Effect of wire fretting on the corrosion resistance of common medical alloys

Synthesis and in-vitro antibacterial properties of a functionally graded Ag impregnated composite surface

Silver is considered promising in medical devices to prevent infection due to its excellent properties of broad antibacterial spectrum and persistent antibacterial activity. Herein, silver impregnated functionally graded composite surfaces have been developed by a novel duplex plasma deposition technique, which combines the double glow sputtering process and active screen plasma nitriding process. The composite surfaces include a surface antibacterial layer and a bottom supporting layer, which are deposited simultaneously. The functionally graded structure endows the composite surfaces with antibacterial activity, combined with improved wear resistance. The multilayer structures were observed by scanning electron microscopy, and the graded distribution of silver and nitrogen was verified by glow discharge optical emission spectroscopy. X-ray diffraction and X-ray photoelectron spectroscopy were used to analyze the microstructures and chemical states of the components. Results from physical properties tests indicated that the composite surfaces have increased hardness, lower contact angles, excellent scratch resistance and wear resistance. The in-vitro antibacterial tests using the Gram-negative E. coli. NCTC 10418 also showed that over 99% of bacteria were killed after 5 h contacting with the composite surface.

The use of electrochemical techniques to evaluate the corrosion performance of metallic biomedical materials and devices

The corrosion performance of metallic biomedical materials and devices is commonly evaluated using electrochemical techniques. Although test standards involving such techniques have been released to address some forms of corrosion, a key issue is application of the results with regard to use of an implantable device in vivo. This review focuses on nitinol, 316L/LVM stainless steel, and Co-Cr alloys and is intended to provide some perspective on the significance of results from tests concerning general corrosion, localized corrosion, galvanic corrosion, and fretting corrosion of these alloys in simulated physiological solutions. It also examines the factors that could cause differences in the corrosion performance between in vitro and in vivo exposure, with the goal of providing some rationale for applying electrochemical characteristics obtained from the tests to predict the corrosion performance in vivo. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1189-1198, 2019.

Characterizing fretting damage in different test media for cardiovascular device durability testing

In vitro durability tests of cardiovascular devices are often used to evaluate the potential for fretting damage during clinical use. Evaluation of fretting damage is important because severe fretting can concentrate stress and lead to the loss of structural integrity. Most international standards call for the use of phosphate buffered saline (PBS) for such tests although there has been little evidence to date that the use of PBS is appropriate in terms of predicting the amount of fretting damage that would occur in vivo. In order to determine an appropriate test media for in vitro durability tests where fretting damage is being evaluated, we utilized an in vitro test that is relevant to cardiovascular devices both in terms of dimensions and materials (nitinol, cobalt-chromium, and stainless steel) to characterize fretting damage in PBS, deionized water (DIW), and heparinized porcine blood. Overall, tests conducted in blood were found to have increased levels of fretting damage over tests in DIW or PBS, although the magnitude of this difference was smaller than the variability for each test media. Tests conducted in DIW and PBS led to mostly similar amounts of fretting damage with the exception of one material combination where DIW had greatly reduced damage compared to PBS and blood. Differences in fretting damage among materials were also observed with nitinol having less fretting damage than stainless steel or cobalt-chromium. In general, evaluating fretting damage in PBS or DIW may be appropriate although caution should be used when selecting test media and interpreting results given some of the differences observed across different materials.

Endovascular Devices and Revascularization Techniques for Limb-Threatening Ischemia in Individuals With Diabetes

Diabetes mellitus (DM) is a rapidly worsening global epidemic over the last thirty-five years. The increased prevalence of DM has changed the phenotypic expression of atherosclerotic limb threatening ischemia (LTI), resulting in an increase in lesions in the tibial vessels. These patients are also afflicted with peripheral neuropathy, foot deformities, and medial calcification of the vasculature. In response to the evolving phenotype of atherosclerosis, newer minimally invasive tools and techniques have been developed to improve the blood supply in LTI. Arterial access, traditionally obtained from the contralateral common femoral artery (CFA) in a retrograde fashion, is now also frequently being obtained in the ipsilateral limb in an antegrade fashion. Retrograde access of the tibial, pedal, tarsal, or calf collateral vessels is also being utilized to provide a route through which wires, catheters, balloons and stents may be placed. Wires have evolved to have a variety of diameters, materials and coatings providing interventionalists with a wide variety of choices when attempting to traverse blockages in the arteries. When catheters and wires fail to traverse the lesion, newer chronic total occlusion (CTO) devices have been developed to aid in the placement of a wire across the offending lesions. Due to medial calcification associated with DM, atherectomy devices have been developed to debulk the atherosclerotic plaque within the vessel. High pressure balloon angioplasty with or without stents remain the mainstay of intervention, with drug-coated balloons (DCBs) and drug-eluting stents (DESs) now being frequently used to prevent reocclusions of atherosclerotic lesions.