Stretchable and Conductive Composite Structural Color Hydrogel Films as Bionic Electronic Skins

Machine Learning Assisted Electronic/Ionic Skin Recognition of Thermal Stimuli and Mechanical Deformation for Soft Robots

Soft robots have the advantage of adaptability and flexibility in various scenarios and tasks due to their inherent flexibility and mouldability, which makes them highly promising for real-world applications. The development of electronic skin (E-skin) perception systems is crucial for the advancement of soft robots. However, achieving both exteroceptive and proprioceptive capabilities in E-skins, particularly in terms of decoupling and classifying sensing signals, remains a challenge. This study presents an E-skin with mixed electronic and ionic conductivity that can simultaneously achieve exteroceptive and proprioceptive, based on the resistance response of conductive hydrogels. It is integrated with soft robots to enable state perception, with the sensed signals further decoded using the machine learning model of decision trees and random forest algorithms. The results demonstrate that the newly developed hydrogel sensing system can accurately predict attitude changes in soft robots when subjected to varying degrees of pressing, hot pressing, bending, twisting, and stretching. These findings that multifunctional hydrogels combine with machine learning to decode signals may serve as a basis for improving the sensing capabilities of intelligent soft robots in future advancements.

Biomimetic Mechanically Robust Chiroptical Hydrogel Enabled by Hierarchical Bouligand Structure Engineering

Natural bouligand structures enable crustacean exoskeletons and fruits to strike a combination of exceptional mechanical robustness and brilliant chiroptical properties owing to multiscale structural hierarchy. However, integrating such a high strength-stiffness-toughness combination and photonic functionalities into synthetic hydrogels still remains a grand challenge. In this work, we report a simple yet general biomimetic strategy to construct an ultrarobust chiroptical hydrogel by closely mimicking the natural bouligand structure at multilength scale. The hierarchical structural engineering of long-range ordered cellulose nanocrystals' bouligand structure, well-defined poly(vinyl alcohol) nanocrystalline domains, and dynamic interfacial interaction synergistically contributes to the integration of high strength (23.3 MPa), superior modulus (264 MPa), and high toughness (54.7 MJ m-3), as well as extraordinary impact resistance, which far exceed their natural counterparts and synthetic photonic hydrogels. More importantly, seamless chiroptical and solvent-responsive patterns with high resolution can also be scalably integrated into the hydrogel by localized manipulation of the photonic band, while maintaining good ionic conductivity. Such exceptional mechanical-photonic combination holds tremendous potential for applications in wearable sensors, encryption, displays, and soft robotics.

Mechanical Field Guiding Structure Design Strategy for Meta-Fiber Reinforced Hydrogel Composites by Deep Learning

Fiber-reinforced hydrogel composites are widely employed in many engineering applications, such as drug release, and flexible electronics, with more flexible mechanical properties than pure hydrogel materials. Comparing to the hydrogel strengthened by continuous fiber, the meta-fiber reinforced hydrogel provides stronger individualized design ability of deformation patterns and tunable stiffness, especially for the elaborate applications in joint, cartilage, and organ. In this paper, a novel structure design strategy based on deep learning algorithm is proposed for hydrogel reinforced by meta-fiber to achieve targeted mechanical properties, such as stress and displacement fields. A solid mechanic model for meta-fiber reinforced hydrogel is first developed to construct the dataset of fiber distribution and the corresponding mechanical properties of the composite. Generative adversarial network (GAN) is then trained to characterize the relationship between stress or displacement field, and meta-fiber distribution. The well-trained GAN is implemented to design meta-fiber reinforced hydrogel composite structure under specific operation conditions. The results show that the deep learning method may efficiently predict the structure of the hydrogel composite with satisfied confidence, and has great potential for applications in drug delivery and flexible electronics.

Electronic Skin for Health Monitoring Systems: Properties, Functions, and Applications

Electronic skin (e-skin), a skin-like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E-skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e-skin, laying the foundation for the application of next-generation wearable medical technologies and devices. Herein, the properties required for e-skin health monitoring devices to achieve long-term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e-skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e-skin and health monitoring systems.

3D Printing Silk Fibroin/Polyacrylamide Triple-Network Composite Hydrogels with Stretchability, Conductivity, and Strain-Sensing Ability as Bionic Electronic Skins

Electronic skins have received increasing attention due to their great application potential in wearable electronics. Meanwhile, tremendous efforts are still needed for the fabrication of multifunctional composite hydrogels with complex structures for electronic skins via simple methods. In this work, a novel three-dimensional (3D) printing composite hydrogel with stretchability, conductivity, and strain-sensing ability is produced using a one-step photocuring method to achieve a dual-signal response of the electronic skin. The composite hydrogel exhibits a triple-network structure composed of silk microfibers (SMF), regenerated silk fibroin (RSF), and polyacrylamide (PAM). The establishment of triple networks is based on the electrostatic interaction between SMF and RSF, as well as the chemically cross-linked RSF and PAM. Thanks to its specific structure and components, the composite hydrogel possesses enhanced mechanical properties (elastic modulus of 140 kPa, compressive stress of 21 MPa, and compression modulus of 600 kPa) and 3D printability while retaining stretchability and flexibility. The interaction between negatively charged SMF and cations in phosphate-buffered saline endows the composite hydrogel with good conductivity and strain-sensing ability after immersion in a low-concentration (10 mM) salt solution. Moreover, the 3D printing composite hydrogel scaffold successfully realizes real-time monitoring. Therefore, the proposed hydrogel-based ionic sensor is promising for skin tissue engineering, real-time monitoring, soft robotics, and human-machine interfaces.

Stimuli‐Responsive Hydrogels for Antibacterial Applications

Hydrogels have emerged as promising candidates for biomedical applications, especially in the field of antibacterial therapeutics, due to their unique structural properties, highly tunable physicochemical properties, and excellent biocompatibility. The integration of stimuli-responsive functions into antibacterial hydrogels holds the potential to enhance their antibacterial properties and therapeutic efficacy, dynamically responding to different external or internal stimuli, such as pH, temperature, enzymes, and light. Therefore, this review describes the applications of hydrogel dressings responsive to different stimuli in antibacterial therapy. The collaborative interaction between stimuli-responsive hydrogels and antibacterial materials is discussed. This synergistic approach, in contrast to conventional antibacterial materials, not only amplifies the antibacterial effect but also alleviates adverse side effects and diminishes the incidence of multiple infections and drug resistance. The review provides a comprehensive overview of the current challenges and outlines future research directions for stimuli-responsive antibacterial hydrogels. It underscores the imperative for ongoing interdisciplinary research aimed at unraveling the mechanisms of wound healing. This understanding is crucial for optimizing the design and implementation of stimuli-responsive antibacterial hydrogels. Ultimately, this review aims to offer scientific guidance for the development and practical clinical application of stimuli-responsive antibacterial hydrogel dressings.

Ultrasensitive Biomimetic Skin with Multimodal and Photoelectric Dual-Signal Sensing

Mimicking biological skin enabling direct, intelligent interaction between users and devices, multimodal sensing with optical/electrical (OE) output signals is urgently required. Owing to this, this work aims to logically design a stretchable OE biomimetic skin (OE skin), which can sensitively sense complex external stimuli of pressure, strain, temperature, and localization. The OE skin consists of elastic thin polymer-stabilized cholesteric liquid crystal films, an ion-conductive hydrogel layer, and an elastic protective membrane formed with thin polydimethylsiloxane. The as-designed OE skin exhibits customizable structural color on demand, good thermochromism, and excellent mechanochromism, with the ability to extend the full visible spectrum, a good linearity of over 0.99, fast response speed of 93 ms, and wide temperature range of 119 °C. In addition, the conduction resistance variation of ion-conductive hydrogel exhibits excellent sensing capabilities under pressure, stretch, and temperature, endowing a good linearity of 0.99998 (stretching from 0 to 150%) and high thermal sensitivity of 0.86% per °C. Such an outstanding OE skin provides design concepts for the development of multifunctional biomimetic skin used in human-machine interaction and can find wide applications in intelligent wearable devices and human-machine interactions.

High-Strength, High-Swelling-Resistant, High-Sensitivity Hydrogel Sensor Prepared with Wood That Retains Lignin

Wood-derived hydrogels possess satisfactory longitudinal strength but lack excellent swelling resistance and dry shrinkage resistance when achieving high anisotropy. In this study, we displayed the preparation of highly dimensional stable wood/polyacrylamide hydrogels (wood/PAM-Al3+). The alkali-treated wood retains lignin as the skeleton of the hydrogel. Second, Al ions were added to the metal coordination with lignin. Finally, by employing free radical polymerization, we construct a conductive electronic network using polyaniline within the wood/PAM-Al3+ matrix to create the flexible sensor. This approach leverages lignin's integrated structure within the middle lamella to provide enhanced swelling resistance and stronger binding strength in the transverse direction. Furthermore, coordination between lignin and Al ions improves the mechanical strength of the wood hydrogel. Polyaniline provides stable linear pressure and temperature responses. The wood/PAM-Al3+ exhibits a transverse swelling ratio of 3.90% while achieving a longitudinal tensile strength of 20.5 MPa. This high-strength and high-stability sensor is capable of monitoring macroscale human behavior. Therefore, this study presents a simple yet innovative strategy for constructing tough hydrogels while also establishing an alternative pathway for exploring lignin networks in new functional materials development.

Advancements in Skin-Mediated Drug Delivery: Mechanisms, Techniques, and Applications

Skin-mediated drug delivery methods currently are receiving significant attention as a promising approach for the enhanced delivery of drugs through the skin. Skin-mediated drug delivery offers the potential to overcome the limitations of traditional drug delivery methods, including oral administration and intravenous injection. The challenges associated with drug permeation through layers of skin, which act as a major barrier, are explored, and strategies to overcome these limitations are discussed in detail. This review categorizes skin-mediated drug delivery methods based on the means of increasing drug permeation, and it provides a comprehensive overview of the mechanisms and techniques associated with these methods. In addition, recent advancements in the application of skin-mediated drug delivery are presented. The review also outlines the limitations of ongoing research and suggests future perspectives of studies regarding the skin-mediated delivery of drugs.

TEMPO bacterial cellulose and MXene nanosheets synergistically promote tough hydrogels for intelligent wearable human-machine interaction

Conductive hydrogels have received increasing attention in the field of wearable electronics, but they also face many challenges such as temperature tolerance, biocompatibility, and stability of mechanical properties. In this paper, a double network hydrogel of MXene/TEMPO bacterial cellulose (TOBC) system is proposed. Through solvent replacement, the hydrogel exhibits wide temperature tolerance (-20-60 °C) and stable mechanical properties. A large number of hydrogen bonds, MXene/TOBC dynamic three-dimensional network system, and micellar interactions endow the hydrogel with excellent mechanical properties (elongation at break ~2800 %, strength at break ~420 kPa) and self-healing ability. The introduction of tannic acid prevents the oxidation of MXene and the loss of electrical properties of the hydrogel. In addition, the sensor can also quickly (74 ms) and sensitive (gauge factor = 15.65) wirelessly monitor human motion, and the biocompatibility can well avoid the stimulation when it comes into contact with the human body. This series of research work reveals the fabrication of MXene-like flexible wearable electronic devices based on self-healing, good cell compatibility, high sensitivity, wide temperature tolerance and durability, which can be used in smart wearable, wireless monitoring, human-machine Interaction and other aspects show great application potential.

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

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

Recent progress and treatment strategy of pectin polysaccharide based tissue engineering scaffolds in cancer therapy, wound healing and cartilage regeneration

Natural polymers and its mixtures in the form of films, sponges and hydrogels are playing a major role in tissue engineering and regenerative medicine. Hydrogels have been extensively investigated as standalone materials for drug delivery purposes as they enable effective encapsulation and sustained release of drugs. Biopolymers are widely utilised in the fabrication of hydrogels due to their safety, biocompatibility, low toxicity, and regulated breakdown by human enzymes. Among all the biopolymers, polysaccharide-based polymer is well suited to overcome the limitations of traditional wound dressing materials. Pectin is a polysaccharide which can be extracted from different plant sources and is used in various pharmaceutical and biomedical applications including cartilage regeneration. Pectin itself cannot be employed as scaffolds for tissue engineering since it decomposes quickly. This article discusses recent research and developments on pectin polysaccharide, including its types, origins, applications, and potential demands for use in AI-mediated scaffolds. It also covers the materials-design process, strategy for implementation to material selection and fabrication methods for evaluation. Finally, we discuss unmet requirements and current obstacles in the development of optimal materials for wound healing and bone-tissue regeneration, as well as emerging strategies in the field.

Masking Strategy Constructed Metal Coordination Hydrogels with Improved Mechanical Properties for Flexible Electronic Sensors

Metal coordination hydrogels (MC-HGs) that introduce dynamically coordinate bonds together with metal ionic conduction have attracted considerable attention in flexible electronics. However, the traditional soaking method alleged to have technical scalability faces the challenge of forming MC-HGs with a "core-shell" structure, which undoubtedly reduces the whole mechanical properties and ionic stimulation responsiveness required for flexible electronics materials. Herein, a novel strategy referred to as "masking" has been proposed based on the theory of the valence bond and coordination chemistry. By regulating the masking agents and their concentrations as well as pairing mode with the metal ions, the whole mechanical properties of the resulting composites (MC-HGsMasking) show nearly double the values of their traditional soaking samples (MC-HGsSoaking). For example, the fracture stress and toughness of Fe-HGsMasking(SA, 5.0 g/L) are 1.55 MPa and 2.14 MJ/m3, almost twice those of Fe-HGsSoaking (0.83 MPa and 0.93 MJ/m3, respectively). Microstructure characterization combined with finite element analysis, molecular dynamics, and first-principles simulations demonstrates that the masking strategy first facilitating interfacial permeation of metal complexes and then effective coordination with functional ligands (carboxylates) of the hydrogels is the mechanism to strengthen the mechanical properties of composites MC-HGsMasking, which has the potential to break through the limitations of current MC-HGs in flexible electronic sensor applications.

Mechanochromic and ionic conductive cholesteric liquid crystal elastomers for biomechanical monitoring and human-machine interaction

Cholesteric liquid crystal elastomers (CLCEs) that combine rubbery elasticity with structural colour from self-assembled helical nanostructures are of paramount importance for diverse applications such as biomimetic skins, adaptive optics and soft robotics. Despite great advances, it is challenging to integrate electrical sensing and colour-changing characteristics in a single CLCE system. Here, we report the design and synthesis of an ionic conductive cholesteric liquid crystal elastomer (iCLCE) through in situ Michael addition and free-radical photopolymerization of CLCE precursors on silane-functionalized polymer ionic liquid networks, in which robust covalent chemical bonding was formed at the interface. Thanks to superior mechanochromism and ionic conductivity, the resulting iCLCEs exhibit dynamic colour-changing and electrical sensing functions in a wide range upon mechanical stretching, and can be used for biomechanical monitoring during joint bending. Importantly, a capacitive elastomeric sensor can be constructed through facilely stacking iCLCEs, where the optical and electrical dual-signal reporting performance allows intuitive visual localization of pressure intensity and distribution. Moreover, proof-of-concept application of the iCLCEs has been demonstrated with human-interactive systems. The research disclosed herein can provide new insights into the development of bioinspired somatosensory materials for emerging applications in diverse fields such as human-machine interaction, prostheses and intelligent robots.

Multi-characteristic tannic acid-reinforced polyacrylamide/sodium carboxymethyl cellulose ionic hydrogel strain sensor for human-machine interaction

Big data and cloud computing are propelling research in human-computer interface within academia. However, the potential of wearable human-machine interaction (HMI) devices utilizing multiperformance ionic hydrogels remains largely unexplored. Here, we present a motion recognition-based HMI system that enhances movement training. We engineered dual-network PAM/CMC/TA (PCT) hydrogels by reinforcing polyacrylamide (PAM) and sodium carboxymethyl cellulose (CMC) polymers with tannic acid (TA). These hydrogels possess exceptional transparency, adhesion, and remodelling features. By combining an elastic PAM backbone with tunable amounts of CMC and TA, the PCT hydrogels achieve optimal electromechanical performance. As strain sensors, they demonstrate higher sensitivity (GF = 4.03), low detection limit (0.5 %), and good linearity (0.997). Furthermore, we developed a highly accurate (97.85 %) motion recognition system using machine learning and hydrogel-based wearable sensors. This system enables contactless real-time training monitoring and wireless control of trolley operations. Our research underscores the effectiveness of PCT hydrogels for real-time HMI, thus advancing next-generation HMI systems.

Mucosa-Inspired Electro-Responsive Lubricating Supramolecular-Covalent Hydrogel

Enabling the living capability of secreting liquids dynamically triggered by external stimuli while maintaining the bulk frame is a significant challenge for mucosa-inspired hydrogels. A mucosa-inspired electro-responsive hydrogel is developed in this study using the synergy between electro-responsive silk fibroin supramolecular non-covalent networks and covalent polyacrylamide and polyvinyl alcohol polymer networks. The formed supramolecular-covalent hydrogel exhibits a partial gel-sol transition upon the application of an electric field, and the liquid layer on the hydrogel surface near the cathode is used to mimic the mucus-secreting capability to regulate lubrication. The electro-responsive lubricating process can operate under a safe voltage and exhibits good reversibility. It is also a universal strategy to construct an electro-responsive hydrogel by introducing an electro-responsive supramolecular network into the polymer network. This mucosa-inspired electro-responsive supramolecular-covalent hydrogel offers a promising method for designing soft actuators or robots that can regulate lubrication using an electric strategy.

Establishing a Corrugated Carbon Network with a Crack Structure in a Hydrogel for Improving Sensing Performance

Electronic conductive hydrogels have prompted immense research interest as flexible sensing materials. However, establishing a continuous electronic conductive network within a hydrogel is still highly challenging. Herein, we develop a new strategy to establish a continuous corrugated carbon network within a hydrogel by embedding carbonized crepe paper into the hydrogel with its corrugations perpendicular to the stretching direction using a casting technique. The corrugated carbon network within the as-prepared composite hydrogel serves as a rigid conductive network to simultaneously improve the tensile strength and conductivity of the composite hydrogel. The composite hydrogel also generates a crack structure when it is stretched, enabling the composite hydrogel to show ultrahigh sensitivity (gauge factor = 59.7 and 114 at strain ranges of 0-60 and 60-100%, respectively). The composite hydrogel also shows an ultralow detection limit of 0.1%, an ultrafast response/recovery time of 75/95 ms, and good stability and durability (5000 cycles at 10% strain) when used as a resistive strain sensing material. Moreover, the good stretchability, adhesiveness, and self-healing ability of the hydrogel were also effectively retained after the corrugated carbon network was introduced into the hydrogel. Because of its outstanding sensing performance, the composite hydrogel has potential applications in sensing various human activities, including accurately recording subtle variations in wrist pulse waves and small-/large-scale complex human activities. Our work provides a new approach to develop economical, environmentally friendly, and reliable electronic conductive hydrogels with ultrahigh sensing performance for the future development of electronic skin and wearable devices.

Bionic ordered structured hydrogels: structure types, design strategies, optimization mechanism of mechanical properties and applications

Natural organisms, such as lobsters, lotus, and humans, exhibit exceptional mechanical properties due to their ordered structures. However, traditional hydrogels have limitations in their mechanical and physical properties due to their disordered molecular structures when compared with natural organisms. Therefore, inspired by nature and the properties of hydrogels similar to those of biological soft tissues, researchers are increasingly focusing on how to investigate bionic ordered structured hydrogels and render them as bioengineering soft materials with unique mechanical properties. In this paper, we systematically introduce the various structure types, design strategies, and optimization mechanisms used to enhance the strength, toughness, and anti-fatigue properties of bionic ordered structured hydrogels in recent years. We further review the potential applications of bionic ordered structured hydrogels in various fields, including sensors, bioremediation materials, actuators, and impact-resistant materials. Finally, we summarize the challenges and future development prospects of bionic ordered structured hydrogels in preparation and applications.

Biomimetic Alveoli System with Vivid Mechanical Response and Cell-Cell Interface

Alveolar microenvironmental models are important for studying the basic biology of the alveolus, therapeutic trials, and drug testing. However, a few systems can fully reproduce the in vivo alveolar microenvironment including dynamic stretching and the cell-cell interface. Here, a novel biomimetic alveolus-on-a-chip microsystem is presented suitable for visualizing physiological breathing for simulating the 3D architecture and function of human pulmonary alveoli. This biomimetic microsystem contains an inverse opal structured polyurethane membrane that achieves real-time observation of mechanical stretching. In this microsystem, the alveolar-capillary barrier is created by alveolar type 2 (ATII) cells cocultured with vascular endothelial cells (ECs) on this membrane. Based on this microsystem, the phenomena of flattening and the tendency of differentiation in ATII cells are observed. The synergistic effects of mechanical stretching and ECs on the proliferation of ATII cells are also observed during the repair process following lung injury. These features indicate the potential of this novel biomimetic microsystem for exploring the mechanisms of lung diseases, which can provide future guidance concerning drug targets for clinical therapies.

Mechanochromic and Conductive Chiral Nematic Nanostructured Film for Bioinspired Ionic Skins

Chameleon skin is naturally adaptive and can sense environmental changes and transform sensing into bioelectrical and optical signals by manipulating ion transduction and photonic nanostructures. The increasing interest in mimicking biological skins has considerably promoted the development of advanced photonic materials with an increasing ionic conductivity. Herein, we report the judicious design and fabrication of a bioinspired mechanochromic chiral nematic nanostructured film with good ionic conductivity by infiltrating fluorine-rich ionic liquids (FILs) into a swollen self-assembled cellulose nanocrystal (CNC) film with helical nanoarchitectures. Notably, the introduction of 2-hydroxyethyl acrylate considerably enhances the compatibility of hydrophobic FILs and hydrophilic CNCs. The resulting FIL-CNC nanostructured films exhibited excellent mechanochromism, good ionic conductivity, and outstanding optical/electrical dual-signal sensing performance when used as a bioinspired ionic skin for real-time monitoring of human motions. Owing to the integration of FILs, the underwater stability of the chiral liquid crystal nanostructures of CNCs was significantly enhanced. Notably, underwater contact/contactless sensing modes and encrypted information transmission have been achieved with the FIL-CNC nanostructured film. This study can offer great insights for the advancement of biomimetic multifunctional artificial skins and emerging interactive devices, which can find important applications in wearable iontronics, human-machine interactions, and intelligent robots.

Visual demonstration and prediction of the Hofmeister series based on a poly(ionic liquid) photonic array

The Hofmeister effect and associated Hofmeister series (HS) are ubiquitous in physicochemical phenomena and have demonstrated fundamental importance in a myriad of fields ranging from chemistry to biology. Visualization of the HS not only helps to straightforwardly understand the underpinning mechanism, but also enables the prediction of new ion positions in the HS and directs the applications of the Hofmeister effect. Owing to the difficulties of sensing and reporting complete multiple and subtle inter- and intramolecular interactions involved in the Hofmeister effect, facile and accurate visual demonstration and prediction of the HS remain highly challenging. Herein, a poly(ionic liquid) (PIL)-based photonic array containing 6 inverse opal microspheres was rationally constructed to efficiently sense and report the ion effects of the HS. The PILs can not only directly conjugate with HS ions due to their ion-exchange properties, but also provide sufficient noncovalent binding diversity with these ions. Meanwhile, subtle PIL-ion interactions can be sensitively amplified to optical signals owing to their photonic structures. Therefore, synergistic integration of PILs and photonic structures gives rise to accurate visualization of the ion effect of the HS, as demonstrated by correctly ranking 7 common anions. More importantly, assisted by principal component analysis (PCA), the developed PIL photonic array can serve as a general platform to facilely, accurately, and robustly predict the HS positions of an unprecedented amount of important and useful anions and cations. These findings indicate that the PIL photonic platform is very promising for addressing challenges in the visual demonstration and prediction of HS and promoting a molecular-level understanding of the Hoffmeister effect.

Dual-crosslinked bioadhesive hydrogel as NIR/pH stimulus-responsiveness platform for effectively accelerating wound healing

Adhesive hydrogels have emerged as promising candidates to solve life-threatening infectious skin injuries. However, the inadequate mechanical characteristics and biological adherence limit the traditional wound dressing unable to adapt to high-frequency movement and real-time monitoring of wound healing, calling for the development of bioadhesive materials guided wound healing. In this work, a multifunctional bioadhesive hydrogel with double colorimetric-integrated of polyethylene glycol (PVA)-dextran (Dex)-borax-bromothymol blue (BTB)-fluorescein thiocyanate (FITC) and functionalization by tungsten disulfide-catechol nanozyme (CL/WS₂) was created. Hydrogel is a perfect biological adhesive, which can achieve repeatable and strong tissue adhesion strength (8.3 ± 0.6 kPa), which is 1.66 times that of commercial dressings. Based on the strong biological adhesion of the hydrogel, a sensor is integrated into the hydrogel to collect visual image of bacterial infection from a smartphone and transform it into an on-site pH signal for remote evaluation of the wound's dynamic status in real time. Ultimately, the adhesiveness hydrogel has high worth in managing the burden related to wound healing and paving the way for intelligent wound management in the future.

Synergetic Lithium and Hydrogen Bonds Endow Liquid-Free Photonic Ionic Elastomer with Mechanical Robustness and Electrical/Optical Dual-Output

Photonic ionic elastomers (PIEs) capable of multiple signal outputs are intriguing in flexible interactive electronics. However, fabricating PIEs with simultaneous mechanical robustness, good ionic conductivity, and brilliant structure color still remains challenging. Here, the limitations are broken through introducing the synergistic effect of lithium and hydrogen bonds into an elastomer. In virtue of lithium bonding between lithium ions and carbonyl groups in the polymer matrix as well as hydrogen bonding between silanol on the surface of silica nanoparticles (SiNPs) and ether groups along polymer chains, the PIEs demonstrate mechanical strength up to 4.3 MPa and toughness up to 8.6 MJ m^-3 . Meanwhile, the synchronous electrical and optical output under mechanical strains can be achieved in the PIEs with the presence of dissociated ions contributed by lithium bond and non-close-packed SiNPs stabilized by the hydrogen bond. Moreover, due to their liquid-free nature, the PIEs exhibit extraordinary stability and durability, which can withstand extreme conditions including both high and low temperatures as well as high humidity. This work provides a promising molecular engineering route to construct high-performance photonic ionic conductors toward advanced ionotronic applications.

Bioinspired Conductive Enhanced Polyurethane Ionic Skin as Reliable Multifunctional Sensors

Ionogels prepared from ionic liquid (IL) have the characteristics of nonevaporation and stable performance relative to traditional hydrogels. However, the conductivities of commonly used ionogels are at very low relative to traditional hydrogels because the large sizes of the cation and anion in an IL impedes ion migration in polymer networks. In this study, ultradurable ionogels with suitable mechanical properties and high conductivities are prepared by impregnating IL into a safe, environmentally friendly water-based polyurethane (WPU) network by mimicking the ion transport channels in the phospholipid bilayer of the cell membrane. The increase in electrical conductivity is attributed to the introduction of carboxylic acid in the hard segment of WPU; this phenomenon regularly arranges hard segment structural domains by hydrogen bonding, forming ionic conduction channels. The conductivities of their ionogels are >28-39 mS cm^-1 . These ionogels have adjustable mechanical properties that make the Young's modulus value (0.1-0.6 MPa) similar to that of natural skin. The strain sensor has an ultrahigh sensitivity that ranges from 0.99 to 1.35, with a wide sensing range of 0.1%-200%. The findings are promising for various ionotronics requiring environmental stability and high conductivity characteristics.

Dual-Mode Fiber Strain Sensor Based on Mechanochromic Photonic Crystal and Transparent Conductive Elastomer for Human Motion Detection

As an important component of wearable and stretchable strain sensors, dual-mode strain sensors can respond to deformation via optical/electrical dual-signal changes, which have important applications in human motion monitoring. However, realizing a fiber-shaped dual-mode strain sensor that can work stably in real life remains a challenge. Here, we design an interactive dual-mode fiber strain sensor with both mechanochromic and mechanoelectrical functions that can be applied to a variety of different environments. The dual-mode fiber is produced by coating a transparent elastic conductive layer onto photonic fiber composed of silica particles and elastic rubber. The sensor has visualized dynamic color change, a large strain range (0-80%), and a high sensitivity (1.90). Compared to other dual-mode strain sensors based on the photonic elastomer, our sensor exhibits a significant advantage in strain range. Most importantly, it can achieve reversible and stable optical/electrical dual-signal outputs in response to strain under various environmental conditions. As a wearable portable device, the dual-mode fiber strain sensor can be used for real-time monitoring of human motion, realizing the direct interaction between users and devices, and is expected to be used in fields such as smart wearable, human-machine interactions, and health monitoring.

Mechanochromic Optical/Electrical Skin for Ultrasensitive Dual-Signal Sensing

Following earlier research efforts dedicated to the realization of multifunctional sensing, recent developments of artificial skins endeavor to go beyond human sensory functions by integrating interactive visualization of strain and pressure stimuli. Inspired by the microcracked structure of spider slit organs and the mechanochromic mechanism of chameleons, this work aims to design a flexible optical/electrical skin (OE-skin) capable of responding to complex stimuli with interactive feedback of human-readable structural colors. The OE-skin consists of an ionic electrode combined with an elastomer dielectric layer, a chromotropic layer containing photonic crystals and a conductive carbon nanotube/MXene layer. The electrode/dielectric layers function as a capacitive pressure sensor. The mechanochromic photonic crystals of ferroferric oxide-carbon magnetic arrays embedded in the gelatin/polyacrylamide stretchable hydrogel film perceive strain and pressure stimuli with bright color switching outputs in the full visible spectrum. The underlying microcracked conductive layer is devoted to ultrasensitive strain sensing with a gauge factor of 191.8. The multilayered OE-skin delivers an ultrafast, accurate response for capacitive pressure sensing with a detection limit of 75 Pa and long-term stability of 5000 cycles, while visualizing complex deformations in the form of high-resolution spatial colors. These findings offer deep insights into the rational design of OE-skins as multifunctional sensing devices.

Soft Electronics for Health Monitoring Assisted by Machine Learning

Due to the development of the novel materials, the past two decades have witnessed the rapid advances of soft electronics. The soft electronics have huge potential in the physical sign monitoring and health care. One of the important advantages of soft electronics is forming good interface with skin, which can increase the user scale and improve the signal quality. Therefore, it is easy to build the specific dataset, which is important to improve the performance of machine learning algorithm. At the same time, with the assistance of machine learning algorithm, the soft electronics have become more and more intelligent to realize real-time analysis and diagnosis. The soft electronics and machining learning algorithms complement each other very well. It is indubitable that the soft electronics will bring us to a healthier and more intelligent world in the near future. Therefore, in this review, we will give a careful introduction about the new soft material, physiological signal detected by soft devices, and the soft devices assisted by machine learning algorithm. Some soft materials will be discussed such as two-dimensional material, carbon nanotube, nanowire, nanomesh, and hydrogel. Then, soft sensors will be discussed according to the physiological signal types (pulse, respiration, human motion, intraocular pressure, phonation, etc.). After that, the soft electronics assisted by various algorithms will be reviewed, including some classical algorithms and powerful neural network algorithms. Especially, the soft device assisted by neural network will be introduced carefully. Finally, the outlook, challenge, and conclusion of soft system powered by machine learning algorithm will be discussed.

Polymerizable rotaxane hydrogels for three-dimensional printing fabrication of wearable sensors

While hydrogels enable a variety of applications in wearable sensors and electronic skins, they are susceptible to fatigue fracture during cyclic deformations owing to their inefficient fatigue resistance. Herein, acrylated β-cyclodextrin with bile acid is self-assembled into a polymerizable pseudorotaxane via precise host-guest recognition, which is photopolymerized with acrylamide to obtain conductive polymerizable rotaxane hydrogels (PR-Gel). The topological networks of PR-Gel enable all desirable properties in this system due to the large conformational freedom of the mobile junctions, including the excellent stretchability along with superior fatigue resistance. PR-Gel based strain sensor can sensitively detect and distinguish large body motions and subtle muscle movements. The three-dimensional printing fabricated sensors of PR-Gel exhibit high resolution and altitude complexity, and real-time human electrocardiogram signals are detected with high repeating stability. PR-Gel can self-heal in air, and has highly repeatable adhesion to human skin, demonstrating its great potential in wearable sensors.

Development of 3D-Printed, Biodegradable, Conductive PGSA Composites for Nerve Tissue Regeneration

Nerve conduits are used to reconnect broken nerve bundles and provide protection to facilitate nerve regeneration. However, the low degradation rate and regeneration rate, as well as the requirement for secondary surgery are some of the most criticized drawbacks of existing nerve conduits. With high processing flexibility from the photo-curability, poly (glycerol sebacate) acrylate (PGSA) is a promising material with tunable mechanical properties and biocompatibility for the development of medical devices. Here, polyvinylpyrrolidone (PVP), silver nanoparticles (AgNPs), and graphene are embedded in biodegradable PGSA matrix. The polymer composites are then assessed for their electrical conductivity, biodegradability, three-dimensional-printability (3D-printability), and promotion of cell proliferation. Through the four-probe technique, it is shown that the PGSA composites are identified as highly conductive in swollen state. Furthermore, biodegradability is evaluated through enzymatic degradation and facilitated hydrolysis. Cell proliferation and guidance are significantly promoted by three-dimensional-printed microstructures and electrical stimulation on PGSA composites, especially on PGSA-PVP. Hence, microstructured nerve conduits are 3D-printed with PGSA-PVP. Guided cell growth and promoted proliferation are subsequently demonstrated by Schwann cell culture combined with electrical stimulation. Consequently, 3D-printed nerve conduits fabricated with PGSA composites hold great potential in nerve tissue regeneration through electrical stimulation.

Pruney Finger-Inspired Switchable Surface with Water-Actuated Dynamic Textures

Switchable surfaces play an important role in the development of functional materials. However, the construction of dynamic surface textures remains challenging due to the complicated structural design and surface patterning. Herein, a pruney finger-inspired switchable surface (PFISS) is developed by constructing water-sensitive surface textures on a polydimethylsiloxane substrate by taking advantage of the hygroscopicity of the inorganic salt filler and the 3D printing technology. Like human fingertips, the PFISS shows high water sensitivity with obvious surface variation in wet and dry states, which is actuated by water absorption-desorption of the hydrotropic inorganic salt filler. Besides, when the fluorescent dye is optionally added into the matrix of the surface texture, water-responsive fluorescent emitting is observed, providing a feasible surface-tracing strategy. The PFISS shows effective regulation of the surface friction and performs a good antislip effect. The reported synthetic strategy for the PFISS offers a facile way for building a wide range of switchable surfaces.

Recent advances in conductive hydrogels: classifications, properties, and applications

Hydrogel-based conductive materials for smart wearable devices have attracted increasing attention due to their excellent flexibility, versatility, and outstanding biocompatibility. This review presents the recent advances in multifunctional conductive hydrogels for electronic devices. First, conductive hydrogels with different components are discussed, including pure single network hydrogels based on conductive polymers, single network hydrogels with additional conductive additives (i.e., nanoparticles, nanowires, and nanosheets), double network hydrogels based on conductive polymers, and double network hydrogels with additional conductive additives. Second, conductive hydrogels with a variety of functionalities, including self-healing, super toughness, self-growing, adhesive, anti-swelling, antibacterial, structural color, hydrophobic, anti-freezing, shape memory and external stimulus responsiveness are introduced in detail. Third, the applications of hydrogels in flexible devices are illustrated (i.e., strain sensors, supercapacitors, touch panels, triboelectric nanogenerator, bioelectronic devices, and robot). Next, the current challenges facing hydrogels are summarized. Finally, an imaginative but reasonable outlook is given, which aims to drive further development in the future.

A multifunctional structural coloured electronic skin monitoring body motion and temperature

Multifunctional e-skins provide information on physiological and environmental parameters. However, the development and fabrication of such devices is challenging. Here, structural coloured electronic skins are presented, which are prepared via scalable methods that can simultaneously monitor the skin temperature and body motion when patched onto the human skin.

Flexible Aggregation-Induced Emission-Active Hydrogel for On-Site Monitoring of Pesticide Degradation

Benefiting from the stimuli-responsive property and powerful loading capacity, functionalized hydrogels are favorable for the fabrication of sensing devices. Herein, we design aggregation-induced emission (AIE)-active hydrogel discs by embedding gold nanoclusters@zeolite-like imidazole framework (AuNCs@ZIF) composites in double-network hydrogels to build a sensitive pesticide biosensor. The hydrogel discs integrate an AIE effect of AuNCs, a stimuli-responsive property of ZIF, and a porous network structure of the hydrogel, which enhances the sensing sensitivity via boosting the stable fluorescent signal and antifouling performance. In conjunction with a homemade device, the fluorescence images of hydrogel discs could be transduced into data information for accurate quantification of chlorpyrifos pesticide with a detection limit of 0.2 ng/mL. The dynamic degradation of chlorpyrifos in Chinese cabbage is demonstrated to confirm the practical application of hydrogel discs. Such AIE-active hydrogel discs could be a plant health sensor for the on-site quantification of pesticide residues on crops, holding great promise for precision agriculture.

Hierarchically Porous Films Architectured by Self-Assembly of Prolamins at the Air-Liquid Interface

Artificial recapitulation of hierarchically porous films gained great interest due to their versatile functionalities and applications. However, the development of novel eco-friendly and nontoxic biopolymer-based porous films is still limited by the time-consuming fabrication processes and toxic organic reagents involved. Here, we reported a novel approach to rapidly (within 5 s) fabricate biopolymer-based hierarchically porous films via inducing the laterally occurring interfacial self-assembly of prolamins at the air-liquid interface during an antisolvent dripping procedure. The as-prepared films exhibited a hierarchically porous microstructure (with sizes of about 500 nm to 5 μm) with location-graded and Janus features. The formation mechanism involved the solvent gradient controlled self-assembly of prolamin into an anisotropic defect structure in longitudinal and lateral directions. Accordingly, the macroscopic morphologies together with the porosity and pore size could be precisely tuned by solvents and operating parameters in a convenient way. Furthermore, alcohol-soluble but water-insoluble bioactive compounds could be incorporated simultaneously via a one-step loading procedure, which endowed films with large loading efficiency and sustained release features suitable for controlled release applications. The effect of the curcumin-loaded porous film on skin wound healing, as one of the potential applications of this novel material, was then investigated in vivo in a full-thickness wound model, wherein satisfying wound healing effects were achieved through multitarget and multipathway mechanisms. This pioneering work offers a novel strategy for the rapid architecture of biopolymer-based hierarchically porous film with versatile application potentials.

Silver-Reduced Poly(Ethylene Glycol) Diacrylate Composites with Microline Arrays for Directional Bending Sensors

Herein, a soft and flexible polymer composite sensor with a surface structure is manufactured that is sensitive to a wide range of mechanical stimuli, including small actions and large motions. A polymer sensor performing with a piezoresistive mechanism is proposed by synthesizing a new conductive polymer composite to fabricate a microline structure by itself, named Ag-reduced poly(ethylene glycol) diacrylate (PEGDA) composite directional bending sensor (ACBS). A simple but effective process of forming nanoparticles (NPs) and surface structures is a notable characteristic. High sensitivity to a small stimulus was achieved by forming Ag NPs within PEGDA, particularly concentrating on the surface and applying the microline structure. With the structural characteristics of a line structure, the ACBS achieved anisotropic sensitivity to bulk motion along the arranged line direction. The excellent sensitivity of this polymer sensor was experimentally demonstrated via water droplets, blowing, and breathing. Combining the advantages of a simple synthetic and simple fabrication process along with the fabrication ability of the microsurface structure with the material itself and the conductive Ag/PEGDA integrated layer, this ACBS is outstanding as a soft and flexible polymer composite sensor and has potential application in physical devices such as wearable devices and biosensors.

Point-of-Care Immunoassay Based on a Multipixel Dual-Channel Pressure Sensor Array with Visual Sensing Capability of Full-Color Switching and Reliable Electrical Signals

The point-of-care (POC) method with affordability and portability for the sensitive detection of biological substances is an emerging topic in rapid disease screening and personalized medicine. In this work, we demonstrated a diverse responsive platform based on a dual-channel pressure sensor (DCPS). The DCPS had a multilayer flexible architecture consisting of a photonic hydrogel with chromatic transitions and a piezoresistive pressure sensor as the electrical data transmission unit, both of which had the property of pressure-induced mechanical stimulus feedback. By incorporating a platinum nanoparticles-labeled detection antibody (PtNPs-dAb) into the sandwich-type immunoreaction for the target carcinoembryonic antigen (CEA, as a model analyte), gas decomposition could be triggered by the addition of hydrogen peroxide (H₂O₂) to induce a significant increase under pressure in a closed chamber. Meanwhile, the DCPS enabled an accurate electrical signal output, and the photonic hydrogel converted spatiotemporal stimuli into eye-readable colorations with string brilliance. In this way, the target concentration could be quantificationally related to the electrical response and intuitively perceived through visible color alterations. Under optimal conditions, a sensitive determination of CEA was performed in a detectable range of 0.3-60 ng/mL with a limit of detection (LOD) of 0.13 ng/mL. In addition, the proposed protocol had satisfactory selectivity, accuracy, and reproducibility. Furthermore, an array-based immunoassay device was fabricated to conceptually validate its application potential in high-throughput biomedical detection and inspire a dual-signal POC diagnostic platform in a friendly way for resource-limited settings.

Tough, Anti-Swelling Supramolecular Hydrogels Mediated by Surfactant-Polymer Interactions for Underwater Sensors

It is a great challenge for traditional hydrogel-based sensors to be effective underwater due to unsatisfactory water resistance and insufficient wet adhesion. Herein, a tough supramolecular hydrogel aiming at underwater sensing is prepared by the modification of hydrophilic poly(acrylic acid) (PAA) with a small amount of hydrophobic lauryl methacrylate (LMA) in the presence of high concentrations of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Owing to the synergistic effects of the electrostatic interactions and hydrophobic associations of CTAB with the P(AA-co-LMA) copolymer, the hydrogel with a water content of approximately 58.5 wt % demonstrates outstanding anti-swelling feature, superior tensile strength (≈1.6 MPa), large stretchability (>900%), rapid room-temperature self-recovery (≈3 min at 100% strain), and robust wet adhesion to diverse substrates. Moreover, the strain sensor based on the hydrogel displays keen sensitivity in a sensing range of 0-900% (gauge factor is 0.42, 3.44, 5.44, and 7.39 in the strain range of 0-100, 100-300, 300-500, and 500-900%, respectively) and pronounced stability both in air and underwater. Additionally, the hydrogel can be easily recycled by dissolving in anhydrous ethanol. This work provides a facile strategy to fabricate eco-friendly, tough supramolecular hydrogels for underwater sensing.

Toward High Sensitivity: Perspective on Colorimetric Photonic Crystal Sensors

The sensitivity of colorimetric photonic crystal (PC) sensors have been significantly improved with the advancement of deformable structural color materials, structures design, sensing signal analysis methods, and fabrication strategies. In this perspective, the strategies toward high-sensitivity colorimetric PC sensors are discussed, from the perspectives of molecular design, single sensor construction, and multisensor assembly, which include incorporation of flexible polymer chains, construction of strong sensor-analyte interactions, incorporation of more soft materials, construction of stimuli-angle/orientation relationship, design of colorimetric sensors in series, and assembly of colorimetric PC sensors in parallel. Based on these strategies, progress of high-sensitivity colorimetric PC sensors in recent years is summarized, in terms of mechano-sensors and chemo-/biosensors. Specifically, PC based optical-electrical dual-signal sensing devices are included. Finally, the future development and challenges of high-sensitivity colorimetric PC sensors are presented, in regards to deformable properties, optical properties, analysis methods, and fabrication strategies.

Low-Angle-Dependent Anticounterfeiting Label Decoded by Alcohol Tissue Wiping Based on a Multilayer Photonic Crystal Structure

The application of photonic crystals (PCs) as anticounterfeiting materials has been widely investigated because of their tunable photonic stop band and corresponding changeable structural colors. In this work, we designed a composite PC structure including an information CdS PC layer at the bottom and a polymer-based layer composed of an inverse opal PC (IOPC) layer and a disordered porous layer on the top, which can be decoded by an alcohol tissue. The high refractive index of the bottom patterned CdS PC layer provides the structure with a vivid low-angle-dependent structural color in the decoded mode, which ensures the stability of the information conveyed by this label. When the incident angle changed from 5 to 45°, the structural color of the patterned CdS layer changed slightly. In the hidden mode, the low transmittance shields the structural color of the CdS layer. When the structure was wiped with the alcohol tissue, the transmittance of the upper IOPC layer could be increased quickly due to the similar refractive indexes of the used polymer and alcohol, and the pattern of the CdS layer was decoded. Thus, the designed composite PC can act as an anticounterfeiting label, in which the encrypted pattern can be decoded by alcohol tissue wiping and shows a vivid low-angle-dependent structural color. To enhance the anticounterfeiting ability of the designed structure, a double-sided label with different encryption patterns on both sides was designed. Based on the simple reversible encryption and decryption process as well as the color stability, the label shows great application potential in the daily anticounterfeiting field.

Ordered micropattern arrays fabricated by lung-derived dECM hydrogels for chemotherapeutic drug screening

AIMS

This study aims to evaluate ECM-coated micropattern arrays derived from decellularization of native porcine lungs as a novel three-dimensional cell culture platform.

METHODS

ECM derived from decellularization of native porcine lungs was exploited to prepare hydrogels. Then, dECM-coated micropattern arrays were fabricated at four different diameters (50, 100, 150 and 200 ​μm) using polydimethylsiloxane (PDMS). Two lung cancer cell lines, A549 and H1299, were tested on a dECM-coated micropattern array as a novel culture platform for cell adhesion, distribution, proliferation, viability, phenotype expression, and drug screening to evaluate the cytotoxicity of paclitaxel, doxorubicin and cisplatin.

RESULTS

The ECM derived from decellularization of native porcine lungs supported cell adhesion, distribution, viability and proliferation better than collagen I and Matrigel as the coated matrix on the surface. Moreover, the optimal diameter of the micropattern arrays was 100-150 ​μm, as determined by measuring the morphology, viability, proliferation and phenotype of the cancer cell spheroids. Cell spheroids of A549 and H1299 on dECM-coated micropattern arrays showed chemoresistance to anticancer drugs compared to that of the monolayer. The different distributions of HIF-1α, MCL-1 (in the center) and Ki-67 and MRP2 (in the periphery) of the spheroids demonstrated the good establishment of basal-lateral polarity and explained the chemoresistance phenomenon of spheroids.

CONCLUSIONS

This novel three-dimensional cell culture platform is stable and reliable for anticancer drug testing. Drug screening in dECM-coated micropattern arrays provides a powerful alternative to existing methods for drug testing and metabolic profiling in the drug discovery process.

A button switch inspired duplex hydrogel sensor based on both triboelectric and piezoresistive effects for detecting dynamic and static pressure

The capability to sense complex pressure variations comprehensively is vital for wearable electronics and flexible human–machine interfaces. In this paper, inspired by button switches, a duplex tactile sensor based on the combination of triboelectric and piezoresistive effects is designed and fabricated. Because of its excellent mechanical strength and electrical stability, a double-networked ionic hydrogel is used as both the conductive electrode and elastic current regulator. In addition, micro-pyramidal patterned polydimethylsiloxane (PDMS) acts as both the friction layer and the encapsulation elastomer, thereby boosting the triboelectric output performance significantly. The duplex hydrogel sensor demonstrates comprehensive sensing ability in detecting the whole stimulation process including the dynamic and static pressures. The dynamic stress intensity (10–300 Pa), the action time, and the static variations (increase and decrease) of the pressure can be identified precisely from the dual-channel signals. Combined with a signal processing module, an intelligent visible door lamp is achieved for monitoring the entire “contact–hold–release–separation” state of the external stimulation, which shows great application potential for future smart robot e-skin and flexible electronics.

Smart Polycationic Hydrogel Dressing for Dynamic Wound Healing

It is challenging for traditional wound dressings to adapt to the complex and changeable environment, due to the lack of stable, efficient, and continuous bactericidal activity. They also cannot be satisfied in a multifunctional sensing platform to reconstruct skin sensory functions for human health monitoring. A multifunctional hydrogel dressing is developed here for the treatment of infected wounds and human health monitoring, which is based on alginate and polycation. The in situ polymerization and solvent displacement method are used to functionalize the hydrogel for the improvement of antifreezing, water retention, and environmental adaptability, as well as the adhesion and photothermal property. As a wound dressing, the as-prepared hydrogel exhibits an excellent antibacterial property against both Escherichia coli and Staphylococcus aureus. In a rat model of full-thickness wound infection, it significantly accelerates the healing of infected wounds with a high healing rate of 96.49%. In the further multifunctional sensory tests, the hydrogel shows multiple response modes of strain, pressure and temperature, and sensing stability. An idea is provided here to develop a smart hydrogel dressing that can accelerate wound healing and achieve human health monitoring.

An injectable and self-healing hydrogel with antibacterial and angiogenic properties for diabetic wound healing

The treatment of diabetic wounds remains a global challenge. Compared with traditional wound dressings, there are higher requirements of antibacterial, anti-inflammatory and pro-angiogenic effects in diabetic wound dressings. Furthermore, it is desirable for dressings to self-adapt to wounds with different morphologies without extra processes and stably (suitable adhesive and self-healing abilities) provide a conducive environment for wound healing. Herein, we construct an injectable and self-healing hydrogel through the combination of chitosan (CS) and metal ions to efficiently improve infected and diabetic wound healing. Benefiting from the amino and hydroxy groups, the CS molecular chains are cross-linked with silver ions (Ag⁺) and copper ions (Cu²⁺) to promote the formation of the CS-Ag-Cu hydrogel, which releases Ag⁺ (an antibacterial agent) and Cu²⁺ (an angiogenic agent) over a prolonged period. Moreover, the hydrogel possesses appropriate adhesive ability, good water absorption ability, antibacterial capability and biocompatibility according to in vitro investigations. In vivo experimental results further prove that the CS-Ag-Cu hydrogel can dramatically accelerate tissue repair in a Staphylococcus aureus (S. aureus)-infected skin incision model in normal rats and diabetic wounds.

Bioinspired Polypeptide Photonic Films with Tunable Structural Color

We report a new synthetic strategy of combining N-carboxyanhydride (NCA) chemistry and photonic crystals for the fabrication of polypeptide structural color films. Driven by surface-initiated ring-opening polymerization, the di-NCA derivative of l-cystine (Cys) is introduced to replicate the functionalized colloidal crystal templates and construct freestanding P(Cys) films with tunable structural color. Furthermore, the feasibility of preparing patterned polypeptide photonic films is demonstrated via template microfabrication. Because of the incorporation of l-glutamate (Glu) components, the P(Cys-co-Glu) co-polypeptide films are endowed with a visual color responsiveness toward pH changes. Additionally, the polypeptide photonic films show on-demand degradability. Given the large family of amino acid building blocks, this powerful and versatile approach paves the way for chemical derivatization of multifunctional peptide-based optical platforms.

Pigmented Structural Color Actuators Fueled by Near-Infrared Light

Cuttlefish can modify their body shape and both their pigmentary and structural colors for protection. This adaptability has inspired the development of appearance-changing polymers such as structural color actuators, although in most cases, the original shape has been confined to being flat, and pigmented structural color actuators have not yet been reported. Here, we have successfully created a pigmented structural color actuator using a cholesteric liquid crystal elastomer with a lower actuation temperature where both actuation and coloration (structural and pigmental) are tunable with temperature and NIR light. The shape, structural color, and absorption of the NIR-absorbing dye pigment of the actuator all change with temperature. Light can be used to trigger local in-plane bending actuation in flat films and local shape changes in a variety of 3D-shaped objects. A cuttlefish mimic that can sense light and respond by locally changing its appearance was also made to demonstrate the potential of pigmented structural color actuators for signaling and camouflage in soft robotics.

Ordered micropattern arrays fabricated by lung-derived dECM hydrogels for chemotherapeutic drug screening

Aims

This study aims to evaluate ECM-coated micropattern arrays derived from decellularization of native porcine lungs as a novel three-dimensional cell culture platform.

Methods

ECM derived from decellularization of native porcine lungs was exploited to prepare hydrogels. Then, dECM-coated micropattern arrays were fabricated at four different diameters (50, 100, 150 and 200 ​μm) using polydimethylsiloxane (PDMS). Two lung cancer cell lines, A549 and H1299, were tested on a dECM-coated micropattern array as a novel culture platform for cell adhesion, distribution, proliferation, viability, phenotype expression, and drug screening to evaluate the cytotoxicity of paclitaxel, doxorubicin and cisplatin.

Results

The ECM derived from decellularization of native porcine lungs supported cell adhesion, distribution, viability and proliferation better than collagen I and Matrigel as the coated matrix on the surface. Moreover, the optimal diameter of the micropattern arrays was 100–150 ​μm, as determined by measuring the morphology, viability, proliferation and phenotype of the cancer cell spheroids. Cell spheroids of A549 and H1299 on dECM-coated micropattern arrays showed chemoresistance to anticancer drugs compared to that of the monolayer. The different distributions of HIF-1α, MCL-1 (in the center) and Ki-67 and MRP2 (in the periphery) of the spheroids demonstrated the good establishment of basal-lateral polarity and explained the chemoresistance phenomenon of spheroids.

Conclusions

This novel three-dimensional cell culture platform is stable and reliable for anticancer drug testing. Drug screening in dECM-coated micropattern arrays provides a powerful alternative to existing methods for drug testing and metabolic profiling in the drug discovery process.

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Lung dECM hydrogels can be used as a beneficial coating matrix for supporting cell adhesion, viability and proliferation.

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Ordered micropattern arrays provide a novel platform for spheroid formation, phenotype expression and drug screening.

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The heterogeneous distributions of the cancer spheroids established basal-lateral polarity and explained the chemoresistance.