Flexoelectricity and thermal fluctuations of lipid bilayer membranes: Renormalization of flexoelectric, dielectric, and elastic properties

Liu, L. P.; Sharma, Pradeep

doi:10.1103/physreve.87.032715

Cited by 52 publications

(24 citation statements)

References 33 publications

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“…Given the absence of any plausible micromechanism for piezoelectricity, flexoelectricity is most likely the key mechanism underpinning the electromechanical coupling in biomembranes. It has been found to be relevant for studying ion channels, thermal fluctuations, equilibrium shape of the vesicle, and electromotility [26,[42][43][44][45][46][47]. Based on several hypotheses and experiments [48][49][50][51][52][53][54][55], the mammalian hearing mechanism appears to be one of the most exciting implications of flexoelectricity in biology.…”

Section: What Is the Role Of Flexoelectricity In Biology?mentioning

confidence: 99%

Flexoelectricity: A Perspective on an Unusual Electromechanical Coupling

Krichen

Sharma

2016

Journal of Applied Mechanics

178

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The ability of certain materials to convert electrical stimuli into mechanical deformation, and vice versa, is a prized property. Not surprisingly, applications of such so-called piezoelectric materials are broad-ranging from energy harvesting to self-powered sensors. In this perspective, written in the form of question-answers, we highlight a relatively understudied electromechanical coupling called flexoelectricity that appears to have tantalizing implications in topics ranging from biophysics to the design of next-generation multifunctional nanomaterials.A uniform mechanical strain electrically polarizes a piezoelectric material. There is extensive literature on the formal development of the phenomenological theory of piezoelectricity; however, simply put, this phenomenon may be described by the following linearized relation between the components of the polarization vector (P) and the strain tensor (e): P i d ijk e jk . The piezoelectric property tensor (d) is third order. Group theory states that only noncentrosymmetric crystals may exhibit properties dictated by third-order tensors [1], and accordingly, common insulators which possess a centrosymmetric crystal structure, such as Si and NaCl, are nonpiezoelectric.However, as schematically alluded to in Fig. 1, a nonuniform strain may break the mirror symmetry even in otherwise centrosymmetric crystals. The relation of the polarization to the extent of the nonuniformity of the strain field, or strain gradient, is known as flexoelectricity: P i d ijk e jk þ f ijkl ð@e jk =@x l Þ, where f ijkl are the components of the so-called flexoelectric tensor. While the piezoelectric property is nonzero only for selected materials, the strain gradient-polarization coupling (i.e., flexoelectricity tensor) is in principle nonzero for all (insulating) materials. This implies that under a nonuniform strain, all dielectric materials are capable of producing a polarization. The reader is referred to the following articles for further information: Refs. [2][3][4][5][6][7][8][9].

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Section: What Is the Role Of Flexoelectricity In Biology?mentioning

confidence: 99%

Flexoelectricity: A Perspective on an Unusual Electromechanical Coupling

Krichen

Sharma

2016

Journal of Applied Mechanics

178

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“…As is well-known, thermal fluctuations cause softening of membrane mechanical properties e.g. [63]. Decrease in stretch modulus will increase the deformation and hence likely increase the sensitivity of the magnetic to electric conversion.…”

Section: Ellipsoidal Shape and Dimensions Changementioning

confidence: 99%

Biological cell as a soft magnetoelectric material: Elucidating the physical mechanisms underpinning the detection of magnetic fields by animals

2017

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Sharks, birds, bats, turtles, and many other animals can detect magnetic fields. Aside from using this remarkable ability to exploit the terrestrial magnetic field map to sense direction, a subset is also able to implement a version of the so-called geophysical positioning system. How do these animals detect magnetic fields? The answer to this rather deceptively simple question has proven to be quite elusive. The currently prevalent theories, while providing interesting insights, fall short of explaining several aspects of magnetoreception. For example, minute magnetic particles have been detected in magnetically sensitive animals. However, how is the detected magnetic field converted into electrical signals given any lack of experimental evidence for relevant electroreceptors? In principle, a magnetoelectric material is capable of converting magnetic signals into electricity (and vice versa). This property, however, is rare and restricted to a rather small set of exotic hard crystalline materials. Indeed, such elements have never been detected in the animals studied so far. In this work we quantitatively outline the conditions under which a biological cell may detect a magnetic field and convert it into electrical signals detectable by biological cells. Specifically, we prove the existence of an overlooked strain-mediated mechanism and show that most biological cells can act as nontrivial magnetoelectric materials provided that the magnetic permeability constant is only slightly more than that of a vacuum. The enhanced magnetic permeability is easily achieved by small amounts of magnetic particles that have been experimentally detected in magnetosensitive animals. Our proposed mechanism appears to explain most of the experimental observations related to the physical basis of magnetoreception.

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“…Reversibly, a substantially large external electric field across the membrane may also redistribute and reorientate these molecules due to electrical attraction and repulsion, resulting in a change in the membrane surface curvature: the reverse flexoelectric effect. Flexoelectricity is found to play a significant role in a number of biological functions, such as ion channels, thermal fluctuation, vesicle equilibrium, and hearing functions [10,29,[36][37][38][39][40]. In neurons in particular, it has been suggested that both the above-mentioned membrane movement during AP propagation, as well as the membrane polarization during an AP, could be related to the flexoelectricity [36,41].…”

Section: Introductionmentioning

confidence: 99%

Computational model of the mechanoelectrophysiological coupling in axons with application to neuromodulation

2019

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For more than half a century, the action potential (AP) has been considered a purely electrical phenomenon. However, experimental observations of membrane deformations occurring during APs have revealed that this process also involves mechanical features. This discovery has recently fuelled a controversy on the real nature of APs: whether they are mechanical or electrical. In order to examine some of the modern hypotheses regarding APs, we propose here a coupled mechanoelectrophysiological membrane finite-element model for neuronal axons. The axon is modeled as an axisymmetric thin-wall cylindrical tube. The electrophysiology of the membrane is modeled using the classic Hodgkin-Huxley (H-H) equations for the Nodes of Ranvier or unmyelinated axons and the cable theory for the internodal regions, whereas the axonal mechanics is modeled by means of viscoelasticity theory. Membrane potential changes induce a strain gradient field via reverse flexoelectricity, whereas mechanical pulses result in an electrical self-polarization field following the direct flexoelectric effect, in turn influencing the membrane potential. Moreover, membrane deformation also alters the values of membrane capacitance and resistance in the H-H equation. These three effects serve as the fundamental coupling mechanisms between the APs and mechanical pulses in the model. A series of numerical studies was systematically conducted to investigate the consequences of interaction between the APs and mechanical waves on both myelinated and unmyelinated axons. Simulation results illustrate that the AP is always accompanied by an in-phase propagating membrane displacement of ≈1 nm, whereas mechanical pulses with enough magnitude can also trigger APs. The model demonstrates that mechanical vibrations, such as the ones arising from ultrasound stimulations, can either annihilate or enhance axonal electrophysiology depending on their respective directionality and frequency. It also shows that frequency of pulse repetition can also enhance signal propagation independently of the amplitude of the signal. This result not only reconciles the mechanical and electrical natures of the APs but also provides an explanation for the experimentally observed mechanoelectrophysiological phenomena in axons, especially in the context of ultrasound neuromodulation.

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Flexoelectricity and thermal fluctuations of lipid bilayer membranes: Renormalization of flexoelectric, dielectric, and elastic properties

Cited by 52 publications

References 33 publications

Flexoelectricity: A Perspective on an Unusual Electromechanical Coupling

Flexoelectricity: A Perspective on an Unusual Electromechanical Coupling

Biological cell as a soft magnetoelectric material: Elucidating the physical mechanisms underpinning the detection of magnetic fields by animals

Computational model of the mechanoelectrophysiological coupling in axons with application to neuromodulation

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