Localized actuation of temperature responsive hydrogel-layers with a PCB-based micro-heater array

The space-resolved manipulation of a surface can be achieved by triggering a temperature induced swelling response locally by using a micro-heater array. In this work, we present the interaction of (i) a rigid array of heating elements that can be selectively activated and (ii) thermo-responsive hydrogel pillars that respond to the local stimulus change. The heating elements are Platinum wire heaters, which are fabricated via surface micromachining techniques on a printed circuit board (PCB). A polyimide thin film is used as a thin membrane beneath the micro heaters and as a protective encapsulation on top of the micro-heaters. The heaters are arranged in a 10 by 10 array and occupy an area of 15mm x 15 mm. The UV-structured smart hydrogel layer is made of poly(N-isopropyl-acrylamide) with Lower Critical Solution Temperature (LCST) behavior. The setup features single pillars with a diameter of 750 mu m on each single microheater. The design of the system is based on continuum-based simulations using the Temperature Expansion Model in the framework of the Finite-Element tool Abaqus. Based on the simulations, the system's capability for micro-manipulation is assessed. The analysis of the described system offers further insights into the behavior of locally actuated active polymers and their interaction with rigid systems.