Fabrication of Endothelial Progenitor Cell-capturing Stents for Vascular Re-endothelialization

Abstract

Endothelial progenitor cells (EPCs) have been identified as a crucial factor for re-endothelialization after stenting, thereby resulting in the prevention of stent thrombosis and neointimal hyperplasia. Because EPCs can be introduced by antibody–antigen interactions, the exploration of suitable antibody and the biocompatible surface modification technology including its immobilization are essential for developing an EPC-capturing stent. In this study, we fabricated a biofunctional stent with EPC specificity by grafting a hydrophilic poly(ethylene glycol) (PEG) and consecutively immobilizing the antibody against vascular endothelial-cadherin (VE-cadherin) which is a specific EPC surface marker. We chose VE-cadherin as an ideal target because it is exclusively expressed on the late EPCs and regulates cellular processes such as proliferation. Above all, the correlation between surface properties and protein adsorption was investigated in terms of hydrophilicy and micro-roughness. From the quantitative fibrinogen adsorption assay, it was suggested that the hydrophilic and smooth surface was the best choice to reduce protein adsorption. When developing EPC-capturing stent, biocompatible surface is important because non-specific protein adsorption usually causes unfavorable responses and the adsorbed proteins interfere with the molecular recognition between antibody on the stent and EPCs in bloodstream. Based on our correlation study, the surface of a stainless steel stent was sequentially modified by acid treatment, silanization and covalent attachment of polymers not only to improve biocompatibility but also to introduce functional groups on the stent surface. This polymer-grafted stent intactly immobilized anti-VE-cadherin antibodies through peptide coupling procedure. A variety of surface analysis methods such as AFM, AES, FE-SEM, and CLSM confirmed whether each step proceeded well as planned. In cellular experiment, our EPC-capturing stent specifically captured the EPCs (96±7 vs. 15±3) whereas THP-1s, human acute monocytic leukemia cells, were not adsorbed, when compared to bare stainless steel as a control. Furthermore, we confirmed that the recruited EPCs immediately developed the endothelial cell layers on the surface-modified stent. Through rabbit iliac artery study model, we compared the capability of bare stainless steel stent and our EPC-capturing stent with regard to re-endothelialization and neointimal hyperplasia. Over 90% of EPC-capturing stent was covered with endothelial cell within 3 days, whereas bare stainless steel stent was covered less than 10%. Neointimal area in stented vessel at 42 days was quite smaller in EPC-capturing stent than in bare stainless steel stent (0.95±0.22 mm2 vs. 1.34±0.43 mm2). These are totally due to high EPC specificity of the modified stent surface. In addition, immunohistochemical analysis revealed that our surface coating did not induce any further inflammation. These positive in vitro and in vivo results will encourage the extensive application of biofunctional surface modification technology for a variety of medical devices.