We describe the design, fabrication, packaging, and operation of a pneumatically driven microcage for microscale object manipulation in biological liquid. Our device overcomes the difficulties facing existing MEMS microgripper devices in liquid environments by its unique cage geometry and its nonintrusive actuation method. Multiple chromium/aluminum cantilevers, or "fingers", arranged in an asterisk pattern curl up by residual stress mismatch to form the roughly spherical cage with an average diameter of 900 /spl mu/m. The microcage opens or closes by pneumatic flexure of the cage platform, an "oxideon-latex" membrane. We introduce some novel design features developed to control beam curling effects from residual stress and a unique processing technique that enables the fabrication of the rubber membrane that actuates the device. Successful operation of the device is observed both in air and in liquids. A capture experiment with live microbes in native springwater has been video recorded and confirms the feasibility of the microcage for biomedical applications.
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