Enhanced bioactivity and mechanical properties of commercially pure titanium sheets processed through Repetitive Corrugation and Straightening technique

Abstract

Commercially pure titanium (Cp-Ti) is a significant biomaterial for load-bearing implant applications. However, it has lesser mechanical strength than titanium alloys, which needs to be addressed for its use as an orthopaedic implant material. Grain refinement of materials as per the Hall-Petch relation leads to the mechanical strengthening of metallic biomaterials. The severe plastic deformation method offers an opportunity for grain refinement of bulk materials to produce bulk nanostructured materials. In this study, Cp-Ti sheets were subjected to repetitive corrugation and straightening (RCS) technique for up to 4 passes. This study focused on the evaluation of the mechanical strength and in-vitro bioactivity of the processed samples. The RCS-processed samples were further characterized to evaluate their average grain size, wettability and protein adsorption properties. The reduction in grain size from 50 µm to 15 µm was observed after 4 passes in the optical micrographs. The hardness and tensile strength also increased proportionally for the processed sample. The reduced contact angle value ascertained the increase in hydrophilicity thereby enhancing the amount of protein adsorption due to the increase in surface energy of the material. The in-vitro bioactivity study of the RCS sample immersed in simulated body fluid (SBF) for 21 days resulted in dense hydroxyapatite formation as compared to the as-received samples. The Ca/P ratio of the apatite was found to be 1.67, which is equal to the stoichiometry of human bone. From this study, it can be concluded that RCS techniques result in enhanced bioactivity and mechanical strength of Cp-Ti sheets which can be used as medical implants.