Controlling Mammalian Cell Spreading and Cytoskeletal Arrangement with Conveniently Fabricated Continuous Wavy Features on Poly(dimethylsiloxane)
Original entry: Tom Kodger, APPHY 226, Spring 2009
G.M. Whitesides et al. Langmuir 18, 3273 (2002);
"This paper reports a simple and versatile technique for generating structures on the surfaces of poly- (dimethylsiloxane) (PDMS), approximately sinusoidal waves with periods between 0.1 and 10 ím, and the use of these structures to study cell contact guidance.1 The features are generated by stretching PDMS slabs mechanically, oxidizing them in an oxygen plasma, and allowing them to relax. These surface features are similar to photolithographically fabricated grooves that have traditionally been used to investigate cell contact guidance, although their edges are rounded rather than angular. Bovine capillary endothelial cells align and elongate on these features. The morphology and cytoskeletal structure of the aligned cells are similar to those of cells described in previous studies of contact guidance on surfaces with other types of topography. These observations and comparisons indicate that sharp edges in the features defining the grooves are not essential in eliciting contact guidance. This technique provides a method for fabricating microfeatures for the studies of the interactions between cells and their environment that does not require a cleanroom or access to photolithographic tools."
Capillarity In Action
The key concept with this is paper is the ability to make submicron and micron sized features in PDMS without photolithography.
The authors are able to make corresponding structures of approximately sinusoidal waves with wavelengths between 0.1 and 10 μm; the corresponding depths of these waves are between 0.01 and 1 μm. The process is described in Fig. 1. The dimensions of the waves is controlled by varying the duration of the oxidation, up to a point, when the oxidized PDMS become brittle (~30min). The wavelength can also be tuned by varying the PDMS crosslinker and thickness; where thin, soft (low modulus) PDMS results in longer wavelengths. A continuous gradient of wavelengths can also be made (Fig. 1 route B).
The underlying chemistry is extremely straightforward. The Si-CH3 surface groups become rigid and oxidized to Si-O groups. When the stretch is released, the bulk PDMS returns to its original shape, whereas the rigid surface is placed under a compressional stress which causes the waves to be pushed normal to the stress plane.
The authors go on to explore how Bovine Epithelial Cells (BEC, not Bose Einstein Condensates :)) align with the waves. They find that while the cell aspect ratio do significantly align, the focal adhesion conplexes (visualized through vinculin staining) do not significantly align.