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Polystyrene (PS) is preferred over polydimethylsiloxane (PDMS) in microfluidics for applications in cell biology. However, PS has not found widespread use in microfluidics due mainly to the lack of rapid prototyping techniques. Here we address this issue by developing a silicon based solvent immersion imprint lithography (Si-SIIL) technique. Silicon is rigid, mechanically robust, and highly compatible with standard microfabrication processes, and therefore, is a promising candidate for molds. Various PS microfluidic channels as small as 20 μm in width with the aspect ratio as high as 5 were demonstrated using Si-SIIL. Bubbles and bending generated in the fabrication process were analyzed and eliminated. The surface roughness was about 27 nm (rms). Compared to the untreated PS, the molded PS retained almost the same surface properties, as characterized by contact angle measurement and X-ray photoelectron spectroscopy. Cell culture was tested to demonstrate the utility of Si-SIIL in cell biology applications. The results show that PS, with the aid of Si-SIIL, can be an alternative material to PDMS in building microfluidic chips.

The aim of this study was to investigate the effects of alginate and agarose on the response of bone marrow stromal cells (BMSCs) to chondrogenic stimuli. Rat BMSCs were expanded in monolayer culture with or without FGF-2 supplementation. Cells were then seeded in 2% alginate and agarose gels and cultured in media with or without TGF-beta1 or dexamethasone (Dex). Sulfated glycosaminoglycans (sGAGs), collagen type II, and aggrecan were expressed in all groups that received TGF-beta1 treatment during hydrogel culture. Expansion of rat BMSCs in the presence of FGF-2 increased production of sGAG in TGF-beta1-treated groups over those cultures that were treated with TGF-beta1 alone in alginate cultures. However, in agarose, cells exposed to FGF-2 during expansion produced less sGAG within TGF-beta1-supplemented groups over those cultures treated with TGF-beta1 alone. Dex was required for optimal matrix synthesis in both hydrogels, but was found to decrease cell viability in agarose constructs. These results indicate that the response of BMSCs to a chondrogenic growth factor regimen is scaffold dependent.