Smart Skin Research Articles

Positive/Negative Temperature Coefficient Behaviors of Electron Beam-Irradiated Carbon Blacks-Loaded Polyethylene Nanocomposites.

Polymer-based materials with positive temperature coefficients (PTC) are regarded as potential candidates for electrical heating elements in a wide range of applications, such as wearable electronics, soft robots, and smart skin. They offer many advantages over ceramic or metal oxide-based composites, including low resistance at room temperature, excellent flexibility and processability, and low cost. However, the electrical resistance instability and poor reproducibility have limited their use in practical applications. In this work, we prepared carbon blacks-reinforced high-density polyethylene nanocomposites (CBs-HDPE) loaded with polar additives (polyols or ionomers), which were subsequently subjected to electron beam (EB) irradiation to explore their PTC behaviors. We found that the EB-treated nanocomposites exhibited PTC behaviors, while the untreated samples showed negative temperature coefficients. Further, EB-ionomer-CBs-HDPE showed the highest PTC intensity of 3.01 Ω·cm, which was ∼35% higher than that of EB-CBs-HDPE. These results suggested that the EB irradiation enabled a specific volume expansion behavior via enhanced crosslinking among CBs, polar additives, and HDPE, inhibiting the formation of conductive networks in the nanocomposites. Thus, it can be concluded that polar additives and further EB irradiation played an important role in enhancing the PTC performances. We believe the findings provide crucial insight for designing carbon-polymer nanocomposites with PTC behaviors in various self-regulating heating devices.

Bioinspired Fouling‐Release Smart Skin Powered by Twisted Spiral Artificial Muscles (TSAMs)

AbstractThe buildup of marine organisms on submerged surfaces, known as biofouling, poses a major threat to the maritime industry. Biofouling on seafaring vessels increases hydrodynamic drag, fuel consumption, and leads to the spread of invasive species. Despite considerable research, a cost‐effective and environmentally friendly strategy for preventing biofouling remains elusive. Silicone‐based fouling release coatings (FRCs) that rely on hydrodynamic shear forces to remove attached biofilms have recently been proposed as a non‐toxic solution for biofouling. However, FRCs are susceptible to fouling in still water or near‐still water conditions. In this study, a smart skin bioinspired by the shape‐changing behavior of octopi for removing biofilms in near‐still water conditions is proposed. Active deformation of the smart skin powered by twisted spiral artificial muscles (TSAMs) leads to the detachment of biofilms. The efficacy of the smart skin is evaluated in both a laboratory setting and a field environment. A maximum of 87% of a laboratory grown and 79% of a heterogeneous field biofilm is detached by the active motion of the skin surface. The results indicate that the actively deformed smart skins bioinspired by octopi are a promising candidate for removing marine biofilms in still or near‐still water environments.

High performance waterproof-breathable fully flexible tactile sensor based on piezotronics coupled OFET

As obtaining flexible tactile sensors with high sensitivity, waterproofness and breathability at the same time is still a huge challenge, which limits their application in advanced fields such as human prosthetics and robotic arms. Herein, a fully flexible piezoelectric tactile sensor with high-performance, energy-efficient, waterproof, and breathable was constructed by capacitive coupling the β-PVDF nanofiber membrane (NM) with electro-mechanical conversion function and organic field effect transistor (OFET) device with signal amplification function. The inherent waterproofed β-phase PVDF NM was fabricated by advanced electrospinning process, such morphology with thousands of micropores not only gives the device excellent breathability, but also increases the deformation tolerance and accelerates the respond/recovery time, so that the obtained device can be bent at will without affecting its performance. At the same time, under the guidance of pizotronics, the charge generated by PVDF membrane based on piezoelectric effect polarization was sufficient to drive the OFET device, the as-fabricated sensor shows great sensing performance in monitoring human physiological signals without applying a gate voltage. Such device exhibits excellent pressure sensitivity, detection limit, and response time of 7.94 KPa-1, 48.54 Pa and 105 ms, respectively, which may become promising device in smart electronic skins, human motion detection, and human−machine interaction.

Development of antibacterial carboxymethyl cellulose/quaternized starch bionanocomposites based on cinnamon essential oil nanoemulsion for wound healing applications

Infectious diseases of skin wound–based bacteria are a considerable issue that often hinders the wound closure, thereby delaying the healing process. The use of wound dressing based-renewable polymers with natural essential oil could overcome the deficiencies of skin wounds. In this work, wound dressings from carboxymethyl cellulose (CMC)/quaternized starch (MS-Q188) in presence antimicrobial cinnamon essential oil (CIEO) nanoemulsion were prepared. Three variable ratios of CIEO (i.e., 1, 3, and 5 wt.%) in nanoemulsion forms were used to fabricate CMC/MS-Q188 bionanocomposites. The resulting bionanocomposites were investigated by XRD, FT-IR, and SEM. The mechanical, hydrophilicity, and barrier properties were evaluated, the outcomes of which demonstrated the tensile properties were achieved. However, the hydrophilicity, water vapor, and oxygen barrier properties were affected when the CIEO nanoemulsion added to the matrix. The migration of polymer components to the skin tissue and cytotoxic effect were investigated by cytotoxicity assays. The outcomes showed that the cell viability was located in the range of ~ 92–100% even at all studied concentrations, indicating there was no cytotoxicity to the cells. The inhibitory effects of CIEO nanoemulsion ratios on different pathogenic microbes were also verified. The developed bionanocomposites open opportunities for their use in smart skin wound dressings and biomedical applications.

Spray-Dried Photonic Balls with a Disordered/Ordered Hybrid Structure for Shear-Stress Indication.

Optical microscale shear-stress indicator particles are of interest for the in situ recording of localized forces, e.g., during 3D printing or smart skins in robotic applications. Recently developed particle systems are based on optical responses enabled by integrated organic dyes. They thus suffer from potential chemical instability and cross-sensitivities toward humidity or temperature. These drawbacks can be circumvented using photonic balls as shear-stress indicator particles, which employ structural color as the element to record forces. Here, such photonic balls are prepared from silica and iron oxide nanoparticles via the scalable and fast spray-drying technique. Process parameters to create photonic balls with a disordered core and an ordered particle structure toward the exterior of the supraparticles are reported. This hybrid disordered-ordered structure is responsible for a color loss of the indicator particles during shear-stress application because of irreversible structural destruction. By adjusting the primary silica particle sizes, nearly all colors of the visible spectrum can be achieved and the sensitivity of the response to shear stress can be adjusted.

Building a Smart EM Environment - AI-Enhanced Aperiodic Micro-Scale Design of Passive EM Skins

An innovative process for the design of static passive smart skins (SPSSs) is proposed to take into account, within the synthesis, the electromagnetic (EM) interactions due to their finite (macro-level) size and aperiodic (micro-scale) layouts. Such an approach leverages on the combination of an inverse source (IS) formulation, to define the SPSS surface currents, and of an instance of the System-by-Design paradigm, to synthesize the unit cell (UC) descriptors suitable for supporting these currents. As for this latter step, an enhanced Artificial Intelligence (IA)-based digital twin (DT) is built to efficiently and reliably predict the relationships among the UCs and the non-uniform coupling effects arising when the UCs are irregularly assembled to build the corresponding SPSS. Towards this end and unlike state-of-the-art approaches, an aperiodic finite small-scale model of the SPSS is derived to generate the training database for the DT implementation. A set of representative numerical experiments, dealing with different radiation objectives and smart skin apertures, is reported to assess the reliability of the conceived design process and to illustrate the radiation features of the resulting layouts, validated with accurate full-wave simulations, as well.

Smart skin-Anew technology in the area of digital dermatology

Numerous developments in the field of digital medicine have helped to improve the treatment and management of diseases. Smart skin is one promising technology. Through sensors that are attached to the skin, awide variety of physiological parameters can be measured, e.g., concentration of hormones, presence of inflammation markers, or the glucose level. As this technology can be applied to different parts of the body, information about various organ systems can be obtained. In the case of diabetes, research is already very advanced due to its endemic relevance and the need for long-term treatment. For example, invasive blood measurement can be replaced by implantable tattoos which react to achange in the glucose level by changing its color. In the context of type1 diabetes, aclosed-loop control circuit can be created with so-called microneedling, which results in independent insulin delivery when blood glucose levels are too high. Moreover, there are also smart skin innovations for the management of chronic wounds. With the continuous measurement of physiological indicators such as pH, temperature, or bacterial milieu, the condition of the wound can be observed. The basic principles of the smart skin technology can be transferred into many areas in the field of dermatological care and, therefore, also represent arelevant aspect for dermatologists in the care of their patients. Continuous developments in the field of smart skin technologies show high potential for further research in awide range of specialties with the aim to facilitate everyday clinical life for patients and physicians.

Spectrally-switchable infrared selective emitters for adaptive camouflage

Infrared (IR) camouflage can conceal and disguise weapons, equipment, and installations in infrared regions to minimize the detection or identification. Current researches focus mainly on statical IR camouflage and cannot readily adapt complex application scenes. Herein, we proposed two adaptive IR camouflage emitters, for which the radiation can be changed to adapt various scenes through switching emissivity spectra. The first emitter based on multilayer film is fabricated and demonstrated of possessing two modes 0 and 1. At mode 0, the emitter can achieve IR camouflage and radiative cooling in 5–8 μm (non-atmosphere window). This mode is valuable for improving operation stability between individual and equipment in low-temperature (below 68 °C) environment. At mode 1, the emitter possesses low emissivity in 3–14 μm, which assures thermally-robust IR camouflage in broad temperature range above 68 °C. This emitter is free from ion etching and simple in fabrication, which is prominent for large scale manufacture. To further improve the radiative cooling effect of mode 0 in 5–8 μm, an enhancement emitter is proposed based on metamaterial design. The propagating surface plasmon resonance (PSPR) is utilized to improve maximum emissivity from 0.69 to 0.92 and average emissivity from 0.52 to 0.78 in 5–8 μm at mode 0. The proposed emitters can facilitate development in adaptive IR camouflage, smart skin, and intelligent compatible camouflage device.

Smart Self-Nourishing and Self-Healing Artificial Skin Composite Using Bionic Microvascular Containing Liquid Agent.

Artificial skin composites have attracted great interest in functional composite materials. The aim of this study was to prepare and characterize a smart artificial skin composite comprising a bionic microvascular with both self-nourishing and self-healing functions. A poly(vinyl alcohol)–glycerol–gelatin double network organic hydrogel was used as the artificial skin matrix. The hydrogel had high mechanical strength because of the strong hydrogen bond formed between the PVA and glycerol (GL). The gelatin (GEL) increased the toughness and elasticity of the hydrogel to ensure the strength of the artificial skin and fit of the interface with the body. The bionic polyvinylidene fluoride (PVDF) microvascular had excellent thermal stability and mechanical property in artificial skin. Results indicated that self-nourishing was successfully realized by liquid release through the pore structures of the bionic microvascular. The bionic microvascular healed microcracks in the artificial skin when damage occurred, based on a self-healing test.

Development and Evaluation of Temperature Sensing Smart Skin for High-Temperature Measurements in Pipes

We designed a temperature sensing smart skin with a composite insulation layer for high-temperature monitoring of pipelines and engine combustion chamber walls, and proposed a thin/thick film hybrid integrated manufacturing process to improve the high temperature stability of the sensor. A PtRh/Pt thick-film thermocouple was installed on an ultra-thin nickel-based alloy substrate by screen printing and then fixed on a pipe inner wall by spot welding. The morphology of the prepared composite insulation layer was studied by scanning electron microscopy, and its insulation resistance was tested at high temperatures, verifying its high insulation performance. In addition, the output voltage has high linearity in the temperature range of 25–1000 °C, and the prepared thermocouple shows consistency and reusability with an average Seebeck coefficient of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.016 ~ \mu \text{V}$ </tex-math></inline-formula> /°C. Upon testing the thermocouple at 1100 °C for 10 hours, the peak voltage output was 10.094 mV and the average output voltage was 10.051 mV. Experiments show that the thick-film thermocouple operates stably at high temperatures and can work at 1400 °C in a short time.

Bioinspired Optical Flexible Cellulose Nanocrystal Films with Strain-Adaptive Structural Coloration.

Recent advances of photonic crystals are driven to mechanical sensors and smart wearable devices; however, for chiral photonic cellulose nanocrystal (CNC) materials, vivid structural coloration and reversible mechanochromism like chameleon skin remain a big challenge. Here, we report a ternary co-assembly and post-UV-irradiation polymerization strategy to develop flexible and elastic CNC composite films, which, notably, have naked-eye-visible brilliant structural colors and stretching-induced color change covering a broad wavelength region at a moderate deformation (like skin). By adjusting the stretching, the film is designed as a smart skin to adapt to surrounding environments for camouflage. This work offers a universal strategy for constructing biomimic optically functional cellulose skins.

Touchless interactive teaching of soft robots through flexible bimodal sensory interfaces

In this paper, we propose a multimodal flexible sensory interface for interactively teaching soft robots to perform skilled locomotion using bare human hands. First, we develop a flexible bimodal smart skin (FBSS) based on triboelectric nanogenerator and liquid metal sensing that can perform simultaneous tactile and touchless sensing and distinguish these two modes in real time. With the FBSS, soft robots can react on their own to tactile and touchless stimuli. We then propose a distance control method that enabled humans to teach soft robots movements via bare hand-eye coordination. The results showed that participants can effectively teach a self-reacting soft continuum manipulator complex motions in three-dimensional space through a “shifting sensors and teaching” method within just a few minutes. The soft manipulator can repeat the human-taught motions and replay them at different speeds. Finally, we demonstrate that humans can easily teach the soft manipulator to complete specific tasks such as completing a pen-and-paper maze, taking a throat swab, and crossing a barrier to grasp an object. We envision that this user-friendly, non-programmable teaching method based on flexible multimodal sensory interfaces could broadly expand the domains in which humans interact with and utilize soft robots.

High-Performance Strain Sensors Based on Au/Graphene Composite Films with Hierarchical Cracks for Wide Linear-Range Motion Monitoring

Stretchable strain sensors based on nanomaterial thin films have aroused extensive interest for the strain perception of smart skins. However, it still remains challenging to have them achieve high sensitivity over wide linear working ranges. Herein, we propose a facile strategy to fabricate stretchable strain sensors based on Au/graphene composite films (AGCFs) with hierarchical cracks and demonstrate their superior sensing performances. The polydimethylsiloxane substrates were covered with self-assembled graphene films (SAGFs) and sputtered with Au, and then prestretching was applied to introduce hierarchical cracks. The AGCF strain sensors exhibited high sensitivity (gauge factor (GF) ≈ 153) and favorable linearity (R2 ≈ 0.9975) in the wide working range (0-20%) with ultralow overshooting (∼1.7% at 20%), fast response (<42.5 ms), and also excellent cycling stability (1500 cycles). Besides, these patternable sensors could further achieve higher GF (∼320) via pattern designing. The dominant effect of the intermediate wrinkled SAGFs in forming hierarchical cracks was studied, and the linear sensing mechanism of the as-formed fractal microstructures was also revealed in detail. Moreover, the AGCF strain sensors were tested for motion monitoring of the human body and electronic bird. Due to the remarkable versatility, scalable fabrication, and integration capability, these sensors demonstrate great potential to construct smart skins.

MDFNet: application of multimodal fusion method based on skin image and clinical data to skin cancer classification.

Skin cancer is one of the ten most common cancer types in the world. Early diagnosis and treatment can effectively reduce the mortality of patients. Therefore, it is of great significance to develop an intelligent diagnosis system for skin cancer. According to the survey, at present, most intelligent diagnosis systems of skin cancer only use skin image data, but the multi-modal cross-fusion analysis using image data and patient clinical data is limited. Therefore, to further explore the complementary relationship between image data and patient clinical data, we propose multimode data fusion diagnosis network (MDFNet), a framework for skin cancer based on data fusion strategy. MDFNet establishes an effective mapping among heterogeneous data features, effectively fuses clinical skin images and patient clinical data, and effectively solves the problems of feature paucity and insufficient feature richness that only use single-mode data. The experimental results present that our proposed smart skin cancer diagnosis model has an accuracy of 80.42%, which is an improvement of about 9% compared with the model accuracy using only medical images, thus effectively confirming the unique fusion advantages exhibited by MDFNet. This illustrates that MDFNet can not only be applied as an effective auxiliary diagnostic tool for skin cancer diagnosis, help physicians improve clinical decision-making ability and effectively improve the efficiency of clinical medicine diagnosis, but also its proposed data fusion method fully exerts the advantage of information convergence and has a certain reference value for the intelligent diagnosis of numerous clinical diseases.

Toward a smart skin: Harnessing cuticle biosynthesis for crop adaptation to drought, salinity, temperature, and ultraviolet stress.

Drought, salinity, extreme temperatures, and ultraviolet (UV) radiation are major environmental factors that adversely affect plant growth and crop production. As a protective shield covering the outer epidermal cell wall of plant aerial organs, the cuticle is mainly composed of cutin matrix impregnated and sealed with cuticular waxes, and greatly contributes to the plant adaption to environmental stresses. Past decades have seen considerable progress in uncovering the molecular mechanism of plant cutin and cuticular wax biosynthesis, as well as their important roles in plant stress adaptation, which provides a new direction to drive strategies for stress-resilient crop breeding. In this review, we highlighted the recent advances in cuticle biosynthesis in plant adaptation to drought, salinity, extreme temperatures, and UV radiation stress, and discussed the current status and future directions in harnessing cuticle biosynthesis for crop improvement.

110 Non-invasive molecular analysis for CTCL detection and differentiation from other skin conditions with adhesive smart sticker skin sample collection

Cutaneous T cell lymphoma (CTCL) is a complex and heterogenous disease with a range of pathogenic, diagnostic, prognostic and therapeutic courses. Broadly, CTCL is characterized by cutaneous infiltrates of aberrant monocolonal T-lymphocytes. Clinically and histopathologically, CTCL often mimics psoriasis, eczema and other benign dermatoses. Diagnosis of CTCL is often delayed by 4-6 years from the time lesions initially appear, and typically requires multiple skin biopsies and blood tests. In this study, we employed non-invasive adhesive patches to collect samples from lesional skin of CTCL (n=12) and psoriasis (n=10) patients as well as non-lesional skin from healthy (n=12) volunteers.

A flexible tactile sensor that uses polyimide/graphene oxide nanofiber as dielectric membrane for vertical and lateral force detection

Flexible force sensors are of great interest in the fields of healthcare, physiological signals, and aircraft smart skin applications because of their compatibility with curved surfaces. However, the simultaneous detection of multidirectional forces remains an engineering challenge, despite the great progress made in recent years. Herein, we present the development of a flexible capacitive force sensor capable of efficiently distinguishing normal and sliding shear forces. A two-layer electrospun polyimide/graphene oxide (PI/GO) nanofiber membrane is used as the dielectric layer, which is sandwiched between one top electrode and four symmetrically distributed bottom electrodes. This composite membrane has an improved dielectric constant, a reduced friction coefficient, and good compressibility, leading to superior performance that includes high sensitivity over a wide operational range with measured results of 3 MPa−1 for 0–242 kPa (0–2.2 N) and 0.92 MPa−1 for 242–550 kPa (2.2–5 N) in the normal direction; and better than 1 N−1 for 0–3 N in the x- and y-axis directions. The system also has a low detection limit of 10 Pa, fast response and recovery times of 39 ms and 13 ms, respectively, a good cyclic stability of 10,000 cycles at a pressure of 176 kPa, and promising potential for use in high-temperature environments (200 °C). Moreover, a prototype 4 × 4 sensor array has been fabricated and successfully used in a robotic system to grasp objects and operate a wireless toy car. As such, the proposed system could offer superior capabilities in simultaneous multidirectional force sensing for applications such as intelligent robots, human–machine interaction, and smart skin.

Next-generation 2D optical strain mapping with strain-sensing smart skin compared to digital image correlation

This study reports next generation optical strain measurement with “strain-sensing smart skin” (S4) and a comparison of its performance against the established digital image correlation (DIC) method. S4 measures strain-induced shifts in the emission wavelengths of single-wall carbon nanotubes embedded in a thin film on the specimen. The new S4 film improves spectral uniformity of the nanotube sensors, avoids the need for annealing at elevated temperatures, and allows for parallel DIC measurements. Noncontact strain maps measured with the S4 films and point-wise scanning were directly compared to those from DIC on acrylic, concrete, and aluminum test specimens, including one with subsurface damage. Strain features were more clearly revealed with S4 than with DIC. Finite element method simulations also showed closer agreement with S4 than with DIC results. These findings highlight the potential of S4 strain measurement technology as a promising alternative or complement to existing technologies, especially when accumulated strains must be detected in structures that are not under constant observation.

Finite element modeling and validation of a soft array of spatially coupled dielectric elastomer transducers

Dielectric elastomer (DE) transducers are suitable candidates for the development of compliant mechatronic devices, such as wearable smart skins and soft robots. If many independently-controllable DEs are closely arranged in an array-like configuration, sharing a common elastomer membrane, novel types of cooperative and soft actuator/sensor systems can be obtained. The common elastic substrate, however, introduces strong electro-mechanical coupling effects among neighboring DEs, which highly influence the overall membrane system actuation and sensing characteristics. To effectively design soft cooperative systems based on DEs, these effects need to be systematically understood and modeled first. As a first step towards the development of soft cooperative DE systems, in this paper we present a finite element simulation approach for a 1-by-3 silicone array of DE units. After defining the system constitutive equations and the numerical assumptions, an extensive experimental campaign is conducted to calibrate and validate the model. The simulation results accurately predict the changes in force (actuation behavior) and capacitance (sensing behavior) of the different elements of the array, when their neighbors are subjected to different electro-mechanical loads. Quantitatively, the model reproduces the force and capacitance responses with an average fit higher than 93% and 92%, respectively. Finally, the validated model is used to perform parameter studies, aimed at highlighting how the array performance depends on a relevant set of design parameters, i.e. DE-DE spacing, DE-outer structure spacing, membrane pre-stretch, array scale, and electrode shape. The obtained results will provide important guidelines for the future design of cooperative actuator/sensor systems based on DE transducers.

Wearable Ionogel-Based Fibers for Strain Sensors with Ultrawide Linear Response and Temperature Sensors Insensitive to Strain.

Fiber-shaped stretchable strain and temperature sensors are highly desirable for wearable electronics due to their excellent flexibility, comfort, air permeability, and easiness to be weaved into fabric. Herein, we prepare a smart ionogel-based fiber composed of thermoplastic polyurethane (TPU) and ionic liquid (IL) by the facile and scalable wet-spinning technique, which can serve as a wearable strain sensor with good linearity (a correlation coefficient of 0.997) in an ultrawide sensing range (up to 700%), ultralow-detection limit (0.05%), fast response (173 ms) and recovery (120 ms), and high reproducibility. Attributed to these outstanding strain sensing performances, the designed TPU/IL ionogel fiber-shaped sensor is able to monitor both subtle physiological activities and large human motions. More interestingly, because of the fast response and high resolution to strain, the fiber-shaped sensor can be sewn into the fabric to secretly encrypt and wirelessly translate message according to the principle of Morse code. More importantly, a wearable strain-insensitive temperature sensor can be obtained from the ionogel fiber if it is designed into an "S" shape, which can effectively eliminate the interference of strain on temperature sense. It is found that the inaccuracy of temperature sense is within 0.15 °C when the sensor is subjected to 30% tensile strain simultaneously. Moreover, this strain-insensitive temperature sensor shows a monotonic temperature response over a wide temperature range (-15 to 100 °C) with an ultrahigh detecting accuracy of 0.1 °C and good reliability, owing to the fast and stable thermal response of IL. This temperature sensor can realize the detection of thermal radiation, proximity, and respiration, exhibiting enormous potential in smart skin, personal healthcare, and wearable electronics. This work proposes a simple but effective strategy to realize the essential strain and temperature sensing capabilities of wearable electronics and smart fabrics without mutual interference.