Understanding molecular interactions at the solid-liquid interface is essential to the development of biomaterials intended to function in the physiologic environment. Superelastic nickel-titanium, widely used for biomaterials applications, is here coated with two different phenolic compounds: pyrogallol and tannic acid. The adsorption of bovine serum albumin protein on these phenolic-coated surfaces is assessed by electrochemical impedance spectroscopy and cyclic voltammetry to understand the behavioural kinetics of proteins in a physiological environment. Using an electrical equivalent model, we show that pyrogallol coated surfaces adsorb more proteins than the native and the tannic acid-treated surfaces. We also show that in all cases, the amount of nickel ions leaching from the biomterial falls well withing the acceptable range for biocompatibility.

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The biocompatibility of implantable nickel-titanium biomaterials relies on the quality of their surfaces. In this study, nickel-titanium surfaces are coated with phenolic thin films of tannic acid and pyrogallol with the purpose of studying their corrosion resistance in physiological environments. Three tests are performed: the open-circuit potential test, potentiodynamic polarisation and potentiostatic electrochemical impedance spectroscopy. Polarisation measurements are scrutinised in order to gain knowledge concerning the kinetics of the cathodic and anodic reactions, while the open-circuit potentials and impedance spectroscopy help to study the electrolyte-surficial interactions. It is found that coating nitinol with polyphenols results in the depletion of the native oxide layer and thus a decrease of corrosion resistance. Pyrogallic treated nitinol surfaces (with a corrosion rate of 0.119 mm/year) are half as electrochemically corrosion resistive as tannic acid-coated substrate. Therefore, it is proposed that tannic treated nitinol would be a better option if implanted on biomaterial surfaces. † first, in 70% vol. ethanol; † second, for 5 min at 40°C in an ultrasonic bath with deionised water Milli-Q Direct (Millipore, Billerica, MA) with a resistivity of 18.2 MΩ cm at 25°C; † third, in 40% NaOH and water bath for 5 min; † fourth, sonicated in deionised water for 5 min with a subsequent rinse with deionised water for 5 min; † fifth, immersed for 10 min in 50% vol. HNO 3 , then sonicated in deionised water for 5 min, and then rinsed in deionised water until reaching a neutral pH, and finally, stored in 70% vol. ethanol. 2.1 Polyphenolic coatings Samples were either treated with pyrogallol (PG) diluted in 100 mM BisTris buffer pH 7.0 with 100 mM magnesium chloride at a concentration of 1 mg ml −1 or with tannic acid (TA) diluted in Biosurface and Biotribology