Surface Modification of Stainless Steel 316L for Application in Biomaterials

Aparna Raman

Defense Date

9-26-2007

Graduation Date

Fall 1-1-2007

Availability

Campus Only

Submission Type

dissertation

Degree Name

PhD

Department

Chemistry and Biochemistry

Committee Chair

Ellen S. Gawalt

Committee Member

Jeffrey Evanseck

Committee Member

H. M. Kingston

Committee Member

Jeffrey Madura

Keywords

Stainless steel 316L, Self assembled monolayer, Biomaterial, Phosphic acid, Carboxylic acid, Native oxide

Abstract

Cardiovascular diseases, especially coronary artery diseases are one of the leading causes of death in the United States. After angioplasty there is a possibility of restenosis (reclosure of the artery) and thrombosis (blood clot formation). A stent, most commonly made of medical grade stainless steel (316L), is used to prevent the reclosure. While these devices are mostly successful, there are still problems that arise due to restenosis and thrombosis formation. To prevent biomaterial failure due to neoinitima and thrombosis formation after the insertion of stents, I have developed a novel method of forming ordered, covalently bound self assembled monolayers (SAMs) on the oxide surface of stainless steel 316L to prevent the non-specific adhesion of cells.

Self assembled monolayers of phosphonic acid and carboxylic acids with different terminal groups were successfully formed by a simple solution deposition method on the native oxide surface of stainless steel 316L. The films formed were analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy for alkyl chain ordering and tested for chemical and mechanical stability using sonication and adhesion tests. X-ray photoelectron spectroscopy (XPS) and DRIFT were used to determine the chemical bonding mode of the acids to the substrate. The coverage and completeness of the film on the surface was determined by contact angle measurements and atomic force microscopy (AFM). The films formed on stainless steel 316L were differentiated as monolayers or multilayers using IR, AFM, XPS and MALDI-TOF MS.

3T3 fibroblast and hUVEC endothelial cells were used to study cell adhesion on modified surfaces. A live-dead assay and viability calculations after 24 hours provided data on non-specific cell adhesion to modified substrates. A one way ANOVA was used to analyze the statistical significance of the data. Specific cell adhesion was performed successfully by modifying the amine terminated SAMs with the RGD tri-peptide.

Cell experiments showed that fewer cells attach to methyl terminated SAMs when compared to the hydrophilic terminated SAMs. Anti-vinculin staining showed more focal adhesion points in cells on amine terminated SAMs than on methyl terminated ones providing further evidence that the methyl terminus does not support cell adhesion and spreading on stainless steel 316L modified surfaces.

Format

PDF

Language

English

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