Soft mold-dry etch: a novel hydrogel patterning technique for biomedical applications

This work introduces a patterning technique for environmentally sensitive hydrogels using a combination of soft mold and dry etch. 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 the traditional microfabrication methods thus allowing the integration of hydrogels with microelectronics and MEMS microstructures. Hydrogels of different shapes and sizes were patterned in a batch scale (wafer-level) with resolutions of up to 2.5 μm. The patterned pH-sensitive hydrogels with micron-sized dimensions were able to respond within seconds. Deposited aluminum thin films on top of hydrogel microstructures was used to fabricate environmentally sensitive free standing micromirrors with a vertical displacement sensitivity of 7 μm/pH at pH 5.0. These structures open the possibility of fabricating on-chip photonic-based hydrogel microsensors.