Biological ferroelectricity uncovered in aortic walls by piezoresponse force microscopy

Abstract

Many biological tissues are piezoelectric and pyroelectric with spontaneous polarization. Ferroelectricity, however, has not been reported in soft biological tissues yet. Using piezoresponse force microscopy, we discover that the porcine aortic walls are not only piezoelectric, but also ferroelectric, with the piezoelectric coefficient in the order of 1 pm/V and coercive voltage approximately 10 V. Through detailed switching spectroscopy mapping and relaxation studies, we also find that the polarization of the aortic walls is internally biased outward, and the inward polarization switched by a negative voltage is unstable, reversing spontaneously to the more stable outward orientation shortly after the switching voltage is removed. The discovery of ferroelectricity in soft biological tissues adds an important dimension to their biophysical properties, and could have physiological implications as well.

FIG. 1

(color online). PFM of inner aortic wall; (a) schematics of PFM; (b) piezoresponse as a function of frequency at two different locations; and mappings of (c) vertical and (d) lateral PFM amplitude overlaid on 3D topography in a 1 × 1 μm² area; the ac frequency was set to be 265.43 kHz for vertical PFM and 888.57 kHz for lateral PFM.

FIG. 2

(color online). Quantitative PFM of inner aortic wall by DFRT; (a) schematics of DFRT with actual experimental data; and mapping of PFM (b) amplitude, (c) resonant frequency, and (d) quality factor in a 700 × 700 nm² area, all overlaid on 3D topography.

FIG. 3

(color online). Ferroelectric switching of inner aortic wall by PFM; (a) schematics of switching PFM; (b) phase-voltage hysteresis loop and (c) amplitude-voltage butterfly loop measured at three different points; SSPFM mapping of (d) remnant PFM amplitude, (e) coercive voltage, and (f) nucleation bias in a 2 × 2 μm² area.

FIG. 4

(color online). Variation of PFM phase with respect to time under triangle dc voltages, showing relaxation and stability of polarization switched by (a) positive, (b) negative, and (c) negative and positive dc voltages.