Thermoresponsive and Strain-Sensitive Hydrogels with Inscribable Transparency-Based Dynamic Memory Behaviors

Personal health management drives the development of intelligent hydrogel dressings, which pursue optical transparency, stretchability, and conductivity and are required to perceive specific environmental stimuli by dynamic structure, shape, or color memory. However, the incorporation of weak perceptive elements or black conductive polymers limits the fabrication of these hydrogels. Herein, we propose smart hydrogels with inscribable dynamic memorizing-forgetting transparency behavior by in situ degrading and immobilizing conductive polydopamine-doped polypyrrole (PDA-PPy) nanodots into an interpenetrating poly(NIPAm-co-acrylic acid) copolymer/polyacrylamide (PNAc/PAM) network. These hydrogels are not only optically transparent (∼64.99%), stretchable (∼1052%), self-adhesive (21-105 kPa), and highly conductive (∼0.8 S/m), but also can perceive temperature changes via structure shifts, which enables temperature-induced reversible transparency control. Especially, the temperature-dependent transparent-opaque transition kinetics of the hydrogels are tuned by the protonation of -COOH groups at pH < pK_a, utilizing which the hydrogels achieve inscribed programmed dynamic memory for information memorizing-forgetting-recalling based on a pH-engraved dynamic transparency evolution of the hydrogel in response to temperature changes. These intelligent hydrogels can not only be used as efficient near-infrared (NIR) light-controlled drug release carriers to realize on-demand drug release, but also serve as a soft sensor to recognize different body postures and movement behaviors with high strain sensitivity (gauge factor, GF = 5.98), broad working strain (5-500%), rapid response (139 ms), and excellent sensing reliability (≈1000 cycles at 50% strain).