BMP Encapsulated Nanoparticles And RGD Immobilized Chitosan/BCP Scaffolds For Synergistic Enhancement Of Bone Marrow Stromal Cell Activity

Development of bone tissue engineering requires the improvement of tissue scaffolds,which need not only large surface area and highly inter-connected porous structure with suitable porosity and pore size to support cell attachment and proliferation,but also signaling molecules to mediate cell activity.In this study,BMP-2 encapsulated nanoparticles and arginine-glycine-aspartic acid(RGD)are immobilized on the chitosan(CS)/biphasic calcium phosphate(BCP)scaffolds for synergistic enhancement of bone marrow stromal cell activity.The study includes three parts:First,CS/BCP scaffolds with different mass ratios of 8:0,8:1,4:1,2:1 were prepared by physical blend and subsequent lyophilization.SEM micrographs revealed that the micropores ranged from 10 ?m to 100 ?m.The BCP microparticles are uniformly distributed in CS.BMSC culture showed that CS/BCP with ratio of 4:1 leaded to cell proliferation and differentiation best.Secondly,RGD peptide was conjugated to the CS/BCP scaffolds via two methods.One is RGD grafted the oxidized sodium alginate(OALG)by the Schiff base reaction to form OALG-RGD,which was fixed on the scaffolds also through Schiff base reaction.The other was that RGD was directly immobilized on scaffold surfaces through EDC/NHS reaction.The results indicated that RGD peptide immobilized CS/BCP scaffolds can regulate cell proliferation and differentiation.The cell activity was related to the surface density of RGD,which could not be too low or too high.Finally,BMP-2 loaded BSA nanoparticles were prepared by a desolvation technique,and CS and OALG layers were assembled on the surface of nanoparticles to protect the activity of growth factors and achieve sustained release.Then BSA+CS+OALG nanoparticles were immobilized on the scaffolds.BMSCs culture indicated that RGD and BMP-2 had synergistically enhanced cell activity by providing an integrin binding and facilitating osteogenetic differentiation,respectively.In vivo study demonstrated that the RGD and BMP-2 immoblized scaffold has good bone repairing ability.