Surface properties and hemocompatibility of alkyl-siloxane monolayers supported on silicone rubber: effect of alkyl chain length and ionic functionality

Self-assembled monolayers of alkylsiloxanes supported on poly(dimethylsilox ane) (PDMS) rubber were used as model systems to study the relation between blood compatibility and surface composition. The inner lumen of PDMS tubes were first treated with an oxygen plasma. The resultant oxidized surfaces were post-derivatized by reaction with alkyltrichlorosilanes to form the mo nolayer films. The alkyl chain lengths used were slightly longer than in a previous study, and this may alter the phase-state of the monolayer from li quid-like to crystalline. The chemical properties of the monolayer were con trolled by varying the chemical composition of the alkyltrichlorosilanes us ed. Terminal functionalities included -CH3, -CF3, -COOH, -SO3H and -(CH2CH2 O)(4)OH. Surface derivatization was verified with static contact angle meas urements and X-ray photoelectron spectroscopy. Blood compatibility was eval uated using a canine ex vivo arterio-venous series shunt model. Surfaces gr afted with hydrophobic head groups such as -CH3 and -CF3 were significantly less thrombogenic than the surfaces composed of ionic head groups such as -COOH and -SO3H. Surfaces enriched in -(CH2CH2O)(4)OH had an intermediate t hrombogenicity. Silastic pump grade tubing and polyethylene tubing, used as controls, were found to be the least thrombogenic of all the surfaces test ed, (C) 1999 Elsevier Science Ltd. All rights reserved.