Strategies to Improve Silicone Elastomer Biocompatibility

Silicone polymers, particularly elastomers, are widely used biomaterials in applications as diverse as wound dressings, hydrocephalic shunts, breast implants and intraocular lenses. 1 While many of the properties of silicones are particularly useful for these applications, including transparency, facile control of shape, high oxygen permeability and good biocompatibility, there can be issues with these polymers in biomaterials applications. Silicone polymers, typically poly(dimethylsiloxane), are highly hydrophobic. As a consequence, proteins readily adsorb on the surface and, in certain cases, undergo unfolding leading eventually to adverse biological events. 2 We were interested in developing silicones that could be readily tuned for various applications, and for which interactions between the silicone interface and local biology could be easily controlled. In this presentation, we will examine a series of complementary strategies that permit the manipulation of surface roughness, hydrophilicity, viscosity, and the presence of small and large tethered biomolecules, and examine the relationship between these modifications and in vitro cellular responses. In addition, we will describe internal structuring of the silicone with hydrophilic entities, which permits polar drugs to be released into the local environment in a controlled manner. Surface Roughness Different cell types exhibit distinct preferences for surfaces of a given roughness. We have therefore developed a series of synthetic strategies to create random and patterned surfaces at scales ranging from about 100 nm to a few mm. While surface chemistry plays an important role in way in which cells adhere and proliferate (see below), surface roughness has a profound influence on cellular preferences. Certain cells (3T3 fibroblasts) are exceptionally productive on flat silicones, even more so than tissue culture polystyrene. However, corneal epithelial cells prefer somewhat rougher surfaces at the hundreds of nm scale. None of the cells we have examined become confluent on micron scale roughness (Figure 1). However the cells that do become adherent are remarkable effective at producing very specific ECM proteins like laminin.