Synthesis and Characteristics of a pH-Sensitive Sol-Gel Transition Colloid for Coal Fire Extinguishing

Coal fires, most of which are triggered by the spontaneous combustion of coal, cause a huge waste of resources and release poisonous and harmful substances into the environment, seriously threatening the safety of industrial production. Gel flame retardant plays a core role in coal fire prevention and extinguishing. Most gel flame retardants used in coal fires possess good sealing and oxygen isolation properties, but it is difficult for them to flow deep into fire areas due to their low fluidity. Some fire extinguishing agents with good fluidity lack leak-blocking performance. In order to simultaneously improve the fluidity, leakage sealing, and oxygen isolation effects of coal fire extinguishing colloids, a novel, pH-sensitive, sol-gel transition colloid was prepared using low methoxyl pectin (LMP), calcium bentonite (Ca-Bt), sodium bentonite (Na-Bt), and water as the main components. When the initial sol-state colloid absorbed acid gas products from coal combustion, the pH value decreased and a large amount of Ca²⁺ in Ca-Bt precipitated, thus immediately growing calcium bridges with LMP molecules that formed a three-dimensional network structure for gelation. The optimum ratio of the new colloid was determined through X-ray diffraction, tube inversion, shock shear-temperature scanning, and genetic algorithm. By testing the fire extinguishing performance of the colloid, the findings proved that the product had good oxygen isolation performance, strong adhesion ability, high thermal stability, and strong inhibition effects on coal combustion.

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.

Digital Light Processing 3D-Printed Silica Aerogel and as a Versatile Host Framework for High-Performance Functional Nanocomposites

Vat-photopolymerization-based 3D printing enables on-demand construction of customized objects with scalable production capacity and high precision. Herein, the sol-gel process for aerogels with digital light processing 3D printing to produce advanced functional materials possessing hierarchical pore structures and complex shapes is combined. It has revealed the temporal evolution of the photorheological behavior of acrylate-modified silica sols in an acid-base catalytic procedure, and confirmed that silica aerogels can be fabricated with very low acrylate content. The resulting aerogels are thermostable with intrinsic silica contents, skeletal densities, and physical characteristics similar to those of commercial silica aerogels yet distinct mechanical behaviors. More importantly, the printed silica aerogels can be used as a versatile nanoengineering platform to produce high-performance and multifunctional interpenetrating phase nanocomposites with complex shapes through programmable post-printing processes. Epoxy-based nanocomposites possessing excellent mechanical performance, ionogel-based conductive nanocomposites with decoupled electrical and mechanical properties, and anti-swelling hydrogel-based nanocomposites are demonstrated. The results of this study offer new guidelines for the design and fabrication of novel materials by additive manufacturing.

The Interplay between the Theories of Mode Coupling and of Percolation Transition in Attractive Colloidal Systems

In the recent years a considerable effort has been devoted to foster the understanding of the basic mechanisms underlying the dynamical arrest that is involved in glass forming in supercooled liquids and in the sol-gel transition. The elucidation of the nature of such processes represents one of the most challenging unsolved problems in the field of material science. In this context, two important theories have contributed significantly to the interpretation of these phenomena: the Mode-Coupling theory (MCT) and the Percolation theory (PT). These theories are rooted on the two pillars of statistical physics, universality and scale laws, and their original formulations have been subsequently modified to account for the fundamental concepts of Energy Landscape (EL) and of the universality of the fragile to strong dynamical crossover (FSC). In this review, we discuss experimental and theoretical results, including Molecular Dynamics (MD) simulations, reported in the literature for colloidal and polymer systems displaying both glass and sol-gel transitions. Special focus is dedicated to the analysis of the interferences between these transitions and on the possible interplay between MCT and PT. By reviewing recent theoretical developments, we show that such interplay between sol-gel and glass transitions may be interpreted in terms of the extended F13 MCT model that describes these processes based on the presence of a glass-glass transition line terminating in an A3 cusp-like singularity (near which the logarithmic decay of the density correlator is observed). This transition line originates from the presence of two different amorphous structures, one generated by the inter-particle attraction and the other by the pure repulsion characteristic of hard spheres. We show here, combining literature results with some new results, that such a situation can be generated, and therefore experimentally studied, by considering colloidal-like particles interacting via a hard core plus an attractive square well potential. In the final part of this review, scaling laws associated both to MCT and PT are applied to describe, by means of these two theories, the specific viscoelastic properties of some systems.

Development of Metronidazole-loaded In situ Thermosensitive Hydrogel for Periodontitis Treatment

Objectives

Periodontal treatment focuses on the thorough removal of specific periodontal pathogens, mainly anaerobic Gram-negative bacteria, by mechanical scaling and root planning. In case the periodontal abscess is detected after treatment, a high dose of antimicrobial agents is commonly applied via oral administration. However, this approach increases the risk of antibiotic resistance and systemic side effects and decreases efficacy. To overcome the aforementioned issues, this study focused on the development of thermosensitive hydrogel to deliver the antibiotic drug metronidazole (MTZ) directly and locally to the oral infection site.

Materials and Methods

The thermosensitive hydrogels were prepared by blending 28% w/v Pluronic F127 with various concentrations of methylcellulose (MC) and silk fibroin (SF). The gel properties, such as sol-gel transition time, viscosity, and gel strength, were investigated. The drug dissolution profiles, together with their theoretical models and gel dissolution characteristics, were also determined.

Results

All hydrogel formulations exhibited sol-gel transitions at 37°C within 1 min. An increase in MC content proportionally increased the viscosity but decreased the gel strength of the hydrogel. By contrast, the SF content did not significantly affect the viscosity but increased the gel strength of the hydrogel. The thermosensitive hydrogels also showed prolonged MTZ release characteristics for 10 days in phosphate-buffered saline (PBS) at pH 6.6, which followed the Higuchi diffusion model. Moreover, MTZ-thermosensitive hydrogel exhibited delayed dissolution in PBS at 37°C for more than 9 days.

Conclusion

MTZ-thermosensitive hydrogels could be considered a prospective local oral drug delivery system to achieve efficient sustained release and improve the drug pharmacological properties in periodontitis treatment.

Structural Transitions During Formation and Rehydration of Proton Conducting Polymeric Membranes

Knowledge of the transitions occurring during the formation of ion-conducting polymer films and membranes is crucial to optimize material performances. The use of non-destructive scattering techniques that offer high spatio-temporal resolution is essential to investigating such structural transitions, especially when combined with complementary techniques probing at different time and spatial scales. Here, a simultaneous multi-technique study is performed on the membrane formation mechanism and the subsequent hydration of two ion-conducting polymers, the well-known commercial Nafion and a synthesized sulfonated poly(phenylene sulfide sulfone) (sPSS). The X-ray data distinguish the multi-stage processes occurring during drying. A sol-gel-membrane transition sequence is observed for both polymers. However, while Nafion membrane evolves from a micellar solution through the formation of a phase-separated gel, forming an oriented supported membrane, sPSS membrane evolves from a solution of dispersed polyelectrolyte chains via formation of an inhomogeneous gel, showing assembly and ionic phase separation only at the end of the drying process. Impedance spectroscopy data confirm the occurrence of the sol-gel transitions, while gel-membrane transitions are detected by optical reflectance data. The simultaneous multi-technique approach presented here can connect the nanoscale to the macroscopic behavior, unraveling information essential to optimize membrane formation of different ion-conducting polymers.

Direct Observation of Photo-Induced Reversible Sol-Gel Transition in Block Copolymer Self-Assembly Containing an Azobenzene Ionic Liquid

Using atomic force microscopy, the photo-induced reversible changes in a block copolymer self-assembly containing an azobenzene ionic liquid, which undergoes sol-gel transition is directly observed. This is the first report on the sol-gel transition of an ABA-type block copolymer consisting of upper critical solution temperature (UCST)-type A blocks in a photoresponsive ionic liquid mixture. The sol-gel transition is accompanied by an order-to-disorder structural change, which subsequently induces a change in the ionic conductivity. Surprisingly, the photo-induced ionic conductivity and rheological changes occurs rapidly (≈30 s) despite the dense (≈80 wt%) polymeric system. The rapid structural change is probably attributable to the fast diffusion of the ionic liquid.

Designing Gelatin Methacryloyl (GelMA)-Based Bioinks for Visible Light Stereolithographic 3D Biofabrication

Bioinks play a key role in determining the capability of the biofabricatoin processes and the resolution of the printed constructs. Excellent biocompatibility, tunable physical properties, and ease of chemical or biological modifications of gelatin methacryloyl (GelMA) have made it an attractive choice as bioinks for biomanufacturing of various tissues or organs. However, the current preparation methods for GelMA-based bioinks lack the ability to tailor their physical properties for desired bioprinting methods. Inherently, GelMA prepolymer solution exhibits a fast sol-gel transition at room temperature, which is a hurdle for its use in stereolithography (SLA) bioprinting. Here, synthesis parameters are optimized such as solvents, pH, and reaction time to develop GelMA bioinks which have a slow sol-gel transition at room temperature and visible light crosslinkable functions. A total of eight GelMA combinations are identified as suitable for digital light processing (DLP)-based SLA (DLP-SLA) bioprinting through systematic characterizations of their physical and rheological properties. Out of various types of GelMA, those synthesized in reverse osmosis (RO) purified water (referred to as RO-GelMA) are regarded as most suitable to achieve high DLP-SLA printing resolution. RO-GelMA-based bioinks are also found to be biocompatible showing high survival rates of encapsulated cells in the photocrosslinked gels. Additionally, the astrocytes and fibroblasts are observed to grow and integrate well within the bioprinted constructs. The bioink's superior physical and photocrosslinking properties offer pathways of tuning the scaffold microenvironment and highlight the applicability of developed GelMA bioinks in various tissue engineering and regenerative medicine applications.

Bioinspired Thermosensitive Hydrogel as a Vitreous Substitute: Synthesis, Properties, and Progress of Animal Studies

In many vitreal diseases, the surgeon removes the natural vitreous and replaces it with silicone oils, gases, or balanced salt solutions to fill the eyeball and hold the retina in position. However, these materials are often associated with complications and have properties that differ from natural vitreous. Herein, we report an extension of our previous work on the synthesis of a biomimetic hydrogel that is composed of thiolated gellan as an analogue of type II collagen and poly(methacrylamide-co-methacrylate-co-bis(methacryloyl)cystamine), a polyelectrolyte, as an analogue of hyaluronic acid. This thermosensitive hydrogel can be injected into the eye as a viscous solution at 45 °C. It then forms a physical gel in situ when it reaches body temperature, and later forms disulfide covalent crosslinks. In this article, we evaluated two different formulations of the biomimetic hydrogels for their physical, mechanical, and optical properties, and we determined their biocompatibility with several cell lines. Finally, we report on the progress of the four-month preclinical evaluation of our bio-inspired vitreous substitute in comparison to silicone oil or a balanced salt solution. We assessed the eyes with a slit-lamp examination, intraocular pressure measurements, electroretinography, and optical coherence tomography. Preliminary results are very encouraging for the continuing evaluation of our bio-inspired hydrogel in clinical trials.

An Overview of Injectable Thermo-Responsive Hydrogels and Advances in their Biomedical Applications

BACKGROUND

Injectable hydrogels are a thermo-responsive system based on biomaterials. Injectable hydrogels have been broadly investigated mainly as vehicles or scaffolds of therapeutic agents that include drugs, proteins, cells, and bioactive molecules among others, utilized in the treatment of diseases such as cancers and the repair and regeneration of tissues.

RESULTS

There are several studies that have described the multiple features of hydrogels. However, the main aspect that breaks the paradigm in the application of hydrogels is the thermoresponsiveness that some of them have, which is an abrupt modification in their properties in response to small variations in temperature. For that reason, the thermo-responsive hydrogels with the unique property of sol-gel transition have received special attention over the past decades. These hydrogels show phase transition near physiological human body temperature. This feature is key for being applied in promising areas of human health-related research.

CONCLUSION

The purpose of this study is the overview of injectable hydrogels and their latest advances in medical applications including bioactive compound delivery, tissue engineering, and regenerative medicine.

Dynamic and Static Mechanical Properties of Crosslinked Polymer Matrices: Multiscale Simulations and Experiments

We studied the static and dynamic mechanical properties of crosslinked polymer matrices using multiscale simulations and experiments. We continued to develop the multiscale methodology for generating atomistic polymer networks, and applied it to the case of phthalonitrile resin. The mechanical properties of the resulting networks were analyzed using atomistic molecular dynamics (MD) and dissipative particle dynamics (DPD). The Young’s and storage moduli increased with conversion, due both to the appearance of a network of covalent bonds, and to freezing of degrees of freedom and lowering of the glass transition temperature during crosslinking. The simulations’ data showed good quantitative agreement with experimental dynamic mechanical analysis measurements at temperatures below the glass transition. The data obtained in MD and DPD simulations at elevated temperatures were conformable. This makes it possible to use the suggested approach for the prediction of mechanical properties of a broad range of polymer matrices, including ones with high structural heterogeneity.

Dynamics of Spinodal Decomposition in a Ternary Gelling System

The phase diagram and phase transitions of the ternary system of gelatin, water and poly(ethylene glycol) oligomers were studied as a function of the weight fraction of gelatin and the weight fraction and molecular weight of poly(ethylene glycol) oligomers. It was found that both phase separation and the sol-gel transition occur in this ternary system. The relative position of the phase separation line and the sol-gel transition line depends on the weight fraction and the molecular weight of the poly(ethylene glycol) oligomer that coexists in the solution. All aspects of the phase diagram are sensitive to the molecular weight of the poly(ethylene glycol) oligomer. Since the phase separation line crosses the sol-gel transition line in the phase space that is created by the temperature and the weight fraction of gelatin, the phase space is typically divided into four regions, where each region corresponds to a definite phase. The transitions between mutual phases were studied using the light-scattering technique.

Thermo-sensitive composite hydrogels based on poloxamer 407 and alginate and their therapeutic effect in embolization in rabbit VX2 liver tumors

Interventional embolization therapy is an effective, most widely used method for inoperable liver tumors. Blood-vessel-embolic agents were essential in transarterial embolization (TAE). In this work, thermo-sensitive composite hydrogels based on poloxamer 407, sodium alginate, hydroxymethyl cellulose and iodixanol (PSHI), together with Ca2+ (PSHI-Ca2+) were prepared as liquid embolic agents for TAE therapy to liver cancer. With increasing temperature, PSHI exhibited two phase states: a flowing sol and a shrunken gel. Rheology tests showed good fluidity and excellent viscoelastic behavior with a gelation temperature (GT) of 26.5°C. The studies of erosion indicated that PSHI had calcium ion-related erosion characteristics and showed a slow erosion rate in an aqueous environment. When incubated with L929 cells, the thermo-sensitive composite hydrogels had low cytotoxicity in vitro. The results of analyzing the digital subtraction angiography and computed tomography images obtained from in vitro and in vivo assays indicated a good embolic effect in the renal arteries of normal rabbits. Angiography and histological studies on VX2 tumor-bearing rabbits indicated that PSHI-Ca2+ successfully occluded the tumors, including the peripheral vessels. In conclusion, PSHI-Ca2+ was a promising embolic agent for transarterial embolization therapy.

Novel Amphiphilic, Biodegradable, Biocompatible, Thermo-Responsive ABA Triblock Copolymers Based on PCL and PEG Analogues via a Combination of ROP and RAFT: Synthesis, Characterization, and Sustained Drug Release from Self-Assembled Micelles

Well-defined novel, linear, biodegradable, amphiphilic thermo-responsive ABA-type triblock copolymers, poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate]-b-poly(ε-caprolactone)-b-poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methacrylate] [P(MEO₂MA-co-OEGMA)-b-PCL-b-P(MEO₂MA-co-OEGMA)] (tBPs), were synthesized via a combination of ring-opening polymerization (ROP) of ε-caprolactone (εCL) and reversible addition-fragmentation chain transfer polymerization (RAFT) of MEO₂MA and OEGMA comonomers. The chemical structures and compositions of these copolymers were characterized using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H NMR). The molecular weights of the copolymers were obtained using gel permeation chromatography (GPC) measurements. Thermo-responsive micelles were obtained by self-assembly of copolymers in aqueous medium. The temperature sensitivity and micelllization behavior of amphiphilic triblock copolymers solutions were studied by transmittance, fluorescence probe, surface tension, dynamic light scattering (DLS) and transmission electron microscopy (TEM). A hydrophobic drug, anethole, was encapsulated in micelles by using the dialysis method. The average particle sizes of drug-loaded micelles were determined by dynamic light scattering measurement. In vitro, the sustained release of the anethole was performed in pH 7.4 phosphate-buffered saline (PBS) at different temperatures. Results showed that the triblock copolymer's micelles were quite effective in the encapsulation and controlled release of anethole. The vial inversion test demonstrated that the triblock copolymers could trigger the sol-gel transition which also depended on the temperature, and its sol-gel transition temperature gradually decreased with increasing concentration. The hydrogel system could also be used as a carrier of hydrophobic drugs in medicine.

Self-Protection of Electrochemical Storage Devices via a Thermal Reversible Sol-Gel Transition

Thermal self-protected intelligent electrochemical storage devices are fabricated using a reversible sol-gel transition of the electrolyte, which can decrease the specific capacitance and increase and enable temperature-dependent charging and discharging rates in the device. This work represents proof of a simple and useful concept, which shows tremendous promise for the safe and controlled power delivery in electrochemical devices.

Microsphere-Incorporated Hybrid Thermogel for Neuronal Differentiation of Tonsil Derived Mesenchymal Stem Cells

Neuronal differentiation of tonsil-derived mesenchymal stem cells (TMSCs) is investigated in a 3D hybrid system. The hybrid system is prepared by increasing the temperature of poly(ethylene glycol)-poly(l-alanine) aqueous solution to 37 °C through the heat-induced sol-to-gel transition, in which TMSCs and growth factor releasing microspheres are suspended. The in situ formed gel exhibits a modulus of 800 Pa at 37 °C, similar to that of brain tissue, and it is robust enough to hold the microspheres and cells during the 3D culture of TMSCs. The neuronal growth factors are released over 12-18 d, and the TMSCs in a spherical shape initially undergo multipolar elongation during the 3D culture. Significantly higher expressions of the neuronal biomarkers such as nuclear receptor related protein (Nurr-1), neuron specific enolase, microtubule associated protein-2, neurofilament-M, and glial fibrillary acidic protein are observed in both mRNA level and protein level in the hybrid systems than in the control experiments. This study proves the significance of a controlled drug delivery concept in tissue engineering or regenerative medicine, and a 3D hybrid system with controlled release of growth factors from microspheres in a thermogel can be a very promising tool.

Characterization of lung-delivered in-situ forming controlled release formulations

OBJECTIVES

This study investigated the controlled drug release potential of formulations revealing temperature-induced sol-gel transition following administration to the respiratory tract.

METHODS

Diverse sildenafil-containing aqueous poloxamer 407 preparations were evaluated for critical gelation temperature and rheological properties. The in-vitro drug release profiles of the in-situ forming formulations were studied in a Franz type cell, while the drug absorption characteristics were determined in an isolated lung model. Furthermore, the weight gain of isolated lungs was monitored and the bronchoalveolar lavage fluid was analysed for the total protein content.

KEY FINDINGS

Poloxamer 407 solutions with concentrations of >12 wt.% revealed gelation upon temperature increase (>20°C). Compared with free sildenafil solution, sildenafil-containing polymer formulations showed a prolonged in-vitro drug release profile. Likewise, 17 and 21 wt.% of poloxamer 407 were characterized by a sustained sildenafil transfer from the lung into the perfusate. However, a 10 wt.% polymer solution displayed an immediate sildenafil absorption. Interestingly, increasing the poloxamer 407 concentration (21 and 17 vs. 10 wt.%) led to decreased organ weight gain kinetics and a lower total protein content found in the bronchoalveolar lavage fluid.

CONCLUSIONS

In-situ forming controlled release hydrogels represent a viable approach for inhalative therapy.

3D culture of tonsil-derived mesenchymal stem cells in poly(ethylene glycol)-poly(L-alanine-co-L-phenyl alanine) thermogel

Poly(ethylene glycol)-poly(L-alanine-co-L-phenyl alanine) (PEG-PAF) aqueous solutions undergo sol-to-gel transition as the temperature increases. The transition is driven by the micelle aggregation involving the partial dehydration of the PEG block and the partial increase in β-sheet content of the PAF block. Tonsil-tissue-derived mesenchymal stem cells (TMSCs), a new stem cell resource, are encapsulated through the sol-to-gel transition of the TMSC-suspended PEG-PAF aqueous solutions. The encapsulated TMSCs are in vitro 3D cultured by using induction media supplemented with adipogenic, osteogenic, or chondrogenic factors, where the TMSCs preferentially undergo chondrogenesis with high expressions of type II collagen and sulfated glycosaminoglycan. As a feasibility study of the PEG-PAF thermogel for injectable tissue engineering, the TMSCs encapsulated in hydrogels are implanted in the subcutaneous layer of mice by injecting the TMSC suspended PEG-PAF aqueous solution. The in vivo studies also prove that TMSCs undergo chondrogenesis with high expression of the chondrogenic biomarkers. This study suggests that the TMSCs can be an excellent resource of MSCs, and the thermogelling PEG-PAF is a promising injectable tissue engineering scaffold, particularly for chondrogenic differentiation of the stem cells.

Hydrogel formation by multivalent IDPs: A reincarnation of the microtrabecular lattice?

Based on high-voltage electron microscopic (HVEM) data of fixed cultured cells, an elaborate three-dimensional network of filaments, including and interconnecting other elements of the cytoskeleton, was observed in cells some half a century ago. Despite many attempts and comparative studies, this “microtrabecular lattice” (MTL) of the cytoplasmic ground substance could not be established as a genuine component of the eukaryotic cell, and is mostly considered today as a sample-preparation artifact of protein adherence and cross-linking to the cytoskeleton. Here we elaborate on the provocative idea that recent observations of hydrogel-forming phase transitions of repetitive regions of intrinsically disordered proteins (IDPs) bear resemblance in creation, organization and physical appearance to the MTL. We review this phenomenon in detail, and suggest that phase transitions of actin regulatory proteins, neurofilament side-arms and other proteins could generate non-uniform spatial distribution of cytoplasmic material in the vicinity of the cytoskeleton that might even give rise to fixation phenomena resembling the MTL. Whether such hydrogel formation by IDPs is a general physical phenomenon, will remain to be seen, nevertheless, the underlying organizational principle provokes novel experimental studies to uncover the ensuing higher-level regulation of cell physiology, in which the despised and long-forgotten concept of MTL might give some interesting leads.