Water‐Stable, Biodegradable, and Flexible Glycine‐Based Piezoelectrics via Multi‐Length‐Scale Composite Engineering

Biomolecular piezoelectrics offer promising alternatives to ceramics for transient electronics and medical devices due to their intrinsic biocompatibility and biodegradability. Among them, β‐glycine exhibits high piezoelectricity, but its practical applications are severely limited by its inherent rigidity and its rapid destabilization in water‐rich environments. Here, we present a multi‐length‐scale engineering strategy that integrates molecular phase selection and stabilization with crystalline alignment and mesoscale composite design. β‐glycine crystals are incorporated as discrete inclusions within a continuous soft hydrophobic Poly(ε‐caprolactone) (PCL) matrix and co‐assembled with racemic DL‐methionine (DLM) to stabilize the piezoelectric β‐phase. A dual‐nozzle electrohydrodynamic spraying printing (DESP) method enables synchronized assembly, phase selection, and controlled orientation. The resulting 0–3 composites exhibit improved flexibility (469 MPa) and a high piezoelectric coefficient (175 mV m/N). The composites maintain β‐phase stability for over two months in aqueous environments, compared to rapid dissolution within seconds or phase transformation within hours for bare crystals. This work establishes a general framework for stabilizing metastable molecular piezoelectrics within flexible matrices for long‐term bio‐integrated applications interfacing with soft living systems.