Plasma processes for cell-adhesive titanium surfaces based on nitrogen-containing coatings

Abstract

Differently deposited amino functionalized surfaces were compared regarding their physico-chemical surface properties in connection with cell biological response. The nitrogen containing coatings were prepared on polished titanium alloy substrates by microwave or radio frequency discharges using allylamine and ethylenediamine as precursors, respectively, or by means of radio frequency magnetron sputtering of nylon 6.6 under N2/H2 1:1 gas mixture. The chemical composition of the deposited films was determined by FT-IR and XPS analyses. Closed pinhole-free polymer films resistant to hydrolysis and delamination were detected in most cases. Advantageous medium hydrophilicities exist. The density of primary amino groups NH2/C differs on plasma polymerized allylamine (2.5%), and plasma polymerized ethylenediamine (3.7%) from the value on plasma sputtered nylon films in N2/H2 1:1atmosphere (7.2%), determined after preparation. The positively charged surfaces improve adhesion and spreading of MG-63 osteoblastic cells as initial cellular effect. Furthermore, it could be demonstrated that a direct correlation does not exist between the densities of primary amino groups and an enhanced cell growth. In fact, not only the primary amino groups but also other nitrogen-functional groups as e.g. acid amides or imides play a role for initial cell functions. All examined plasma polymer coatings enable the cells to literally melt into the structure of the titanium alloy substrate. The edges of the cells can hardly be distinguished from the surface.