Novel Phosphorescent Hydrogels Based on an IrIII Metal Complex

Stimulus-responsive luminescent hydrogels: Design and applications

Luminescent hydrogels are emerging soft materials with applications in photoelectric, biomedicine, sensors and actuators, which are fabricated via covalently conjugation of luminophors to hydrogelators or physical loading of luminescent organic/inorganic materials into hydrogel matrices. Due to the intrinsic stimulus-responsiveness for hydrogels such as thermo-, pH, ionic strength, light and redox, luminescent hydrogels could respond to external physical or chemical stimuli through varying the luminescent properties such as colors, fluorescent intensity and so on, affording diverse application potential in addition to the pristine individual hydrogels or luminescent materials. Based on the rapid development of such area, here we systematically summarize and discuss the design protocols, properties as well as the applications of stimulus-responsive luminescent hydrogels. Because of the stimuli-responsiveness, biocompatibility, injectable and controllability of luminescent hydrogels, they are widely used as functional smart materials. We illustrate the applications of luminescent hydrogels. The future developments about luminescent hydrogels are also presented.

Dynamic covalent bonding-triggered supramolecular gelation derived from tetrahydroxy-bisurea derivatives

A new class of bisurea derivatives bearing tetrahydroxy groups have been proven to be non-gelators in water and various organic solvents even under long-term sonication or efficient heating treatment. We found that it is possible to trigger physical gelation behaviour by constructing dynamic covalent bonding. The results show that formation of dynamic covalent bonding between the borate anion and ethanediol substituent in these bisurea derivatives brings about rapid physical gelation at ambient temperature in a mixture of DMSO and water. During dynamic covalent bonding-triggered gelation, the stepgrowth polymerization from the B-O bonds would increase the size of the molecules and reduce the entropy of mixing as well as facilitate ion-dipole interactions in the linear polymeric gelators. They would drive a self-assembly transition and boost the construction of gel networks in coordination with α-tape urea-urea hydrogen bonding. The gelation mechanism was explored by ¹H NMR, FTIR and rheology techniques. Moreover, the resulting gels are transparent and thixotropic, and could be turned into the sol state under CO₂ or water-stimulus. Furthermore, they are stable in the presence of HAuCl₄ and alkali. Therefore, they would afford another new medium for the growth of Au nanocrystals via in situ reduction and a new sensing medium for detecting Hg²⁺ ions.

Recent Advances in Metal-Containing Polymer Hydrogels

Metal-containing polymer hydrogels have attracted increasing interest in recent years due to their outstanding properties such as biocompatibility, recoverability, self-healing, and/or redox activity. In this short review, methods for the preparation of metal-containing polymer hydrogels are introduced and an overview of these hydrogels with various functionalities is given. It is hoped that this short update can stimulate innovative ideas to promote the research of metal-containing hydrogels in the communities.

Dual Physically Cross-Linked Double Network Hydrogels with High Mechanical Strength, Fatigue Resistance, Notch-Insensitivity, and Self-Healing Properties

Double-network (DN) hydrogels with high strength and toughness have been developed as promising materials. Herein, we explored a dual physically cross-linked polyacrylamide/xanthan gum (PAM/XG) DN hydrogel. The nonchemically cross-linked PAM/XG DN hydrogels exhibited fracture stresses as high as 3.64 MPa (13 times higher than the pure PAM single network hydrogel) and compressive stresses at 99% strain of more than 50 MPa. The hydrogels could restore their original shapes after continuously loading-unloading tensile and compressive cyclic tests. In addition, the PAM/XG DN hydrogels demonstrated excellent fatigue resistance, notch-insensitivity, high stability in different harsh environments, and remarkable self-healing properties, which might result from their distinctive physical-cross-linking structures. The attenuated total reflectance infrared spectroscopy (ATR-IR) and dynamic thermogravimetric analysis (TGA) results indicated that there were no chemical bonds (only hydrogen bonds) between the XG and PAM networks. The PAM/XG DN hydrogel synthesis offers a new avenue for the design and construction of DN systems, broadening current research and applications of hydrogels with excellent mechanical properties.

Pd-porphyrin-cross-linked implantable hydrogels with oxygen-responsive phosphorescence

Development of long-term implantable luminescent biosensors for subcutaneous oxygen has proved challenging due to difficulties in immobilizing a biocompatible matrix that prevents sensor aggregation yet maintains sufficient concentration for transdermal optical detection. Here, Pd-porphyrins can be used as PEG cross-linkers to generate a polyamide hydrogel with extreme porphyrin density (≈5 × 10(-3) m). Dye aggregation is avoided due to the spatially constraining 3D mesh formed by the porphyrins themselves. The hydrogel exhibits oxygen-responsive phosphorescence and can be stably implanted subcutaneously in mice for weeks without degradation, bleaching, or host rejection. To further facilitate oxygen detection using steady-state techniques, an oxygen-non-responsive companion hydrogel is developed by blending copper and free base porphyrins to yield intensity-matched luminescence for ratiometric detection.

Self-healing gels based on constitutional dynamic chemistry and their potential applications

This review presents recent developments and potential applications of physical and chemical self-healing gels based on constitutional dynamic chemistry.