Surface properties of Ti-6Al-4V alloy part III: Biostability of deposited DPPC monolayer and bilayer

Abstract

Solid supported lipid layer has been of broad interest for decades. DPPC modified Ti-6Al-4V could be used as dental and orthopedic implants because of excellent mechanical property, corrosive resistance and enhanced biocompatibility. However, to be long time lasting, biostability is also a crucial property of implanted surface. In previous Part I and Part II surface properties of Ti-6Al-4V depending on the surface smoothness (AFM and Profilometry images, wettability) both of bare surface as well with the deposited monolayer and bilayer of DPPC were investigated. In this paper stability of the deposited DPPC layers on Ti-6Al-4V alloy was examined. The plates with the DPPC film were placed in water, phosphate buffer saline, or 1% Triton X-100 solution for 2h at 37°C and then dried in a vacuum desiccator at room temperature over night. Optical profilometer and atomic force microscopy (AFM) were applied to obtain surface topography. From the measured advancing and receding contact angles of water, formamide and diiodomethane, the surface free energy was calculated using Lifshitz-van der Waals/Acid Base (LWAB) and Contact Angle Hysteresis (CAH) approaches. The obtained results exhibited significant changes in the surface structure occurring during these treatments. The most drastic changes were observed for the layers treated with Triton X-100, where in the case of DPPC monolayer it might be completely removed from the surface. The changes in topography reflected also in those of the apparent surface free energy, which were the greatest after the contact with Triton where both the surface of monolayer and bilayer became highly polar. However, the contact with pure water reduced only to some extent the surface free energy of the layers, except for the hydrogen bonding interactions γs− on the bilayer surface.