Skin Sensors Research Articles

Direct Fabrication of Electronic Circuits on Wooden Surfaces

AbstractEquipping otherwise passive surfaces with electronic functionality enables advanced interactive robotics, consumer products, sensor skins, and structural health monitoring. Concurrently, the rapidly growing number of electronic devices fuels the search for sustainable materials and processes that aid in reducing electronic waste. Wood is CO2‐neutral, omnipresent in the construction industry, in furniture, musical instruments, or packaging, yet so far, its potential for direct integration with electronics remains largely unexplored. Complications arise as traditional methods of equipping wood with electronics often compromise structural integrity and thus limit applications requiring load‐bearing capabilities. Here, seamless fabrication methods that allow the direct enhancement of wooden surfaces with electrically conducting structures, sensors, and microelectronic components based on screen printing of conducting inks or physical vapor deposition of thin metal films in conjunction with laser engraving are presented. Such electronic circuits imperceptibly operate on the surface of structural elements or as parts of decorative wooden furniture. These types of electronic wooden surfaces enable touch‐sensing applications, monitoring temperature, or the curing of varnishes without compromising functionality and mechanical stability. This multidisciplinary approach opens up new avenues for the development of smart wooden structures with embedded electronics, revolutionizing the way it is monitored, controlled, and interacted with wood‐based constructions.

A novel photonic skin sensor based on tapered micro nano fiber structure coated with sodium polyacrylate film

Biomimetic skin sensing devices play an important role in next-generation healthcare, robotics, and bioelectronics. In recent years, biomimetic skin-sensing technologies have gained significant attention due to their broad-ranging utility in the fields of healthcare and automation, and future wearable devices designed for health monitoring, robotic applications, and ultra-precise industrial positioning will necessitate the incorporation of flexible optical systems. A novel photonic skin flexible sensor (PSFS) based on partially neutralized sodium polyacrylate (PAS-50) is reported for the first time in this paper. In this study, a novel wearable sensor was designed for real-time detection of temperature and humidity. A single-mode tapered fiber (SMTF) structure based on the principle of evanescent wave is proposed for fast response and real-time monitoring of humidity and temperature. The sensor incorporates an optical micro/nanofiber (MNF) as the core sensing node, while a hydrophilic and ductile Sodium Polyacrylate (PAS) is chosen as the humidity-sensitive material that overcomes the limitation of commonly reported electrical, optical, and material-based flexible devices. Due to the strain amplification effect of the MNF, the sensitivity of the material to relative humidity (RH) is significantly improved, reaching 0.1411 dB/%. In addition, the temperature response exhibits outstanding sensitivity (0.4 dB/°C) in the human skin surface temperature range (30 ∼ 48 °C). Notably, the sensor exhibits a rapid response with a remarkable response time of 170 ms. The proposed PSFS presents novel opportunities for the advancement of future biomimetic skin devices, thus playing a pivotal role in the advancement of next-generation robotics and medical monitoring technologies.

Development of a wearable monitor to identify stress levels using internet of things

Modern life's ubiquitous component of stress has a significant impact on many facets of human existence. This article presents the development of a wearable device integrated with internet of things (IoT) technology, aiming to identify and quantify stress levels in real-time. This technology provides a possible means of improving stress assessment, enabling prompt treatments and individualized stress management techniques. ESP32-PICO computation platform was used as part of wearable stress monitor. The developed wearable monitor also includes a high-sensitivity pulse oximeter and heart-rate sensor (MAX30102) and galvanic skin response (GSR) sensors to acquire physiological signals associated with stress status. The wearable monitor device delivers data to the firebase platform via Wi-Fi. The benefits and prospective uses of the IoT-enabled wearable device are also covered in the article. It demonstrates the mobile wearable monitor adaptability in a variety of scenarios, such as offices, classrooms, and healthcare facilities, where stress management is vita and required for activity optimization. Continuous monitoring capabilities allow users to learn about their stress levels and take proactive self-care measures. During the validation experiments, the accuracy of measurement capabilities of the developed wearable monitor were evaluated reduced errors of heart rate and respiratory rate being observed.

A 10-micrometer-thick nanomesh-reinforced gas-permeable hydrogel skin sensor for long-term electrophysiological monitoring.

Hydrogel-enabled skin bioelectronics that can continuously monitor health for extended periods is crucial for early disease detection and treatment. However, it is challenging to engineer ultrathin gas-permeable hydrogel sensors that can self-adhere to the human skin for long-term daily use (>1 week). Here, we present a ~10-micrometer-thick polyurethane nanomesh-reinforced gas-permeable hydrogel sensor that can self-adhere to the human skin for continuous and high-quality electrophysiological monitoring for 8 days under daily life conditions. This research involves two key steps: (i) material design by gelatin-based thermal-dependent phase change hydrogels and (ii) robust thinness geometry achieved through nanomesh reinforcement. The resulting ultrathin hydrogels exhibit a thickness of ~10 micrometers with superior mechanical robustness, high skin adhesion, gas permeability, and anti-drying performance. To highlight the potential applications in early disease detection and treatment that leverage the collective features, we demonstrate the use of ultrathin gas-permeable hydrogels for long-term, continuous high-precision electrophysiological monitoring under daily life conditions up to 8 days.

Transparent multifunctional cellulose-based conductive hydrogel for wearable strain sensors and arrays

Conductive hydrogels as promising candidate materials for flexible strain sensors have gained considerable attentions. However, it is still a great challenge to construct hydrogel with multifunctional performance via natural polymer. Herein, a novel multifunctional conductive hydrogel based on methylcellulose and cellulose nanocrystal was prepared via a facile and low-cost strategy. Methylcellulose (MC) was introduced to not only guarantee the stability of tannic acid coated cellulose nanocrystal (TA@CNCs) in LiCl solution, but also improve anti-freezing ability. The obtained hydrogel exhibited high transparency (98 % at 800 nm), good stretchability (663.1 %), low temperature tolerance (−23.9 °C), superior conductivity (2.89 S/m) and excellent UV shielding behavior. Flexible strain sensor assembled by the prepared hydrogels can be used to detect human body motions include subtle and large motions, and exhibited good sensitivity and stability over a wide temperature range. Multiple flexible hydrogels can also be assembled into a 3D sensor array to detect the distribution and magnitude of spatial pressure. Therefore, the hydrogels prepared via natural polymers will have broad application prospects in wearable devices, electronic skin and multifunctional sensor components.

Soft and Stretchable Humidity‐Insensitive Thermoresistive Temperature Sensor with A Tensile Strain Modulated Sensitivity

AbstractSoft and stretchable electronics represents a high potential paradigm shift in field of electronics, for example, in applications related to solar cells, organic displays, electronic skin, and wearable sensors. In this work, a soft and stretchable humidity‐insensitive thermoresistive sensor is developed using interdigitated electrodes made of silver‐plated nylon fabric coated with silver‐ink and a layer of poly(3,4‐ethylenedioxythiophene)–poly(styrene sulfonate) (PEDOT: PSS) embedded into elastomer. The mechanical and thermoelectrical properties of the soft sensor are characterized and analyzed. The fabricated soft sensor provides a combination of linear temperature sensitivity of 0.46% °C−1 with an R2 of 0.986 from 30 to 55 °C at 0% uniaxial tensile strain. It also exhibits excellent stability in environmental humidity ranging from ≈30% RH to ≈80% RH. The linear sensitivity is improved to 1.49% °C−1 by applying a 40% pre‐measurement stretch to the sensor. Due to its good temperature sensitivity (0.46 to 1.49% °C−1), excellent linearity (0.986), and high stretchability (≈125%), the soft and stretchable temperature sensor proves to be a very promising solution for wearable temperature sensing.

A conductive hydrogel with excellent self-adhesion, sensitivity, and stability for wearable strain sensors to monitor human motion

A high adhesion and stable hydrogel was synthesized using CS-DOPA and AA for monitoring human motion.

Flexible Accelerated-Wound-Healing Antibacterial Hydrogel-Nanofiber Scaffold for Intelligent Wearable Health Monitoring.

Flexible epidermal sensors hold significant potential in personalized healthcare and multifunctional electronic skins. Nonetheless, achieving both robust sensing performance and efficient antibacterial protection, especially in medical paradigms involving electrophysiological signals for wound healing and intelligent health monitoring, remains a substantial challenge. Herein, we introduce a novel flexible accelerated-wound-healing biomaterial based on a hydrogel-nanofiber scaffold (HNFS) via electrostatic spinning and gel cross-linking. We effectively engineer a multifunctional tissue nanoengineered skin scaffold for wound treatment and health monitoring. Key features of HNFS include high tensile strength (24.06 MPa) and elasticity (214.67%), flexibility, biodegradability, and antibacterial properties, enabling assembly into versatile sensors for monitoring human motion and electrophysiological signals. Moreover, in vitro and in vivo experiments demonstrate that HNFS significantly enhances cell proliferation and skin wound healing, provide a comprehensive therapeutic strategy for smart sensing and tissue repair, and guide the development of high-performance "wound healing-health monitoring" bioelectronic skin scaffolds. Therefore, this study provides insights into crafting flexible and repairable skin sensors, holding potential for multifunctional health diagnostics and intelligent medical applications in intelligent wearable health monitoring and next-generation artificial skin fields.

The Influence of Instrumental Music Alam Menyapa for Prenatal and Postnatal Patients at the Martha Friska Multatuli Hospital

The research was a trial of instrumental music therapy on prenatal and postnatal patients at the Martha Friska Multatuli Hospital in Medan. The aim of this research is to be a solution to reduce pain and stress so that mothers who are about to give birth and after giving birth can feel relaxed. The tool used in the research is BmT (Music Box Therapy). Previously, BmT (Music Box Therapy) was tested on patients affected by drugs at the Mutiara Abadi Binjai Foundation (2019) and hypertension patients at the Medan Methodist Hospital (2021). The method used in the research was a quasi-experiment on four patients before and after giving birth. The BmT is designed to use two types of sensors, namely the MPX5050dp sensor as a blood pressure sensor and Galvanic Skin Resistance (GSR) as a sensor to measure the patient's skin conductivity level. One of the components of BmT is 16 pieces of instrumental music which are musical compositions by Prof. Junita Batubara, S.Sn., M.Sn., Ph.D.. The results of this trial show that the use of the instrumental music Alam Selamat, which is one of the therapeutic music in BmT, can reduce stress levels in mothers who are about to give birth and after giving birth.

A Breathable, Reliable, and Flexible Siloxene Incorporated Porous SEBS‐Based Triboelectric Nanogenerator for Human–Machine Interactions

AbstractThe breathability of wearable sensors is of utmost necessity as it facilitates heat dissipation and sweat evaporation from the skin–sensor interface for improving the user's comfort and minimizing the inflammation risk. In this work, a Siloxene/porous styrene–ethylene–butylene–styrene (SEBS)‐based breathable triboelectric sensor is newly designed and fabricated for increasing user comfort and reliability. The reliability of the fabricated sensor is evaluated by measuring the heat dissipation through the skin–sensor interface using a thermal IR imaging test. Similarly, the sensor's breathability is quantified through a water vapor transmission rate (WVTR) test, where the achieved breathability of 5.88 mg cm−2 h−1 is sufficient for sweat evaporation, as an average person loses 1.2–4.2 mg cm−2 h−1 of sweat. Furthermore, a porous, metal‐free, hybridized nanoporous carbon (H‐NPC)/laser‐induced graphene (LIG) is utilized as a charge‐collecting electrode, which is transferred and conformally attached to the Siloxene/SEBS substrate. This results in a reduction in the interfacial resistance and an improvement in bonding between the dielectric and electrode layers. With a pressure sensitivity of 0.75 VkPa−1, the fabricated sensor demonstrates successful application in gesture recognition. Thus, this research showcases the considerable potential for developing triboelectric naongenerators (TENGs) with breathable and reliable features and underscores their broad applicability in human–machine interfaces and soft robotics systems.

Regulating the π–π interactions of copolymer gelators: Effective molecular design of highly stretchable and tough ionogels for wearable ionotronics

The emergence of stretchable ionic conductors has facilitated the development of wearable devices that can perceive changes in their surrounding environment and interpret external stimuli. An example of this is ionic skin, a form of artificial skin that is worn constantly for the real-time monitoring of temperature, pressure, and tension. However, ionic skins are vulnerable to physical damage and stress, which reduces their functionality, performance, and longevity. To obtain mechanically durable ionic skins, the toughness of their constituent ionogels must be improved by increasing their strength and/or stretchability. However, the molecular design and synthesis of these materials remain challenging due to the inherent trade-off between mechanical durability and ionic conductivity. In the present study, we introduced three styrene derivatives containing pendant groups of different sizes to copolymer gelators as ionic liquid (IL)-solvophobic components that form physically crosslinked domains and compared the mechanical and conductivity performance of the resulting ionogels. As the packing density of the styrene decreased, the IL-solvophobic domains became softer and more deformable due to the weaker physical crosslinking via π–π interactions. The optimal ionogel exhibited high stretchability (∼1200 %), excellent toughness (∼3.4 MJ·m−3), and high transparency (∼98 %). The successful use of the optimal ionogel in ionic skin sensors and deformable alternating-current electroluminescent displays demonstrated its broad range of practical applications.

Serpentine liquid electrode based Dual-mode skin Sensors: Monitoring biomechanical movements by resistive or triboelectric mode

Flexible and stretchable electrodes are crucial components for wearable electronic devices. Herein, a serpentine liquid electrode based dual-mode skin sensors (SLEDSS) that leverages a highly deformable and serpentine liquid electrode is developed. The functional carboxylated multi-walled carbon nanotubes / Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (MWCNT-COOH / PEDOT: PSS) network structure endows the SLEDSS with a stable linear change in resistance. Additionally, a solid–liquid double electric layer generated between the solid surface and liquid electrode facilitates a higher triboelectric output performance. As a result, the SLEDSS features dual-modal sensing capabilities, including both resistive and triboelectric modes. The flowability of the liquid electrode enables it to fully adapt to different types of deformation, thereby allowing SLEDSS to effectively collect energy in different forms of movement, such as tapping, stretching, bending, twisting, and unpredictable transformations based on practical applications. SLEDSS can maintain its performance even at up to 550.32% strain, displaying a monotonically increasing relationship between the stretchable length and open-circuit voltage. Finally, the SLEDSS is applied as a wearable power source and self-powered sensor for monitoring biomechanical movements, the excellent stretchable performance and ultra-high sensitivity to mechanical stimulation provided by the SLEDSS offer new prospects for self-powered sensors.

A temperature and pressure dual-responsive, stretchable, healable, adhesive, and biocompatible carboxymethyl cellulose-based conductive hydrogels for flexible wearable strain sensor

The study aimed to develop a novel temperature and pressure dual-responsive conductive hydrogel with self-healing, self-adhesive, biocompatible, and stretchable properties, for the development of multifunctional anti-counterfeiting and wearable flexible electronic materials. A conductive hydrogel based on carboxymethyl cellulose (CMC) was synthesized by simple “one pot” free radical polymerization of CMC, acrylamide (AAm) and acrylic acid (AAc). The hydrogel displayed temperature responsiveness and possessed an upper critical solution temperature (UCST) value. In addition, hydrogels also had surprising pressure responsiveness. The synthesized hydrogels were characterized by FTIR, TGA, DSC, and XRD analysis. Importantly, the obtained hydrogels exhibited exceptional mechanical properties (stress: 730 kPa, strain: 880%), fatigue resistance, stretchability, self-healing capability, self-adhesive properties, and conductivity. In addition, valuable insights were obtained into the synthesis and application of flexible anti-counterfeiting and camouflage materials by the temperature and pressure dual-responsive hydrogels. Moreover, the prepared hydrogel, with an electrically sensitive perception of external strain (GF = 2.61, response time: 80 ms), can be utilized for monitoring human movement, emotional changes, physiological signals, language, and more, rendering it suitable for novel flexible anti-counterfeiting materials and versatile wearable iontronics. Overall, this study provided novel insights into the simple and efficient synthesis and sustainable manufacturing of environmentally friendly multifunctional anti-counterfeiting materials and flexible electronic skin sensors.

Plant-Inspired conductive hydrogels with long-lasting stability and low temperature tolerance for flexible sensors and signal transmission carriers

Pliable and conductive hydrogels have been widely studied in soft robots, electronic skin, and artificial sensors. However, their poor water-retention capability and inferior low temperature tolerance make the practical application unrealistic. Inspired by the freezing tolerant plants, a zwitterionic osmolyte (proline) is introduced to the Polyvinylpyrrolidone-Polyacrylamide/Ca-alginate (PACL) hydrogel system through simple solvent displacement strategy. The resulting hydrogel shows excellent stretchability (up to 1226 %), high conductivity (11.96 S/m) and long-term stability. It can successfully remain flexibility and conductivity even at ultra-low temperature (-40 °C). The hydrogel-based wearable sensors demonstrate rapid and accurate response to both large-scale movements and subtle motions. Moreover, it can transmit signals as network cables under subzero temperature.

Effects of heat and personal protective equipment on thermal strain in healthcare workers: part B—application of wearable sensors to observe heat strain among healthcare workers under controlled conditions

PurposeAs climate change accelerates, healthcare workers (HCW) are expected to be more frequently exposed to heat at work. Heat stress can be exacerbated by physical activity and unfavorable working requirements, such as wearing personal protective equipment (PPE). Thus, understanding its potential negative effects on HCW´s health and working performance is becoming crucial. Using wearable sensors, this study investigated the physiological effects of heat stress due to HCW-related activities.MethodsEighteen participants performed four experimental sessions in a controlled climatic environment following a standardized protocol. The conditions were (a) 22 °C, (b) 22 °C and PPE, (c) 27 °C and (d) 27 °C and PPE. An ear sensor (body temperature, heart rate) and a skin sensor (skin temperature) were used to record the participants´ physiological parameters.ResultsHeat and PPE had a significant effect on the measured physiological parameters. When wearing PPE, the median participants’ body temperature was 0.1 °C higher compared to not wearing PPE. At 27 °C, the median body temperature was 0.5 °C higher than at 22 °C. For median skin temperature, wearing PPE resulted in a 0.4 °C increase and higher temperatures in a 1.0 °C increase. An increase in median heart rate was also observed for PPE (+ 2/min) and heat (+ 3/min).ConclusionLong-term health and productivity risks can be further aggravated by the predicted temperature rise due to climate change. Further physiological studies with a well-designed intervention are needed to strengthen the evidence for developing comprehensive policies to protect workers in the healthcare sector.

An Asymmetric Interlocked Structure with Modulus Gradient for Ultrawide Piezocapacitive Pressure Sensing Applications

AbstractHighly sensitive electronic skin (e‐skin) sensors with considerable operating range offer great possibilities for health care, human–‐machine interfaces, and intelligent robotics. Although subtle microstructures have been used in recent years to improve the sensitivity and sensing range of e‐skin sensors, the trade‐off between these features remains a big challenge to overcome. Here, an asymmetric interlocked gradient elastic modulus (AIGM) structure is designed for the first time to provide sufficient deformation space to the traditional interlocked structure while ensuring high sensitivity, and the gradient elastic modulus further extends the sensing range of the AIGM structure‐based sensors, which exhibit a maximum sensitivity of as high as 9.89 kPa−1 with an ultrawide working range that extends to above 530 kPa at the same time. As a demo, this sensor is integrated into an intelligent adjustable mouse platform for physiological signal monitoring, pressure feedback, and modulus adjustment, providing a viable alternative for hand disease prevention.

Enhanced Mechanical Strength of Metal Ion-Doped MXene-Based Double-Network Hydrogels for Highly Sensitive and Durable Flexible Sensors.

Development of conductive hydrogels with high sensitivity and excellent mechanical properties remains a challenge for constructing flexible sensor devices. Herein, a universal strategy is presented for enhancing the mechanical strength of Mxene-based double-network hydrogels through metal ion coordination effects. Polyacrylamide (PAM)/sodium alginate (SA)/Mxene double-network (PSM-DN) hydrogels were prepared by metal ion impregnation of PAM/SA/Mxene (PSM) hydrogels. High electrical conductivity is achieved due to MXene nanosheets, while the strong coordination bond between metal ions and SA constructs a second network that increases the mechanical strength of the hydrogel by an order of magnitude. Mechanical tests demonstrated that the elastic modulus of hydrogels matches that of human tissues. Hence, they can be used as a highly sensitive electronic skin sensor to recognize the movement of different joints in humans and also as a pressure sensing interface to recognize characters for anticounterfeiting and information transfer. This work can promote the practical application of conductive hydrogels in high-tech fields, such as flexible electronic skin and interface interaction.

Water-Assisted Programmable Assembly of Flexible and Self-Standing Janus Membranes.

Janus membranes with asymmetric wettability have been considered cutting-edge for energy/environmental-sustainable applications like water/fog harvester, breathable skin, and smart sensor; however, technical challenges in fabrication and accurate regulation of asymmetric wettability limit their development. Herein, by using water-assisted hydrogen-bonded (H-bonded) assembly of small molecules at water/oil interface, a facile strategy is proposed for one-step fabrication of membranes with well-regulable asymmetric wettability. Asymmetric orderly patterns, beneficial for mass transport based on abundant high-permeability sites and large surface area, are constructed on opposite membrane surfaces. Upon tuning water-assisted H-bonding via H-sites/configuration design and temperature/pH modulation, double-hydrophobic, double-hydrophilic, and hydrophobic-hydrophilic membranes are facilely fabricated. The Janus membranes show smart vapor-responsive curling and unidirectional water transport with promising flux of 1158±25Lm-2 h-1 under natural gravity and 31500±670L·(m-2 h-1 bar-1 ) at negative pressure. This bottom-up approach offers a feasible-to-scalable avenue to precise-manipulation of Janus membranes for advanced applications, providing an effective pathway for developing tailor-made self-assembled nanomaterials.

Flexible pressure sensor based on multi-layer with gradient structure P(VDF-HFP)/MXene/BaTiO3 composite film for human motion monitoring

In recent years, flexible pressure sensors have been widely used in fields such as human health monitoring, flexible energy storage, wearable electronic devices, and flexible sensing due to their advantages of simple and efficient preparation process, highly sensitive, fast response, and strong piezoelectric performance. In this paper, we studied a kind of polyvinylidene fluoride hexafluoropropylene (P(VDF-HFP))/MXene/BaTiO3 nanofiber prepared by electrospinning technology, and designed a multi-layer structure system with gradient to prepare a flexible pressure sensor. The piezoelectric properties, mechanical properties and dielectric properties are obviously improved. At the same time, the addition of nano fillers and structural design have increased the sensitivity of multi-layer composite fiber membrane-based sensors by 16.5 times compared to pure P(VDF-HFP) in the low-pressure range (<1 kPa), and by 1.5 times compared to PFP-0.5M5BT nanofiber-based sensors, reaching 0.23 kPa−1. When pressed by the palm of the hand, the output voltage of the three-layer gradient structure thin film sensor can be up to about 100 V. Compared with the output voltage of 5 V when the P(VDF-HFP) thin film is pressed by the palm, the output voltage of the flexible pressure sensor of the three-layer gradient structure thin film after adding the filler is 20 times higher. The flexible pressure sensor can analyze and recognize the form of human motion based on the peak, frequency, and shape characteristics of the voltage signals generated by different forms of human motion. This makes it possible for flexible pressure sensors to be used in pressure detection, flexible sensing, electronic skin sensors and other fields.

Low-temperature strain-sensitive sensor based on cellulose-based ionic conductive hydrogels with moldable and self-healing properties

Bioelectronics based on high-performance conductive ionic hydrogels, which can create novel technological interfaces with the human body, have attracted significant interest from both academia and industry. However, it is still a challenge to fabricate hydrogel sensor with integration of good mechanical properties, fast self-healing ability and flexible strain sensitivity below 0 °C. In this paper, we present a moldable, self-healing and adhesive cellulose-based ionic conductive hydrogel with strain-sensitivity, which was prepared by forming dual-crosslinked networks using poly(vinyl alcohol) (PVA) with borax, calcium chloride (CaCl2), zinc chloride (ZnCl2) and 2,2,6,6-tetramethylpiperidine-1-oxyl oxidized cellulose nanofibril (TCNF). The hydrogel exhibited fast self-healing within 10 s, moderate modulus of 5.13 kPa, high elongation rate of 1500 % and excellent adhesion behavior on various substrates. Due to multiple hydrogen bonding and the presence of CaCl2 and ZnCl2, the hydrogel presented a reduced freezing point as low as −41.1 °C, which enabled its application as a low-temperature strain sensor. The proposed hydrogel provides a simple and facile method for fabricating multi-functional hydrogels that can be used as suitable strain sensors for applications such as wearable electronic sensor, soft robotics and electronic skins in a wide temperature range.