The Preliminary Experimental Study Of Repairing Animal's Bone Defect By Using Brushite Stone Composite Materials

Objective:This experiment is to make brushite and evaluate its physical-chemical properties/performance, and to implant it into the animal's bone defect as the composite materials, observing its bone formation on large bone and investigating its performance of possibility of repairing bone defect.Methods:The experiment was mainly divided into materials preparation and physical-chemical properties test, observation of its effect of repairing bone defect when implanted in vivo, the preparation and physical-chemical properties test of the poly lactic acid-glycolic acid copolymer (PLGA)/recombinant human bone morphogenetic protein-2 (rhBMP-2) drug releasing micro-spheres.1. Composites materials preparation and Properties study. The main components:β-TCP, MCPM, magnesium hydrogen phosphate trihydrate are mixed in a certain proportion, adding curing solution, then be made into brushite under room temperature. Detect the curing time, strength, PH, biological compatibility in vitro of composite materials, and scan microstructure by using SEM.2. Study new composite materials ability to repair animal's bone defects in vivo.32 Healthy adult New Zealand rabbits were randomly divided into A and B two groups,and all of them were established the right radial bone defect model, animal bone defect of A group implanted with Brushite stone composite materials,while B implanted calcium phosphate cement (CPC)complex. with, then assess brushite ability to repair bone defects through imaging detection, histological of such testing and other means.3. Use double emulsion solvent evaporation method, and PLGA as a carrier to prepare the release micro-spheres wrapping rhBMP-2. Observe the morphology, detect the rate of drug loading and the law of releasing in vitro.Results:1. The strength of brushite average 20.4MPa, close to the degree of cancellous bone; initial setting time is 3.0～4.0 min, while final setting time 10.0～12.0min, and is similar to the commercial CPC materials, basically meet the clinical requirements; hemolysis experiment suggests that the hemolytic rate of its extracts lower than 5%, no toxic effects on red cell membrane, not leading to hemolysis causing by cell membrane damage, having good biocompatibility, and SEM scanning photographs showing a lot of 50～150μm micro-pores in the microstructure.2. Composite materials have no toxic effects on the the animals inthis experiments, and other animals haven't got adverse reactions such as hemolysis,allergic and poisoning,no one died,has good biocompatibility; X-ray films showed differences between brushite group and the CPC group at 4w,and further accelerated at 6w and to 8w basically finished degradation,but CPC has no significant degradation. Biopsy showed trabecular at two ends of the implants and the junction between bone ends when 6w,while 8w showed the formation of cellular matrix and the original bone marrow cavity in brushite group,compared with CPC of the control group,both of them have the ability to and with the promote bone formation,but the brushite rapidly absorbed degraded,didn't repaired the bone defects completely.3. Use double emulsion solvent evaporation method to prepare rhBMP-2/PLGA sustain release micro-sphere preparation,which is a round ball shape and had an average diameter of 80% between 100～350μm, the average particle diameter was (250±54)μm, span= 0.6,Use ELISA detection of micro-spheres to calculate drug loading rate:0.52%±0.16%. Releasing in vitro is faster Within 24 hours, showing an increased burst release, followed by slower release, and up to 47.3%±3.6% when on the 28th day, the drug release law in vitro meets the Higuichi equation.Conclusions:The brushite absorbed and degraded too fast, osteogenesis effect is not obvious, and didn't complete bone repair; Use double emulsion solvent evaporation method to prepare rhBMP-2/PLGA sustain release micro-sphere, which has good morphology, ideal drug loading rate and sustained release effect; It needs further experimental studies to explore whether adding osteogenic factors into brushite have beneficial effect on improving its bone formation.