Current and advanced microfluidic and implantable biomedical devices present an increasing need for controlled mechanical actuation at the micro-scale, without the use of batteries or external power. Implantable applications such as drug delivery microdevices require long term, battery free operation to perform their operation over the course of many months or years. In this paper, we present a micro-electro-mechanical systems (MEMS) microactuator which is water-powered and does not require any external power or control for its operation. Furthermore, we have demonstrated that by controlling the diffusion of water through a lithographically defined semipermeable membrane, we can control the rate of this mechanical actuation. The microactuator uses a water-swellable polymer as the working agent and a thin membrane of PDMS (polydimethylsiloxane) as the semi-permeable membrane to allow selective diffusion of water into the actuator. The swelling of the polymer upon contact with water and the resulting pressure generated is used as the actuation mechanism. Self-powered microactuators that use this technology can be important for many microfluidic and biomedical applications such as pulsatile drug delivery.
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