Surface Treatments in Chitosan Coating of Titanium and Alumina Substrates for Biomedical Application

Introduction Surface modification plays an important role in improving service life and performance of components, enabling features such as antibacterial effect. In this framework, implant coating is a way to place a barrier between substrate and body environment, effectively tuning contact stiffness. Herein, different medical implant substrates have been coated with chitosan, analyzing mechanical properties and adhesion. Experimental methods Substrates were made of Ti6Al4V and α-Al๜O๝. Coating was deposited by dip-coating, leaving samples drying at room temperature. Mechanical characterization has been performed through nanoindentation and scratch tests. Results and discussion Ambient drying was found necessary as faster drying procedure would imply, under conditions of poor chemical affinity between coating and substrate, a detachment of the coating. Concerning nanoindentation and scratch, a good repeatability has been found in terms of mechanical properties of coating and scratch failure, although its reduced thickness. For both types of substrates, several failure zones of interest have been recognized: (i)plowing; (ii)cracking; (iii)substrate exposure; (iv)substrate damage. During tip penetration the coating gradually gets thinner and penetration depth stabilizes at the onset of substrate damage. Ti6Al4V substrate performed better, in terms of cohesive failure, which may be related to local variations in coating properties and thickness and adhesive failure, likely due to different surface topography of substrates. Indeed, it has been confirmed that irregularities induced on the substrate surface provide mechanical interlocking effect between coating and substrate, improving its performance. Conclusion Concluding, it can be stated that: (i)the preparation of chitosan coating requires attention to avoid delamination phenomena due to thermal gradients; (ii)surface roughness and topography become important elements in case of poor chemical affinity; (iii)failure mechanism substantially remains the same for both investigated cases. Further research will lead to improve performance of biomedical devices varying coating thickness.