In Vivo Experiment Of Porous Bioactive Bone Cement Modified By Bioglass And Chitosan

There were80million osteoporosis patients in our country, and every year1.81million patients suffer from new vertebral compression fracture. The most commonlyclinical treatment of vertebral compression fractures was vertebroplasty, and the widelyused material for vertebroplasty was polymethyl methacrylate. The material had someadvantage as moderate curing speed and high mechanical strength, but there were obviousdisadvantage as no osteogenic activity, no absorbable and high modulus of elasticity. Theattempt to develop materials with appropriate elastic modulus, partially degradable andabsorbable has become one of the focuses of orthopedics. Bioactive glass was a newbioactive material that was also considered to be osteoconductive as well as osteoinductive.It supported new bone growth. Chitosan is a natural polymer, it has great potential as a biomaterial due to its good biodegradability and biocompatibility and its important role inthe attachment, proliferation, differentiation and morphogenesis of osteoblasts and thebone forming cells. One strategy attempted is to develop a porous, low-modulus, andpartial degradation porous bioactive bone cement by incorporation of bioglass andchitosan into PMMA bone cement.Objective: To investigate the biomechanical properties of Porous Bioactive BoneCement（PBC）with different proportions in vivo and observe the degradation of PBC andthe formation of new bone to prefer the appropriate proportions bone cement with betterbiomechanics and osteogenic activity.Methods: According to the different weight percentage (wt%) of PMMA to bioglassto chitosan in the powders, three types of PBC were prepared： PBCⅠ(50：40：10),PBCⅡ(40：50：10)and PBCⅢ(30：60：10). The bilateral femoral condylar defect models (4mm in diameter and10mm in depth) were established in48rabbits (male or female,weighing4.0-4.5kg). The defect models were randomly divided into4groups(8for eachgroup), pure PMMA, PBCⅠ, PBCⅡand PBCⅢwere implanted in the bilateral femoralcondyle of the knees，respectively. X-ray films were taken after1week. Three and6months after operation，6animals in each group were sacrificed, respectively. Bonecements were removed in situ for mechanical testing (n=6) and the rest of specimens wereunderwent micro-CT and histological examination. Four kinds of unplanted cement werealso used for biomechanical test as control.(n=6).The experimental data was analyzed bystatistical analysis software SPSS13.0Results:1. Three months after operation, Micro-CT reconstruction results showed that a gapwas formed between the host bone and the PMMA, and close integration occurredbetween the PBCs and host bone. Histological observation showed a fibrous tissue layerintervenes between the PMMA cement and bone，while PBCⅠ, PBCⅡ and PBCⅢgroup degraded with different levels. Six months after operation, similar results wereobtained. Micro-CT reconstruction indicated more volume of bone ingrowth was observedin the PBC II and PBC III. histological observation showed the PBCⅡ and PBCⅢ group were partly degraded，with an amount of new bone ingrowth. Quantitative analysisresults indicated that3and6months after operation, the bone tissue percentage of PBCⅠ,PBCⅡ and PBCⅢ group showed significantly difference when compared with that ofPMMA group（P<0.05）; Six months after operation, bone tissue percentage of PBCⅠ,PBCⅡ and PBCⅢ groups increased significantly than that of3months after operation（P<0.05）, while PMMA group showed no difference（P>0.05）.2. Before implanted, three months and six months after operation，the compressivestrength and Young’s modulus of PBCⅡ and PBCⅢ group decreased significantlycompared with PMMA group（P<0.05）; PBCⅡompressive strength of PBCⅠ groupdecreased significantly compared with PMMA group（P<0.05）, while no difference wasfound for Young’s modulus of PBCⅠ group before implanted when compared with thatof PMMA group（P>0.05）；No difference was found for compressive strengthand Young’smodulus of PBCⅢ when compared with that of PBCⅡ group（P>0.05）. Comparedwith that of not implanted group, compressive strength and Young’s modulus of PBCⅠ,PBCⅡ and PBCⅢ groups at three and6months after operation decreased significantly（P<0.05）, PMMA group showed no difference（P>0.05）. Compared withthat of threemonths after operation group, compressive strength of PBC Ⅱ and PBCⅢ groupsincreased significantly（P<0.05）, while Young’s modulus of PBCⅡ and PBCⅢ groupsshowed no difference（P>0.05）.Conclusion: According to the weight percentage (W/W,%) of PMMA to bioglassto chitosan, PBCs made by the composition of40︰50︰10and30︰60︰10have betterbiocompatible and biomechanical properties than current PMMA cement，it may reducethe fracture risk of the adjacent vertebrae after vertebroplasty by using PBCII and PBCIII.