Effect of passivation and dry heat-sterilization on surface energy and topography of unalloyed titanium implants

Abstract

The effects of nitric acid passivation (P) and dry heat-sterilization (S) on the surface topography and energy of unalloyed titanium were examined. Surfaces were treated using the following sequences: cleaned in phosphoric acid (C), C and passivated (CP), CP and dry heat-sterilized (CPS), CPS and resterilized (CPSS), and C and dry heat-sterilized (CS). Surface roughnesses were examined with atomic force microscopy (AFM) and mechanical profilometry. Critical surface tensions γ c and solid surface tensions γ t were determined from contact angles of distilled water and diiodomethane. Analysis of micro-roughness using AFM revealed no statistically significant differences among most roughness parameters for the various treatment conditions. However, the CS samples had a lower ratio of real to projected surface area. Macro-roughness analysis using mechanical profilometry showed that CPSS had lower peak count (PC, i.e. number of peaks above the mean line) values than CP and CS; PC values for C surfaces were also lower than CS. Also, CPSS had higher macro- R q values than C and CPS. Values of γ c correlated positively with the non-polar/dispersive components of γ t; values were highest with the CS specimens. Higher γ t values were found for the CPSS and CPS treated surfaces, reflecting greater polar contributions on these surfaces. Thus, P and S together resulted in increased surface energy, which is thought to be a desirable surface property for bone implants.