Energy Harvesters Incorporating Silk from the Taiwan-Native Spider Nephila pilipes

Silks from Nephila pilipes spiders native to Taiwan, obtained from the major ampullate gland, display novel piezoelectric properties that have been exploited in the preparation of energy harvesters. An energy harvester incorporating approximately 100 pieces of spider silk, each approximately 10 mm long, produced a voltage output of 13.4 mV when vibrated at 4 Hz. A repolarization process enhanced the piezoelectric properties of the spider silks significantly, notably increasing the output voltage to 40.7 mV at 4 Hz. Electrical testing indicated that the output voltages of the energy harvesters incorporating the repolarized silks were 3- to 4-fold higher than those of the harvesters containing the nonpolarized silks. The maximum output power (59.5 pW) was generated by the energy harvester incorporating the repolarized silks when connected to an external load resistor of 8.2 MΩ. The mechanical properties of the spider silks were examined through both microtensile and nanoindenter tests, revealing elastic moduli between 5 and 7 GPa, strengths ranging from 510 to 850 MPa, and percentages of elongation of 20–25%. Thus, these spider silks exhibited excellent mechanical strength and ductility. Fourier transform infrared spectra of the repolarized silks revealed a significant increase in intensity and sharpening of the amide I absorption peak, suggesting that the repolarized silk proteins featured a superior arrangement of α-helices and β-sheets, relative to the nonpolarized ones. Thus, Taiwan-native Nephila pilipes silks, with their intrinsic piezoelectricity and good mechanical properties, exhibit great potential for use in energy harvesters