| AVS 55th International Symposium & Exhibition | |
| BioMEMS Topical Conference | Tuesday Sessions |
| Session BM-TuP |
| Session: | BioMEMS |
| Presenter: | P.-Y. Li, University of Southern California |
| Authors: | P.-Y. Li, University of Southern California D.P. Holschneider, University of Southern California J.-M.I. Maarek, University of Southern California E. Meng, University of Southern California |
| Correspondent: | Click to Email |
Two single-use electrothermal valves featuring low power (mW) and rapid operation (ms) were designed, modeled, fabricated, and tested. They share a common layout consisting of a composite membrane (Parylene/Pt/Parylene) situated in the flow path between two catheter segments. Current applied to the Pt thermal element initiates Joule heating that leads to thermal degradation or melting of the membrane and causes the valve to open. Compared to previous work employing metal membranes, Parylene enables low power operation (thermally degraded (125-200°C) or melted (290°C) at much lower temperatures). Parylene also enables large robust membranes for larger effective valve opening area (in this case, 330-500 µm). Membrane designs were mechanically modeled to assess performance using a large deflection (Parylene only) and nonlinear FEM models (composite). The nonlinear model indicates 1.53GPa maximum stress of the Pt element under 1 atm pressure (peak under normal operation) which is less than its tensile strength (1.83GPa); modeling and load deflection experiments showed good agreement. Transient thermal FEM modeling and video microscopy were used to investigate thermal events leading to valve opening; simulation and experimental results were in close agreement. The temperature coefficient of resistivity of the Pt element and the resistance change as a function of applied current were obtained. These results allowed prediction of the temperature of the Pt thermal element and determination of the appropriate operating current. For the prototype valve having a serpentine Pt element spanning the valve area, 25-50 mW was required to open the valve under constant current operation in air and a current ramping rate of 0.1 mA/sec was the optimal condition for valve opening for use with water. The best opening time achieved with this design was 100 ms in air but several seconds in water. The optimized valve further improves the opening speed; the Pt element (straight and serpentine) was defined only at the perimeter of the valve except for a small gap where the element connects to contact pads. Preliminary results indicate that the optimized valve can be opened in water in the millisecond range (100 mW). We also demonstrate successful application of our valve in a wirelessly operated minipump that allows bolus drug infusion in animals.