Grain boundary etched 316L stainless steel (SS) surfaces for cardiovascular stents.

摘要

The goal of this research project was to study the role of metal microstructure in inhibiting adverse responses of the arterial wall to stent implantation by both (i) accelerating endothelialization and (ii) the controlled release of anti-inflammatory drugs. The hypothesis was that the combined strategy will enhance the formation of an endothelial cell (EC) lining and also provide a sustained release of anti-inflammatory drug, dexamethasone, both of which would reduce the implant's adverse responses. The goal of the project was accomplished through seven specific aims.;The first aim was to expose the microstructure of 316L stainless steel (SS) surface that has good adhesion properties, increases endothelialization and provides depot volume and provides a decelerated release kinetic of anti-inflammatory drug dexamethasone. Chemical etching with Glycergia (HNO3+HCl+C 3H5(OH)3) produced a microstructured surface which showed higher endothelial cell density, cell spreading area and number of activated focal adhesion sites as compared to on 316L SS surfaces etched with other etching reagents tested.;Second aim was to investigate the effect of varying grain sizes of 316L SS on the attachment and spreading of human aortic endothelial cells (HAECs). Four different grain size samples; from 16microm to 66microm (ASTM 9.0-4.9) were sectioned from sheets/wires. Grain structure was revealed by mechanical polishing and subsequent etching with optimized etching reagent, Glycergia. Results indicated that the 16microm grain size etched specimen had significantly higher number of (p0.01) cells attached per cm 2 than other specimens investigated, which may be attributed to the greater grain boundary area and associated higher surface free energy.;Human blood plasma protein adsorption on as-received (AR), mechanically polished (MP), electrochemically polished (EP) and chemically etched (CE) 316L stainless steel (SS) substrates was studied in specific aim three. Atomic force microscopy (AFM) and time of flight secondary ion mass spectrometery (ToF SIMS) were used to characterize the substrates. AFM measurements performed in a low saline aqueous medium at physiological pH and ToFSIMS measurements confirm the high positive charge distribution on CE specimens, specifically at the grain boundaries. Specific adsorption of albumin, fibronectin and vitronectin on the grain boundaries was observed on chemically etched samples and quantitative analysis revealed significantly higher amounts of albumin, fibronectin and vitronectin adsorption on CE specimens as compared to other sample types. On CE samples, the adsorption of fibrinogen adsorption was lowest among the four proteins examined.;Adsorption of Gly-Arg-Glu-Asp-Val-Tyr (GREDVY) peptide on AR, MP, EP and CE substrates and subsequent HAEC behavior was studied in specific aim four. HAEC density, spreading and number of activated focal adhesion contacts formed on CE substrates were significantly higher as compared to other specimen which indicates that GREDVY peptide was effectively grafted on CE samples. Cell seeding on GREDVY adsorbed samples after 7 and 31 days of shelf life showed higher endothelial cell density and spreading on CE surfaces, which demonstrates the stability of the peptide on this surface.;Specific aim five was to examine and compare the HAEC adhesion (8 hrs, 3 days, and 7 days) response to differently finished 316L SS surfaces. Higher HAEC density, spreading and proliferation was observed on CE samples relative to AR, MP and EP samples which can be attributed to high positive charge concentration on CE specimens; specifically on the grain boundaries.;HAEC migration on as-received (AR), mechanically polished (MP), electrochemically polished (EP) and chemically etched (CE) 316L SS surfaces was studied in specific aim six. Higher HAEC migration distance, rate and percentage coverage was observed on CE surfaces relative to AR, MP and EP samples.;Electrochemically polished and chemically etched 316L SS surfaces were probed for anti-inflammatory drug dexamethasone loading and delivery in specific aim seven. Drug loading and elution from CE and EP surfaces were analyzed using fluorescence microscopy, HPLC and XPS. The data suggested that chemically etched specimens can be successfully used to attach and store drugs. Drug release kinetics indicated a sustained slow release of the drug from CE surfaces for three weeks.;Overall, the goal of the project was achieved, and it was demonstrated that 16 microm grain size, single phase austenitic (gamma) microstructure of 316L SS can be utilized to enhance endothelialization and controlled release of anti-inflammatory drug. The superior endothelialization and drug delivery potential of 316L SS material microstructure will serve as a natural barrier for reducing thrombosis, inflammation, and restenosis; the release of drugs loaded on the material will likely prevent the inflammation and proliferative responses at the site of stent implantation. (Abstract shortened by UMI.)