Future, portable, continuously-monitoring micro-total-analysis-systems are likely to require low-power portable microfluidic delivery systems allowing the actuation of fluids with a minimum expenditure of electrical energy. One method to accomplish this is to utilize a micro-osmotic pump coupled with a microfluidic accumulator and a low-power, low-leak microvalve making possible an actively-controlled, low-power, portable microfluidic delivery system
A key component of the low-power portable microfluidic delivery system is the microfluidic accumulator. The microfluidic accumulator is an energy storage element capable of storing liquid at an elevated pressure. This work represents the pioneering design efforts for microfluidic accumulators. Three microfluidic accumulators weredesigned, fabricated, and tested.
One of the microfluidic accumulators was integrated with a low-power microvalve to enable a low-power portable microfluidic delivery system. This dissertation contains the initial design efforts to create a low-power fluid delivery system capable of delivering flow whilst remaining under the power constraints of portable electrical energy sources (i.e. batteries).
All devices were fabricated in the UC Berkeley Microlab. Two of the microfluidic accumulators use novel fabrication processes that were developed in this thesis research. The microfluidic accumulator driven by surface tension is fabricated using a selective deposition of hydrophobic materials over deep reactive ion etched features. This is a critical step in fabricating a completely enclosed hydrophobic capillary in a wafer-level process. The microfluidic accumulator driven by strain energy uses a very inexpensive process involving a stainless steel substrate, photo-patternable adhesive, commercially available membranes, and a biocompatible Parylene encapsulation layer.
The low-power portable microfluidic delivery system was composed of the microfluidic accumulator driven by kinetic molecular theory and a low-power, low-leak microvalve. The two devices were integrated into a system by using a planar wafer-level process including a novel snap-away silicon piece revealing the microvalve actuation electrodes. Following the fabrication process, the devices could be very easily diced apart and tested.
The low-power portable microfluidic delivery system is capable of delivering 18μL samples requiring only 10μW at 5 V. These flow rates and volumes are sufficient to perform human health diagnostics. This system has the capability of delivering drugs and monitoring medical treatments.
December 31, 2004
Hobbs, E. D. (2004). Low-power Portable Microfluidic Delivery System. United States: University of California, Berkeley.