Development of a cytomic force transducer for experimental mechanobiology

Development of electrostatic actuators capable of functioning in ionic aqueous environments opens the possibility of manipulating cellular behavior with unprecedented fidelity. Creating a biocompatible cytomic force transduction system will provide scientists with the necessary tools to carry out systematic studies on adherent cell phenotypes with a versatile range of operating parameters. In order to generate this biotic/abiotic system a unique packaging system was combined with advanced cell patterning techniques on comb drive actuators.;The device consists of two components, an electrostatic comb drive actuator and a protective silicon cap. The actuator is fabricated from an SOI substrate and consists of a folded flexure spring that supports a 220x568microm shuttle with 139 fingers. The packaging cap is fabricated from a 200microm thick silicon substrate that is backside etched to eliminate contact with the actuator and topside though etched to provide access for cellular attachment. Once fabricated the lid is manually aligned and bound to the SOI wafer using an intermediate layer of AZ5214. To further enhance the hydrophobicity of the device vapor phase surface treatment with Trichloro(1H,1H,2H,2H-Perfluorooctyl)Silane is employed. The silane treatment of the device creates an inert hydrophobic coating that has been shown to effectively block liquid penetration into the protected comb drive cavity for over two weeks.;Characterization of the device was carried out by applying varying DC voltages and measuring the corresponding displacements. Testing of the devices in air indicates excellent continuity in performance from die to die as well as close matching of theoretical displacement vs. experimental values. Subsequent testing in culture media demonstrated actuation with as little as 20V, though per voltage displacement was noticeably less. The displacement discrepancy between air and culture media can be explained through an energy balance, which show surface tension to be the main contributing factor.;The biotic/abiotic elements were fused through the creation of a cell-silicon interface using the thermoresponsive hydrogel, poly-N-isopropylacrylimide (PNIPAAm), along with a gold adhesion layer patterned through a shadow mask. 5% PNIPAAm in DI H2O was deposited into the cell adhesion area with a microdeposition system and subsequently patterned with O2 plasma RIE to create a planar surface between the actuator and cell anchor pad. Cell studies on substrates patterned with PNIPAAm and gold have demonstrated preferential adhesion of neonatal ventricular myocytes onto gold patterned areas. The device as currently constituted shows great promise for providing scientists with a novel means of studying the effects of mechanical stimulation on cellular activity.