| Hydrogels and polymers are developed and tested for microscale applications. A fabrication method that creates active hydrogel components inside microchannels through direct photopatterning of a liquid phase is demonstrated. The approach greatly simplifies system construction and performance since the functional components are fabricated in situ and the stimuli responsive hydrogel components perform both sensing and actuation functions. Dramatically improved time response (less than 10 seconds) is demonstrated for hydrogel structures capable of autonomous control of local flow.; A second fabrication technique developed involves the polymerization of a liquid meniscus. Provided the polymerization process does not significantly alter the meniscus shape, the resulting solidified structure will also be curved. As a demonstration, we have placed objects in contact with the interface of a photopolymerizable liquid and air to create various liquid menisci that were subsequently solidified with ultraviolet radiation. Comparisons between the polymerized structures and theoretical predictions for liquid menisci indicate that the polymerization process results in repeatable changes in contact angle and meniscus size.; To gain information on the swelling kinetics of the active hydrogel components, we have developed a process for the measurement of the instantaneous deformation rate of hydrogel microstructures. In developing this technique, we have adapted microscopic particle-image velocimetry, a method for measuring velocity fields in microfluidic devices. Small fluorescent seed particles are incorporated into hydrogel microstructures, and as the structures swell or contract, the displacement of the seed particles over some small time Δt is measured using a cross-correlation technique. By supplying local deformation rate data in hydrogel microstructures, this technique will allow for optimization of device designs and provide a means for determining the validity of hydrogel expansion models.; Analysis of swelling kinetics is also possible with the assumption that the rate of swelling is proportional to the square of the amount of water that the gel has to absorb from the solution. This assumption produces a linear relationship between t/v and t, where t is time and v is a dimensionless volume. Various chemical and physical cases are compared in an attempt to determine their influence on the kinetic response of constrained microscale hydrogels. |
