Particle imaging technique for measuring the deformation rate of hydrogel microstructures

A technique for measuring the instantaneous deformation rate of hydrogel microstructures is introduced. 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 the hydrogel microstructure, and as the structure swells or contracts, the displacement of the seed particles over some small time Dt is measured using a cross-correlation technique. By providing local deformation rate data in hydrogel microstructures, this technique will allow for optimization of device designs as well as providing a means for determining the validity of hydrogel expansion models. © 2000 American Institute of Physics. @S0003-6951~00!01622-3#