Conformal Transfer Printing on Curved Surfaces Using a Programmable-Adhesive Hydrogel Stamp

Abstract Transfer printing is a key manufacturing method for flexible and conformal electronics. Nonetheless, the transfer of functional structure and components onto non-planar surfaces is a big challenge due to the inherent trade-off between strong adhesion for effective pickup and weak adhesion for clean release. We present a hydrogel-based conformal transfer printing strategy with dynamically tunable adhesion achieved through the synergistic coupling of temperature, surface microstructures, and surface wetting. Our hydrogel stamp has high adhesion in a dry, low-temperature state that can effectively pick up functional components, and the adhesion decreases rapidly when heated above its lower critical solution temperature (≈45 °C) or by the stimulus of water, allowing for gentle and clean release. The hydrogel has a low elastic modulus (≈26.6 kPa), allowing it to conformally contact rough or curved substrates. Meanwhile, the surface structure of micropillars reduces the real area of contact, allowing for controlled detachment of microscale features. This mechanism for the regulation of adhesion enables programming of adhesion, tracking a free switching ratio of about 4 or 20 times between the maximum and minimum adhesion forces. Using this strategy, the transferring of metal circuits and LED arrays onto non-planar substrates is achieved successfully while preserving structural and electrical functionalities. This work establishes a versatile platform for programmable adhesion control, with strong potential for applications in the next-generation flexible and wearable electronics.