Protein adsorption onto medical alloys: Voltage effects
Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering
Protein adsorption, Medical alloys, Fibrinogen, AFM, Electrowetting, Electrochemical impedance spectroscopy
Biomedical Engineering and Bioengineering | Engineering | Engineering Science and Materials
This work examined the adsorption of an important-plasma protein, fibrinogen (Fb), onto a clinically-relevant-biomedical alloy, 316L stainless steel (SS) and electrically polarized 316L SS. Then, several key-interfacial properties important to protein adsorption were examined. The overriding role of electrochemical (EC) charge-transfer processes in the behavior of both the adsorption of Fb and interfacial properties was apparent.
Adsorption of Fb onto polarized 316L SS was observed and quantified using both in situ and ex situ atomic force microscopy (AFM) techniques. Significant differences in Fb adsorption were observed across potential. Ex situ studies showed significantly lower area coverage and height of adsorbed Fb at cathodic potentials. In situ studies showed significantly slower kinetics below -100 mV. Current density data showed large charge-transfer processes (∼1x10 -5 to 1x10 -4 A/cm 2 ) taking place at voltages below -100 mV.
A parallel-plate electrocapillary method was used to measure changes in metal-electrolyte surface energy ( Δγ sl ) with potential. The results showed increasingly negative Δγ sl values on 316L SS at more cathodic voltages (i.e., more hydrophilic) and little to no change above -100 mV. These data correlate linearly with current density.
Force measurements using a colloidal-AFM probe measured interfacial forces. Increasingly repulsive forces scaled with increasingly cathodic potentials; little interaction was detected at anodic potentials. These data correlated linearly with current density.
The EC impedance was also studied. Electrochemical AFM (ECAFM) simultaneously gave impedance and structural changes with potential. Several regions of oxide topography/impedance characteristic were apparent which matched closely with the impedance behavior of the system. Through Mott-Schottky analysis the presence of the flatband potential was determined to be around -150 mV.
Property observations of polarized 316L SS, specifically the interdependence of current density, surface energy and interfacial forces indicate the importance of Faradaic processes at this interface. The striking importance of Faradaic processes in this aspect of the biological system (Fb adsorption) provides a basis for further investigation, both of this and other biomedical-alloy systems. Electrochemistry matters.
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Gettens, Robert T. T., "Protein adsorption onto medical alloys: Voltage effects" (2007). Biomedical and Chemical Engineering - Dissertations. Paper 9.