Surface Modification of a Titanium Alloy: Effects on a Polymer-Based Coating Adhesion

Title: SURFACE MODIFICATION OF A TITANIUM ALLOY: EFFECTS ON THE ADHESION OF A POLYMER-BASED COATING Objectives: This work aims to critically identify how different textures generated on a titanium alloy through mechanical and thermal processing affect the adhesion of a polymer-based coating, for application in tissue-contacting implants. Methods: Four preparation processes were studied on the Ti6Al4V titanium alloy: polishing, face milling, grit-blasting, and electrical discharge machining. Surface contact angle after processing was probed employing the sessile drop technique, supported by surface composition mapping and surface topography analysis performed in preliminary works. Chitosan-bioglass coatings were deposited via drop casting, in triplicates for each surface processing condition. Coating adhesion was measured via scratch testing. Results: Best performance is found for grit-blasted surfaces, ensuring mechanical interlocking with the coating due to their peculiar surface topography. The worst adhesion is given by the electrical discharge machined surfaces: the coating is easily detached due to a detrimental oxide layer, although the texture being similar to grit blasted samples. Coating on milled samples has slightly improved behavior compared to polished ones. Conclusions: The tests demonstrated a marked influence of titanium alloy surface processing and related texture on coating adhesion. The processes investigated in this work involve a wide range of surface modification mechanisms. Thus, this work is a step forward towards deepening of the correlation between texture parameters and adhesion of polymer-based coatings.