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Doping Poly (dimethylsiloxane) for Intentional Leaching of Small Molecules into Microdevices

The goal of this study is to show that diffusion of a dopant from poly(dimethylsiloxane) (PDMS) may be applied to deliver small molecules to a microfluidic channel. Native PDMS is hydrophobic and often requires surface modifications for biologically relevant applications. Surface modification is not permanent, as the surface reverts to a hydrophobic state via bulk diffusion of monomers to the surface. Likewise, solid substances can be added into PDMS prepolymer mixture prior to curing and these particles can diffuse from the cured polymer bulk to the surface and surrounding fluid media. This characteristic of PDMS has applications for drug delivery to cell culture, cell and analyte labeling, on chip live/dead assays, flow and diffusion visualization, gradient generation, and transport phenomena in microfluidic systems. We use fluorescein to quantify and model this small molecule diffusion out of PDMS thin films and microchannels into fluid flow. The results from microchannel leaching show steady state leaching into the fluid flow over 90 minutes at concentrations around 150 nM. Results from immersion of doped PDMS shows continued leaching of fluorescein from the polymer over 4 days. The results show promise to use PDMS substrates for administering small amounts of substances to microfluidic cell cultures, as well as developing systems for studying cellular behavior with minimal interference.