Fully physically crosslinked POSS-based hydrogel with low swelling, high stretchable, self-healing, and conductive properties for human motion sensing

Conductive composite hydrogels are attracting much attention as artificial skin-like materials, with great potential for applications in wearable electronics, flexible printable electronics, and tissue engineering scaffolds. However, the design of conductive hydrogels possessing multifunctional properties such as excellent mechanical properties, self-healing, high conductivity, low swelling ratio (SR), and high strain sensitivity remains a challenge. Here, we designed and synthesized a polyhedral oligomeric silsesquioxane (POSS)-based composite hydrogel (OCAPS/PAA–Na/PAM) via the copolymerization of acrylamide and an ionic supramolecular monomer consisting of a cationic octa(3–chloroammoniumpropyl) silsesquioxane (OCAPS) core surrounded by sodium acrylate to achieve a combination of high stretchability, low SR, self-healing, high conductivity, biocompatibility, and strain sensing properties. The introduction of OCAPS as a physical crosslinking agent enhanced the toughness and compression properties of the hydrogel. The SR of the OCAPS/PAA–Na/PAM hydrogel was greatly suppressed, with a much lower value (SR: 200 %) than that of the hydrogel without POSS (SR: ~22,000 %). The elongation at break and fracture energy reached 4396 % and 3.7 kJ·m−2, respectively. OCAPS/PAA–Na/PAM hydrogels also had good self-healing properties due to the sufficient electrostatic interactions and hydrogen bonding between OCAPS and the polymer chains. Moreover, the supramolecular monomers provided abundant ion sites and in-situ generated NaCl, which imparted good electrical conductivity (0.678 mS·cm−1) and excellent strain sensitivity (gauge factor = 3.78) to the hydrogel. The OCAPS/PAA–Na/PAM hydrogel could detect electrical signal changes in large strain and small limb deformation and they showed good biological transmission sensitivity, which is expected to contribute to the fields of safety detection, gait detection, and wearable devices.