NH₃/O₂ mixed gas plasmas alter the interaction of blood components with stainless steel

Stainless steel treated with a mixed gas plasma of NH₃ plus O₂ had chemical and biologic characteristics distinct from untreated stainless steel or stainless steel treated with NH₃ or O₂ plasmas used separately. NH₃/O₂ plasmas deposited nitrogen as both -CN (organic) and -NO (nitrate, nitrite)-materials not found on untreated stainless steel-and the contact angle changed from 44° to 23°. Treatment of stainless steel (and titanium) resulted in surfaces with enhanced resistance to platelet and leukocyte attachment. A gas plasma of N ₂O/O₂ also was found to reduce platelet and leukocyte attachment, suggesting that these properties may be common to surfaces coated with oxynitrites (nitrides). Upon subcutaneous implantation, no inflammation, hemolysis, or untoward thrombosis was noted in the tissue surrounding the wafers treated with the NH₃/O₂ plasmas, although the cellular density was considerably reduced by 2 weeks after implant. Collectively, the results suggest that NH₃/O₂ plasmas impart a unique character to stainless steel that may be useful in the construction of medical devices.