Addition of hydroxyapatite improves stiffness, interconnectivity and osteogenic potential of a highly porous collagen-based scaffold for bone tissue regeneration

There is an enduring and unmet need for a bioactive, load-bearing tissue-engineering scaffold, which is biocompatible, biodegradable and capable of facilitating and promoting osteogenesis when implanted in vivo. This study set out to develop a biomimetic scaffold by incorporating osteoinductive hydroxyapatite (HA) particles into a highly porous and extremely biocompatible collagen-based scaffold developed within our laboratory over the last number of years to improve osteogenic performance. Specifically we investigated how the addition of discrete quantities of HA affected scaffold porosity, interconnectivity, mechanical properties, in vitro mineralisation and in vivo bone healing potential. The results show that the addition of HA up to a 200 weight percentage (wt%) relative to collagen content led to significantly increased scaffold stiffness and pore interconnectivity (approximately 10 fold) while achieving a scaffold porosity of 99%. In addition, this biomimetic collagen-HA scaffold exhibited significantly improved bioactivity, in vitro mineralisation after 28 days in culture, and in vivo healing of a critical-sized bone defect. These findings demonstrate the regenerative potential of these biodegradable scaffolds as viable bone graft substitute materials, comprised only of bone's natural constituent materials, and capable of promoting osteogenesis in vitro and in vivo repair of critical-sized bone defects.