Hard and soft micromachining for BioMEMS: review of techniques and examples of applications in microfluidics and drug delivery.

Recent development in microfabrication (micromachining, microelectromechanical systems, MEMS) permits the integration of hard and soft structures, and enables the design of controllable microfluidic systems, which may be applied to drug delivery. In this paper, we present a tutorial review of both classical "hard" and more recent "soft" micromachining techniques. We then provide examples where these techniques are combined to produce hydrogel-based microfluidic control systems. The most complex of these systems utilizes a very small hydrogel based on phenylboronic acid to control the flow of an insulin solution in response to changes in glucose concentration.