Electromechanical Coupling of Murine Lung Tissues Probed by Piezoresponse Force Microscopy

Elastin is a major constituent of lung that makes up approximately 30% of lung’s dry weight, and the piezoelectricity of elastin is expected to be exhibited in lung tissues. Because hundreds of millions of cycles of inhalation and exhalation occur in one’s lifetime, such piezoelectric effect leads to hundreds of millions of cycles of charge generations in lung tissues, suggesting possible physiological significance. Using piezoresponse force microscopy (PFM), we show that the murine lung tissues are indeed piezoelectric, exhibiting predominantly first harmonic piezoresponse in both vertical and lateral modes. The second harmonic response, which could arise from ionic motions, electrochemical dipoles, and electrostatic interactions, is found to be small. The mappings of amplitude, phase, resonance frequency, and quality factor of both vertical and lateral PFM are also obtained, showing small fluctuation in frequency, but larger variation in quality factor, and thus energy dissipation. The phase mapping is confined in a small range, indicating a polar distribution with preferred orientation. It is also found that the polarity of the electromechanical coupling in lung tissues can be switched by an external electric field, resulting in characteristic hysteresis and butterfly loops, with a presence of internal bias in the polar structure. It is hypothesized that the piezoelectric charge generation during inhalation and exhalation could play a role in binding of oxygen to hemoglobin, and the polarity switching can help damp out the possible sudden increase in air pressure. We hope such observation of piezoelectricity and its polarity switching in lung lay the foundation for the subsequent studies of its physiological significance

Multifield Control of Domains in a Room-Temperature Multiferroic 0.85BiTi_0.1Fe_0.8Mg_0.1O₃–0.15CaTiO₃ Thin Film

Single-phase materials that combine electric polarization and magnetization are promising for applications in multifunctional sensors, information storage, spintronic devices, etc. Following the idea of a percolating network of magnetic ions (e.g., Fe) with strong superexchange interactions within a structural scaffold with a polar lattice, a solid solution thin film with perovskite structure at a morphotropic phase boundary with a high level of Fe atoms on the B site of perovskite structure is deposited to combine both ferroelectric and ferromagnetic ordering at room temperature with magnetoelectric coupling. In this work, a 0.85BiTi_0.1Fe_0.8Mg_0.1O₃–0.15CaTiO₃ thin film has been deposited by pulsed laser deposition (PLD). Both the ferroelectricity and the magnetism were characterized at room temperature. Large polarization and a large piezoelectric effective coefficient <i>d</i>₃₃ were obtained. Multifield coupling of the thin film has been characterized by scanning force microscopy. Ferroelectric domains and magnetic domains could be switched by magnetic field (<i>H</i>), electric field (<i>E</i>), mechanical force (<i>F</i>), and, indicating that complex cross-coupling exists among the electric polarization, magnetic ordering and elastic deformation in 0.85BiTi_0.1F_e0.8Mg_0.1O₃–0.15CaTiO₃ thin film at room temperature. This work also shows the possibility of writing information with electric field, magnetic field, and mechanical force and then reading data by magnetic field. We expect that this work will benefit information applications