Investigating the energetics of bioadhesion on microengineered siloxane elastomers - Characterizing the topography, mechanical properties, and surface energy and their effect on cell contact guidance

The energetics of a polydimethylsiloxane (PDMS) elastomer biointerface were micro-engineered through topographical and chemical modification to elicit controlled cellular responses. The PDMS elastomer surfaces were engineered with micrometer scale pillars and ridges on the surface and variable mechanical properties intended to effect directed cell behavior. The topographical features were created by casting the elastomer against epoxy replicas of micropatterned silicon wafers. Using UV photolithography and a reactive ion etching process, highly controlled and repeatable surface microtextures were produced on these wafers. AFM, SEM and white light interference profilometry (WLIP) confirmed the high fidelity of the pattern transfer process from wafer to elastomer. Ridges and pillars 5 mum wide and 1.5 mum or 5 mum tall separated by valleys at 5 mum, 10 mum, or 20 mum widths were examined. Mechanical properties were modulated by addition of linear and branched nonfunctional trimethylsiloxy terminated silicone oils. The modulus of the siloxane elastomer decreased from 1.43 MPa for the unmodified formulation to as low as 0.81 MPa with additives. The oils had no significant effect on the surface energy of the siloxane elastomer as measured by goniometry. Two main biological systems were studied: spores of the green alga Enteromorpha and porcine vascular endothelial cells (PVECs). The density of Enteromorpha spores that settled increased as the valley width decreased. The surface properties of the elastomer were altered by Argon plasma, radio frequency glow discharge (RFGD) treatment, to increase the hydrophilicity for PVEC culture. The endothelial cells formed a confluent layer on the RFGD treated smooth siloxane surface that was interrupted when micro-topography was introduced.