Molecular Engineering of Amino Acid Crystals with Enhanced Piezoelectric Performance for Biodegradable Sensors

Amino acid crystals have emerged as promising piezoelectric materials for biodegradable and biocompatible sensors; however, their relatively low piezoelectric coefficients constrain practical applications. Here, we introduce a fluoro-substitution strategy to overcome this limitation and enhance the piezoelectric performance of amino acid crystals. Specifically, we substituted hydrogen atoms on the aromatic rings of L-tryptophan, L-phenylalanine, and N-Cbz-L-phenylalanine with fluorine, resulting in significantly elevated piezoelectric coefficients. Density functional theory calculations further indicate that fluorination strengthens polarization by modifying molecular dipole moments. Consequently, these fluoro-substituted crystals achieve piezoelectric coefficients of up to 50.36 pm/V, surpassing those of other organic piezoelectric materials such as polyvinylidene fluoride (PVDF), poly(L-lactic acid) (PLLA), and gelatin. When integrated into flexible, biodegradable force sensors, the fluoro-substituted crystals exhibit a broad sensing range, high sensitivity, and stable in vivo operation over extended periods. This work establishes a versatile route for boosting piezoelectricity in biomaterials, thereby broadening their scope in biomedical applications.