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Patch-type drug delivery has garnered increased attention as an attractive alternative to the existing drug delivery techniques. Thus far, needle phobia and efficient drug delivery remain huge challenges. To address the issue of needle phobia and enhance drug delivery, we developed a needle-free and self-adhesive microcup patch that can be loaded with an ultrathin salmon DNA (SDNA) drug carrier film. This physically integrated system can facilitate efficient skin penetration of drugs loaded into the microcup patch. The system consists of three main components, namely, a cup that acts as a drug reservoir, an adhesive system that attaches the patch to the skin, and physical stimulants that can be used to increase the efficiency of drug delivery. In addition, an ultrathin SDNA/drug film allows the retention of the drug in the cup and its efficient release by dissolution in the presence of moisture. This latter feature has been validated using gelatin as a skin mimic. The cup design itself has been validated by comparing its deformation and displacement with those of a cylindrical structure. Integration of the self-adhesive microcup patch with both ultrasonic waves and an electric current allows the model drug to penetrate the stratum corneum of the skin barrier and the whole epidermis, thereby enhancing transdermal drug delivery and reducing skin irritation. This system can be used as a wearable biomedical device for efficient transdermal and needle-free drug delivery.

Many conventional micropatterning and nanopatterning techniques employ toxic chemicals, rendering them nonbiocompatible and unsuited for biodevice production. Herein the formation of water bridges on the surface of hyaluronic acid (HA) films is exploited to develop a transfer-based nanopatterning method applicable to diverse structures and materials. The HA film surface, made deformable via water bridge generation, is brought into contact with a functional material and subjected to thermal treatment, which results in film shrinkage, allowing a robust pattern transfer. The proposed biocompatible method, which avoids the use of extra chemicals, enables the transfer of nanoscale, microscale, and thin-film structures as well as functional materials such as metals and metal oxides. A nanopatterned HA film is transferred onto a moisture-containing contact lens to fabricate smart contact lenses with unique optical characteristics of rationally designed optical nanopatterns. These lenses demonstrated binocular parallax-induced stereoscopy via nanoline array polarization and acted as cutoff filters, with nanodot arrays, capable of treating Irlen syndrome.

The fabrication of large-area and flexible nanostructures currently presents various challenges related to the special requirements for 3D multilayer nanostructures, ultrasmall nanogaps, and size-controlled nanomeshes. To overcome these rigorous challenges, a simple method for fabricating wafer-scale, ultrasmall nanogaps on a flexible substrate using a temperature above the glass transition temperature (Tg) of the substrate and by layer-by-layer nanoimprinting is proposed here. The size of the nanogaps can be easily controlled by adjusting the pressure, heating time, and heating temperature. In addition, 3D multilayer nanostructures and nanocomposites with 2, 3, 5, 7, and 20 layers were fabricated using this method. The fabricated nanogaps with sizes ranging from approximately 1 to 40 nm were observed via high-resolution transmission electron microscopy (HRTEM). The multilayered nanostructures were evaluated using focused ion beam (FIB) technology. Compared with conventional methods, our method could not only easily control the size of the nanogaps on the flexible large-area substrate but could also achieve fast, simple, and cost-effective fabrication of 3D multilayer nanostructures and nanocomposites without any post-treatment. Moreover, a transparent electrode and nanoheater were fabricated and evaluated. Finally, surface-enhanced Raman scattering substrates with different nanogaps were evaluated using rhodamine 6G. In conclusion, it is believed that the proposed method can solve the problems related to the high requirements of nanofabrication and can be applied in the detection of small molecules and for manufacturing flexible electronics and soft actuators.

Electronic skin (E-skin) capable of detecting various physical stimuli is required for monitoring external environments accurately. Here, we report an all-soft multiaxial force sensor based on liquid metal microchannel array for electronic skin applications. The proposed sensor is composed of stretchable elastomer and Galinstan, a eutectic gallium-indium alloy, providing a high mechanical flexibility and electro-mechanical durability. Liquid metal microchannel arrays are fabricated in multilayer and positioned along a dome structure to detect multi-directional forces, supported by numerical simulation results. By adjusting the height of the dome, we could control the response of the multiaxial sensor with respect to the deflection. As a demonstration of multiaxial force sensing, we were able to monitor the direction of multidirectional forces using a finger by the response of liquid metal microchannel arrays. This research could be applied to various fields including soft robotics, wearable devices, and smart prosthetics for artificial intelligent skin applications.

This study proposes a reliable and self-powered hydrogen (H2) gas sensor composed of a chemo-mechanically operating nanostructured film and photovoltaic cell. Specifically, the nanostructured film ...

The growing interest in wearable devices has drawn increased attention to smart textiles, and various transfer methods have therefore been introduced to realize the desired functions using textiles as substrates. However, the existing transfer techniques are not suited for the production of sophisticated nanoscale patterns on textiles, as textile roughness and difficulty of precise pattern size control hinder miniaturization, deteriorate device performance, and complicate the use of optical phenomena such as surface plasmon resonance. To address these limitations, we have developed a method based on simple dissolution of a water-soluble nanopatterned polymer film for the facile transfer of nanostructures of on-film-deposited functional materials onto textile substrates. The above method tolerates a variety of functional materials, e.g., metals and SiO

A novel method for fabricating shape-controlled and well-arrayed heterogeneous nanostructures by altering the melting point of the metal thin film at the nanoscale is proposed. Silver nanofilms (AgNFs) are transformed into silver nanoislands (AgNIs), silver nanoparticles (AgNPs), and silver nanogaps (AgNGs) that are well-ordered and repositioned inside the gold nanoholes (AuNHs) depending on the diameter of the AuNHs, the thickness of the AgNF, and the heating temperature (120-200 °C). This method demonstrates the ability to fabricate uniform, stable, and unique structures with a fast, simple, and mass-producible process. For demonstrating the diverse applicability of the developed structures, high-density AgNGs inside the AuNHs are utilized as surface-enhanced Raman spectroscopy (SERS) substrates. These AgNGs-based SERS substrates exhibit a performance enhancement, which is 1.06 × 106 times greater than that of a metal film, with a relative standard deviation of 19.8%. The developed AgNP/AgNI structures are also used as nonreproducible anti-counterfeiting signs, and the anti-counterfeiting/readout system is demonstrated via image processing. Therefore, our method could play a vital role in the nanofabrication of high-demand nanostructures.

This study proposes a reliable and self-powered hydrogen (H

In vivo sensing of various physical/chemical parameters is gaining increased attention for early prediction and management of various diseases. However, there are major limitations on the fabrication method of multiparameter needle-based in vivo sensing devices, particularly concerning the uniformity between sensors. To address these challenges, we developed a microscale biosensor array for the measurement of electrical conductivity, pH, glucose, and lactate concentrations on a flexible polymeric polyimide platform with electrodeposited electrochemically active layers. The biosensor array was then transferred to a medical needle toward multiparametric in vivo sensing. The flexibility of the sensor platform allowed an easy integration to the curved surface (φ = 1.2 mm) of the needle. Furthermore, the electrodeposition process was used to localize various active materials for corresponding electrochemical sensors on the microscale electrodes with a high precision (patterning area = 150 μm × 2 mm). The biosensor array-modified needle was aimed to discriminate cancer from normal tissues by providing real-time discrimination of glucose, lactate concentration, pH, and electrical conductivity changes associated with the cancer-specific metabolic processes. The sensor performance was thus evaluated using solution samples, covering the physiological concentrations for cancer discrimination. Finally, the possibility of in vivo electrochemical biosensing during needle insertion was confirmed by utilizing the needle in a hydrogel phantom that mimicked the normal and cancer microenvironments.

In this research, an ultrathin, biocompatible, and flexible pressure sensor with a wide pressure range has been developed and applied in biomedical applications. The pressure sensing mechanism is based on the variation of contact resistance between an electrode and a three-dimensional microstructured polyimide/carbon nanotube composite film. The sensor has a thickness of about 31.3 μm, a maximum sensitivity of 41.0 MPa-1, and a sensing range of 10-500 kPa. Moreover, in situ temperature measurement by an integrated resistive temperature detector enables data correction for varying temperature conditions. In order to show the advantages of the fabricated sensor, it is attached to the human body and integrated with the surface of a radiofrequency ablation (RFA) needle with small radius of curvature. In the experiments, the proposed pressure sensor measured subtle pressure levels (pulse pressure) and high pressure levels (fingertip pressure) without losing conformal contact with the skin. In addition, when the pressure-sensor-integrated RFA needle was inserted into a bovine liver, successful detection of steam popping phenomenon was observed.

Wearable pressure sensors have been attracting great attention for a variety of practical applications, including electronic skin, smart textiles, and healthcare devices. However, it is still challenging to realize wearable pressure sensors with sufficient sensitivity and low hysteresis under small mechanical stimuli. Herein, we introduce simple, cost-effective, and sensitive capacitive pressure sensor based on porous Ecoflex-multiwalled carbon nanotube composite (PEMC) structures, which leads to enhancing the sensitivity (6.42 and 1.72 kPa

In the field of soft strain sensors, piezo-transmittance based strain sensors, which detect strains by optical transmittance change, have promising advantages of fast response, high sensitivity, long-term stability, and negligible effect from environmental factors. However, they feature low sensor-to-sensor and in-sensor uniformity as well as unpredictable response and high stiffness. This study exploits the gap control of an auxetic-patterned elastomer to develop a piezo-transmittance based strain sensor. Gap opening mechanism in the negative Poisson’s ratio metamaterial with rotating square structures makes the sensor free from these limitations; thus, achieving a designable response and low stiffness. In addition, high sensor-to-sensor ((root-mean-square deviation (RSD)

Hierarchical structures allow one to improve device performance by exploiting the synergistic effects of micro/nano multiscale components. However, the structural complexity of hierarchical structures places limits on their fabrication and applications. Herein, a novel morphology-controllable wrinkled micro/nano hierarchical structure (WHS) was developed by integrating micropatterns, nanopatterns, and wrinkles on a single substrate to overcome these limitations. Each structure could be individually controlled, which offers unlimited design diversity. The produced WHS was used as a superhydrophobic triboelectric nanogenerator. Compared to a nanogenerator with on a film structure, the WHS-based nanogenerator showed a superior contact angle of 152.5°, which is indicative of high hydrophobicity, and an enhanced (by 608%) triboelectric effect, which was ascribed to the highly rough surface of the WHS. The WHS-based nanogenerator was used to fabricate a self-powered and water-repellent cough detection sensor with an entirely superhydrophobic structure and stable superior sensing performance during repeated water spraying.

The importance of the nanotransfer technique has been increased owing to its possibility in nanoscale mass-production, enabled by cost-effective and simply fabricable features. In this study, we developed a novel method for robust nanotransfer printing based on imidization-induced mechanical interlocking. The proposed imidization-induced nanotransfer printing (InTP) method enables various metal nanostructures to be easily transferred onto a polyimide substrate based on the mechanical interlocking force by using a controlled imidization process. The designed functional nanopatterns are transferred with high robustness. In addition, using a partial imidization process, we apply an additional adhesion force at the pattern-substrate interface to transfer materials with poor intrinsic adhesion, such as nickel, successfully. Owing to the exceptional robustness of the method, various 3D nanostructures, such as asymmetric sidewalls, suspended nanowires, and dual-layer line patterns, can be successfully transferred. Moreover, the InTP method was used to fabricate a uniform and high-temperature film heater and an asymmetric blind film.

We developed a new method to directly fabricate 3D multiaxial force sensor using fused deposition modeling (FDM) 3D printing of functionalized nanocomposite filaments. Here, 3D cubic cross shaped force sensor is suggested to measure the forces from three axes (x, y and z). The sensor has two components – a structural part and a sensing part – both of which are concurrently fabricated by 3D printing with different functional filaments. The structural part is printed with thermoplastic polyurethane (TPU) filament and the sensing part is printed with carbon nanotube (CNT)/TPU nanocomposite filament with a piezoresistivity on the surface of the structural part. The resistances of the sensing part are measured in three axial directions; Rx, Ry, and Rz and the force applied on each axis is measured by the resistance change. The 3D-printed multiaxial force sensor could detect the sub-millimeter scale deflection and its corresponding force on each axis. According to the sensing principle, when Fz = 4 N was applied, Rz was decreased by 2% while only 0.2% resistance change of Ry was induced. In addition, a simultaneous resistance measurement system was developed for a real-time force sensing in three axes. With its customizability, rapid manufacturing, and economic feasibility, this manufacturing approach allows direct fabrication of multiaxial sensors without additional assembly or integration processes.

A biopsy needle integrated with a multi-modal physical/chemical sensor array for electrical conductivity, pH, and glucose concentration measurement was developed. A flexible device with an electrical conductivity sensor, a pH sensor, and a glucose sensor was fabricated on a flexible polyimide substrate with thickness less than 20 μm. Then, the sensor was directly integrated onto the surface of biopsy needle by attaching with a pressure sensitive adhesive. The performance factors of the sensor were examined, showing that it could properly measure the parameters in the ranges of human body conditions (conductivity = 0.0265 S/m - 1.027 S/m, pH = 6.6–7.4, and glucose concentration = 2 mM–13 mM). The capabilities of dual-modal and multi-modal sensing were demonstrated by tests with a liver cancer mimicking hydrogel phantom, a solution sample, and porcine liver tissue with exchanged parameters by perfusion of the phosphate buffer saline. Based on these results, we expect that the biopsy needle integrated with the multi-modal sensor array could help to increase the accuracy of the image-guided biopsy process by providing the information of tissue types at the needle tip.

Wearable pressure sensors capable of sensitive, precise, and continuous measurement of physiological and physical signals have great potential for the monitoring of health status and the early diagnosis of diseases. This work introduces a 3D-printed rigid microbump-integrated liquid metal-based soft pressure sensor (3D-BLiPS) for wearable and health-monitoring applications. Using a 3D-printed master mold based on multimaterial fused deposition modeling, the fabrication of a liquid metal microchannel and the integration of a rigid microbump array above the microchannel are achieved in a one-step, direct process. The microbump array enhances the sensitivity of the pressure sensor (0.158 kPa-1 ) by locally concentrating the deformation of the microchannel with negligible hysteresis and a stable signal response under cyclic loading. The 3D-BLiPS also demonstrates excellent robustness to 10 000 cycles of multidirectional stretching/bending, changes in temperature, and immersion in water. Finally, these characteristics are suitable for a wide range of applications in health monitoring systems, including a wristband for the continuous monitoring of the epidermal pulse rate for cuffless blood pressure estimation and a wireless wearable device for the monitoring of body pressure using a multiple pressure sensor array for the prevention of pressure ulcers.

Inspired by the turbinate structure in the olfaction system of a dog, a biomimetic artificial nose based on 3D porous laser-induced graphene (LIG) decorated with palladium (Pd) nanoparticles (NPs) has been developed for room-temperature hydrogen (H2) detection. A 3D porous biomimetic turbinate-like network of graphene was synthesized by simply irradiating an infrared laser beam onto a polyimide substrate, which could further be transferred onto another flexible substrate such as polyethylene terephthalate (PET) to broaden its application. The sensing mechanism is based on the catalytic effect of the Pd NPs on the crystal defect of the biomimetic LIG turbinate-like microstructure, which allows facile adsorption and desorption of the nonpolar H2 molecules. The sensor demonstrated an approximately linear sensing response to H2 concentration. Compared to chemical vapor-deposited (CVD) graphene-based gas sensors, the biomimetic turbinate-like microstructure LIG-gas sensor showed ∼1 time higher sensing performance with much simpler and lower-cost fabrication. Furthermore, to expand the potential applications of the biomimetic sensor, we modulated the resistance of the biomimetic LIG sensor by varying laser sweeping gaps and also demonstrated a well-transferred LIG layer onto transparent substrates. Moreover, the LIG sensor showed good mechanical flexibility and robustness for potential wearable and flexible device applications.

Flexible and wearable pressure sensors have attracted a tremendous amount of attention due to their wider applications in human interfaces and healthcare monitoring. However, achieving accurate pressure detection and stability against external stimuli (in particular, bending deformation) over a wide range of pressures from tactile to body weight levels is a great challenge. Here, we introduce an ultrawide-range, bending-insensitive, and flexible pressure sensor based on a carbon nanotube (CNT) network-coated thin porous elastomer sponge for use in human interface devices. The integration of the CNT networks into three-dimensional microporous elastomers provides high deformability and a large change in contact between the conductive CNT networks due to the presence of micropores, thereby improving the sensitivity compared with that obtained using CNT-embedded solid elastomers. As electrical pathways are continuously generated up to high compressive strain (∼80%), the pressure sensor shows an ultrawide pressure sensing range (10 Pa to 1.2 MPa) while maintaining favorable sensitivity (0.01-0.02 kPa

In this research, we introduce a strain-insensitive soft pressure sensor using 3D-printed microchannel mold and liquid metal for health monitoring applications. Our soft pressure sensor consists of elastomer and liquid metal for its intrinsic stretchable property. Also, serpentine geometric pattern of the microchannel enabled the sensor to be strain-insensitive for stable signal response and recovery in wearable applications. Various experiments for sensor characterizations were conducted and the study of FEM simulation verified the strain-insensitive behavior of serpentine pattern. As a health monitoring application, body pressure distribution was monitored using several pressure sensors attached on the clothes and the body pressures were compared according to various lying conditions.

This paper first reports a highly reliable self-powered hydrogen (H 2 ) sensor employing a palladium (Pd)-based nano-transducer. The developed sensor is based on the principle of a novel chemomechanical mechanism of the Pd nano-transducer exploiting a solar cell. We theoretically and experimentally demonstrated that the proposed device can achieve highly durable operation for a wide range of H 2 concentrations with remarkable sensitivity (3.1% at 2%-H 2 ) and response time (111 s at 2%-H 2 ) without external power. Significantly, the proposed sensor, which has a novel sensing mechanism, maintains high sensing performance for more than 150 cycles under various H 2 conditions (0.5 to 2%).

This paper reports a wide range-sensitive, bending-insensitive pressure sensor based on a carbon nanotube (CNT)-coated porous elastomer for a wearable healthcare application. (1) Sensing performance was evaluated over ~1MPa, which includes whole human tactile and body weight levels. The sensor exhibits a very wide sensing range from ultralow to high pressure (50Pa-1MPa) with maintenance of favorable sensitivity and reliable dynamic responses. (2) To our knowledge this is the first to investigate bending-insensitivity of the CNTs-coated porous PDMS, which facilitates accurate detection of normal pressures even on curved surfaces like human skins. (3) Finally, we demonstrated a foot insole for real-time monitoring of foot plantar pressure distribution.

In this research, we introduce a wearable soft microfluidic pressure sensor using 3D-printed microbumps and liquid metal and its potential applications in health monitoring. Our pressure sensor fabricated with elastomer and liquid metal which provide stretchability has an enhanced sensitivity (0.3 kPa−1@100kPa) compared to other reported microfluidic pressure sensors [1] and a good recovery characteristic in pressure range to 100 kPa. It has an enough sensitivity to be applied in pressure monitoring applications. Blood pressure could be estimated through monitoring pulse rate and electrocardiogram (ECG) data simultaneously. Also, human body pressure distribution was monitored using multiple pressure sensors attached on the clothes when lying on the bed. Biosignals and human body pressure data achieved through the proposed pressure sensor would be applied to early diagnosis and prevention of diseases such as diabetes and bedsores.

In this work, we report a novel stretchable fabric heater based on silver nanowire, carbon nanotube composites. We propose improved spray coating method to develop a stretchable fabric heater with excellent mechanical properties and electrical properties. The combination of the carbon nanotubes (CNTs) with high structural stability and silver nanowires (Ag NWs) with high conductivity could highlight the advantage of each nanomaterials. The proposed fabric heater showed a stable temperature control even in the folded and rolled states. In addition, fabric heaters were applied in commercial cotton gloves successfully.

Conventional flexible pressure sensors are not suitable for high-pressure applications due to their low saturation pressure. In this study, an ultra-wide range pressure sensor is designed based on the optimized microstructure of the polyimide/carbon nanotubes (PI/CNT) nanocomposite film. The sensing range of the pressure sensor is expanded by adopting polyimide (PI) with a high elastic modulus as a matrix material and its sensitivity is improved through functional sensing film with tip-flattened microdome arrays. As a result, the pressure sensor can measure a wide pressure range (≈ 0-3000 kPa) and possesses the sensitivity of ≈ 5.66 × 10-3 -0.23 × 10-3 kPa-1 with high reliability and durability up to 1000 cycles. The proposed sensor is integrated into the hand and foot pressure monitoring systems for workout monitoring. The representative values of the pressure distribution in the hands and feet during the powerlifting are acquired and analyzed through Pearson's correlation coefficient (PCC). The analyzed results suggest that the pressure sensor can provide useful real-time information for healthcare and sports performance monitoring.

Radiofrequency ablation (RFA) method is an effective method in cancer surgery. However, due to its high temperature and pressure, explosive behavior called ‘steam popping’ was occurred during RFA. This phenomenon can cause recurrence and metastasis of the cancer. Though this is a critical problem, but steam popping still can be detected by the explosive sound. In this research, thin film based flexible pressure sensor with the range of 100–400 kPa was developed, and attached to the RFA needle to monitor the steam popping through pressure variation. Fabricated needle showed low interference from temperature variation, electromagnetic noise, and chemical environment noise. Proposed needle successfully monitor the steam popping phenomenon.

This paper presents a wireless ground reaction force (GRF) sensing system for ambulatory GRF recording. The system is largely divided into three parts: force sensing modules based on optical sensor, outsole type frame, and embedded system for wireless communication. The force sensing module has advantages of the low height, robustness to the moment interference, and stable response in long term use. In simulation study, the strain and stress properties were examined to satisfy the requirements of the GRF sensing system. Four sensing modules were mounted on the toe, ball, and heel of foot shaped frame, respectively. The GRF signals were extracted using Micrpcontroller unit and transferred to the smart phone via Bluetooth communication. We measured the GRF during the normal walking for the validation of the continuous recording capability. The recorded GRF was comparable to the off the shelf stationary force plate.

We report microscale flexible biosensor with multi-modal sensing capabilities (electrical impedance, pH level and glucose concentration) and application to the sensor integrated biopsy needle towards accurate cancer tissue targeting during biopsy process. The sensor is thin enough to be integrated onto the surface of biopsy needle, which allows minimal increase of needle diameter to avoid additional tissue damage during the needle insertion. Also, the sensor shows sensing performance that can cover the physical/chemical differences between cancer and normal tissues. We expect that our sensor integrated on the biopsy needle can overcome the limitation and inaccuracy of conventional image-guided biopsy process.