Highly Stretchable Potentiometric pH Sensor Fabricated via Laser Carbonization and Machining of Carbon-Polyaniline Composite

Toward Integrated Multifunctional Laser-Induced Graphene-Based Skin-Like Flexible Sensor Systems

The burgeoning demands for health care and human-machine interfaces call for the next generation of multifunctional integrated sensor systems with facile fabrication processes and reliable performances. Laser-induced graphene (LIG) with highly tunable physical and chemical characteristics plays vital roles in developing versatile skin-like flexible or stretchable sensor systems. This Progress Report presents an in-depth overview of the latest advances in LIG-based techniques in the applications of flexible sensors. First, the merits of the LIG technique are highlighted especially as the building blocks for flexible sensors, followed by the description of various fabrication methods of LIG and its variants. Then, the focus is moved to diverse LIG-based flexible sensors, including physical sensors, chemical sensors, and electrophysiological sensors. Mechanisms and advantages of LIG in these scenarios are described in detail. Furthermore, various representative paradigms of integrated LIG-based sensor systems are presented to show the capabilities of LIG technique for multipurpose applications. The signal cross-talk issues are discussed with possible strategies. The LIG technology with versatile functionalities coupled with other fabrication strategies will enable high-performance integrated sensor systems for next-generation skin electronics.

Water-powered, electronics-free dressings that electrically stimulate wounds for rapid wound closure

Chronic wounds affect ~2% of the U.S. population and increase risks of amputation and mortality. Unfortunately, treatments for such wounds are often expensive, complex, and only moderately effective. Electrotherapy represents a cost-effective treatment; however, its reliance on bulky equipment limits its clinical use. Here, we introduce water-powered, electronics-free dressings (WPEDs) that offer a unique solution to this issue. The WPED performs even under harsh conditions-situations wherein many present treatments fail. It uses a flexible, biocompatible magnesium-silver/silver chloride battery and a pair of stimulation electrodes; upon the addition of water, the battery creates a radial electric field. Experiments in diabetic mice confirm the WPED's ability to accelerate wound closure and promote healing by increasing epidermal thickness, modulating inflammation, and promoting angiogenesis. Across preclinical wound models, the WPED-treated group heals faster than the control with wound closure rates comparable to treatments requiring expensive biologics and/or complex electronics. The results demonstrate the WPED's potential as an effective and more practical wound treatment dressing.

Smart wireless flexible bandage containing drug loaded polycaprolactone microparticles for real-time monitoring and treatment of chronic wounds

The quality of life is negatively impacted by chronic wounds for more than 25 million people in the US. They are quite prone to infection, which may lead to the eventual loss of a limb. By exposing the ulcers to treatment agents at the appropriate time, the healing rate is increased. On-demand drug release in a closed-loop system will aid us in reaching our goal. In this study, we have developed a platform capable of real-time diagnosis of bacterial infection by wirelessly reading wound pH, as well as slow and on-demand local administration of antibiotics. The drug carrier microparticles, an electrical patch, a thermoresponsive hydrogel with an integrated microheater, and a flexible pH sensor comprised the closed-loop patch. Here it is reported that slow and smart release of cefazolin can be addressed by incorporation of drug encapsulated hydrophobic microparticles embedded into a thermo-responsive hydrogel. The utilization of a programmable bandage to provide antibiotic medication highlights the need of not only choosing appropriate therapeutic substances but also the controlled release of the medicine and its rate of release within the wound area. The results of our study indicate that the use of cefazolin encapsulated polycaprolactone (PCL) microparticles can effectively regulate the application of antibiotic treatment for chronic skin wounds. The results also showed a substantial gradual release of cefazolin from the thermo-responsive Pnipam hydrogel when the wound dressing was subjected to a temperature of 37°C. We believe that the developed flexible smart bandage can have a significant impact on chronic wound healing.

Direct Laser Processing and Functionalizing PI/PDMS Composites for an On-Demand, Programmable, Recyclable Device Platform

Skin-interfaced high-sensitive biosensing systems to detect electrophysiological and biochemical signals have shown great potential in personal health monitoring and disease management. However, the integration of 3D porous nanostructures for improved sensitivity and various functional composites for signal transduction/processing/transmission often relies on different materials and complex fabrication processes, leading to weak interfaces prone to failure upon fatigue or mechanical deformations. The integrated system also needs additional adhesive to strongly conform to the human skin, which can also cause irritation, alignment issues, and motion artifacts. This work introduces a skin-attachable, reprogrammable, multifunctional, adhesive device patch fabricated by simple and low-cost laser scribing of an adhesive composite with polyimide powders and amine-based ethoxylated polyethylenimine dispersed in the silicone elastomer. The obtained laser-induced graphene in the adhesive composite can be further selectively functionalized with conductive nanomaterials or enzymes for enhanced electrical conductivity or selective sensing of various sweat biomarkers. The possible combination of the sensors for real-time biofluid analysis and electrophysiological signal monitoring with RF energy harvesting and communication promises a standalone stretchable adhesive device platform based on the same material system and fabrication process.

Portable Photoacoustic Analytical System Combined with Wearable Hydrogel Patch for pH Monitoring in Chronic Wounds

Timely diagnosis, monitoring, and management of chronic wounds play crucial roles in improving patients' quality of life, but clinical evaluation of chronic wounds is still ambiguous and relies heavily on the experience of clinician, resulting in increased social and financial burden and delay of optimal treatment. During the different stages of the healing process, specific and dynamic changes of pH values in the wound exudate can be used as biomarkers to reflect the wound status. Herein, a pH-responsive agent with well-behaved photoacoustic (PA) properties, nitrazine yellow (NY), was incorporated in poly(vinyl alcohol)/sucrose (PVA/Suc) hydrogel to construct a wearable pH-sensing patch (PVA/Suc/NY hydrogel) for monitoring of pH values during chronic wound healing. According to Rosencwaig-Gersho theory and the combination of 3D printing technology, the PA chamber volume and chopping frequency were systematically optimized to improve the sensitivity of the PA analytical system. The prepared PVA/Suc/NY hydrogel patch had excellent mechanical properties and flexibility and could maintain conformal contact with skin. Moreover, combined with the miniaturized PA analytical device, it had the potential to detect pH values (5.0-9.0) free from the color interference of blood and therapeutic drugs, which provides a valuable strategy for wound pH value monitoring by PA quantitation. This strategy of combining the wearable hydrogel patch with portable PA analysis offers broad new prospects for the treatment and management of chronic wounds due to its features of simple operation, time savings, and anti-interference.

Ultra-Sensitive and Stable Multiplexed Biosensors Array in Fully Printed and Integrated Platforms for Reliable Perspiration Analysis

Electrochemical biosensors have emerged as one of the promising tools for tracking human body physiological dynamics via non-invasive perspiration analysis. However, it remains a key challenge to integrate multiplexed sensors in a highly controllable and reproducible manner to achieve long-term reliable biosensing, especially on flexible platforms. Herein, a fully inkjet printed and integrated multiplexed biosensing patch with remarkably high stability and sensitivity is reported for the first time. These desirable characteristics are enabled by the unique interpenetrating interface design and precise control over active materials mass loading, owing to the optimized ink formulations and droplet-assisted printing processes. The sensors deliver sensitivities of 313.28 µA mm-1 cm-2 for glucose and 0.87 µA mm-1 cm-2 for alcohol sensing with minimal drift over 30 h, which are among the best in the literature. The integrated patch can be used for reliable and wireless diet monitoring or medical intervention via epidermal analysis and would inspire the advances of wearable devices for intelligent healthcare applications.

Comparative analysis of electrochemical and optical sensors for detection of chronic wounds biomarkers: A review

Chronic wounds (CW) present a significant healthcare challenge due to their prolonged healing time and associated complications. To effectively treat these wounds and prevent further deterioration, monitoring their healing progress is crucial. Traditional wound assessment methods relying on visual inspection and subjective evaluation are prone to inter-observer variability. Biomarkers play a critical role in objectively evaluating wound status and predicting healing outcomes, providing quantitative measures of wound healing progress, inflammation, infection, and tissue regeneration. Recent attention has been devoted to identifying and validating CW biomarkers. Various studies have investigated potential biomarkers, including growth factors, cytokines, proteases, and extracellular matrix components, shedding light on the complex molecular and cellular processes within CW. This knowledge enables a more targeted and personalized approach to wound management. Accurate and sensitive techniques are necessary for detecting CW biomarkers. Thus, this review compares and discusses the use of electrochemical and optical sensors for biomarker determination. The advantages and disadvantages of these sensors are highlighted. Differences in detection capabilities and characteristics such as non-invasiveness, portability, high sensitivity, specificity, simplicity, cost-effectiveness, compatibility with point-of-care applications, and real-time monitoring of wound biomarkers will be pointed out and compared. In summary, this work provides an overview of CW, explores the emerging field of CW biomarkers, and discusses methods for detecting these biomarkers, with a specific focus on optical and electrochemical sensors. The potential of further research and development in this field for advancing wound care and improving patient outcomes will also be noted.

Conductivity-Based Gas Sensors Using Tamarindus indica Polysaccharide-Capped Gold Nanoparticles for the Detection of Volatile Gases

Gold nanoparticles (nAu) were synthesized by a sustainable approach utilizing tamarind seed polysaccharide (TSP). Polysaccharides are naturally occurring polymers derived from tamarind seeds, which function both as capping and reducing agents. Polyaniline (PANI) was subsequently capped over the as-prepared gold nanoparticles in order to facilitate the sensor property. The TSP-nAu-PANI film was fabricated by Methods I and II and utilized in the investigation of active sensor devices for the detection of organic pollutants such as benzene, toluene, and chloroform. The synthesized gold nanoparticles and the TSP-nAu-PANI films were analyzed using several analytical and spectral tools. Among the two methods, the Method II (TSP-nAu-PANI) film has a high sensing response toward benzene (105.69%), toluene (96.99%), and chloroform (74.98%). TSP is also a proton-conducting biopolymer, which enhances the conductivity of the material. The combination with the PANI layer of the film adsorbs the vapors easily and the prepared film material is more effective and ideal for sensing toxic gases.

A flexible pH sensor based on polyaniline@oily polyurethane/polypropylene spunbonded nonwoven fabric

To fabricate a two-electrode flexible pH sensor based on polypropylene spunbonded nonwoven fabric (PP SF), oily polyurethane (OPU) was first coated on the surface of PP SF to obtain OPU/PP SF. Then, silver/silver chloride (Ag/AgCl) paste, used as the reference electrode and conductive carbon (C) paste were transferred to the OPU/PP SF surface through screen printing. Polyaniline (PANI) was deposited on the surface of the C paste to form a sensing working electrode via the electro-chemical deposition method. The results showed that the surface of the obtained PANI@OPU/PP SF flexible pH sensor (3D PANI pH sensor) presented a three-dimensional (3D) porous network structure. The 3D PANI pH sensor had good mechanical properties, an excellent Nernst response (-67.67 mV pH-1) and linearity (R2 = 0.99) in the pH range from 2.00 to 8.00 in the normal state. In the bent state, the 3D PANI pH sensor retained similar sensitivity (-68.87 mV pH-1) and linearity (R2 = 0.99). Moreover, the 3D PANI pH sensor exhibited a short response time (8 s), excellent reversibility (1.20 mV), low temperature drift (-0.0872 mV pH-1 °C-1) and long-term stability (0.83 mV h-1) in the normal state. Furthermore, the 3D PANI pH sensor can be effectively applied for pH monitoring of liquids and fruits with irregular curved surfaces. The error margin is no more than 0.16 compared to a commercial pH meter.

A light-sensitive protein-based wearable pH biometer

Bacteriorhodopsin is a biological material with excellent photosensitivity properties. It can directly convert optical signals into electrical signals and is widely used in various biosensors. Here, we present a bR-based wearable pH biometer that can be used to monitor wound infection. The mechanism of the pH-sensitive effect of the bR electrode is explained, which generates a transient photovoltage under light irradiation and a negative photovoltage when the lamp is turned off. Since the photoelectric signal of bR is affected by different pH values, the photovoltage is changed by adjusting the pH value. The ratio (Vn/Vp) of negative photovoltage (Vn) to positive photovoltage (Vp) has a good linear relationship (R2 = 0.9911) in the pH range of 4.0-10.0. In vitro experiments using rats as a model confirmed that this wearable pH biometer can monitor pH changes that occur in wound infection.

Next-generation of smart dressings: Integrating multiplexed sensors and theranostic functions

Non-healing wounds represent a significant burden for healthcare systems and society, giving rise to severe economic and human issues. Currently, the use of dressings and visual assessment represent the primary and standard care for wounds. Conventional dressings, like cotton gauze, provide only passive physical protection. Besides, they end up paradoxically hampering the wound-healing process by producing tissue damage and pain when removed during routine check-ups. In response to these limitations, researchers, engineers, and technologists are developing innovative dressings that incorporate advanced diagnostic and therapeutic functionalities, coined as "smart dressings". Now, the maturation of smart dressing is bringing them closer to real-life applications, leading to an exciting new generation of these devices. The next generation of smart dressings is capable of monitoring in real-time multiple biomarkers while including pro-healing capabilities in a single platform. Such multiplexed and theranostic smart dressings are expected to offer a timely biomarker-directed diagnosis of non-healing wounds while enabling rapid, automated, and personalized treatments of infection and chronicity. Herein, we provide an insightful overview of these advantageous devices, delving into the diverse spectrum of possible engineering strategies. This encompasses the use of electrochemical and optical platforms with diverse multiplexing architectures, such as multi-zone sensing arrays and multi-layered devices. Open or closed-loop theranostic mechanisms using various stimuli-responsive materials that could be internally or externally controlled are also included. Finally, a critical discussion on the main challenges and future directions of smart dressings is also offered.

Recent advances in wearable iontronic sensors for healthcare applications

Iontronic sensors have garnered significant attention as wearable sensors due to their exceptional mechanical performance and the ability to maintain electrical performance under various mechanical stimuli. Iontronic sensors can respond to stimuli like mechanical stimuli, humidity, and temperature, which has led to exploration of their potential as versatile sensors. Here, a comprehensive review of the recent researches and developments on several types of iontronic sensors (e.g., pressure, strain, humidity, temperature, and multi-modal sensors), in terms of their sensing principles, constituent materials, and their healthcare-related applications is provided. The strategies for improving the sensing performance and environmental stability of iontronic sensors through various innovative ionic materials and structural designs are reviewed. This review also provides the healthcare applications of iontronic sensors that have gained increased feasibility and broader applicability due to the improved sensing performance. Lastly, outlook section discusses the current challenges and the future direction in terms of the applicability of the iontronic sensors to the healthcare.

Recent advances in biosensors for real time monitoring of pH, temperature, and oxygen in chronic wounds

Chronic wounds are among the major healthcare issues affecting millions of people worldwide with high rates of morbidity, losses of limbs and mortality. Microbial infection in wounds is a severe problem that can impede healing of chronic wounds. Accurate, timely and early detection of infections, and real time monitoring of various wound healing biomarkers related to infection can be significantly helpful in the treatment and care of chronic wounds. However, clinical methodologies of periodic assessment and care of wounds require physical visit to wound care clinics or hospitals and time-consuming frequent replacement of wound dressing patches, which also often adversely affect the healing process. Besides, frequent replacements of wound dressings are highly expensive, causing a huge amount of burden on the national health care systems. Smart bandages have emerged to provide in situ physiochemical surveillance in real time at the wound site. These bandages integrate smart sensors to detect the condition of wound infection based on various parameters, such as pH, temperature and oxygen level in the wound which reduces the frequency of changing the wound dressings and its associated complications. These devices can continually monitor the healing process, paving the way for tailored therapy and improved quality of patient's life. In this review, we present an overview of recent advances in biosensors for real time monitoring of pH, temperature, and oxygen in chronic wounds in order to assess infection status. We have elaborated the recent progress in quantitative monitoring of several biomarkers important for assessing wounds infection status and its detection using smart biosensors. The review shows that real-time monitoring of wound status by quantifying specific biomarkers, such as pH, temperature and tissue oxygenation to significantly aid the treatment and care of chronic infected wounds.

Laser-Carbonization - A Powerful Tool for Micro-Fabrication of Patterned Electronic Carbons

Fabricating electronic devices from natural, renewable resources is a common goal in engineering and materials science. In this regard, carbon is of special significance due to its biocompatibility combined with electrical conductivity and electrochemical stability. In microelectronics, however, carbon's device application is often inhibited by tedious and expensive preparation processes and a lack of control over processing and material parameters. Laser-assisted carbonization is emerging as a tool for the precise and selective synthesis of functional carbon-based materials for flexible device applications. In contrast to conventional carbonization via in-furnace pyrolysis, laser-carbonization is induced photo-thermally and occurs on the time-scale of milliseconds. By careful selection of the precursors and process parameters, the properties of this so-called laser-patterned carbon (LP-C) such as porosity, surface polarity, functional groups, degree of graphitization, charge-carrier structure, etc. can be tuned. In this critical review, a common perspective is generated on laser-carbonization in the context of general carbonization strategies, fundamentals of laser-induced materials processing, and flexible electronic applications, like electrodes for sensors, electrocatalysts, energy storage, or antennas. An attempt is made to have equal emphasis on material processing and application aspects such that this emerging technology can be optimally positioned in the broader context of carbon-based microfabrication.

A Reconfigurable Tri-Mode Frequency-Locked Loop Readout Circuit for Biosensor Interfaces

In this article, a frequency-locked loop (FLL) based multimodal readout integrated circuit (IC) for interfacing with off-chip temperature, electrochemical, and pH sensors is presented. By reconfiguring its switched-capacitor feedback network, the readout circuit is able to measure resistance, current, and voltage without additional active analog front-end circuits. A prototype IC was fabricated in a 0.18 μm CMOS process. Measured results show that when measuring resistance, the input-referred resistance resolution is 10.5 Ω for 100 Hz integration bandwidth. Using an off-chip thermistor, the readout circuit covers a temperature range of 0-75 °C and achieves an equivalent temperature resolution of 16.4 mKrms. In current mode, the readout circuit has an input range of 0.5μA and an input-referred current noise as low as 40.6 pArms for 100 Hz bandwidth. Interfacing with an on-chip potentiostat, glucose chronoamperometry is demonstrated. In voltage mode, a minimum input-referred voltage noise of 31.7 μVrms is achieved, and the IC can measure a pH range from 1.6 to 12 using a commercial pH probe. At a 1.2 V supply, power consumption of the readout circuit is below 10 μW for all three measurement modes. Additionally, the prototype IC includes an integrated wireless transmitter that implements on-off keying modulation, and a wireless multimodal sensing system utilizing the FLL-based readout circuit is demonstrated.

Platinum Black/Gold Nanoparticles/Polyaniline Modified Electrochemical Microneedle Sensors for Continuous In Vivo Monitoring of pH Value

Continuous in vivo monitoring (CIVM) of pH value is essential for personalized medicine, as many diseases are closely related to acid-base imbalances. However, conventional pH meters are limited in their ability to perform CIVM due to excessive blood consumption, large device volume, frequent calibration, and inadequate real-time monitoring. There is thus an urgent need for a portable method for CIVM of pH value. To address this need, we propose a minimally invasive, continuous monitoring solution in the form of an implantable pH microneedle sensor (MNS) in this study. The MNS is based on the integration of an acupuncture needle (AN) and a Ag/AgCl reference electrode. We fabricate the sensor by electrochemically depositing platinum black and gold nanoparticles onto the AN and further modifying it with polyaniline to increase its sensitivity to hydrogen ions. The pH value is obtained by calculating the open circuit voltage between the modified AN and the reference electrode. The resulting MNS demonstrates excellent selectivity and a high nernstian response to pH (-57.4 mV per pH) over a broad range (pH = 4.0 to pH = 9.0). Both in vitro and in vivo experiments have verified the performance of the sensor, showcasing its potential for biomedical research and clinical practice. The MNS provides an alternative to conventional pH meters, offering a less invasive and more convenient way to perform CIVM of pH value. Moreover, this electrochemical implantable sensor based on AN and silver wires provides a simple and sensitive method for continuous in vivo detection of other biomarkers.

Graphene-interfaced flexible and stretchable micro-nano electrodes: from fabrication to sweat glucose detection

Flexible and stretchable wearable electronic devices have received tremendous attention for their non-invasive and personal health monitoring applications. These devices have been fabricated by integrating flexible substrates and graphene nanostructures for non-invasive detection of physiological risk biomarkers from human bodily fluids, such as sweat, and monitoring of human physical motion tracking parameters. The extraordinary properties of graphene nanostructures in fully integrated wearable devices have enabled improved sensitivity, electronic readouts, signal conditioning and communication, energy harvesting from power sources through electrode design and patterning, and graphene surface modification or treatment. This review explores advances made toward the fabrication of graphene-interfaced wearable sensors, flexible and stretchable conductive graphene electrodes, as well as their potential applications in electrochemical sensors and field-effect-transistors (FETs) with special emphasis on monitoring sweat biomarkers, mainly in glucose-sensing applications. The review emphasizes flexible wearable sweat sensors and provides various approaches thus far employed for the fabrication of graphene-enabled conductive and stretchable micro-nano electrodes, such as photolithography, electron-beam evaporation, laser-induced graphene designing, ink printing, chemical-synthesis and graphene surface modification. It further explores existing graphene-interfaced flexible wearable electronic devices utilized for sweat glucose sensing, and their technological potential for non-invasive health monitoring applications.

Encoded Structural Color Microneedle Patches for Multiple Screening of Wound Small Molecules

Detection of biomarkers associated with wound conditions provides in-depth healthcare information and benefits wound healing treatment. The current aim of wound detection is to achieve in situ multiple detections. Novel encoded structural color microneedle patches (EMNs) combining photonic crystals (PhCs) and microneedle arrays (MNs) for multiple wound biomarker detection in situ are described here. Using a partitioned and layered casting strategy, the EMNs can be divided into different modules and each serves for the detection of small molecules , including pH, glucose, and histamine. pH sensing is based on the interaction between hydrogen ions and carboxyl groups from hydrolyzed polyacrylamide (PAM); glucose sensing is achieved with the help of glucose-responsive fluorophenylboronic acid (FPBA); while histamine sensing relies on specific recognition of aptamers and target molecules. Owing to the responsive volume change of these three modules in the presence of target molecules, the EMNs can create structural color change and characteristic peak shift of the PhCs, thus realizing the qualitative measurement of target molecules with a spectrum analyzer. It is further demonstrated that the EMNs behave well in the multivariate detection of rat wound molecules. These features indicate that the EMNs can be valuable smart detection systems for wound status screening.

Basic amino acid-mediated cationic amphiphilic surfaces for antimicrobial pH monitoring sensor with wound healing effects

BACKGROUND

The wound healing process is a complex cascade of physiological events, which are vulnerable to both our body status and external factors and whose impairment could lead to chronic wounds or wound healing impediments. Conventional wound healing materials are widely used in clinical management, however, they do not usually prevent wounds from being infected by bacteria or viruses. Therefore, simultaneous wound status monitoring and prevention of microbial infection are required to promote healing in clinical wound management.

METHODS

Basic amino acid-modified surfaces were fabricated in a water-based process via a peptide coupling reaction. Specimens were analyzed and characterized by X-ray photoelectron spectroscopy, Kelvin probe force microscopy, atomic force microscopy, contact angle, and molecular electrostatic potential via Gaussian 09. Antimicrobial and biofilm inhibition tests were conducted on Escherichia coli and Staphylococcus epidermidis. Biocompatibility was determined through cytotoxicity tests on human epithelial keratinocytes and human dermal fibroblasts. Wound healing efficacy was confirmed by mouse wound healing and cell staining tests. Workability of the pH sensor on basic amino acid-modified surfaces was evaluated on normal human skin and Staphylococcus epidermidis suspension, and in vivo conditions.

RESULTS

Basic amino acids (lysine and arginine) have pH-dependent zwitterionic functional groups. The basic amino acid-modified surfaces had antifouling and antimicrobial properties similar to those of cationic antimicrobial peptides because zwitterionic functional groups have intrinsic cationic amphiphilic characteristics. Compared with untreated polyimide and modified anionic acid (leucine), basic amino acid-modified polyimide surfaces displayed excellent bactericidal, antifouling (reduction ~ 99.6%) and biofilm inhibition performance. The basic amino acid-modified polyimide surfaces also exhibited wound healing efficacy and excellent biocompatibility, confirmed by cytotoxicity and ICR mouse wound healing tests. The basic amino acid-modified surface-based pH monitoring sensor was workable (sensitivity 20 mV pH-1) under various pH and bacterial contamination conditions.

CONCLUSION

Here, we developed a biocompatible and pH-monitorable wound healing dressing with antimicrobial activity via basic amino acid-mediated surface modification, creating cationic amphiphilic surfaces. Basic amino acid-modified polyimide is promising for monitoring wounds, protecting them from microbial infection, and promoting their healing. Our findings are expected to contribute to wound management and could be expanded to various wearable healthcare devices for clinical, biomedical, and healthcare applications.

A "Two-Part" Resonance Circuit Based Detachable Sweat Patch for Noninvasive Biochemical and Biophysical Sensing

Wearable electronics play important roles in noninvasive, continuous, and personalized monitoring of multiple biosignals generated by the body. To unleash their full potential for next-generation human centered bio-integrated electronics, the wireless sensing capability is a desirable feature. However, state-of-the-art wireless sensing technologies exploit rigid and bulky electronic modules for power supply, signal generation, and data transmission. This study reports a battery-free device technology based on a "two-part" resonance circuit model with modularized, physically separated, and detachable functional units for magnetic coupling and biosensing. The resulting platform combines advantages of electronics and microfluidics with low cost, minimized form factors, and improved performance stability. Demonstration of a detachable sweat patch capable of simultaneous recording of cortisol concentration, pH value, and temperature highlights the potential of the "two-part" circuit for advanced, transformative biosensing. The resulting wireless sensors provide a new engineering solution to monitoring biosignals through intimate and seamless integration with skin surfaces.

Fully Screen-Printed PI/PEG Blends Enabled Patternable Electrodes for Scalable Manufacturing of Skin-Conformal, Stretchable, Wearable Electronics

Recent advances in soft materials and nano-microfabrication have enabled the development of flexible wearable electronics. At the same time, printing technologies have been demonstrated to be efficient and compatible with polymeric materials for manufacturing wearable electronics. However, wearable device manufacturing still counts on a costly, complex, multistep, and error-prone cleanroom process. Here, we present fully screen-printable, skin-conformal electrodes for low-cost and scalable manufacturing of wearable electronics. The screen printing of the polyimide (PI) layer enables facile, low-cost, scalable, high-throughput manufacturing. PI mixed with poly(ethylene glycol) exhibits a shear-thinning behavior, significantly improving the printability of PI. The premixed Ag/AgCl ink is then used for conductive layer printing. The serpentine pattern of the screen-printed electrode accommodates natural deformation under stretching (30%) and bending conditions (180°), which are verified by computational and experimental studies. Real-time wireless electrocardiogram monitoring is also successfully demonstrated using the printed electrodes with a flexible printed circuit. The algorithm developed in this study can calculate accurate heart rates, respiratory rates, and heart rate variability metrics for arrhythmia detection.

Improving disease prevention, diagnosis, and treatment using novel bionic technologies

Increased human life expectancy, due in part to improvements in infant and childhood survival, more active lifestyles, in combination with higher patient expectations for better health outcomes, is leading to an extensive change in the number, type and manner in which health conditions are treated. Over the next decades as the global population rapidly progresses toward a super-aging society, meeting the long-term quality of care needs is forecast to present a major healthcare challenge. The goal is to ensure longer periods of good health, a sustained sense of well-being, with extended periods of activity, social engagement, and productivity. To accomplish these goals, multifunctionalized interfaces are an indispensable component of next generation medical technologies. The development of more sophisticated materials and devices as well as an improved understanding of human disease is forecast to revolutionize the diagnosis and treatment of conditions ranging from osteoarthritis to Alzheimer's disease and will impact disease prevention. This review examines emerging cutting-edge bionic materials, devices and technologies developed to advance disease prevention, and medical care and treatment in our elderly population including developments in smart bandages, cochlear implants, and the increasing role of artificial intelligence and nanorobotics in medicine.

Material Choice and Structure Design of Flexible Battery Electrode

With the development of flexible electronics, the demand for flexibility is gradually put forward for its energy supply device, i.e., battery, to fit complex curved surfaces with good fatigue resistance and safety. As an important component of flexible batteries, flexible electrodes play a key role in the energy density, power density, and mechanical flexibility of batteries. Their large-scale commercial applications depend on the fulfillment of the commercial requirements and the fabrication methods of electrode materials. In this paper, the deformable electrode materials and structural design for flexible batteries are summarized, with the purpose of flexibility. The advantages and disadvantages of the application of various flexible materials (carbon nanotubes, graphene, MXene, carbon fiber/carbon fiber cloth, and conducting polymers) and flexible structures (buckling structure, helical structure, and kirigami structure) in flexible battery electrodes are discussed. In addition, the application scenarios of flexible batteries and the main challenges and future development of flexible electrode fabrication are also discussed, providing general guidance for the research of high-performance flexible electrodes.

Non-invasive biomedical sensors for early detection and monitoring of bacterial biofilm growth at the point of care

Bacterial infections have long been a serious global health issue. Biofilm formation complicates matters even more. The biofilm's extracellular polymeric substances (EPSs) matrix protects bacteria from the host's immune responses, yielding strong adhesion and drug resistance as the biofilm matures. Early bacterial biofilm detection and bacterial biofilm growth monitoring are crucial to treating biofilm-associated infections. Current detection methods are highly sensitive but not portable, are time-consuming, and require expensive equipment and complex operating procedures, limiting their use at the point of care. Therefore, there is an urgent need to develop affordable, on-body, and non-invasive biomedical sensors to continuously monitor and detect early biofilm growth at the point of care through personalized telemedicine. Herein, recent advances in developing non-invasive biomedical sensors for early detection and monitoring bacterial biofilm growth are comprehensively reviewed. First, biofilm's life cycle and its impact on the human body, such as biofilm-associated disease and infected medical devices, are introduced together with the challenges of biofilm treatment. Then, the current methods used in clinical and laboratory settings for biofilm detection and their challenges are discussed. Next, the current state of non-invasive sensors for direct and indirect detection of bacterial biofilms are summarized and highlighted with the detection parameters and their design details. Finally, commercially available products, challenges of current devices, and the further trend in biofilm detection sensors are discussed.

Low-Cost Nonreversible Electronic-Free Wireless pH Sensor for Spoilage Detection in Packaged Meat Products

Contamination of meat with pathogenic microorganisms can cause severe illnesses and food waste, which has significant negative impacts on both general health and the economy. In many cases, the expiration date is not a good indicator of meat freshness as there is a high risk of contamination during handling throughout the supply chain. Many biomarkers, including color, odor, pH, temperature, and volatile compounds, are used to determine spoilage. Among these, pH presents a simple and effective biomarker directly linked to the overgrowth of bacteria and degradation of the meat tissue. Low-cost methods for wireless pH monitoring are crucial in detecting spoilage on a large commercial scale. Existing technologies are often limited to short-range detection, with the use of batteries and different electronic components that increases both the manufacturing complexity and cost of the final device. To address these shortcomings, we have developed a cost-effective wireless pH sensor, which uses passive resonant frequency (RF) sensing, combined with a pH-responsive polymer that can be placed within packaged meat products and provide a remote assessment of the risk of microbial spoilage throughout the supply chain. The sensor tag consists of a sensing resonator coated with a pH-sensitive material and a passivated reference resonator operating in a differential frequency configuration. Upon exposure to elevated pH levels >6.8, the coating on the sensing resonator dissolves, which in turn results in a distinct change in the resonant frequency with respect to the reference resonator. Systematic theoretical and experimental results at different pH levels demonstrated that a 20% shift in resonant frequency demarcates the point for spoilage detection. As a proof of concept, the performance of the sensor in remotely detecting the risk of food spoilage was validated in packaged poultry over 10 days. The sensor fabrication process takes advantage of recent developments in the scalable manufacturing of flexible, low-cost devices, including selective laser etching of metalized plastic films and doctor-blade coating of stimuli-responsive polymer films. Furthermore, the biocompatibility of all the materials used in the sensor was confirmed with human intestinal cells (HCT-8 cells).

Insights into the Role of Natural Polysaccharide-Based Hydrogel Wound Dressings in Biomedical Applications

Acute skin damage caused by burns or cuts occurs frequently in people's daily lives. Such wounds are difficult to heal normally and have persistent inflammation. Wound dressings not only improve the speed of wound healing, but also protect and cover the wound well. Hydrogels have the characteristics of good flexibility, high water content, and good biocompatibility, and are widely used in biomedicine and other fields. Common hydrogels are mainly natural hydrogels and synthetic hydrogels. Hydrogels cross-linked using different raw materials and different methods have different performance characteristics. Natural hydrogels prepared using polysaccharides are simple to obtain and have good biocompatibility, but are inferior to synthetic hydrogels in terms of mechanical properties and stability, and a single polysaccharide hydrogel cannot meet the component requirements for wound healing. Therefore, functional composite hydrogels with high mechanical properties, high biocompatibility, and high antibacterial properties are the current research hotspots. In this review, several common polysaccharides for hydrogel synthesis and the synthesis methods of polysaccharide hydrogels are introduced, and functional composite hydrogel dressings from recent years are classified. It is hoped that this can provide useful references for relevant research in this field.

Double-Sided Wearable Multifunctional Sensing System with Anti-interference Design for Human-Ambience Interface

Multifunctional sensing systems play important roles in a variety of applications, incluing health surveillance, intelligent prothetics, human-machine/ambinece interfaces, and many others. The richness of the signal and the decoupling among multiple parameters are essential for simultaneous, multimodal measurements. However, current multifunctional sensing fails to decouple interferences from various signals. Here, we propose a double-sided wearable system that both enables multifunctional sensing and avoids the interferences among multiple parameters. Specifically, the sensitivities of system modules to strain are controlled through customizing the pattern and morphology of sensing electrodes as well as the modification of active materials. Compensation of temperature drift and selection of sensing mechanisms ensure the thermal stability of the system. The encapsulation of modules resists the interferences of proximity, normal pressure, and gas molecules at the same time. A double-sided partition layout with serpentine interconnections reduces the effect of motion artifacts and ensures simultaneous operation of electrochemical-sensing modules. Cooperation among decoupled modules acts as the bridge between the perception of ambience changes and the timely feedback of the human body. In addition, to sense the signal at the interface, modules for energy harvesting and storage are also integrated into the system to broaden its application scenarios.

Potentiometric pH Sensor Based on Flexible Screen-Printable Polyaniline Composite for Textile-Based Microfluidic Applications

Skin pH can be used for monitoring infections in a healing wound, the onset of dermatitis, and hydration in sports medicine, but many challenges exist in integrating conventional sensing materials into wearable platforms. We present the development of a flexible, textile-based, screen-printed electrode system for biosensing applications, and demonstrate flexible polyaniline (PANI) composite-based potentiometric sensors on a textile substrate for real-time pH measurement. The pH response of the optimized PANI/dodecylbenzene sulfonic acid/screen-printing ink composite is compared to electropolymerized and drop-cast PANI sensors via open circuit potential measurements. High sensitivity was observed for all sensors between pH 3-10, with a composite based on PANI emeraldine base, demonstrating sufficient response time and a linear sensitivity of -27.9 mV/pH. This exceeded prior flexible screen-printed pH sensors in which all parts of the sensor, including the pH sensing material, are screen-printed. Even better sensitivity was observed for a PANI emeraldine salt composite (-42.6 mV/pH), although the response was less linear. Furthermore, the sensor was integrated into a screen-printed microfluidic channel demonstrating sample isolation during measurement for wearable, micro cloth-based analytical devices. This is the first fully screen-printed flexible PANI composite pH sensor demonstrated on a textile substrate that can additionally be integrated with textile-based microfluidic channels.

Rational Design of Intelligent and Multifunctional Dressing to Promote Acute/Chronic Wound Healing

Currently, the clinic's treatment of acute/chronic wounds is still unsatisfactory due to the lack of functional and appropriate wound dressings. Intelligent and multifunctional dressings are considered the most advanced wound treatment modalities. It is essential to design and develop wound dressings with required functions according to the wound microenvironment in the clinical treatment. This work summarizes microenvironment characteristics of various common wounds, such as acute wound, diabetic wound, burns wound, scalded wound, mucosal wound, and ulcers wound. Furthermore, the factors of transformation from acute wounds to chronic wounds were analyzed. Then we focused on summarizing how researchers fully and thoroughly combined the complex microenvironment with modern advanced technology to ensure the usability and value of the dressing, such as photothermal-sensitive dressings, microenvironment dressing (pH-sensitive dressings, ROS-sensitive dressings, and osmotic pressure dressings), hemostatic dressing, guiding tissue regeneration dressing, microneedle dressings, and 3D/4D printing dressings. Finally, the revolutionary development of wound dressings and how to transform the existing advanced functional dressings into clinical needs as soon as possible have carried out a reasonable and meaningful outlook.

Intelligent Wearable Sensors Interconnected with Advanced Wound Dressing Bandages for Contactless Chronic Skin Monitoring: Artificial Intelligence for Predicting Tissue Regeneration

Toward the adoption of artificial intelligence-enabled wearable sensors interconnected with intelligent medical objects, this contactless multi-intelligent wearable technology provides a solution for healthcare to monitor hard-to-heal wounds and create optimal efficiencies for clinical professionals by minimizing the risk of disease infection. This article addressed a flexible artificial intelligence-guiding (FLEX-AI) wearable sensor that can be operated with a deep artificial neural network (deep ANN) algorithm for chronic wound monitoring via short-range communication toward a seamless, MXENE-attached, radio frequency-tuned, and wound dressing-integrated (SMART-WD) bandage. Based on a supervised training set of on-contact pH-responsive voltage output, the confusion matrix for healing-stage recognition from this deep ANN machine learning revealed an accuracy of 94.6% for the contactless measurement. The core analytical design of these smart bandages integrated wound dressing of poly(vinyl acrylic) gel@PANI/Cu₂O NPs for instigating pH-responsive current during the wound healing process. Effectively, a chip-free bandage tag was fabricated with a capacitive Mxene/PTFE electret and adhesive acrylic inductance to match the resonance frequency generated by the intelligent wearable antenna. Under zero-current electrochemical potential, the wound dressing attained a slope of -76 mV/pH. With the higher activation voltage applied toward the wound dressing electrodes, cuprous ions intercalated more into the hybrid PVA gel/PANI shell, resulting in an exponential increase of the two-terminal current response. The healing phase diagram was classified into regimes of fast-curing, slow-curing, and no-curing for skin disease treatment with corticosteroids. Ultimately, the near-field sensing technology offers adequate information for guiding treatment decisions as well as drug effectiveness for wound care.

Wearable Bioelectronics for Chronic Wound Management

Chronic wounds are a major healthcare issue and can adversely affect the lives of millions of patients around the world. The current wound management strategies have limited clinical efficacy due to labor-intensive lab analysis requirements, need for clinicians' experiences, long-term and frequent interventions, limiting therapeutic efficiency and applicability. The growing field of flexible bioelectronics enables a great potential for personalized wound care owing to its advantages such as wearability, low-cost, and rapid and simple application. Herein, recent advances in the development of wearable bioelectronics for monitoring and management of chronic wounds are comprehensively reviewed. First, the design principles and the key features of bioelectronics that can adapt to the unique wound milieu features are introduced. Next, the current state of wound biosensors and on-demand therapeutic systems are summarized and highlighted. Furthermore, we discuss the design criteria of the integrated closed loop devices. Finally, the future perspectives and challenges in wearable bioelectronics for wound care are discussed.

Flexible Sensors Based on Conductive Polymers

Conductive polymers have attracted wide attention since their discovery due to their unique properties such as good electrical conductivity, thermal and chemical stability, and low cost. With different possibilities of preparation and deposition on surfaces, they present unique and tunable structures. Because of the ease of incorporating different elements to form composite materials, conductive polymers have been widely used in a plethora of applications. Their inherent mechanical tolerance limit makes them ideal for flexible devices, such as electrodes for batteries, artificial muscles, organic electronics, and sensors. As the demand for the next generation of (wearable) personal and flexible sensing devices is increasing, this review aims to discuss and summarize the recent manufacturing advances made on flexible electrochemical sensors.

Low-Cost Flexible Glass-Based pH Sensor via Cold Atmospheric Plasma Deposition

Many commercially available pH sensors are fabricated with a glass membrane as the sensing component because of several advantages of glass-based electrodes such as versatility, high accuracy, and excellent stability in various conditions. However, because of their bulkiness and poor mechanical properties, conventional glass-based sensors are not ideal for wearable or flexible applications. Here, we report for the first time the fabrication of a flexible glass-based pH sensor suitable for biomedical and environmental applications where flexibility and stability of the sensor are critical for long-term and real-time monitoring. The sensor was fabricated via a simple and facile approach using the cold atmospheric plasma technique in which a pH sensitive silica coating was deposited from a siloxane precursor onto a carbon electrode. In order to increase the sensitivity and stability of the sensor, we employed a postprocessing step which involves annealing of the silica coated electrode at elevated temperatures. This process was optimized to ensure that the crucial properties such as porosity and hydration functionality were balanced to obtain the best and most reliable sensitivity of the sensor. Our sensitivity test results indicated that these sensors exhibit excellent and stable sensitivity with a slope of about 48 mV/pH (r² = 0.998) and selectivity across a pH range of 4 to 10 in the presence of various cations. The optimized sensor has shown stable sensitivity for a long period of time (30 h of immersion) and in different bending conditions. We demonstrate in this investigation that this flexible cost-effective pH sensor can withstand the sterilization process resulting from ultraviolet radiation and shows repeatable sensitivity with less than ±5 mV potential drift from the sensitivity values of the standard optimized sensor.

Recent advances in flexible and wearable sensors for monitoring chemical molecules

In recent years, real-time health management has received increasing attention, benefiting from the rapid development of flexible and wearable devices. Conventionally, flexible and wearable devices are used for collecting health data such as electrophysiological signals, blood pressure, heart rate, etc. The monitoring of chemical factors has shown growing significance, providing the basis for the screening, diagnosis, and treatment of many diseases. Nowadays, in order to understand the health status of the human body more comprehensively and accurately, researchers in the community have started putting effort into developing wearable devices for monitoring chemical factors. Progressively, more flexible chemical sensors with wearable real-time health-monitoring functionality have been developed thanks to advances relating to wireless communications and flexible electronics. In this review, we describe the variety of chemical molecules and information that can currently be monitored, including pH levels, glucose, lactate, uric acid, ion levels, cytokines, nutrients, and other biomarkers. This review analyzes the pros and cons of the most advanced wearable chemical sensors in terms of wearability. At the end of this review, we discuss the current challenges and development trends relating to flexible and wearable chemical sensors from the aspects of materials, electrode designs, and soft-hard interface connections.

Multifunctional hybrid skin patch for wearable smart healthcare applications

Recent advances in wearable patches have included various sensors to monitor either physiological signs, such as the heart rate and respiration rate, or metabolites. Nevertheless, most of these have focused only on a single physiological measurement at a time, which significantly inhibits the calibration of various biological signals and diagnostic facilities. In this study, a novel multifunctional hybrid skin patch was developed for the electrochemical analysis of sweat glucose levels and simultaneous monitoring of electrocardiograms (ECGs). Furthermore, pH and temperature sensors were co-integrated onto the same patch for the calibration of the glucose biosensor to prevent inevitable inhibition and weakening of enzyme activity due to changes in the sweat pH and temperature levels. The fabricated electrochemical glucose biosensor exhibited excellent linearity (R² = 0.9986) and sensitivity (29.10 μA mM^-1 cm^-2), covering the normal range of human sweat. The potentiometric pH sensor displayed a good response with an excellent sensitivity of -77.81 mV/pH and high linearity (R² = 0.991), indicating that it can distinguish variations in the typical pH range for human sweat. Furthermore, the P, QRS complex, and T peaks in the measured ECG waveforms could be clearly distinguished, indicating the reliability of the fabricated flexible dry electrodes for continuous monitoring. The fabricated skin patch overcomes the inconvenience of the mandatory attachment of multiple patches on the human body by fully integrating all the electrochemical and electrophysiological sensors on a single patch, thus facilitating advanced glycemic control and continuous ECG monitoring for smart management of chronic diseases and healthcare applications.

Highly Efficient Self-Healing Multifunctional Dressing with Antibacterial Activity for Sutureless Wound Closure and Infected Wound Monitoring

Wound healing represents a major clinical and public healthcare problem that is frequently challenged by infection risks, detrimental consequences on the surrounding tissues, and difficulties to monitor the healing process. Here we report on a novel self-healing, antibacterial, and multifunctional wound dressing for sutureless wound closure and real-time monitoring of the healing parameters. The self-healing elastomer contains cetyltrimethylammonium bromide (CTAB) and has high mechanical toughness (35 MJ m^-3 ), biocompatibility, and outstanding antibacterial activity (bactericidal rate is ≈90% in 12 h), enabling the wound dressing to effectively inhibit bacterial growth and accelerate infected wound healing. In vivo tests based on full-thickness skin incision model shows that the multifunctional wound dressing can help in contracting wound edges and facilitate wound closure and healing, as could be evidenced by notably dense and well-organized collagen deposition. The test provides an evidence that the integrated sensor array within the multifunctional wound dressing can monitor temperature, pH, and glucose level of the wound area in real-time, providing reliable and timely information of the condition of the wound. Ultimately, the reported multifunctional dressing would be of high value in managing the burden associated with wound healing via personalised monitoring and treatment approaches, digital and other people-centred solutions for health care.

A Review of Recent Advances in Flexible Wearable Sensors for Wound Detection Based on Optical and Electrical Sensing

Chronic wounds that are difficult to heal can cause persistent physical pain and significant medical costs for millions of patients each year. However, traditional wound care methods based on passive bandages cannot accurately assess the wound and may cause secondary damage during frequent replacement. With advances in materials science and smart sensing technology, flexible wearable sensors for wound condition assessment have been developed that can accurately detect physiological markers in wounds and provide the necessary information for treatment decisions. The sensors can implement the sensing of biochemical markers and physical parameters that can reflect the infection and healing process of the wound, as well as transmit vital physiological information to the mobile device through optical or electrical signals. Most reviews focused on the applicability of flexible composites in the wound environment or drug delivery devices. This paper summarizes typical biochemical markers and physical parameters in wounds and their physiological significance, reviews recent advances in flexible wearable sensors for wound detection based on optical and electrical sensing principles in the last 5 years, and discusses the challenges faced and future development. This paper provides a comprehensive overview for researchers in the development of flexible wearable sensors for wound detection.

Wearable Sensors for the Detection of Biomarkers for Wound Infection

Infection represents a major complication that can affect wound healing in any type of wound, especially in chronic ones. There are currently certain limitations to the methods that are used for establishing a clinical diagnosis of wound infection. Thus, new, rapid and easy-to-use strategies for wound infection diagnosis need to be developed. To this aim, wearable sensors for infection diagnosis have been recently developed. These sensors are incorporated into the wound dressings that are used to treat and protect the wound, and are able to detect certain biomarkers that can be correlated with the presence of wound infection. Among these biomarkers, the most commonly used ones are pH and uric acid, but a plethora of others (lactic acid, oxygenation, inflammatory mediators, bacteria metabolites or bacteria) have also been detected using wearable sensors. In this work, an overview of the main types of wearable sensors for wound infection detection will be provided. These sensors will be divided into electrochemical, colorimetric and fluorimetric sensors and the examples will be presented and discussed comparatively.

Progress of Wearable and Flexible Electrochemical Biosensors With the Aid of Conductive Nanomaterials

Conductive nanomaterials have recently gained a lot of interest due to their excellent physical, chemical, and electrical properties, as well as their numerous nanoscale morphologies, which enable them to be fabricated into a wide range of modern chemical and biological sensors. This study focuses mainly on current applications based on conductive nanostructured materials. They are the key elements in preparing wearable electrochemical Biosensors, including electrochemical immunosensors and DNA biosensors. Conductive nanomaterials such as carbon (Carbon Nanotubes, Graphene), metals and conductive polymers, which provide a large effective surface area, fast electron transfer rate and high electrical conductivity, are summarized in detail. Conductive polymer nanocomposites in combination with carbon and metal nanoparticles have also been addressed to increase sensor performance. In conclusion, a section on current challenges and opportunities in this growing field is forecasted at the end.

Harnessing Multifaceted Next-Generation Technologies for Improved Skin Wound Healing

Dysregulation of sequential and synchronized events of skin regeneration often results in the impairment of chronic wounds. Conventional wound dressings fail to trigger the normal healing mechanism owing to the pathophysiological conditions. Tissue engineering approaches that deal with the fabrication of dressings using various biomaterials, growth factors, and stem cells have shown accelerated healing outcomes. However, most of these technologies are associated with difficulties in scalability and cost-effectiveness of the products. In this review, we survey the latest developments in wound healing strategies that have recently emerged through the multidisciplinary approaches of bioengineering, nanotechnology, 3D bioprinting, and similar cutting-edge technologies to overcome the limitations of conventional therapies. We also focus on the potential of wearable technology that supports complete monitoring of the changes occurring in the wound microenvironment. In addition, we review the role of advanced devices that can precisely enable the delivery of nanotherapeutics, oligonucleotides, and external stimuli in a controlled manner. These technological advancements offer the opportunity to actively influence the regeneration process to benefit the treatment regime further. Finally, the clinical relevance, trajectory, and prospects of this field have been discussed in brief that highlights their potential in providing a beneficial wound care solution at an affordable cost.

Electronic Drugs: Spatial and Temporal Medical Treatment of Human Diseases

Recent advances in diagnostics and medicines emphasize the spatial and temporal aspects of monitoring and treating diseases. However, conventional therapeutics, including oral administration and injection, have difficulties meeting these aspects due to physiological and technological limitations, such as long-term implantation and a narrow therapeutic window. As an innovative approach to overcome these limitations, electronic devices known as electronic drugs (e-drugs) have been developed to monitor real-time body signals and deliver specific treatments to targeted tissues or organs. For example, ingestible and patch-type e-drugs could detect changes in biomarkers at the target sites, including the gastrointestinal (GI) tract and the skin, and deliver therapeutics to enhance healing in a spatiotemporal manner. However, medical treatments often require invasive surgical procedures and implantation of medical equipment for either short or long-term use. Therefore, approaches that could minimize implantation-associated side effects, such as inflammation and scar tissue formation, while maintaining high functionality of e-drugs, are highly needed. Herein, the importance of the spatial and temporal aspects of medical treatment is thoroughly reviewed along with how e-drugs use cutting-edge technological innovations to deal with unresolved medical challenges. Furthermore, diverse uses of e-drugs in clinical applications and the future perspectives of e-drugs are discussed.

Multifunctional Dressing for Wound Diagnosis and Rehabilitation

A wound dressing is a sterile pad or compress that is used in direct contact with a wound to help it heal and prevent further issues or complications. Though wound healing is an intricate dynamic process that involves multiple biomolecular species, conventional wound dressings have a limited ability to provide timely information of abnormal conditions, missing the best time for early treatment. The current perspective presents and discusses the design and development of smart wound dressings that are integrated with multifunctional materials, wearable sensors and drug delivery systems as well as their application ranging from wound monitoring to timely application of therapeutics. The perspective also discusses the ongoing challenges and exciting opportunities associated with the development of wearable sensor-based smart wound dressing and provide critical insights into wound healing monitoring and management.

Novel Self-Calibrating Amperometric and Ratiometric Electrochemical Nanotip Microsensor for pH Measurement in Rat Brain

Brain pH has been proven to be a key factor in maintaining normal brain function. The relationship between local pH fluctuation and brain disease has not been extensively studied due to lack of the accurate in situ analysis technology. Herein, we have for the first time proposed a voltammetric pH sensor by measuring the ratio of current signals instead of the previously reported potential based on the Nernst equation. Single-walled carbon nanotubes (CNT) were first self-assembled on the electrode surface of a carbon-fiber nanotip electrode (CFNE). Then, poly-o-phenylenediamine (PoPD) molecules were deposited as pH-responsive molecules through in situ electrochemical polymerization. The compact CFNE/CNT/PoPD exhibited a good redox process with the on-off-on ratiometric electrochemical response to pH ranging from 4.5 to 8.2, providing self-correction for in situ pH detection. Thus, the proposed sensor enabled the accurate measurement of pH with excellent selectivity even in the presence of proteins or electroactive species. In addition, the sensor showed high repeatability, reproducibility, and reversibility in measuring pH and even demonstrated good stability when it was exposed to air for 5 months. Finally, we successfully detected the fluctuation of pH in rat brains with cerebral ischemia and rat whole blood. Overall, this research not only provides a good tool for the detection of rat brain pH but also provides a new strategy for further designing nanosensors for intracellular or subcellular pH.

Three-Dimensional (3D) Laser-Induced Graphene: Structure, Properties, and Application to Chemical Sensing

Notwithstanding its relatively recent discovery, graphene has gone through many evolution steps and inspired a multitude of applications in many fields, from electronics to life science. The recent advancements in graphene production and patterning, and the inclusion of two-dimensional (2D) graphenic materials in three-dimensional (3D) superstructures, further extended the number of potential applications. In this Review, we focus on laser-induced graphene (LIG), an intriguing 3D porous graphenic material produced by direct laser scribing of carbonaceous precursors, and on its applications in chemical sensors and biosensors. LIG can be shaped in different 3D forms with a high surface-to-volume ratio, which is a valuable characteristic for sensors that typically rely on phenomena occurring at surfaces and interfaces. Herein, an overview of LIG, including synthesis from various precursors, structure, and characteristic properties, is first provided. The discussion focuses especially on transport and surface properties, and on how these can be controlled by tuning the laser processing. Progresses and trends in LIG-based chemical sensors are then reviewed, discussing the various transduction mechanisms and different LIG functionalization procedures for chemical sensing. A comparative evaluation of sensors performance is then provided. Finally, sensors for glucose detection are reviewed in more detail, since they represent the vast majority of LIG-based chemical sensors.

Electrochemical deposition of highly hydrophobic perfluorinated polyaniline film for biosensor applications

Highly hydrophobic perfluorinated polyaniline thin films with water contact angle of ∼140° and low internal resistance properties are prepared through electrochemical polymerization. UV-visible spectroscopy demonstrates a gradual evolution of the polaron band which indicates the electronic conductive properties of the polymers. Simultaneous possession of the water-repelling property and electron conductivity for superhydrophobic perfluorinated polyaniline leads to a unique polymer that is suitable as a solid contact in ion-selective electrodes for in situ monitoring of pH changes during early stages of inflammation and septic shock. The superhydrophobic properties should suppress interactions with interfering salts and proteins, and the sensitivity towards protons could be monitored by measuring the phase boundary potential, which depends on the H⁺ concentration. The potentiometric measurements demonstrate a fast response with a slope of 44.4 ± 0.2 mV per unit pH. The presence of interfering ions and/or human serum albumin does not have any significant effect on the performance of the perfluorinated film. Moreover, it is demonstrated that the response of the perfluorinated film is reversible within the biomedically relevant pH range from 4.0 to 8.5, and stable over time.

Simultaneous possession of the water-repelling property and electron conductivity for superhydrophobic perfluorinated polyaniline leads to a unique polymer that is suitable for in situ monitoring of pH changes during early stages of inflammation and septic shock.

Selective Direct Laser Writing of Pyrolytic Carbon Microelectrodes in Absorber-Modified SU-8

Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 photoresist by irradiation with a low-power, 806 nm, continuous wave, semiconductor-diode laser. The SU-8 was modified by adding Pro-Jet 800NP (FujiFilm) in order to ensure absorbance in the 800 nm range. The SU-8 precursor with absorber was successfully converted into pyrolytic carbon upon laser irradiation, which was not possible without an absorber. We demonstrated that the local laser pyrolysis (LLP) process in an inert nitrogen atmosphere with higher laser power and lower scan speed resulted in higher electrical conductance. The maximum conductivity achieved for a laser-pyrolyzed line was 14.2 ± 3.3 S/cm, with a line width and thickness of 28.3 ± 2.9 µm and 6.0 ± 1.0 µm, respectively, while the narrowest conductive line was just 13.5 ± 0.4 µm wide and 4.9 ± 0.5 µm thick. The LLP process seemed to be self-limiting, as multiple repetitive laser scans did not alter the properties of the carbonized lines. The direct laser writing of adjacent lines with an insulating gap down to ≤5 µm was achieved. Finally, multiple lines were seamlessly joined and intersected, enabling the writing of more complex designs with branching electrodes and the porosity of the carbon lines could be controlled by the scan speed.

Wearable Sensors and Systems for Wound Healing-Related pH and Temperature Detection

Wound healing is a complex tissue regeneration process involving many changes in multiple physiological parameters. The pH and temperature of a wound site have long been recognized as important biomarkers for assessing wound healing status. For effective wound management, wound dressings integrated with wearable sensors and systems used for continuous monitoring of pH and temperature have received much attention in recent years. Herein, recent advances in the development of wearable pH and temperature sensors and systems based on different sensing mechanisms for wound status monitoring and treatment are comprehensively summarized. Challenges in the areas of sensing performance, infection identification threshold, large-area 3-dimensional detection, and long-term reliable monitoring in current wearable sensors/systems and emerging solutions are emphasized, providing critical insights into the development of wearable sensors and systems for wound healing monitoring and management.