Ultrastretchable, Tissue-Matched Piezoelectric Gel with Preferentially Oriented Molecular Ferroelectric Crystallization

Molecular ferroelectrics hold great potential for bioelectronics because of their excellent piezoelectric responses and biocompatibility. However, conventional integration into gel matrices suffers from two major drawbacks: solvent evaporation methods often yield brittle films with poor modulus matching with soft tissues, whereas physical blending typically leads to filler agglomeration and random crystal dispersion, making it difficult to achieve preferential crystal orientation and thereby limiting the piezoelectric performance. Here, we report an in situ crystallization strategy assisted by solvent exchange. This approach enables preferentially oriented triglycine sulfate (TGS) crystals to form within a polyacrylamide (PAM) network reinforced by glycidyl methacrylate-grafted bovine serum albumin (B-G). The B-G macromer strengthens the network through covalent integration and reversible hydrogen-bonding interactions. Subsequent treatment with a choline chloride/sorbitol deep eutectic solvent (DES) induced the preferential orientation of TGS within the gel matrix. The resulting gel achieved a fracture strain exceeding 2800%, maintained mechanical integrity over 10000 loading–unloading cycles, and exhibited mechanical compliance within the range of human soft tissues (10–5–10–4 Pa–1). In vitro and in vivo evaluations further demonstrated favorable biocompatibility and its potential for flexible piezoelectric sensing applications. This work provides molecular-level insight into the design of highly conformable piezoelectric gels containing preferentially oriented molecular ferroelectrics for tissue-matched biointerfaces.