Abstract
Conventional bone grafts are fraught with limitations and three dimensional (3D) electrospun fibrous nanocomposites of gelatin and hydroxyapatite (HA) similar to the extracellular matrix (ECM) of bone are viable bone graft substitutes but there is limited research in this area. In this project, fibrous scaffolds of gelatin-HA nanocomposites were fabricated using electrospinning and crosslinked using glutaraldehyde vapour. The microstructural, physical and mechanical properties of the scaffolds were measured and the effects of applied voltage, HA concentration and crosslinking duration on scaffold properties were determined and used to optimise the electrospinning process. Human foetal osteoblast cells were grown on the scaffolds and cell seeding efficiency, cell proliferation, cell viability, alkaline phosphatase activity, collagen matrix synthesis and mineralisation were quantified. Tissue engineered 3D bone grafts were developed by stacking together optimised seeded scaffolds using the three-stack and the four-stack models and also cultured under dynamic conditions in a perfusion bioreactor to improve nutrient and oxygen transport to cells. Mathematical models were developed for nutrient and oxygen transport and cellular response in the scaffolds and layer-by-layer oxygen and cell concentrations were predicted in the 3D bone graft models. Models were developed for cell growth and oxygen consumption rates and their constants were determined and used as input parameters for the mathematical models along with the determined physical and biological scaffold properties in the computer simulations of bone tissue engineering. The scaffolds exhibited a good degree of fibre alignment and both fibre and pore diameters exhibited inverse relationships with applied voltage and HA concentration. The scaffolds possessed reasonable levels of porosity and permeability which were a function of the fibre diameter. Young’s modulus and ultimate tensile strength were functions of fibre diameter, porosity and direction of loading and exhibited proportional relationships with applied voltage, HA concentration and crosslinking duration. Initial cell seeding efficiency was over 90% in all scaffolds with cell proliferation, alkaline phosphatase activity, collagen synthesis and mineralisation all exhibiting inverse relationships with applied voltage and proportional relationships with HA concentration as a result of the concomitant variations in fibre diameter, pore diameter and porosity of the scaffolds. The 25 wt% HA scaffold electrospun at 20 kV had optimum osteogenic, physical and mechanical properties and contained mineralised bone tissue after 18 days of cell culture. Functional 3D bone grafts were obtained with favourable cell proliferation, which improved under dynamic culture, albeit with limited cell migration and a 3D multi-thin-layered stacked bone graft model was proposed based on these findings. Finally, the mathematical models were successfully validated against the experimental cell concentration and migration depth data.