Membrane Motion Research Articles

Unsynchronized motion of inner and outer membranes of compound capsules in shear flow

Despite its significance in understanding behaviors of biological cells with nucleus or designing functions of complex artificial capsules in applications, the dynamics of elastic capsules enclosing complicated internal structures in flow is still largely unexplored. In this study, by using our own three-dimensional front-tracking finite-difference model, we present a numerical investigation into the dynamics of a compound capsule in a simple shear flow whose inner and outer membranes have the same prolate ellipsoidal shape at the rest state. Particular interest is focused on the unsynchronized motion of the inner and outer membranes. Regarding the dynamical regime, both the inner and outer capsules can undergo either synchronized or unsynchronized dynamical regimes (i.e., swinging or tumbling), which strongly depends on the inner-to-outer capillary number ratio Cain/Caout, the inner-to-outer volume ratio ϕ, and the prolate aspect ratio a/b. Particularly, via establishing a phase diagram based on a/b and ϕ at Cain/Caout = 1, we find that the inner and outer membranes can exist simultaneously in different dynamical regimes, even if they have the same deformability and the same shape. More importantly, if the detailed oscillation behavior is also concerned besides the capsule’s dynamical regime, such as the transient shape and the oscillating period, unsynchronization is always obvious between the inner and outer capsules. Specifically, the inner capsule exhibits a slower oscillation than the outer capsule no matter if they lie in the swinging or tumbling regime.

Actin-Membrane Release Initiates Cell Protrusions.

Despite the well-established role of actin polymerization as a driving mechanism for cell protrusion, upregulated actin polymerization alone does not initiate protrusions. Using a combination of theoretical modeling and quantitative live-cell imaging experiments, we show that local depletion of actin-membrane links is needed for protrusion initiation. Specifically, we show that the actin-membrane linker ezrin is depleted prior to protrusion onset and that perturbation of ezrin's affinity for actin modulates protrusion frequency and efficiency. We also show how actin-membrane release works in concert with actin polymerization, leading to a comprehensive model for actin-driven shape changes. Actin-membrane release plays a similar role in protrusions driven by intracellular pressure. Thus, our findings suggest that protrusion initiation might be governed by a universal regulatory mechanism, whereas the mechanism of force generation determines the shape and expansion properties of the protrusion.

Detection of cellular micromotion by advanced signal processing

Cellular micromotion—a tiny movement of cell membranes on the nm-µm scale—has been proposed as a pathway for inter-cellular signal transduction and as a label-free proxy signal to neural activity. Here we harness several recent approaches of signal processing to detect such micromotion in video recordings of unlabeled cells. Our survey includes spectral filtering of the video signal, matched filtering, as well as 1D and 3D convolutional neural networks acting on pixel-wise time-domain data and a whole recording respectively.

Frequency and damping effect of suspended silicon nitride membranes in water near the megahertz range

Understanding the behavior of water-immersed membranes in the megahertz range is critical to develop novel acoustic metamaterials compatible with biomedical ultrasound applications. Herein, we study the influence of water on the resonance frequency and quality factor near the megahertz range of silicon nitride membranes fully immersed in water using laser Doppler vibrometry. The resonance frequency of silicon nitride membranes significantly decreases in water compared to air. For a 40 µm wide membrane, the resonance frequency is reduced from 11.2 MHz in air to 1.24 MHz after immersion in water, which is confirmed by finite element method simulations. Our results indicate that the water mass loading plays a major role in the resonance frequency reduction, with a ratio of water mass to membrane mass of 102 and NAVMI factors of Γ∼1.3. We attribute the main losses to acoustic radiation with small contributions from viscous damping. We estimate that silicon nitride membranes with widths below 50 µm are required to build negative metamaterials operating above 1 MHz. The large NAVMI factors suggest strong coupling between membrane motion and acoustic waves in water, which is important to develop metamaterials able to manipulate acoustic fields.

Transition of Ultrathick Polyamide Tubes into Vesicles with Great Stability.

This work reports on the transition of a polyamide ultrathick wall microtubes to microvesicles through self-assembly. An amphiphilic polyamide is synthesized first by the solution polycondensation of sodium isophthalate-5-sulfonate (SIPA) and poly(propylene glycol) bis(2-aminopropyl ether) 2000. Then, its self-assembly in aqueous solution is investigated through direct hydration. The size and morphology of the self-assemblies is investigated by transmission electron microscope (TEM), scanning electron microscope (SEM), atomic force microscope (AFM), and optical microscope (OM) measurements. The result shows that the as-prepared polyamide first self-assembles to thick walled tubes, then these tubes can gradually evolve to ultrathick wall microvesicles with an unusually thick membrane above 330 nm.Both the transition pathway and the mechanism are investigated in micromicroscopy. Most importantly, the microvesicles show great thermal and chemical stability. The novel superstable self-assembly structures as well as the transition mechanism presented here offer a promising perspective for the application in the scope of the biological membrane movements and nanoelectromechanics in medical devices.

Identifying three otopathologies in humans

ObjectivesHearing-in-noise (HIN) is a primary complaint of both the hearing impaired and the hearing aid user. Both auditory nerve (AN) function and outer hair cell (OHC) function are thought to contribute to HIN, but their relative contributions are still being elucidated. OHCs play a critical role in HIN by fine tuning the motion of the basilar membrane. Further, animal studies suggest that cochlear (auditory) synaptopathy, which is the loss of synaptic contact between hair cells and the AN, may be another cause of HIN difficulty. While there is evidence that cochlear synaptopathy occurs in animal models, there is debate as to whether cochlear synaptopathy is clinically significant in humans, which may be due to disparate methods of measuring noise exposure in humans and our high variability in susceptibility to noise damage. Rather than use self-reported noise exposure to define synaptopathic groups, this paper assumes that the general population exhibits a range of noise exposures and resulting otopathologies and defines cochlear synaptopathy “operationally” as low CAP amplitude accompanied by normal DPOAE levels in persons with low pure tone averages. The first question is whether the standard audiogram detects AN dysfunction and OHC dysfunction? The second question is whether HIN performance is primarily dependent on AN function, OHC function, or both functions? DesignAdult subjects have been recruited to participate in an ongoing study and variables such as age, self-reported gender, pure tone audiometry (0.25–20 kHz), subjective perception of HIN difficulty, Quick Speech-in Noise (QuickSIN) test, 45% time compressed word recognition (WR) in 10% reverberation and WR in the presence of ipsilateral speech-weighted noise have been collected. These variables were correlated with OHC function measured by distortion-product otoacoustic emission (DPOAE) signal to-noise-ratio (SNR), and AN function measured by compound action potential (CAP) peak amplitude and ratio to summating potential measured using electrocochleography. ResultsSynaptopathy, by this operational definition, may be present in as many as 30% of individuals with normal hearing. Persons hearing within normal limits may exhibit HIN difficulties, and persons with hearing within normal limits may exhibit two distinct types of otopathologies undetected by the standard audiogram (a.k.a. hidden hearing loss) namely operational cochlear synaptopathy and OHC dysfunction. AN untuning secondary to OHC dysfunction is a third otopathology that occurs in subjects with a Mild–Moderate sensorineural hearing loss (SNHL). Clinical norms for each of these otopathologies are presented. Finally, the data show that operational cochlear synaptopathy does not correlate with HIN dysfunction. Rather, HIN performance is primarily governed by OHC function, while AN untuning also plays a lesser but statistically significant role. ConclusionsThe results of this study suggest the following: (1) persons hearing within normal limits may exhibit HIN difficulties; (2) persons hearing within normal limits may exhibit undetected otopathologies, namely AN dysfunction and OHC dysfunction; (3) AN untuning secondary to OHC dysfunction occurs in subjects with Mild–Moderate SNHL; (4) HIN performance is primarily governed by OHC function rather than AN function.

Gene therapy as a possible option to treat hereditary hearing loss

Abstract The process of hearing involves a series of events. The energy of sound is captured by the outer ear and further transferred through the external auditory canal to the middle ear. In the middle ear, sound waves are converted into movements of the tympanic membrane and the ossicles, thereby amplifying the pressure so that it is sufficient to cause movement of the cochlear fluid. The traveling wave within the cochlea leads to depolarization of the inner ear hair cells that, in turn, release the neurotransmitter glutamate. Thereby, the spiral ganglion neurons are activated to transfer the signals via the auditory pathway to the primary auditory cortex. This complex combination of mechanosensory and physiological mechanisms involves many distinct types of cells, the function of which are impacted by numerous proteins, including those involved in ion channel activity, signal transduction and transcription. In the last 30 years, pathogenic variants in over 150 genes were found to be linked to hearing loss. Hearing loss affects over 460 million people world-wide, and current treatment approaches, such as hearing aids and cochlear implants, serve to improve hearing capacity but do not address the underlying genetic cause of hearing loss. Therefore, therapeutic strategies designed to correct the genetic defects causative for hearing loss offer the possibility to treat these patients. In this review, we will discuss genetic causes of hearing loss, novel gene therapeutic strategies to correct hearing loss due to gene defects and some of the preclinical studies in hearing loss animal models as well as the clinical translation of gene therapy approaches to treat hearing loss patients.

Membrane trafficking in the retinal pigment epithelium at a glance.

The retinal pigment epithelium (RPE) is a highly specialised pigmented monolayer sandwiched between the choroid and the photoreceptors in the retina. Key functions of the RPE include transport of nutrients to the neural retina, removal of waste products and water from the retina to the blood, recycling of retinal chromophores, absorption of scattered light and phagocytosis of the tips of the photoreceptor outer segments. These functions place a considerable membrane trafficking burden on the RPE. In this Cell Science at a Glance article and the accompanying poster, we focus on RPE-specific adaptations of trafficking pathways. We outline mechanisms underlying the polarised expression of membrane proteins, melanosome biogenesis and movement, and endocytic trafficking, as well as photoreceptor outer segment phagocytosis and degradation. We also briefly discuss theories of how dysfunction in trafficking pathways contributes to retinal disease.

An investigation of the viscoelastic behavior of MCF-10A and MCF-7 cells

Breast cancer is the most frequent female malignancy in the world. In this regard, cancer detection by assessing the biomechanical properties of cells is a promising method in oncology. Cell state can be identified by studying viscosity behavior; however, a more complex understanding of cells requires a profound insight into the solidity and fluidity of cells via the characterization of cell viscoelasticity. The present study aimed to compare the viscoelasticity of healthy human breast epithelial cells (MCF-10A) with that of cancerous cells (MCF 7). The experiment included the addition of nano magnetic particles (NMP) to the cell culture environment and placement of the Petri Dishes under a microscope after the completion of primary culture stages and, ultimately, adoption of a magnetic tweezer technique to perform a creep test. A viscoelastic model of cells was suggested with discrete differential equations for both groups of healthy and cancerous cells after obtaining information about cell membrane movements and performing image processes on these data. A comparison of cell stiffness was made under two conditions of static and dynamic. According to the findings, cancerous static stiffness was lower than that of healthy cells by a factor of 3.5. The creep test results showed that MCF 7 cells would exhibit solid-like behavior. At a higher gel point frequency, these cells emerged more solidity compared to their corresponding healthy cells. The obtained results revealed the clear changes in cancerous cells’ viscoelastic properties and the potential alterations of their cytoskeleton.

Self-Blinking Dyes Unlock High-Order and Multiplane Super-Resolution Optical Fluctuation Imaging.

Most diffraction-unlimited super-resolution imaging critically depends on the switching of fluorophores between at least two states, often induced using intense laser light and specialized buffers or UV radiation. Recently, so-called self-blinking dyes that switch spontaneously between an open, fluorescent "on" state and a closed, colorless "off" state were introduced. Here, we exploit the synergy between super-resolution optical fluctuation imaging (SOFI) and spontaneously switching fluorophores for 2D and 3D imaging. SOFI analyzes higher order statistics of fluctuations in the fluorophore emission instead of localizing individual molecules. It thereby tolerates a broad range of labeling densities, switching behavior, and probe brightness. Thus, even dyes that exhibit spontaneous blinking characteristics that are not suitable or suboptimal for single molecule localization microscopy can be used successfully for SOFI-based super-resolution imaging. We demonstrate 2D imaging of fixed cells with almost uniform resolution up to 50-60 nm in 6th order SOFI and characterize changing experimental conditions. Next, we investigate volumetric imaging using biplane and eight-plane data acquisition. We extend 3D cross-cumulant analysis to 4th order, achieving super-resolution in 3D with up to 29 depth planes. Finally, the low laser excitation intensities needed for single and biplane self-blinking SOFI are well suited for live-cell imaging. We show the perspective for time-resolved imaging by observing slow membrane movements in cells. Self-blinking SOFI thus provides a more robust alternative route for easy-to-use 2D and 3D high-resolution imaging.

Diagnosis of the Patulous Eustachian Tube.

To review the diagnosis of patulous Eustachian tube (PET) based on the diagnostic criteria for the PET proposed by Japan Otological Society (JOS). We reviewed typical aural symptoms of PET, Eustachian tube (ET) obstruction procedure to confirm diagnosis of PET, objective findings of a patent ET obtainable from observation of the movement of the tympanic membrane, and by ET function tests (tubo-tympano-aerodynamic graphy, sonotubometry). In addition, usefulness of other tests such as patulous Eustachian tube handicap inventory-10 (PHI-10), sonotubometry with postural change (Ohta method), and sitting computed tomography (CT) to diagnose PET is described. We have described the diagnosis of PET based on the diagnostic criteria for PET proposed by JOS; PHI-10, Ohta method, and sitting CT are also useful for the diagnosis of PET. Further investigation is needed for an accurate diagnosis and precise evaluation of the pathophysiology of this challenging disease.

Efficient viscosity contrast calculation for blood flow simulations using the lattice Boltzmann method

SummaryThe lattice Boltzmann method (LBM) combined with the immersed boundary method is a common tool to simulate the movement of red blood cel ls (RBCs) through blood vessels. With very few exceptions, such simulations neglect the difference in viscosities between the hemoglobin solution inside the cells and the blood plasma outside, although it is well known that this viscosity contrast can severely affect cell deformation. While it is easy to change the local viscosity in LBM, the challenge is to distinguish whether a given lattice point is inside or outside the RBC at each time step. Here, we present a fast algorithm to solve this issue by tracking the membrane motion and computing the scalar product between the local surface normal and the distance vector between the closest LBM lattice point and the surface. This approach is much faster than, for example, the ray‐casting method. With the domain tracking applied, we investigate the shape transition of a RBC in a microchannel for different viscosity contrast and validate our method by comparing with boundary‐integral simulations.

Middle Ear Effusion in Children With Congenital Cytomegalovirus Infection.

Sensorineural hearing loss (SNHL) is well described in children with congenital cytomegalovirus (CMV) infection, but limited data are available on middle ear effusion (MEE) occurrence in this population. We assessed the prevalence of MEE and the degree of transient hearing change associated with MEE among children with congenital CMV infection. Children with congenital CMV infection enrolled in a longitudinal study received hearing and tympanometric testing during scheduled follow-up visits annually up to 6 years of age. We used a generalized linear mixed-effect logistic regression model to compare the odds of MEE, defined as type B tympanogram (normal ear canal volume with little tympanic membrane movement) among patients categorized as symptomatic or asymptomatic based on the presence of congenital CMV-associated signs in the newborn period. Forty-four (61%) of 72 symptomatic and 24 (28%) of 87 asymptomatic patients had ≥1 visit with MEE. After controlling for the number of visits, symptomatic patients had significantly higher odds of MEE (odds ratio: 2.09; 95% confidence interval: 1.39-3.14) than asymptomatic patients. Transient hearing decrease associated with a type B tympanogram ranged from 10 to 40 dB, as measured by audiometric air-bone gap in 11 patients. Among children with congenital CMV, MEE can result in transient hearing decrease, which can reduce the efficacy of a hearing aid in those with SNHL. It is warranted that children with congenital CMV infection and SNHL receive routine audiologic and tympanometric testing to better manage hearing aid amplification levels.

Effects of Efferent Activity on Hair Bundle Mechanics.

Hair cells in both the auditory and vestibular systems receive efferent innervation. A number of prior studies have indicated that efferent regulation serves to diminish the overall sensitivity of the auditory system. The efferent pathway is believed to affect the sensitivity and frequency selectivity of the hair cell by modulating its membrane potential. However, its effect on the mechanical response of the hair cell has not been established. We explored how stimulation of the efferent neurons affects the mechanical responsiveness of an individual hair bundle. We tested this effect on in vitro preparations of hair cells in the sacculi of American bullfrogs of both genders. Efferent stimulation routinely resulted in an immediate increase of the frequency of hair bundle spontaneous oscillations for the duration of the stimulus. Enlarging the stimulus amplitude and pulse length, or conversely, decreasing the interpulse interval led to oscillation suppression. Additionally, we tested the effects of efference on the hair bundle response to mechanical stimulation. The receptive field maps of hair cells undergoing efferent actuation demonstrated an overall desensitization with respect to those of unstimulated cells.SIGNIFICANCE STATEMENT The efferent system is an important aide for the performance of the auditory system. It has been seen to contribute to sound detection and localization, ototoxicity prevention, and speech comprehension. Although measurements have demonstrated that efference suppresses basilar membrane movement, there is still much unknown about how efferent activity affects hearing mechanics. Here, we explore the mechanical basis for the efferent system's capabilities at the level of the hair bundle. We present optical recordings, receptive field maps, and sensitivity curves that show a hair bundle is desensitized by efferent stimulation. This supports the hypothesis that efferent regulation may be a biological control parameter for tuning the hair bundle's mechanical sensitivity.

Nonlinear cochlear mechanics without direct vibration-amplification feedback.

Recent in vivo recordings from the mammalian cochlea indicate that although the motion of the basilar membrane appears actively amplified and nonlinear only at frequencies relatively close to the peak of the response, the internal motions of the organ of Corti display these same features over a much wider range of frequencies. These experimental findings are not easily explained by the textbook view of cochlear mechanics, in which cochlear amplification is controlled by the motion of the basilar membrane (BM) in a tight, closed-loop feedback configuration. This study shows that a simple phenomenological model of the cochlea inspired by the work of Zweig [J. Acoust. Soc. Am. 138, 1102 (2015)] can account for recent data in mouse and gerbil. In this model, the active forces are regulated indirectly, through the effect of BM motion on the pressure field across the cochlear partition, rather than via direct coupling between active-force generation and BM vibration. The absence of strong vibration-amplification feedback in the cochlea also provides a compelling explanation for the observed intensity invariance of fine time structure in the BM response to acoustic clicks.

Energy based model of the human Ear canal and tympanic membrane for sound transmission

The objective of this paper is to present a unique energy based model of the human outer ear and the tympanic membrane. The developed model employs the Port Hamiltonian modelling approach. The tympanic membrane is modelled as an Euler-Bernoulli beam. The frequency response of the model at speech frequencies which are significant for sound transmission are found to comparable to existing results in literature. This model can also be used for investigation of tympanic membrane rupture or perforations. Future work will include modelling of the ear canal as horn shaped and inclusion of the angular motion of the tympanic membrane.

Neurodynamics analysis of cochlear hair cell activity

There have been many studies on the effect of cochlea basal membrane movement on the resolution of different frequencies and intensities. However, these studies did not take into account the influence of power and energy consumption of the hair cells in the process of the electromotility movement, as well as the neurodynamic mechanism that produced this effect. This makes previous studies unable to fully clarify the function of outer hair cells (OHCs) and the mechanism of sound amplification. To this end, we introduce the gate conductance characteristics of the hair cells in the mechanical process of increasing frequency selectivity. The research finds that the low attenuation of OHCs membrane potential and the high gain in OHC power and energy consumption caused that OHC amplification is driven by electromotility. The research results show that the amplification of the OHCs is driven by low attenuation of membrane potential and high gain of power and energy consumption. This conclusion profoundly reveals the physiological mechanism of the electromotility movement.

Trackosome: a computational toolbox to study the spatiotemporal dynamics of centrosomes, nuclear envelope and cellular membrane.

During the initial stages of mitosis, multiple mechanisms drive centrosome separation and positioning. How they are coordinated to promote centrosome migration to opposite sides of the nucleus remains unclear. Here, we present Trackosome, an open-source image analysis software for tracking centrosomes and reconstructing nuclear and cellular membranes, based on volumetric live-imaging data. The toolbox runs in MATLAB and provides a graphical user interface for easy access to the tracking and analysis algorithms. It provides detailed quantification of the spatiotemporal relationships between centrosomes, nuclear envelope and cellular membrane, and can also be used to measure the dynamic fluctuations of the nuclear envelope. These fluctuations are important because they are related to the mechanical forces exerted on the nucleus by its adjacent cytoskeletal structures. Unlike previous algorithms based on circular or elliptical approximations, Trackosome measures membrane movement in a model-free condition, making it viable for irregularly shaped nuclei. Using Trackosome, we demonstrate significant correlations between the movements of the centrosomes, and identify specific oscillation modes of the nuclear envelope. Overall, Trackosome is a powerful tool that can be used to help unravel new elements in the spatiotemporal dynamics of subcellular structures.

Cell membrane movement imitation using tensegrity structures

Cell membrane movement imitation using tensegrity structures

The characteristic of patulous eustachian tube patients diagnosed by the JOS diagnostic criteria.

The objective is to describe characteristics of patients diagnosed with patulous Eustachian tube (PET) using the Diagnostic Criteria proposed by Japan Otological Society, and to evaluate the efficiency of objective tests to determine patent Eustachian tube. Retrospective. Tertiary referral center. A retrospective survey of medical records in Sen-En Rifu Hospital identified 78 ears of 56 patients with "Definite PET" diagnosed by the JOS Diagnostic Criteria between January 2017 and December 2017. Initial diagnosis, aural symptoms (voice autophony, aural fullness and breathing autophony), tubal obstruction procedures (posture change and pharyngeal orifice obstruction) and objective findings (tympanic membrane movement, Tubo-Tympano-Aerodynamic Graphy (TTAG) and sonotubometry) were evaluated. In addition, sonotubometry with postural change (Ohta's method), sitting CT and a newly devised PHI-10 score were also examined. Voice autophony, aural fullness, and breathing autophony were observed in 93.6%, 87.2%, 78.2%, respectively. In 91% of the ears, PET symptoms improved by postural change from sitting to the lying / forward-bending position. Synchronous movement of the TM upon respiration was observed in 69.1% of the ears. Positive findings of TTAG were observed in 75.6% of ears. Positive findings of sonotubometry were found in 55.1% of ears. Sonotubometry with postural change (Ohta's method), when the cut-off value of over 10dB was used, was positive in 45.2% of ears. Newly devised PHI-10 score representing severity of subjective symptoms classifying patients into no handicap, mild handicap, moderate handicap and severe handicap were observed in 12.2%, 10.8%, 18.9% and 58.1% of ears, respectively. The evaluation of the extent of patency of the ET by sitting CT indicated completely open, closed-short, and closed-long, in 68.6%, 11.4% and 21.4% of ears, respectively. Compared to the closed group, the completely open group had a significantly higher frequency of positive breathing autophony, positive sonotubometry, and positive Ohta's method. The characteristics of main symptoms and the efficiency of various tests in PET diagnosis were analyzed based on data obtained from "Definite PET" patients diagnosed by the JOS Diagnostic Criteria. The greater the availability of tests to evaluate PET, the greater the opportunities to diagnose "Definite PET". In particular, tests measuring pressure transmission between the nasopharynx and middle ear, such as TM observation and TTAG, are more sensitive than sonotubometry measuring sound transmission.