Skin-Interfaced Superhydrophobic Insensible Sweat Sensors for Evaluating Body Thermoregulation and Skin Barrier Functions

Ultraconformal Skin-Interfaced Sensing Platform for Motion Artifact-Free Monitoring

Capable of directly capturing various physiological signals from human skin, skin-interfaced bioelectronics has emerged as a promising option for human health monitoring. However, the accuracy and reliability of the measured signals can be greatly affected by body movements or skin deformations (e.g., stretching, wrinkling, and compression). This study presents an ultraconformal, motion artifact-free, and multifunctional skin bioelectronic sensing platform fabricated by a simple and user-friendly laser patterning approach for sensing high-quality human physiological data. The highly conductive membrane based on the room-temperature coalesced Ag/Cu@Cu core-shell nanoparticles in a mixed solution of polymers can partially dissolve and locally deform in the presence of water to form conformal contact with the skin. The resulting sensors to capture improved electrophysiological signals upon various skin deformations and other biophysical signals provide an effective means to monitor health conditions and create human-machine interfaces. The highly conductive and stretchable membrane can also be used as interconnects to connect commercial off-the-shelf chips to allow extended functionalities, and the proof-of-concept demonstration is highlighted in an integrated pulse oximeter. The easy-to-remove feature of the resulting device with water further allows the device to be applied on delicate skin, such as the infant and elderly.

Hierarchical Piezoelectric Composites for Noninvasive Continuous Cardiovascular Monitoring

Continuous monitoring of blood pressure (BP) and multiparametric analysis of cardiac functions are crucial for the early diagnosis and therapy of cardiovascular diseases. However, existing monitoring approaches often suffer from bulky and intrusive apparatus, cumbersome testing procedures, and challenging data processing, hampering their applications in continuous monitoring. Here, a heterogeneously hierarchical piezoelectric composite is introduced for wearable continuous BP and cardiac function monitoring, overcoming the rigidity of ceramic and the insensitivity of polymer. By optimizing the hierarchical structure and components of the composite, the developed piezoelectric sensor delivers impressive performances, ensuring continuous and accurate monitoring of BP at Grade A level. Furthermore, the hemodynamic parameters are extracted from the detected signals, such as local pulse wave velocity, cardiac output, and stroke volume, all of which are in alignment with clinical results. Finally, the all-day tracking of cardiac function parameters validates the reliability and stability of the developed sensor, highlighting its potential for personalized healthcare systems, particularly in early diagnosis and timely intervention of cardiovascular disease.

Long-term monitoring of ultratrace nucleic acids using tetrahedral nanostructure-based NgAgo on wearable microneedles

Real-time and continuous monitoring of nucleic acid biomarkers with wearable devices holds potential for personal health management, especially in the context of pandemic surveillance or intensive care unit disease. However, achieving high sensitivity and long-term stability remains challenging. Here, we report a tetrahedral nanostructure-based Natronobacterium gregoryi Argonaute (NgAgo) for long-term stable monitoring of ultratrace unamplified nucleic acids (cell-free DNAs and RNAs) in vivo for sepsis on wearable device. This integrated wireless wearable consists of a flexible circuit board, a microneedle biosensor, and a stretchable epidermis patch with enrichment capability. We comprehensively investigate the recognition mechanism of nucleic acids by NgAgo/guide DNA and signal transformation within the Debye distance. In vivo experiments demonstrate the suitability for real-time monitoring of cell-free DNA and RNA with a sensitivity of 0.3 fM up to 14 days. These results provide a strategy for highly sensitive molecular recognition in vivo and for on-body detection of nucleic acid.

Glycosaminoglycans' Ability to Promote Wound Healing: From Native Living Macromolecules to Artificial Biomaterials

Glycosaminoglycans (GAGs) are important for the occurrence of signaling molecules and maintenance of microenvironment within the extracellular matrix (ECM) in living tissues. GAGs and GAG-based biomaterial approaches have been widely explored to promote in situ tissue regeneration and repair by regulating the wound microenvironment, accelerating re-epithelialization, and controlling ECM remodeling. However, most approaches remain unacceptable for clinical applications. To improve insights into material design and clinical translational applications, this review highlights the innate roles and bioactive mechanisms of native GAGs during in situ wound healing and presents common GAG-based biomaterials and the adaptability of application scenarios in facilitating wound healing. Furthermore, challenges before the widespread commercialization of GAG-based biomaterials are shared, to ensure that future designed and constructed GAG-based artificial biomaterials are more likely to recapitulate the unique and tissue-specific profile of native GAG expression in human tissues. This review provides a more explicit and clear selection guide for researchers designing biomimetic materials, which will resemble or exceed their natural counterparts in certain functions, thereby suiting for specific environments or therapeutic goals.

Skin-Interfaced Bifluidic Paper-Based Device for Quantitative Sweat Analysis

The erratic, intermittent, and unpredictable nature of sweat production, resulting from physiological or psychological fluctuations, poses intricacies to consistently and accurately sample and evaluate sweat biomarkers. Skin-interfaced microfluidic devices that rely on colorimetric mechanisms for semi-quantitative detection are particularly susceptible to these inaccuracies due to variations in sweat secretion rate or instantaneous volume. This work introduces a skin-interfaced colorimetric bifluidic sweat device with two synchronous channels to quantify sweat rate and biomarkers in real-time, even during uncertain sweat activities. In the proposed bifluidic-distance metric approach, with one channel to measure sweat rate and quantify collected sweat volume, the other channel can provide an accurate analysis of the biomarkers based on the collected sweat volume. The closed channel design also reduces evaporation and resists contamination from the external environment. The feasibility of the device is highlighted in a proof-of-the-concept demonstration to analyze sweat chloride for evaluating hydration status and sweat glucose for assessing glucose levels. The low-cost yet highly accurate device provides opportunities for clinical sweat analysis and disease screening in remote and low-resource settings. The developed device platform can be facilely adapted for the other biomarkers when corresponding colorimetric reagents are exploited.

Interindividual- and blood-correlated sweat phenylalanine multimodal analytical biochips for tracking exercise metabolism

In situ monitoring of endogenous amino acid loss through sweat can provide physiological insights into health and metabolism. However, existing amino acid biosensors are unable to quantitatively assess metabolic status during exercise and are rarely used to establish blood-sweat correlations because they only detect a single concentration indicator and disregard sweat rate. Here, we present a wearable multimodal biochip integrated with advanced electrochemical electrodes and multipurpose microfluidic channels that enables simultaneous quantification of multiple sweat indicators, including phenylalanine and chloride, as well as sweat rate. This combined measurement approach reveals a negative correlation between sweat phenylalanine levels and sweat rates among individuals, which further enables identification of individuals at high metabolic risk. By tracking phenylalanine fluctuations induced by protein intake during exercise and normalizing the concentration indicator by sweat rates to reduce interindividual variability, we demonstrate a reliable method to correlate and analyze sweat-blood phenylalanine levels for personal health monitoring.

Skin-interfaced microfluidic sweat collection devices for personalized hydration management through thermal feedback

Non-electronic wearables that utilize skin-interfaced microfluidic technology have revolutionized the collection and analysis of human sweat, providing valuable biochemical information and indicating body hydration status. However, existing microfluidic devices often require constant monitoring of data during sweat assessment, thereby impeding the user experience and potentially missing anomalous physiological events, such as excessive sweating. Moreover, the complex manufacturing process hampers the scalability and large-scale production of such devices. Herein, we present a self-feedback microfluidic device with a unique dehydration reminder through a cost-effective "CAD-to-3D device" approach. It incorporates two independent systems for sweat collection and thermal feedback, including serpentine microchannels, reservoirs, petal-like bursting valves and heating chambers. The device operates by sequentially collecting sweat in the channels and reservoirs, and then activating thermal stimulators in the heating chambers through breaking the valves, initiating a chemical exothermic reaction. Human trials validate that the devices effectively alert users to potential dehydration by inducing skin thermal sensations triggered by sweat sampling. The proposed device offers facile scalability and customizable fabrication, and holds promise for managing hydration strategies in real-world scenarios, benefiting individuals engaged in sporting activities or exposed to high-temperature settings.

Aramid Nanodielectrics for Ultraconformal Transparent Electronic Skins

On-skin electronics require minimal thicknesses and decent transparency for conformal contact, imperceptible wearing, and visual aesthetics. It is challenging to search for advanced ultrathin dielectrics capable of supporting the active components while maintaining bending softness, easy handling, and wafer-scale processability. Here, self-delaminated aramid nanodielectrics (ANDs) are demonstrated, enabling any skin-like electronics easily exfoliated from the processing substrates after complicated nanofabrication. In addition, ANDs are mechanically strong, chemically and thermally stable, transparent and breathable, therefore are ideal substrates for soft electronics. As demonstrated, compliant epidermal electrodes comprising silver nanowires and ANDs can successfully record high-quality electromyogram signals with low motion artifacts and satisfying sweat and water resistance. Furthermore, ANDs can serve as both substrates and dielectrics in single-walled carbon nanotube field-effect transistors (FETs) with a merely 160-nm thickness, which can be operated within 4 V with on/off ratios of 1.4 ± 0.5 × 105 , mobilities of 39.9 ± 2.2 cm2 V-1 s-1 , and negligible hysteresis. The ultraconformal FETs can function properly when wrapped around human hair without any degradation in performance.

Observing Real-Time Adhesion of Microparticles on Glass Surfaces

Fouling on glass surfaces reduces the solar panel efficiency and increases water consumption for cleaning. Superhydrophobic coatings on glass enable self-cleaning by allowing water droplets to carry away dirt particles. Observing the interaction between charged particles and surfaces provides insights into effective cleaning. Using a high-speed camera and a long-distance objective, we analyzed the in situ deposition of variously functionalized and charged silica dust microparticles on chemically treated glass. The ambient charges for the control, hydrophobic, and positively charged particles were approximately -0.5, -0.13, and +0.5 nC, respectively. We found that a positively charged particle of 2.3 ± 1.2 μm diameter adhered to hydroxylated glass in ∼0.054 s, compared to 0.40 and 0.45 s for quaternary ammonium- and fluorosilane-functionalized hydrophobic glass. Experiments suggest that quaternary ammonium-functionalized glass surfaces are about 77.8% more resistant to soiling than bare surfaces.

Photothermal, Magnetic, and Superhydrophobic PU Sponge Decorated with a Fe3O4/MXene/Lignin Composite for Efficient Oil/Water Separation

Frequent oil spills and the discharge of industrial oily wastewaters have become a serious threat to the environment, ecosystem, and human beings. Herein, a photothermal, magnetic, and superhydrophobic PU sponge decorated with a Fe3O4/MXene/lignin composite (labeled as S-Fe3O4/MXene/lignin@PU sponge) has been designed and prepared. The obtained superhydrophobic/superoleophilic PU sponge possesses excellent chemical stability, thermal stability, and mechanical durability in terms of being immersed in corrosive solutions and organic solvents and boiling water and being abrased by sandpapers, respectively. The oil adsorption capacities of the S-Fe3O4/MXene/lignin@PU sponge for various organic liquids range from 29.1 to 70.3 g/g, and the oil adsorption capacity for CCl4 can remain 69.6 g/g even after 15 cyclic adsorption tests. The separation efficiencies of the S-Fe3O4/MXene/lignin@PU sponge for n-hexane and CCl4 are higher than 98% in different environments (i.e., water, hot water, 1 mol/L NaOH, 1 mol/L NaCl, and 1 mol/L HCl). More importantly, the introduction of three light absorbers (i.e., Fe3O4, MXene, and lignin) into the S-Fe3O4/MXene/lignin@PU sponge shows a synergistic effect in the photothermal heat conversion performance, and the maximum surface temperature reaches 64.4 °C under sunlight irradiation (1.0 kW/m2). The separation flux of the S-Fe3O4/MXene/lignin@PU sponge for viscous LT147 vacuum pump oil reaches 35,469 L m-2 h-1 under sunlight irradiation, showing an increase of 27.3% compared to that of oil adsorption processes without the photothermal effect. Thus, the rational design of superhydrophobic sponges by introducing proper photothermal heat absorbers provides new insights into facile and cost-effective preparation of sponges for efficient oil/water separation.

Preparation of a Stable Superhydrophobic Mortar Surface Using a One-Step Method

Research efforts have intensified on developing superhydrophobic surfaces on concrete structures to limit the damage caused by the natural porosity and hydrophilicity of cementitious materials. However, the feasibility idea is impeded by the complex preparation process and weak adhesion/stability performance. Therefore, superhydrophobic coatings were rapidly prepared on mortar surfaces by a straightforward and effective one-step method using zinc oxide (ZnO) modified with stearic acid and epoxy resin. The microstructure, physical/chemical properties, hydrophobic properties, and stability of the coatings were systematically investigated. The experimental results showed that the water contact angle of the samples reached a maximum value of 164.2° and a sliding angle of 4.6° when the stearic acid content was 0.5 g. The water absorption of the coated superhydrophobic mortar was reduced by approximately 61% compared to that of ordinary mortar, and neither particulate pollutants nor liquid pollutants could contaminate the superhydrophobic mortar. The coating maintained a superhydrophobic state and exhibited good physical durability after sandpaper abrasion, tape peeling, and high-temperature resistance tests. The water cluster diffusion coefficient on surface of the ordinary coating was 0.1645 × 10-4 and 0.0328 × 10-4 cm2/s on surface of the modified coating after molecular dynamics simulation.

Ultrathin hierarchical hydrogel-carbon nanocomposite for highly stretchable fast-response water-proof wearable humidity sensors

Wearable humidity sensors play an important role in human health monitoring. However, challenges persist in realizing high performance wearable humidity sensors with fast response and good stretchability and durability. Here we report wearable humidity sensors employing an ultrathin micro-nano hierarchical hydrogel-carbon nanocomposite. The nanocomposite is synthesized on polydimethylsiloxane (PDMS) films via a facile two-step solvent-free approach, which creates a hierarchical architecture consisting of periodic microscale wrinkles and vapor-deposited nanoporous hydrogel-candle-soot nanocoating. The hierarchical surface topography results in a significantly enlarged specific surface area (>107 times that of planar hydrogel), which along with the ultrathin hydrogel endow the sensor with high sensitivity and a fast response/recovery (13/0.48 s) over a wide humidity range (11-96%). Owing to the wrinkle structure and interpenetrating network between the hydrogel and PDMS, the sensor is stable and durable against repeated 180° bending, 100% strain, and even scratching. Furthermore, encapsulation of the sensor imparts excellent resistance to water, sweat, and bacteria without influencing its performance. The sensor is then successfully used to monitor different human respiratory behaviors and skin humidity in real time. The reported method is convenient and cost-effective, which could bring exciting new opportunities in the fabrication of next-generation wearable humidity sensors.

Recent Advances in Skin-Interfaced Wearable Sweat Sensors: Opportunities for Equitable Personalized Medicine and Global Health Diagnostics

Recent advances in skin-interfaced wearable sweat sensors enable the noninvasive, real-time monitoring of biochemical signals associated with health and wellness. These wearable platforms leverage microfluidic channels, biochemical sensors, and flexible electronics to enable the continuous analysis of sweat-based biomarkers such as electrolytes, metabolites, and hormones. As this field continues to mature, the potential of low-cost, continuous personalized health monitoring enabled by such wearable sensors holds significant promise for addressing some of the formidable obstacles to delivering comprehensive medical care in under-resourced settings. This Perspective highlights the transformative potential of wearable sweat sensing for providing equitable access to cutting-edge healthcare diagnostics, especially in remote or geographically isolated areas. It examines the current understanding of sweat composition as well as recent innovations in microfluidic device architectures and sensing strategies by showcasing emerging applications and opportunities for innovation. It concludes with a discussion on expanding the utility of wearable sweat sensors for clinically relevant health applications and opportunities for enabling equitable access to innovation to address existing health disparities.

Mechanically-Guided 3D Assembly for Architected Flexible Electronics

Architected flexible electronic devices with rationally designed 3D geometries have found essential applications in biology, medicine, therapeutics, sensing/imaging, energy, robotics, and daily healthcare. Mechanically-guided 3D assembly methods, exploiting mechanics principles of materials and structures to transform planar electronic devices fabricated using mature semiconductor techniques into 3D architected ones, are promising routes to such architected flexible electronic devices. Here, we comprehensively review mechanically-guided 3D assembly methods for architected flexible electronics. Mainstream methods of mechanically-guided 3D assembly are classified and discussed on the basis of their fundamental deformation modes (i.e., rolling, folding, curving, and buckling). Diverse 3D interconnects and device forms are then summarized, which correspond to the two key components of an architected flexible electronic device. Afterward, structure-induced functionalities are highlighted to provide guidelines for function-driven structural designs of flexible electronics, followed by a collective summary of their resulting applications. Finally, conclusions and outlooks are given, covering routes to achieve extreme deformations and dimensions, inverse design methods, and encapsulation strategies of architected 3D flexible electronics, as well as perspectives on future applications.

Stretchable and Self-Adhesive Humidity-Sensing Patch for Multiplexed Non-Contact Sensing

The slippage of moisture-sensitive materials from substrates during bending or stretching is a common issue that causes baseline drift and even failure of the flexible humidity sensors, which are essential components of wearable electronic devices. In this study, we report a stretchable, self-adhesive, and transparent humidity-sensing electronic patch comprising liquid metal particle electrodes with a stretchable serpentine structure and a humidity-sensing layer made of Ti3C2Tx MXene/carboxymethyl cellulose. This patch is constructed on a soft-hard integrated heterostructure substrate and demonstrates stable humidity-sensitive response performance at 100% tensile strain, along with autonomous adhesion to human skin. Additionally, it exhibits maximum response (1145.4%) at 90% relative humidity (RH), fast response and recovery time (1.4/5.9 s), elevated sensitivity (64.63%/% RH), and preserved humidity sensing under deformation, as well as easy scalability for multiplexed detection. We further illustrate the patch's potential applications in healthcare and environmental monitoring through a non-contact security door control system and wind monitor system. Our proposed strain-isolation strategy can be extended to other rigid conductive materials and stretchable substrates, providing a feasible mechanism for producing stretchable electronic skin patches.