Surface Properties of Ti-6Al-4V Alloy: Part II: DPPC Monolayer and Bilayer Deposition in Aspect of Wettability

Abstract

Phospholipids as the principal constituents of biological cell membranes play important roles in cell communication, signal transportation and various intra- and extra-cellular processes. Therefore, they could be prospective modifier for Ti-6Al–4V alloy used as implants. In this research, 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer or bilayer were deposited on the titanium plate surface using Langmuir-Blodgett and Langmuir-Schaefer (LB/LS) techniques, and spreading method to investigate the change of the surface wettability caused by the deposition. Simultaneously the surface topography was investigated by optical profilometer and atomic force microscopy (AFM). The wettability was investigated by measurement of advancing and receding contact angles of water, formamide and diiodomethane on the deposited DPPC monolayer and bilayer surfaces. Then the surface free energy was calculated applying four approaches, i.e. Lifshitz-van der Waals/Acid Base (LWAB), Contact Angle Hysteresis (CAH), Owens-Wendt (O-W) and Neumann’s equation of state (Eq.State). It is obvious that the films prepared by LB/LS technique are uniform and well-packed, just opposite to those obtained by spreading. This reflects in the surface free energy, which is higher of the DPPC films produced by spreading than by LB/LS technique, which is probably caused by exposure of more DPPC hydrophilic groups outward on the Ti-6Al–4V surface. It appeared that total surface free energy of DPPC bilayer were comparable to that of monolayer. This could be explained by reorganization of DPPC molecule in contact with air atmosphere. However, the electron-donor component was larger suggesting that more polar groups were exposed outward on the bilayer than monolayer surface.