Modulation of drug delivery rate by hydrogel-incorporating MEMS devices

We describe two approaches for modulating fluid flow and drug delivery rate in response to external stimuli using hydrogels incorporated in MEMS devices. The first design, a hydrogel-gated flow controller (HFC), consists of two components, a 3-dimensional crosscut structure and a loaded hydrogel. For a temperature-sensitive HFC, temperature cycling between 25 and 40/spl deg/C results in a flow rate change between 0 and 12 ml/minute, with a 30 second response time. In the second design, a hydrogel-actuated microvalve (HAM) was constructed. In such a device, a hydrogel disc is sandwiched between a porous plate and a flexible silicone rubber membrane. Swelling of the hydrogel produced by diffusion of chemical species through the porous plate, resulting in the deflection of the membrane and closure of the valve intake orifice. A HAM loaded with phenylboronic acid (PBA)-based glucose-sensitive hydrogel was tested. This glucose-sensitive HAM opens and closes in response to changes in glucose concentration and pH. The fastest response time achieved was 16 minutes using a 70 /spl mu/m thick hydrogel and a 60 /spl mu/m porous back plate.