| The use of Degradable Material to fix bone fracture is a breakthrough in the study of bone fixation materials, which can elevate the healing rate of bone injury and avoid the operation to take out of plates or screws. Because PLA can dissolve to Lactic Acid (LA) which is the normal metabolites without any harm. And then LA changes into H20 and CO2. Therefore PLA became more and more important in the medical field. But, with development of the study and application, the shortcomings of PLA become clear. First, the mechanical power rises with the raise of molecular weight, and too big molecular weight will be benefit for internal fixation but this can lead to long time of degradation with several side effects. Second, the locally pile-up of LA causes down regulation of PH, which trigger the aseptic inflammation and retard the healing of bone fracture. What's more, the compatibility of PLA need more development. In some cases, reject reaction is severe.Chitin, polysaccharide rich in nature, turns into Chitosan after deacetylation. Chitosan contains many (-NH2) s and (-OH) s, which is easy for chemical modification and characteristic deformation. This basic material has good biological compatibility and degradability. And the degradation products (N-acetylglucose and aminoglucose) will not store up in vivo and harm human body, and they have lower immunogenicy.PLA has lots of (-OH) s~ (-COOH) s; While Chitin has lots of (-NH2) s and (-OH) s. can be formed between PLA and Chitin, which can strengthen the mechanical power. This can satisfied the need of bone fracture fixation without increase molecular weight.During degradation of PLA-Chitin compound, PLA release LA and Chitinrelease basic molecule to neutalize LA and produce salts and HzO. This avoids LApiIed uP locaIly, and so eliminate aseptic infiammation, cell degeneration andnecrosis. On the other hand, the decrease of LA can acce1erate the degradation ofPLA. What's more, the excellent hydrophilic affinity of Chitin enhance waterpermeate iDto PLAChitin ComPound. This also accelerates the rate ofdegrdation.In this study, we made PLAChitin plates and screws, Which is buff andsmoOth (3.0CmX0.8CmX0.3Cm: Q=0.2Cm). The molecular weight of it is25M, Bent intensity is 2l0MPa; Shear intensity is l60 MPa: Standard caPacity ofbent is 5GPa. As for contro1, we use plates and screws (3.0CmX 0.8CmX 0.3Cm:Q=0.2Cm) made of PLA, Which is lack of colof, and their surfaces are smooth.These tWo maetals are provide by our partnee Ingh Polymer Institute ofZhongshan UniversityThe animal model f NeW Zealand rabbits are anesthetized by injection 2.5%sodium pentobarbital (l.0ml/kg to ear vein. And then the rabbits are fixed onoperation table, shearing hair clearng skin. sterilizing, covering the surroundingarea by disinfect cloth. We inCised the skin and SUbCutaneous tissue along femorallongitudinal axis. 5.0CmX 2.5Cm femoral surface was exPosed. The periosteum wasincised and detached, and two holes were made by electric drill. TwO tyPes of platesand screws wer used according to experiment P1an. Stop bleeding, rinse theoperation area tO prevent remaining of haif, tale powder and so on. Finally SUtUredoperation area careful1y In 2,4,6,8,l0,l2 week after operation, one rabbit inexperment group and control grOup respectively wer put to death. The sampleswere drew from the material fixation area, and bone and soft tissue seCtion weremade. And also the ultrathin seCtions for transmission e1ectric scope were made.By osteoblaSts in vitro, the interaction between PLA-Chitin compound andcells was investigated.Results f Envelops were formed 2-4 weeks after operation and the envelop inexperiment become thin early than that in control group. One case in control groupoccurred aseptic inflammation 8 weeks after operation. In this case, the implafltdisplaced, and the surrounding fibroconnective envelope became coarse. Part ofcortical bone dissolved, but cultivation showed no bacteria exiSted. The imP...
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