Boosting Piezoelectricity and Mechanical Properties of Silk Fibroin Films via Polyethylene Glycol Phase Manipulation

Piezoelectric silk fibroin (SF) shows great potential in fabricating sustainable wearable electronics toward health monitoring and human–machine interfacing, yet the processing difficulty and brittleness restrict its practical applications severely. This study proposes a simple strategy to achieve the boosted piezoelectricity and mechanical properties in electrospun regenerated silk fibroin (RSF) nanofiber mats by adding polyethylene glycol (PEG) with different molecular weights to induce the formation of β-sheets via hydrogen bonding and the regulation of PEG phase morphology. Specifically, RSFs consisting of PEG of 2000 and 1000 Da exhibit a significant improvement in the tensile strength (from 6.1 to 9.92 MPa) and elongation at break (from 5.72% to 117.58%), respectively. Meanwhile, RSFs consisting of PEG with a molecular weight of 2000 and 400 Da show a direct piezoelectric force sensitivity of 0.2 mV/N·μm and 0.14 mV/N·μm respectively, superior to that of pure RSF (0.04 mV/N·μm). The piezoelectric force sensors fabricated with RSFs show potential applications in the detection of diverse human motions, including finger tapping for Morse code, grip strength, and knee flexion. Thus, this work unveils a facile strategy to fabricate RSF-based biodegradable piezoelectric force sensors with a trade-off in processability, mechanical ductility, and piezoelectricity.