Anti-fouling silicone coatings prepared with PEO-silane amphiphiles
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abstract
The protein resistance, subsequent thromboresistance, and marine anti-biofouling ability of poly(ethylene oxide) (PEO) was enhanced by the addition of a flexible, hydrophobic siloxane tether which imparts configurational mobility and amphiphilicity to the PEO. Conventional PEO-silanes (i.e. no tether) lack these beneficial properties and thus are limited in their ability to reduce biological adhesion onto bulk-crosslinked, silicone medical devices (e.g. hemodialysis catheters) or onto silicone marine coatings. To achieve antifouling behavior, PEO-modified silicones require the ability to undergo extensive water-driven surface restructuring so as to form a hydrophilic, PEO-enriched layer. A siloxane tether, due to its flexibility and similar hydrophobic nature as a silicone matrix, may potently enhance PEO migration to the silicone-water interface. New PEO-silane amphiphiles were prepared by variations to the siloxane tether length and PEO end-group chemistry to enhance water-driven surface-restructuring and PEO hydration, respectively. General formulas for the PEO-silane amphiphiles include -(EtO)3Si-(CH2)2-oligodimethylsiloxanem-block-poly(ethylene oxide)8-OCH3 for those with variable siloxane tether length (m = 0, 4, 13, 17, 24, and 30) and -(EtO)3Si-(CH2)2-oligodimethylsiloxane13-block-poly(ethylene oxide)11-sulfobetaine for those with a zwitterion PEO end-group. PEO-silane amphiphiles were used to bulk-modify silicones towards the goal of reducing protein adsorption and biofouling. First, a PEO-silane amphiphile bearing a siloxane tether of length m = 13 was incorporated into medical-grade silicone with variable amounts. It was determined that only a small amount ( 5wt%) was necessary for high protein resistance. PEO-silane amphiphiles of variable siloxane tether length (m = 030) and a conventional PEO-silane control (i.e. no tether) were bulk-crosslinked into silicones and surface-grafted onto silicon wafers. Although the surface-grafted PEO-silane amphiphiles were less protein resistant than the PEO-silane control, when incorporated into a bulk-modified silicone, the PEO-silane amphiphiles exhibited superior surface restructuring and, hence, protein resistance. An intermediate siloxane tether length was observed to maximize surface restructuring and subsequent protein and biofouling resistance. Lastly, the chemistry of PEO-silane amphiphiles was modified to include a zwitterion PEO end-group. These novel PEO-silane amphiphiles may be used for the bulk-modification of silicones to achieve high levels of PEO hydration while maintaining the ability of the PEO to restructure to the surface via a siloxane tether.
