Calcium Phosphate Apatite Filament Co-Wrapped With Perforated Electrospun Sheet of Phosphorylated Chitosan—A Bioinspired Approach Toward Bone Graft Substitute

Abstract

Bioinspired bone graft substitutes hold incredible opportunities in tissue engineering, potentiating the healing aspect. Here we have fabricated stacks of glutaraldehyde–genipin crosslinked, microporous nanofibrous N-methyl phosphonic chitosan sheets (NMPC) with impregnated eggshell-derived CaP fibers to mimic osteonal architecture. This composite 3D rolled eggshell-derived calcium phosphate (ESCAP) scaffold (RCS), with density and modulus variation from the center to the periphery, has superior mechanical strength. The zwitterionic nature of NMPC, following the surface modulus of the CaP fibers, upgraded the biological performance. The low modulus of the flexible micro-perforated nanofibrous sheet increases along the ceramic phase, which prompts migration and distribution of proliferated MSCs from the outer polymeric surface to the inner ceramic region through micro-perforations. This movement stimulates endochondral ossification, observed by a gradual increment of collagen II expression alongside a decrement of collagen I expression. In vivo assessment of rabbit tibia bone defects revealed prominent healing in the presence of a scaffold by Day 60, accompanied by scaffold resorption. The cellular activity during healing revealed osteoblasts, osteocytes, blood vessels, and chondroblast cells at the boundary of the scaffolds, indicating neotissue and hypertrophic cartilage formation. Thus, the RCS bone grafts promote faster bone healing by osteogenesis and bone remodeling.