Study On Alginate-based Injectable Bone Regenerative Materials

The injectable materials have become one of the major hotspots in the biomaterialfield due to the advantage of being able to fill any bone defect shapes, bringcompliance andcomfort to patients for non-or minimal invasive surgery. Especially,injectable hydrogels mimic features of extracellular matrix, and they can be utilizedas carrier for transplantion cells and release of growth factors. Therefore, we havedeveloped an injectable bone regeneration composite (IBRC) using calcium alginatehydrogel as matrix to carry nano-hydroxyapatite/collagen (nHAC) particlesbiomimetically. The IBRC was characterized by physical and chemical properties,gelation mechanism, in vitro and in vivo degradation properties and their mechanisms,biocompatibility and bone formation ability, controlled release ability for rhBMP-2and its osteoinductivity. Finally, a thermo-sensitive comb-like alginate based hyrogelwas synthesized, and its properties and biocompatibility were evaluated.The results of XRD and FTIR confirmed that the alginate and nHAC can maintaintheir own structural characters during the process of IBRC preparation and gelationreaction. Rheological results and injectable property test showed that the injectabilityof IBRC was tunable. The compressive elastic modulus and shear modulus are in therange of17.0~56.0kPa and24.7~55.0kPa, respectively. The structural homogeneitywas determined by controlling the molar ratios (MR) of trisodium phosphate tocalcium sulfate. In vitro degradation indicated that IBRC had a controllabledegradability; Meanwhile, the degradation medium had influence on degradation ofIBRC and alginate. In the in vivo degradation study, IBRC degraded mostly after24weeks implantation and was replaced by connective tissue. No fibrous capsule andacute inflammatory reaction were found at all time. In vitro cell culture showed thatthe morphology and viability of cells are related to structural homogeneity of IBRC.Cells were adhered, spreaded and survived on IBRC with MR0.260very well. Inaddition, the excellent ability of IBRC to promote bone healing was confirmed by5-mm-diameter cranial defects using histological analysis and bone mineral densitymeasurement.Controlled release of recombinant human bone morphogenetic protein-2(rhBMP-2) from IBRC was evaluated by in vitro and in vivo studies. The results of an in vitrostudy confirmed that rhBMP-2released with controllable rate, and its bioactivity waswell preserved during this period. The bone formation ability was assessed using a ratcalvarial defect model with critical size (8mm). Micro-computed tomography(micro-CT) and histological analysis demonstrated that the IBRC had good boneformation ability, which was promoted through rhBMP-2released from IBRC/rhBMP-2.A thermo-sensitive comb-like copolymer was synthesized by grafting poly(N-isopropylacrylamide) onto aminated alginate (AAlg) through amide bond linkages.Encapsulation of human bone mesenchymal stem cells (hBMSCs) within hydrogelsshowed that the AAlg-g-PNIPAAm hydrogel not only preserved the viability of theentrapped cells but also stimulates the cell proliferation.