A pH-Sensitive, Stretchable, Antibacterial Artificial Tongue Based on MXene Cross-Linked Ionogel

Renewable Photosensitive Castor Oil to Fabricate Ionogels: Freezing-Tolerance, Stretchability, and Degradation for 3D Printing and Flexible Sensor Applications

With the escalating demands for sustainability in flexible sensing materials, the development of a novel, environmentally friendly, and multifunctional ionogel utilizing bio-based raw materials has become paramount. However, castor oil with abundant modified sites and natural flexible long carbon chain structure, is rarely explored in the context of ionogels. Here a novel approach is proposed to fabricate high-performance ionogels through rapid photopolymerization of photosensitive modified acrylate-based castor oil (ACO) with ACMO (acrylomorpholine), and [Mim-BS] [HSO4] (1-sulfobutyl-3-methylimidazolium hydrogen sulfate). Herein, ACO not only participates in the photochemical crosslinking of the ionogel but also imparts exceptional stretchability to the ionogel due to its flexible structure. By modulating the content of acrylate-based castor oil, the transparency, conductivity, and mechanical properties of the ionogel can be significantly enhanced. Furthermore, the ionogel incorporating a bio-sourced component (castor oil) obtained through this photochemical crosslinking process enables high-precision 3D printing and demonstrates remarkable degradability, low-temperature resistance, excellent self-healing capabilities, and sensing performance. These findings provide new perspectives for the design of green ionogels and beyond.

Bio-Inspired Ionic Sensors: Transforming Natural Mechanisms into Sensory Technologies

Many natural organisms have evolved unique sensory systems over millions of years that have allowed them to detect various changes in their surrounding environments. Sensory systems feature numerous receptors-such as photoreceptors, mechanoreceptors, and chemoreceptors-that detect various types of external stimuli, including light, pressure, vibration, sound, and chemical substances. These stimuli are converted into electrochemical signals, which are transmitted to the brain to produce the sensations of sight, touch, hearing, taste, and smell. Inspired by the biological principles of sensory systems, recent advancements in electronics have led to a wide range of applications in artificial sensors. In the current review, we highlight recent developments in artificial sensors inspired by biological sensory systems utilizing soft ionic materials. The versatile characteristics of these ionic materials are introduced while focusing on their mechanical and electrical properties. The features and working principles of natural and artificial sensing systems are investigated in terms of six categories: vision, tactile, hearing, gustatory, olfactory, and proximity sensing. Lastly, we explore several challenges that must be overcome while outlining future research directions in the field of soft ionic sensors.

MXene Hydrogels for Soft Multifunctional Sensing: A Synthesis-Centric Review

Intelligent wearable sensors based on MXenes hydrogels are rapidly advancing the frontier of personalized healthcare management. MXenes, a new class of transition metal carbon/nitride synthesized only a decade ago, have proved to be a promising candidate for soft sensors, advanced human-machine interfaces, and biomimicking systems due to their controllable and high electrical conductivity, as well as their unique mechanical properties as derived from their atomistically thin layered structure. In addition, MXenes' biocompatibility, hydrophilicity, and antifouling properties render them particularly suitable to synergize with hydrogels into a composite for mechanoelectrical functions. Nonetheless, while the use of MXene as a multifunctional surface or an electrical current collector such as an energy device electrode is prevalent, its incorporation into a gel system for the purpose of sensing is vastly less understood and formalized. This review provides a systematic exposition to the synthesis, property, and application of MXene hydrogels for intelligent wearable sensors. Specific challenges and opportunities on the synthesis of MXene hydrogels and their adoption in practical applications are explicitly analyzed and discussed to facilitate cross gemination across disciplines to advance the potential of MXene multifunctional sensing hydrogels.

Review of ionic liquid and ionogel-based biomaterials for advanced drug delivery

Ionic liquids (ILs) play a crucial role in the design of novel materials. The ionic nature of ILs provides numerous advantages in drug delivery, acting as a green solvent or active ingredient to enhance the solubility, permeability, and binding efficiency of drugs. They could also function as a structuring agent in the development of nano/micro particles for drug delivery, including micelles, vesicles, gels, emulsion, and more. This review summarize the ILs and IL-based gel structures with their advanced drug delivery applications. The first part of review focuses on the role of ILs in drug formulation and the applications of ILs in drug delivery. The second part of review offers a comprehensive overview of recent drug delivery applications of IL-based gel. It aims to offer new perspectives and attract more attention to open up new avenues in the biomedical applications of ILs and IL-based gels.

Multifunctional Janus Membrane for Diabetic Wound Healing and Intelligent Monitoring

The complex microenvironment of diabetic wounds often hinders the healing process, ultimately leading to the formation of diabetic foot ulcers and even death. Dual monitoring and treatment of wounds can significantly reduce the incidence of such cases. Herein, a multifunctional Janus membrane (3D chitosan sponge-ZE/polycaprolactone nanofibers-ZP) was developed by incorporating the zinc metal-organic framework, europium metal-organic framework, and phenol red into nanofibers for diabetic wound monitoring and treatment. The directional water transport capacity of the resulting Janus membrane allows for unidirectional and irreversible drainage of wound exudate, and the multifunctional Janus membrane creates up to a 99% antibacterial environment, both of which can treat wounds. Moreover, the pH (5-8) and H2O2 (0.00-0.80 μM) levels of the wound can be monitored using the color-changing property of phenol red and the fluorescence characteristic of Eu-MOF on the obtained membrane, respectively. The healing stages of the wound can also be monitored by analyzing the RGB values of the targeted membrane images. This design can more accurately reflect the wound state and treat the wound to reduce bacterial infection and accelerate wound healing, which has been demonstrated in in vivo experiments. The results provide an important basis for early intervention in diabetic patients.

MXene Crosslinked Hydrogels with Low Hysteresis Conferred by Sliding Tangle Island Strategy

Single-network hydrogels are often too fragile to withstand mechanical loading, whereas double-network hydrogels typically exhibit significant hysteresis during cyclic stretching-releasing process due to the presence of a sacrificial network. Consequently, it is a considerable challenge for designing hydrogels that are both low in hysteresis and high in toughness for applications requiring dynamic mechanical loads. Herein, the study introduced a novel "sliding tangle island" strategy for creating tough and low-hysteresis hydrogels, which are prepared through in situ polymerization of highly concentrated acrylamides (AM) to form numerous entanglements within the MXene spacing without any chemical crosslinker. The MXene entangled with long polyacrylamide (PAM) chains to form tangle island that served as a relay station to transmit stress to neighboring molecular chains. This mechanism helps alleviate stress concentration and enhances energy dissipation efficiency, thereby reducing mechanical hysteresis. The resulting hydrogel exhibited exceptional properties, including high stretchability (≈900%), low hysteresis (less than 7%), high toughness (1.34 MJ m-3), and excellent sensing performance to rival the commercial hydrogel electrode. Therefore, this work sheds light on feasible design of energy dissipation structure to reduce the hysteresis of the composite hydrogels.

Green, pH-Sensitive, Highly Stretchable, and Hydrogen Bond-Dominated Ionogel for Wound Healing Activity

Traditional hydrogel dressings generally have poor mechanical properties and stability when subjected to external stress due to the undesirable chain entanglement structure of their single valence bond compositions. Therefore, it is particularly important to develop a type of gel dressing with good mechanical strength, stability, and environment-friendly monitoring. In this work, a transparent, pH-sensitive, highly stretchable, and biocompatible anthocyanidin ionogel dressing was prepared, realizing green and accurate detection. Attributed to the antibacterial activity of the ionic liquid, the biocompatibility of the pectin, and the ability to scavenge free radicals of the anthocyanidin, the ionogel dressing exhibited excellent re-epithelialization in the 14 day wound healing process. Besides, changes in pH values monitoring of the ionogel over 3 days coincided with normal wound exudate. The obtained ionogel also showed good water retention, swelling properties, mechanical stretchability, and 5 week stability, illustrating great potential in wound dressings.

Degradable Supramolecular Eutectogel-Based Ionic Skin with Antibacterial, Adhesive, and Self-Healable Capabilities

The development of degradable, cost-effective, and eco-friendly ionic conductive gels is highly required to reduce electronic waste originating from flexible electronic devices. However, biocompatible, degradable, tough, and durable conductive gels are challenging to achieve. Herein, we develop a facile strategy for the design and synthesis of degradable tough eutectogels by integrating an electrostatically driven supramolecular network composed of branched polyacrylic acid (PAA) and monoethanolamine (MEA) into a green deep eutectic solvent with chitosan quaternary ammonium salt (CQS). The specially designed PAA/MEA/CQS eutectogels present multiple desired properties, including high transparency, widely adjustable mechanical properties, high resilience, reliable adhesiveness, excellent self-healing ability, good conductivity, remarkable anti-freezing performance, and antibacterial properties. The dynamic and reversible supramolecular interactions not only significantly enhance the mechanical properties of the PAA/MEA/CQS eutectogels but also enable fast degradation, addressing the dilemma between mechanical strength and degradability. More importantly, a biocompatible and degradable multifunctional ionic skin is successfully fabricated based on the PAA/MEA/CQS eutectogel, exhibiting high sensitivity, a wide sensing range, and a rapid response speed toward strain, pressure, and temperature. Thus, this study offers a promising strategy for fabricating degradable tough eutectogels, which show great potential as high-performance ionic skins for next-generation flexible wearable electronic devices.

Stretchable and recyclable gelatin Ionogel based ionic skin with extensive temperature tolerant, self-healing, UV-shielding, and sensing capabilities

Fabricating sustainable ionic skin with multi-functional outstanding performances using biocompatible natural polymer-based ionogel is highly desired but remains a great challenge up to now. Herein, a green and recyclable ionogel has been fabricated by in-situ cross-linking of gelatin with a green bio-based multifunctional cross-linker of Triglycidyl Naringenin in ionic liquid. Benefiting from the unique multifunctional chemical crosslinking networks along with multiple reversible non-covalent interactions, the as-prepared ionogels exhibit high stretchability (>1000 %), excellent elasticity, fast room-temperature self-healability (>98 % healing efficiency at 6 min), and good recyclability. These ionogels are also highly conductive (up to 30.7 mS/cm at 150 °C), and exhibit extensive temperature tolerance (-23 to 252 °C) and outstanding UV-shielding ability. As a result, the as-prepared ionogel can easily be applied as stretchable ionic skin for wearable sensors, which exhibits high sensitivity, fast response time (102 ms), excellent temperature tolerance, and stability over 5000 stretching-relaxing cycles. More importantly, the gelatin-based sensor can be used in signal monitor system for various human motion real-time detection. This sustainable and multifunctional ionogel provides a new idea for easy and green preparation of advanced ionic skins.