Bubble engineering for biomedical valving applications

Within the overall objective of developing a low dead volume technology for basic microfluidic valving, shunting and switching functionalities, the use of microbubbles is proposed. As a case study, a normally-closed, bubble-based microvalve design is presented. The valve, implemented using an all-Pyrex technology, can withstand high pressures limited only by the degree to which the vertical etch rate of Pyrex can be controlled. Measurements made on several prototypes show valve breaking pressures of approximately 180 kPa (gage) which closely match theoretically predicted values. A geometry-based trap is used to form bubbles of air with long persistence times (>24 hours). Presentation of the microvalve is followed by a general discussion of design and engineering issues surrounding the control and creation of microbubbles for microfluidic applications. Issues include bubble pinning at sharp transitions and inclusions, and actuation.