| Abstract
| - The fabrication of hydrogel microstructures based upon poly(ethylene glycol) diacrylates, dimethacrylates,and tetraacrylates patterned photolithographically on silicon or glass substrates is described. A silicon/silicon dioxide surface was treated with 3-(trichlorosilyl)propyl methacrylate to form a self-assembledmonolayer (SAM) with pendant acrylate groups. The SAM presence on the surface was verified usingellipsometry and time-of-flight secondary ion mass spectrometry. A solution containing an acrylated ormethacrylated poly(ethylene glycol) derivative and a photoinitiator (2,2-dimethoxy-2-phenylacetophenone)was spin-coated onto the treated substrate, exposed to 365 nm ultraviolet light through a photomask, anddeveloped with either toluene, water, or supercritical CO2. As a result of this process, three-dimensional,cross-linked PEG hydrogel microstructures were immobilized on the surface. Diameters of cylindricalarray members were varied from 600 to 7 μm by the use of different photomasks, while height varied from3 to 12 μm, depending on the molecular weight of the PEG macromer. In the case of 7 μm diameterelements, as many as 400 elements were reproducibly generated in a 1 mm2 square pattern. The resultanthydrogel patterns were hydrated for as long as 3 weeks without delamination from the substrate. Inaddition, micropatterning of different molecular weights of PEG was demonstrated. Arrays of hydrogeldisks containing an immobilized protein conjugated to a pH sensitive fluorophore were also prepared. ThepH sensitivity of the gel-immobilized dye was similar to that in an aqueous buffer, and no leaching of thedye-labeled protein from the hydrogel microstructure was observed over a 1 week period. Changes influorescence were also observed for immobilized fluorophore labeled acetylcholine esterase upon the additionof acetyl acholine.
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