Electromechanical Coupling of Murine Lung Tissues Probed by Piezoresponse Force Microscopy

Abstract

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.

Racemic Amino Acid Piezoelectric Transducer

“…The potential of biomolecular piezoelectricity is emphasised in the work of Kholkin and co-workers as regards glycine crystal structures [16][17][18] and the peptide diphenylalanine [19,20], and also Li and co-workers whose work has focused on piezoelectricity of biological tissues [21,22], most notably elastin [23]. However, there has been a lack of theoretical and experimental studies on amino acid crystals outside of the three glycine polymorphs, in particular, the two piezoelectric racemic amino acids, namely, DL alanine and DL tyrosine [24].…”

“…However, there has been a lack of theoretical and experimental studies on amino acid crystals outside of the three glycine polymorphs, in particular, the two piezoelectric racemic amino acids, namely, DL alanine and DL tyrosine [24]. We present this study as the development and characterization of a technologically useful, biocompatible energy harvester vs the tangential area of physiological piezoelectricity addressed in a number of works by Li and co-workers and ourselves [21][22][23]25,26].…”

The intrinsic piezoelectric properties of materials – a review with a focus on biological materials

“…113 Proteins such as collagen, elastin, actin and myosin have been shown to be piezoelectric. 112,[114][115][116][117][118][119][120] Their piezoelectric properties have been attributed to their constituent amino acids, electrical dipoles and the packing of the peptide chains. 21,109,121 A summary of the reported piezoelectric coefficients for some protein/amino acid based biological materials is provided in Table 1.…”

“…It can be found in organs such as lung, skin and blood vessel walls. 112,117,118,150 Both piezoelectricity and ferroelectricity has been conrmed in elastin. 112,117,118 The piezoelectric coefficient of elastin has been found to be 0.1 pm V À1 .…”

Piezoelectric Materials for Medical Applications

“…Muscle Actin and myosin [18] Hair Keratin [16] Bone Collagen [32] Tendon Collagen [33] Lung tissue Elastin [34] Skin (dermis) Collagen [28] Skin (horny layer and epidermis) Keratin [28] Breast tissue Collagen [35] Outer hair cell Prestin [36] detection of atherosclerosis in the aorta, however as mentioned in a prior paragraph the validity of the aorta's piezoelectric nature is still under debate [48]. In this paper, they claimed the PFM amplitude increased as a function of advancing atherosclerosis and could help with early detection of the disease.…”