Relationship between osseointegration and superelastic biomechanics in porous NiTi scaffolds

The superelastic nature of bones requires matching biomechanical properties from the ideal artificial biomedical implants in order to provide smooth load transfer and foster the growth of new bone tissues In this work we determine the biomechanical characteristics of porous Nil) implants and investigate bone ingrowth under actual load-bearing conditions in vivo In this systematic and comparative study porous Nil) porous Ti dense NiTi and dense Ti are implanted into 5 mm diameter holes in the distal part of the femur/tibia of rabbits for 15 weeks The bone Ingrowth and interfacial bonding strength are evaluated by histological analysis and push-out test The porous NiTi materials bond very well to newly formed bone tissues and the highest average strength of 357 N and best ductility are achieved from the porous NiTi materials The bonding curve obtained from the NiTi scaffold shows similar superelasticity as natural bones with a deflection of 0 30-0 85 mm thus shielding new bone tissues from large load stress This is believed to be the reason why new bone tissues can penetrate deeply into the porous NiTi scaffold compared to the one made of porous Ti Histological analysis reveals that new bone tissues adhere and grow well on the external surfaces as well as exposed areas on the inner pores of the NiTi scaffold The in vitro study indicates that the surface chemical composition and topography of the porous structure leads to good cytocompatibility Consequently osteoblasts proliferate smoothly on the entire implant including the flat surface embossed region exposed area of the pores and interconnected channels In conjunction with the good cytocompatibility the superelastic biomechanical properties of the porous NiTi scaffold bodes well for fast formation and ingrowth of new bones and porous NiTi scaffolds are thus suitable for clinical applications under load-bearing conditions (C) 2010 Elsevier Ltd All rights reserved