Bio-piezoelectric β-glycine/gelatin composite films fabricated via synergistic molecular self-assembly and thermally assisted evaporation-induced crystallization.

Abstract

Developing bio-piezoelectric materials that simultaneously provide high piezoelectric output and superior mechanical flexibility remains challenging, largely due to difficulties in achieving self-alignment and barriers to scalable synthesis. This study introduces a bio-piezoelectric composite film simply composed of β-glycine and gelatin, fabricated via thermally assisted solvent evaporation. This mechanically flexible film exhibits uniformly oriented β-glycine crystals, with gelatin serving as a biomolecular template to guide crystallization. Hydrogen bonding and electrostatic interactions between gelatin and glycine stabilize the non-centrosymmetric β-phase structure while suppressing α-glycine formation and facilitating directional self-alignment. Molecular dynamics (MD) simulations elucidate synergistic self-assembly mechanisms governed by hydrogen bonding, van der Waals forces, and electrostatic interactions. Mechanical characterization highlights the pivotal role of gelatin in reducing the brittleness of β-glycine, with Young's modulus exhibiting a proportional increase with glycine content. Piezoresponse force microscopy (PFM) and quasi-static piezoelectric coefficient (d₃₃) measurements confirm polarization uniformity in β-glycine crystals, yielding a piezoelectric coefficient of 8.6 pC N^-1, low dielectric constant of 2.8, and voltage output up to 21.9 V, which surpasses current bio-piezoelectric materials. Our β-glycine/gelatin (β-Gly/Gel) composite films exhibit sensitive electromechanical coupling for the detection of dynamic stimuli and possess favorable characteristics, including bio-nontoxicity and biodegradability. This work establishes a bi-phase biomaterial synthesis strategy that integrates high piezoelectric performance, mechanical flexibility, and biocompatibility, thereby advancing next-generation biomedical devices for physiological sensing and energy harvesting. STATEMENT OF SIGNIFICANCE: This work reports a biodegradable, biocompatible, and non-toxic bio-piezoelectric film composed solely of β-glycine and gelatin, fabricated via a simple solvent evaporation method. Gelatin guides the self-aligned crystallization of piezoelectric β-glycine, enhancing mechanical flexibility and stability. The film exhibits high piezoelectric output (piezoelectric coefficient d₃₃=8.6 pC N⁻¹, voltage output of 21.9 V), low dielectric constant, and strong electromechanical sensitivity. Owing to its natural origin, environmental safety, and tissue compatibility, the film holds promise not only for wearable sensors and energy harvesters but also as a potential implantable biomaterial for physiological sensing and bioelectronic repair.