Tunable mechanical properties of environmentally-sensitive hydrogels for soft robotics

Abstract

Stimuli-responsive hydrogels are increasingly valued for their adaptability in soft robotic applications, both as sensors and actuators. This study investigates the tunable swelling and mechanical properties of N-isopropylacrylamide (NIPAM)-based hydrogels modified with poly(ethylene glycol)-diacrylate (PEG-DA) as a crosslinker and triethyleneglycol monoethylether methacrylate (TEG-MA) as a softener. Increasing PEG-DA and TEG-MA content lowers the glass transition temperature ( T G ) from ≈ 137°C to ≈ 60°C, enhancing flexibility. Dynamic mechanical thermal humidity analysis (DMTHA) reveals a pronounced humidity sensitivity: materials become markedly softer at higher relative humidity, allowing them to adapt to dry or variable ambient environments. This tunability expands the functionality of conventional NIPAM-based hydrogels beyond the aqueous setting. The ability to independently tune swelling and stiffness further broadens the design space of these materials, enabling the precise adjustment of mechanical and swelling behavior to meet specific environmental or functional requirements. Together, these findings offer a design strategy for hydrogels with tailored thermo-hygro-mechanical performance, making them promising candidates for adaptive and stimuli-responsive components in next-generation soft robotic systems, for example, pneumatic actuators.