| BACKGROUND:Internal fixation devices have long been used to reduce and stabilize bone fractures, including metal wires, metal plates, et al. The advantage of metal plates in osteosynthesis includes accurate three-dimensional stabilization of fracture segments, direct bone healing, and early mobilization. Nevertheless, permanent metal plating systems have several shortcomings. Palpability, infection, migration, and extrusion are the most commonly reported complications. The metal plates have also been reported to hinder local structural growth and interfere with diagnostic and therapeutic radiation. Other reported drawbacks of metal plates include stress shielding, cortical osteopenia, thermal sensitivity, and potential for more severe damage with repeated injury. Moreover, many trauma surgeons, including those of the AO-ASIF school, recommend that all metallic implants used for the fixation of fractures be removed in due course. The development of biodegradable internal bone fixation was fueled by these disadvantages. Over the last three decades, there has been considerable development and subsequent application of degradable biomaterials. One of the most commonly tested biodegradable biomaterials is polylactic acid (PLA), which has excellent biocompatibilityand can disintegrate completely after a sufficient time of osseofixation in the body. However, with the development of the study and application, the shortcomings of PLA have become clear. First, the lactic acid piled up locally may cause down-regulation of pH, which triggers the aseptic inflammation. Second, PLA biodegrades slowly, which also might hinder local structural growth. What's more, the compatibility of PLA needs more development. In some cases, foreign body reaction is severe.Chitin, rich in nature, resembles GAG (glycosaminoglycan) in structure and turns into Chitosan after deacetylation. Chitosan takes the positive charge. And it contains many (-NEs and (-OH)s, which is easy for chemical modification and characteristic deformation. The chitosan also has good biological compatibility and its degradation products (N-acetylglucose and aminoglucose) will not store up in vivo or do harm to human body.In this study, PLA-Chitin Compound was made into Plates and Screws as internal bone fixation devices. On the one hand, PLA has lots of (-OH)s and (-COOH)s; while chitin has lots of (-NH2)s and (-OH)s. These activity groups can combine together, which will strengthen the mechanical power of the compound and satisfied the need of bone fracture fixation. On the other hand, as PLA-Chitin plates degrade in the body, PLA discharge lactic acid which could be neutralized by the basic molecules that Chitin discharges. This process avoids lactic acid piled up locally, and might eliminate aseptic inflammation. What's more, the excellent hydrophilic affinity of Chitin enhances water to enter PLA-Chitin Compound, which will accelerate the degradation of PLA and shorten the degradation period of PLA-Chitin Compound. On the whole, we assume that PLA-Chitin Compound is one of the most prospective implants in osteosynthesis.OBJECTIVES:1. To evaluate the cytotoxicity of the Biodegradable Polylactic Acid-ChitinPlates in different assays using the cell line L-929 in vitro, for all medical devices are required to be evaluated before their clinical application. 2. To investigate the osteocompatibility of the Biodegradable Polylactic Acid-Chitin Plates using osteoblast in vitro.Methods:1. The cytotoxicity of the Polylactic Acid-Chitin Plates was evaluated in extract assay (the RGR assay and the MTT assay), direct contact assay, and FCM assay using the cell line L-929 in vitro.2. The cytotoxicity and osteocompatibility of the Polylactic Acid-Chitin Plates was evaluated in the MTT assay and the direct contact assay using osteoblast in vitro. Cell growth, proliferation, and attachment were studied when osteoblasts, together with Polylactic Acid-Chitin Plates, were cultured.3. Statistical method: All data were analyzed with SPSS 10.0 statist... |
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