Metal-ion-mediated hydrogels with thermo-responsiveness for smart windows

Thermoreversible and tunable supramolecular hydrogels based on chitosan and metal cations

A new thermoreversible and tunable hydrogel CS-M with high water content prepared by metal cation (M = Cu²⁺, Zn²⁺, Cd²⁺ and Ni²⁺) and chitosan (CS) was reported. The influence of metal cations on the thermosensitive gelation of CS-M systems were studied. All prepared CS-M systems were in the transparent and stable sol state and could become the gel state at gelation temperature (T_g). These systems after gelation could recover to its original sol state at low temperature. CS-Cu hydrogel was mainly investigated and characterized due to its large T_g scale (32-80 °C), appropriate pH range (4.0-4.6) and low Cu²⁺ concentration. The result showed that the T_g range was influenced and could be tuned by adjusting Cu²⁺ concentration and system pH within an appropriate range. The influence of anions (Cl^-, NO3^- and Ac^-) in cupric salts in the CS-Cu system was also investigated. Scale application as heat insulation window was investigated outdoors. The different supramolecular interactions of the -NH₂ group in chitosan at different temperatures were proposed to dominate the thermoreversible process of CS-Cu hydrogel.

Preparation and properties of a photocrosslinked MCl n -doped PDMA-g-PSMA hydrogel

To treat damaged joint areas, photocrosslinked hydrophobically associating PDMA-g-PSMA hydrogels can act as mild and easily regulated materials due to their rich pore structure, which have been widely applied in articular cartilage replacement research. In this study, the effects of ADS-MCl _n (ADS-NaCl, ADS-MgCl₂ and ADS-CaCl₂) doping systems on the micro morphology, mechanical, self-healing, and friction properties and cytotoxicity of PDMA-g-PSMA hydrogels were studied. The results showed that the solubilization behavior of the ADS-MCl _n ionic micelles affected the hydrophobic association stability, thereby changing the toughness, self-healing and friction properties of the hydrogel. Ca²⁺-doping resulted in the crystallization and precipitation of the anionic surfactants, destroying the solubilization ability of the ionic micelles for the hydrophobic units, and thus hydrogels with high hardness, low toughness and no self-healing function were obtained. Doping with Na⁺ greatly improved the dissolving power of the ADS micelles for SMA, yielding PDMA-g-PSMA hydrogels with good mechanical strength and good self-healing ability. However, in this case, a drawback is that the Na⁺-doped system will lose its components during the swelling process, leading to the degradation of its self-healing performance. Interestingly, Mg²⁺ doping resulted in the formation of highly stable ADS micellar aggregates, and then PDMA-g-PSMA hydrogels with a lower friction coefficient (0.023), less wear (35.0 mg), higher elongation at break and 100% self-healing efficiency were obtained. The hydrogel products obtained from the three doping systems all exhibited good biocompatibility. Our research provides important guidelines for the design and preparation of anti-friction artificial articular cartilage.

Application of New Energy Thermochromic Composite Thermosensitive Materials of Smart Windows in Recent Years

Thermochromic smart windows technology can intelligently regulate indoor solar radiation by changing indoor light transmittance in response to thermal stimulation, thus reducing energy consumption of the building. In recent years, with the development of new energy-saving materials and the combination with practical technology, energy-saving smart windows technology has received more and more attention from scientific research. Based on the summary of thermochromic smart windows by Yi Long research groups, this review described the applications of thermal responsive organic materials in smart windows, including poly(N-isopropylacrylamide) (PNIPAm) hydrogels, hydroxypropyl cellulose (HPC) hydrogels, ionic liquids and liquid crystals. Besides, the mechanism of various organic materials and the properties of functional materials were also introduced. Finally, opportunities and challenges relating to thermochromic smart windows and prospects for future development are discussed.

Natural-based Hydrogels: A Journey from Simple to Smart Networks for Medical Examination

Natural hydrogels, due to their unique biological properties, have been used extensively for various medical and clinical examinations that are performed to investigate the signs of disease. Recently, complex-crosslinking strategies improved the mechanical properties and advanced approaches have resulted in the introduction of naturally derived hydrogels that exhibit high biocompatibility, with shape memory and self-healing characteristics. Moreover, the creation of self-assembled natural hydrogels under physiological conditions has provided the opportunity to engineer fine-tuning properties. To highlight recent studies of natural-based hydrogels and their applications for medical investigation, a critical review was undertaken using published papers from the Science Direct database. This review presents different natural-based hydrogels (natural, natural-synthetic hybrid and complex-crosslinked hydrogels), their historical evolution, and recent studies of medical examination applications. The application of natural-based hydrogels in the design and fabrication of biosensors, catheters and medical electrodes, detection of cancer, targeted delivery of imaging compounds (bioimaging) and fabrication of fluorescent bioprobes is summarised here. Without doubt, in future, more useful and practical concepts will be derived to identify natural-based hydrogels for a wide range of clinical examination applications.