Curvature Sensitivity Research Articles

DNA-Assisted Assays for Studying Lipid Transfer Between Membranes.

Extended-synaptotagmins (E-Syts) are proteins located on the endoplasmic reticulum (ER) that tether the ER to the plasma membrane (PM) and regulate their lipid homeostasis via its lipid transfer module, the synaptotagmin-like mitochondrial lipid-binding protein (SMP) domain. Here, we describe in vitro DNA nanostructure-assisted lipid transfer assays investigating how the SMP domain transports lipids between membranes and associates with the membranes to extract and release lipids. The lipid transfer signal was detected through fluorescence resonance energy transfer (FRET). This method overcomes the limitations of commonly used lipid transfer assays in accurately controlling inter-liposome distance and liposome size, enabling us to further understand the details involved in the process of SMP domain-mediated lipid transfer. Similar platforms can be extended to studying the lipid transfer distance and membrane curvature sensitivity of other lipid transfer proteins.

Nanoscale in silico and in vitro modeling of lipid bilayers for curvature induction and sensing

Cellular functions like motility, differentiation, or protein trafficking often require a change in membrane curvature and protein distribution. Defects associated with curvature sensitive proteins can cause several diseases. However, the mechanisms of the interactions between these proteins and lipid bilayers are not well known at the nanoscale. To study them, a combination of in-vitro and computational modeling of membranes is crucial. Here, we explore the curvature sensitivity and inducing properties of an F-BAR domain protein through in-vitro experiments with lipid coated nanobars in conjunction with all-atom molecular dynamics simulations. We simulated Formin Binding Protein 17 (FBP17) with different lipid compositions on flat and buckled bilayers. We determined the main residues involved in the interactions and proposed a mechanism. Our results, which suggest the range of local curvature induced and sensed by FBP17, give an insight into the role of BAR domain proteins in the context of membrane structural fluctuations.

A Novel MZI Fiber Sensor with Enhanced Curvature and Strain Sensitivity Based on Four-Core Fiber.

We present a high-sensitivity curvature and strain Mach-Zehnder interferometer (MZI) fiber sensor based on a configuration of no-core fiber (NCF) and four-core fiber (FCF). We used an optical fiber fusion splicer to directly splice a segment of FCF between two segments of NCF, with both the FCF and NCF made of SiO2, where the FCF exhibits multi-path interference characteristics that allow for higher sensitivity. The NCF, with its self-focusing property, excites higher-order modes, which split and transmit it into the four cores of the FCF. The experimental results show that within a curvature range of 0.0104 m-1-0.1515 m-1, the maximum sensitivity can reach -78.04 dB/m-1 with a high linear value of ~0.99. Additionally, the strain response is also experimentally studied. In the range of 0-600 με, the maximum strain sensitivity is -6.49 pm/με. The sensor demonstrates high curvature and strain sensitivity, indicating its potential applications in sensing measurements.

Parallel Farby-Perot Interferometers in an Etched Multicore Fiber for Vector Bending Measurements.

Vector bending sensors can be utilized to detect the bending curvature and direction, which is essential for various applications such as structural health monitoring, mechanical deformation measurement, and shape sensing. In this work, we demonstrate a temperature-insensitive vector bending sensor via parallel Farby-Perot interferometers (FPIs) fabricated by etching and splicing a multicore fiber (MCF). The parallel FPIs made in this simple and effective way exhibit significant interferometric visibility with a fringe contrast over 20 dB in the reflection spectra, which is 6 dB larger than the previous MCF-based FPIs. And such a device exhibits a curvature sensitivity of 0.207 nm/m-1 with strong bending-direction discrimination. The curvature magnitude and orientation angle can be reconstructed through the dip wavelength shifts in two off-diagonal outer-core FPIs. The reconstruction results of nine randomly selected pairs of bending magnitudes and directions show that the average relative error of magnitude is ~4.5%, and the average absolute error of orientation angle is less than 2.0°. Furthermore, the proposed bending sensor is temperature-insensitive, with temperature at a lower sensitivity than 10 pm/°C. The fabrication simplicity, high interferometric visibility, compactness, and temperature insensitivity of the device may accelerate MCF-based FPI applications.

Hole-assisted three-core fiber directional coupler operated in reflection mode for vector bending measurement

We demonstrate a vector bending sensor operated in reflection mode based on a hole-assisted three-core fiber (HATCF) coupler. The sensor is built by splicing a piece of HATCF with a gold film-coated end to a single-mode fiber (SMF). The gold film on the center core end is etched with femtosecond laser and only the lights transmitted in the two suspended cores of the HATCF are reflected. The center core couples with the two suspended cores at different wavelengths, respectively. The bending direction and curvature are identified by monitoring the wavelength of the two coupled peaks. The maximum curvature sensitivity of the sensor is 15.146 nm/m−1. The temperature sensitivity is less than −58.8 pm/°C. The vector bending sensor operated in reflection mode has the advantages of a compact structure and simple transmission line, which is conducive to the miniaturization and integration of optical fiber bending sensors.

A single-particle analysis method for detecting membrane remodelling and curvature sensing.

In biology, shape and function are related. Therefore, it is important to understand how membrane shape is generated, stabilised and sensed by proteins and how this relates to organelle function. Here, we present an assay that can detect curvature preference and membrane remodelling with free-floating liposomes using protein concentrations in physiologically relevant ranges. The assay reproduced known curvature preferences of BAR domains and allowed the discovery of high-curvature preference for the PH domain of AKT and the FYVE domain of HRS (also known as HGS). In addition, our method reproduced the membrane vesiculation activity of the ENTH domain of epsin-1 (EPN1) and showed similar activity for the ANTH domains of PiCALM and Hip1R. Finally, we found that the curvature sensitivity of the N-BAR domain of endophilin inversely correlates to membrane charge and that deletion of its N-terminal amphipathic helix increased its curvature specificity. Thus, our method is a generally applicable qualitative method for assessing membrane curvature sensing and remodelling by proteins.

Displaced thinned single-mode fiber Mach-Zehnder interferometer tested for temperature and curvature applications

This article explains the features and qualities of employing a thinned manufacturing fiber to assemble a Mach-Zehnder interferometer (MZI) for detecting two physical variables: temperature and curvature. The MZI comprises a filter by splicing core-offset sections of a thinned fiber (TF) cladding diameter of 80 μm in an SMF-TF-SMF configuration. The TF splices act as the arms of the MZI, while the mismatch diameter sections serve as optical fiber couplers. The optical spectrum analyzer (OSA) detects the transmitted light and analyzes its optical transmission characteristics, showing 11 peaks of modal interferences into the longitude region. As a result of the experimental arrangement, the curvature and temperature sensitivities are 0.49 nm/m−1, 0.01 nm/°C, and 0.09 nm/°C for temperatures of 0–60 °C and 70–130 °C, respectively. The proposed sensor has potential advantages for measuring refractive index, pH, torsion, curvature, and temperature.

A Simultaneous Measurement Sensor for Temperature and Curvature Based on Congruent Quasi-Helical Long-Period Fiber Grating.

This article presents a long-period fiber-grating sensor based on a congruent quasi-helical structure (CQH-LPFG) with the two-parameter measurement of both temperature and curvature. The CQH-LPFG sensor was manufactured using a high-frequency CO2 laser, and an innovative quasi-helical structure was introduced into the two-parameter measurement of the temperature and curvature of the optical fiber sensor with excellent results. The experiment and analysis demonstrate that the curvature sensitivities of the three resonance peaks in the 1440 nm to 1540 nm transmission spectrum were 11.88 nm/m-1, 8.05 nm/m-1, and 11.11 nm/m-1, and the curvature varied ranging from 0.156 m-1 to 0.494 m-1. The three resonance peaks showed temperature responsivities of 29.87 pm/°C, 24.65 pm/°C, and 36.85 pm/°C, respectively, and the linear fit was of excellent quality. In the case of measuring both curvature and temperature changes simultaneously, the resonant peak wavelength of the CQH-LPFG sensor was demodulated through matrix analysis, with dip A and dip C providing superior simultaneous measurements. These features make it a promising candidate for applications such as engineering machinery and the health inspection of buildings.

In-Fiber Hybrid Structure Sensor Based on the Vernier Effect for Vector Curvature and Temperature Measurement

A vector curvature and temperature sensor based on an in-fiber hybrid microstructure is proposed and experimentally demonstrated. The proposed scheme enables the dimensions of the Fabry–Perot and Mach–Zehnder hybrid interferometer to be adjusted for the formation of the Vernier effect by simply changing the length of a single optical fiber. The sensor is fabricated using a fiber Bragg grating (FBG), multimode fiber (MMF), and a single-hole dual-core fiber (SHDCF). The sensor exhibits different curvature sensitivities in four vertical directions, enabling two-dimensional curvature sensing. The temperature and curvature sensitivities of the sensor were enhanced to 100 pm/°C and −25.55 nm/m−1, respectively, and the temperature crosstalk was minimal at −3.9 × 10−3 m−1/°C. This hybrid microstructure sensor technology can be applied to high-sensitivity two-dimensional vector curvature and temperature detection for structural health monitoring of buildings, bridge engineering, and other related fields.

High-Sensitivity Curvature Fiber Sensor Based on Miniature Two-Path Mach-Zehnder Interferometer.

This paper introduces a new high-sensitivity curvature fiber sensor based on a miniature two-path Mach-Zehnder interferometer (MTP-MZI). The sensor is fabricated by coupling and fusing the multimode fiber (MMF) with the single-mode fiber (SMF) using arc fusion technology (AFT), resulting in a centimeter-level two-path MZI structure. The sensor represents an innovative approach to MZI coupling technology, which reduces device size, simplifies manufacturing, and lowers costs. In curvature-sensing experiments, the MTP-MZI sensor achieves a maximum curvature sensitivity of -96.70 dB/m-1 in the curvature range of 0.0418 m-1 to 0.0888 m-1, which is an extremely high sensitivity among intensity-modulated curvature sensors. Additionally, temperature-sensing measurements of the MTP-MZI sensor show a maximum temperature sensitivity of 212 pm/°C in the range of 30 °C to 70 °C, which is low temperature sensitivity and solves the cross-sensitivity problem. Thanks to the miniature two-path structure of the MTP-MZI, it provides a new perspective for developing multidimensional and multiparameter measurement methods in MZI fiber sensors.

Adaptively Isotropic Remeshing Based on Curvature Smoothed Field.

With the development of 3D digital geometry technology, 3D triangular meshes are becoming more useful and valuable in industrial manufacturing and digital entertainment. A high quality triangular mesh can be used to represent a real world object with geometric and physical characteristics. While anisotropic meshes have advantages of representing shapes with sharp features (such as trimmed surfaces) more efficiently and accurately, isotropic meshes allow more numerically stable computations. When there is no anisotropic mesh requirement, isotropic triangles are always a good choice. In this paper, we propose a remeshing method to convert an input mesh into an adaptively isotropic one based on a curvature smoothed field (CSF). With the help of the CSF, adaptively isotropic remeshing can retain the curvature sensitivity, which enables more geometric features to be kept, and avoid the occurrence of obtuse triangles in the remeshed model as much as possible. The remeshed triangles with locally isotropic property benefit various geometric processes such as neighbor-based feature extraction and analysis. The experimental results show that our method achieves better balance between geometric feature preservation and mesh quality improvement compared to peers. We provide the implementation codes of our resampling method at github.com/vvvwo/Adaptively-Isotropic-Remeshing.

Softening in Two-Component Lipid Mixtures by Spontaneous Curvature Variance.

The bending modulus of a lipid bilayer quantifies its mechanical resistance to curvature. It is typically understood in terms of thickness; e.g., thicker bilayers are usually stiffer. Here, we describe an additional and powerful molecular determinant of stiffness─the variance in the distribution of curvature sensitivity of lipids and lipid conformations. Zwitterionic choline and ethanolamine headgroups of glycerophospholipids dynamically explore inter- and intraspecies interactions, leading to transient clustering. We demonstrate that these clusters couple strongly to negative curvature, exciting undulatory membrane modes and reducing the apparent bending modulus. Three force fields (Martini 2, Martini 3, and all-atom CHARMM C36) each show the effect to a different extent, with the coarse-grained Martini models showing the most clustering and thus the most softening. The theory is a guide to understanding the stiffness of biological membranes with their complex composition, as well as how choices of force field parameterization are translated into mechanical stiffness.

Temperature-insensitive vector curvature sensor based on four-core fiber offset structure

Vector curvature measurement is very important in industrial fields with the unavoidable problem of temperature crosstalk. To improve the detection performance, a novel temperature-insensitive vector bending sensor have been proposed in the paper. The sensor is fabricated by core-offset splicing a segment of four-core fiber (FCF) between two single-mode fibers (SMFs). The Mach-Zehnder interference and the recognition ability of bending directions are enhanced by the core-offset structure. The experimental results demonstrate the curvature sensitivities of our sensor reach 38.16 nm/m−1, 37.46 nm/m−1, 4.99 nm/m−1 and −7.12 nm/m−1 in different bending directions within the range of 0.346–0.49 m−1. The average temperature sensitivity is only −6.67 pm/℃ in the range of 30–90 °C. The all-fiber, low cost, high sensitivity, and excellent vectoriality make our sensor more potential in harsh, complex industrial environment.

Research on aberration correction methods of conformal dome based on haack curve

Conformal optics arose from the need for better aerodynamic performance. The Haack curve has the lowest air drag under given conditions. It has superior aerodynamic properties compared to hemispherical domes and quadric conformal domes. Most in line with the concept of conformal optics. But aberration correction is also the most difficult. At present, there is no research on this conformal dome with the best aerodynamic performance. Therefore, a new design method for the internal surface is proposed in this paper to reduce the fluctuation range of aberrations. This method can eliminate the position error on the detector, reduce the fluctuation range of coma and spherical aberration, and even suppress the sensitivity of the defocus-field curvature to the parameters change. A condition for eliminating astigmatism is also proposed for the conformal dome. The fluctuation range of astigmatism and the difficulty of corrector design are reduced by reasonably choosing the rotation center. The research of this paper is of great significance in improving the aerodynamic performance of conformal optical systems.

Research on the preparation of multi-core photonic crystal fiber and the curvature sensing performance of three-core photonic crystal fiber

Two- and three-core photonic crystal fibers are prepared by using the same photonic crystal fiber preform structure. Not only the fiber diameter is reduced to standard size of 125μm, but also the core diameter is reduced to below 4μm. A curvature and temperature sensing system is built, and the curvature and temperature sensing performance of the three-core optical fiber is tested. When the length of three-core optical fiber is 150 mm, the measured curvature sensitivity is −7.27069 nm/m−1 in the range of 0 to 0.990 m−1, and the temperature sensitivity is −34 pm/°C during the temperature reduction from 75 to 45 °C. When the length of three-core photonic crystal fiber is 68 mm, the curvature sensitivity and temperature sensitivity are 2.42419 nm/m−1 and −7 pm/°C, respectively. In a small range of temperature, the sensor is insensitive to temperature, and the cross interference of temperature to curvature is very small.

A Mach-Zehnder-based optical fiber sensor enables multi-directional and wide-range curvature sensing with the assistance of CNN

In this work, wide-range curvature sensing in multiple directions was achieved by combining a Mach-Zehnder-based optical fiber sensor (OFS) with convolutional neural networks (CNNs). The experimental results show that the curvature sensitivity of the proposed sensor is − 8.8320 nm/m−1 in the range of 0–3.1171 m−1. The application of CNNs significantly improves the measurement range to 0–10.4167 m−1, and the sensor can realize measurements over a wide curvature range in four directions. The accuracy of the measurements can still be guaranteed despite a sudden decrease in the number of wavelength sampling points, and curvature direction recognition was realized. Further, OFSs can achieve a wide range of curvature sensing in 12 directions by taking full advantage of the information contained in the transmission spectrum. The proposed technique is highly versatile and conducive to the popularization of OFSs in the field of curvature measurement.

Multiparameter sensor based on long-period grating in few-mode ring-core fiber for vector curvature and torsion measurement

With the rapid development of optical fiber sensor in physical measurement, it is of practical significant to realize multi-parameter measurement. In this work, we proposed and demonstrated a multiparameter sensor for curvature, torsion and temperature. The sensor is formed from CO2 laser-inscribed long-period grating (LPG) in few-mode ring-core fiber (RCF), which can convert fundamental mode to LP11 mode. One-side inscription enhances asymmetric index modulation in fiber, resulting in directionally sensitive to bend by intensity interrogation. The curvature sensitivities in various bending directions perform linearity in curvature range of 5–9.466 m−1. Curvature sensitivities are related to the bending directions. The intensity sensitivity achieves − 0.584 dB/m−1, 0.879 dB/m−1, and − 0.735 dB/m−1, respectively. And torsion sensitivity from -6.98 rad/m to 6.98 rad/m displays linearity with −0.554 dB/(rad/m). The measured influence of temperature can be negligible. The proposed RCF-LPG could not only be used as high-efficiency mode converter in mode division multiplexing systems but also be potential in few-mode fiber based multiparameter sensing fields.

A minimal physical model for curvotaxis driven by curved protein complexes at the cell’s leading edge

Cells often migrate on curved surfaces inside the body, such as curved tissues, blood vessels, or highly curved protrusions of other cells. Recent in vitro experiments provide clear evidence that motile cells are affected by the curvature of the substrate on which they migrate, preferring certain curvatures to others, termed "curvotaxis." The origin and underlying mechanism that gives rise to this curvature sensitivity are not well understood. Here, we employ a "minimal cell" model which is composed of a vesicle that contains curved membrane protein complexes, that exert protrusive forces on the membrane (representing the pressure due to actin polymerization). This minimal-cell model gives rise to spontaneous emergence of a motile phenotype, driven by a lamellipodia-like leading edge. By systematically screening the behavior of this model on different types of curved substrates (sinusoidal, cylinder, and tube), we show that minimal ingredients and energy terms capture the experimental data. The model recovers the observed migration on the sinusoidal substrate, where cells move along the grooves (minima), while avoiding motion along the ridges. In addition, the model predicts the tendency of cells to migrate circumferentially on convex substrates and axially on concave ones. Both of these predictions are verified experimentally, on several cell types. Altogether, our results identify the minimization of membrane-substrate adhesion energy and binding energy between the membrane protein complexes as key players of curvotaxis in cell migration.

A curvature fiber optic sensor with expandable measurement points based on anti-resonant hollow-core optical fiber

This work presents an expandable fiber optic curvature sensor. The sensor achieves multi-point curvature measurements by cascading different lengths of anti-resonant hollow-core fiber sensing units. The sensing unit is formed by connecting the anti-resonant hollow-core fiber between two single-mode fibers. The highest curvature sensitivity achieved by a single sensing unit is −11.86 nm/m−1, with a low temperature sensitivity of only 3 pm/°C. This sensing unit is readily manufacturable and exhibits good curvature sensitivity, temperature insensitivity, and stability. In contrast to traditional multi-point distributed sensors, this sensor can be flexibly installed at various positions, providing curvature sensing at desired locations. Moreover, it demonstrates the potential for multi-point curvature measurements, offering a promising solution for practical applications such as structural monitoring and robotic posture detection.

Experimental Demonstration to Enhance the Curvature Sensitivity of a Fiber Mach–Zehnder Interferometer Based on a Waist-Enlarged Technique Using Polymer

A fiber curvature sensor based on a Mach–Zehnder Interferometer (MZI) constructed using the waist-enlarged technique to splice a segment of non-zero dispersion-shifted fiber (NZ-DSF) between two segments of single mode fiber (SMF) is proposed and experimentally demonstrated. All fabricated sensors presented an improvement in their curvature sensitivity when they were coated with polydimethylsiloxane (PDMS) polymer. The sensor that exhibited the best performance was 6.5 cm long, with a curvature sensitivity of 8.27 nm/m−1 in a range of 0.69 m−1 (from 1.08 to 1.77 m−1). This sensitivity is 3.22 times higher than that of the sensor without polymer. Additionally, the sensor coated with polymer exhibited cross-sensitivity that is 2.23 times smaller than the sensor without polymer. The easy fabrication and notable performance of this device makes it alluring for structural health monitoring.