Nanomechanics of bone and bioactive bone-cement interfaces

Nanoindentation is an ideal technique to investigate mechanical behaviour at the bone/implant interface. A viscoelasticity correction method was developed and validated for use on biological specimens. Using this new technique the nanomechanics of the interface between strontium-containing hydroxyapatite (Sr-HA) bone cement with cancellous and cortical bone were investigated under weight-bearing conditions. At 6 months after implantation, Young's modulus and hardness at the interface between cancellous bone and Sr-HA cement were significantly higher than those at the cancellous bone and Sr-HA cement, whereas Young's modulus and hardness at interface between cortical bone and Sr-HA cement were significantly lower than those at cortical bone, but significantly higher than Sr-HA cement These results were supported by histological observation and chemical composition. Osseointegration of Sr-HA cement with cancellous bone was observed. An apatite layer with a high content of calcium and phosphorus was found between cancellous bone and Sr-HA cement; however, no such apatite layer was observed at the interface between cortical bone and Sr-HA cement. And the contents of calcium and phosphorus of the interface were lower than those of cortical bone. The mechanical properties indicated that these two interfaces were diffused interfaces, and cancellous bone or cortical bone was grown into Sr-HA cement 6 months after the implantation.