| Background and significance:Bone defects from trauma, infection, tumor and congenital pathologic factors, have always been concerned by the researchers of orthopaedics, maxillofacial surgery and biomaterial. All kinds of bone defect, as well as delayed union or nonunion, will bring about serious dysfunction and abnormality to the human body. Many kinds of substitute can be chosen, such as vascularized autograft, allograft, heterogeneous bone grafts, engineered bone transplantation and so on, but each of them has its limitation. Sufficient autograft is hard to gain, allograft and heterogeneity bone are suspected to cause disease spreading and immunological rejection. Researchers in this field have always been trying to find out ideal materials to repair bone defect. Ideal bone substitute should be characterized as good biocompatibility, osteoinduction, osteoconduction, porosity, pore size, mechanical strength, degradablility and easy-shapedness.At present, there are many kinds of artificial bone, which are classified as inorganic material and organic material by structure and function; artificial high polymer material and natural biomaterial by source. Nowadays, artificial bone and extracellular matrix (ECM) are widely used, mainly including natural material, artificial high polymer. However, they are much different from human skeleton, such as lack of bioactivity, difficult to be shaped or degradable, poor mechanical strength.Among all kinds of materials, bio-derived material is mostly close to strong skeleton framework, good mechanical strength and part of bioactivity factors, fit to cell adhesion, growth and educing physiological function. It is becoming the tendency of bone substitute research.Nacre is the inner layer of the shell of the bivalve marine mollusks, such as pearl shell, oyster, abalone and fan mussel. It's mainly composed of calcium carbonate, besides little organic matrix and trace element. Organic matrix consist of a little of protein. Rousseau drew off four kinds of molecule fragment, SE1-4, from water-solubility organic matrix of Nacre with high efficiency liquid chromatography. Study showed that WSM and SE4 could have some signaling molecules that stimulate OBs to disintegrate, proliferate, promote mineralization and add activity of ALP. In 1992, Lopez assured that Nacre had good biocompatibility and some molecule that could induce OBs and make OBs assemble, grow and differentiate in vitro. In 1999, Lamghari M confirmed that nacre could induce bone marrow cell to differentiate and stimulated bone-forming in vivo and vitro. In 2001, Lamghari M demonstrated that nacre stimulated bone-forming cells in vertebrae and appeared to result in new bone formation. However, nacre is difficult to be used alone for bone substitute because nacre is much brittle and difficult to be shaped. PLA has been used widely for clinic because it is degradable quickly and easy to be shaped, while it is lack of mechanical strength and has no bioactivity. Nacre is combined with PLA by special technology and may make up for shortage of each other.We have made the artificial bone of nacre combined with PLA and have confirmed that the artificial bone has good porosity, pore size, mechanical strength, biocompatibility and osteoconduction which have been demonstrated by many experiments. While there has never been any report about whether heterogeneous protein in nacre will bring about serious immune reaction, neither is NPAB ever usedto repair skull defect. Any unified evaluation guide and method for immunology of biomaterial in the world has not been made yet. This study will evaluate the impact of immune function of NPAB implanted into body to make sure whether NPAB implanted into body bring about immunological rejection in cell immunity, humoral immunity and hemat. At the same time, NPAB will be used to repair rabbit skull defect to further demonstrate the capability of NPAB to repair bone defect. Objective:1. To evaluate the immune response of nacre-polylactide artificial bone (NPAB) incell immunity and humoral immunity, after implanted into bodies of rabbits and to provide experimental evidence for further clinical application.2. To explore the security of nacre-polylactide artificial bone (NPAB) after implanted into body.3. To investigate the morphological change and bone regeneration after repair of rabbit skull defect with nacre-polylactic acid artificial bone (NPAB).Methods:1. The nacre powder was mixed with Poly-Lactic Acid and Nacl, going through special technology, and obtain artificial bone substitute.2. Nacre-polylactide artificial bone (NPAB) was implanted into the dorsal muscle pouches of rabbits. The venous blood was drawn for 1, 2, 3, 4weeks after operation for the hepatic and renal function, IL-2, TNF and serum specific antibodies test. The results were compared with the control group's to see whether there was any difference. Histological observation were done for 2, 4, 8 weeks after operation.3. Rabbit skull defects 1.5cmxl.5cm in area were induced in 16 New Zealand rabbits and immediately filled with NPAB or nothing. The animal local and whole body responses to the implants were observed after the operation. Gross, histological and X-ray were used respectively to evaluate the morphologicalchange and bone regeneration after the operation. Results:1. There were no obvious specific antibodies produced. The results of the hepatic and renal function, IL-2 and TNF test had no significant difference between the groups. After operation, all the rabbits survived and the incisions healed smoothly. Histological observation revealed that little inflammatory cells around the implant were found 2 weeks after operation, inflammatory cells decreased 4 weeks after operation, inflammatory cells disappeared and part of the implant begun biodegradation 8 weeks after operation.2. After operation, all the rabbits survived and the incisions healed smoothly. Gross, histological and X-ray revealed that NPAB possessed osteoconductive activity and new bone ingrowth in the implants was found during the whole experiment, at 16th week, the defects were almost completely repaired with NPAB while the defects in the control group remained nonunion.Conclusions:1. Nacre -polylactide artificial bone (NPAB) has no significant immune response in rabbits and possesses good biocompatibility and security. The material is degradable.2. Nacre -polylactide artificial bone (NPAB) has no immunity in rabbit.3. Nacre -polylactide artificial bone (NPAB) has the conspicuous ability of osteogenesis and-is easy to degrade.4. Osteoconduction contributes mainly to osteogenesis of Nacre-polylactide artificial bone.5. Nacre -polylactide artificial bone (NPAB) is a kind of safe and ideal bone substitute and may be applied to clinical experiment.
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