Page 34 - Improved endothelialization by silicone surface modification and fluid hydrodynamics modulation- Implications for oxygenator biocompatibility Nasim

adhesion, the ability of endothelial cells seeded on surface-modified silicone membranes in artificial lungs to secrete NO could be used as a measure for the anti-thrombotic property of the cell-seeded material [11, 27].
Surface modification of materials with functional groups peroxide, carboxyl, amine, and hydroxyl result in different wettability and chemistry, which are the main parameters affecting the interaction of cells with a material's surface [13, 14]. These functional groups have been claimed to improve endothelialization [16, 17], but their effect on endothelial cell stability under fluid shear stress and cell anti- thrombotic functionality, e.g. cell-mediated NO release, have been not thoroughly investigated. In the present study, silicone tubes with three different chemical functional groups, i.e. peroxide, carboxyl, and amine, but similar wettability, were developed to determine the surface chemical entity that allows strong collagen immobilization and improvement of endothelialization, cell stability, and anti- thrombotic functionality. Plasma pre-modification was performed to introduce peroxide groups acting as initiators for graft polymerization [13, 21]. Then silicone tubes containing peroxide groups were graft polymerized with acrylic acid to introduce carboxyl groups, or with aminosilane to introduce amine groups. The contact time of monomer with silicone tubes was variable to achieve the same wettability of the silicone tubes. We compared the graft density, immobilized collagen amount, mechanical properties, endothelialization (e.g. cell attachment, cell proliferation), cell stability under fluid shear stress, and cell-mediated NO release, between surfaces with carboxyl and amine groups, and between surfaces with peroxide groups, which are the initiator groups of carboxyl and amine groups in the plasma graft polymerization process.
MATERIALS AND METHODS
Materials
Surface modification and cell studies were performed in the lumen of large diameter tubular silicone (Si) membranes (inner diameter 2 mm) donated by Raumedic (Helmbrechts, Germany), with the same chemical composition as silicone membrane hollow fibers used in artificial lungs. (3-Aminopropyl) trimethoxysilane (APTES) as an aminosilane (AmS) agent was supplied by Sigma- Aldrich (Schnelldorf, Germany). Acrylic acid (AAc) was obtained from Fluka (Buchs, Switzerland) and redistilled under vacuum to remove impurities and stabilizers. Chemicals for the Griess assay were obtained from Merck (Kenilworth, NJ, USA), and were of the highest purity available. De-ionized water was used in all experiments.
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