| The promotion or acceleration of bone repair is the most important area of biomaterials. The development of bone substitutes based on biopolymers-ceramic bonelike composites has been proposed. In that way, the beneficial properties of the biopolymers can be combined with the excellent osteoconductive and mechanical properties of CaP ceramics. However, in the conventional preparation of biopolymer-hydroxyapatite composites, blending the ceramic with the biopolymers directly may lead to masking of the ceramic particles by hydrogel, and thus diminishes the osteoconductive properties offered by them. From a biomimetic point of view the development of synthetic bone substitutes mimicking the composition, structure and biological performances of natural bone is of great importance for enabling a range of applications in bone tissue regenerative medicine. This study examined the potency of photo-crosslinked polymethacrylate hydrogels containing anionic gelatin in templating3D hydroxyapatite-mineralization. Further, practical controls over the mineralization outcome, including crystallinity, content, and morphology of the mineral growth within the3D gelatin methacrylate scaffold, were systematically investigated by altering crosslinker contents of the hydrogel. To improve the biocompatibility, a gelatin-HA composites by photochemical graft and subsequent biomimetic mineralization were covalently-immobilized on titanium substrates.1. Regulation of hydroxyapatite crystal growth by gelatin hydrogels.Gelatin methacrylate (GelMA) is formed by incorporating methacrylate groups onto the amine-containing side groups of gelatin, yielding a gelatin-based, and photocrosslinkable hydrogel. Furthermore, we have also demonstrated that degree of methacrylation (DM) can be controlled by varying the amount of methacrylic acid added during the synthesis of GelMA. This study also demonstrated that the chemical crosslinker content (DM) of the hydrogel as a parameter regulated the growth of minerals. Homogeneous surface and interior carbonated hydroxyapatite were achieved on the resulting mineralized porous hydrogel composites, and were confirmed to resemble apatite-like structures. It was found that increasing the degree of methacrylation (DM) of the hydrogel suppressed the growth of carbonated hydroxyapatite layers, as was evident from the extent of calcification and morphology of the minerals. The dependency of the mineralization on hydrogel variables was related to the change in physicochemical properties of gel, including charge density and swelling. Compressive mechanical testing demonstrated that the compressive modulus and strength of the hydrogels increased with increasing DM and mineralization extent.2. Preparation of gelatin hydrogels-hydroxyapatite composite coating on titanium surface.In this study, in order to improve the osteoconductivity osseointegration of titanium implants, we sought to apply a universal biomineralization route that can covalently immobilize GelMA/mineral composite layer on a Ti implant surface. This is a simple two-step process that consisted of (i) the photochemical immobilization and (ii) biomimetic mineralization. Photochemistry immobilization is a convenient to obtain stable designated polymer films on metal surface. The immobilized bioactive polymerlayer was mineralized via a simple biomimetic approach. We aimed to decrease the immersion time with formation of apatite, a2SBF solution was used. The structure of the prepared GelMA/HA composite coating was studied by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectra (EDS), attenuated total refraction Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Water contact angle measurement revealed the hydrophilicity properties of composite coatings. GelMA/HA on titanium after the TMSPMA treatment is very stable when tested in vitro with a PBS solution at37℃, due to the role of TMSPMA as a molecular bridge. |
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