Material Properties Direct Osteogenic Differentiation Of Stem Cells And Chitosan-based Bone Repair Materials

The interaction between biomaterials and cells, and the relationship between biomaterials and growth factor involved in bone tissue engineering are of significant importance. In this study, the effect of materials properties on the osteogenic differentiation of mesenchymal stem cells and the chitosan based bone repair materials for the delivery of BMP-2 peptide were investigated.Allylamine(AAm), acrylic acid(AAc), 1,7-octadiene(OD) and ethanol(ET) were used as precursors for plasma polymerization in order to generate thin films rich in amine(–NH2), carboxyl(–COOH), methyl(–CH3) and hydroxyl(–OH) functional groups, respectively. The effects of surface chemical compositions on the behavior, especially the osteogenic differentiation of human adipose-derive stem cells(hASCs) were evaluated in vitro. To understand the role of surface chemistry on cell behavior and the associated molecular mechanisms, we developed and utilized a surface chemical gradient of amine functional groups by carefully adjusting the gas composition of OD and AA of the plasma phase above a moving substrate. The results show that AAm based plasma polymerized coatings can promote the attachment, spreading and in turn proliferation of hASCs, as well as promote the osteogenic differentiation of hASCs. The possible mechanism involved is that surface chemistry affects the response of hASCs through cell-adhesive serum proteins, rather than interacting directly with the cells, and ERK1/2 may be an important downstream signaling pathway.The uptake of silver nanoparticles(Ag NPs) and its effect on the osteogenic differentiation of human mesenchymal stem cells(hMSCs) were investigated in vitro. Ag NPs with a diameter of ~30 nm were prepared. The hMSCs were exposed to different concentrations of Ag NPs, i.e. 0, 10, 50 and 100 μg/m L. The results show that Ag NPs cause cytotoxicity of hMSCs. It is also demonstrated that the uptake of Ag NPs does not affect the alkaline phosphatase activity, osteocalcin gene expression, osteopontin expression and mineralization level of hMSCs. The uptake of Ag NPs does not influence the osteogenic differentiation of hMSCs. This will give a positive reference for the application of Ag NPs in bone tissue engineering, especially their incorporation with stem cells in bone grafts.As for chitosan based bone repair materials for the delivery of BMP-2 peptide(P24), a thiolated chitosan, chitosan-4-thio-butylamidine(CS-TBA) conjugate was synthesized using 2- iminothiolane hydrochloride. CS-TBA was used to react with P24 terminated with cysteine. A CS-P24/HA scaffold was prepared and characterized based on the resulting peptide grafted chitosan(CS-P24) and hydroxyapatite(HA). In addition, a novel thermo-sensitive hydrogel was prepared based on CS-TBA/hydroxyapatite(HA)/beta-glycerophosphate disodium(β-GP) and used for the delivery of P24. The CS-TBA/HA/β-GP hydrogel has a porous structure with a uniform distribution of nano-hydroxyapatite, an appropriate degradation rate and low cytotoxicity. Futhermore, the thiol groups existed in CS-TBA/HA/β-GP hydrogel can interact with the thiol groups of P24, thus decreasing P24 release rate and maintaining P24 release for a longer time.