Morphologic and nanomechanical characterization of bone tissue growth around bioactive sol–gel coatings containing wollastonite particles applied on stainless steel implants

Abstract

Metals are the most widely used materials in orthopaedic and dental implants due to their excellent mechanical properties. However, they do not bond naturally with mineralized bone. Further, they can release metallic particles that may finally result in the removal of the implant. There are two strategies to avoid these drawbacks: one is to protect the metallic implant with a biocompatible coating and the other is to add bioactive particles to enhance implant fixation to the existing bone. In this work, surgical grade stainless steel implants coated with tetraethoxysilane (TEOS)-methyltriethoxysilane (MTES) and 10 wt.% of commercial wollastonite particles were implanted in the Hokkaido femur rats. Transversal sections of the tibia samples were examined with SEM, AFM, histological analysis and nanoindentation experiments in air and under physiological conditions to characterize the hydroxyapatite deposits and the composition of the newly formed tissue around the implant. The results showed no presence of harmful ions or metallic particles in the surrounding tissues and that the coating promoted formation and growth of new bone in the periphery of the implant, both in contact with the old bone (remodellation zone) and the marrow (new bone). The relative mechanical behavior of old, remodeled and new bone tissues obtained in air cannot be directly extrapolated to live or in vivo-physiological response. This may be caused by the different degree of hydration and SBF/structure interaction among the three types of bones but these values are near the normal hydrated bone response.