Early detection and monitoring of chronic wounds using low-cost, omniphobic paper-based smart bandages

Electrochemical Detection of Multianalyte Biomarkers in Wound Healing Efficacy

The targeted diagnosis and effective treatments of chronic skin wounds remain a healthcare burden, requiring the development of sensors for real-time monitoring of wound healing activity. Herein, we describe an adaptable method for the fabrication of carbon ultramicroelectrode arrays (CUAs) on flexible substrates with the goal to utilize this sensor as a wearable device to monitor chronic wounds. As a proof-of-concept study, we demonstrate the electrochemical detection of three electroactive analytes as biomarkers for wound healing state in simulated wound media on flexible CUAs. Notably, to follow pathogenic responses, we characterize analytical figures of merit for identification and monitoring of bacterial warfare toxin pyocyanin (PYO) secreted by the opportunistic human pathogen Pseudomonas aeruginosa. We also demonstrate the detection of uric acid (UA) and nitric oxide (NO^•), which are signaling molecules indicative of wound healing and immune responses, respectively. The electrochemically determined limit of detection (LOD) and linear dynamic range (LDR) for PYO, UA, and NO^• fall within the clinically relevant concentrations. Additionally, we demonstrate the successful use of flexible CUAs for quantitative, electrochemical detection of PYO from P. aeruginosa strains and cellular NO^• from immune cells in the wound matrix. Moreover, we present an electrochemical examination of the interaction between PYO and NO^•, providing insight into pathogen-host responses. Finally, the effects of the antimicrobial agent, silver (Ag⁺), on P. aeruginosa PYO production rates are investigated on flexible CUAs. Our electrochemical results show that the addition of Ag⁺ to P. aeruginosa in wound simulant decreases PYO secretion rates.

Highly Stretchable Fiber-Based Potentiometric Ion Sensors for Multichannel Real-Time Analysis of Human Sweat

Wearable potentiometric ion sensors are attracting attention for real-time ion monitoring in biological fluids. One of the key challenges lies in keeping the analytical performances under a stretchable state. Herein, we report a highly stretchable fiber-based ion-selective electrode (ISE) prepared by coating an ion-selective membrane (ISM) on a stretchable gold fiber electrode. The fiber ISE ensures high stretchability up to 200% strain with only 2.1% increase in resistance of the fiber electrode. Owing to a strong attachment between the ISM and gold fiber electrode substrate, the ISE discloses favorable stability and potential repeatability. The Nernst slope of the ion response fluctuates from 59.2 to 57.4 mV/dec between 0 and 200% strain. Minor fluctuation of the intercept (E⁰) (±4.97 mV) also results. The ISE can endure 1000 cycles at the maximum stretch. Sodium, chloride, and pH fiber sensors were fabricated and integrated into a hairband for real-time analysis of human sweat. The result displays a high accuracy compared with ex situ analysis. The integrated sensors were calibrated before and just after on-body measurements, and they offer reliable results for sweat analysis.

Modern evolution of paper-based analytical devices for wearable use: from disorder to order

Paper devices have attracted great attention for their rapid development in multiple fields, such as life sciences, biochemistry, and materials science. When manufacturing paper chips, flexible materials, such as cellulose paper or other porous flexible membranes, can offer several advantages in terms of their flexibility, lightweight, low cost, safety and wearability. However, traditional cellulose paper sheets with chaotic cellulose fiber constitutions do not have special structures and optical characteristics, leading to poor repeatability and low sensitivity during biochemical sensing, limiting their wide application. Recent evidence showed that the addition of ordered structure provides a promising method for manufacturing intelligent flexible devices, making traditional flexible devices with multiple functions (microfluidics, motion detection and optical display). There is an urgent need for an overall summary of the evolution of paper devices so that readers can fully understand the field. Hence, in this review, we summarized the latest developments in intelligent paper devices, starting with the fabrication of paper and smart flexible paper devices, in the fields of biology, chemistry, electronics, etc. First, we outlined the manufacturing methods and applications of both traditional cellulose paper devices and modern smart devices based on pseudopaper (order paper). Then, considering different materials, such as cellulose, nitrocellulose, nature sourced photonic crystals (photonic crystals sourced from nature directly) and artificial photonic crystals, we summarized a new type of smart flexible device containing an ordered structure. Next, the applications of paper devices in biochemical sensing, wearable sensing, and cross-scale sensing were discussed. Finally, we summarized the development direction of this field. The aim of this review is to take an integral cognition approach to the development of smart flexible paper devices in multiple fields and promote communications between materials science, biology, chemistry and electrical science.

Advances in Sweat Wearables: Sample Extraction, Real-Time Biosensing, and Flexible Platforms

Wearable biosensors for sweat-based analysis are gaining wide attention due to their potential use in personal health monitoring. Flexible wearable devices enable sweat analysis at the molecular level, facilitating noninvasive monitoring of physiological states via real-time monitoring of chemical biomarkers. Advances in sweat extraction technology, real-time biosensors, stretchable materials, device integration, and wireless digital technologies have led to the development of wearable sweat-biosensing devices that are light, flexible, comfortable, aesthetic, affordable, and informative. Herein, we summarize recent advances of sweat wearables from the aspects of sweat extraction, fabrication of stretchable biomaterials, and design of biosensing modules to enable continuous biochemical monitoring, which are essential for a biosensing device. Key chemical components of sweat, sweat capture methodologies, and considerations of flexible substrates for integrating real-time biosensors with electronics to bring innovations in the art of wearables are elaborated. The strategies and challenges involved in improving the wearable biosensing performance and the perspectives for designing sweat-based wearable biosensing devices are discussed.

Nanoparticle-Based Wound Dressing: Recent Progress in the Detection and Therapy of Bacterial Infections

Bacterial infections in wounds often delay the healing process, and may seriously threaten human life. It is urgent to develop wound dressings to effectively detect and treat bacterial infections. Nanoparticles have been extensively used in wound dressings because of their specific properties. This review highlights the recent progress on nanoparticle-based wound dressings for bacterial detection and therapy. Specifically, nanoparticles have been applied as intrinsic antibacterial agents or drug delivery vehicles to treat bacteria in wounds. Moreover, nanoparticles with photothermal or photodynamic property have also been explored to endow wound dressings with significant optical properties to further enhance their bactericidal effect. More interestingly, nanoparticle-based smart dressings have been recently explored for bacteria detection and treatment, which enables an accurate assessment of bacterial infection and a more precise control of on-demand therapy.

Multisensor Systems and Arrays for Medical Applications Employing Naturally-Occurring Compounds and Materials

The significant improvement of quality of life achieved over the last decades has stimulated the development of new approaches in medicine to take into account the personal needs of each patient. Precision medicine, providing healthcare customization, opens new horizons in the diagnosis, treatment and prevention of numerous diseases. As a consequence, there is a growing demand for novel analytical devices and methods capable of addressing the challenges of precision medicine. For example, various types of sensors or their arrays are highly suitable for simultaneous monitoring of multiple analytes in complex biological media in order to obtain more information about the health status of a patient or to follow the treatment process. Besides, the development of sustainable sensors based on natural chemicals allows reducing their environmental impact. This review is concerned with the application of such analytical platforms in various areas of medicine: analysis of body fluids, wearable sensors, drug manufacturing and screening. The importance and role of naturally-occurring compounds in the development of electrochemical multisensor systems and arrays are discussed.

Conformal, waterproof electronic decals for wireless monitoring of sweat and vaginal pH at the point-of-care

While the monitoring of pH has demonstrated to be an effective technique to monitor an individual's health state, the design of wearable biosensors is subject to critical challenges, such as high fabrication costs, thermal drift, sensitivity to moisture, and the limited applicability for users with metal allergies. This work describes the low-cost fabrication of waterproof electronic decals (WPEDs): highly conformable disposable biosensors capable of monitoring sweat and vaginal pH. WPEDs contain a polyaniline/silver microflakes sensing layer optimized for accurate impedance-based pH quantification across the clinically relevant range of variation of most biofluids. WPEDs also contain a heating layer that serves to both stimulate sweating and prevent saturation of the sensing area, reducing the variability of the measurements. The conformability of WPEDs enables their simple and allergy-free attachment to skin, where they can monitor sweat pH, or to the surface of paper-based sample containers, for the pH-based diagnosis of bacterial vaginosis. WPEDs are mostly transparent, self-adhesive, breathable, flexible, moisture-insensitive, and able to maintain their accuracy under significant mechanical and thermal stresses. A cost-effective wearable and portable impedance analyzer wirelessly transmits pH data in real-time to the smartphone of the user, where a custom-developed App enables long term monitoring and telemedicine applications. Our results demonstrate the feasibility of using inexpensive single-use WPEDs and a reusable, wireless impedance analyzer to provide a wearable solution for the real-time monitoring of sweat pH and the accurate at-home diagnosis of bacterial vaginosis, improving the capabilities of current low-cost, point-of-care diagnostic tests.

Recent Developments of Flexible and Stretchable Electrochemical Biosensors

The skyrocketing popularity of health monitoring has spurred increasing interest in wearable electrochemical biosensors. Compared with the traditionally rigid and bulky electrochemical biosensors, flexible and stretchable devices render a unique capability to conform to the complex, hierarchically textured surfaces of the human body. With a recognition element (e.g., enzymes, antibodies, nucleic acids, ions) to selectively react with the target analyte, wearable electrochemical biosensors can convert the types and concentrations of chemical changes in the body into electrical signals for easy readout. Initial exploration of wearable electrochemical biosensors integrates electrodes on textile and flexible thin-film substrate materials. A stretchable property is needed for the thin-film device to form an intimate contact with the textured skin surface and to deform with various natural skin motions. Thus, stretchable materials and structures have been exploited to ensure the effective function of a wearable electrochemical biosensor. In this mini-review, we summarize the recent development of flexible and stretchable electrochemical biosensors, including their principles, representative application scenarios (e.g., saliva, tear, sweat, and interstitial fluid), and materials and structures. While great strides have been made in the wearable electrochemical biosensors, challenges still exist, which represents a small fraction of opportunities for the future development of this burgeoning field.

Recent progress, challenges, and prospects of fully integrated mobile and wearable point-of-care testing systems for self-testing

The rapid growth of research in the areas of chemical and biochemical sensors, lab-on-a-chip, mobile technology, and wearable electronics offers an unprecedented opportunity in the development of mobile and wearable point-of-care testing (POCT) systems for self-testing. Successful implementation of such POCT technologies leads to minimal user intervention during operation to reduce user errors; user-friendly, easy-to-use and simple detection platforms; high diagnostic sensitivity and specificity; immediate clinical assessment; and low manufacturing and consumables costs. In this review, we discuss recent developments in the field of highly integrated mobile and wearable POCT systems. In particular, aspects of sample handling platforms, recognition elements and sensing methods, and new materials for signal transducers and powering devices for integration into mobile or wearable POCT systems will be highlighted. We also summarize current challenges and future prospects for providing personal healthcare with sample-in result-out mobile and wearable POCT.

Lock Stock and Barrel of Wound Healing

Any kind of injury may lead to wound formation. As per World Health Organization Report, "more than 5 million people die each year due to injuries. This accounts for 9% of the world's population death, nearly 1.7 times the number of fatalities that result from HIV/AIDS, tuberculosis and malaria combined. In addition, ten million people suffer from non-fatal injuries which require treatment". This scenario leads to increased health and economic burden worldwide. Rapid wound healing is exigent subject-field in the health care system. It is imperative to be updated on wound care strategies as impaired wound healing may lead to chronic, non-healing wounds and thus further contributes to the national burden. This article is a comprehensive review of wound care strategies. The first and second part of this review article focuses on the understanding of wound, its types and human body's healing mechanism. Wound healing is natural, highly coordinated process that starts on its own, immediately after the injury. However, individual health condition influences the healing process. Discussion of factors affecting wound healing has also been included. Next part includes the detailed review of diverse wound healing strategies that have already been developed for different types of wound. A detailed description of various polymers that may be used has been discussed. Amongst drug delivery systems, oligomers, dendrimers, films, gels, different nano-formulations, like nanocomposites, nanofibers, nanoemulsions and nanoparticles are discussed. Emphasis on bandages has been made in this article.

Low-Cost and Highly Sensitive Wearable Sensor Based on Napkin for Health Monitoring

The development of sensors with high sensitivity, good flexibility, low cost, and capability of detecting multiple inputs is of great significance for wearable electronics. Herein, we report a napkin-based wearable capacitive sensor fabricated by a novel, low-cost, and facile strategy. The capacitive sensor is composed of two pieces of electrode plates manufactured by spontaneous assembly of silver nanowires (NWs) on a polydimethylsiloxane (PDMS)-patterned napkin. The sensor possesses high sensitivity (>7.492 kPa⁻¹), low cost, and capability for simultaneous detection of multiple signals. We demonstrate that the capacitive sensor can be applied to identify a variety of human physiological signals, including finger motions, eye blinking, and minute wrist pulse. More interestingly, the capacitive sensor comfortably attached to the temple can simultaneously monitor eye blinking and blood pulse. The demonstrated sensor shows great prospects in the applications of human–machine interface, prosthetics, home-based healthcare, and flexible touch panels.

Simultaneous electrophysiological recording and self-powered biosignal monitoring using epidermal, nanotexturized, triboelectronic devices

The fabrication of multifunctional epidermal electronic devices capable of efficiently reading electrophysiological signals and converting low-amplitude mechanical signals into electric outputs promises to pave the way towards the development of self-powered wearable sensors, smart consumer electronics, and human-machine interfaces. This article describes the scalable and cost-effective fabrication of epidermal, nanotexturized, triboelectronic devices (EnTDs). EnTDs can be conformably worn on the skin and efficiently monitor electrophysiological signals, temperature, and hydration levels. EnTDs, while measuring electrophysiological signals, can also convert imperceptible time-variant body motions into electrical signals using a nanotexturized triboelectric layer, enabling the self-powered monitoring of respiration, swallowing, and arterial pulse. These results suggest the potential of EnTDs as a new class of multifunctional skin-like sensors for biomedical monitoring and self-powered sensing applications.

Two-layer Electrospun System Enabling Wound Exudate Management and Visual Infection Response

The spread of antimicrobial resistance calls for chronic wound management devices that can engage with the wound exudate and signal infection by prompt visual effects. Here, the manufacture of a two-layer fibrous device with independently-controlled exudate management capability and visual infection responsivity was investigated by sequential free surface electrospinning of poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) and poly(acrylic acid) (PAA). By selecting wound pH as infection indicator, PMMA-co-MAA fibres were encapsulated with halochromic bromothymol blue (BTB) to trigger colour changes at infection-induced alkaline pH. Likewise, the exudate management capability was integrated via the synthesis of a thermally-crosslinked network in electrospun PAA layer. PMMA-co-MAA fibres revealed high BTB loading efficiency (>80 wt.%) and demonstrated prompt colour change and selective dye release at infected-like media (pH > 7). The synthesis of the thermally-crosslinked PAA network successfully enabled high water uptake (WU = 1291 ± 48 - 2369 ± 34 wt.%) and swelling index (SI = 272 ± 4 - 285 ± 3 a.%), in contrast to electrospun PAA controls. This dual device functionality was lost when the same building blocks were configured in a single-layer mesh of core-shell fibres, whereby significant BTB release (~70 wt.%) was measured even at acidic pH. This study therefore demonstrates how the fibrous configuration can be conveniently manipulated to trigger structure-induced functionalities critical to chronic wound management and monitoring.

Wearable and Implantable Epidermal Paper-Based Electronics

Traditional manufacturing methods and materials used to fabricate epidermal electronics for physiological monitoring, transdermal stimulation, and therapeutics are complex and expensive, preventing their adoption as single-use medical devices. This work describes the fabrication of epidermal, paper-based electronic devices (EPEDs) for wearable and implantable applications by combining the spray-based deposition of silanizing agents, highly conductive nanoparticles, and encapsulating polymers with laser micromachining. EPEDs are inexpensive, stretchable, easy to apply, and disposable by burning. The omniphobic character and fibrous structure of EPEDs make them breathable, mechanically stable upon stretching, and facilitate their use as electrophysiological sensors to record electrocardiograms, electromyograms, and electrooculograms, even under water. EPEDs can also be used to provide thermotherapeutic treatments to joints, map temperature spatially, and as wirelessly powered implantable devices for stimulation and therapeutics. This work makes epidermal electronic devices accessible to high-throughput manufacturing technologies and will enable the fabrication of a variety of wearable medical devices at a low cost.