Abstract
We have successfully demonstrated a passive microfluidic chip that can perform preprogrammed, rate-switchable osmotic pumping in a controlled manner. A polydimethylsiloxane diaphragm powered by osmosis is employed to provide the desired volumetric displacement for microfluidic pumping. Regulated by integrated time switches, the diaphragm is actuated intermittently to realize time-varying pumping patterns. Meanwhile, vacuum generators with dedicated check valves and breather valves are employed to achieve the priming of liquid samples. This preprogrammed microfluidic chip is composed of functional polymers and microfabricated by milling, laser machining, molding and multilayer bonding processes. In the prototype demonstration, vapor-permeable thermoplastic polyurethane is used as the semi-permeable material for osmosis. With an effective permeating area of 10.6 mm2 and a thickness of 15 μm, a constant osmotic pumping rate of 9.3 nl/s is measured. It is demonstrated that the passive micro-chip can be preprogrammed to realize operating sequences of constant-rate pumping alternated with pauses for minutes. The actual pumping rates and on/off periods are found to be less than 5 % different from preprogrammed, while can be readily tailored to achieve desired time-varying transport patterns. As such, timed reaction and incubation sequences can be realized on this passive micro-chip, which could fulfill the needs of a variety of portable and point-of-care testing applications.