A Programmable Hydrogel Platform with Tunable Phase Transition Temperature and Mechanical Properties for Information Encryption and Soft Actuation.

Abstract

It is still challenging to enable a precise and editable hydrogel design by quantitatively relating the molecular composition and hierarchy with the properties and functions. Herein, a programmable hydrogel system was successfully produced by copolymerizing N-isopropylacrylamide (NIPAM) with N, N'-dimethylacrylamide (DMAA) and acrylamide (AM), combined with the physical entanglement effect of hydroxypropyl cellulose (HPC). The incorporation of DMAA increased the hydrophilicity of the network, enabling precise adjustment of the lower critical solution temperature (LCST) within the range of 34°C∼49°C. The compressive modulus decreased from 18.3 to 12.3 kPa with increasing DMAA content, while the incorporation of AM significantly improved the compressive modulus from 16.2 to 24.0 kPa and reduced the mechanical loss rate to only 3.6% after 100 compressive cycles. The application of the hydrogel in information encryption was demonstrated by utilizing its quick and reversible transparent-opaque transition to achieve temperature-dependent quick response (QR) code encryption and dynamic password display. A soft actuator capable of rapid thermally induced bending was developed by constructing a bilayered poly(N-isopropylacrylamide)-co-poly(N,N-dimethylacrylamide)/poly(N-isopropylacrylamide)-co-poly(N,N-dimethylacrylamide-co-acrylamide) (P(NIPAM-co-DMAA)/P(NIPAM-co-DMAA-co-AM))structure with a modulus gradient. Finite element simulation confirmed the exponential relationship between the bending curvature and the interlayer modulus difference. This study provides a simple and rational strategy for designing a smart hydrogel platform.