Comparative in vitro performances of bare Nitinol surfaces

Comparative fibrinogen adsorption and platelet morphology were evaluated on a wide array of well-characterized Nitinol surfaces (polished, chemically etched, boiled in water, electropolished in different electrolytes and heat treated). XPS, SEM, AFM, atomic adsorption spectroscopy and electrochemistry were employed to acquire information on surface chemistry, topography and Ni release. Obtained surfaces, of various topographies and crystallinity from mostly amorphous to nano-crystalline with Ni concentration from 1 to 8%, induced Ni release into biological medium in a subtoxic range (0-11 ng/ml/cm(2)). Fibrinogen adsorption to Nitinol surfaces ranged from that characteristic to pure Ni (130 ng/cm(2)) to pure Ti (300 ng/cm(2)). It was directly proportional to the Ti surface concentration and correlated with open circuit potential related to surface charge. Human platelet morphology varied from round to fully spread depending on surface treatment. Base layer of fully spread cells detected on all surfaces could be even and smooth with no propensity for thrombosis or sticky causing platelet aggregation and thrombus-like structures. Using appropriate surface treatments thrombogenicity of Nitinol can be manipulated to satisfy both the requirements for stents and defect closures.