An Electronically Perceptive Bioinspired Soft Wet-Adhesion Actuator with Carbon Nanotube-Based Strain Sensors.

The development of bioinspired switchable adhesive systems has promising solutions in various industrial/medical applications. Switchable and perceptive adhesion regardless of the shape or surface shape of the object is still challenging in dry and aquatic surroundings. We developed an electronic sensory soft adhesive device that recapitulates the attaching, mechanosensory, and decision-making capabilities of a soft adhesion actuator. The soft adhesion actuator of an artificial octopus sucker may precisely control its robust attachment against surfaces with various topologies in wet environments as well as a rapid detachment upon deflation. Carbon nanotube-based strain sensors are three-dimensionally coated onto the irregular surface of the artificial octopus sucker to mimic nerve-like functions of an octopus and identify objects via patterns of strain distribution. An integration with machine learning complements decision-making capabilities to predict the weight and center of gravity for samples with diverse shapes, sizes, and mechanical properties, and this function may be useful in turbid water or fragile environments, where it is difficult to utilize vision.

A Hierarchically Tailored Wrinkled Three-Dimensional Foam for Enhanced Elastic Supercapacitor Electrodes.

Recently, three-dimensional (3D) porous foams have been studied, but further improvement in nanoscale surface area and stretchability is required for electronic and energy applications. Herein, a general strategy is reported to form a tailored wrinkling structure on strut surfaces inside a 3D polydimethylsiloxane (PDMS) polymeric foam. Controlled wrinkles are created on the struts of 3D foam through an oxygen plasma treatment to form a bilayer surface of PDMS on uniaxially prestretched 3D PDMS foam, followed by relaxation. After plasma treatment for 1 h and prestretching of 40%, the wrinkled 3D foam greatly improves specific surface area and stretchability by over 60% and 75%, respectively, compared with the pristine 3D PDMS foam. To prove its applicability with improved performances, supercapacitors are prepared by coating a conductive material on the wrinkled 3D foam. The resulting supercapacitors exhibit an increased storage capacity (8.3 times larger), maintaining storage capacity well under stretching up to 50%.

Highly Air/Water-Permeable Hierarchical Mesh Architectures for Stretchable Underwater Electronic Skin Patches.

The development of an electronic skin patch that can be used in underwater environments can be considered essential for fabricating long-term wearable devices and biomedical applications. Herein, we report a stretchable conductive polymer composite (CPC) patch on which an octopus sucker-inspired structure is formed to conformally contact with biological skin that may be rough and wet. The patch is patterned with a hexagonal mesh structure for water and air permeability. The patch films are suited for a strain sensor or a stretchable electrode as their piezoresistive responses can be controlled by changing the concentration of conductive fillers to polymeric polyurethane. The CPC patch with a hexagonal mesh pattern (HMP) can be easily stretched for a strain sensor and is insensitive to tensile strain, making the patch suitable as a stretchable electrode. Furthermore, the octopus-like structures formed on the skeleton of the HMP allow the patch to maintain strong adhesion underwater by easily draining excess water trapped between the patch and skin. The sensor patch (<50 wt % carbon nanotubes (CNTs)) can sensitively detect the bending strain of a finger, and the electrode patch (50 wt % CNTs with addition of Ag flakes) can stably measure biosignals (e.g., electrocardiogram signals) under both dry and wet conditions owing to the octopus-like structure and HMP.

Hexagonal deposits of colloidal particles.

Colloidal particles are essential materials for modern inkjet printing and coating. Here we demonstrate a versatile method to achieve hexagonal deposits of colloidal particles through droplet evaporation on hexagonal micropillar arrays. We identify how colloidal fluids turn into hexagonal deposits during evaporation with x-ray tomography. Interestingly, evaporation-driven hexagonal deposits are quite crack-free uniform. We attribute hexagonal deposit shape control to local contact line pinning by colloidal particles and geometric constraints by micropillar arrays. This deposition strategy offers a feasibility for high-quality evaporation-driven crack-free uniform polygonal deposits of colloidal particles for diverse applications.

Capillarity-Enhanced Organ-Attachable Adhesive with Highly Drainable Wrinkled Octopus-Inspired Architectures.

Mimicking the attachment of octopus suction cups has become appealing for the development of skin/organ adhesive patches capable of strong, reversible adhesion in dry and wet conditions. However, achieving high conformity against the three-dimensionally (3D) rough and curved surfaces of the human body remains an enduring challenge for further medical applications of wound protection, diagnosis, or therapeutics. Here, an adhesive patch inspired by the soft wrinkles of miniaturized 3D octopus suction cups is presented for high drainability and robust attachment against dry and wet human organs. Investigating the structural aspects of the wrinkles, a simple model is developed to maximize capillary interactions of the wrinkles against wet substrates. A layer of soft siloxane derivative is then transferred onto the wrinkles to enhance fixation against dry and sweaty skin as well as various wet organ surfaces. Our bioinspired patch offers opportunities for enhancing the versatility of adhesives for developing skin- and/or organ-attachable devices.

Water-Resistant and Skin-Adhesive Wearable Electronics Using Graphene Fabric Sensor with Octopus-Inspired Microsuckers.

Wearable and skin-attachable electronics with portable/wearable and stretchable smart sensors are essential for health-care monitoring devices or systems. The property of adhesion to the skin in both dry and wet environments is strongly required for efficient monitoring of various human activities. We report here a facile, low-cost, scalable fabrication method for skin-adhesive graphene-coated fabric (GCF) sensors that are sensitive and respond fast to applied pressure and strain. With octopus-like patterns formed on the side of the GCF that touches the skin, the GCF adheres strongly to the skin in both dry and wet environments. Using these characteristics, we demonstrate efficient monitoring of a full range of human activities, including human physiological signals such as wrist pulse and electrocardiography (ECG), as well as body motions and speech vibrations. In particular, both measurements of ECG and wrist-bending motions were demonstrated even in wet conditions. Our approach has opened up a new possibility for wearable and skin-adherent electronic fabric sensors working even in wet environments for health-care monitoring and medical applications in vitro and in vivo.

Bioinspired Hairy Skin Electronics for Detecting the Direction and Incident Angle of Airflow.

The human skin has inspired multimodal detection using smart devices or systems in fields including biomedical engineering, robotics, and artificial intelligence. Hairs of a high aspect ratio (AR) connected to follicles, in particular, detect subtle structural displacements by airflow or ultralight touch above the skin. Here, hairy skin electronics assembled with an array of graphene sensors (16 pixels) and artificial microhairs for multimodal detection of tactile stimuli and details of airflows (e.g., intensity, direction, and incident angle) are presented. Composed of percolation networks of graphene nanoplatelet sheets, the sensor array can simultaneously detect pressure, temperature, and vibration, all of which correspond to the sensing range of human tactile perceptions with ultrahigh response time (<0.5 ms, 2 kHz) for restoration. The device covered with microhairs (50 µm diameter and 300 µm height, AR = 6, hexagonal layout, and ∼4400/cm2) exhibits mapping of electrical signals induced by noncontact airflow and identifying the direction, incident angle, and intensity of wind to the sensor. For potential applications, we implement the hairy electronics to a sailing robot and demonstrate changes in locomotion and speed by detecting the direction and intensity of airflow.