Stimuli-responsive biodegradable soft gripper composed of pH-responsive alginate/gelatin/acrylic acid and non-pH-responsive acrylamide bilayer

Abstract

• A biodegradable pH-responsive hydrogel is synthesized, exhibiting swelling at high pH and shrinking at low pH. • A hybrid pH- and non-pH-responsive hydrogel gripper is precisely fabricated using a dual 3D/4D bio-printing strategy informed by the rheological analysis. • The untethered programmed actuation of the 3D/4D printed hybrid hydrogels is characterized through a series of pH variations. • The biodegradability and toxicity of the hybrid hydrogels are characterized through a series of cell viability assays. Stimuli-responsive soft robots have attracted considerable attention for their potential applications in fields such as soft robotics, flexible electronics, and bionics. Despite rapid advancements of the stimuli-responsive soft robot, many of the existing external triggering systems and materials still face limitations in selectivity. To address the dynamic pH conditions present in different regions of the human body, we have developed pH-responsive soft grippers using naturally derived, biodegradable hydrogels composed of alginate, gelatin, and acrylic acid (AAc). These hydrogels were fabricated using direct ink writing (DIW) 3D printing technology, allowing precise control over material composition and layer structure. The inherent biodegradability of these grippers offers a major functional advantage, particularly in tasks requiring intelligent shape transformation based on fluctuating pH levels. Their ability to degrade naturally after completing tasks eliminates the need for manual removal following repeated operations. This innovation enables pH-responsive actuation, tailored to the varying pH levels found in different organs and tissues, making it highly suitable for drug delivery applications. We believe that this biodegradable pH-responsive soft gripper represents a critical step forward in advancing both drug delivery systems and biodegradable soft robotics.