| Objective:Absorbable synthetic material applying to substitute material for fracture fixation is one of central issues in Orthopedics. Polylactic acid (PLA), polyglycolic acid (PGA) and their copolymers has attracted more and more attentions. Among absorbable fixation materials, PLA and PGA tend to be used more frequently than the others because their favorable biocompatibility and absorbability. However, several complications have been reported, including biological inactivity, fast degradation rate, lower mechanical strength and elastic modulus than natural cortical bone, aseptic inflammation caused by degradable product. Poly lactic-co-glycolic acid (PLGA), the copolymer of PLA and PGA, raised higher mechanical strength, but still biological inactivity. Hydroxylapatite (HA), with favorable biocompatibility and bone conduction, can form direct combination with bone structure.So, we choose the PLLA and PLGA as the matrix of the absorbable materials, and the Hydroxylapatite as the bioactive composition, fabricate PLGA/PLLA/HA Synthetic Material. Investigations in vitro and vivo biocompatibility assays and mechanics experiments of PLGA/PLLA/HA Synthetic Material were carried out. Methods:(1) Preparation of PLGA/PLLA/HA Synthetic Material: Mix the PLGA, PLLA and HA powder as certain proportion [PLLA: (PLGA+HA) =3:1, mol ratio], mill uniformly, blend, and shape as rods by hydraulic forming. The test materials were grouped by proportion of HA (5%,10%, 15%) as Group A, Group B, Group C.(2)Cytotoxicity test: Mg-63 cell were incubated on 96 pore plate, cultured with the leaching liquor of 3 group of test material after 24h, tested optical density value in MTT assay in 1d, 3d, 5d, 7d. With the results, we calculated the cell proliferation levels (RGR) and assessed the cytotoxicity grade.(3) Adherence test: Mg-63 cell were incubated on 6 pore plate with adherence materials and cultured for 3d. The test materials, washed with PBS liquid, fixed by 2% cold glutaric dialdehyde and 1% osmic acid, dehydrated with gradient of alcohol, dried in critical point, sprayed metal, were observed with Scanning Electron Microscopy (SEM).(4)Alkaline Phosphatase (ALP) activity test: Mg-63 cell were incubated on 6 pore plate, cultured with the leaching liquor of 3 group of test material after 24h. Make cell homogenate liquid by digesting cell after 5d. Alkaline Phosphatase (ALP) activity of cell homogenate liquid was measured by alkaline Phosphatase test kit and Braford protein content test kit. (5)Implant test: Test material was implanted in back muscle bladder in 12 New Zealand rabbits. These rabbits were executed after anesthesia at 1w, 4w, 12w post-operation to conduct paraffin section and hematoxylin-eosin (HE) staining in the surrounding tissues of materials and observe the tissue reaction degree.Results:(1) Cytotoxicity test: The toxic levels of test materials are ranged from 0 to 1 degree, which indicates PLGA/PLLA/HA Synthetic Material has no or only minimal cytotoxity.(2)Adherence test: Observed with Scanning Electron Microscopy (SEM), the morphology of the cells close to test materials was normal.(3)Alkaline Phosphatase (ALP) activity test: Alkaline Phosphatase (ALP) activity is very lowly expressed in negative control group, has significant difference with test groups. It indicates PLGA/PLLA/HA Synthetic Material is favorable biocompatible, and can stimulate the growth and osteogenic activity of osteoplast.(4)Implant test: Ranged the tissue reaction degree with national standard GB/T 16175-1996, PLGA/PLLA/HA Synthetic Material meet the criterion, has favorable biocompatibility.Conclusions:PLGA/PLLA/HA Synthetic Material has favorable biocompatibility, and can stimulate the growth and osteogenic activity of osteoplast. It has reached the requirements of the bio-safety initial testing and the clinical application pre-test, provides a reliable laboratory basis for the next phase of clinical application. It has broad prospects as a substitute material for conventional metallic materials internal fixation.
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