INFLUENCE OF TOPOGRAPHY OF ENDOVASCULAR STENT MATERIAL ON SMOOTH MUSCLE CELL RESPONSE

Although implantation of endovascular stents for the treatment of coronary and peripheral artery diseases has been one of the most rapidly used medical interventions, significant limitations in terms of a restenosis rate of 10-30% still persists. Neointimal hyperplasia characterized by a phenotypic shift of smooth muscle cells from contractile to synthetic type, has been deemed to be the predominant cause of restenosis. A number of stent surface parameters, including topography, have been attributed to play an important role in stent performance. Although endothelial cell and thrombotic response to surface roughness have been well evaluated, the effect of topography of the outer stent struts on smooth muscle cells has not been reported yet. The objective of this study, therefore, was to examine the effects of topography of a regularly used endovascular stent material (316L stainless steel) on smooth muscle cell phenotype as an indicator of neointimal hyperplasia and restenosis. A model simulating the contact of stent material in the arterial wall was developed by utilizing 316L stainless steel of varying topography. Topography of as received 316L stainless steel was modified to get electropolished and micro-grooved surfaces using electropolishing and metallographic grinding respectively. Surface characterization was done using non contact profilometry, EDS and SEM. Cell morphology was analyzed using confocal microscopy, while a standard cell proliferation assay and DAPI cell counting were employed to study cellular growth. Also, a cell based ELISA assay was developed to quantify smooth muscle α-actin expression as a marker of contractile phenotype of smooth muscle cells. It was observed that cells grown on micro-grooved surfaces were significantly more elongated than the cells on both of the other surface types. Ascertained by repeated proliferation studies, cells grown on micro-grooved surface demonstrated as much as 44% lower cell count when compared to the electropolished surface. Results of ELISA assay indicated upto 63% higher α-actin expression in cells cultured on micro-grooved surface compared to the electropolished surface. Furthermore, cells on electropolished surface demonstrated a loss of 47% smooth muscle α-actin content per cell between day1 and day 4, while that on micro-grooved surface remained the same. Since contractile smooth muscle cells are characterized by elongated spindle shaped morphology, low proliferation rate, and high α-actin expression, our results suggest that micro-grooves on 316L stainless steel promote contractile phenotype in smooth muscle cells when compared to the current industry standard - electropolished surface