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 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 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 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 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 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.
The esophageal disease is a major clinical disease. The esophageal stent has extensive clinical applications in the treatment of esophageal diseases. However, the clinical application of esophageal stent is limited, because there are lots of complications after implantation of esophageal stent. Biodegradable esophageal stent has two advantages: biodegradability and good histocompatibility. It is expected to solve a variety of complications of esophageal stent and provide a new choice for the treatment of esophageal diseases. Standardized esophageal stents are not fully applicable to all patients. The application of 3D printing technology in the manufacture of biodegradable esophageal stent can realize the individualized treatment of esophageal stent. And meanwhile, the 3D printing technology can reduce the manufacturing cost of the stent. This review aimed to summarize and discuss the application of esophageal stent, the current research status and prospect of biodegradable esophageal stent and the prospect of 3D printing technology in degradable esophageal stent, hoping to provide evidence and perspectives for the research of biodegradable esophageal stent.
[Abstract]Esophageal stricture is a common esophageal lesion in adults and children, and endoscopic dilatation is currently the standard treatment. However, high recurrence rate and frequent dilations have become a major problem in patients. Esophageal stents provide sustained dilation therapy but can lead to serious complications such as displacement, perforation, and bleeding, necessitating removal. Biodegradable stents, with the advantage of both dilation and self-degradation, are promising potential solutions to this problem. Currently, biodegradable materials are mainly categorized into metals and polymers, leading to the development of magnesium alloy esophageal stents and polymer esophageal stents. Among polymer stents, PLLA stents and SX-ELLA stents have been put into clinical application. In recent years, with the advancement of 3D bioprinting technology, the personalized fabrication of biodegradable stents has become feasible. In this paper, we will outline the current research status and progress of biodegradable magnesium alloy stents and polymer stents, introduce the new process of constructing esophageal stents by 3D bioprinting technology, focus on the clinical research of SX-ELLA stents in pediatric and adult patients. We will also analyze the existing problems with biodegradable stents and the directions for future development.
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.