Thermo-responsive Characteristics Research Articles

Precise tailoring of thermoresponsive characteristics: Revealing ATRP opportunities for controlled poly(ethylene glycol)-based monomers composition in cyclodextrin-containing polymers

Star-shaped copolymers consisting of centrally located β-cyclodextrin and fifteen side chains containing di(ethylene glycol) methyl ether methacrylate (DEGMA) and poly(ethylene glycol) methyl ether methacrylate (OEGMA500) distributed statistically were synthesized using three different atom transfer radical polymerization (ATRP) techniques. For the first time, the use of β-cyclodextrin as a naturally-derived core for thermoresponsive polymeric drug delivery systems was thoroughly investigated depending on the chosen ATRP concept, focusing on precise control of the lower critical solution temperature (LCST) modulating the monomer content. The thermoresponsive properties of the received copolymers were investigated by UV–Vis and dynamic light scattering (DLS) measurement to determine the transmittance of solutions containing polymers with different monomer compositions and hydrodynamic diameter of prepared macromolecules upon temperature changes. The developed method allows for fine-tuning of the LCST by adjusting only the composition of the monomers. Synthesized copolymers were subsequently tested for residual copper catalyst content using atomic absorption spectrometry (AAS) to ensure compliance with the daily intake framework. The attained results showed negligible copper concentration in the purified products. Encouraged by these findings, cytotoxicity tests were conducted on normal fibroblast, cancer liver, and cancer breast cells, revealing no significant reduction in cell viability even at high polymer concentrations.

Modulating the Thermoresponsive Characteristics of PLGA-PEG-PLGA Hydrogels via Manipulation of PLGA Monomer Sequences.

Hydrogels are promising materials for biomedical applications, particularly in drug delivery and tissue engineering. This study highlights thermoresponsive hydrogels, specifically poly(lactic-co-glycolic acid) (PLGA)-poly(ethylene glycol) (PEG)-PLGA triblock copolymers, and introduces a feed rate-controlled polymerization (FRCP) method. By utilizing an organic catalyst and regulating the monomer feed rate, the sequence distribution of PLGA within the triblock copolymer is controlled. Various analyses, including 13C NMR and rheological measurements, were conducted to investigate the impact of sequence distribution. Results show that altering sequence distribution significantly influences the sol-gel transition, hydrophobicity-hydrophilicity balance, and drug release profile. Increased sequence uniformity lowers the glass transition temperature, raises the sol-gel transition temperature due to enhanced hydrophilicity, and promotes a more uniform drug (curcumin) distribution within the PLGA domain, resulting in a slower release rate. This study emphasizes the importance of PLGA sequence distribution in biomedical applications and the potential of FRCP to tailor thermoresponsive hydrogels for biomedical advancements.

Thermoresponsive Electrolytes for Safe Lithium-Metal Batteries.

Exploring advanced strategies in alleviating the thermal runaway of lithium-metal batteries (LMBs) is critically essential. Herein, a novel electrolyte system with thermoresponsive characteristics is designed to largely enhance the thermal safety of 1.0 Ah LMBs. Specifically, vinyl carbonate (VC) with azodiisobutyronitrile is introduced as a thermoresponsive solvent to boost the thermal stability of both the solid electrolyte interphase (SEI) and electrolyte. First, abundant poly(VC) is formed in SEI with thermoresponsive electrolyte, which is more thermally stable against lithium hexafluorophosphate compared to the inorganic components widely acquired in routine electrolyte. This increases the critical temperature for thermal safety (the beginning temperature of obvious self-heating) from 71.5 to 137.4°C. The remained VC solvents can be polymerized into poly(VC) as the battery temperature abnormally increases. The poly(VC) can not only afford as a barrier to prevent the direct contact between electrodes, but also immobilize the free liquid solvents, thereby reducing the exothermic reactions between electrodes and electrolytes. Consequently, the internal-short-circuit temperature and "ignition point" temperature (the starting temperature of thermal runaway) of LMBs are largely increased from 126.3 and 100.3°C to 176.5 and 203.6°C. This work provides novel insights for pursuing thermally stable LMBs with the addition of various thermoresponsive solvents in commercial electrolytes.

Fluorescent Nanoassemblies in Water Exhibiting Tunable LCST Behavior and Responsive Light Harvesting Ability.

Responsive fluorescent nanomaterials have been received considerable attention in recent years. In this work, a bola-type amphiphilic molecule, CSO, was synthesized which contains a hydrophobic cyanostilbene core and hydrophilic oligo(ethylene glycol) (OEG) coils at both sides. The cyanostilbene group is aggregation-induced emission (AIE) active, while the OEG coils are thermo-responsive. As a result, the CSO molecules can self-assemble into blue-fluorescent nanoassemblies with lower critical solution temperature (LCST) behavior in aqueous media. It is noteworthy that the LCST behavior can be reversibly regulated with changes in concentration and the introduction of K+ . Intriguingly, fluorescence of CSO assembly shows a blue-shift upon heating. Finally, by employing CSO as a light capturing antenna and energy donor, an artificial light harvesting system with tunable emission and thermo-responsive characteristics was fabricated. This study not only demonstrates an integrated approach to create responsive fluorescent nanomaterials, but also shows great potential for producing luminescent materials and mimicking photosynthesis in nature.

Synthesis, optimization, and cell response investigations of natural-based, thermoresponsive, injectable hydrogel: An attitude for 3D hepatocyte encapsulation and cell therapy.

For the purpose of developing a 3D vehicle for the delivery of hepatocytes in cell therapy, the improved system of crosslinker and new gelling agent combinations consisting of glycerophosphate and sodium hydrogen carbonate have been employed to produce injectable, thermoresponsive hydrogels based on chitosan and silk fibroin. Adjusting the polymer-to-gelling agent ratio and utilizing a chemical crosslinker developed hydrogel scaffolds with optimal gelling time and pH. Applying sodium hydrogen carbonate neutralizes chitosan while keeping its thermoresponsive characteristics and decreases glycerophosphate from 60% to 30%. Genipin boosts the mechanical properties of hydrogel without affecting the gel time. Due to their stable microstructure and lower amine availability, genipin-containing materials have a low swelling ratio, around six compared to eight for those without genipin. Hydrogels that are crosslinked degrade about half as fast as those that are not. The slowerr degradation of Silk fibroin compared to chitosan makes it an efficient degradation inhibitor in silk-containing formulations. All of the optimized samples showed less than 5% hemolytic activity, indicating that they lacked hemolytic characteristics. The acceptable cell viability in crosslinked hydrogels ranges from 72% to 91% due to the decreasing total salt concentration, which protects cells from hyperosmolality. The pH of hydrogels and their interstitial pores kept most encapsulated cells alive and functioning for 24h. Urea levels are higher in the encapsulation condition compared to HepG2 cultivated alone, and this may be due to cell-matrix interactions that boost liver-specific activity. Urea synthesis in genipin crosslinked hydrogels increased dramatically from day 1 (about 4mgdl-1) to day 3 (approximately 6mgdl-1), suggesting the enormous potential of these hydrogels for cell milieu preparation. All mentioned findings represent that the optimized system may be a promising candidate for liver regeneration.

Injectable thermoresponsive hydrogels based on (Me)PEG–poly(menthide) amphiphilic block copolymers from bioderived lactone

Synthesis of (Me)PEG–PM block copolymers from a sustainable source, (−)-menthone, and their thermoresponsive characteristics.

Experimental Investigation of a Thermally Responsive Actuator Based on Metallic Molybdenum Disulfide: A Conceptual Analysis

Abstract Actuators that convert external stimuli to mechanical energy have aroused strong attention for emerging applications in robotics, artificial muscles, and other fields. However, their limited performance under harsh operating conditions evidenced by the low cycle life and hysteresis has restricted their practical applications. Here, a thermal-driven actuator based on layered metallic molybdenum disulfide (1T MoS2) nanosheets is demonstrated. The active actuator film exhibits fully reversible and highly stable (>99.296% in 2700 cycles) thermal-mechanical conversion over a wide temperature window (from −60 °C to 80 °C). Importantly, 1T MoS2 film shows a fast response with the bending rate and the recovery rate of >1.090 rad s−1 and >0.978 rad s−1, respectively. The assembled actuator can lift 20 times its weight over several centimeters for more than 200 cycles. This work, for the first time, demonstrates the thermoresponsive characteristics of 1T MoS2 in developing the thermal actuator, which may open new opportunities for various applications, such as robotics, artificial muscles, and human assist devices.

Investigation of Eutectic Mixtures of Fatty Acids as a Novel Construct for Temperature-Responsive Drug Delivery.

BackgroundMost of the traditional nanocarriers of cancer therapeutic moieties present dose-related toxicities due to the uptake of chemotherapeutic agents in normal body cells. The severe life-threatening effects of systemic chemotherapy are well documented. Doxorubicin, DOX is the most effective antineoplastic agent but with the least specific action that is responsible for severe cardiotoxicity and myelosuppression that necessitates careful monitoring while administering. Stimuli-sensitive/intelligent drug delivery systems, specifically those utilizing temperature as an external stimulus to activate the release of encapsulated drugs, have become a subject of recent research. Thus, it would be ideal to have a nanocarrier comprising safe excipients and controllable drug release capacity to deliver the drug at a particular site to minimize unwanted and toxic effects of chemotherapeutics. We have developed a simple temperature-responsive nanocarrier based on eutectic mixture of fatty acids. This study aimed to develop, physicochemically characterize and investigate the biological safety of eutectic mixture of fatty acids as a novel construct for temperature-responsive drug release potential.MethodsWe have developed phase change material, PCM, based on a series of eutectic mixtures of fatty acids due to their unique and attractive physicochemical characteristics such as safety, stability, cost-effectiveness, and ease of availability. The reversible solid-liquid phase transition of PCM is responsible to hold firm or actively release the encapsulated drug. The eutectic mixtures of fatty acids (stearic acid and myristic acid) along with liquid lipid (oleic acid) were prepared to exhibit a tunable thermoresponsive platform. Doxorubicin-loaded lipid nanocarriers were successfully developed with combined hot melt encapsulation (HME) and sonication method and characterized to achieve enhanced permeability and retention (EPR) effect-based solid tumor targeting in response to exogenous temperature stimulus. The cytotoxicity against melanoma cell lines and in vivo safety studies in albino rats was also carried out.ResultsDoxorubicin-loaded lipid nanocarriers have a narrow size distribution (94.59–219.3 nm), and a PDI (0.160–0.479) as demonstrated by photon correlation microscopy and excellent colloidal stability (Z.P value: −22.7 to −32.0) was developed. Transmission electron microscopy revealed their spherical morphology and characteristics of a monodispersed system. A biphasic drug release pattern with a triggered drug release at 41°C and 43°C and a sustained drug release was observed at 37°C. The thermoresponsive cytotoxic potential was demonstrated in B16F10 cancer cell lines. Hemolysis assay and acute toxicity studies with drug-free and doxorubicin lipid nanocarrier formulations provided evidence for their non-toxic nature.ConclusionWe have successfully developed a temperature-responsive tunable platform with excellent biocompatibility and intelligent drug release potential. The formulation components being from natural sources present superior characteristics in terms of cost, compatibility with normal body cells, and adaptability to preparation methods. The reported preparation method is adapted to avoid complex chemical processes and the use of organic solvents. The lipid nanocarriers with tunable thermoresponsive characteristics are promising biocompatible drug delivery systems for improved localized delivery of chemotherapeutic agents.

Development of emamectin benzoate-loaded liposome nano-vesicles with thermo-responsive behavior for intelligent pest control.

Pesticides play an important role in agricultural disease and pest control. However, the low utilization efficiency and environmentally unfriendly disadvantages of conventional pesticide formulations cause substantial environmental and ecological damage. Constructing intelligent controlled-release pesticide systems via nanotechnology is a feasible way to overcome these defects. In this research, an emamectin benzoate-loaded liposome nano-vesicle (EB-Lip-NV) with a multicompartment structure and thermo-responsive characteristics was developed to accurately control nocturnal pests and improve insecticidal activity. EB-Lip-NV is an unusual low-temperature rapid-release system based on phase transitions of the liposome membrane. Compared with the conventional water-soluble granule (SG), the EB-Lip-NV exhibited higher control activity on Spodoptera exigua. More importantly, the control efficacy of Spodoptera exigua at 20 °C was around 1.4 times that at 40 °C because of low temperature-induced rapid release. This controlled-release behavior of EB-Lip-NV in response to temperature change could effectively control the population of nocturnal pests. In addition, the toxicity of the EB-Lip-NV towards zebrafish was lower than that of SG by above 50%. This study provides a new strategy for constructing intelligent controlled-release pesticide systems with improving utilization rate and reducing harm to the environment and non-target organisms.

A ready-to-use, thermoresponsive, and extended-release delivery system for the paranasal sinuses.

A drug delivery system for the paranasal sinuses consisting of a freeze-dried thermoresponsive hydrogel with degradable microspheres, called FD-TEMPS (Freeze Dried-Thermogel, Extended-release Microsphere-based delivery to the Paranasal Sinuses), was developed. Glass transition temperatures (Tg') of the maximally freeze concentrated solutions consisting of poly(N-isopropylacrylamide) (pNIPAAm) and polyethylene glycol (PEG) were determined by differential scanning calorimetry, which informed optimization of the thermogel formulation. By replacing low molecular weight (MW) PEG (200Da) with a higher MW PEG (2000Da), the resulting freeze-dried gel exhibited a brittle texture, porous structure, and low residual moisture (< 3% measured by thermal gravimetric analysis). When combined with poly(lactic-co-glycolic acid) microspheres (PLGA MSs) and freeze dried, the complete system (FD-TEMPS) exhibited enhanced shelf-stability. Specifically, the smooth, spherical morphology of the MSs and initial release kinetics were maintained following 6weeks of storage under ambient conditions. Furthermore, FD-TEMPS remained in place after application to a simulated mucosal surface, suggesting that it could be more uniformly distributed along the sinonasal mucosa in vivo. Freeze drying enables this delivery system to be stored as a ready-to-use product for better ease of clinical translation without compromising the thermoresponsive or sustained release characteristics that would enable local delivery of therapeutics to the sinonasal mucosa.

Thermo-responsive polymer encapsulated gold nanorods for single continuous wave laser-induced photodynamic/photothermal tumour therapy

Owing to strong and tunable surface plasmon resonance (SPR) effect and good biocompatibility, gold nanoparticles have been suggested to be a versatile platform for a broad range of biomedical applications. In this study, a new nanoplatform of thermo-responsive polymer encapsulated gold nanorods incorporating indocyanine green (ICG) was designed to couple the photothermal properties of gold nanorods (AuNRs) and the photodynamic properties of ICG to enhance the photodynamic/photothermal combination therapy (PDT/PTT). In addition to the significantly increased payload and enhancing photostability of ICG, the polymer shell in the nanoplatform also has thermo-responsive characteristics that can control the release of drugs at tumour sites upon the laser irradiation. On the basis of these improvements, the nanoplatform strongly increased drug aggregation at the tumour site and improved the photothermal/photodynamic therapeutic efficacy. These results suggest that this nanoplatform would be a great potential system for tumour imaging and antitumour therapy.

Thermoresponsive polysaccharides with tunable thermoresponsive properties via functionalisation with alkylamide groups

Polysaccharides have been used widely in many industries, from food technology and mining to cosmetics and biomedical applications. Over recent years there has been growing interest in the development of responsive polysaccharides with unique and switchable properties, particularly systems that display lower-critical solution temperatures (LCSTs). Therefore, in this study we aimed to investigate a novel strategy that would allow the conversion of non-responsive polysaccharides into thermoresponsive polysaccharides with tuneable LCSTs. Through the functionalisation of dextran with alkylamide groups (isopropyl amide, diethyl amide, piperidinyl and diisobutyl amide) using a carbodiimide coupling approach in conjunction with amic acid derivatives, we prepared a library of novel dextrans with various degrees of substitution (DS), which were characterised via nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The alkylamide-functionalised dextrans were found to have good solubility in aqueous solutions, with the exception of those having a high DS of large hydrophobic substituents. Determination of the thermoresponsive characteristics of the polymer solutions via UV–vis spectroscopy revealed that the LCST of the alkylamide-functionalised dextrans was highly dependent on the type of alkylamide group and the DS and could be tuned over a large range (5–35 °C). Above the LCST, all of the thermoresponsive alkylamide-functionalised dextrans formed colloidal dispersions with particles sizes ranging from 400 -600 nm, as determined by dynamic light scattering (DLS). In addition, the polymers were found to exhibit a fast and reversible phase transition in solution with narrow hysteresis (∼ 1–5 °C). Finally, the injectability and biocompatibility of the novel thermoresponsive dextrans was confirmed in vivo via subcutaneous and intracranial ventricle injections, with no local or systemic toxicity noted over a 14 d period. Overall, the alkylamide-functionalised dextrans display interesting thermoresponsive properties and trends that may make them useful in biomedical applications, such as drug-delivery.

Recovery of human mesenchymal stem cells grown on novel microcarrier coated with thermoresponsive polymer.

The cultivation of cells on microcarriers (MCs) in stirred suspension system is useful method for the large-scale culture of human mesenchymal stem cells (hMSCs) for allogenic transplantation. To harvest hMSCs from MCs without using proteolytic enzyme treatment but by lowering temperature, polystyrene MCs coated with a copolymer called CAT having zwitterionic and thermoresponsive characteristics, which has a lower critical solution temperature (LCST) in the range of 28-32℃, were developed and compared with those coated with poly(N-isopropylacrylamide) (PNIPAM), which has an LCST almost the same as that of the CAT copolymer. A preliminary study using polystyrene dishes coated with the CAT copolymer at various densities showed superior adhesion efficiency and cell growth compared with those coated with PNIPAM; however, the rate of cell recovery by lowering the temperature to 24℃ was only about 80% in both cases. Although cells grew on polystyrene MCs coated with PNIPAM (0.64-16µg/cm2) and on those coated with CAT (0.0050-1.0µg/cm2), the cell recovery rate at 24℃ was lower than 20%. The decrease in recovery temperature from 24 to 4℃ resulted in about 50% cell recovery from CAT-coated (0.010-0.10µg/cm2) MC, whereas the rate of cell recovery from PNIPAM-coated MC remained at about 20%. CAT (0.20µg/cm2) coating after treatment of polystyrene MCs with oxygen plasma discharge increased the cell recovery rate to 72% at 4℃. Consequently, the combination of oxygen plasma discharge treatment and CAT coating of polystyrene MCs might provide not only adhesion efficiency and growth of MSCs comparable to those on polystyrene MCs without any treatment but also a high cell recover rate of more than 70%.

N-heterocyclic carbene bearing thermoresponsive poly(NIPAM) supported palladium (II) complex: Synthetic strategy and application

In this article, we have reported the synthesis of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) bearing N-heterocyclic carbene (NHC) based palladium complex through carbene formation. The complex was synthesized from the polymer, which was obtained by SET-LRP (Single Electron Transfer - Living Radical Polymerization) technique using suitable N-heterocyclic carbene (NHC) based initiator. The single-crystal X-ray diffraction (XRD) confirms the structure of the initiator. Furthermore, NMR, FTIR and XPS studies confirmed the formation of the NHC–Pd (II) complex. Our complex possessed unique thermoresponsive characteristics in water i.e, water-soluble at below lower critical solution temperature (LCST) and water-insoluble at LCST. Hence, it can be used as a smart catalyst for Suzuki coupling reactions of various aryl halides in water medium at ambient temperature (30 °C). Due to its thermoresponsive behavior, it can be easily recovered from the reaction medium simply by the elevation of temperature and reused for several cycles.

Thermoresponsive Poly(ε-Caprolactone)-Poly(Ethylene/Propylene Glycol) Copolymers as Injectable Hydrogels for Cell Therapies.

Injectable, thermoresponsive hydrogels are promising candidates for the delivery, maintenance and controlled release of adoptive cell therapies. Therefore, there is significant interest in the development of cytocompatible and biodegradable thermoresponsive hydrogels with appropriate gelling characteristics. Towards this end, a series of thermoresponsive copolymers consisting of poly(caprolactone) (PCL), poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) segments, with various PEG:PPG ratios, were synthesised via ring-opening polymerisation (ROP) of ε-caprolactone and epoxy-functionalised PEG and PPG derivatives. The resultant PCL–PEG–PPG copolymers were characterised via proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The thermoresponsive characteristics of the aqueous copolymer solutions at various concentrations was investigated using the inversion method. Whilst all of the copolymers displayed thermoresponsive properties, the copolymer with a ratio of 1:2 PEG:PPG exhibited an appropriate sol–gel transition (28 °C) at a relatively low concentration (10 wt%), and remained a gel at 37 °C. Furthermore, the copolymers were shown to be enzymatically degradable in the presence of lipases and could be used for the encapsulation of CD4+ T-cell lymphocytes. These results demonstrate that the thermoresponsive PCL–PEG–PPG hydrogels may be suitable for use as an adoptive cell therapy (ACT) delivery vehicle.

Tunable Mode Converter Device Based on Photonic Crystal Fiber with a Thermo-Responsive Liquid Crystal Core

A compact tunable mode converter device based on the thermo-optically characteristics of liquid crystals (LCs) is proposed and numerically analyzed herein. The proposed mode converter consists of an asymmetric dual-core photonic crystal fiber (PCF) with a highly thermo-responsive LC core. The verification of the proposed mode converter was ensured through an accurate PCF analysis based on the vector finite element method. With an appropriate choice of the design parameters associated with the LC core, phase matching at a single wavelength is available in the important O-band wavelength region. The simulation results showed that high conversion efficiencies between LP01 and LP11 mode are readily achieved over a broad wavelength range from 1278 nm to 1317 nm. Likewise, the tunable capability of the proposed mode converter was evaluated when it was submitted to thermal changes; thus, we evidence the strong thermo-responsive dependence of the operating wavelength, mode conversion efficiency and full-width at the half maximum (FWHM) bandwidth. Finally, the fabrication tolerances of the devices were also investigated. Therefore, the thermo-responsive characteristics of this novel PCF mode converter can be of fundamental importance in the future space division multiplexing technology.

Novel Multifunctional Luminescent Electrospun Fluorescent Nanofiber Chemosensor-Filters and Their Versatile Sensing of pH, Temperature, and Metal Ions.

Novel multifunctional fluorescent chemosensors composed of electrospun (ES) nanofibers with high sensitivity toward pH, mercury ions (Hg2+), and temperature were prepared from poly(N-Isopropylacrylamide-co-N-methylolacrylamide-co-rhodamine derivative) (poly(NIPAAm-co-NMA-co-RhBN2AM)) by employing an electrospinning process. NIPAAm and NMA moieties provide hydrophilic and thermo-responsive properties (absorption of Hg2+ in aqueous solutions), and chemical cross-linking sites (stabilization of the fibrous structure in aqueous solutions), respectively. The fluorescent probe, RhBN2AM is highly sensitive toward pH and Hg2+. The synthesis of poly(NIPAAm-co-NMA-co-RhBN2AM) with different compositions was carried on via free-radical polymerization. ES nanofibers prepared from sensory copolymers with a 71.1:28.4:0.5 NIPAAm:NMA:RhBN2AM ratio (P3 ES nanofibers) exhibited significant color change from non-fluorescent to red fluorescence while sensing pH (the λPL, max exhibited a 4.8-fold enhancement) or Hg2+ (at a constant Hg2+ concentration (10−3 M), the λPL, max of P3-fibers exhibited 4.7-fold enhancement), and high reversibility of on/off switchable fluorescence emission at least five times when Hg2+ and ethylenediaminetetraacetic acid (EDTA) were sequentially added. The P3 ES nanofibrous membranes had a higher surface-to-volume ratio to enhance their performance than did the corresponding thin films. In addition, the fluorescence emission of P3 ES nanofibrous membranes exhibited second enhancement above the lower critical solution temperature. Thus, the ES nanofibrous membranes prepared from P3 with on/off switchable capacity and thermo-responsive characteristics can be used as a multifunctional sensory device for specific heavy transition metal (HTM) in aqueous solutions.

Rheological and thermo-responsive characteristics of the mixed aqueous solution of gemini cationic surfactant and hydroxyl naphthalene carboxylic acid sodium

ABSTRACTThe new thermo-switchable wormlike micellar systems were developed by mixing the gemini cationic surfactant, 2-hydroxypropyl-1,3-bis (dimethylmyristylammonium chloride) (14-3(OH)-14(2Cl) and sodium 1-hydroxynaphthalene-2-carboxylate (1SHNC) and sodium 2-hydroxynaphthalene- 3-carboxylate (2SHNC) in a certain concentration range. Their viscoelastic and thermos-responsive behaviors as a function of the salts concentration or temperature were investigated via rheological and cryo-TEM investigations. The results demonstrated that the zero-shear viscosity (η0) significantly increased while raising salt concentrations above a threshold concentration (CS*) until reaching maximum and then decreased. For the mixed solutions before the maximum, the zero-shear viscosity linearly decreased with increasing temperature and conformed to the Arrhenius law. However, for those mixed systems displaying thermo-responsive characteristic after the summit, the curve of η0 as a function of temperature exhibited a maximum over the whole temperature range, namely, the systems showed thermo-thickening and thermo-thinning behaviors at low and high temperatures. The abovementioned phenomena were explained by the formation of hydrogen bond in 14-3(OH)-14(2Cl) molecules and the different solubility of SHNC under different temperatures, and the transition mechanisms of the aggregates were analyzed accordingly.

A Novel Thermoresponsive Catalytic Membrane with Multiscale Pores Prepared via Vapor-Induced Phase Separation.

A novel thermoresponsive catalytic polyethersulfone membrane with multiscale pores is developed by constructing silver nanoparticles (Ag NPs) loaded poly(N-isopropylacrylamide) (PNIPAM) nanogels on pore walls of cellular pores as thermoresponsive gates and catalysts via vapor-induced phase separation. The Ag NPs are stably immobilized on the PNIPAM nanogels by an in situ reduction method based on the versatile adhesion and reduction properties of polydopamine. The micrometer cellular pores decorated with Ag NPs loaded PNIPAM nanogels are formed throughout the membrane and act as numerous microreactors with a large pore surface. The proposed membrane exhibits both satisfactory thermoresponsive characteristics and stable catalytic properties. The effects of operation temperature and reactant concentration of feed solution on the catalytic properties are investigated systematically. The results show that the apparent kinetic rate constant of catalytic reduction of 4-nitrophenol (4-NP) in water by reductant sodium borohydride (NaBH4 ), is ranging from 3.7 to 37.9 min-1 at temperatures from 20 to 45 ºC and the molar ratio of NaBH4 to 4-NP from 100:1 to 500:1. When the reactant concentration in feed solution fluctuates, the permeability or throughput of the membrane is simply adjusted by virtue of the thermoresponsive characteristics of membranes to achieve high catalytic conversion of reactant.

Effect of freeze drying on stability, thermo-responsive characteristics, and in vivo wound healing of erythropoietin-loaded trimethyl chitosan/glycerophosphate hydrogel.

Erythropoietin (EPO) was successfully incorporated into a bioadhesive thermosensitive hydrogel based on trimethyl chitosan (TMC)/β-glycerophosphate (GP) for prevention and treatment of oral mucositis in cancerous patients. The aim of the present study was to evaluate the effect of freeze drying on thermo-responsive property of the hydrogel and structural stability of the loaded protein. The freeze-dried EPO-loaded hydrogel were characterized using various methods. Gelation property by rheological analysis, EPO aggregation in formulations by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), protein secondary structure by far ultraviolet-circular dichroism (CD), and the antigenic activity of EPO with ELISA techniques. The healing effects of the freeze-dried formulation was also investigated in Sprague-Dawley rats with chemotherapy-induced mucositis and compared with freshly prepared mixture. Finally, the retention time of the gel in the oral cavity was assessed in healthy volunteers. SDS-PAGE, CD, and ELISA confirmed the stability of conformational structure of loaded and released EPO. Severity of mucositis was markedly reduced in animals treated with freeze-dried EPO hydrogel; whereas the group received normal saline did not show any significant healing. EPO salvia level was decreased rapidly following EPO solution compared to the gel application. Approximately, 40% of EPO was maintained on the buccal areas in patients receiving the hydrogel system after 30 min. Therefore, the TMC/GP could preserve EPO stability after freeze drying and has the potential in the treatment of oral mucositis and other oral or subcutaneous wounds.