novel therapeutic strategies that regulate the spatial distributions of CSPGs to use them as an axon guidance cue.

A comparative study of gelatin sponge scaffolds and PLGA scaffolds transplanted to completely transected spinal cord of rat.

This study sought to investigate whether gelatin sponge (GS) scaffold would produce less acidic medium in injured spinal cord, as compared with poly(lactic-co-glycolic acid) (PLGA) scaffold, to determine which of the two scaffolds as the biomaterial is more suitable for transplantation into spinal cord. GS scaffold or PLGA scaffold was transplanted into a transected spinal cord in this study. Two months after transplantation of scaffolds, acid sensing ion channel 1a (ASIC1a) positive cells expressing microtubule associated protein 2 (Map2) were observed as well as expressing adenomatous polyposis coli (APC) in spinal cord. GFAP positive cells were distributed at the rostral and caudal of the injury/graft area in the GS and PLGA groups. Western blot showed ASIC1a and GFAP expression of injured spinal cord was downregulated in the GS group. The number of CD68 positive cells was fewer and NF nerve fibers were more in the GS group. Nissl staining and cell counting showed that the number of survival neurons was comparable between the GS and PLGA groups in the pyramidal layer of sensorimotor cortex and the red nucleus of midbrain. However, in the Clarke's nucleus at L1 spinal segment, the surviving neurons in the GS group were more numerous than that in the PLGA group. H&E staining showed that the tissue cavities in the GS group were smaller in size than that in the PLGA group. The results suggest that GS scaffold is more suitable for transplantation to promote the recovery of spinal cord injury compared with PLGA scaffold.

[Fabrication of tissue engineered vein containing valve scaffolds].

OBJECTIVE: To fabricate porous biodegradable tissue engineered vein containing valve scaffolds. METHODS: Based on the self-made cast, the tissue engineered vein containing valve scaffolds was fabricated by injection molding plus thermally induced phase separation. Poly (lactic-co-glycolic acid) (PLGA, LA/GA mole ratio 75:25) was used as matrices. Morphological structures and biocompatibility of scaffolds were tested. Cell seeding on scaffold was performed and the mechanic characteristics of cellular constructs evaluated. RESULTS: The scaffold had an inner diameter of 9 mm with a wall thickness of 0.9 mm and the thickness of valves was (0.32 ± 0.04) mm. Scanning electron microscopic (SEM) micrographs showed regular ladder-like porous structures and the average pore size and porosity of scaffolds were 10 - 20 µm and 90%. The PLGA scaffolds were biocompatible. The cellular constructs were tested in vitro, and the valve leaflets were functionally capable of opening and closing when stimulated. CONCLUSION: Based on the self-made cast, the tissue engineered vein containing valve scaffolds can be fabricated by injection molding plus thermally induced phase separation. Further researches are warranted.

Coseeded Schwann cells myelinate neurites from differentiated neural stem cells in neurotrophin-3-loaded PLGA carriers.

Biomaterials and neurotrophic factors represent promising guidance for neural repair. In this study, we combined poly-(lactic acid-co-glycolic acid) (PLGA) conduits and neurotrophin-3 (NT-3) to generate NT-3-loaded PLGA carriers in vitro. Bioactive NT-3 was released stably and constantly from PLGA conduits for up to 4 weeks. Neural stem cells (NSCs) and Schwann cells (SCs) were coseeded into an NT-releasing scaffold system and cultured for 14 days. Immunoreactivity against Map2 showed that most of the grafted cells (>80%) were differentiated toward neurons. Double-immunostaining for synaptogenesis and myelination revealed the formation of synaptic structures and myelin sheaths in the coculture, which was also observed under electron microscope. Furthermore, under depolarizing conditions, these synapses were excitable and capable of releasing synaptic vesicles labeled with FM1-43 or FM4-64. Taken together, coseeding NSCs and SCs into NT-3-loaded PLGA carriers increased the differentiation of NSCs into neurons, developed synaptic connections, exhibited synaptic activities, and myelination of neurites by the accompanying SCs. These results provide an experimental basis that supports transplantation of functional neural construction in spinal cord injury.

Neurotrophin-3 gene-modified Schwann cells promote TrkC gene-modified mesenchymal stem cells to differentiate into neuron-like cells in poly(lactic-acid-co-glycolic acid) multiple-channel conduit.

Rapid progress in the field of nerve tissue engineering has opened up the way for new therapeutic strategies for spinal cord injury (SCI). Bone marrow-derived mesenchymal stem cells (MSCs) could be differentiated into neural lineages, which can be used as a potential cell source for nerve repair. Schwann cells (SCs) have been reported to support structural and functional recovery of SCI. In this study, we co-cultured neurotrophin-3 (NT-3) gene-modified SCs and NT-3 receptor tyrosine protein kinase C (TrkC) gene-modified MSCs in a three-dimensional porous poly(lactic-acid-co-glycolic acid) (PLGA) conduit with multiple channels in vitro for 14 days. Our results showed that more than 50% of the grafted MSCs were MAP2- and ß-III-tubulin-positive cells, and the MSCs expressed a high level of ß-III-tubulin detected by Western blotting, indicating a high rate of neuronal differentiation. Furthermore, immunostaining of PSD95 revealed the formation of a synapse-like structure, which was confirmed under electron microscopy. In conclusion, co-culture of NT-3 gene-modified SCs and TrkC gene-modified MSCs in the PLGA multiple-channeled conduit can promote MSCs' differentiation into neuron-like cells with synaptogenesis potential. Our study provides a biological basis for future application of this artificial MSCs/SCs/PLGA complex in the SCI treatment.

Transplantation of artificial neural construct partly improved spinal tissue repair and functional recovery in rats with spinal cord transection.

Delivery of cellular and/or trophic factors to the site of injury may promote neural repair or axonal regeneration and return of function after spinal cord injury. Engineered scaffolds provide a platform to deliver therapeutic cells and neurotrophic molecules. To explore therapeutic potential of engineered neural tissue, we generated an artificial neural construct in vitro, and transplanted this construct into a completely transected spinal cord of adult rats. Two months later, behavioral analysis showed that the locomotion recovery was significantly improved compared with control animals. Immunoreactivity against microtubule associated protein 2 (Map2) and postsynaptic density 95 (PSD95) demonstrated that grafted cells had a higher survival rate and were able to differentiate toward neuronal phenotype with ability to form synapse-like structure at the injury site; this was also observed under the electron microscope. Immunostaining of neurofilament-200 (NF-200) showed that the number of nerve fibers regrowing into the injury site in full treatment group was much higher than that seen in other groups. Furthermore, Nissl staining revealed that host neuron survival rate was significantly increased in rats with full treatments. However, there were no biotin dextran amine (BDA) anterograde tracing fibers crossing through the injury site, suggesting the limited ability of corticospinal tract axonal regeneration. Taken together, although our artificial neural construct permits grafted cells to differentiate into neuronal phenotype, synaptogenesis, axonal regeneration and partial locomotor function recovery, the limited capacity for corticospinal tract axonal regeneration may affect its potential therapy in spinal cord injury.

Bone induction by biomimetic PLGA-(PEG-ASP)n copolymer loaded with a novel synthetic BMP-2-related peptide in vitro and in vivo.

BMP-2 is one of the most important growth factors of bone regeneration. Polylactide-co-glycolic acid (PLGA), which is used as a biodegradable scaffold for delivering therapeutic agents, has been intensively investigated. In previous studies, we synthesized a novel BMP-2-related peptide (designated P24) and found that it could enhance the osteoblastic differentiation of bone marrow stromal cells (BMSCs). The objective of this study was to construct a biomimetic composite by incorporating P24 into a modified PLGA-(PEG-ASP)n copolymer to promote bone formation. In vitro, our results demonstrated that PLGA-(PEG-ASP)n scaffolds were shown to be an efficient system for sustained release of P24. Significantly more BMSCs attached to the P24/PLGA-(PEG-ASP)n and PLGA-(PEG-ASP)n membranes than to PLGA, and the cells in the two groups subsequently proliferated more vigorously than those in the PLGA group. The expression of osteogenic markers in P24/PLGA-(PEG-ASP)n group was stronger than that in the PLGA-(PEG-ASP)n and PLGA groups. Radiographic and histological examination, Western blotting and RT-PCR showed that P24/PLGA-(PEG-ASP)n scaffold could induce more effective ectopic bone formation in vivo, as compared with PLGA-(PEG-ASP)n or gelatin sponge alone. It is concluded that the PLGA-(PEG-ASP)n copolymer is a good P24 carrier and can serve as a good scaffold for controlled release of P24. This novel P24/PLGA-(PEG-ASP)n composite promises to be an excellent biomaterial for inducing bone regeneration.

[Preparation and property of platinum microcoil modified by a copolymer-VEGF conjugate].

OBJECTIVE: To prepare a platinum microcoil coated with polymers and vascular endothelial growth factor (VEGF), and evaluate its surface characteristics and property of sustained VEGF release. METHODS: The surface of the platinum microcoils (GDC) were modified by coating P(DLLA-co-TMC) copolymer and immobilizing heparin on the surface of GDC. VEGF was then loaded onto the surface of GDC and the controlled release of VEGF within GDC was achieved. The morphology was observed by scanning electron microscope, and the sustained release of VEGF was evaluated by enzyme-linked immunosorbent assay (ELISA). RESULTS: Platinum coils were prepared by successive deposition of P(DLLA-co-TMC) copolymer and anionic heparin, and VEGF was immobilized through affinity interaction with heparin. The accumulative release of VEGF increased obviously during the entire testing period without burst release. CONCLUSION: The use of P(DLLA-co-TMC) copolymer allows immobilization of VEGF on the platinum coils for controlled VEGF release, and improves the biological property of the coils.

Synaptic transmission of neural stem cells seeded in 3-dimensional PLGA scaffolds.

To explore therapeutic potential of engineered neural tissue, we combined genetically modified neural stem cells (NSCs) and poly(lactic acid-co-glycolic acid) (PLGA) polymers to generate an artificial neural network in vitro. NSCs transfected with either NT-3 or its receptor TrkC gene were seeded into PLGA scaffold. The NSCs were widely distributed and viable in the scaffold after culturing for 14 days. Immunoreactivity against Map2 was detected in >70% of these grafted cells, suggesting a high rate of differentiation toward neurons. Immunostaining of synapsin-I and PSD95 revealed formation of synaptic structures, which was also observed under electron microscope. Furthermore, using FM1-43 dynamic imaging, synapses in these differentiated neurons were found to be excitable and capable of releasing synaptic vesicles. Taken together, our artificial PLGA construct permits NSCs to differentiate toward neurons, establish connections and exhibit synaptic activities. These findings provide a biological basis for future application or transplantation of this artificial construct in neural repair.

Preliminary study of the effect of FK506 nanospheric-suspension eye drops on rejection of penetrating keratoplasty.

OBJECTIVE: The aim of this study was to investigate the effect of a topical FK506 nanospheric suspension in a rat model of penetrating keratoplasty. METHODS: FK506 nanospheres were prepared by using a biodegradable poly (lactic-co-glycolic acid) copolymer (PLGA). Its distribution in the eye and blood after a single instillation was examined in rabbits. Sprague-Dawley (SD) rats received corneal heterografts and were topically treated with phosphate-buffered saline (PBS), PLGA, FK-506 0.01% (nanospheres), or dexamethasone 0.05% solutions twice a day for 28 days. Rejection index and graft-survival time were recorded and compared between the four groups. Three grafts were collected at different time points for immunohistochemical studies. RESULTS: In the cornea, the FK-506 concentration reached its peak within 1 h of a single eye-drop instillation and then decreased by half (1667.85 +/- 611.87 ng/g) at 8 h. FK-506 cannot be detected in rabbit blood. There were significant differences in the graft-survival time between the FK-506 nanosphere group (15.09 +/- 4.81 days) and the other three groups [PBS (7.90 +/- 1.20, t = -4.594, P < 0.001), PLGA (8.44 +/- 0.88, t = - 4.074, P = 0.001) and dexamethasone (10.44 +/- 1.42, t = -2.790, P = 0.012)]. The rejected corneas in the FK506 nanosphere group showed significantly fewer CD4, CD8, CD68, CD79, vascular endothelial growth factor, ICAM, and tumor growth factor-beta(1)-positive cells than those in the other groups. CONCLUSIONS: FK506 0.01% nanospheric-suspension eye drops delayed the occurrence of corneal allograft rejection and prolonged allograft survival time. The FK506 nanospheres may be valuable in suppressing corneal graft rejection.

Preparation and characterization of cationic chitosan-modified poly(D,L-lactide-co-glycolide) copolymer nanospheres as DNA carriers.

Chitosan (CS)-modified poly(D,L-lactide-co-glycolide) (PLGA/CS) nanoparticles with cationic surface were prepared by means of emulsion-solvent evaporation technique using polyviny alcohol and chitosan as costabilizers. The preparation conditions of the cationic nanoparticles were optimized by orthogonal factorial design, and the influences of the experiment variables such as polymer concentration, the molecular weight of chitosan, etc., on the size and zeta potential of the nanoparticles were evaluated. It was shown that the diameter of the PLGA/CS nanoparticles can be controlled in the range of 150-200 nm as determined by dynamic light scattering with the optimized conditions. The zeta potential of PLGA/CS nanoparticles increased with increasing the concentration of CS (C(CS)) or decreasing the pH, it was up to 55 mV when C(CS) was 3 mg/mL at pH 4 and inversed around pH 8. The optimization conditions for fabricating the relatively small diameter and high zeta potential cationic nanoparticles were C(CS) 3 mg/mL, C(PLGA) 10 mg/mL, and the volume ratio of organic solution to aqueous medium 1/4. X-ray photo electron spectroscopy and fluorescence inverted microscope observations approved that CS molecules were adsorbed on the surface of PLGA nanoparticles, DNA-condensing ability of the PLGA/CS nanoparticles and cell transfection efficiency of the nanoparticle-DNA complexes were estimated by gel electrophoresis and transfection experiment to 293FT cell, respectively.

Biodegradable chitosan scaffolds containing microspheres as carriers for controlled transforming growth factor-beta1 delivery for cartilage tissue engineering.

BACKGROUND: Natural articular cartilage has a limited capacity for spontaneous regeneration. Controlled release of transforming growth factor-beta1 (TGF-beta1) to cartilage defects can enhance chondrogenesis. In this study, we assessed the feasibility of using biodegradable chitosan microspheres as carriers for controlled TGF-beta1 delivery and the effect of released TGF-beta1 on the chondrogenic potential of chondrocytes. METHODS: Chitosan scaffolds and chitosan microspheres loaded with TGF-beta1 were prepared by the freeze-drying and the emulsion-crosslinking method respectively. In vitro drug release kinetics, as measured by enzyme-linked immunosorbent assay, was monitored for 7 days. Lysozyme degradation was performed for 4 weeks to detect in vitro degradability of the scaffolds and the microspheres. Rabbit chondrocytes were seeded on the scaffolds containing TGF-beta1 microspheres and incubated in vitro for 3 weeks. Histological examination and type II collagen immunohistochemical staining was performed to evaluate the effects of released TGF-beta1 on cell adhesivity, proliferation and synthesis of the extracellular matrix. RESULTS: TGF-beta1 was encapsulated into chitosan microspheres and the encapsulation efficiency of TGF-beta1 was high (90.1%). During 4 weeks of incubation in lysozyme solution for in vitro degradation, the mass of both the scaffolds and the microspheres decreased continuously and significant morphological changes was noticed. From the release experiments, it was found that TGF-beta1 could be released from the microspheres in a multiphasic fashion including an initial burst phase, a slow linear release phase and a plateau phase. The release amount of TGF-beta1 was 37.4%, 50.7%, 61.3%, and 63.5% for 1, 3, 5, and 7 days respectively. At 21 days after cultivation, type II collagen immunohistochemical staining was performed. The mean percentage of positive cells for collagen type II in control group (32.7% +/- 10.4%) was significantly lower than that in the controlled TGF-beta1 release group (92.4% +/- 4.8%, P < 0.05). Both the proliferation rate and production of collagen type II in the transforming growth factor-beta1 microsphere incorporated scaffolds were significantly higher than those in the scaffolds without microspheres, indicating that the activity of TGF-beta1 was retained during microsphere fabrication and after growth factor release. CONCLUSION: Chitosan microspheres can serve as delivery vehicles for controlled release of TGF-beta1, and the released growth factor can augment chondrocytes proliferation and synthesis of extracellular matrix. Chitosan scaffolds incorporated with chitosan microspheres loaded with TGF-beta1 possess a promising potential to be applied for controlled cytokine delivery and cartilage tissue engineering.

[Bone defect repair with a new tissue-engineered bone carrying bone morphogenetic protein in rabbits].

OBJECTIVE: To construct a new tissue-engineered bone with poly (D, L-lactide-co-glycolide) (PLGA), bone morphogenetic protein (BMP) and bone marrow-derived stem cells (BMSCs) and observe its effect in repairing segmental bone defects. METHODS: A 15-mm bone defect in the right radius was induced in New Zealand white rabbits, and the models were randomized into three groups to receive implantation of the tissue-engineered bone grafts constructed with PLGA carrying 5 mg BMP and about 1 x 10(6) BMSCs (experimental group), grafts of PLGA with about 1 x 10(6) BMSCs (control group), or grafts of exclusive PLGA (blank control group), respectively. The osteogenesis in the bone defect after the implantation on was evaluated X-ray films, and the histological changes of the tissues sampled from the bone defect 4, 8, and 12 weeks after operation were observed and new bone formation was measured by image analysis. RESULTS: The bone defect was completely repaired in the experimental group 12 weeks after the implantation, showing the best results among the 3 groups. The bone defects in the blank control group was filled with only fibrous and connective tissues at 12 weeks. CONCLUSION: This tissue-engineered bone constructed with PLGA, BMP and BMSCs possesses good ability in repairing segmental bone defect.

[In vitro degradation and subsequent biomechanical changes of poly(lactide-co-glycolide) scaffolds prepared by mild heating under high pressure].

OBJECTIVE: To study the changes in biomechanics and such indices as intrinsic viscosity poly (lactide-co-glycolide) (PLGA) scaffolds produced by mild heating under high pressure after in vitro degradation. METHODS: PLGA scaffolds with the porosity of 90.0% and 92.5% respectively were immerged in 37 degrees Celsius; saline for 8 weeks, and the changes in their mass, intrinsic viscosity and loss of compressive strength were assessed on a weekly basis, and the acidity of the degradation solution was also measured regularly. RESULTS: Significant differences was noted in the mass reduction between the scaffolds, and the intrinsic viscosity began to decrease in both groups in the first week to half of the original value till the sixth week. A 50% reduction in the compressive strength of the scaffolds occurred at the fourth week, and till the eighth week, obvious structural collapse was observed. Along with the changes, the acidity of the degradation solution increased from 6.0 to 6.5, and the solution of 90.0% porosity group had lower pH value during the first 4 weeks than 92.5% porosity group, but such difference was no longer seen afterwards. CONCLUSIONS: PLGA scaffolds made by mild heating under high pressure have stable biomechanical performance with the half-life of approximately 6 weeks, which can be applicable for tissue engineering.

Effect of pore size of D, L-polylactic acid as bone repair material on bone regeneration.

OBJECTIVE: To study the bone regeneration behavior in porous D,L-polylactic acid (D,L-PLA) with different pore sizes. METHOD: A particulate-leaching method was employed to prepare porous biodegradable D,L-PLA with different pore sizes (75, 250, 400, 750 micrometer) and with porosity of 75% as the materials to repair bone defects in rabbits. The materials were then implanted at random into 40 rabbits with bilateral radius bone defect, leaving another 10 rabbits without implantation as blank control. Gross observation and X-ray and histomorphological examination as well as assessment of the biomechanics of the implants were performed in 2, 4, 8 and 12 weeks respectively after the operation. RESULTS: New bone tissue occurred around the implanted materials with pore sizes of 250, 400 or 750 micrometer 12 weeks after the operation. In the control group and in the rabbits with implants with pore size of 75 micrometer, the bone defect was filled with connective tissues. The implants with 250-micrometer pores had the strongest biomechanical strengths of all the materials (P<0.01) at 8 weeks and 12 weeks after the operation. CONCLUSION: The pore size of the porous implants decides the behavior of bone regeneration, and D, L-PLA polymer with 250-micrometer pores produces the most desired effects.

[Analysis of three-dimensional microstructure of poly(lactide-co-glycolide) scaffolds made by mild heating under high pressure].

OBJECTIVE: To develop a poly(lactide-co-glycolide)(PLGA) copolymer scaffold with good three-dimensional microstructure and free of organic solvent, which can be used in bone repairing for tissue engineering, and to explore a novel method for developing polymeric scaffolds. METHODS: The polymer and sodium chloride were ground to powder and mixed in 2 different proportions as the materials for preparing the scaffolds by mild heating under high pressure. The porosity and the ratio of open pores in the product were analyzed in light of its density and by sodium chloride approaches, with the pore size, surface and internal structures examined under scanning electron microscope (SEM). RESULTS: The PLGA scaffolds made by this method had porosity of 90 % and 92.5 % respectively, their pore size ranging from 200 to 250 micro m with the ratio of open pores exceeding 98 % (P<0.01). The average sodium chloride leaching time was 12 to 13 h. CONCLUSIONS: The scaffolds made in this way possess stable three-dimensional microstructure with controllable parameters and without cytotoxic effects caused by organic solvent.