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We studied sorption processes, adsorption and incorporation, of sulfate and chloride anions on the surface of well-characterized aluminum 2024 alloy using electrochemical, radiochemical, and ultrahigh-vacuum spectroscopic techniques. The measurements were carried out at an open-circuit potential and in the electrode potential range on the negative side of the open-circuit potential (cathodic polarization conditions), at various pH values. The focus was on sorption reversibility as well as on the relationship between anion's surface concentration and the electrode potential. We have found that sorption of sulfate anion is controlled by pH, surface charge, and the stability of aluminum oxide films. We have also found that adsorption of chloride is weaker than sulfate and is more irreversible since chloride incorporation occurs more readily than sulfate. The change in the alloy surface composition and morphology induced by the electrochemical treatment and anion adsorption was monitored by scanning Auger microscopy and energy-dispersive X-ray spectroscopy. The characterization exhibits copper-rich intrusions and extrusions that may act as either local cathodes or anodes in the overall alloy dissolution process. The distribution and evolution of such Cu-rich inclusions under studied experimental conditions were monitored and are reported. The dissolution of aluminum from the alloy affects both sulfate and chloride adsorption/incorporation processes. While sulfate and chloride adsorption have no effect on cathodic current measured in the studied electrode potential range, the high anion surface concentration may have a detrimental effect on the alloy stability, particularly when the beneficial influence of the cathodic polarization (protection) ends.

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Drug delivery systems incorporated onto the end of cardiac leads are used to reduce inflammation and fibrosis at the lead-tissue interface and enable optimal lead performance. In this research, confocal Raman microscopy was used to capture chemical images of the drug delivery system on pacemaker leads in different elution media in real-time. Raman images in ambient air showed that drug was dispersed in the polymer matrix as discrete particles with size ranging from 1 to 3 microm. Upon immersion into an aggressive elution medium, drug near the surface dissolved immediately and solvent started to penetrate into the polymer matrix through channels from which drug was eluted. The drug depletion depth was a function of time, which was consistent with the drug release profiles obtained by HPLC. Comparing the drug elution in aggressive solvent and biorelevant solvent, a mechanism of drug release is proposed.