Investigation of silicon and shape memory polymer microactuators for deployment in biological media

There is an increasing demand for the integration of microactuators in biomedical microelectromechanical systems or BioMEMS. However, several issues arise in in vitro and in vivo deployment of microactuators. The important issues in deploying silicon electrostatic and thermal actuators in the in vitro cell culture media are electrode polarization, electrolysis, anodization, and increased heat dissipation. These issues are addressed in the first part of this thesis with a focus on in-plane actuators. The issues with deploying microactuators in vivo are further complicated due to material biocompatibility and device reliability concerns. Issues relating to the use of a shape memory polymer microactuator for a unique in vivo application are discussed in the second part of this thesis.; First, a generalized model to predict frequency-dependent electrostatic actuation of silicon MEMS in conducting liquids is presented and shown to have good agreement with the experimental results. The model provides guidelines for the design of electrostatic actuators in conducting solutions. The challenges in deployment of electrostatic comb-drive actuators in high electrical conductivity solutions such as the cell culture media are discussed and solutions are presented. We have also investigated the performance of silicon thermal actuators in saline solutions. It has been found that thermal actuators can be operated in saline solutions and cell culture media with relatively low drive frequencies compared to the electrostatic actuators. However, a reduced efficiency due to excessive heat dissipation limits the performance of thermal actuators in liquids. To address this issue, an encapsulation solution is demonstrated for in-plane thermal actuators by preventing direct contact of the thermal actuator with the liquid. As an application of the silicon actuators, design and characterization of a BioMEMS device for mechanical stimulation on single adherent cells in vitro is presented.; Additionally, a novel actuation solution to deploy soft polymeric probes inside brain tissue at a controlled rate using shape memory polymers (SMP) is proposed. Design, fabrication and characterization of the SNIP neuronal probes are described. It is shown that these probes can be deployed at body temperature at a desired slow rate and generate enough force to overcome the tissue resistance during deployment.