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Despite the potential of hydrogel-based localized cancer therapies, their efficacy can be limited by cancer recurrence. Therefore, it is of great significance to develop a hydrogel system that can provoke robust and durable immune response in the human body. This study has developed an injectable protein-polymer-based porous hydrogel network composed of lysozyme and poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide (PCLA) (Lys-PCLA) bioconjugate for the active recruitment dendritic cells (DCs). The Lys-PCLA bioconjugates are prepared using thiol-ene reaction between thiolated lysozyme (Lys-SH) and acrylated PCLA (PCLA-Ac). The free-flowing Lys-PCLA bioconjugate sols at low temperature transformed to immovable gel at the physiological condition and exhibited stability upon dilution with buffers. According to the in vitro toxicity test, the Lys-PCLA bioconjugate and PCLA copolymer were non-toxic to RAW 263.7 cells at higher concentrations (1000 µg/mL). In addition, subcutaneous administration of Lys-PCLA bioconjugate sols formed stable hydrogel depot instantly, which suggested the in situ gel forming ability of the bioconjugate. Moreover, the Lys-PCLA bioconjugate hydrogel depot formed at the interface between subcutaneous tissue and dermis layers allowed the active migration and recruitment of DCs. As suggested by these results, the in-situ forming injectable Lys-PCLA bioconjugate hydrogel depot may serve as an implantable immune niche for the recruitment and modification of DCs. [ABSTRACT FROM AUTHOR]

This work is concerned with the dynamics of a polymerization process coupled with mass transfer and monomers injection, modeled by means of an infinite-dimensional system of Smoluchowski's equations in a finite graph. Under suitable assumptions on the system's aggregation coefficients, we show that, as a consequence of the injection mechanism, a sizable depletion of the pool of available reacting substances occurs at some finite time, that can be estimated in terms of the parameters of the problem. By analogy with well-known results in chemical engineering, we interpret that result as the onset of a sol-gel phase transition. According to the chemical engineering terminology, a sol-gel transition is characterized by the appearance of a "gel" defined as a fraction of the total chemical species which is not able to add to the polymerization process anymore. A gel just removes reacting species from the available pool but does not contributes back to the ongoing reaction. We suggest that this property might have some interest in the mathematical modeling of neurodegenerative processes, where the polymerization of some soluble proteins and their eventual aggregation into insoluble plaques play a remarkable role, which is not well understood as yet. [ABSTRACT FROM AUTHOR]

Standard hydrogels prepared by free radical polymerization (FRP) have heterogeneous structures with a wide mesh size distribution, which affect their mechanical and separation properties. Recent research has identified four-armed poly(ethylene glycol) (tetra-PEG) as a solution to this problem. tetra-PEG gels with a homogeneous network can be prepared and applied as high-strength gels and cell-culture substrates by reacting two types of tetra-PEG with different reactive groups at the ends. In this study, we report a photoresponsive tetra-PEG that undergoes a phase transition from a sol to a gel state in response to light. tetra-PEGs containing cinnamoyl and maleimide groups at the ends of the four-armed chains were found to gel when exposed to light. The effects of polymer concentration and light irradiation time on the gelation of tetra-PEG containing photodimerization groups were investigated. The results showed that the elastic modulus of the gel increased with the increase in the light irradiation time.

Here, we report for the first time that resonance in dynamic-mode cantilever sensors persists in hydrogels and enables the real-time characterization of hydrogel viscoelastic properties and the continuous monitoring of sol-gel phase transitions (i.e., gelation and dissolution processes). Real-time tracking of piezoelectric-excited millimeter cantilever (PEMC) sensor resonant frequency (fair = 55.4 ± 8.8 kHz; n = 5 sensors) and quality factor (Q; Qair = 23.8 ± 1.5) enabled continuous monitoring of high-frequency hydrogel shear storage and loss moduli (G′f and G″f, respectively) calculated by sensor data and fluid–structure interaction models. Changes in the sensor phase angle, quality factor, and high-frequency shear moduli obtained at the resonant frequency (G′f and G″f) correlated with low-frequency moduli obtained at 1 Hz using dynamic mechanical analysis. Characterization studies were performed using physically and chemically crosslinked hydrogel systems, including gelatin hydrogels (6–10 wt. %) and alginate hydrogels (0.25–0.75 wt. %). The sensor exhibited a dynamic range from the rheological properties of inviscid solutions to hydrogels with high-frequency moduli of 80 kPa and low-frequency moduli of 26 kPa. The sensor exhibited a limit of detection of 260 Pa and 1.9 kPa for changes in hydrogel storage modulus (E′) based on the sensor's phase angle and quality factor responses, respectively. We also show that sensor data enable quantitative characterization of gelation process dynamics using a modified Hill model. This work suggests that cantilever sensors provide a promising platform for the sensor-based characterization of hydrogels, such as quantification of viscoelastic properties and real-time monitoring of gelation processes. [ABSTRACT FROM AUTHOR]

We examined the effect of high pressure on the sol–gel phase transition of a resorcinol–formaldehyde (RF) aqueous solution to a RF hydrogel, which was hold under a certain pressure varied in the range from the ambient pressure to 400 MPa. By employing the dynamic light scattering method, we analyzed the scattered intensity of a He–Ne laser which was irradiated to the RF solution to determine the hydrodynamic diameter of the structure formed during the phase transition. Before the completion of the phase transition, we measured the transient change in the size of colloidal particles, i.e. the unit of the porous structure formed in the RF hydrogel. It was revealed that the size of the colloidal particles increased with the increase in the pressure added to the RF solution. After the completion of the phase transition, we prepared a RF cryogel by removing solvent from a RF hydrogel by freeze-drying. The specific surface area of the RF cryogel was found to decrease with the increase in the added pressure, as a result of the increase in the size of the unit of the porous structure. [ABSTRACT FROM AUTHOR]

We investigate the influence of inter-particle affinity on the microstructure and rheological behavior in the bimodal suspension systems. For this purpose, we design the suspensions using two kinds of polystyrene beads (PS, size ∼530 nm) as a large particle which are electrostatically stabilized and are different in surface properties only, while keeping unstable alumina coated silica (Al-silica, size ∼12 nm) as a small particle. To change the affinity, hydrogen bonding is induced by modifying surface of PS as poly (vinyl pyrrolidone) (PVP). The influence of affinity between large and small particles is investigated by observing the changes in rheological properties and microstructure. Even with the same, the formation of Al-silica cluster which connects large particles is dominant when sulfate modified PS is used and the affinity between the particles is not strong. On the contrary, the Al-silica particles cover the surface of large particles rather than making bridges when PVP modified PS is used and the affinity is strong. The phase map which shows fluid-gel transition according to the composition of the suspension is also obtained. The affinity is found to affect the shape of the phase map too. This research explains how the differences in affinity between large and small particles affect the bimodal suspensions according to the surface properties of the particles, and provides an insight on the complex behavior of particulate fluids. [ABSTRACT FROM AUTHOR]

Particle aggregation containing a sol-gel phase transition governed by a general gelling kernel ( K( u, v) ∼ ( u · v)(1/2 < ω ≤ 1)) has been studied by means of a new Monte Carlo method. With this stochastic method, the aggregation process can be described straightforwardly requiring relatively minor programming. The gelation time, a crucial characteristic of the sol-gel transition, can be determined in a fairly simple manner. Investigations of evolutions of other interesting properties associated with particle system in aggregation are also more easily tractable with this scheme. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The effect of fat content in cheese curds on their rheological properties was examined using dynamic shear measurements. Surplus fat addition to milk samples caused two distinct types of changes in the temperature dependence of the viscoelastic moduli of resultant curds. The first was a significant reduction in the moduli over a wide temperature range, which is attributed to the presence of liquefied fat globules within the milk protein network. The second was the excess contribution to the low-temperature moduli owing to the reinforcing effect of solidified fat globules. An upward shift in the sol-gel phase transition temperature driven by an increased fat content was also observed. [ABSTRACT FROM AUTHOR]

Context: Hydrogels are promising polymeric network capable of sustaining the release of drug but have a major limitation for encapsulation of hydrophobic drugs. Objective: This study was undertaken to encapsulate etoposide in poloxamer 407-based thermosensitive hydrogels with an aim to sustain its release. Materials and methods: Etoposide-loaded hydrogels were prepared by the cold method and optimized for encapsulation efficiency (EE) by a 32 factorial design. Poloxamer 407-poloxamer 188 hydrogel (E-P407-P188) and poloxamer 407-poly(ethylene glycol) (E-P407-PEG) hydrogel were characterized for SEM, swelling, sol-gel phase transition and injectability study. Results and discussion: In E-P407-P188 hydrogel the EE of 75% could be obtained and in E-P407-PEG hydrogels the EE was 84%. The SEM images showed a porous structure. The release of ETO was sustained up to 48 h by E-P407-PEG hydrogel and 24 h by E-P407-P188 hydrogel. The drug release was governed by first-order kinetics and followed Fickian diffusion mechanism in both the cases. Conclusion: Such injectable thermosensitive hydrogel of etoposide could be effectively used for continuous release of drug to the tumor and surrounding tissues. [ABSTRACT FROM AUTHOR]

We performed a replica-exchange molecular dynamics (REMD) simulation of a lipid bilayer system in order to study sol-gel phase transitions. The REMD method allows one to enhance conformational sampling efficiency and to study the system in a wide temperature range at once. We used a coarse-grained model MARTINI. The results show a large jump in internal energy and thickness of the bilayer around 295 K, which suggests a sol-gel phase transition. The bilayer seems to have two states in the gel state. One is a tilted gel state and the other is an untilted gel state. A previous work with MARTINI force field reported only the untitled gel state. This indicates that conformational sampling efficiency is crucial even with a coarse-grained model, which has smoother energy landscapes and reaches longer time scales than atomistic models. [ABSTRACT FROM PUBLISHER]

The article discusses the role of hydrophobic interactions in the gel network formation by applying atomic force microscopy (AFM) to image marine gel samples taken during episodes of macroscopic gel phase formation in the northern Adriatic Sea and to follow initial stages of the gel network formation in a mesocosm phytoplankton bloom experiment. Sampling was done on board a research vessel during regular cruises along the transect Po River Delta-Rovinj, Istrian coast. It suggests that AFM is a powerful technique for characterizing marine gel network.

Abstract: In-plane (bio)matter aggregations of amphiphilic nature are modeled extensively by Monte Carlo simulation in their natural entropic contexts. The modeling starts by designing the aggregations at a molecular level, pointing to its well-known configuration vs conformation character. Then, the conformational behavior is distributed over the aggregations obtained, with the aim of revealing their main sol–gel type (viscoelastic) effects. The passage between the resulting sol and gel phases is not controlled by a scan in the temperature domain, on the contrary, the control parameter is selected to be the hydrophobic-interaction strength while the temperature remains unchanged. The distribution of ordered fringed micelles, and the overall crystalline inclusions of the gel phase, suggested a first-order phase change, reasonably conceivable in terms of Avrami–Kolmogorov formalism for such hydrophobic-force driven and percolation-in-nature systems. A phase transition diagram has been presented as a novel proposition to discern between sol vs gel phases. As specific results, also of high experimental value, a damped-oscillating cluster-involving effect on the resulting hydrophobic-polar matrices has been detected and analysed. Other additional intermolecular-sharing entropy-influenced effects on clustering, as seen in terms of chain-to-chain connectivities, have been addressed as being of sufficient relevance to the gelation mechanism described. The microcrystalline inclusions downgrade to some extent the overall picture of entropy-affected gelation, being all together suitable for experimental check-out. [Copyright &y& Elsevier]

Abstract: This work describes the synthesis and characterization of novel thermoresponsive highly branched polyamidoamine–polyethylene glycol–poly(d,l-lactide) (PAMAM–PEG–PDLLA) core–shell nanoparticles. A series of dendritic PEG–PDLLA nanoparticles were synthesized through conjugation of PEG of various chain lengths (1500, 6000 and 12,000gmol−1) to polyamidoamine (PAMAM) dendrimer G3.0 and subsequent ring-opening polymerization of DLLA. The ninhydrin assay, 1H NMR, Fourier transform infrared spectroscopy, dynamic light scattering and atomic force microscopy were used to characterize the structure and compositions of dendritic PEG–PDLLA nanoparticles. The sol–gel phase transition of aqueous dendritic PEG–PDLLA solutions was measured using UV–visual spectroscopy. According to our results dendritic PEG–PDLLA nanoparticles in aqueous solution can self-assemble into sub-micron/micron aggregates, the size of which is dependent on temperature and PEG–PDLLA chain length. Further, dendritic PEG–PDLLA solutions exhibit a sol–gel phase transition with increasing temperature. The constructed dendritic PEG–PDLLA nanoparticles possessed high cytocompatibility, which was significantly improved compared with PAMAM dendrimers. The potential of dendritic PEG–PDLLA nanoparticles for encapsulation of water-insoluble drugs such as camptothecin was demonstrated. The dendritic PEG–PDLLA nanoparticles we developed offer greater structural flexibility and provide a novel nanostructured thermoresponsive carrier for drug delivery. [Copyright &y& Elsevier]

Aqueous solutions that undergo reversible thermosensitive gelation around body temperature were developed based on hydrophobically-modified methyl cellulose (HMMC). The approach involved HMMC as the main component of aqueous compositions to provide a system with fast gelling properties, which has not been accomplished with aqueous solutions of unmodified methyl cellulose (MC). MC was modified with the stearyl group as a hydrophobic modifier by controlling the degree of modification. The gelation rate of aqueous solutions containing identical amounts of HMMC and NaCl increased as the temperature increased. The HMMC solutions gelled at a fixed temperature and concentration range, while the unmodified MC solutions did not show sol-to-gel transition. In addition, HMMC solutions exhibited much faster gelation than MC solutions at given polymer and NaCl concentrations. The HMMC/NaCl solutions exhibited the reversible gel-to-sol transition upon cooling below 25°C. The rate of sol-to-gel transition at body temperature, and the reversible gel-to-so! transition at room temperature, were modulated by adjusting the concentration of HMMC and NaCl, respectively. The HMMC/NaCl compositions provided a simple system for accurate control of the thermogelling temperature and the thermogelation rates. [ABSTRACT FROM AUTHOR]

Fast transient fluorescence (FTRF) technique was used to study the sol–gel phase transition in free-radical crosslinking copolymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA) and their mixtures with ethylene glycol dimethacrylate (EGDM). Fluorescence lifetimes of pyrene (Py) from its decay traces were monitored during sol–gel phase transitions. Consumption of MMA and/or EMA in pregel solutions due to gel formation dramatically increased the Py fluorescence lifetimes, in which were used to study the gelation of MMA, EMA and their mixtures as a function of time, at various temperatures and monomer concentrations. Monomer consumption rates, kr were measured during sol–gel transition process by using Stern–Volmer model. Gelation activation energies ΔEG were determined and found to be 14 and 10 kcal mol−1 for MMA and EMA respectively. [Copyright &y& Elsevier]

The similarities between the formation of hydrogen bonds and polycondensation reactions are stated from the statistical viewpoint, and then taking the hydrogen bonding system of A a D d type as an example, the growing process of hydrogen bonding clusters is investigated in terms of the theory of reaction dynamics and statistical theory for polymeric reactions. The two methods lead to the same conclusions, stating that the statistical theory for polymerization is applicable to the hydrogen bonding systems. Based on this consideration, the explicit relationship between the conversions of proton-donors and proton-acceptors and the Gibbs free energy of the system under study is given. Furthermore, the sol-gel phase transition is predicted to take place in some hydrogen bonding systems, and the corresponding generalized scaling laws describing this kind of phase transition are obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] • Floating-gate thin-film transistor biosensor. • Sol-gel phases transformation to determine alkaline phosphatase activity. • Sensing platform to detect alkaline phosphatase activity and sol-gel state. • A peptide-based supramolecular hydrogel material on EFG-TFT. Herein, we developed an extended floating-gate thin-film transistor (EFG-TFT) together with various sol-gel phases to determine alkaline phosphatase (ALP) activity. The EFG-TFT was fabricated with ZnO as the channel material and YO X as the dielectric layer, which provided an extended area for sensing the analyte interacting with the designed hydrogelator. A peptide-based supramolecular hydrogel material, i.e., 2-naphthylacetic acid- l -phenylalanine- l -phenylalanine- l - O -phosphor tyrosine (named Nap-FF-Yp) was synthesized as our sensing platform to detect ALP activity and the sol-gel state. Nap-FF-Yp could be cleaved by ALP during hydrolysis, leading to π-π stacking, and finally changed to a hydrogel. Due to the difference in the potential drop between the liquid phase and gel phase of the hydrogel, the sol-gel transition reaction could be monitored by the electrical signal. The greater the extent of hydrogelation, the smaller the threshold voltage (V th) variation, and the threshold voltage shifted to the left. Under the device's optimal conditions with oxygen plasma treatment, the limit of detection (LOD) reached 0.024 U/L. The development of this novel sol-gel state for a high-speed screening sensing platform with an excellent electrical response demonstrates the potential capabilities of future high-speed response sensors. [ABSTRACT FROM AUTHOR]

• Dox@PNA-Pt nanogels are programmatically fabricated via a simple mixing approach. • Dox@PNA-Pt nanogels show sol-gel transition, ensuring long-term retention in tumor. • Dox@PNA-Pt nanogels exhibit sustained and parallel release of Dox and cisplatin. • Dox@PNA-Pt nanogels show best synergistic antitumor and antimetastasis effects. • Dox@PNA-Pt nanogels reduce toxicity of Dox and cisplatin on normal tissues. Combination chemotherapy, such as doxorubicin (Dox) plus cisplatin, based on co-assembling nanoparticles plays increasingly important role in the clinical treatment of cancer. But their synergistic antitumor effect is highly limited by unmatched release behavior of Dox and cisplatin. To enhance the synergistic antitumor effect of Dox and cisplatin, herein, an acidic triblock polymer (p AA 100 - b - p NIPAM 200 - b - p AA 100 , PNA) was developed as a temperature sensitive template for programmable fabrication of two antitumor drugs (Dox and cisplatin). In these co-assembly nanogels, Dox@PNA-Pt nanogels show compact 3D network cisplatin-shell surrounding Dox-loading core, enabling parallel release of Dox and cisplatin, which is beneficial to maximizing the synergistic effect of Dox and cisplatin. Moreover, Dox@PNA-Pt nanogels could be efficiently internalized into tumor cells mainly by caveolin-mediated pathway. In in vivo evaluation on 4T1-bearing BALB/c mice, after single injection, Dox@PNA-Pt nanogels exhibited much stronger suppression of tumor growth, proliferation and metastasis, and induction of apoptosis and necrosis of tumor tissue/cells than Pt@PNA + Dox@PNA and Pt@PNA-Dox groups thanks to the parallel release of Dox and cisplatin. In addition, Dox@PNA-Pt nanogels showed a distinct transition from free-flowing sol to free-standing gel at critical gellating temperature (CGT), facilitating the long-term tumor retention and the optimally synergistic antitumor effect of Dox and cisplatin. The programmable fabrication with PNA was promising to be developed as an efficient approach for improving the antitumor efficacy of combination chemotherapy. [ABSTRACT FROM AUTHOR]

Biological stimuli-responsive DNA hydrogels have attracted much attention in the field of medical engineering owing to their unique phase transitions from gel to sol through cleavage of DNA cross-linking points in response to specific biomolecular inputs. In this paper, a new class of biological stimuli-responsive DNA hydrogels with a dynamically programmed DNA system that relies on a DNA circuit system through cascading toehold-mediated DNA displacement reactions is constructed, allowing the catalytic cleavage of cross-linking points and main chains in response to an appropriate DNA input. The dynamically programmed DNA hydrogels exhibit a significant sharp phase transition from gel to sol in comparison to another DNA hydrogel showing noncatalytic cleavage of cross-linking points due to synchronization of the catalytic cleavage of cross-linking points and the main chains. Further, the sol-gel phase transitions of the DNA hydrogels in response to the DNA input are easily tunable by changing the cross-linking density. Additionally, with a structure-switching aptamer, DNA hydrogels encapsulating PEGylated gold nanoparticles can be used as enzyme-free signal amplifiers for the colorimetric detection of adenosine 5'-triphosphate (ATP); this detection system provides simplicity and higher sensitivity (limit of detection: 5.6 × 10 -6 m at 30 min) compared to other DNA hydrogel-based ATP detection systems., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)