Phys. Rev. Lett. 108, 078103 (2012)

Ferroelectric materials, which are used to make memories and sensors, exhibit a spontaneous electric polarization that can be reversed by applying an electric field. This property has been observed in numerous inorganic and synthetic substances, and is accompanied by piezoelectric and pyroelectric abilities in which polarization behaviour can be altered by mechanical forces or temperature, respectively. However, whilst piezoelectricity and pyroelectricity have been observed before in soft biological tissues, evidence of ferroelectricity in such materials has remained elusive. Jiangyu Li and colleagues at the University of Washington and Boston University have now shown that mammalian tissue can be both piezoelectric and ferroelectric.

The researchers used piezoresponse force microscopy — a scanning probe technique that detects local piezoelectric deformations of a material induced by an external electric field — to examine the walls of a pig aorta. To measure the piezoelectric effect at an aortic wall, the tip of the microscope was placed in contact with the sample and an a.c. bias was applied through the conducting tip to excite the piezoelectric vibration of the wall. To explore whether the walls were also ferroelectric, a sequence of d.c. voltages with a triangular saw-tooth profile were applied to try to switch the polarization of the material. An a.c. voltage was simultaneously applied to measure the corresponding piezoresponse. Phase–voltage hysteresis loops and amplitude–voltage butterfly loops, which are characteristic of polarization reversal, were obtained.

Li and colleagues suggest this biological ferroelectricity could have implications for cardiovascular and other diseases.