Proangiogenic Nano-Biomaterials for Bone Tissue Engineering

Abstract

Effective replacement / restoration of traumatized, damaged or lost bone is a major clinical and socio-economic challenge. In recent years, emergence of the bone tissue engineering (BTE) as a therapeutic alternative of conventional clinical modalities especially as a replacement of auto- and allo- grafting has brought new hope in clinical orthopaedics. The success of the BTE depends on the integration of the biologically active osteogenic scaffolds (with / without bone cells) to the native osteo-chondral system after implantation at the injury or defect site. It has now been confirmed that such integration process seemingly relies on angiogenesis, which leads to the generation of vascular network in the neo-bone tissue. Angiogenesis is essential for the delivery of nutrients and gases to the cells present at the distal location of an implant, which can hardly be reached through interstitial fluid diffusion. Plenty of clinical evidence showed that impaired vascularisation results in atrophic non-union of the bone. Keeping this perspective in mind, people have adopted diverse strategies to improve the extent and the quality of angiogenesis in BTE. However, those strategies have failed to be a commercial success because of number of factors including cost, technical difficulties, genotypic variation of cells and potential health risks. To overcome the stalemate, research focus has now been shifted towards the angiogenic biomaterials, materials that can stimulate the cells for biased production of angiogenic factors, both in vitro and in vivo. Different research groups has now working on the development of angiogenic biomaterials. We are one of the leading research groups, involved in developing low cost proangiogenic nano-hydroxyapatite (nHAp). Hydroxyapatite is the most common bioceramic used in bone tissue engineering because of its chemical resemblance with bone apatite. We have adopted a novel strategy that leads to the angiogenesis through the activation of tissue hypoxia mimicking HIF-1α pathway. Following that strategy we have developed several types of proangiogenic hydroxyapatite either by doping 'group - d' bivalent ions like Co+2 , Ni+2 in nHAp crystal or by conjugating the hydroxyapatite with natural biopolymers like gum tragacanth. All the chemically modified nHAp are subjected for extensive physico-chemical characterization that includes XRD, FT-IR, SEM, TEM, BET, DLS and Zeta potential analysis. we confirm the osteo-conductive property of the modified nHAp by checking the response of the osteoblast cells (MG-63) in vitro. For this purpose , detailed studies pertaining to the cell viability and proliferation ( MTT and flow cytometry based live -dead assay, cell cycle analysis ), and cell differentiation (done by RT-PCR and Western blot ) was done. We also test the osteogenic properties in vitro using human mesenchymal stem cell. The angiogenic property especially the expression of cellular VEGF and its related mechanistic pathways is proved in both MG-63 cell line and in human mesenchymal stem cells. We finally confirm the formation of endothelial linkage in vitro through tube formation assay. We believe that these set of experimental evidences will help the researcher in designing and developing proangiogenic biomaterials in coming future.