A water-powered osmotic microactuator

Abstract

This paper presents a microactuator that utilizes osmosis to produce mechanical actuation without consuming any electrical energy. The microactuator is made of cellulose acetate with cylindrical chamber of 500 to 2000 /spl mu/m in diameter and of 200 to 1000 /spl mu/m in depth. Sodium chloride is chosen as the osmotic driving agent to be placed inside the chamber. A semipermeable diaphragm made of cellulose acetate is processed at the bottom of the chamber to control the water flow. Either a cellulose acetate diaphragm or an impermeable diaphragm made of vinylidene chloride and acrylonitrile copolymer is spin-coated on top of the chamber as the actuation diaphragm. Using the principle of osmosis, this water-powered, osmotic microactuator can employ high osmotic pressure (a chemical potential) up to 35.6 MPa to provide hydrostatic pressure for mechanical actuation. Experimental measurements show that up to 800 /spl mu/m vertical diaphragm movement (diaphragm size of 800 /spl mu/m in diameter) and constant volume expansion rate of 4.5 to 11.5 nL/h can be achieved. When integrated with other microfluidic devices, this osmotic microactuator could serve as a clean, compact and inexpensive fluidic actuation source.