Soft Skin Research Articles

Liquid Metal Elastomer-Based U-Shaped Electrode Flexible Strain Sensors with Enhanced Stability and Sensitivity.

Soft and stretchable strain sensors are crucial for applications in human-machine interfaces, flexible robotics, and electronic skin. Among these, capacitive strain sensors are widely used and studied; however, they face challenges due to material and structural constraints, such as low baseline capacitance and susceptibility to external interference, which result in low signal-to-noise ratios and poor stability. To address these issues, we propose a U-shaped electrode flexible strain sensor based on liquid metal elastomer (LME). By incorporating liquid metal into the elastomer, we create a high-dielectric constant LME dielectric layer. Additionally, we innovatively introduce an external U-shaped flexible textile electrode in conjunction with an internal planar flexible textile electrode to form the flexible strain sensor, effectively resolving the trade-off between stability and integration in capacitive sensors. We also investigated the dielectric and mechanical properties of the LME at varying liquid metal volume fraction (ϕLM). A comparative simulation was conducted between parallel plate structure and U-shaped package structure designs, leading to the fabrication of the U-shaped electrode flexible strain sensor based on LME. Furthermore, we demonstrated its potential applications in monitoring human motion, soft gripper electronic skin, and robotic arm movements.

Human Collaborative Control of Lower-Limb Prosthesis Based on Game Theory and Fuzzy Approximation.

For leg prosthesis user, the soft tissue and skin under the stump of are not accustomed to weight bearing, excessive continuous contact pressure can lead to the risk of degenerative tissue ulceration. This article presents a novel human-robot collaborative control scheme that achieves control weight self-adjustment for robotic prostheses to minimize interaction torque. To establish the human-robot interaction relationship, we regard the contact pressure between human residual limb and the prosthetic receiving cavity as the interaction force. We aim at reducing the interaction force under the premise of minimally changing the original motion trajectory of the robotic prosthesis. The control scheme mainly includes trajectory optimization based on a dual-agent game control scheme under a cooperative relationship, and a fuzzy logic system for improving the control accuracy of trajectory tracking of robotic prostheses with unknown dynamic parameters. Experiments were carried out on two amputee participants to verify the proposed human-robot interactive control scheme in a robotic prosthesis. The results show that the interaction torque could be reduced while maintaining minimal trajectory tracking error. The proposed control scheme could potentially facilitate the dexterous manipulation of leg prostheses, thus benefiting amputees.

Soft Magnetic Skin With Motion and Contact Sensing for Anthropomorphic Robotic Finger

Soft Magnetic Skin With Motion and Contact Sensing for Anthropomorphic Robotic Finger

Synthesis, characterization, and application potential of chitosan/acrylamide composite hydrogels as skin expanders

Hydrogels are currently widely used in regenerative medicine and wound repair due to their superior biocompatibility, reliable mechanical strength, and good morphological memory. We aimed to prepare a self-expanding hydrogel that can be used as a skin expander for the repair of large soft skin tissue defects. Self-expanding hydrogels were prepared by chemical cross-linking, which consisted of water-soluble chitosan (CS), acrylamide (AM), methylene bisacrylamide (NMBA), etc. Five groups of in vitro experiments, including (CS-AM) of 0% (pure AM group), 13.9%, 27.8%, 41.7%, and 55.6%, were conducted to determine mechanical properties, swelling properties, cytotoxicity, etc. In the rat model, both a tight skin area (neck) and a loose skin area (back) were selected for expansion with hydrogels. A total of 27.8% of the CS-AM samples expanded stably under the skin of the rats, achieving 370% expansion in the tight zone and 490% expansion in the flaccid zone. Subcutaneous histopathological examination suggested that the inflammation index of the pericolloid tissue was lower in the CS-AM group than in the pure AM group. Our results demonstrate that self-expanding CS-AM hydrogels have great potential for application as skin expanders.Graphical

A soft skin with self-decoupled three-axis force-sensing taxels

A soft skin with self-decoupled three-axis force-sensing taxels

A soft electronic skin simulating the multi-scale human touch for the detection of fruit freshness

Realizing biomimicry for human tactile perception is a meaningful challenge. In this work, a soft matter system with multi-scale energy dissipation structure is designed to realize flexible sensing and detection by biomimetic human touch. At the molecular scale, the supramolecular interactions are introduced into the hydrogel system, including the hydrophobic interaction and the ion attraction between macromolecular segments. At the micron scale, a system of “button” permeable macromolecules is constructed to absorb external forces and store energy through the sliding of macromolecules inside the “button”. By adjusting the molecular scale and micron scale structure, the obtained hydrogels demonstrate excellent mechanical properties, electrical conductivity and response sensitivity. This novel hydrogel withstands 200 compression cycles without creep deformation and outputs a stable response signal in terms of compression cycles with the signal volatility of around 1 %. Based on its good durability, this hydrogel, which simulates human multi-scale tactility, has outstanding application potential in detecting fruit damage that is difficult to observe. Notably, the construction of this multi-scale energy dissipation structure is universal for increasing the mechanical property of ACG hydrogels. The high-strength hydrogels adjusted by this strategy is significantly toughened, and the mechanical properties increased by 38 %. This work is of guiding significance for the preparation of high-performance hydrogels.

Mormyroidea-inspired electronic skin for active non-contact three-dimensional tracking and sensing

The capacity to discern and locate positions in three-dimensional space is crucial for human-machine interfaces and robotic perception. However, current soft electronics can only obtain two-dimensional spatial locations through physical contact. In this study, we report a non-contact position targeting concept enabled by transparent and thin soft electronic skin (E-skin) with three-dimensional sensing capabilities. Inspired by the active electrosensation of mormyroidea fish, this E-skin actively ascertains the 3D positions of targeted objects in a contactless manner and can wirelessly convey the corresponding positions to other devices in real-time. Consequently, this E-skin readily enables interaction with machines, i.e., manipulating virtual objects, controlling robotic arms, and drones in either virtual or actual 3D space. Additionally, it can be integrated with robots to provide them with 3D situational awareness for perceiving their surroundings, avoiding obstacles, or tracking targets.

Bioinspired Ultra‐Stretchable and Highly Sensitive Structural Color Electronic Skins

AbstractOrganisms possess remarkably adaptive ability to complex environments. For example, chameleons can alter their skin color to adapt to varying environments, which has inspired significant advances in bioinspired soft electronic skins (E‐skins), and their wide applications in wearable sensors, intelligent robots, and health monitoring. However, current bioinspired E‐skins face challenges in ultra‐stretchability, high sensitivity, and long‐term stability owing to the intrinsic limitations associated with their mismatched interface between soft matrix and hard conductive fillers, hindering their practical applications. Here, it is reported that bioinspired structural color electronic skins (SC E‐skins) that consist of liquid metal particles (LMPs), periodical ordered colloidal crystal arrays, and ultra‐stretchable hydrogel, imparting synergistic and durable electrical–optical sensing capabilities. Such SC E‐skins demonstrate outstanding performances including superior flexibility (elongation at break > 1100%), high sensitivity (gauge factor = 3.26), fast synergetic electric–optical response time (≈100 ms), outstanding durability (over 1500 cycles), and high accuracy (R2 > 99.5%). These bioinspired SC E‐skins with excellent capability of converting mechanical signals into synergetic electrical–optical outputs hold great promise for smart wearable devices, affording a new horizon in developing advanced health monitoring technologies.

Multi-layered morphing soft structure with high-performance embedded electrothermal artificial muscles along with touch and temperature sensors

Abstract In this paper, we present a novel multilayered morphing structure, having similar topology resembling the structures found in nature to grasp delicate objects effectively as well as sense contact force and temperature. The structure consists of two actuation layers, two U-shaped cooling channel layers, piezoelectric based touch sensors and temperature sensors. Employing shape memory alloy (SMA) spring actuators for bending and twisted and coiled polymer fishing line with nichrome (TCPFL NMC) artificial muscles for antagonistic return, the soft silicone-based composite skin exhibits unique capabilities of large bidirectional movement, avoid rigid passive springs for return motion, soft grasping, safe interaction with humans, and ease fabrication. The SMA (0.38 mm wire diameter) serves as relatively fast actuating muscle and the TCPFL NMC (0.8 mm fiber diameter) as a slow actuating (considering mainly heating cycle), which was programmed/designed to mimic the fast and slow twitching muscles found in nature. Bending and return operations of skin samples of length 100 mm and thickness of 9 mm, with three different widths 20 mm, 25 mm, 30 mm, were experimentally studied. The 25 mm wide multilayered soft skin demonstrated cyclic actuation with a maximum bending angle of ∼70°, which was attributed due to the active cooling. The fluidic channels for active cooling were fabricated using 3D printed PVA tubes, casting within the silicone in a mold and subsequently dissolving in a circulating water. The study also included the integration and voltage response of mini-piezodisk sensor PIC255 having a diameter of 2 mm and thickness of 0.15 mm, which was embedded at different depths within the silicone (on the surface, 1 mm depth and 2 mm depth). The multilayered soft skin was also able to detect the temperature of the object during grasping, suggesting its potential application as a soft gripper in robotic systems.

Wet stability soft skin electronic sensor based on biochar-polypyrrole conductive hydrogel

Hydrogels have the softness and stretchability of similar tissues and are considered as materials for smart flexible electronic devices. However, the durability and reliability of most polypyrrole hydrogels in wet environments are still insufficient, especially its wet stability in the wet environment of seawater, limiting its development as flexible conductive electrodes. In this study, the porous solid carbon material after pyrolysis of natural materials is introduced into hydrogel, which is conducive to the migration and propagation of electrolyte ions, and can improve the moisture resistance stability of hydrogel. At the same time, polypyrrole material is introduced to further improve its electrical conductivity. With this method, the conductivity of conventional hydrogel materials can be increased by 12.2 times. The triboelectric nanogenerator device prepared with polypyrrole/biochar composite hydrogel can not only accurately monitor human joint motion, but also easily light up at least 300 light-emitting diodes when rubbed with aluminum materials, which proves the practical performance of the device. This study provides an alternative material for sensing hydrogels that can be used for human health monitoring of marine operators.

A dynamic model of tensegrity robotic fish considering soft fish skin and tail

A dynamic model of tensegrity robotic fish considering soft fish skin and tail

Myeloid sarcoma mimicking as recurrent squamous cell carcinoma: What is the etiology?

Abstract Introduction/Objective Myeloid sarcoma is an extramedullary malignancy of primitive myeloid cells and can occur during, preceding, or as a relapse of acute myeloid leukemia that occurs mostly in the soft tissue and skin. Methods/Case Report A 77-year-old white male with a history of oral squamous cell carcinoma status post resection (18 months ago) followed by radiation and chemotherapy (15 months prior), presented to the ear nose and throat clinic with increasing weakness and dizziness. He received two doses of Cisplatin and was currently on Pembrolizumab. On examination, there were two lesions in the oral cavity, one on the right gingivobuccal sulcus and a second on the left posterior mandibular ridge, suspicious for squamous cell carcinoma recurrence. Interestingly, the biopsy did not show evidence of recurrent squamous cell carcinoma but showed sheets of blasts that were positive for MPO, CD117, CD43, and CD68, consistent with myeloid sarcoma. Subsequent peripheral blood and bone marrow examinations showed acute myeloid leukemia. Results (if a Case Study enter NA) NA Conclusion Myeloid neoplasms post-cytotoxic therapy (MN-pCT) occur after radiation, alkylating agents, DNA topoisomerase II inhibitors, antimetabolites, and PARP1 inhibitors for a non-myeloid malignancy. Topoisomerase inhibitors are associated with MN-pCT after a latency period of 1 to 3 years; alkylating agents and radiation are associated with MN-pCT after a latency period of 5 to 7 years. Interestingly, this patient developed myeloid sarcoma in a previously irradiated area within 2 years. Cisplatin was discontinued after 2 doses due to side effect complications and is unlikely to be the culprit. Pembrolizumab is not considered to be a cytotoxic therapy and has not been reported to be associated with MN-pCT, however, the latency period for radiation-induced MN-pCT is unusually short in this patient and this raises the possibility of a Pembrolizumab-induced secondary myeloid neoplasm; additional investigation with other patients on this medication with second subsequent malignancies is required.

Evaluating the Antibiotic Effectiveness of Green-Synthesized Copper Nanoparticles Against Soft Tissue and Skin Infections

Evaluating the Antibiotic Effectiveness of Green-Synthesized Copper Nanoparticles Against Soft Tissue and Skin Infections

Directly Printable, Non‐Smearable and Stretchable Conductive Ink Enabled by Liquid Metal Microparticles Interstitially Engineered in Highly Entangled Elastomeric Matrix

AbstractLiquid metal or liquid metal microparticles (LMP) based conductive inks, though promising for fabrication of circuits for use in soft and stretchable electronics, are constrained by a few drawbacks such as need for encapsulation, need for sintering to induce conductivity, and smearing. To address these issues, herein, a stretchable conductive composite ink is developed by combining LMPs with carbon black (CB) in highly entangled polysiloxane elastomer. LMP‐dispersed elastomer lacks conductivity because of its non‐percolated network, however, the CB can interconnect LMPs to act as a bridge, thereby imparting conductivity to the elastomer. Due to presence of fluidic LMPs, the LMPs‐dispersed elastomer lies in soft regime with initial conductivity of 5.6 S m−1, aided by the presence of CB in the interstitial spaces between the LMPs. The highly entangled molecular network of the encapsulating elastomer endows the resulting composite with high stretchability (≈286%) and softness (0.648 MPa) and its long pot life enables rheological modulation of the ink to achieve pressure‐driven direct printed non‐smearing traces. The LMPs‐based conductive ink developed in this work is expected to be further utilized in the fabrication of soft robotics and electronic skin and integrated into electronic modules by facile direct 3D printing.

Stretchable and Elastic Triboelectric Nanogenerator with Liquid-Metal Grid-Patterned Single Electrode for Wearable Energy-Harvesting Devices.

Triboelectric nanogenerators (TENGs) have garnered significant attention as efficient energy-harvesting systems for sustainable energy sources in the field of self-powered wearable devices. Various conductive materials are used to build wearable devices, among which, gallium-based liquid metal (LM) is a preferred electrode owing to its fluidity and metallic conductivity even when strained. In this study, a stretchable, elastic, and wearable triboelectric nanogenerator is designed using a single electrode fabricated by embedding LM grid patterns into a stretchable silicone substrate through a two-step spray-coating process. Contrary to conventional double-electrode TENG that is challenging to integrate to human body, the LM grid-patterned single-electrode TENG (LMG-SETENG) has a simplified design and provides more flexibility. The LMG-SETENG can generate voltages of up to 100V via triboelectrification upon contact with the human body, even under various degrees of strain, owing to the fluidity of the LM electrode. The generated energy can be utilized as a sustainable energy source to power various small appliances. Moreover, the proposed LMG-SETENG can be utilized in soft robotics, electronic skin, and healthcare devices.

A tough, stretchable, adhesive and electroconductive polyacrylamide hydrogel sensor incorporated with sulfonated nanocellulose and carbon nanotubes

Recently, hydrogel sensors have been widely applied in wearable and portable electronics, but the low mechanical property, intolerance of fatigue, and low sensitivity and adhesion limit their further applications. In this study, sulfonated nanocellulose (SCNF) with dual functionality was blended into polyacrylamide (PAM) hydrogel matrix to reinforce the mechanical strength and facilitate the homogeneous dispersion of carbon nanotubes (CNTs). The SCNF-CNT/PAM hydrogel was designed through free radical polymerization to achieve commendable mechanical, electrical, and multifunctional properties. The environmental-friendly SCNF serves as bio-templates to facilitate the assembling of CNT into integrated SCNF-CNT structures with good dispersity, thus enabling the establishment of an integrated conducting and reinforcing network. The fabricated SCNF-CNT/PAM hydrogel exhibited outstanding compressive strength (∼0.45 MPa at 50 % strain), tensile strength (∼169.12 kPa), and antifatigue capacity under cyclic stretching and pressing. Furthermore, the multifunctional sensors assembled using this hydrogel demonstrated high strain sensitivity (gauge factor ~ 3.7 at 100–400 % strain) and effectively detected human motions. This design principle provides promising prospects for constructing next-generation multifunctional flexible sensors, and the integration of these distinctive properties enables the prepared composite hydrogels to find potential applications in various areas, such as implantable soft electronic devices, electronic skin, and human movement monitoring.

Mammary gland, skin and soft tissue tumors in pet cats: findings of the feline tumors collected from 2002 to 2022.

Cancer is a leading cause of death in cats, and the rate of such disease has been increasing recently. Nonetheless, feline oncology represents an important area of study not only for the health and wellbeing of cats but also for human health since various types of cancer in cats share similarities to those found in humans. Therefore, epidemiological studies on feline oncology may suggest environmental and genetic factors contributing to cancer in cats, which can eventually be translated to improve human cancer care. To provide an initial understanding of the epidemiology of feline neoplasms, a descriptive study was undertaken using a dataset documenting cases of feline cancer gathered from the Liguria region (northwest Italy) spanning from 2002 to 2022. The database includes tumor location, morphological codes of the International Classification of Diseases for Oncology, 3rd Edition (ICD-O-3), feline's breed, sex, neuter status, date of birth, date of diagnosis, national territorial unit code of the town of the owner's residence, and an alphanumeric string uniquely identifying the owner's surname. The dataset involves a population of 4,399 cats, including 3,195 females (1,425 neutered) and 1,204 males (750 neutered). Our results indicate that mammary gland tumors are the most represented tumors in the female population, while soft tissue and skin cancers appear to have a higher abundance in the male population during the periods investigated (2002-2022). Moreover, Poisson regression analysis showed that not neutered female cats have a significantly increased risk of developing mammary gland tumors compared to the neutered female population [proportional morbidity ratio (PMR) neutered vs. not neutered = 0.58, 95% CI: 0.47-0.72]; meanwhile, for both sexes, for soft tissue and skin tumors, being neutered appears to be a risk factor (PMR neutered vs. not neutered = 2.26, 95% CI: 1.86-2.73; PMR neutered vs. not neutered = 1.16, 95% CI: 0.89-1.51). Finally, the evaluation of the Ligurian municipalities pollution, based on wild boars data (i.e., biomonitors), which coexisted with cats, was correlated to cancer development for all the tumors investigated (in polluted areas, estimated PMRs ranged from 42.61 to 80.13, 95% CI: 29.94-105.11). Overall, the data presented here suggest the use of the feline population as a possible animal model for human health, i.e., sentinel.

AcousTac: Tactile Sensing with Acoustic Resonance for Electronics-Free Soft Skin.

Sound is a rich information medium that transmits through air; people communicate through speech and can even discern material through tapping and listening. To capture frequencies in the human hearing range, commercial microphones typically have a sampling rate of over 40 kHz. These accessible acoustic technologies are not yet widely adopted for the explicit purpose of giving robots a sense of touch. Some researchers have used sound to sense tactile information, both monitoring ambient soundscape and with embedded speakers and microphones to measure sounds within structures. However, these options commonly do not provide a direct measure of steady state force or require electronics integrated somewhere near the contact location. In this work, we present AcousTac, an acoustic tactile sensor for electronics-free, force-sensitive soft skin. Compliant silicone caps and plastic tubes compose the resonant chambers that emit pneumatic-driven sound measurable with a conventional off-board microphone. The resulting frequency changes depend on the external loads on the compliant endcaps. The compliant cap vibrates with the resonant pressure waves and is a nonidealized boundary condition, initially producing a nonmonotonic force response. We characterize two solutions-adding a distal hole and mass to the cap-resulting in monotonic and nonhysteretic force readings with this technology. We can tune each AcousTac taxel to specific force and frequency ranges, based on geometric parameters including tube length, and thus uniquely sense each taxel simultaneously in an array. We demonstrate AcousTac's functionality on two robotic systems: a 4-taxel array and a 3-taxel astrictive gripper. Simple to implement with off-the-shelf parts, AcousTac is a promising concept for force sensing on soft robotic surfaces, especially in situations where electronics near the contact are not suitable. Equipping robots with tactile sensing and soft skin provides them with a sense of touch and the ability to safely interact with their surroundings.

Erratum to: Soft multifunctional neurological electronic skin through intrinsically stretchable synaptic transistor

Erratum to: Soft multifunctional neurological electronic skin through intrinsically stretchable synaptic transistor

Jellyfish-Inspired Visual and Sensory Bubbling Robots with Automatic 3D Morphable Films for Underwater Environmental Interactions.

Coelenterates, such as Atolla jellyfish, are capable of integrating color, communication, and motion in a sophisticated manner, thereby enabling them to function as intelligent biological systems that can adapt to the challenges of the underwater environment. Extensive efforts have been dedicated to exploiting underwater visual, sensory, actuating, or combined systems. However, current biomimetic soft systems are still limited by the lack of comprehensive, integrated functional skins that can automatically deform, dynamically sense, and further send color signals when diving into underwater conditions. Here, we propose the synthetic soft skins composed of assembled entangled carbon nanotube networks and fluorescent unit-embedded elastomers which can be applied in a suspended form to allow autonomic 3D deformation, real-time perception, and dynamic fluorescence color transformation. The capabilities of the sensory and color display thresholds were controlled through the entanglement density of carbon nanotubes and the suspended area. As a demonstration, the soft thin skin was integrated into an artificial jellyfish robot, enabling the realization of a closed-loop feedback system for dynamic sensory processing, signal processing, and further 3D morphing-induced fluorescent color change, demonstrating significant potentials in underwater visual display, danger warning, and environmental exploration.