Bonds and bio- properties of hybrid laser Cr- doped DLC for implants

Full text: Diamond – like carbon (DLC) thin films are frequently used for coating of implants. The problem of DLC layers lies in bad layer adhesion to metal implants. Chromium is used as a dopant for improvement of adhesion of DLC films. Cr-DLC layers were prepared by a hybrid technology using combination of pulsed laser deposition (PLD) from graphite target and magnetron sputtering (continuous stream of material from Cr target). Atomic concentrations of carbon, oxygen, and chromium were determined from C 1s, O 1s, and Cr 2p photoelectron peak areas. Carbon (sp² and sp³ bonds) and concentration of trivalent and toxic hexavalent chromium bonds were also determined by XPS. The sp³/sp² ratio is generally decreasing for higher chromium content and carbide content increasing. The Cr ⁶⁺ spectral signal was identified from the sample surface with the highest Cr contents. Depending on the deposition conditions (laser rep. rate and magnetron power), the concentration of Cr in DLC layers moved from zero to 8.4 at%. XRD revealed no chromium peaks. In all evaluated time intervals, the population density of Saos-2 cells was the highest on samples containing higher concentrations of chromium (7.1 and 8.4 at%). On day three after seeding, the most apparent focal adhesion plaques revealed by confocal microscopy were also found on samples with the higher concentrations of chromium. The intensity of fluorescence of vinculin, i.e. a protein participating in cell adhesion, was significantly higher on all DLC and Cr-DLC samples than on control microscopic glass slides. However, the expression of collagen type I and alkaline phosphatase was the highest on Cr-DLC samples with lower concentration of Cr (0-1.5 at%). This finding was further confirmed by measurement of the intensity of fluorescence of collagen type I. We can conclude that higher concentrations of chromium supported cell adhesion and proliferation; however DLC and DLC doped with lower concentration of chromium supported cell differentiation. Closer experimental details, comparison with contact angles and antibacterial properties and differences in creation and properties of Cr-DLC layers by PLD+ magnetron or by double PLD will be also discussed. (author)