Fig. 2. Schematic representation and piezoelectric analysis of bio-NGs.

(A) Schematic diagram of the fabrication of highly discrete piezoelectric Fe₃O₄/PAN fibers. With the help of the neodymium iron boron magnet, Fe₃O₄ magnetic nanoparticles were introduced into PAN electrospun solution to break through the surface tension of water. (B) The PEDOT conductive layer was loaded with the method of in situ polymerization; GO nanosheets were adsorbed on the outermost layer of fibers by the contribution of electrostatic adsorption force to form the target GO/PEDOT/Fe₃O₄/PAN fibers. Transmission electron microscopy images of the single fiber obtained in every step. (C to E) Optical image and scanning electron microscopy (SEM) images of the bio-NGs. The inset of (D) shows pore size distribution and porosity. The inset of (E) shows the fiber diameter distribution range of the GO/PEDOT/Fe₃O₄/PAN fibers. (F) Finite element analysis simulation of piezoelectric fibers coupled with a living cell generating a maximum voltage of 141 mV when strained by a tangential force of 10 nN. (G) Piezoelectric potential generated by a single fiber as a function of the applied tangential cell force. (H) Simplified resistor-capacitor circuit created by the NG, the NG-cell interface, and the cell membrane. (I) Piezoelectric force microscopy (PFM) phase and PFM amplitude images of a single fiber in bio-NGs. (J) Phase-electric potential hysteresis and butterfly amplitude loops of fibers in bio-NGs, obtained with a DC voltage varying from −10 to 10 V. (K) Voltage outputs from the bio-NGs under the same impact force of 1 N (blue) and under a vibration at 0.7 Hz (red). The inset represented the impact (left) and vibration (right) methods used to characterize the fibers in bio-NGs. F, force. Photo credit: Chuanmei Shi, Nanjing University of Science and Technology.