Microsystems based on polypyrrole microactuators : microrobots and cell clinics

Sammanfattning: Conducting polymers like polypyrrole (PPy) are suitable materials for actuators. PPy undergoes a volume change, driven by redox processes accompanied by ion movement. This volume change is reversible. By combining PPy with a support and/or electrode layer into a bilayer, actuators can be made. These actuators are operated in a liquid electrolyte. The microactuators presented in this thesis are based on an Au/PPy bilayer in which the Au acts both as a structural layer and electrode. PPy doped with DBS- ( dodecylbenzenesulfonate) anions (PPy(DBS)) is used and the microactuators are operated in an aqueous salt solution, usually NaDBS. However, the microactuators function also in other biological more relevant media, like blood plasma, urine, and cell culture media, making them excellent tools for cell biology and biomedicine. The thesis is focussed on methods to microfabricate devices, and their operation and use.PPy/Au microactuators, which have all the electrodes necessary for the actuation --the working, counter, and reference electrodes -- on-chip, were developed. The microactuators' performance was as good as when standard, off-chip counter and reference electrodes were used. Specifically, the speed of actuation was the same.A novel microfabrication method based on a Ti sacrificial layer was developed in order to create individually addressable and controllable polypyrrole-gold microactuators. Using these individually controlled microactuators, a micrometer-sized manipulator or microrobotic arm was fabricated. This microrobotic arm can pick up, lift, move, and place micrometer-sized objects within an area of about 250 x 100 μm2, making the microrobot an excellent tool for single cell manipulation. Also, these individually controlled microactuators were used to obtain movements both out of and in the plane of the substrate surface. A scheme to make true three-dimensional movements is demonstrated.Finally, the development of a cell clinic is presented. This is a micromachined cavity, or microvial, that can be closed with a lid. The lid is activated by two PPy/Au microactuators. A pair of Au electrodes was placed inside the microvials in order to perform impedance studies on single or a small number of cells. Impedance measurements on Xenopus leavis melanophores are reported. A change in the impedance upon cell spreading was measured and intracellular events such as the aggregation of pigment granules were identified. The electrical data are correlated to optical microscopy.