A microstructured silicon membrane with entrapped hydrogels for environmentally sensitive fluid gating

In this paper, we report on the fabrication and characterization of a new hydrogel-basedmicrovalve. The basic structure is a silicon membrane having an array of orifices with aninternal structure designed to anchor the hydrogel while allowing it to gate the flow across themembrane. Each orifice (140μm diameter) has a central post suspend by four tethers on eachside of the membrane. A stimuli-sensitive hydrogel is polymerized inside each orifice. In theswollen state, the hydrogel completely occupies the void space of the orifice, completelyblocking pressure-driven fluid flow. In the shrunken state, the hydrogel contracts around thepost, allowing fluid to flow through an opened annular gap. Fabrication of the microstructuredsilicon membrane requires only two masking steps and involves a combination of deep trenchand KOH etch. Two different hydrogels, based on N-isopropylacrylamide (temperaturesensitive)and phenylboronic acid (pH and glucose-sensitive) were trapped and tested in thismicrovalve. The measured response times were 10 seconds (temperature), 4 minutes (pH), and10 minutes (glucose). The maximum pressure drop the microvalve can sustain before breakageof the hydrogel is 21 and 16kPa for temperature-sensitive and (pH/glucose)-sensitive hydrogels,respectively.Peer reviewe