A temperature-responsive supramolecular hydrogel: preparation, gel-gel transition and molecular aggregation

Unusual Increasing Viscoelasticity of Wormlike Micelles Composed of Imidazolium Gemini Surfactants with Temperature

The viscoelasticity of wormlike micelles composed of ionic surfactants typically shows an exponential decrease with increasing temperature, which limits their application in relatively high-temperature (>90.0 °C) oilfields and the synthesis of functional materials as supramolecular templates at high temperatures. In this work, a series of imidazolium gemini surfactants, 1,9-(ethane-1,2-diyl)bis(3-alkyl-1H-imidazol-3-ium) bromide ([C_n-2-C_nim]Br₂, n = 12, 14, 16, 18, 20), were synthesized. Their surface activities and aggregation behaviors in water were studied by electrical conductivity, rheology, polarization optical microscopy, small-angle X-ray scattering, ζ potential, and hydrogen nuclear magnetic resonance measurements. [C₁₂-2-C₁₂im]Br₂ and [C₁₄-2-C₁₄im]Br₂ mainly precipitate in water. [C_n-2-C_nim]Br₂ (n = 16, 18, 20) forms lamellar liquid crystals over a large range of concentrations at low temperatures. With the increase of temperature, the lamellar liquid crystals transit to wormlike micelles. Interestingly, the viscoelasticity of the three wormlike micelles first increases to the maximum and then decreases with increasing temperature. These wormlike micelles without additives retain high viscoelasticity up to 90.0 °C or above. With the increase of the alkyl chain length of the surfactants, the transition temperature of lamellar liquid crystal to wormlike micelles and the disintegration temperature of wormlike micelles increase. The unusual increase of the viscoelasticity of wormlike micelles was due to the desorption of weakly bound counterions and the extension of the long hydrophobic chains of surfactants at high temperatures.

Injectable, self-healable and antibacterial multi-responsive tunicate cellulose nanocrystals strengthened supramolecular hydrogels for wound dressings

Wound dressing with an improved structural and functional recapitulation of damaged organs, efficient self-healing and antibacterial properties that can well integrate with tissue are urgently needed in wound management. Supramolecular hydrogels confer control over structural properties in a reversible, dynamic and biomimetic fashion. Herein, a kind of injectable, self-healing and antibacterial supramolecular hydrogel with multi-responses were fabricated by mixing phenylazo-terminated Pluronic F127, quaternized chitosan-graft-cyclodextrin and polydopamine coated tunicate cellulose nanocrystals under physiological conditions. By exploiting the photoisomerization of azobenzene under different wavelengths, a supramolecular hydrogel featuring a changing crosslink density of network was obtained. The corporation of polydopamine coated tunicate cellulose nanocrystals strengthens the hydrogel network with Schiff base bonds and hydrogen bonds, which avoids complete gel-sol transition. The inherent antibacterial property, drug release behavior, self-healing ability, hemostatic performance and biocompatibility were investigated to confirm superiority in wound healing. Moreover, the curcumin loaded hydrogel (Cur-hydrogel) showed multi-responsive release profiles (light, pH, and temperature). A full-thickness skin defect model was built to confirm that Cur-hydrogels significantly accelerated wound healing rate with better granulation tissue thickness and collagen disposition. Overall, the novel photo-responsive hydrogel with coherent antibacterial property has great potential in the healthcare of wound healing.

Supramolecular Hydrogels: Design Strategies and Contemporary Biomedical Applications

Self-assembly of supramolecular hydrogels is driven by dynamic, non-covalent interactions between molecules. Considerable research effort has been exerted to fabricate and optimise supramolecular hydrogels that display shear-thinning, self-healing, and reversibility, in order to develop materials for biomedical applications. This review provides a detailed overview of the chemistry behind the dynamic physicochemical interactions that sustain hydrogel formation (hydrogen bonding, hydrophobic interactions, ionic interactions, metal-ligand coordination, and host-guest interactions). Novel design strategies and methodologies to create supramolecular hydrogels are highlighted, which offer promise for a wide range of applications, specifically drug delivery, wound healing, tissue engineering and 3D bioprinting. To conclude, future prospects are briefly discussed, and consideration given to the steps required to ultimately bring these biomaterials into clinical settings.

Novel Temperature-Responsive Rosin-Derived Supramolecular Hydrogels Constructed by New Semicircular Aggregates

A highly water-soluble rosin-based surfactant (C₁₄-MPA-Na) was synthesized. Novel temperature-responsive supramolecular hydrogels were further prepared using C₁₄-MPA-Na. The microstructure and the mechanical properties of the hydrogels were investigated. Unexpectedly, instead of the long one-dimensional structure, a new kind of twisted semicircular aggregate was formed in the hydrogels, which was rarely reported. Besides, the hydrogels possessed excellent shear-recovery properties. Upon heating to 40 °C, the hydrogels transformed into viscoelastic solutions, which were constructed by worm-like micelles. By adjusting the temperature, the hydrogels and the viscoelastic solutions could be freely transformed. Nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy were used to further explore the possible self-assembly mechanism of C₁₄-MPA-Na. The curved alkane chain which partially overlapped with rosin's rigid skeleton became stretched when heated to 40 °C. The introduction of the rosin rigid skeleton endowed the supramolecular hydrogels with a novel microstructure and contributed to the development of strategies for the utilization of forest resources.

On the effects of organic-acids isomers on temperature-responsiveness in wormlike micelles (WLMs) systems

Responsive wormlike micelles (WLMs) consisted of cationic surfactants and organic-acids are fascinating due to their reversible molecular recognition properties. However, it is unknown how the structure of organic-acids alters the stimuli-responsiveness of WLMs systems. Herein, the peculiar nature of temperature-responsive behaviors in three WLMs systems were systematically investigated. These were manufactured by combining N-erucamidopropyl-N,N-dimethylamine (UC₂₂AMPM) with isomers of organic-acids: o-phthalic acid (o-PA), m-phthalic acid (m-PA) and p-phthalic acid (p-PA) at molar ratio of 2:1 (named as o-EAPA, m-EAPA and p-EAPA respectively). The phase behaviors, macro- and micro-rheology, as well as the mechanism of temperature-responsiveness were explored by visual inspection, rheological and optical methods. The results showed that the three systems exhibited different responsiveness with increase of temperature. Among them, the viscosity and viscoelasticity of o-EAPA were gradually decreased with temperature increase from 30 °C to 90 °C. On the other hand, those of p-EAPA were firstly increased and subsequently decreased, exhibiting the highest viscosity during the heating process. This peculiar phenomenon was attributed to the hydrophilic difference of organic-acids isomers, leading to variations of micelle transitions upon temperature increase. This study is the first report of aromatic-acids isomers inducing different on temperature-responsiveness, and finding beneficial for the development of responsive WLMs for different applications.

Stimuli responsive dynamic transformations in supramolecular gels

Supramolecular gels are formed by the self-assembly of small molecules under the influence of various non-covalent interactions. As the interactions are individually weak and reversible, it is possible to perturb the gels easily, which in turn enables fine tuning of their properties. Synthetic supramolecular gels are kinetically trapped and usually do not show time variable changes in material properties after formation. However, such materials potentially become switchable when exposed to external stimuli like temperature, pH, light, enzyme, redox, and chemical analytes resulting in reconfiguration of gel matrix into a different type of network. Such transformations allow gel-to-gel transitions while the changes in the molecular aggregation result in alteration of physical and chemical properties of the gel with time. Here, we discuss various methods that have been used to achieve gel-to-gel transitions by modifying a pre-formed gel material through external perturbation. We also describe methods that allow time-dependent autonomous switching of gels into different networks enabling synthesis of next generation functional materials. Dynamic modification of gels allows construction of an array of supramolecular gels with various properties from a single material which eventually extend the limit of applications of the gels. In some cases, gel-to-gel transitions lead to materials that cannot be accessed directly. Finally, we point out the necessity and possibility of further exploration of the field.

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.

Photo-responsive supramolecular hyaluronic acid hydrogels for accelerated wound healing

Supramolecular hydrogels confer control over structural properties in a reversible, dynamic, and biomimetic fashion. The design of supramolecular hydrogels with an improved structural and functional recapitulation of damaged organs is important for clinical applications. For wound healing management, in particular, an effective healing process, through the modulation of epidermal growth factor (EGF) delivery using supramolecular polysaccharide hydrogels, has yet to be developed. In this study, photo-responsive supramolecular polysaccharide hydrogels were formed through host-guest interactions between azobenzene and β-cyclodextrin groups conjugated to hyaluronic acid chains. By exploiting the photoisomerization properties of azobenzene under different wavelengths, a supramolecular hydrogel featuring a dynamic spatial network crosslink density through the application of a light stimulus was obtained. Under ultra violet (UV) light, the loosened hydrogel can rapidly release EGF, thereby enhancing EGF delivery at the wound site. Based on an in vivo assessment of the healing process through a full-thickness skin defect model, the controlled EGF release from a supramolecular hydrogel exhibited superior wound healing efficiency with respect to granulation tissue formation, growth factor levels, and angiogenesis. Therefore, the proposed supramolecular hydrogels are potentially valuable as controlled delivery systems for future clinical wound healing applications.

Temperature-Induced Mechanomodulation of Interpenetrating Networks of Star Poly(ethylene glycol)-Heparin and Poly(N-isopropylacrylamide)

Thermoresponsive interpenetrating networks (IPNs) were prepared by sequential synthesis of a biohybrid network of star-shaped poly(ethylene glycol) [starPEG] and heparin and a poly(N-isopropylacrylamide)-polymer network. Amide bond formation was used for cross-linking of the starPEG-heparin network and photo-cross-linking with N,N'-methylenebis(acrylamide) was applied for the formation of the second polymer network. Both networks were linked by chain entanglements and hydrogen bonds only. The obtained sequential IPNs (seq-IPNs) showed temperature-dependent network properties as reflected by swelling and elasticity data as well as by the release of glycosaminoglycan-binding growth factors. The elastic modulus of the seq-IPNs was found to be amplified up to 50-fold upon temperature change from 22 to 37 °C compared to the intrinsic elastic moduli of the two combined networks. The heparin concentration (as well as the complexation of growth factors with the hydrogel-contained heparin) was demonstrated to be variably independent from the mechanical properties (elastic moduli) of the hydrogels. Illustrating the usability of the developed seq-IPN platform for cell fate control, the thermo-modulation of the release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) is shown as well as the osteogenic differentiation of human mesenchymal stem cells exposed to stiff and BMP-2 releasing seq-IPNs.

Effects of Temperature and Ionic Strength of Dissolution Medium on the Gelation of Amorphous Lurasidone Hydrochloride

PURPOSE

Amorphous lurasidone hydrochloride (LH) showed decreased dissolution behavior in comparison to crystalline LH owing to gelation during dissolution as reported in our previous study. The current study aims to investigate external factors including temperature and ionic strength on the gelation and hence the dissolution of amorphous LH.

METHODS

Dissolution tests of amorphous LH were performed under different temperatures and buffer ionic strengths. The formed gels were characterized by rheology study, texture analysis, PLM, SEM, DSC, XRPD and FTIR.

RESULTS

With the increase of temperature and ionic strength of medium, the dissolution of amorphous LH decreased, while the strength, hardness and adhesiveness of in situ formed gel enhanced. Amorphous LH converted into its crystalline state during dissolution and the crystallization rate was affected by medium conditions. With medium temperature increasing from 30°C to 45°C, the gel microstructure changed from interconnecting fibrillar network to spherical particle aggregate. On the other hand, the formed spherulitic gel aggregate exhibited increased particle size when increasing the ionic strength of medium.

CONCLUSIONS

With increase of temperature and ionic strength, the gel strength of in situ formed gel from amorphous LH enhanced with more compact microstructure, subsequently leading to decreased dissolution profiles.

Spontaneously hierarchical self-assembly of nanofibres into fluorescent spherical particles: a leap from organogels to macroscopic solid spheres

The spontaneous hierarchical self-assembly of organic small molecules into macroscopic architectures with excellent photophysical properties and highly-ordered structures has rarely been reported to date. In this work, we find that the organogel of SY1 formed in ethyl acetate could spontaneously assemble into macroscopic spherical particles with a unique morphology and photophysical properties. Upon increasing the aging time, the gel gradually collapsed and then transformed into many macroscopic spheres (SY1-balls) with an average diameter of ca. 500 μm and strong yellow emission. In view of the emission properties and the porous structure of the SY1-balls, they were successfully applied in the adsorption and detection of heavy metal ions. More interestingly, SY1 shows different assembly behaviours in toluene solution when mixed with a triphenylamine derivative (TPA1). Macroscopic particles (ST-balls) with a core-shell structure were obtained, which were quite different from the SY1-balls in morphology and emission colour. So far as we know, many studies have focused on the change of the micromorphology of a gel, while the spontaneous self-assembly of organogels into macroscopic particles has been reported in this work for the first time. This work enriches the present study on organogels and plays an important role in further understanding the hierarchical self-assembly of organogels.

Stimuli-Responsive Supramolecular Hydrogels and Their Applications in Regenerative Medicine

Supramolecular hydrogels are a class of self-assembled network structures formed via non-covalent interactions of the hydrogelators. These hydrogels capable of responding to external stimuli are considered to be smart materials due to their ability to undergo sol-gel and/or gel-sol transition upon subtle changes in their surroundings. Such stimuli-responsive hydrogels are intriguing biomaterials with applications in tissue engineering, delivery of cells and drugs, modulating tissue environment to promote innate tissue repair, and imaging for medical diagnostics among others. This review summarizes the recent developments in stimuli-responsive supramolecular hydrogels and their potential applications in regenerative medicine. Specifically, various structural aspects of supramolecular hydrogelators involved in self-assembly, the role of external stimuli in tuning/controlling their phase transitions, and how these functions could be harnessed to advance applications in regenerative medicine are focused on. Finally, the key challenges and future prospects for these versatile materials are briefly described.

A facile preparation method for new two-component supramolecular hydrogels and their performances in adsorption, catalysis, and stimuli-response

In this study, we prepared a novel multifunctional two-component supramolecular hydrogel (T-G hydrogel) via two organic molecules in ethanol/water mixed solvents. In addition, we prepared gold nanoparticle/T-G (AuNPs/T-G) composite hydrogels using T-G hydrogel as a template for stabilizing AuNPs by adding HAuCl₄ and NaBH₄ during the heating and cooling process of T-G hydrogels. The morphology and microstructure of the as-prepared hydrogels were characterized using SEM, TEM, XRD, and FT-IR. The hydrogels prepared by solutions that contained different ethanol/water volume ratios exhibited different microstructures, such as sheets, strips, and rods. The obtained T-G hydrogels exhibited a sensitive response to pH changes in the process of sol–gel transformation and showed good adsorption properties for model organic dyes. In the presence of NaBH₄, the obtained AuNP/T-G composite hydrogels exhibited the excellent catalytic performance for 4-nitrophenol (4-NP) degradation. Thus, the current research provides new clues in developing new multifunctional two-component supramolecular gel materials and exhibits potential applications for wastewater treatment.

New two-component supramolecular hydrogels were prepared via a self-assembly process, demonstrating potential applications in adsorption and catalysis as well as sensor materials.