Related Research Of A Novel Composite Of Amino Acid Copolymer/tricalcium Phosphate For Bone Repair

Objective: A new type of composite material, multi-amino acid copolymer/amorphous tricalcium phosphate(MAACP/ACP), is prepared through polymerizing and compositing multi-amino acid copolymer and calcium carbonate. In this dissertation, the physical and chemical properties and biological properties of the composite materials are studied, and the relevant animal experiments are also carried out.Methods: 1 Prepare ACP, MAACP and MAACP/ACP with raw materials. Using the synthetic MAACP/ACP to get five kinds of composite materials, in which the contents of ACP are 5 wt %, 10 wt %, 20 wt %, 30 wt % and 40 wt %. Analyze the five composite materials by infrared spectroscopy and X-ray diffraction(XRD) analysis, compression strength test, combustion test, in vitro degradation of performance testing. 2 Sterilize MAACP and MAACP/ACP by radiation. Six healthy adult New Zealand white rabbits are randomly divided into intramuscular implan group and bone implant group, with three rabbits in each group. Each group is divided into the left side for MAACP group and the right side for MAACP/ACP group. First making animal experimental model, and then two kinds of materials are implanted in rabbit suscle pouches on both sides of the spine with strict aseptic operation, and implanted in rabbit femoral shaft bone defect model with aseptic operation. After 12 w the rabbits are killed for histologic observation, and for observing and analyzing the changes of X-ray diffraction. 3 35 healthy adult New Zealand white rabbits are randomly divided into control group with only 5, MAACP and MAACP/ACP group with each 15. Experimental animal model is same as the above bone defect model, implanting the two kinds of material. Chosing randomly 3 rabbits respectively at 3d, 1w, 4w and 8w, 12 w after the surgery, and 1 rabbit from the control group, blood is taken from the central artery of ears and then the phase of IL-1, IL-6 is measured. After killing the rabbits, being away from the implant materials of the femur, which is measured by bone mineral density(BMD).Results: 1 Infrared spectrum analysis results: comparison of ACP, MAACP and MAACP/ACP three material maps state clearly that, peak positions of the new MAACP/ACP composite materials shift little, which indicates that composite material is composed of MAACP and ACP. In addition, carboxy peak do not appear in the map of the composite material, which suggest that the amino acid form into amide copolymer. It can be deduced that ACP and the polybasic amino acid polymercompositeds without chemical combination interface. X-ray diffraction analysis results: all peaks appear in the maps, which indicate that the composite material is composed of MAACP and ACP. But in the composite material, the height of the polymer significantly decreases. It might be in the process of the composite, due to the presence of ACP, the degree of polymer crystallization decreases. Comparing strength test shows that the mechanics strength of MAACP/ACP composite material achieve the most appropriate state when content of ACP reaches 30%. Fire test shows that in MAACP/ACP composite material the two phases distribute equally. Vitro degradation analyses that: when the content of ACP in the MAACP/ACP composite material is < 40 wt%, compared with ACP and MAACP, the rate of weightlessness and bibulous have not obvious change. However, when the content of ACP in the MAACP/ACP composite material is 40 wt%, the rate of weightlessness significantly increases, the rate of bibulous increases, and the material begins to burst. For the new MAACP/ACP composite materials, in the process of degradation, p H of the environment is declined, but the impact is very small. The material do not generate a large amount of acid degradation products, and at the same time it is conducive to the growth of bone tissue. Scanning electron microscopy analyse during the process of degradation: it is observed that for new MAACP/ACP composite materials when the content of ACP is 30%, there are some obvious deposition of hydroxyapatite composite material on the surface. The result is related with the nucleation effect of ACP in the composite material during the hydroxyapatite deposition process. 2 Muscle implanting experimental results shows that for both MAACP and MAACP/ACP composite samples, no obvious inflammatory reaction is observed. The material is coated with a thin layer of fibrous tissue, and the materials are closely combined with tissue. Comparing the two groups of composite material histology images, it is observed that MAACP/ACP composite materials are closely integrated with the surrounding tissue, formation of fibrous tissue encapsulation is very thin, and it has better compatibility with the surrounding tissue than MAACP materials. However in the pictures, on the surface of two kinds of materials surface no obvious absorption is observed. Bone implant experimental histology observation picture of MAACP and MAACP/ACP composite materials, inflammatory reaction is not observed, as well as no inflammatory cells appear. There are not continuity of the fibrous tissue encapsulation. Close combination between materials and bone tissue is observed, but the material is not obviously absorpted. X-ray diffraction pattern shows that: the crystallinity of MAACP is declined, which indicates that the material is degraded. On the surface of MAACP/ACP composite material the weak structure of hydroxyapatite is formed, which shows that composite material has good biological activity. 3 General situations of different postoperative phases after animal experiment: there are not cracks, drainage, infection, fistula or abscess, and heal well. In the experimental group, there are 3 cases of postoperative wound infection. In the MAACP/ACP group, there is only one case of postoperative wound swelling appeared three days after surgery without obvious drainage. Comparison of serum IL-1 contents: after the surgery three IL-1 levels gradually decrease. Comparing MAACP group, MAACP/ACP group and the control group, 3d after the surgery, the difference is not statistically significant(P>0.05), while 1w, 4w, 8w after the surgery, the difference is statistically significant(P<0.05), and in the postoperative 12 w, comparing MAACP/ACP group with the control group, the difference is statistically significance(P<0.05), comparing MAACP group with the control group, the difference is not statistically significant(P>0.05). Comparing the MAACP group with the MAACP/ACP group at the same phase, 8w and 12 w after the surgery, the difference is statistically significant(P<0.05). At other phases, comparing the groups, the difference is not statistically significant(P>0.05). Comparison of serum IL-6 contents: in the three groups at postoperative IL-6 contents of 1w show a decreasing trend. In the control group IL-6 content reaches a plateau after 4w. Comparing MAACP group, MAACP/ACP group and the control group, at 3d and 1w after the surgery, the difference is not statistically significant(P>0.05), at the subsequents 4w, 8w phases, when the two groups are compared with the control group differences are statistically significant(P<0.05), at 12 w phase after surgery when the two groups are compared with the control group, the difference is not statistically significant(P>0.05). As far as comparison between MAACP group and MAACP/ACP group is concerned, at 4w and 8w phases, levels of MAACP/ACP group is significantly higher than those of MAACP group, the difference is statistically significant P<0.05), in terms of comparions at other phases, the difference is not statistically significant(P>0.05). Comparison of BDM values: numerical values of MAACP group and MAACP/ACP group at 3d and 1w are significantly lower than those of the control group(P<0.05), BDM values of two groups gradually increase from 4w, and values of MAACP/ACP group reach peak, while values of MAACP group reach peak at 8w. Comparing values of MAACP/ACP group with those of MAACP group at 4w, P<0.05, while with the control group, P>0.05. Comparing values of MAACP group 4w after the surgery with those of the control group P<0.05. Comparing values of the two groups with those of the control group at 8w and 12 w after the surgery, P>0.05.Conclusion: New MAACP/ACP composite material is composed of amino acid copolymer and ACP, there is not chemical interfacial combination, degradation products of the material is without strong acid; the degradation mechanism might be surface corrosion degradation, and the material has good water absorption and good mechanical properties. Moreover, the composite materials are non-toxic and nonirritating for surrounding tissue, the materials do not affect the generation of surrounding bone tissue, have good biocompatibility, can form a hydroxyl apatite layer on the surface, and have good biological activity. Because of its good performance degradation and absorption, the new MAACP/ACP composite material increase serum IL-1 and IL-6 levels of the body. At the same time, it promote the proliferation of osteoblasts, the rise of bone mineral density, and repairment of bone defect.