Abstract： The first generation scaffolds of bare metal stents （BMS） and the second generation of drug eluting stents （DES） have been widely used in the treatment of coronary heart diseases. However, long term incidences of major adverse cardiovascular events and revascularization treatments are still high because of in-stent re-stenosis and thrombosis. These may be caused by chronic inflammations and vascular wall damages due to persistent metal stents stimulation. What’s more, the eluting drugs within metal stents could also disturb normal growth of vascular endothelial cell, intima, tunica media, smooth muscle and epimysium. Therefore, in order to meet these demands several fully biodegradable scaffolds and drug carried stents have been manufactured using polymers polyester, polycarbonate and polyphosphate, etc. Among them, the security and histo-and hemo-compatibilities of coronary scaffolds made from poly-lactic acid （PLA）, poly-glycolic acid（PGA）, chitosan as coating, poly-caprolactone （PCL） and other copolymer like poly-lactic-co-glycolic acid （PLGA） have been testified to be sound. Nevertheless, there exist several different shortages for these stents such as tensile strength deficiency and slow degradation. PLA is hard and brittle with slow degradation, while PGA is soft with insufficient support force and fast degradation. Whether stents degrade too fast or too slow, they could not supply sufficient strength and effective support after implantation, and also they may cause target vascular injuries and elastic shrink inducing restenosis and thrombosis in long terms. Using optimized molar ratio component of PLA and PGA with chitosan coating, we can get sound composite materials with better biocompatibility, moderate degradation （approximately 3 - 6 months of completedegradation）, adequate mechanical strength, lower inflammatory response and good range of extension, and establish an experiment ground for fully biodegradable vascular scaffolds fabrication.
Objective To study and test novel hybrid valves in vitro and in vivo, and provide basis for clinical use in future. Methods The hybrid valves were fabricated from decellularized porcine aortic valves coated with poly (3-hydroxybutyrate-co-3hydroxyhexanoate, PHBHHx).（1）In the mechanical test in vitro, the uniaxial tensile biomechanics test of the fresh (n=12), uncoated (n=12) and hybrid valve leaflets (n=12) were investigated. (2）In study in vivo, hybrid valves(n=5) implanted in pulmonary position in sheep without cardiopulmonary bypass. Uncoated grafts (n=5) used as control. The specimens of the hybrid or uncoated valve in sheep were explanted and examined by scanning electron microscopy, histology, calcium content and immunofluorescence staining 18 weeks after surgery. Results The mechanical test in vitro revealed that coating with PHBHHx increased maximal tensile strength of hybrid valves compared with the fresh and uncoated state (P＜0.05). The results in vivo indicated the hybrid valves maintained original shape and softness. Immunofluorescence staining for CD31 confirmed that the surface of hybrid valve was covered by confluent CD31+ cells.The interstitium of hybrid valve indicated that smooth muscle actin (SMA)+ cells population were similar to native valvular tissue. The calcium content of hybrid valve was significantly lower than that of uncoated valve leaflets (P＜0.05). Conclusion Decellularized porcine aortic valves coated with PHBHHx have good biological and biomechanical characteristics. The hybrid valve may provide superior valve replacement with current techniques.
Objective To summarize the basic research and the cl inical appl ication of biodegradable interbody fusion Cage. Methods Recent l iterature concerning biodegradable interbody fusion Cage at home and abroad was extensively reviewed, and current developments of the basic research and the cl inical appl ication of biodegradable interbody fusion Cage were investigated. Results Basic research showes that the stiffness of biodegradable interbody fusion Cage is lower than that of metall ic Cage, so it can enhance interbody fusion. As interbody fusion proceeded, biodegradable interbody fusion Cage degrades constantly, but the speed of degradation can not keep in parallel with that of fusion. In addition, the tissue response to degradation products is controversy. Cl inical appl ication showes that the biodegradable interbody fusion Cage can enhance interbody fusion and maintain disc space height. The short term results are good, however, the long term results need further observation. Conclusion Biodegradable interbody fusion Cage can effectively enhance interbody fusion.
Objective To sum up the recent progress of common biodegradable internal fixation materials and to forecast the possible directions for further research. Methods The latest original articles about biomechanical properties, degradation characteristics, advantages and disadvantages of biodegradable internal fixation materials were extensively reviewed.Several common biodegradable materials were selected and expounded in different categories. Results The disadvantages of stress shielding and the second time removal, could be avoided by using biodegradable internal fixation materials instead of metal materials. Biodegradable internal fixation materials could fix fracture stably and they were ideal orthopedic internal fixation materials. Natural biodegradable polymers had excellent biocompatibil ity but poor mechanical strength. Synthetic biodegradable materials could be artificially regulated their degradation rate and had better mechanical strength, however, they had shortcomings in biocompatibil ity. Composite materials could learn from others’ b points to offset their weakness, therefore, they had pronounced advantages over the former two materials. Conclusion There still exist many problems in present biodegradable internal fixation materials although they are of great potential in its appl ication. Combining various biomaterials and using the specific processing technology to develop a biodegradable material which has better biomechanical properties, chemical properties and physical structure is the direction for future research.
Objective To explore a way to make a new kind of chitosan-basedmicrosphere (MS), which can be used as a novel biodegradable haemostatic powder, and to confirm its haemostatic efficiency. MethodsChitosan(CTS), a haemostatic polysaccharide, was selected as a main material for the haemostatic powder; alginate (ALG), another haemostatic polysaccharide that has been found to be effective in promoting haemostasis in surgical procedures, was selected to be thecostar. The emulsification and the cross-link were chosen as a preparation process based on the interaction between the polysaccharides. The diameter of the prepared MS was determined by SPOS, and the surface of MS was observed under SEM. The swelling characteristics of MS in the simulative wound efflusion were investigated. In a splenic bleeding model in 6 rabbits, MS and Yunnanbaiyao were randomly used as a haemostatic agent, and the corresponding bleeding time was recorded. Results The MS prepared in the above-mentioned process was well proportioned and was similarly shaped. It became a kind of white powder after dehydration, and had a coralloid surface under SEM. The diameter of the MS was 4.05±2.55 μm, which was determined by SPOS. The swelling ratio of the MS was 280.139% within 5 min. The bleeding time was significantly decreased in the MStreated group (2.83±0.17 min) when compared with that in the control group (5.33±0.49 min)(P＜0.01). Conclusion The CTS/ALG-MS, which is made from haemostatic biomaterials (CTS, ALG) by emulsification and the cross-link processes, can be provided with favorable haemostatic efficiency. It can be used as a novel haemostaticpowder.However, its biodegrading rate and mode still remain to be further studied.
Objective To evaluate the biocompatibility and in vivo degradation of novel chest wall prosthesis materials and provide some data for their clinical application. MethodsAccording to the standard for the biological evaluation of the medical devices, several tests were performed to evaluate the tissue toxic effects induced by polydioxanone (Group A), chitosan (Group B), and hydroxyapitite/collagen (Group C),which were tested as component materials of the chest wall prosthesis. In the hemolysis test, 0.2 ml of the anticoagulant rabbit blood was added to the component materials and the normal saline (negative control) and to the distilled water(positive control). Five samples were made in each group. Absorbency was measured and the hemolysis rate was determined. In the acute systemic toxicity test, 20 mice were randomly divided into 4 groups (Groups A, B and C, and the normal saline group, n=5). The leaching liquid (50 ml/kg) was injected through the caudal vein, which was observed at 24, 48 and 72 hours. In the pyrogen test, 12 rabbits were randomly divided into 4 groups (Groups A, B, C and the normal saline group, n=3) the leaching liquid(10 ml/kg) was injected through the ear vein,and the body temperature was recorded within 3 hours. In the in vivo degradable test, the component materials (10 mm×10 mm) were implanted in 12 rabbits at 2, 4, 8, 12, 16 and 24 weeks, respectively, after operation. Two rabbitswere sacrificed for the macroscopic and the microscopic examinations. Results The chest wall component materials had no hemolytic reaction, no acute systemic toxicity, and no pyrogen reaction. The results demonstrated that the implanted materials had only a mild inflammatory reaction during the early days of the grafting, which subsided gradually. There was no tissue denaturation, necrosis or pathological hyperplasia when the prosthesis materials were degraded. Conclusion The degradable materials of the chest wall prosthesis have a good biocompatibility and agreat biological safety though their surgical application still requires a further clinical research.
OBJECTIVE: To prepare the compound biodegradable matrices, polyglycolic acid (PGA), polylactic acid (PLA) mesh and poly-beta-hydroxybutyrate(PHB) which precoated with collagen, and to observe the growth and differentiation of bovine vascular endothelial cells on these scaffolds. METHODS: By enzymatic digestion methods, bovine vascular endothelial cell (VEC) were isolated from calf thoracic aorta, then cultured and purified. PGA, PLA, PHB meshes were dipped into cross-linked type I collagen solution, dried under vacuum frozen condition. VEC were seeded into these scaffolds. The growth of VEC on scaffolds was analyzed by MTT method. RESULTS: The collagen, PGA/collagen, PLA/collagen scaffolds were elasticity and tenacity. VEC grew better on collagen, PGA/collagen, and PLA/collagen membranes than on the PHB/collagen one. CONCLUSION: The PGA/collagen scaffold has elasticity, plasticity and tenacity. VEC grow best on it. It is an ideal scaffold for tissue engineered vessel reconstruction for it integrating both advantages of biomaterials and degradable materials.
OBJECTIVE: To investigate protection of biological activity and controlled release of growth factor by means of drug controlled release technique in tissue engineering. METHODS: Using drug controlled release technique that to embed or microcapsulate the biological drug with biodegradable polymer. RESULTS: The aliphatic polylactone could be used as drug carrier for each drug including the biological matter. And the release behavior of the drug could be controlled by adjusting the molecular structure of the carrier and the controlled release method. The successful example, that to realize regeneration of rat’s sciatic nerve with 5, 10, 15 and 20 mm of gap by using polylactide as nerve guide and the embedding growth factor, had been obtained. CONCLUSION: It is possible to realize protection of biological activity and sustained release of growth factor by using aliphatic polylactone as drug carrier.
OBJECTIVE: To investigate the selection and manufacture of ideal extracellular matrix materials in bone tissue engineering. METHODS: The recent literatures about biodegradable polymers served as culture scaffolds of osteoblasts were widely reviewed, the advantages and disadvantages of biodegradable synthetic polymers and natural polymers were analysed. RESULTS: The ideal extracellular matrix material in bone tissue engineering should be made up of inorganic materials, synthetic polymers and natural polymers, which possesses morphological structure of three-dimensional foam with self-mediated drug slow delivery system of bone growth factors. CONCLUSION: The design and manufacture of combined extracellular matrix materials in bone tissue engineering is a very important and urgent challenge.
Objective To evaluate the suitability of the biodegradable microsphere encapsulation of adenovirus as a targeting vector for gene therapy of hepatocellular carcinoma. Methods Encapsulate the recombinant adenovirus in PLG 〔poly (lactic/glycolic)〕 copolymer by the solution evaporation method, the release test and the bioactivity of viruses incorporated in vitro were studied. Results More than 19.3% of adenovirus was encapsulated in PLG microspheres. The release test shows that the adenovirus was released for more than 200 h, 50% were shed within the first 100 h, and their activity was retained. Conclusion Recombinant adenovirus can be formulated in a polymer preparation of PLG with retention of bioactivity. It may be a valuable vector for the gene therapy of liver cancer.