Engineering Micrometer and Nanometer Scale Features in Polydimethylsiloxane Elastomers for Controlled Cell Function

Abstract

Cell movement, differentiation and metabolic function must be controlled in precise ways to produce both regenerated tissues such as bone and functional tissue equivalents such as immuno-isolated islet cells. Close examination of extracellular matrix (ECM) reveals structures on the micron and nanometer scale that are shown to influence these factors and therefore we hypothesize that cells will move based on topographical cues in the scaffold. We have engineered siloxane elastomer surfaces that mimic the ECM by combining micron and nanometer scale topographic features. Micron scale pillars and ridges ranging in height from 1.5 to 5 microns and separated by 5, 10 and 20 microns were fabricated in a silicon wafer using micro- processing techniques and replicated in polydimethylsiloxane (PDMS) elastomer. Nanometer scale pillars, ridges and more complex shapes ranging in height from 12 to 300 nanometers were superimposed on the micron scale features using nanolithography. This was achieved by using a tapping mode tip in the atomic force microscope (AFM) to plastically deform the substrate surface. The AFM enabled nano-features to be placed on sloped surfaces and added directly to the PDMS elastomer surface. Surface topography was examined using scanning electron microscopy, atomic force microscopy and white light interference profilometry to verify surface modifications and fidelity of the replication process. Results indicate that it is possible to create spatially engineered surface textures from 10^-5 m to 10^-8 m in size, in specified patterns, by using a combination of microprocessing and nanolithography techniques. As better understanding of ECM function and design is gained, the processing methods outlined here will assist in fabricating tissue engineering scaffolds optimized at the nanometer and micron scale.