Page 13 - Improved endothelialization by silicone surface modification and fluid hydrodynamics modulation- Implications for oxygenator biocompatibility Nasim

GENERAL ABSTRACT
Endothelialization of hollow fibers in new types of artificial lungs, so-called biohybrid artificial lungs, is promising to decrease thrombotic complications resulting from blood flow through these devices. This thesis aimed to develop a stable and anti-thrombotic functional endothelial cell layer on the surface of silicone hollow fibers using silicone surface modification and fluid hydrodynamics modulation. We started by collagen immobilization on the inside surface of silicone tubes using different functional groups. Collagen-immobilized silicone tubes with amine or carboxyl groups increased the number of endothelial cells by 3-4-fold after 6 days of culture and stimulated nitric oxide release by endothelial cells by approximately 3-fold. Collagen immobilization with carboxyl groups was applied to the outside surface of silicone hollow fibers, but 27% of the cells still detached at a high fluid shear stress of 30 dyn/cm2. Therefore, flow preconditioning of endothelial cells with 12 dyn/cm2 fluid shear stress in a parallel-plate flow chamber for 24 h was used to stimulate cell monolayer retention under high fluid shear stress. Flow preconditioning of endothelial cells decreased cell detachment under high fluid shear stress of 30 dyn/cm2 by 8-fold, compared with un-preconditioned cells. Shear stress simulation at the cell’s surface by COMSOL software coupled with cell experimental results showed that flow preconditioning of endothelial cells tailors a smooth surface of the cells, which resulted in a more homogenous shear stress distribution at the cell’s surface, and decreased cell detachment.
The ultimate success of developing biocompatible materials depends on the anti-thrombogenicity of the surface and the degree of confluency of the endothelial cell layer. Therefore, sodium nitrite as an anti-thrombotic agent and/or growth hormone as a growth-inducing agent in free-form or in nanoliposomes were blended with collagen solution, and immobilized on silicone tubes. Sodium nitrite- collagen conjugate with 25 μM initial sodium nitrite maximally increased endothelial cell number by 28% after 6 days of culture. Five hundred μM initial sodium nitrite maximally decreased platelet adhesion by 3-fold compared with collagen coating. The biomimetic nanoliposomal sodium nitrite (nNitrite)-nanoliposomal growth hormone (nGH)-collagen (Col) coatings resulted in endothelial cell confluency of 83-119%, and decreased platelet adhesion by 50-76% after 6 days of endothelial cell culture.
The application potential of the biomimetic nNitrite-nGH-Col coating on the outside surface of silicone hollow fibers was also assessed under blood flow shear stress with the aim to improve the performance of biohybrid artificial lungs. Quantification of the nitrite production from surface-modified fibers under different shear stresses coupled with simulations of nitrite transport in a parallel-plate flow chamber using COMSOL software were used to determine nitrite bioavailability at the hollow fiber-blood interface, which is of crucial importance to inhibit thrombus