Silicone materials are commonly used for implantable medical devices because of their favorable bulk properties. Unfortunately, due to their hydrophobicity, silicones have a high affinity for protein adsorption which makes them susceptible to thrombosis. In this work, novel PEO-silane amphiphiles [α-(EtO)3Si-(CH2)2-ODMSm-block-PEOn-OCH3] were developed to act as surface-modifying additives (SMAs) for silicone. Based on prior work, the PEO-silane amphiphiles were expected to rapidly migrate to the material surface in response to water exposure and result in a hydrophilic and protein-resistant silicone. These were distinguishable from conventional PEO-silanes due to the hydrophobic oligodimethylsiloxane (ODMS) tether which rendered the SMAs amphiphilic. They were also unique as SMAs due to their diblock structure and crosslinking group (triethoxysilane) to prevent leaching from condensation-cure elastomers.
The PEO-silane amphiphiles were prepared with three PEO lengths (n = 3, 8, and
16) and compared to analogous non-amphiphilic PEO-silanes (PEO-controls). When incorporated into silicone via bulk-modification, the PEO-silane amphiphiles exhibited rapid and extensive water-driven restructuring versus silicones modified with the PEO-controls. Multiple concentrations of each PEO-silane amphiphile were evaluated (5, 10, 25, 50, and 100 µmol per 1 g silicone) in terms of their ability to confer hydrophilicity and protein resistance. From these results, it was determined that PEO length dictates restructuring behavior of PEO-silane amphiphiles. Only n = 8 and 16 were able to achieve substantial hydrophilicity and reduce protein adsorption, but the n = 8 length was more effective and maximized protein resistance with concentrations as low as 10 µmol per 1 g silicone (1.68 wt%).
Finally, PEO-silane amphiphiles were evaluated in terms of their ability to overcome the limitations associated with SMAs (leaching and poor abrasion recovery). It was found that triethoxysilane did not prevent leaching of PEO-silane amphiphiles (m = 13, n = 8) from silicone in water. However, increasing the ODMS tether length (m = 30) dramatically reduced leaching and water uptake for both the PEO-silane and diblock amphiphiles without impairing restructuring behavior. For all tested SMAs, excellent water-driven surface restructuring behavior persisted on bulk-modified silicones after material abrasion
