Gel Transition Temperature Research Articles

Effect of Pluronic F127 Concentration on Gelling Temperature and other Parameters of Lomustine Mucoadhesive In-Situ Gel

Pluronic F127 is one of the widely used thermoreversible gelling agent, and used in sol-to-gel transformation. It has been used to localize drug delivery such as nose-to-brain delivery which allows the direct targeting of drug molecules bypassing the systemic effect and BBB (Blood Brain Barrier). The anticancer drug lomustine had poor oral bioavailability in addition to its serious side effect, therefore, developing more effective drug delivery with direct targeting towards the brain through intra-nasal administration applying nanoemulsion-based-in situ gel technology is a promising alternative. The work involved formulation of lomustine as in situ gel using Pluronic F127 and study the effect of the polymer on solution to gel transition temperature, gelation behaviour, spreadability, mucoadhesive force, residence time and residence drug percentage, as well as in vitro drug release. The results showed acceptable pH and high drug content, beside increased Pluronic percentage (from 15 to 20%) led to reduced gelation temperature from 33°C to 27°C and spreadability, improved gelling properties from + to +++, increasing mucoadhesive force from 4965.33 to 9866.30 dyne/cm2 as well as prolonged residence time from 30 to 66 min and in vitro drug release where was 120 min for 100% drug release from F1 that contained 15% of the polymer to 210 min for F3 with 20% polymer. Therefore, modifying the Pluronic F127 percent in the in situ formulas could optimize the required formula for targeting the anticancer to treat brain cancer via nose-to-brain delivery.

Investigation of the rheological behaviour for improved extrusion-based additive manufacturing of polymer composites based on dissociative dynamic covalent bonds

More complex 3D structures were manufactured out of reversible covalent polymer networks using multi-material extrusion-based additive manufacturing. The rheological behaviour of reversible polymer networks based on the thermoreversible Diels-Alder reaction was optimized through the addition of different types of nanoclays and carbon black. The extrudability and deposition of the composites improved up to 5 wt% nanoclay, as the viscosity behaviour increased by an order of magnitude in the nozzle and by two orders of magnitude at the print bed temperature, without affecting the reversible gel transition temperature and the healing performance. An electrically conductive composite with 20 wt% carbon black and 1 wt% nanoclay could be printed using nozzle sizes down to 0.3 mm, resulting in higher resolution and accuracy than the pristine polymer networks. The percolating filler network enabled the printing of overhangs and hollow structures without the need for support material with perfect mechanical and electrical isotropy. Multi-material printing combining the electrically conductive and non-conductive composites enabled manufacturing self-healing deformation and force sensors that could recover their sensing performance upon damage healing at 90 °C for one hour.

Gel‐forming properties of Bambara groundnut globulin and protein subfractions: structural and rheological characterisation

SummaryThe gel‐forming ability of the pulse proteins influences the formation of food products with desirable texture, structure, and stability. In this study, Bambara globulin was fractionated into legumin and vicilin for structural and physicochemical analyses, and heat‐induced gel rheological characterisation. Bambara globulin showed major vicilin (7S, Mw: 120 kDa) and minor legumin (11S, Mw: 410 kDa) components by size exclusion chromatography and gel electrophoresis analyses. Legumin had the lowest amount of all the charged amino acids. One basic subunit (22 kDa) was identified in the legumin fraction with predominant helical structures. The sol–gel transition temperatures increased in the order of globulin (40 °C) < legumin (50 °C) < vicilin (80 °C). The G′ and G″ of globulin showed relatively low dependency on heating time beyond the gel point compared to legumin and vicilin subfractions, suggesting a more rapid establishment of its gel network during gelation. Vicilin gel consisted of a microporous structure with a small lath sheet‐like structure compared to others. Bambara vicilin could be a prospective ingredient in the development of new products with defined textural characteristics.

Design, Development and In-Vitro Characterization of Insulin Loaded Topical Pluronic-Lecithin Based Organogel Formulation for the Management of Diabetic Wound.

To develop and characterize the topical insulin-loaded organogel formulation for the management of diabetic wounds. To formulate and evaluate organogel of insulin that can serve as a topical administration for promoting enhanced wound healing in diabetic patients by providing sustained and localized delivery of drug to the wound site. The insulin organogel formulated by the micro-emulsion method involves mixing the "aqueous and oil phases" at high shear. Physical and chemical properties, as well as an in vitro study with a Franz diffusion chamber, were used to evaluate the prepared organogel. All formulations proved to be off-white, homogeneous, washable, and had a pH between 6 and 6.5; moreover, they were non-irritating and skin-compatible. Formulations F1-F6 had viscosity ranging from 2058 to 3168 cps, spreadability ranges of 0.35 to 0.52 g*cm/s, and gel transition ranges of 28.33 to 35.33 °C. In formulations F1-F3, the concentration of lecithin was gradually increased, and in formulations F4-F6, the concentration of PF-127 was increased, resulting in a decrease in gel transition temperature, an increase in viscosity, and a gradual change in spreadability. The higher-viscosity formulations were much more stable and had better drug release. All formulations were fitted to a kinetic model belonging to first-order kinetics. However, after examining the parameter evaluation, it was found that the formulations F2 and F6 were better suited to the kinetic model and were consistent with the first-order and Higuchi models in Korsmeyer-Peppas F2 (r2 = 0.9544 and n = 1.0412); F6 (r2 = 0.9019 and n = 1.0822), which was a confirmation of the sustainability of the release system with matrix diffusion and drug delivery mechanisms that were based on the Super-Case II transport. Further research and clinical trials are needed to validate its efficacy, optimize the formulation, and establish its long-term safety. Topical insulin organogel has the potential to revolutionize diabetic wound management by improving healing outcomes, reducing complications, and raising the standard of living for those who have diabetes.

Bioactive-Loaded Hydrogels Based on Bacterial Nanocellulose, Chitosan, and Poloxamer for Rebalancing Vaginal Microbiota.

Biocompatible drug-delivery systems for soft tissue applications are of high interest for the medical and pharmaceutical fields. The subject of this research is the development of hydrogels loaded with bioactive compounds (inulin, thyme essential oil, hydro-glycero-alcoholic extract of Vitis vinifera, Opuntia ficus-indica powder, lactic acid, citric acid) in order to support the vaginal microbiota homeostasis. The nanofibrillar phyto-hydrogel systems developed using the biocompatible polymers chitosan (CS), never-dried bacterial nanocellulose (NDBNC), and Poloxamer 407 (PX) incorporated the water-soluble bioactive components in the NDBNC hydrophilic fraction and the hydrophobic components in the hydrophobic core of the PX fraction. Two NDBNC-PX hydrogels and one NDBNC-PX-CS hydrogel were structurally and physical-chemically characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and rheology. The hydrogels were also evaluated in terms of thermo-responsive properties, mucoadhesion, biocompatibility, and prebiotic and antimicrobial effects. The mucin binding efficiency of hydrogel base systems was determined by the periodic acid/Schiff base (PAS) assay. Biocompatibility of hydrogel systems was determined by the MTT test using mouse fibroblasts. The prebiotic activity was determined using the probiotic strains Limosilactobacillus reuteri and Lactiplantibacillus plantarum subsp. plantarum. Antimicrobial activity was also assessed using relevant microbial strains, respectively, E. coli and C. albicans. TEM evidenced PX micelles of around 20 nm on NDBNC nanofibrils. The FTIR and XRD analyses revealed that the binary hydrogels are dominated by PX signals, and that the ternary hydrogel is dominated by CS, with additional particular fingerprints for the biocompounds and the hydrogel interaction with mucin. Rheology evidenced the gel transition temperatures of 18-22 °C for the binary hydrogels with thixotropic behavior and, respectively, no gel transition, with rheopectic behavior for the ternary hydrogel. The adhesion energies of the binary and ternary hydrogels were evaluated to be around 1.2 J/m2 and 9.1 J/m2, respectively. The hydrogels exhibited a high degree of biocompatibility, with the potential to support cell proliferation and also to promote the growth of lactobacilli. The hydrogel systems also presented significant antimicrobial and antibiofilm activity.

Ophthalmic Bimatoprost-Loaded Niosomal In Situ Gel: Preparation, Optimization, and In Vivo Pharmacodynamics Study.

This study aimed at formulating the antiglaucoma agent, Bimatoprost (BMT), into niosomal in situ gel (BMT-ISG) for ocular delivery. Niosomes containing cholesterol/span 60 entrapping BMT were fabricated using a thin-film hydration method. The fabricated niosomes were optimized and characterized for entrapment efficiency (%EE) and size. The optimized BMT-loaded niosomal formulation prepared at a cholesterol/span 60 ratio of 1:2 exhibited the highest entrapment (81.2 ± 1.2%) and a small particle size (167.3 ± 9.1 nm), and they were selected for incorporation into in situ gelling systems (BMT-ISGs) based on Pluronic F127/Pluronic F68. Finally, the in vivo efficiency of the BMT-ISG formulation, in terms of lowering the intraocular pressure (IOP) in normotensive male albino rabbits following ocular administration, was assessed and compared to that of BMT ophthalmic solution. All the formulated BMT-ISGs showed sol-gel transition temperatures ranging from 28.1 °C to 40.5 ± 1.6 °C. In addition, the BMT-ISG formulation sustained in vitro BMT release for up to 24 h. Interestingly, in vivo experiments depicted that topical ocular administration of optimized BMT-ISG formulation elicited a significant decline in IOP, with maximum mean decreases in IOP of 9.7 ± 0.6 mm Hg, compared to BMT aqueous solution (5.8 ± 0.6 mm Hg). Most importantly, no signs of irritation to the rabbit's eye were observed following topical ocular administration of the optimized BMT-ISG formulation. Collectively, our results suggested that niosomal in situ gels might be a feasible delivery vehicle for topical ocular administration of anti-glaucoma agents, particularly those with poor ocular bioavailability.

Construction and properties of curdlan gum/gellan gum binary composite gel system

In the present study, the synergetic gelation of curdlan gum (CG) and gellan gum (CG) at different biopolymer ratios were investigated. The optimal gelation of CG and GG was determined at total biopolymer concentration of 0.6% and a mass ratio of 1:1 according to visual observation and viscoelastic properties. The gelation behavior of the CG/GG binary composite gel exhibited ratio-dependent behavior at different biopolymer mixing ratios (2:8–8:2). With the increase in the CG/GG ratio from 2:8 to 8:2, the gel strength and transition temperature of the CG/GG gel showed an increasing trend followed by a decrease, reaching a peak at 5:5, with corresponding G′, melting and gelling temperatures of 335.8 Pa, 82.5 °C and 33.7 °C, respectively. The improved gel properties could be ascribed to hydrogen bonds between CG and GG, as reflected by the blueshift of the O–H vibration peaks and water associated regional variation. Moreover, the CG/GG binary composite gel exhibited a significantly increasing water holding capacity (WHC) as the ratio of CG/GG decreased from 8:2 to 4:6, while the excess involvement of GG had no effect on the WHC improvement. Furthermore, the CG/GG binary composite gel exhibited denser and more homogeneous microstructures in comparison to individual CG and GG and performed the most compact gel network at ratio of 5:5, supporting the stronger gel rigidity and WHC. Therefore, these novel CG/GG hydrogels showed considerable gel strength and microstructures, which would provide a better mechanistic understanding of the polysaccharide complex in practical applications as a hydrogel base material.

Evaluation of pilocarpine in situ forming buccal gels as potential formulations for the management of xerostomia

Buccally administrated pilocarpine (PIL) can be a unique formulation approach for the management of xerostomia. In this way the severity of systemically induced side effects can be effectively controlled, while maintaining a high level of therapeutic efficacy. The aim of the present study was to evaluate the sol–gel and mucoadhesive properties of an in situ thermoresponsive hydrogel designed for PIL's buccal administration. For this purpose, poloxamer 407 (P407) and 188 (P188) were used as in situ gel forming agents, while xanthan gum (XG) was added as a mucoadhesion enhancer. Implementation of a Box-Behnken experimental design, combined with multi-linear regression (MLR) fitting, unraveled the role of formulation factors on several critical product attributes (such as gel transition temperature, gelation time, solution viscosity and gel viscosity). Artificial neural networks (ANNs) showed excellent generalizing ability, with verification experiments showing good agreement between the ANN- predicted and the experimentally-obtained results. The optimum sol-gel formulations were sprayable at room/storage temperature, while forming a strong gel at temperatures prevailing in the buccal cavity. In vitro dissolution profiles of all optimum formulations exhibited a sustained release pattern (releasing almost 80% of the total dose in 360 min) characterized by an initial rapid release followed by a steady state plateau. The evaluation of drug release kinetics, by applying different release kinetic models, suggested that the drug release from the in situ gels predominantly follows Fick's law and is primarily diffusion-controlled. The in vitro studies were complemented with ex vivo studies, performed on a freshly excised porcine buccal mucosa, showing good mucoadhesion properties with approximately 27% of the total drug permeating the buccal porcine mucosa, while no damage to the epithelium was observed based on the histological evaluation.

Chitosan with enhanced deprotonation for accelerated thermosensitive gelation with β-glycerophosphate

Chitosan (CS)/β-sodium glycerophosphate (β-GP) gels have low temperature sensitivity, which limits their biomedical application. The protonation and deprotonation of the CS amino groups are regulated by pH. It is possible to accelerate thermosensitive gelation by increasing the pH of the CS solution to maximize the degree of CS amino deprotonation and enhance hydrophobic interactions. In this study, a CS solution with a higher pH (HpHCS; pH 6.19, close to pKa 6.2) was obtained by means of the consumption of hydrogen ions using excessive chitosan. Raman spectroscopy showed that strong hydrogen bonds might exist in HpHCS. Gelation was accelerated significantly at 37 °C using HpHCS due to the decreased sol–gel transition temperature. Support vector machine and t-distributed stochastic neighbor embedding analyses confirmed that the gel derived from HpHCS was significantly different from that of the other groups. In addition, the HpHCS gel exhibited a low degradation rate and low cytotoxicity. Furthermore, a mathematical equation was established to predict the gelation time of HpHCS/β-GP at 37 °C. A better concentration of HpHCS for in vivo injection was obtained due to the shorter gelation time and lower viscosity. We found that human mesenchymal stem cells survived and proliferated in vitro in the HpHCS/β-GP hydrogel. Therefore, this study provides an optimized HpHCS solution with enhanced deprotonation for accelerated thermosensitive gelation with β-GP.

Effects of ε‐polylysine or ε‐polylysine hydrochloride on the pH responsive ι‐carrageenan gel

AbstractThe binding of oppositely charged polyelectrolytes is a well‐known gel strategy, and pH is an important factor affecting the gel properties. In this work, the influence of pH (3, 5, 7, 9, 11) on the rheological and textural properties, molecular structure and micromorphology of binary mixed gels of ι‐carrageenan (IC) and ε‐polylysine (PLL) or ε‐polylysine hydrochloride (PLH) was investigated. The results showed that a change in pH led to a change in the properties of binary mixed gels. The lower the pH, the higher were G′, G″, complex viscosity and gel transition temperature. At the same time, the water holding capacity and gel strength of IC/PLL (IP) and IC/PLH (IPH) were also improved accordingly, and the gel properties of IPH were always better than those of IP. As the pH increased to alkalinity, the density of the gel network structure decreased, the pore size decreased, the pore wall became thinner and the surface smoothed. When the pH dropped into the acidic range, there was a red shift of the hydroxyl group and the sulfate group bands, an enhancement of the hydrogen bonding interaction and a blue shift of the methyl band and the amide I band. At pH 3, the microscopic network structure of IP and IPH were dense and uniform with small pore size, rough surface and thick pore wall. These results showed that the binary mixed gels had better gel properties at pH 3. The results provided a theoretical basis for the preparation of IP and IPH gels, and also enabled a deeper understanding of the mechanism of interaction between polypeptides and carrageenan. © 2023 Society of Industrial Chemistry.

Toughening and Stiffening in Thermoreversible Diels–Alder Polymer Network Blends

The thermophysical properties, mechanical behavior, and healing performance of Diels–Alder-based polymer networks can be tuned widely by changing the molar mass, functionality, and stoichiometric ratio of the multifunctional diene (e.g., furan) and dienophile (e.g., maleimide) monomers. Blending furan-functionalized monomers with a high and low molar mass opens a new dimension in tuning the properties of the resulting reversible polymer network blends (RPNBs), containing different ratios of elastomeric and thermoset phases, with low and high crosslink densities and glass transitions below and above room temperature, respectively. Increasing the thermoset content up to 20 wt % raises the gel transition temperature (Tgel), relaxation time (τ), rubbery plateau modulus, ultimate stress, and Young’s modulus of the stiffened elastomers, while the strain at fracture and self-healing efficiency remained mostly unchanged. Conversely, the addition of up to 20 wt % of the elastomer phase drastically toughens the thermosets because of stress dissipation, which can suppress the stress concentration in the phase-separated network blends. The blends showed higher stress and strain at break while retaining similar Young’s moduli. The toughness increases up to an order of magnitude at 50 wt %, compared to the pure thermoset. The phase-separated morphologies were evidenced by the presence of the Tg’s of the pure networks in DSC and DMA.

Dielectric Study on Supramolecular Gels by Fiber Structure Formation from Low-Molecular-Weight Gelator/Water Mixtures.

There are various types of gel materials used in a wide range of fields, and their gelation mechanisms are extremely diverse. Furthermore, in the case of hydrogels, there exist some difficulties in understanding complicated molecular mechanisms especially with water molecules interacting through hydrogen bonding as solvents. In the present work, the molecular mechanism of the structural formation of fibrous super-molecular gel by the low molecular weight gelator, N-oleyl lactobionamide/water mixture was elucidated using the broadband dielectric spectroscopy (BDS) method. The dynamic behaviors observed for the solute and water molecules indicated hierarchical structure formation processes in various time scales. The relaxation curves obtained at various temperatures in the cooling and heating processes showed relaxation processes respectively reflecting the dynamic behaviors of water molecules in the 10 GHz frequency region, solute molecules interacting with water in MHz region, and ion-reflecting structures of the sample and electrode in kHz region. These relaxation processes, characterized by the relaxation parameters, showed remarkable changes around the sol-gel transition temperature, 37.8 °C, determined by the falling ball method and over the temperature range, around 53 °C. The latter change suggested a structure formation of rod micelles appearing as precursors before cross-linking into the three-dimensional network of the supramolecular gels. These results clearly demonstrate how effective relaxation parameter analysis is for understanding the gelation mechanism in detail.

Synthesis and characterization of reversible thermosensitive methylated chitin and its application in zinc‐ion battery thermal runaway

AbstractNovel water‐soluble methylated chitins (MCHs) were synthesized homogeneously in aqueous alkaline solution. The relatively mild reaction conditions resulted in the MCH with high degree of acetylation (DA >0.76). The chemical structure of the obtained MCHs was analyzed and the degree of methylation substitution (DS) and DA were determined by proton NMR in both D2O and 20% DCl/D2O. The MCH aqueous solutions (DS = 0.46 ~ 0.71) showed a reversible thermosensitive sol–gel–sol transition upon heating and cooling. The gel transition temperature of these MCHs (in the range of 15–85 °C) increased with increasing DS and decreasing polymer concentration. Thermal runaway has been an important safety issue impeding the development of high‐energy‐density zinc‐ion batteries. A smart thermosensitive reversible electrolyte was prepared based on this MCH for the aqueous zinc‐ion battery to prevent thermal runaway. When the temperature of zinc‐ion battery rises or even gets out of control, the thermosensitive electrolyte can quickly gel and inhibit the migration of zinc ions, resulting in increase of the internal resistance and realizing intelligent and efficient thermal self‐protection. Thus the novel thermosensitive methylated chitin shows promise for safe aqueous zinc‐ion batteries.

Engineering the Structure and Rheological Properties of P407 Hydrogels via Reverse Poloxamer Addition.

Aqueous solutions of poloxamer 407 (P407), a commercially available and nontoxic ABA triblock polymer (PEO-PPO-PEO), undergo a solution-to-gel transition with increasing temperature and are promising candidates for injectable therapeutics. The gel transition temperature, modulus, and structure are all dictated by polymer concentration, preventing independent tuning of these properties. Here, we show that addition of BAB reverse poloxamers (RPs) to P407-based solutions dramatically alters the gelation temperature, modulus, and morphology. Gelation temperature and RP localization within the hydrogel are dictated by RP solubility. Highly soluble RPs increase gelation temperature and incorporate primarily into the micelle corona regions. Alternatively, RPs with low aqueous solubility decrease gelation temperature and associate within the micelle core and core-corona interface. These differences in RP localization have significant implications for the hydrogel modulus and microstructure. The ability to tune gelation temperature, modulus, and structure through RP addition allows for the design of thermoresponsive materials with specific properties that are unobtainable with neat P407-based hydrogels.

Self-healing magnetorheological elastomers based on thermoreversible Diels–Alder networks

Magnetorheological (MR) elastomers are a class of stimuli-responsive materials of which the damping and stiffness can be reversibly tailored by applying magnetic fields. However, concerns such as fatigue damage, insufficient MR efficiencies with low loadings of magnetic particles or highly crosslinked elastomers, and lack of reprocessability remain unaddressed for conventional MR elastomers. To this end, a series of self-healing MR elastomers (SHMRE) were prepared based on thermoreversible Diels–Alder covalent crosslinks. The application of magnetic pulses yielded pre-aligned magnetic particles chains within the curing matrix which strongly influenced the SHMRE rheological properties. The resulting composites do not only exhibit a large MR effect but also efficient self-healing properties at room temperature. We found that the particle loading and the field-induced orientation of the aggregates affect the magnitude of the MR response, the mechanical strength and the healing efficiency. In addition, the MR response is also strongly influenced by the temperature. With a temperature increase from room temperature to 70 °C, a change in the MR response from 90% to 462% is observed while the SHMRE retain a solid viscoelastic state at 50 wt% particles loading. Interestingly, the thermoreversible features of the synthesized networks also allow potential reprocessability of SHMRE when heating these systems above the gel transition temperature (89 °C–90 °C). The final low viscous state makes it possible for the magnetic particles to be potentially restructured as chains by applying a magnetic field, which are retained upon cooling when the solid network state is recovered. The proposed SHMRE systems are shown to be a highly efficient and reprocessable solution to substitute classical MR elastomers in a wider context of generalized MR materials.

Injectable Composite Systems of Gellan Gum:Alginate Microparticles in Pluronic Hydrogels for Bioactive Cargo Controlled Delivery: Optimization of Hydrogel Composition based on Rheological Behavior

Due to the high complexity of some treatments, there is a need to develop drug-delivery systems that can release multiple drugs/bioactive agents at different stages of treatment. In this study, a thermoresponsive injectable dual-release system was developed with gellan gum/alginate microparticles (GG:Alg) within a thermoresponsive Pluronic hydrogel composed of a mixture of Pluronic F127 and F68. The increase in F68 ratio and decrease in F127 lead to higher transition temperatures. The addition of the GG:Alg microparticles decreased the transition temperatures with a linear tendency. In Pluronic aqueous solutions (20 wt.%), the F127:F68 ratios of 16:4 and 17:3 (wt.%:wt.%) and the addition of microparticles (up to 15 wt.%) maintained the sol–gel transition temperatures within a suitable range (between 25 °C and 37 °C). Microparticles did not hinder the injectability of the system in the sol phase. Methylene blue was used as a model drug to evaluate the release mechanisms from microparticles, hydrogel, and composite system. The hydrogel delayed the release of methylene blue from the microparticles. The hydrogel loaded with methylene blue released at a faster rate than the microparticles within the hydrogel, thus demonstrating a dual-release profile.

Combining Krafft Point and Volume Phase Transition Temperature Toward Regulation of Solar Radiation and Privacy Protection

AbstractEverlasting pursuit of high energy efficiency as well as meeting fluctuant temperatures raise various lighting requirements, which is driving the originality of thermochromic smart windows (SWs). SWs with dual‐temperature response upon rational designs are identified as an effective approach to regulate solar radiation and protect privacy. Here, combining the Krafft point (Tk) of ionic surfactants and the volume phase transition temperature (VPTT) of gels toward SW materials is utilized to achieve a transition of opacity‐transparence‐opacity as temperature change, maintaining transparency at an intermediate temperature range with favorable optical modulation parameters. Cationic surfactant, hexadecylpyridinium bromide (HPB), and poly(N‐isopropylacrylamide) (PNIPAM) are combined using Tk and VPTT to serve as the dual thermo‐responsive switches for regulating solar radiation and protecting privacy. Tk of HPB can be adjusted by adding salts and VPTT is turned by introducing hydrophilic and hydrophobic comonomer. This work provides a realizable pathway by which in situ adjustable parameters may be performed and operated in external environment conditions, completely changing the smart window materials.

Effect of electrolytes on the sol–gel phase transitions in a Pluronic F127/carboxymethyl cellulose aqueous system: Phase map, rheology and NMR self-diffusion study

This investigation aims to obtain a thermosensitive platform useful for specific nanomedicine applications through the addition of suitable salts. An aqueous mixture consisting of the copolymer Pluronic F127 and sodium carboxymethyl-cellulose, in a ratio of 20/4 by weight, in the presence of different concentrations of Na2SO4, NaCl, and NaSCN, was investigated using the visual inversion tube approach to estimate a phase map, and then characterized through rheological measurements. The formation of a cubic liquid crystalline phase at temperatures higher than 37 °C was suggested in all systems. The complex viscosity, decreases in the presence of salts in the order Na2SO4 > NaCl > NaSCN with more marked effect for lower concentrations. Salt addition allows to tune the crowding effect of NaCMC. For the polymer mixture and for a sample containing NaCl, 1H NMR self-diffusion experiments display a non-mono-exponential decay of the echo signals of Pluronic F127, caused by the polydispersity of commercial Pluronic F127. The rheological properties along with the diffusion behaviour of the liquid crystal micelles suggest that a sample containing NaCl 0.07 mol/kg, with a sol-hard gel transition temperature around 35 °C, close to that of the body, may be a suitable and biocompatible thermosensitive platform to administer both hydrophobic and hydrophilic drugs such as antibiotics, anticancer drugs or growing factors.Synopsis: A simple thermoresponsive platform for drug delivery: Pluronic F127, NaCMC and NaCl.

Photothermal activation in the near infrared range for 4-dimensional printing using relevant organic dyes

4D printing has become an exciting sector of 3D printing since its appearance in the 2010 s. This technology consists in adding time as an extra dimension of 3D printing. Different stimuli can be used to modify a 3D object after the printing process such as solvent, temperature, magnetic field, electricity or light. In this paper, a 4D behavior was investigated using Near Infrared (NIR) light in combination with a low amount of NIR organic dyes in-situ embedded in the 3D printed object. As a first step, the influence of several parameters on the photothermal effect generated have been followed such as the NIR dye structure, the NIR dye concentration, the irradiation wavelength, the light irradiance and the polymer matrix. Due to the light-triggered process, the deformation of the 3D printed object could be reversibly achieved in the presence of a NIR organic dye in a few amount of time (20 s). In fact, the photothermal effect in-situ generated in the 3D printed object allowed to reach a temperature above the gel transition temperature (T g ) of the latter. This phenomenon has been highlighted with tensile tests. Indeed, these tests showed the passage of the 3D printed object from a glassy state to a rubbery state upon NIR irradiation. Finally, the photothermal effect produced was used to rapidly bond or repair two parts of a broken 3D printed object.

The dual effects of non-solvent on the sol-gel transition of polyacrylonitrile solution: The promotion in thermodynamics and hindrance in kinetics

The effects of non-solvent on the sol-gel transition of polyacrylonitrile (PAN) solution were investigated in thermodynamics and kinetics by the means of rheology method. The facilitating effects of non-solvent in thermodynamics was illustrated by the variety of viscoelasticity and gel transition temperature (Tgel). With the addition of non-solvent, the mobility of PAN molecular chains are limited due to its increased entanglement. As a result, the PAN solution with higher non-solvent content has lower conformation entropy to satisfy the occurrence of sol-gel transition at higher temperature. It means that less thermodynamic driving is demanded. The kinetical characteristics of PAN solution with different non-solvent content in sol-gel transition process were also discussed. The kinetic hindrance of non-solvent was proved by the gradually stronger time-dependence of loss tangent with the addition of non-solvent during sol-gel transition. This apparent extending of relaxation time is resulted from the more restriction of the mobility of PAN molecules. The gelation activation energy (Egel) was calculated according to Ozawa method. The results also indicated that the activity of PAN molecules in this transition became weaken with the addition of non-solvent since a relative tight connection between PAN molecules was there. Therefore, the formation of physical junction points for sol-gel transition was hindered due to the decreasing of the mobility of self-adjustment for PAN molecules. This is the fundamental reason for the kinetic hindrance role of non-solvent.