High-resolution technique for fabricating environmentally sensitive hydrogel microstructures

This communication introduces a novel high-resolution technique for fabricating hydrogel microstructures using photoresist lithography and dry etching. This method alleviates the need for photoinitiators used in conventional approaches and is applicable to a broad range of hydrogels. This technique is also compatible with traditional microfabrication methods, thus allowing the integration of hydrogels with microelectronics and microelectromechanical system microstructures. Environmentally sensitive hydrogels of different shapes and sizes were patterned in a batch scale (wafer-level) with resolutions down to 2.5 mum. The patterned pH-sensitive hydrogels with micron-sized dimensions exhibit volume responses within seconds of change in pH. Deposited aluminum thin films on top of hydrogel microstructures were used to fabricate environmentally sensitive free-standing micromirrors with a vertical displacement sensitivity of 7 mum/pH at pH 5.0. These structures open the possibility of fabricating on-chip photonic-based hydrogel microsensors.