A polysaccharide/tetraphenylethylene-mediated blue-light emissive and injectable supramolecular hydrogel

Engineered Dynamic Hydrogel Niches for the Regulation of Redox Homeostasis in Osteoporosis and Degenerative Endocrine Diseases

Osteoporosis and degenerative endocrine diseases are some of the major causes of disability in the elderly. The feedback loop in the endocrine system works to control the release of hormones and maintain the homeostasis of metabolism, thereby regulating the function of target organs. The breakdown of this feedback loop results in various endocrine and metabolic disorders, such as osteoporosis, type II diabetes, hyperlipidemia, etc. The direct regulation of redox homeostasis is one of the most attractive strategies to redress the imbalance of the feedback loop. The biophysical regulation of redox homeostasis can be achieved through engineered dynamic hydrogel niches, with which cellular mechanics and redox homeostasis are intrinsically connected. Mechanotransduction-dependent redox signaling is initiated by cell surface protein assemblies, cadherins for cell-cell junctions, and integrins for cell-ECM interactions. In this review, we focused on the biophysical regulation of redox homeostasis via the tunable cell-ECM interactions in the engineered dynamic hydrogel niches. We elucidate processes from the rational design of the hydrogel matrix to the mechano-signaling initiation and then to the redox response of the encapsulated cells. We also gave a comprehensive summary of the current biomedical applications of this strategy in several degenerative endocrine disease models.

Macrocycle Self-Assembly Hydrogel for High-Efficient Oil-Water Separation

Supramolecular hydrogels involved macrocycles have been explored widely in recent years, but it remains challenging to develop hydrogel based on solitary macrocycle with super gelation capability. Here, the construction of lantern[33 ]arene-based hydrogel with low critical gelation concentration (0.05 wt%), which can be used for efficient oil-water separation, is reported. The lantern[33 ]arenes self-assemble into hydrogen-bonded organic nanoribbons, which intertwine into entangled fibers to form hydrogel. This hydrogel which exhibits reversible pH-responsiveness characteristics can be coated on stainless-steel mesh by in situ sol-gel transformation. The resultant mesh exhibits excellent oil-water separation efficiency (>99%) and flux (>6 × 104 L m-2 h-1 ). This lantern[33 ]arene-based hydrogel not only sheds additional light on the gelation mechanisms for supramolecular hydrogels, but also extends the application of macrocycle-based hydrogels as functional interfacial materials.

Fluorescent Mechanism and Optical Switching of Fluorophore-Free Organogel

Fluorophore is essential to enable the fluorescence and optical switching in most of polymer gels. Herein, a novel concept is proposed to develop a fluorophore-free organogel that is capable of generation of blue fluorescence at transparent state, while it proceeds with optical switching from blue to purple upon phase transition into non-transparent state in water. Ammonium persulphate (APS) is utilized to initiate co-crosslinking of hydrophilic acrylamide (AM) and hydrophobic 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) in dimethyl sulphoxide (DMSO) to give organogel of AM@HFBA at 80 °C. APS decomposes to generate not only radicals, but also ammonium bisulfate (ABS) during heating, in which the elements of ABS produce blue fluorescence (λ = 440 nm), excited by UV light (λ = 365 nm). After the phase transition into non-transparent state, light-reflection behavior at the phase-transitioned surface triggers the optical switching of the organogel from blue to purple under UV light. The optical switching is patternable and reversible, which enables the applications of organogel of AM@HFBA for information encoding/encryption and optical-switchable soft actuators. This method is universal to achieve fluorescence and optical switching for free radical polymerization-based gel systems as long as they are initiated by APS in DMSO.

Investigation and Characterization of Factors Affecting Rheological Properties of Poloxamer-Based Thermo-Sensitive Hydrogel

Poloxamers are negatively temperature-sensitive hydrogels and their hydrophilic groups interact with water molecules at lower temperatures (liquid phase) while their hydrophobic groups interact more strongly with increases in temperature causing gelation. To investigate the factors affecting the rheological properties of poloxamers, various parameters including different poloxamer P407 concentrations, poloxamers P407/P188 blending ratios and additives were examined. The results presented a clear trend of decreasing gelling temperature/time when P407 was at higher concentrations. Moreover, the addition of P188 enhanced the gelling temperature regardless of poloxamer concentration. Polysaccharides and their derivatives have been widely used as components of hydrogel and we found that alginic acid (AA) or carboxymethyl cellulose (CMC) reduced the gelling temperature of poloxamers. In addition, AA-containing poloxamer promoted cell proliferation and both AA -and CMC-containing poloxamer hydrogels reduced cell migration. This study investigated the intriguing characteristics of poloxamer-based hydrogel, providing useful information to compounding an ideal and desired thermo-sensitive hydrogel for further potential clinical applications such as development of sprayable anti-adhesive barrier, wound-healing dressings or injectable drug-delivery system for cartilage repair.

Aggregation-Induced Emission-Active Gels: Fabrications, Functions, and Applications

Chromophores that exhibit aggregation-induced emission (i.e., aggregation-induced emission luminogens [AIEgens]) emit intense fluorescence in their aggregated states, but show negligible emission as discrete molecular species in solution due to the changes in restriction and freedom of intramolecular motions. As solvent-swollen quasi-solids with both a compact phase and a free space, gels enable manipulation of intramolecular motions. Thus, AIE-active gels have attracted significant interest owing to their various distinctive properties and promising application potential. Herein, a comprehensive overview of AIE-active gels is provided. The fabrication strategies employed are detailed, and the applications of AIEgens are summarized. In addition, the gel functions arising from the AIE moieties are revealed, along with their structure-property relationships. Furthermore, the applications of AIE-active gels in diverse areas are illustrated. Finally, ongoing challenges and potential means to address them are discussed, along with future perspectives on AIE-active gels, with the overall aim of inspiring research on novel materials and ideas.

Cyclodextrin-Cross-Linked Hydrogels for Adsorption and Photodegradation of Cationic Dyes in Aqueous Solution

Possessing three-dimensional porous structures and tunable mechanical strengths, cyclodextrin-containing polymeric hydrogels are one of the most promising water-based adsorbent materials due to their easy availability, simple chemical modification and environmental friendliness. In this work, two kinds of hydrogels were prepared via the copolymerization with acrylic acid and vinyl-derivatized β-cyclodextrins in water. These two gels have showed good adsorption performance towards cationic dyes through the noncovalent interactions with their anionic backbones and porous network. Meanwhile, pseudo-second-order model was selected to clarify the adsorption kinetics process. Moreover, nano-scaled TiO₂ was doped into these resultant cyclodextrins-based hydrogels to achieve efficient degradation of dyes upon light irradiation. The obtained TiO₂ -loaded hydrogels could exhibit improved adsorption performance and make the adsorbed dyes photo-degraded with the decolorization rates above 95%. It can be envisioned that such cyclodextrin-based soft materials may find applications in dye clearance and water treatment.

Role of Hydrogels in Bone Tissue Engineering: How Properties Shape Regeneration

Bone defect that resulted from trauma, tumors, and other reasons is believed as a common clinical problem, which exists mainly in post-traumatic healing. Additionally, autologous/allogeneic transplantation, bone tissue engineering attracts increasing attention due to the existing problem of the limited donor. The applications of biomaterials can be considered as a rising and promising strategy for bone regeneration. Especially, hydrogel is featured with hydrophilic characteristic, good biocompatibility, and porous structure, which shows unique properties for bone regeneration. The main properties of hydrogel such as surface property, adhesive property, mechanical property, porosity, and degradation property, generally present influences on the migration, proliferation, and differentiation of mesenchymal stem cells exclusively or in combination, which consequently affect the regeneration of bones. This review mainly focuses on the theme: "how properties of hydrogel shape bone regeneration." Moreover, the latest progress achieved in the above mentioned direction is further discussed. Despite the fascinating advances researchers have made, certain potential challenges continue to exist in the research field, which need to be addressed for accelerating the clinical translation of hydrogel in bone regeneration.

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.

Supramolecular Hyaluronic Assembly with Aggregation-Induced Emission Mediated in Two Stages for Targeting Cell Imaging

Supramolecular aggregation-induced emission (AIE) has become a research hotspot in cell imaging. Herein, supramolecular assembly with AIE effect was constructed in two stages, where adamantane modified tetraphenylethene self-assembly emitted weak fluorescence, and then after adding β-cyclodextrin modified hyaluronic acid, the formed nanoparticles enhanced AIE fluorescence for targeted cancer cell imaging.

Multicolor luminescent supramolecular hydrogels based on cucurbit[8]uril and OPV derivative

Supramolecular hydrogels have received considerable attention because of their various fascinating applications. Herein, an alkyl chain-modified oligo(p-phenylenevinylene) (Py-OPV) derivative was synthesized. When assembled with cucurbit[7]uril, its fluorescence intensity was enhanced without any change in color. However, the molecules underwent J-type dimerization when encased in the cavity of cucurbit[8]uril, which possessed different emission properties based on the monomer. By simply changing the concentration of cucurbit[8]uril, the fluorescence properties of the assemblies were easily altered. In addition, luminescent supramolecular hydrogels were constructed with Py-OPV and cucurbit[8]uril based on the photopolymerization of acrylamide. By embedding the assembly in the polymer to confine it, hydrogels emitting various tones of blue light were easily constructed. The preparation method of such luminescent hydrogels provides a new reference method for the construction of specific luminescent materials.

Supramolecular hydrogel with tunable multi-color and white-light fluorescence from sulfato-β-cyclodextrin and aminoclay

A multi-color-tunable supramolecular hydrogel is constructed from aminoclay (AC), sulfato-β-cyclodextrin (SCD), and 4-methyl-styrylpyridinium (SP), in which the SCD⊃SP complex emits monomer fluorescence, and AC provides a restricted environment for excimer emission. The emission color of the supramolecular hydrogel can be tuned from yellow → white → blue by adjusting the SCD/SP molar ratio.

Construction and heterogeneous photooxidization reactivity of a cyclodextrin/porphyrin polyrotaxane network

A supramolecular polyrotaxane network, based on a CD-based inclusion complex and porphyrin derivative, was synthesized by imine condensation reactions. Then it could be applied as a heterogeneous catalyst for generating singlet oxygen under photoirradiation, which showed its good ability to photooxidize anthracene derivatives.

Construction and efficient dye adsorption of supramolecular hydrogels by cyclodextrin pseudorotaxane and clay

Supramolecular hydrogels, which are usually used to develop excellent smart soft materials, are widely applied in miscellaneous fields due to their inherent reversible properties, unique functions and mechanical properties. Compared with covalently linked hydrogels, supramolecular hydrogels have advantages of easy preparation, stimulus responsiveness and good biocompatibility. Herein, after threading amino-modified β-cyclodextrins onto poly(propyleneglycol)bis(2-amionopropylether) (PPG-NH2) chains, the resultant pseudorotaxanes non-covalently interacted with a clay nanosheet (CNS) matrix to construct supramolecular hydrogels bearing negative charges, and the mechanical properties of these hydrogels were positively correlated with the number of amino groups on the pseudorotaxane. Significantly, these hydrogels presented good adsorption properties for cationic dyes. The adsorption capacity (Qe) of the hydrogels towards rhodamine B (RhB), crystal violet (CV), and methylene blue (MB) could reach 181-228 mg g-1, and most of the dyes were adsorbed within 5 min. Thus, these hydrogels may have potential applications in the field of waste water treatment.

Self-agglomerated crystalline needles harnessing ESIPT and AIEE features for the ‘turn-on’ fluorescence detection of Al3+ ions

We report the synthesis of probe 2 for the fluorescence “turn-on” detection of Al³⁺ ions in CH₃OH.

Tunable photo-luminescence behaviors of macrocycle-containing polymer networks in the solid-state

Two porous polymers were synthesized from tetraphenylethylene (TPE) crosslinked β-cyclodextrins (β-CD) and sulfonatocalix[4]arene (SC4A).