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Micrometer-scale poly(N-isopropylacrylamide) (poly-NIPAAm) hydrogel monolith patterns were fabricated on solid surfaces using soft lithography. At sufficiently high aspect ratios, the hydrogel monoliths swell and contract laterally with temperature. The spaces between the monoliths form a series of trenches that catch, hold, and release appropriately sized targets. A series of poly-NIPAAm monoliths were fabricated with dry dimensions of 40 microm height, 12 microm diameter, and a spacing of 12 microm between monoliths. Above the lower critical solution temperature (LCST), the monoliths collapse to their dry dimensions and the spacing between monoliths is 12 microm. Below the LCST, the monoliths swell by 70% in the lateral direction, reducing the gap size between monoliths to 3 microm. The potential use of the hydrogel monoliths as size-selective "catch and release" structures was demonstrated with a mixture of 6 and 20 microm polystyrene microspheres, where the 6 microm diameter particles were selectively concentrated and separated from the larger particles.

This paper shows the synthesis of a robust predictive controller from a process model that represents a good approximation for nonlinear chemical processes. The controller is designed using the internal model and sliding mode control concepts. This approach results in a fixed controller structure that depends on the characteristic parameters of the model. The controller performance is compared with internal model control and sliding mode control for different linear examples. All linear models present a controllability relationship (t 0/τ) of greater than 1. Simulation results indicate that the proposed controller can work for processes with elevated deadtime, despite modeling errors.