Bioactive surfaces for improved coronary stent performance

Drug eluting stents (DES) are widely used to treat coronary heart disease. Although current DES generally perform well, restenosis and delayed endothelium healing still remains an issue following stent implantations. Research efforts are now focused on the development of stent coatings that address these limitations. Amongst many different materials currently being investigated as stent coatings, conducting polymers, such as polypyrrole (PPy) have particular promise. Drug-containing polypyrrole coatings can be deposited onto metal surfaces through electropolymerisation, a process that may be superior to the spray coating techniques commonly used by stent manufacturers. However, the full potential of this approach for use in stent coatings remains to be determined. An anti-inflammatory agent, Salicylate (Sa) was incorporated into PPy coatings by electropolymerisation in the present study and four key aspects of the coatings were characterised. Firstly, the surface morphology and topography of the polypyrrole/salicylate (PPy/Sa)coatings were examined using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). These methods were optimised through an initial investigation into surface topography of a limited number of existing bare metal stents (BMS) and DES. The surface roughness (RMS) ranged from 14 ± 11 nm (GazelleTM, scan size 5µm) to 182 ± 37 nm (Yukon®, scan size 5µm) with similarities noted between the DES. The surfaces roughness values of the PPy/Sa coatings were found to be within this range of roughness values.Secondly, the release of Sa from the PPy/Sa coatings was examined. Coatings produced by either galvanostatic or potentiostatic electropolymerisation were immersed in phosphate buffered saline and the release of salicylate monitored over time using UV-spectroscopy. Both polymerisation methods released a similar total mass of drug (~12 µg), with the release period ranging from 1 day for potentiostatic coatings to 3 days for galvanostatic coatings. Thirdly, the biocompatibility of the coatings was analysed by live/dead staining and LDHassay, showing porcine endothelial cells to successfully grow on both PPy/Sa coating types. Finally, the antioxidative activity of the coatings was investigated using a DPPH assay. The coatings were found to possess antioxidative activity for a period of 24 hours, an effect which was independent of salicylate release. This represents a potentially beneficial action that has not previously been demonstrated within a stent coating. By virtue of their controllable drug release properties and a novel anti-oxidant mechanism, polypyrrole surfaces warrant further development as a potential stent coating.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2018

Author dc:creator

• Morgan, Sarah

Advisors dc:contributor.advisor

• McCormick, Christopher
• Black, Richard

DOI

10.48730/4hjf-9z20

Identifier

T14865

Author Identifier

201250724

OAI identifier oai:identifier

oai:strathclyde:qz20ss57q