The Osteoblast Effect Of Modified Composite Calcium Phosphate Bone Cement In Vitro

Background: Bone grafting is the most commonly used method in treatment of bone defectsand nonunion. Since autogenous or allogeneic bone is limited in sourse and has poor quality ofplasticity, artificial bone graft material is becoming the research hotspot currently. The earliestapplicable artificial graft material in clinic with good plasticity was poly(methyl methacrylate)(PMMA), but PMMA could generate heat during curing which may burn the surrounding normalbone tissue, and it can not be absorbed and reshaped in the body which would impede fracturehealing. Therefore PMMA was not suitable as a bone graft material for traumatic bone defectsand bone nonunion. Subsequent arisen bone graft substitutes mainly included calcium sulfate,various calcium phosphates and so on. Calcium sulfate degradated fast in the body and wasinconsistent with the time for new bone grow. Its brittle texture and poor mechanical madecalcium sulfate generally not suitable for the treatment of defect in bone shaft.Calcium phosphate bone cement is of excellent biological and mechanical properties and hasbe applicated widely in clinic. Although the curing product hydroxyapatite of ordinary calciumphosphate bone cement contains microporous structure, the pore size, however, usually variedfrom below micron to several microns and can not allow cells and blood vessels to grow into itsdeep surface. Furthermore this type of bone cement is very stable in the body.The absorption anddegradation usually only occurs on its surface and the absorption rate is very slow, it is belived tohas no osteoinductive activity and the"bone creeping substitution"process usually needs a longtime. These deficiency limits their clinical application to a certain extent.Therefore there is aneed to improve its formulation so as to make it more adaptive in clinic.We developed a modified absorbable calcium phosphate bone cement composite (Bone &Calcium phosphate cement, BCPC) through optimizating the formulation of common calciumphosphate cement and mixing it with allogeneic bone meal. Animal experiment had showed thatthis BCPC could induce bone formation when as a bone graft material. In this study, we planedto further study its proliferation and osteoblast differentiation effect on rabbit bone mesenchymalstem cells(BMSCs) in vitro so as to explore its clinical value.Objective To investigate in vitro the biocompatibility of modified calcium phosphate bone cement(BCPC) and its effect on the growth state and osteogenic differentiation of rabbit BMSCs,as well as its capacity for loading relative factors to promote bone formation.Methods The experiment included four different groups:â‘ control group;â‘¡ordinary calciumphosphate bone cement group(CPC group);â‘¢modified composite calcium phosphate bonecement group(BCPC group);â‘£BCPC added exogenous BMP factor group(BMP group).BMSCs of rabbit were co-cultured with vectors respectively in the four groups. Cells growth wasobserved by an inverted phase microscope everyday and through drawing the cell growth curve.The activity changement of alkaline phosphatase (ALP) was detected by an alkaline phosphatasetest kit and the growth state of BMSCs on the surface of vectors was observed by a scanningelectron microscpe. Real-time PCR was used to measure the expression of relative genemRNA(ALP,OSX,Collagenâ… ,Collagenâ…¡,Aggrecan) for osteogenesis and chondroblast.Results There was no statistical difference of cell proliferation amone the four groups. TheBMSCs contacted well with the edges of vectors and had a good growth on the surface of thecarriers. Investigation through scanning electron microscpe showed the pseudopodias wasextended from the cells into the pores of BCPC,while in CPC group, cells growed only on thesurface of vector. Higher activity of ALP was detected in BMP group and BCPC group than theother two groups 7 days after co-culturing with vectors. In the 10th day after co-culturing, theexpression of relative gene mRNA(ALP,OSX,Collagenâ… ,Collagenâ…¡,Aggrecan) forosteogenesis and chondroblast was significant higher in BCPC group and BMP group than thecontrol group.Conclusion The BCPC has good biocompatibility and can induce osteoblast to a certain degree.Its loose structure and the larger aperture enable cells to grow into its deep layers as well as afavorble delivery system of BMP factor to strengthen the effect of osteoblast differentiation ofthe BMSCs.