| This thesis describes development of microfluidic devices for chip scale fluid handling, specifically, passive chaotic micromixers, hydrogel microvalves, and pH regulation microsystems. All these devices have relatively simple design, high performance, low power consumption, and ease of fabrication and integration into a system.; Diffusion-limited mixing at low Reynolds number (Re) is often inefficient for many biological processes. Chaotic advection, which results in rapid distortion and elongation of stream interfaces and increases the interfacial area across which diffusion occurs, can lead to rapid mixing at low Re. Based on the principle of chaotic advection, two passive in-line micromixers consisting of a 3D channel geometry were designed, fabricated, and tested. Flow experiments have confirmed the effectiveness of these designs to produce chaos and enhance mixing for small Re (1 ∼ 100).; To simplify system construction and assembly, an in-situ photopolymerization technique that is used to create functional polymer microvalves within microchannels for local flow control was developed. Several hydrogel microvalves, including three 2D valves and one 3D hybrid valve, were fabricated using in-situ photopolymerization. The valves consist of a single smart material that undergoes a volume change in response to changes in local pH. Experiments showed that the hydrogel microvalves have a number of advantages over conventional microvalves, including high performance, relatively simple fabrication and assembly, no power requirement, and no integrated electronics.; In the last part of the thesis, two integrated microsystems designed to provide self regulation of pH in bioassays are demonstrated. The first system is based on the counterflow microdialysis principle, whereas the second system involves direct addition of an acidic or basic buffer solution into a sample solution. In both systems, a hydrogel component is used as a pH sensor, controller, and valve, simultaneously. Oscillatory modulation of the flow was achieved, and the feasibility of autonomous control of pH in microsystems has been demonstrated. |
