Self-actuated, pH-responsive hydrogel-driven microneedle actuator (pH-MA) patch for smart depth-controlled wound interface

Abstract Chronic wounds are frequently associated with bacterial infection, elevated alkalinity, and persistent inflammation that collectively impair the normal healing process. Yet current wound care devices are passive and cannot actively respond to critical biochemical cues in real time. To address this limitation, we present a self-actuated, pH-responsive, hydrogel-driven microneedle actuator (pH-MA) that adaptively modulates its insertion depth in response to the local wound environment, enabling autonomous and site-specific control of microneedle–tissue engagement. The pH-MA system consists of a microneedle array supported by a pH-sensitive chemomechanical acrylamide-based hydrogel layer underneath. In an alkaline environment, the hydrogel swells and mechanically advances the microneedles to achieve deeper penetration into the wound bed, whereas in acidic conditions, i.e., in an acute wound, the hydrogel shrinks and retracts the microneedles. Experimental results show that the pH-MA produces microneedle expansion of up to 148 μm and contraction of up to 191 μm from the baseline during multi-cycle actuation. The force during insertion reaches up to 260 mN, exceeding the reported skin insertion threshold by more than threefold. In vivo testing using an LAC-infected murine wound model further demonstrated the feasibility of patch application and microneedle–tissue engagement. This pH-MA platform demonstrates compelling potential as a smart wound interface capable of adaptive, depth-controlled microneedle actuation.