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• The sol–gel phase transition of the sodium deoxycholate (NaDC) solutions is experimentally characterized. • Transition temperature and enthalpy are found to be highly sensitive to pH and concentration variations. • Transition volume shows that there is a contraction from the sol to the gel phase almost pH and concentration insensitive. • The thermodynamic properties are linked with the mesophases observed through electron microscopy. Sodium deoxycholate forms supramolecular aggregates in aqueous solution that are strongly dependent on temperature and pH. Upon fine tuning of these physicochemical parameters, two supramolecular aggregates can be achieved: a nanotubular phase having viscoelastic, gel-like, behavior and a sponge liquid phase. In this work, the thermodynamics of the transition between the two phases is characterized. Temperatures, volumes, and enthalpies of such transition have been experimentally determined using vibrating tube densitometry and differential scanning calorimetry. In addition, electron microscopy is used to follow the morphological transition between the two supramolecular structures. The dependencies of the thermodynamic properties with the pH and surfactant concentration of the solution are characterized, and the micrographs obtained from electron microscopy is used to explain the thermodynamics of the system. [ABSTRACT FROM AUTHOR]

Stimuli-responsive sol-gel transitions of biopolymers triggered by stimuli (e.g., temperature, pH, light, and electric field) have received tremendous attention due to their potential applications in controlled release of drugs, tissue engineering, and new functional materials. Herein, we use a simple approach to generate a fluorescent composite of quantum dots/gelatin with reversible sol-gel transition triggered by temperature stimuli. We initially prepared the aqueous CdS quantum dots with clear yellow fluorescence by a single-step process. These CdS quantum dots can reserve their fluorescence after they were combined with gelatin. Specifically, rheological measurements and vial inversion tests both confirm that CdS quantum dots/gelatin composite can undergo reversible sol-gel transition initiated by temperature stimuli near physiological temperature. Furthermore, it is shown that loading, preservation and release of CdS quantum dots in aqueous medium can be controlled by adjusting the temperature to trigger the sol-gel transition of the composite. Consequently, it can be expected that this fluorescent quantum dots/gelatin composite with thermo-responsive and reversible sol-gel transition has promising applications in biomedical fields such as bioimaging, biosensing, and drug delivery. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

In this paper we present the performance of the classical approach to polymer solutions in evaluation and interpretation of the experimental SAXS data obtained for aqueous solutions of two gelling polysaccharides κ-carrageenan and methylcellulose and a non-gelling polysaccharide λ-carrageenan. In a systematic structural SAXS study of various types of polymer solutions we pointed out and discussed the issues encountered and connected to the fact that the studied gels are obviously not "homogeneous gels" in terms of the structural details that the SAXS technique can resolve and the issues connected to the limited experimental resolution of the SAXS technique for such systems. In parallel the necessary modifications of the classical approach equations for the evaluation of the SAXS data are discussed. Furthermore, the detailed structural results of the studied aqueous polymeric systems in liquid state, during the onset of the gelation, and even in the gel state are presented. [ABSTRACT FROM AUTHOR]

The performances of a conducting paste and the thick film fabricated from it depend critically on the dispersion state of the functional powders. Detailed mechanisms dictating the interactions between functional powder, surfactant, and, in particular, polymer binder that lead to optimum particle dispersion remain elusive in general. For a series of practical micrometer-sized silver pastes (with a powder content of ~47 wt% or 7 vol%, in a commonly used solvent α-terpineol), we reported rheological fingerprints (i.e., significantly promoted sample elasticity) suggesting that while the surfactant (stearic acid, SA) aids the initial, local (~1 nm) particle dispersion, the polymer binder (ethyl cellulose, EC) then becomes effective to help achieve larger-scale (~30 nm) particle dispersion, permitting the development of colloidal fractals and time-evolving microphase transition closely mimicking typical sol-gel transition. The enhanced particle dispersion is evidenced also by the scanning electronic microscope morphologies of dried printing thick films. Overall, similar phase transition had rarely been reported for metal pastes, yet the underlying particle dispersion seems crucial to achieve as (environmentally required) decreasing powder content makes a paste and the fabricated thick film increasingly unlikely to fulfill the percolated state desirable for efficient electron conduction. [ABSTRACT FROM AUTHOR]

As one of the most widely used thermosensitive polymers, commercially available Pluronic F127 copolymer has been used as an attractive candidate for injectable hydrogel system. To tune its characteristics for better biomedical applications, the effects of collagen incorporation on its thermogelation in aqueous system and resultant hydrogel properties were investigated by dynamic rheological tests, scanning electron microscopic observation, in vitro drug release, and cytocompatibility assays. For its aqueous solution, the collagen incorporation was found to improve appropriately the sol-gel transition temperature for good injectability at room temperature and enhance obviously the temperature sensitivity for fast thermogelation. When compared to single Pluronic F127 copolymer thermogel, the composite thermogel with collagen showed a prolonged release for encapsulated drug and better cell compatibility. In addition, the effects on the morphology and viscoelastic behavior of resultant thermogel were also studied with respect to the concentration of incorporated collagen. [ABSTRACT FROM AUTHOR]

A well-defined temperature responsive ABA triblock copolymer, poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b- poly(ethylene glycol)-b-poly (2-(2-methoxyethoxy) ethyl methacrylate-co-N- hydroxymethyl acrylamide) [P(MEO2MA-co-HMAM)-b-PEG-b-P(MEO2MA-co- HMAM)], was synthesized by atom transfer radical polymerization (ATRP). The synthesized triblock copolymer was characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy and Gel Permeation Chromatography (GPC). The aqueous solution phase behaviors of the triblock copolymers were investigated by UV transmittance measurements, surface tension measurement, laser particle size and viscosity analysis. The micellization of temperature responsive triblock copolymer was investigated by fluorescence probe technique, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the molecular weight of the poly(ethylene glycol) (PEG), the N-hydroxymethylacrylamide (HMAM) content, and the degree of polymerization (DP) of the P(MEO2MA-co- HMAM) block for the synthesized triblock copolymers could all affect the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The higher the molecular weight of the PEG and the HMAM content for a given triblock copolymer are, the higher the LCST of its aqueous solution. The higher the DP of the P(MEO2MA-co-HMAM) block is, the lower the LCST of the copolymer aqueous solution. Sol–gel transition temperature (Tsol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the molecular weights of the PEG, the DP of the P(MEO2MA-co-HMAM) blocks and the concentration of the copolymer aqueous solution. Copolymer hydrogels loaded with bovine serum albumin (BSA) were used for the release study. The results revealed that 1) the hydrogels had sustained release for the BSA, 2) the release rate for the BSA is dependent of the length of the PEG chain, and 3) the longer the PEG chain is, the faster the release rate of the hydrogel for the BSA. [ABSTRACT FROM AUTHOR]

Novel hydrophilic, temperature responsive, and biodegradable ABA tribl°Ck-graft copolymers, [poly( ɛ-caprolactone)- g-poly(2-(2-methoxyethoxy) ethyl methacrylate- co-oligo(ethylene glycol) methacrylate)]- b-poly(ethylene glycol)- b-[poly(-caprolactone)- g-poly(2-(2-methoxyethoxy) ethyl methacrylate- co-oligo(ethylene glycol) methacrylate)] ([PCL- g-P(MEOMA- co-OEGMA)]- b-PEG- b-[PCL- g-P(MEOMA- co-OEGMA)]) (tBGs), were synthesized via a combination of ring-opening polymerization (ROP) of ɛ-caprolactone ( ɛCL) and α-chloro- ɛ-caprolactone ( αCl ɛCL) in the presence of PEG and atom transfer radical polymerization (ATRP) of MEOMA and OEGMA. Temperature responsive P(MEOMA- co-OEGMA) graft chains on the hydrophobic PCL block of PCL- b-PEG- b-PCL not only improved the solubility of PCL- b-PEG- b-PCL in water, but also endowed it with temperature sensitivity. The synthesized temperature responsive triblock-graft copolymers formed well-defined core-shell micelles as the temperature was above their LCST ( ca. 35 °C), with hydrophilic PEG block as shell, P(MEOMA- co-OEGMA) graft chains on the PCL block and hydrophobic PCL block aggregates as core. The micellization induced by temperature for the tBGs in aqueous solutions had been investigated by transmittance measurement, laser particle size measurement, HNMR in DO, DLS and TEM. For a given tBG5 aqueous solution (30 wt%), a weak hydrogel was available at 35 °C, and its sol-gel transition temperature gradually decreased with increasing concentration. In addition, the tBG5 hydrogels loaded with anethole were used for hydrophobic drug release, and in vitro the sustained release of anethole from the tBG5 hydrogels was examined, which is a significant for anethole for their biomedical applications. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Poly(ethylene glycol) (PEG) is partially furanylated with different feed ratios of furfuryl isocyanate and used as the macro initiator of ring-opening polymerization of l- and d-lactides to synthesize copolymer mixtures of furan-terminated AB diblock and ABA triblock copolymers (poly(oxyethylene)-poly( l-lactide)/poly( l-lactide)-poly(oxyethylene)-poly( l-lactide) and poly(oxyethylene-poly( d-lactide)/poly( d-lactide)-poly(oxyethylene)-poly-( d-lactide)) having different diblock/triblock ratios. The mixed micelle solutions of these enantiomeric copolymer mixtures undergo sol-to-gel or gel-to-sol transition depending on the diblock/triblock ratio of the copolymer mixtures. The rheological properties of the mixed micelle solutions could also be controlled by changing the diblock/triblock ratios or the initial furanylation ratio of PEG. [ABSTRACT FROM AUTHOR]

Hydrocarbons are easily extracted by organic solvents such as n-decane from wet samples of Botryococcus braunii by thermal pretreatment at 90 °C even after being cooled to room temperature. However, hydrocarbon recoveries are not as readily achieved at room temperature from samples pretreated at temperatures lower than 80 °C. This suggests that there is the point of no return for pretreatment temperature that enables effective solvent extraction of hydrocarbons at room temperature from wet algal samples of B. braunii. To elucidate the mechanism of hydrocarbon recovery from B. braunii following thermal pretreatments, we investigated the thermophysical properties of the water phase separated from heated algal slurry. Differential scanning calorimetry (DSC) measurements revealed sol-gel transitions in the water phase of algal slurry after protein denaturation at 64 °C in samples that was pretreated at 70 or 80 °C but not in those pretreated at 90 °C. Furthermore, the pretreated >70 °C water-soluble polymers revealed polysaccharides composed of galactose, arabinose, and uronic acid. These results suggest that the transition from sol state to gel state of water-soluble polysaccharides in algal slurry prevented hydrocarbon recovery with organic solvents since hydrocarbons were easily recovered from sol state samples pretreated at 70 or 80 °C when the extraction temperature was kept the same as the pretreatment temperature. These results reveal that the presence of water-soluble polymers with gelation ability in the water phase and removal of these polymers in sol state enable effective recovery of hydrocarbons at room temperature after thermal pretreatments. [ABSTRACT FROM AUTHOR]

pH and temperature-sensitive biodegradable poly( β-aminoester)-graft-poly( ε-caprolactone)-block-methoxy poly(ethylene glycol) (PBAE-g-PCL-b-mPEG) amphiphilic graft copolymers with different molecular weights were synthesized. The structure of these copolymers was adjusted by varying the feed ratios of ε-caprolactone to methoxy poly(ethylene glycol)s (mPEG), amine and diacrylate monomer amounts and the molecular weight of mPEG. Aqueous solutions of these copolymers formed micelles at lower concentrations; however, the concentrated solutions showed a reversible sol-gel transition property depending on both pH and temperature changes under representative physiological conditions (pH 7.4, 37°C). The effects of the molecular weight of pH-sensitive poly( β-aminoester) block and mPEG group, the hydrophobic to hydrophilic block ratio (PCL/mPEG) and the concentration of the copolymer on the sol-gel transition were investigated. Proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography measurements were used to characterize the structure of the synthesized copolymers. The self-assemble behavior and critical micelle concentration of the amphiphilic copolymers were estimated in phosphate buffer solution using fluorescence spectroscopy. The gelling behavior was measured by using tube inversion method. At pH 7.4, all copolymer solutions prepared 20 wt% concentration indicated sol-gel transition with increasing temperature. In vitro degradation experiments displayed that the synthesized graft copolymers mostly degraded hydrolytically within 20 days under physiological conditions. In order to investigate the potential application of synthesized hydrogels in drug delivery, Methylene Blue was used and approximately 70% of the loaded amount was released in 120 hr. The findings indicate that obtained graft copolymers can be used as injectable biodegradable carriers for pharmaceutical drugs. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The paper at hand deals with the properties of a particular organogel, namely the binary system n -decane/12-hydroxyoctadecanoic acid (12-HOA). To provide a complete characterisation we firstly determined the sol–gel transition temperatures as a function of the gelator concentration with DSC and rheometry. Moreover, we calculated thermodynamic parameters from the DSC measurements such as the sol–gel transition enthalpy. Secondly, we studied the rheological properties with an oscillating shear rheometer. Thirdly, we investigated the structure of the gel network and of the gelator fibers. For this purpose, we carried out SANS measurements from which we obtained structural parameters such as the mean radius of the fibers and the mean thickness of the fiber nodes, but also the mole fraction of gelator involved in building up the gelator network. Additionally we present electron microscopy (EM) pictures of a 12-HOA gel prepared with the freeze-fracture method (FFEM). FFEM allows imaging a sample in its original state due to cryofixation while other EM methods require modifications like evaporation of the gel solvent. From our pictures we were able to determine the sense of the helical twist of the gelator fibers and we also observed a layered fine structure, which – to the best of our knowledge – has not been seen in EM pictures of 12-HOA gels yet. Our study allows an in-depth understanding of the gelator network in the model system n -decane/12-HOA. Moreover, our results are in perfect agreement with all data published for binary organogels consisting of an oil and 12-HOA, which, in turn, will help to understand many of the unanswered questions that still exist in relation to gels. [ABSTRACT FROM AUTHOR]

The phase behaviors are studied in the ternary system of gelatin-water–poly(ethylene glycol) oligomer. It is found that both the phase separation and the sol–gel transition occur simultaneously when the poly(ethylene glycol) oligomers are added to the aqueous gelatin solution. The phase separation boundary is found to shift in the higher temperature than the sol–gel transition line when the higher molecular weight oligomers of poly(ethylene glycol) coexist in the solution. The competition of these two transitions creates two new phases in the system, the phase separated solution of gelatin and poly(ethylene glycol) and the opaque gelatin gel in which the density fluctuation due to the phase separation is frozen in. [ABSTRACT FROM AUTHOR]

The sol–gel transition of nanoparticles (NPs)/polymer mixture in aqueous medium was investigated for the sustained delivery of exenatide to treat type 2 diabetes mellitus. Exenatide-loaded multilayer NPs were prepared using a layer-by-layer approach which utilized the interaction between Pluronics and lipid bilayers as the main driving force for the construction of the multilayer. Pluronic F-127 was the polymer used, and it forms a gel at body temperature. Although the antidiabetic effects of exenatide-loaded multilayer NPs have been demonstrated previously in an animal model, in this work, the attempt was made to demonstrate the extended duration of antidiabetic effects, which was accomplished by localizing the exenatide-loaded NPs in muscular areas in the body through the gelation of Pluronic F-127. Transmittance electron microscopy and dynamic light scattering were used to examine the morphology of the multilayer NPs/polymer mixture. A change in the release pattern of exenatide was observed after gel formation at body temperature, and Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis was performed using native exenatide and a reference biomarker as control to observe whether exenatide extracted from the multilayer NPs and the multilayer NPs/Pluronic F-127 mixture degraded or not. We then observed the antidiabetic effect of exenatide-loaded multilayer NPs/Pluronic F-127 mixture by monitoring blood-glucose levels in db/db mice. In vitro and in vivo correlation was discussed regarding structural variation in the delivery vehicles. [ABSTRACT FROM AUTHOR]

Block ratio and block sequence of polypeptide influenced the self-assembly of copolymer significantly. Tuning self-assembly to form various nanostructures with different properties through molecular design was a rather feasible strategy. Triblock copolymers based on poly(l -alanine) (PA), poly(l -valine) (PV) and poly (ethylene glycol) (PEG) with various block ratio and block sequence were synthesized. The number of amino acid residues was kept at 10. The sol-gel transition behavior, self-assemble nanostructure, secondary structure of the copolymers in aqueous solution were investigated to reveal that PA block between PEG and PV segment interfered the β-sheet structure, resulting in the reduced or increased sol-gel transition temperature or precipitation depended on the block ratio of PA and PV. Shorter PA or PV block displayed more significant influence on sol-gel transition. Interestingly, PV block between PEG and PA segment induced the formation of more stable β-sheet stacking structures, leading to sol-gel transition at higher temperature. PEG dehydration and the enhancement of ordered structure with temperature rising caused the sol-gel transition of these copolymers. We concluded herein that disordered structure in co-polypeptide can enhance thermo-sensitivity. [Display omitted] • Conformation of synthesized non-natural polypeptides based on side-chain design. • Block sequence of non-natural polypeptides affected sol-gel transition. • Shorter peptide block influenced more significantly on sol-gel transition. • Less hydrophobic and weaker steric hindrance block at the tail enhanced the stability of nanostructures. • Disordered structure in co-polypeptide enhanced thermo-sensitivity. [ABSTRACT FROM AUTHOR]

Developing fully rigid-chain polyimides with reversible sol-gel/gel-sol transitions is of great interest for designing high-performance materials. To date, few approaches have been employed to construct polyimide gels other than hydrogen bonding. Here, we report a polyimide-Zn(II) complex with thermo-responsive sol-gel/gel-sol transition behavior by introducing supramolecular coordination interactions. The tunable dynamic sol-gel behaviors of polyimide-Zn(II) complexes were confirmed using rheological methods. Microstructure analysis shows that coordination interactions occur between the benzimidazole molecules and Zn(II) ions. As a result, the apparent viscosity of the polyimide-Zn(II) complex even rises approximately four orders of magnitude higher than that of the PI-neat oligomer solution. Based on the 2D-correlation spectra and X-ray diffraction results, we deduced that the formation of dense chain stacking caused by coordination effects plays an essential part in the reversible sol-gel transition. As a preliminary experiment, this work gives a novel strategy to construct polyimide gels, showing application prospects in the fabrication of porous polyimide membranes, high-performance polyimide fibers, and aerogels, etc. • A novel polyimide-Zn(II) organogel was prepared by introducing supramolecular coordination bonds. • Strong interactions undergo between the benzimidazole molecules and Zn(II) ions. • The chain stacking behavior caused by coordination effects plays an essential part in the reversible sol-gel transition. [ABSTRACT FROM AUTHOR]

[Display omitted] • PUFA rich-W 1 /O/W 2 double emulsions developed by the sol–gel transition of W 1 and O. • κ-Carrageenan and monoglyceride changed to gel-like structures with thermal treatment. • Effect of O gelation on improved physical stability was more dominant than W 1 gelation. • Gelation reduced the oxidative stability in the presence of iron in W 1 droplets. • α-Tocopherol was more effectively than gallic acid on improved chemical stability. In this study, the effect of sol–gel transition of oil phase (O) and inner aqueous phase (W 1) on the physical and chemical stability of a model PUFA rich-W 1 /O/W 2 double emulsion (DE) was investigated. Thermal-driven gelation of O and W 1 was performed using monoglyceride and κ-carrageenan, respectively. To accelerate lipid oxidation, ferrous sulfate was encapsulated in W 1. Using this approach, O gelation reduced the volume-weighted size (d 4,3) of DEs droplets and provided good physical stability. However, non-gelled DEs and those containing gelled W 1 exhibited extensive flocculation and coalescence. Moreover, oleogelation resulted in a predominant elastic behavior with weak frequency dependence of viscoelastic properties. Oxidation was significantly reduced by W 1 gelation; however, the O gelation led to a higher oxidation rate. Oxidation kinetic parameters induced by a hydrophilic (gallic acid) and a lipophilic (α-tocopherol) antioxidant showed that DEs containing gelled O droplets presented high physical and oxidative stability when α-tocopherol was present. [ABSTRACT FROM AUTHOR]

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We report a study where we follow a chemical crosslinking process and record the intensity autocorrelation functions for two polymer systems, hydroxyethylcellulose (HEC) and hydrophobically modified hydroxyethylcellulose (HMHEC), by dynamic light scattering (DLS). Due to the distinct chemical structures, the measured intensity autocorrelation function shows significant difference between the two systems. Two relaxation modes were found for both systems, which were attributed to the cooperative relaxation and the structural relaxation. The decay rate for cooperative diffusion was found to decrease during the gelation for HEC, but it remains constant for HMHEC. The same trend was found for the structural relaxation where the decay rate decreased as a function of the gelation time for HEC, but not for HMHEC. By analyzing the amplitudes of both relaxation modes, we also found that during the gelation the structural relaxation was suppressed, which was caused by the decrease of the elastic modulus. [ABSTRACT FROM AUTHOR]

ABSTRACT When PEG (M.W.∼5000 Daltons) is conjugated to poly( l-alanine), the polymer aqueous solutions (<10.0 wt.%) undergo sol-to-gel (thermal gelation), whereas it is conjugated to poly( l-lactic acid), the polymer aqueous solutions (>30.0 wt.%) undergo gel-to-sol (gel melting) as the temperature increases. In the search for molecular origins of such a quite different phase behavior, poly(ethylene glycol)-poly( l-alanine) (PEG-PA; EG113-A12) and poly(ethylene glycol)-poly( l-lactic acid) (PEG-PLA; EG113-LA12) are synthesized and their aqueous solution behavior is investigated. PEG-PAs with an α-helical core assemble into micelles with a broad size distribution, and the dehydration of PEG drives the aggregation of the micelles, leading to thermal gelation, whereas increased molecular motion of the PLA core overwhelms the partial dehydration of PEG, thus gel melting of the PEG-PLA aqueous solutions occurs. The core-rigidity of micelles must be one of the key factors in determining whether a polymer aqueous solution undergoes sol-to-gel or gel-to-sol transition, as the temperature increases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, , 52, 2434-2441 [ABSTRACT FROM AUTHOR]

ABSTRACT When PEG (M.W.∼5000 Daltons) is conjugated to poly( l-alanine), the polymer aqueous solutions (<10.0 wt.%) undergo sol-to-gel (thermal gelation), whereas it is conjugated to poly( l-lactic acid), the polymer aqueous solutions (>30.0 wt.%) undergo gel-to-sol (gel melting) as the temperature increases. In the search for molecular origins of such a quite different phase behavior, poly(ethylene glycol)-poly( l-alanine) (PEG-PA; EG113-A12) and poly(ethylene glycol)-poly( l-lactic acid) (PEG-PLA; EG113-LA12) are synthesized and their aqueous solution behavior is investigated. PEG-PAs with an α-helical core assemble into micelles with a broad size distribution, and the dehydration of PEG drives the aggregation of the micelles, leading to thermal gelation, whereas increased molecular motion of the PLA core overwhelms the partial dehydration of PEG, thus gel melting of the PEG-PLA aqueous solutions occurs. The core-rigidity of micelles must be one of the key factors in determining whether a polymer aqueous solution undergoes sol-to-gel or gel-to-sol transition, as the temperature increases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, , 52, 2434-2441 [ABSTRACT FROM AUTHOR]

The colloidal sol-gel transition based on zirconyl nitrate solution systems is investigated in this work. The different steps occurring in the transition have been identified by coupling small angle X-ray scattering with Raman spectroscopy and rheology measurements. The effect of the experimental conditions, such as the zirconium precursor concentration and pH, on the transition is studied. The precise mechanisms involved during the transition are based on a detailed understanding of the nanostructure of these systems. In particular, the dissolution of the zirconium salt leads to the formation of cyclic tetramers that self-organize into a cylindrical shape. We clearly demonstrate that increasing the pH induces a strong attractive interaction between the cylinders, giving rise to a mass fractal dimension. For each system, two characteristic pH values have been determined via rheological measurements analysis, where gelation is notably slow below the first pH value and precipitation occurs above the second one. The complete description of the quaternary system (zirconyl nitrate + acetylacetone + ammonia + water) is an efficient formulation guide for the further combination with a templating route leading to structured Zr-based materials. [ABSTRACT FROM AUTHOR]

In this study, various surfactants were added to control the gelation time of silk fibroin (SF) aqueous solution. The gelation behaviors of SF aqueous solution in the presence of surfactant were investigated with attenuated total reflectance infrared, SEM, and a viscometer. When surfactants other than chitooligosaccharide were added into an SF aqueous solution, the gelation time of the solution was decreased under the fixed conditions. Particularly, anionic surfactant was found to be more effective than non-ionic and cationic surfactants in accelerating the gelation of SF. In addition, the conformational changes of SF hydrogel with or without surfactant were investigated in a time-resolved manner using infrared spectroscopy. Conformational transitions of SF nanofibers from random coil to β-sheet forms were strongly dependent on the inherent properties of surfactant, and on the different interactions between surfactant and SF molecules in aqueous solution. This approach to controlling the gelation of SF aqueous solution by the surfactant, and to monitoring their conformational changes on a real-time scale, may be critical in the design and tailoring of SF hydrogels useful for biomedical applications. [ABSTRACT FROM AUTHOR]

Abstract: The phase diagrams of kappa/iota-hybrid carrageenan (KI) in KCl and NaCl are reported for the first time, together with the large strain properties of obtained KI gels. KI shows salt specificity as phase diagrams in KCl and NaCl are different. These diagrams do not comply with those of a mixture of kappa- and iota-carrageenan (K + I). Concentrated KI solutions in NaCl up to 0.3 mol/L exhibit viscoelastic properties reminiscent from entangled neutral polymers with no aggregation. Both KI and K + I gels are strain hardening, and show a concentration scaling of the elasticity with exponents ranging from 1.2 to 3.2 depending on the type of salt and ionic strength. The strain at break of KI gels does not show salt specificity in contrast to K + I gels. In NaCl, KI gels are less brittle than K + I gels. In KCl, KI gels show the same level of strain at break as the corresponding carrageenan mixture. [Copyright &y& Elsevier]

Methylcellulose (MC), a hydrophobically modified cellulose derivative, in an aqueous solution undergoes sol-to-gel and gel-to-sol transitions on heating and cooling, respectively. Using differential scanning calorimetry, MC in light (HO) and heavy (DO) water solutions has been investigated to elucidate the solvent isotope effect on the transitions. As a result, their transition temperatures are higher in HO by about 4 °C than DO. This phenomenon is rationalized in terms of the strength of the hydrophobic attractive interaction; the strength is enhanced by DO. We discuss the reason for the enhancement and the difference in the isotope effect between MC and a poly( N-isopropylacrylamide) polymer which shows an opposite trend to MC. [ABSTRACT FROM AUTHOR]

Protein concentration, pH, the types and concentrations of metallic ions, and extensional flow are thought to be important environment parameters affecting the natural spinning process. In this study, we investigate the effects of the types and concentrations of metallic ions (Ca, Mg, and K ions), pH, and silk fibroin concentration on the sol-gel transition and the rheological behavior of a regenerated silk fibroin (RSF) aqueous solution. The results show that with an increase in the silk fibroin concentration, the weak acidic RSF aqueous solutions containing Mg or Ca ions undergo a phase transition to a weak gel state. Moreover, the rheological characterization of RSF aqueous solutions shows a dramatic change, and their apparent viscosities increase by almost three orders of magnitude and approach the apparent viscosity of the native dope in the silkworm gland. By using conventional pressure equipment, we investigate the dry-spinnability of weak gels. Further, we observe that the as-spun fibers exhibit a smooth surface and have inferior mechanical properties. The structure of the as-spun fibers is predominantly in a random coil or Silk I conformation. [ABSTRACT FROM AUTHOR]

PolyP (inorganic polyphosphate) is a linear polymer of tens to hundreds of orthophosphate residues linked by high-energy phosphoanhydride bonds. This polymer is present in all living organisms from bacteria to mammals. Until recently, most of the studies on polyP have focused on its function in prokaryotes. In prokaryotes, polyP has been implicated in many unrelated processes ranging from basic metabolism to structural functions. However, polyP analysis and function in higher eukaryotes has been gainingmomentum recently. In the present review, we mainly aim to discuss the proposed intracellular functions of polyP in higher eukaryotes and its detection methods. [ABSTRACT FROM AUTHOR]

The chitosan-human-like collagen/β-sodium glycerophosphate (CS-HLC/β-GP) hydrogel, is sensitive to pH and temperature changes and has proved to be a potential candidate as an injectable filling biomaterial in plastic and reconstruction surgery. The formation and pH/temperature-sensitivity mechanism of the novel CS-HLC/β-GP hydrogel were explored by Fourier transform infrared spectroscopy (FTIR) and swelling tests. Our results showed that an amide bond (-CONH) is formed between the carbonyl (CO) of HLC and the amino of CS and -NRH2+is formed between the amide bond and β-GP; the temperature sensitivity depended on the hydrophobic-hydrophilic interaction of molecular chains, and the pH sensitivity depended on the electrostatic interaction of ionic groups (-NRH2+and -OPO32-). The properties of the novel CS-HLC/β-GP hydrogel were also examined using the tube inverting method, the swelling test, the liquid displacement method, and mechanical testing. The gelling time before and after addition of HLC is 30 min and 8 min, respectively, at 37°C. Compared with conventional CS/β-GP hydrogels, such as CS-AC (animal-derived collagen)/β-GP hydrogel, the CS-HLC/β-GP hydrogel showed a desirable porosity level, swelling ratio, pH/temperature sensitivity, a smooth surface, regular porous networks, and adequate mechanical strength and cross-linking densities. Therefore, the CS–HLC/β-GP hydrogels are excellent candidates for use in biomedical fields, such as in soft tissue defect filling and drug delivery. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microbeads containing tranexamic acid for oral controlled release application. [•] Microbeads were prepared in complete aqueous environment thereby toxicity due to organic solvents was bypassed. [•] In vivo study confirmed the controlled release activity of these newly prepared microbeads. [•] pH sensitive drug delivery system. [ABSTRACT FROM AUTHOR]

A sol-gel transition and the self-healing of the resultant hydrogels are achieved utilizing a metallo-supramolecule composed of terpyridine-terminated low-molecular-weight three-armed poly(ethylene glycol) (trisPEGtpy450) in water at ambient temperature. The gelation of trisPEGtpy450 with cobalt ions occurs by aerobic oxidation (mild conditions), and therefore the solution can be moulded into any shape hydrogel. The solation of the cured hydrogels occurs spontaneously upon the addition of the reductant, and the solution is then re-gelled by exposure to air due to the consumption of the reductant. Both a sol-gel transition by aeration and self-healing of the resultant hydrogels without any stimuli are observed when replacing some of the cobalt ions with nickel ions. [ABSTRACT FROM AUTHOR]

In recent years, intensive research has been carried out on the use of hydrogels obtained from natural polymers, mainly chitosan. These products are increasingly replacing solutions based on synthetic materials in medicine. This publication presents the results of studies on the sol-gel transition of chitosan solutions as the base material for the preparation of thermosensitive hydrogels for potential applications in tissue engineering. The measurements were carried out for systems consisting of chitosan lactate and chitosan chloride solutions using β-glycerol phosphate disodium salt pentahydrate and uridine 5'-monophosphate disodium salt as the cross-linking agents. The sol-gel transition point of the solutions was determined based on the rheological measurements in the cone-plate configuration of the rotational rheometer and experiments performed using the method of nuclear magnetic resonance. The obtained results showed a significant influence of the cross-linking agent on the course of the sol-gel transition of chitosan salt solutions, and the systems that consisted of chitosan lactate seemed to be especially interesting for biomedical applications.

The progress of nanotechnology enables us to make use of the special properties of materials on the nanoscale and open up many new fields of biomedical research. Among them, thermosensitive nanomaterials stand out in many biomedical fields because of their "intelligent" behavior in response to temperature changes. However, this article mainly reviews the research progress of thermosensitive nanomaterials, which are popular in biomedical applications in recent years. Here, we simply classify the thermally responsive nanomaterials according to the types of polymers, focusing on the mechanisms of action and their advantages and potential. Finally, we deeply investigate the applications of thermosensitive nanomaterials in drug delivery, tissue engineering, sensing analysis, cell culture, 3D printing, and other fields and probe the current challenges and future development prospects of thermosensitive nanomaterials., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Guo, Sun, Wang, Wang, Jing and Liu.)

Dexamethasone (DEX) loaded supramolecular gelatin-based composite; DEX release from UPy modified gelatin scaffold (A; GelUPy); and GelUPy incorporated with UPy grafted Zn-doped hydroxyapatite (B). [Display omitted] Synthesis of a supramolecular composite hydrogel, a novel class of physical and dynamic hydrogels, is reported. The hydrogel comprised gelatin (Gel), Zn-doped nano-hydroxyapatite (nZnHAp), and dexamethasone disodium phosphate (DEX). nZnHAp was functionalized with ureidopyrimidinone (UPy; quadruple hydrogen-bond-forming groups). The nHAp, nZnHAp, and nZnHApUPy were characterized by FTIR, EDX, SEM, and TGA analysis. Gelatin was also functionalized with UPy groups (GelUPy), and the nanocomposites were prepared in solution (GelUPy/nZnHApUPy). Dexamethasone was added to the composite hydrogels (15, 20, and 25 wt%), as an osteoinductive and anti-inflammation medicine (GelUPy/nZnHApUPy/DEX). The mechanical (in compression mode), rheological, and thermal properties of the GelUPy/nZnHApUPy/DEX were compared with those of GelUPy/nZnHAp/DEX. The GelUPy/nZnHApUPy/DEX series showed the maximum compressive modulus (about 841 KPa) for GelUPy/nZnHApUPy/DEX25% in the swollen state. DSC analysis indicated that T g of the pure GelUPy decreased significantly upon composite preparation and drug loading from 160 °C for GelUPy, down to 107 °C for GelUPy/nZnHApUPy/DEX15%. In-vitro drug release studies confirmed sustained release of DEX over a period of 12 days for GelUPy/nZnHApUPy composites with no remarkable initial burst compared to that of the pure GelUPy. Overall, our data suggests that the DEX carrying supramolecular nanocomposite can be used as an osteogenic hydrogel scaffold for bone tissue engineering applications. [ABSTRACT FROM AUTHOR]

Gummies are gelatin-based confectionery gel products where the sweeteners play vital roles in the product texture. This study focused on the impacts of sweeteners, which make up ~70–80% of the total solids, on the sol properties , gelling, and melting behaviors of gelatin (4–6%) gels. Gelling and melting properties of gelatin solutions with and without sweeteners (sucrose and glucose syrup) were characterized with rheology and differential scanning calorimetry, while the final gel texture and surface properties were analyzed with texture analyzer and tensiometer. In contrast to the plain systems without sweeteners, which gelled at around 22 °C and melted at 35 °C, the high-sweetener systems exhibited coil-to-helix transition at a higher temperature level, and the subsequent sol-gel transition depended greatly on the bulk viscosity. Below the sucrose-syrup level of 75.9%, the transition was observed at 34–43 °C; higher levels of saccharides postponed or inhibited the transition. The internal interactions of high-sugar gels were considerably weaker than the plain gels, suggesting smaller and more dispersed junction zones. The quantities of melting enthalpy and internal interactions increased with gelatin concentration but decreased with sucrose-syrup level, due to the high viscosity. Gel surfaces were generally hydrophobic (non-polar) except for the 4% gelatin gels, whose surface polarity increased with sugar level. Gel hardness and tackiness increased with gelatin concentration but did not change significantly with moisture/sugar content at 5–6% gelatin. [Display omitted] • Gelling and melting behaviors of plain and high-sugar gelatin gels were compared. • Renaturation rate decreased with the sucrose-syrup levels due to high viscosity. • Rheology and texture of gels were governed by both gelation and glass transition. • Gelatin gels had hydrophobic surfaces except for high-sugar gels with 4% gelatin. • Surface tackiness was strongly correlated with the hardness of the gels. [ABSTRACT FROM AUTHOR]

Alginate hydrogels have the most extensively explored injection system among natural molecular. The injectable alginate hydrogel has special physical and biological properties without toxicity, therefore, it has been served as minimally invasive treatments to treat various irregular defects. However, the inconvenient truth is low formability and poor mechanical properties of injectable alginate hydrogels; besides, there are little relevant studies about controlling, measurement and analysis of the sol-gel transition and degradation process. We synthesized an injectable nanocomposite alginate hydrogel, used specific methods and equipment to regulate and evaluate the sol-gel transition of the hydrogel, moreover, we researched the degradation behaviour using scanning electron microscope, nano-indenter and titration analysis. The results showed that gelation time and mechanical properties could be regulated and effectively described. Compression properties of the hydrogels increased to 150%–300% compared with common alginate hydrogels, in addition, the degradation behaviour with ions release could be regulated by the formula. The results will be propitious to solve problems in quality control of hydrogel manufacturing engineering and the nanocomposite hydrogels with good biocompatibility will have great potential for multifunctional biological scaffolds and tissue engineering. • Low formability and poor mechanical properties limit injectable alginate hydrogels' application. • Nanocomposite alginate hydrogels with regulable sol-gel transition and double-network structure. • Designed new methods and provided detailed observations of the sol-gel transition for quality control. • Relatively stable mechanical property and sustained release property during degradation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Systematic rheological investigation on alkylamine-ethylene glycol organogel was conducted. [•] Scaling laws of elasticity vs concentration was used to infer the structural features. [•] Growth mechanism of newly born fibers is controlled by supersaturation. [Copyright &y& Elsevier]

Because of both its complexing ability toward Ti cations and reactivity in highly acidic medium, N, N-dimethylformamide (DMF) can be used to control the hydrolysis and condensation of Titanium oxide frameworks, starting from Ti oxychloride as precursor. The addition of water allows promotion of hydrolysis of the aldehyde while controlling the size of the nanoparticles formed in the solution. The as-prepared colloidal solutions are very stable, up to 3 months, depending on the initial titanium concentration, the DMF/Water ratio, and the thermal treatment. The sol to gel transformation was monitored by viscosimetry measurements as a function of ageing time and heat treatment temperature. Optimization of pre-treatment at moderate temperature leads to fine control over the gelation process. [ABSTRACT FROM AUTHOR]

Furan-terminated poly(oxyethylene)- block-poly(L-lactide) (MePEG-PLLA-F) and poly(oxyethylene)- block-poly(D-lactide) (MePEG-PDLA-F) are synthesized by ring-opening polymerization of L- and D-lactides, respectively, in the presence of poly(ethylene glycol) monomethyl ether (MePEG) and the following terminal reaction with furfuryl isocyanate. Their mixed micelle solution turns to gel quickly with stereocomplexation of the enantiomeric PLLA and PDLA. When 1,8-bis(maleimido)diethylene glycol (BMG) is added to the mixed micelle solution, the gelation is promoted by the terminal coupling of the copolymers driven by the Diels-Alder reaction of the furanyl groups and BMG giving a gel having higher strength. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this study was to investigate the effect of the asymmetry of the triblock copolymers on their thermoresponsive self-assembly behavior. To this end, nine ABA-type triblock copolymers with n-butyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) consisting of the A and the B blocks, respectively, were synthesized. Polymers of three different DMAEMA contents (50, 60, and 70 wt %) were synthesized while varying the length ratio of the two hydrophobic A blocks. Specifically, one symmetric ABA triblock copolymer and two asymmetric ABA′ triblock copolymers with the length of the second A block to be twice or four times bigger than the length of the first A block (AB2A and AB4A triblock copolymer) were synthesized for each DMAEMA composition. Three statistical copolymers were also synthesized for comparison. The thermoresponsive behavior of the copolymers was studied and it was found that the cloud point and rheological properties of the polymers were strongly affected by the architecture (statistical vs. block) and less strongly by the DMAEMA composition and the asymmetry of the polymers. Nevertheless, interestingly the asymmetry of the ABA triblock copolymers did influence the thermoresponsive behavior with the more symmetric polymers presenting a sol-gel transition at lower temperatures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2850-2859. [ABSTRACT FROM AUTHOR]

Abstract: The sol–gel transition temperatures of 0.1–1.0% high acyl gellan (HAG) with 0–200 mM NaCl or KCl and 0–20 mM CaCl2 or MgCl2 were determined using rheological measurements. Transition temperatures for monovalent cations, Na+ and K+, in the range of 50–80 °C were not significantly different (p > 0.5). Absence of thermal hysteresis was the salient feature. However, thermal hysteresis (∼4.4 °C) was observed for 0.1% HAG without added salt, but disappeared on increasing HAG and counterion concentrations. Few concentrations of HAG and added monovalent and divalent cations showed thermal hysteresis not higher than 2.5 °C. Transition temperatures for divalent cations were similar to those for monovalent cations although for considerably lower concentrations of Ca2+ or Mg2+. Increasing concentrations of monovalent and divalent counterions give rise to higher transition temperatures but not to higher storage moduli. This was interpreted as a lack of cross-link formation in the three-dimensional network structure of the gels. A single sol–gel transition diagram for monovalent cations is proposed, in which different zones associated with the presence of ordered and disordered conformations serve to identify the conditions in which HAG can exist in aqueous media. [Copyright &y& Elsevier]

A series of amphiphilic temperature-responsive star-shaped poly(D,L-lactic-co-glycolic acid)-b-methoxy poly(ethylene glycol) (PLGA-mPEG) block copolymers with different arm numbers were synthesized via the arm-first method. Gel permeation chromatography data confirmed that star-shaped PLGA-mPEG copolymers had narrow polydispersity index, indicating the successful formation of star-shaped block copolymers. Indirectly, the 1H NMR spectra in two kinds of solvents and dye solubilization method had confirmed the formation of core-shell micelles. Further, core-shell micelles with sizes of about 30-50 nm were directly observed by transmission electron microscopy. Subsequently, the micellar sizes and distributions as a function of concentrations and temperature were measured. At various copolymer concentrations, individual micelles with size of 20-40 nm and grouped micelles with size of 600-700 nm were found. Micellar mechanism of star-shaped block copolymers in aqueous solution was simultaneously discussed. In addition, sol-gel transition of star-shaped block copolymers in water was also investigated via the inverting test method. The critical gel temperature (CGT) and critical gel concentration (CGC) values of two-arm, three-arm and four-arm copolymer solutions were markedly higher than ones of one-arm copolymer. Moreover, the same CGC values of copolymer solution with different molecular weight and the same arm composition were ~15 wt %, and CGT values increased from ~38 to ~47°C with increasing arm numbers. Finally, the temperature-dependent micellar packing gelation mechanism of star-shaped block copolymer was schematically illustrated. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a new thermo-sensitive polymer, glycol chitin, was synthesized by controlled N-acetylation of glycol chitosan and evaluated as a thermogelling system. The physico-chemical properties of glycol chitins with different degrees of acetylation (DA) were investigated in terms of degradation, cytotoxicity, rheological properties, and in vitro and in vivo gel formation. Aqueous solutions of glycol chitins were flowable freely at room temperature but quickly became a durable gel at body temperature. Thermo-reversible sol–gel transition properties were observed with fast gelation kinetics. Glycol chitins with higher DA showed faster degradation in the presence of lysozyme. They exhibited no significant biological toxicity against human cell lines. An anti-cancer drug, doxorubicin, could be incorporated into the hydrogel by a simple mixing process and released in a sustained pattern over 13 days. Our findings suggest that glycol chitins could be useful as a new thermogelling biomaterial for drug delivery and injectable tissue engineering. [Copyright &y& Elsevier]