Biological response of stainless steel surface modified by N2O/O2 glow discharge plasma

Stainless steel wafers were treated with the glow discharge plasma of mixed N₂O and O₂ at different molar ratios at a certain discharge condition to create desirable biological characteristics to the surfaces. It was found that the molar ratio of N₂O to O₂ in the mixture at 1:1 used for plasma surface modification caused high apoptotic percentage. Contact angle measurement showed that the surface of stainless steel samples became very hydrophilic after the plasma modification with a value of 15°-30°. The control stainless steel chips without plasma treatment had a contact angle of 40 ± 2°. The data of Electron Spectroscopy for Chemical Analysis (ESCA) indicated that there was a certain amount of oxynitrites formed on the plasma treated surfaces, which was considered to play an important role to cell apoptosis and anti-clot formation in cell culture tests. The ESCA depth profile of up to 250 Å from the top surface showed the change of elemental compositions within 40-50 Å of the surface by the plasma treatment. The decreased platelet attachment, combined with increased apoptosis in fibroblasts is a distinct combination of biological responses arising from the mixed gas plasma treatment. These initial results suggest it may be of particular use relative to stainless steel stents where decreased platelet attachments are advantageous and induction of apoptosis could limit in-stent restenosis.