Hypersensitive meta-crack strain sensor for real-time biomedical monitoring.

Real-time monitoring of infinitesimal deformations on complex morphologies is essential for precision biomechanical engineering. While flexible strain sensors facilitate real-time monitoring with shape-adaptive properties, their sensitivity is generally lower than spectroscopic imaging methods. Crack-based strain sensors achieve enhanced sensitivity with gauge factors (GFs) exceeding 30,000; however, such GFs are only attainable at large strains exceeding several percent and decline below 10 for strains under 10, rendering them inadequate for minute deformations.

A shape-reconfigurable electronic composite for stimulus customizable detection neutral plane shifting.

Three-dimensional (3D) sensors selectively measure the applied force in a particular direction through the designed shape. However, such a fixed sensor design incurs a relatively low sensitivity and narrow measurement range to forces applied from other directions. Here, we report a shape-reconfigurable electronic composite based on a stiffness-tunable polymer and a crack-based strain sensor.

Real-time counting of wheezing events from lung sounds using deep learning algorithms: Implications for disease prediction and early intervention.

This pioneering study aims to revolutionize self-symptom management and telemedicine-based remote monitoring through the development of a real-time wheeze counting algorithm. Leveraging a novel approach that includes the detailed labeling of one breathing cycle into three types: break, normal, and wheeze, this study not only identifies abnormal sounds within each breath but also captures comprehensive data on their location, duration, and relationships within entire respiratory cycles, including atypical patterns. This innovative strategy is based on a combination of a one-dimensional convolutional neural network (1D-CNN) and a long short-term memory (LSTM) network model, enabling real-time analysis of respiratory sounds.

Scale dependence in hydrodynamic regime for jumping on water.

Momentum transfer from the water surface is strongly related to the dynamical scale and morphology of jumping animals. Here, we investigate the scale-dependent momentum transfer of various jumping organisms and engineered systems at an air-water interface. A simplified analytical model for calculating the maximum momentum transfer identifies an intermediate dynamical scale region highly disadvantageous for jumping on water.

High-performance electrified hydrogel actuators based on wrinkled nanomembrane electrodes for untethered insect-scale soft aquabots.

Hydrogels have diverse chemical properties and can exhibit reversibly large mechanical deformations in response to external stimuli; these characteristics suggest that hydrogels are promising materials for soft robots. However, reported actuators based on hydrogels generally suffer from slow response speed and/or poor controllability due to intrinsic material limitations and electrode fabrication technologies. Here, we report a hydrogel actuator that operates at low voltages (<3 volts) with high performance (strain > 50%, energy density > 7 × 10 joules per cubic meter, and power density > 3 × 10 watts per cubic meter), surpassing existing hydrogel actuators and other types of electroactive soft actuators.

Actuating compact wearable augmented reality devices by multifunctional artificial muscle.

An artificial muscle actuator resolves practical engineering problems in compact wearable devices, which are limited to conventional actuators such as electromagnetic actuators. Abstracting the fundamental advantages of an artificial muscle actuator provides a small-scale, high-power actuating system with a sensing capability for developing varifocal augmented reality glasses and naturally fit haptic gloves. Here, we design a shape memory alloy-based lightweight and high-power artificial muscle actuator, the so-called compliant amplified shape memory alloy actuator.

Design of a Biologically Inspired Water-Walking Robot Powered by Artificial Muscle.

The agile and power-efficient locomotion of a water strider has inspired many water-walking devices. These bioinspired water strider robots generally adopt a DC motor to create a sculling trajectory of the driving leg. These robots are, thus, inevitably heavy with many supporting legs decreasing the velocity of the robots.

Vital signal sensing and manipulation of a microscale organ with a multifunctional soft gripper.

Soft grippers that incorporate functional materials are important in the development of mechanically compliant and multifunctional interfaces for both sensing and stimulating soft objects and organisms. In particular, the capability for firm and delicate grasping of soft cells and organs without mechanical damage is essential to identify the condition of and monitor meaningful biosignals from objects. Here, we report a millimeter-scale soft gripper based on a shape memory polymer that enables manipulating a heavy object (payload-to-weight ratio up to 6400) and grasping organisms at the micro/milliscale.

Design of a Sensitive Balloon Sensor for Safe Human-Robot Interaction.

As the safety of a human body is the main priority while interacting with robots, the field of tactile sensors has expanded for acquiring tactile information and ensuring safe human-robot interaction (HRI). Existing lightweight and thin tactile sensors exhibit high performance in detecting their surroundings. However, unexpected collisions caused by malfunctions or sudden external collisions can still cause injuries to rigid robots with thin tactile sensors.

Electroosmosis-Driven Hydrogel Actuators Using Hydrophobic/Hydrophilic Layer-By-Layer Assembly-Induced Crack Electrodes.

Development of soft actuators with higher performance and more versatile controllability has been strongly required for further innovative advancement of various soft applications. Among various soft actuators, electrochemical actuators have attracted much attention due to their lightweight, simple device configuration, and facile low-voltage control. However, the reported performances have not been satisfactory because their working mechanism depends on the limited electrode expansion by conventional electrochemical reactions.

Foot Plantar Pressure Measurement System Using Highly Sensitive Crack-Based Sensor.

Measuring the foot plantar pressure has the potential to be an important tool in many areas such as enhancing sports performance, diagnosing diseases, and rehabilitation. In general, the plantar pressure sensor should have robustness, durability, and high repeatability, as it should measure the pressure due to body weight. Here, we present a novel insole foot plantar pressure sensor using a highly sensitive crack-based strain sensor.

Uniaxially crumpled graphene as a platform for guided myotube formation.

Graphene, owing to its inherent chemical inertness, biocompatibility, and mechanical flexibility, has great potential in guiding cell behaviors such as adhesion and differentiation. However, due to the two-dimensional (2D) nature of graphene, the microfabrication of graphene into micro/nanoscale patterns has been widely adopted for guiding cellular assembly. In this study, we report crumpled graphene, i.

FEP Encapsulated Crack-Based Sensor for Measurement in Moisture-Laden Environment.

Among many flexible mechanosensors, a crack-based sensor inspired by a spider's slit organ has received considerable attention due to its great sensitivity compared to previous strain sensors. The sensor's limitation, however, lies on its vulnerability to stress concentration and the metal layers' delamination. To address this issue of vulnerability, we used fluorinated ethylene propylene (FEP) as an encapsulation layer on both sides of the sensor.

Design of Polarization-Independent and Wide-Angle Broadband Absorbers for Highly Efficient Reflective Structural Color Filters.

We propose a design of angle-insensitive and polarization-independent reflective color filters with high efficiency (>80%) based on broad resonance in a Fabry⁻Pérot cavity where asymmetric metal-dielectric-metal planar structures are employed. Broadband absorption properties allow the resonance in the visible range to remain nearly constant over a broad range of incident angles of up to 40° for both s- and p-polarizations. Effects of the angles of incidence and polarization state of incident light on the purity of the resulting colors are examined on the CIE 1931 chromaticity diagram.

Relation between blood pressure and pulse wave velocity for human arteries.

Continuous monitoring of blood pressure, an essential measure of health status, typically requires complex, costly, and invasive techniques that can expose patients to risks of complications. Continuous, cuffless, and noninvasive blood pressure monitoring methods that correlate measured pulse wave velocity (PWV) to the blood pressure via the Moens-Korteweg (MK) and Hughes Equations, offer promising alternatives. The MK Equation, however, involves two assumptions that do not hold for human arteries, and the Hughes Equation is empirical, without any theoretical basis.

Effect of Metal Thickness on the Sensitivity of Crack-Based Sensors.

Among many attempts to make a decent human motion detector in various engineering fields, a mechanical crack-based sensor that deliberately generates and uses nano-scale cracks on a metal deposited thin film is gaining attention for its high sensitivity. While the metal layer of the sensor must be responsible for its high performance, its effects have not received much academic interest. In this paper, we studied the relationship between the thickness of the metal layer and the characteristics of the sensor by depositing a few nanometers of chromium (Cr) and gold (Au) on the PET film.

Three-Dimensional Silicon Electronic Systems Fabricated by Compressive Buckling Process.

Recently developed approaches in deterministic assembly allow for controlled, geometric transformation of two-dimensional structures into complex, engineered three-dimensional layouts. Attractive features include applicability to wide ranging layout designs and dimensions along with the capacity to integrate planar thin film materials and device layouts. The work reported here establishes further capabilities for directly embedding high-performance electronic devices into the resultant 3D constructs based on silicon nanomembranes (Si NMs) as the active materials in custom devices or microscale components released from commercial wafer sources.

A semi-permanent and durable nanoscale-crack-based sensor by on-demand healing.

Although sensitivity and durability are desirable in a sensor, both of them cannot be easily achieved. Site-specific and effective signal acquisition on the limited area of a sensor inevitably allows fatigue accumulation and contamination. For example, an ultrasensitive nanoscale-crack-based sensor for detecting a mechanical stimulus with tremendous sensitivity (a gauge factor greater than 2000 under 2% strain), yet limited durability (up to a few thousand stretching cycles in tensile tests) has been presented previously.

Soft, skin-mounted microfluidic systems for measuring secretory fluidic pressures generated at the surface of the skin by eccrine sweat glands.

During periods of activity, sweat glands produce pressures associated with osmotic effects to drive liquid to the surface of the skin. The magnitudes of these pressures may provide insights into physiological health, the intensity of physical exertion, psychological stress factors and/other information of interest, yet they are currently unknown due to absence of means for non-invasive measurement. This paper introduces a thin, soft wearable microfluidic system that mounts onto the surface of the skin to enable precise and routine measurements of secretory fluidic pressures generated at the surface of the skin by eccrine sweat glands (surface SPSG, or s-SPSG) at nearly any location on the body.

Thin, Soft, Skin-Mounted Microfluidic Networks with Capillary Bursting Valves for Chrono-Sampling of Sweat.

Systems for time sequential capture of microliter volumes of sweat released from targeted regions of the skin offer the potential to enable analysis of temporal variations in electrolyte balance and biomarker concentration throughout a period of interest. Current methods that rely on absorbent pads taped to the skin do not offer the ease of use in sweat capture needed for quantitative tracking; emerging classes of electronic wearable sweat analysis systems do not directly manage sweat-induced fluid flows for sample isolation. Here, a thin, soft, "skin-like" microfluidic platform is introduced that bonds to the skin to allow for collection and storage of sweat in an interconnected set of microreservoirs.

Ultra-sensitive Pressure sensor based on guided straight mechanical cracks.

Recently, a mechanical crack-based strain sensor with high sensitivity was proposed by producing free cracks via bending metal coated film with a known curvature. To further enhance sensitivity and controllability, a guided crack formation is needed. Herein, we demonstrate such a ultra-sensitive sensor based on the guided formation of straight mechanical cracks.

Artificial Slanted Nanocilia Array as a Mechanotransducer for Controlling Cell Polarity.

We present a method to induce cell directional behavior using slanted nanocilia arrays. NIH-3T3 fibroblasts demonstrated bidirectional polarization in a rectangular arrangement on vertical nanocilia arrays and exhibited a transition from a bidirectional to a unidirectional polarization pattern when the angle of the nanocilia was decreased from 90° to 30°. The slanted nanocilia guided and facilitated spreading by allowing the cells to contact the sidewalls of the nanocilia, and the directional migration of the cells opposed the direction of the slant due to the anisotropic bending stiffness of the slanted nanocilia.

A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat.

Capabilities in health monitoring enabled by capture and quantitative chemical analysis of sweat could complement, or potentially obviate the need for, approaches based on sporadic assessment of blood samples. Established sweat monitoring technologies use simple fabric swatches and are limited to basic analysis in controlled laboratory or hospital settings. We present a collection of materials and device designs for soft, flexible, and stretchable microfluidic systems, including embodiments that integrate wireless communication electronics, which can intimately and robustly bond to the surface of the skin without chemical and mechanical irritation.

Dramatically Enhanced Mechanosensitivity and Signal-to-Noise Ratio of Nanoscale Crack-Based Sensors: Effect of Crack Depth.

The sensitivity of a nanoscale crack-based sensor is enhanced markedly by modulating the crack depth. The crack-depth-propagated sensor exhibits ≈16 000 gauge factor at 2% strain and a superior signal-to-noise ratio of ≈35, which facilitates detection of target signals for voice-pattern recognition.