Fabrication of poly(ethylene glycol) hydrogel microstructures using photolithography

The fabrication of hydrogel microstructures based upon poly(ethylene glycol ) diacrylates, dimethacrylates, and tetraacrylates patterned photolithograp hically on silicon or glass substrates is described. A silicon/silicon diox ide surface was treated with 3-(trichlorosilyl)propyl methacrylate to form a self-assembled monolayer (SAM) with pendant acrylate groups. The SAM pres ence on the surface was verified using ellipsometry and time-of-flight seco ndary ion mass spectrometry. A solution containing an acrylated or methacry lated poly(ethylene glycol) derivative and a photoinitiator (2,2-dimethoxy- 2-phenylacetophenone) was spin-coated onto the treated substrate, exposed t o 365 nm ultraviolet light through a photomask, and developed with either t oluene, water, or supercritical CO2. As a result of this process, three-dim ensional, cross-linked PEG hydrogel microstructures were immobilized on the surface. Diameters of cylindrical array members were varied from 600 to 7 mum by the use of different photomasks, while height varied from 3 to 12 mu m, depending on the molecular weight of the PEG macromer. In the case of 7 mum diameter elements, as many as 400 elements were reproducibly generated in a 1 mm(2) square pattern. The resultant hydrogel patterns were hydrated for as long as 3 weeks without delamination from the substrate. In addition , micropatterning of different molecular weights of PEG was demonstrated. A rrays of hydrogel disks containing an immobilized protein conjugated to a p H sensitive fluorophore were also prepared. The pH sensitivity of the gel-i mmobilized dye was similar to that in an aqueous buffer, and no leaching of the dye-labeled protein from the hydrogel microstructure was observed over a 1 week Period. Changes in fluorescence were also observed for immobilize d fluorophore labeled acetylcholine esterase upon the addition of acetyl ac holine.