Thermoreversible Gels Research Articles

Critical Dependence of Molecular Weight on Thermoresponsive Behavior of Diblock Copolymer Worm Gels in Aqueous Solution.

Reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate was used to prepare three poly(glycerol monomethacrylate)x–poly(2-hydroxypropyl methacrylate)y (denoted Gx-Hy or PGMA-PHPMA) diblock copolymers, namely G37-H80, G54-H140, and G71-H200. A master phase diagram was used to select each copolymer composition to ensure that a pure worm phase was obtained in each case, as confirmed by transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) studies. The latter technique indicated a mean worm cross-sectional diameter (or worm width) ranging from 11 to 20 nm as the mean degree of polymerization (DP) of the hydrophobic PHPMA block was increased from 80 to 200. These copolymer worms form soft hydrogels at 20 °C that undergo degelation on cooling. This thermoresponsive behavior was examined using variable temperature DLS, oscillatory rheology, and SAXS. A 10% w/w G37-H80 worm dispersion dissociated to afford an aqueous solution of molecularly dissolved copolymer chains at 2 °C; on returning to ambient temperature, these chains aggregated to form first spheres and then worms, with the original gel strength being recovered. In contrast, the G54-H140 and G71-H200 worms each only formed spheres on cooling to 2 °C, with thermoreversible (de)gelation being observed in the former case. The sphere-to-worm transition for G54-H140 was monitored by variable temperature SAXS: these experiments indicated the gradual formation of longer worms at higher temperature, with a concomitant reduction in the number of spheres, suggesting worm growth via multiple 1D sphere–sphere fusion events. DLS studies indicated that a 0.1% w/w aqueous dispersion of G71-H200 worms underwent an irreversible worm-to-sphere transition on cooling to 2 °C. Furthermore, irreversible degelation over the time scale of the experiment was also observed during rheological studies of a 10% w/w G71-H200 worm dispersion. Shear-induced polarized light imaging (SIPLI) studies revealed qualitatively different thermoreversible behavior for these three copolymer worm dispersions, although worm alignment was observed at a shear rate of 10 s–1 in each case. Subsequently conducting this technique at a lower shear rate of 1 s–1 combined with ultra small-angle x-ray scattering (USAXS) also indicated that worm branching occurred at a certain critical temperature since an upturn in viscosity, distortion in the birefringence, and a characteristic feature in the USAXS pattern were observed. Finally, SIPLI studies indicated that the characteristic relaxation times required for loss of worm alignment after cessation of shear depended markedly on the copolymer molecular weight.

Formulation and in vitro evaluation of a thermoreversible mucoadhesive nasal gel of itopride hydrochloride

Itopride hydrochloride (ITO HCl) is a prokinetic agent, used in the treatment of gastrointestinal motility disorders. The aim of the study was to develop stable mucoadhesive thermoreversible nasal gel to avoid first pass effect. ITO HCl was incorporated into the blends of thermoreversible polymers like poloxamer 407 and various mucoadhesive polymers in different concentrations to increase the contact of the formulations with nasal mucosa. The compatibility between the drug and the suggested polymers was studied by Fourier transform infrared and differential scanning calorimetry (DSC). The formulations were evaluated for clarity, pH, gelation temperature, mucoadhesive strength, gel strength, viscosity, and drug content. In addition, the in vitro drug release and the dissolution efficiency (DE)% were measured. The optimized formulations that showed the highest dissolution efficiency% (DE%) in saline phosphate buffer of pH 6.4 at 35 ± 0.5 °C were chosen for stability testing at temperatures of 4 ± 2 and 25 ± 2 °C/60 ± 5% RH. It was found that F1 and F17 that contain 18% w/v poloxamer 407 and 0.5% w/v of hydroxypropylmethyl cellulose K4M or methyl cellulose (MC), respectively, showed higher stability results as indicated by their higher t90 values (days).

High concentration solubility and stability of ɛ-poly-l-lysine in an ammonium-based ionic liquid: A suitable media for polypeptide packaging and biomaterial preparation

Packaging of structurally sensitive biomolecules such as proteins, peptides and DNA in non-aqueous media at ambient conditions with chemical and structural stability is important to explore the potential of such biomacromolecules as substrate for functional biomaterial design and for biotechnological applications. In this perspective, solubility, chemical and structural stability of ɛ-poly-l-lysine (ɛ-PL), a homopolypeptide produced by Streptomyces albulus in different ionic liquids (ILs) namely 2-hydroxyethyl ammonium formate (2-HEAF), 2-hydroxyethyl ammonium acetate (2-HEAA), choline formate (Ch-Formate) and choline acetate (Ch-Acetate) was studied. Maximum solubility (15% w/v) of the homopolypeptide was observed in 2-HEAF and lowest was found in Ch-Formate (2% w/v). After regeneration of the dissolved polypeptide in the IL, the IL could be recycled and reused in the dissolution process. Unlike in other ILs, 3–15% w/v of ɛ-PL in 2-HEAF gave formation of a thixotropic thermoreversible soft gel. Molecular docking studies established favourable interactions of [2-HEA]+ cation over [Ch]+ with ɛ-PL indicating [2-HEA]+ as the most promising cation for the dissolution process. However, the role of the anions was also found to be important, which could lead to improvement in polypeptide solubility when combined to the selected cation. The findings demonstrate suitability of the ionic liquids for functionalization of polypeptides for biomaterial preparation.

A Smart Flexible Solid State Photovoltaic Device with Interfacial Cooling Recovery Feature through Thermoreversible Polymer Gel Electrolyte.

Quasi-solid-state dye-sensitized solar cells (DSSCs) fabricated with lightweight flexible substrates have a great potential in wearable electronic devices for in situ powering. However, the poor lifespan of these DSSCs limits their practical application. Strong mechanical stresses involved in practical applications cause breakage of the electrode/electrolyte interface in the DSSCs greatly affecting their performance and lifetime. Here, a mechanically robust, low-cost, long-lasting, and environment-friendly quasi-solid-state DSSC using a smart thermoreversible water-based polymer gel electrolyte with self-healing characteristics at a low temperature (below 0 °C) is demonstrated. When the performance of the flexible DSSC is hindered by strong mechanical stresses (i.e., from multiple bending/twisting/shrinking actions), a simple cooling treatment can regenerate the electrode/electrolyte interface and recover the performance close to the initial level. A performance recovery as high as 94% is proven possible even after 300 cycles of 90° bending. To the best of our knowledge, this is the first aqueous DSSC device with self-healing behavior, using a smart thermoreversible polymer gel electrolyte, which provides a new perspective in flexible wearable solid-state photovoltaic devices.

DNA-Coated Functional Oil Droplets.

Many industrial soft materials include oil-in-water (O/W) emulsions at the core of their formulations. By using tuneable interface stabilizing agents, such emulsions can self-assemble into complex structures. DNA has been used for decades as a thermoresponsive, highly specific binding agent between hard and, recently, soft colloids. Up until now, emulsion droplets functionalized with DNA had relatively low coating densities and were expensive to scale up. Here, a general O/W DNA-coating method using functional nonionic amphiphilic block copolymers, both diblock and triblock, is presented. The hydrophilic poly(ethylene glycol) ends of the surfactants are functionalized with azides, allowing for efficient, dense, and controlled coupling of dibenzocyclooctane-functionalized DNA to the polymers through a strain-promoted alkyne-azide click reaction. The protocol is readily scalable due to the triblock's commercial availability. Different production methods (ultrasonication, microfluidics, and membrane emulsification) are used with different oils (hexadecane and silicone oil) to produce functional droplets in various size ranges (submicron, ∼20 and >50 μm), showcasing the generality of the protocol. Thermoreversible submicron emulsion gels, hierarchical "raspberry" droplets, and controlled droplet release from a flat DNA-coated surface are demonstrated. The emulsion stability and polydispersity is evaluated using dynamic light scattering and optical microscopy. The generality and simplicity of the method opens up new applications in soft matter, biotechnological research, and industrial advances.

Novel Thermo-Reversible Gel of Riboflavin Acetate for the Treatment of Keratoconus: An Assessment of Ex-Vivo Permeation and Hemolytic Toxicity

Novel Thermo-Reversible Gel of Riboflavin Acetate for the Treatment of Keratoconus: An Assessment of<i> Ex-Vivo</i> Permeation and Hemolytic Toxicity

A comparison of the self-assembly behaviour of sodium N-lauroyl sarcosinate and sodium N-lauroyl glycinate surfactants in aqueous and aqueo-organic media

Self-assembly of surfactants is influenced by various intermolecular interactions and molecular structure, which dictate packing of molecules in the aggregate and its microstructure. Hydrogen-bonding between amide groups plays a key role in the self-assembly process of N-acyl amino acid surfactants (NAAS). The self-assembly properties of two NAAS, sodium N-lauroyl sarcosinate (SLS) and sodium N-lauroyl glycinate (SLG) that differ only in the head-group structure were compared in aqueous and aqueo-organic media by using a number of methods, including surface tension fluorescence, dynamic light scattering, calorimetry, and microscopy. It was observed that aggregate formation is more favoured in SLG. Studies revealed that while SLS formed small spherical micelles, SLG produced unilamellar vesicles in pH 7 buffer above critical micelle concentration at 25 °C. The stability of SLG vesicles with respect to pH and temperature was also investigated. Furthermore, both SLG and SLS were found to gelify aquo-organic mixtures of varying composition upon heat-cool treatment. Their gelation behaviour was compared by measuring minimum gelation concentration, molecular packing, and morphology and mechanical stability of the thermoreversible gels. The difference in self-assembly behaviour in water as well as in aqueo-organic mixtures was attributed to the steric repulsion and hydrogen-bonding interaction at the head-group of the molecules.

Nose-to-Brain Delivery of Antiviral Drugs: A Way to Overcome Their Active Efflux?

Although several viruses can easily infect the central nervous system (CNS), antiviral drugs often show dramatic difficulties in penetrating the brain from the bloodstream since they are substrates of active efflux transporters (AETs). These transporters, located in the physiological barriers between blood and the CNS and in macrophage membranes, are able to recognize their substrates and actively efflux them into the bloodstream. The active transporters currently known to efflux antiviral drugs are P-glycoprotein (ABCB1 or P-gp or MDR1), multidrug resistance-associated proteins (ABCC1 or MRP1, ABCC4 or MRP4, ABCC5 or MRP5), and breast cancer resistance protein (ABCG2 or BCRP). Inhibitors of AETs may be considered, but their co-administration causes serious unwanted effects. Nasal administration of antiviral drugs is therefore proposed in order to overcome the aforementioned problems, but innovative devices, formulations (thermoreversible gels, polymeric micro- and nano-particles, solid lipid microparticles, nanoemulsions), absorption enhancers (chitosan, papaverine), and mucoadhesive agents (chitosan, polyvinilpyrrolidone) are required in order to selectively target the antiviral drugs and, possibly, the AET inhibitors in the CNS. Moreover, several prodrugs of antiretroviral agents can inhibit or elude the AET systems, appearing as interesting substrates for innovative nasal formulations able to target anti-Human Immunodeficiency Virus (HIV) agents into macrophages of the CNS, which are one of the most important HIV Sanctuaries of the body.

Triarylamine-Cored Dendritic Molecular Gel for Efficient Colorometric, Fluorometric, and Impedometeric Detection of Picric Acid.

Detection of nitroaromatics at ultralow concentration is a major security concern in defense, forensics, and environmental science. To this end, a new triarylamine-cored dendritic gelator (OGR) was synthesized, which produced thermoreversible, thixotropic, and fluorescent gels in n-octanol. On gelation, both π-π* transitions and the emission peak of the gelator show redshifts with a 4.5-fold increase of fluorescence intensity in the gel state indicating J-aggregation. The nitrogen lone-pair electrons of OGR make it a donor, and electron transfer occurs to acceptor nitroaromatics causing fluorescence quenching, which is further promoted due to its acidity. The Stern-Volmer rate constants measured for different nitroaromatics showed that it senses picric acid (PA) best. The contact-mode technique with OGR-treated paper strips can allow naked-eye detection of PA under UV light down to 10-11 m concentration within 30 s. Reusability of the gel is achieved by treating OGR@PAx with NaOH solution. Impedance spectroscopic results indicated a decrease of both charge-transport resistance and Warburg impedance on successive addition of PA. The limits of detection of PA determined from fluorescence and impedance measurements match well. Thus, the OGR gel is a reusable, low-cost, specific sensor for PA by naked-eye colorimetric, fluorescence, and impedance techniques.

Generating vascular channels within hydrogel constructs using an economical open-source 3D bioprinter and thermoreversible gels

The advent of 3D bioprinting offers new opportunities to create complex vascular structures within engineered tissues. However, the most suitable sacrificial material for producing branching vascular conduits within hydrogel-based constructs has not yet been resolved. Here, we assess two leading contenders, gelatin and Pluronic F-127, for a number of characteristics relevant to their use as sacrificial materials (printed filament diameter and its variability, toxicity, rheological properties, and compressive moduli). To aid in our assessment and help accelerate the adoption of 3D bioprinting by the biomedical field, we custom-built an inexpensive (< $3000 CAD) 3D bioprinter. This open-source 3D printer was designed to be fabricated in a modular manner with 3D printed/laser-cut components and off-the-shelf electronics to allow for easy assembly, iterative improvements, and customization by future adopters of the design. We found Pluronic F-127 to produce filaments with higher spatial resolution, greater uniformity, and greater elastic modulus than gelatin filaments, and with low toxicity despite being a surfactant, making it particularly suitable for engineering smaller vascular conduits. Notably, the addition of hyaluronan to gelatin increased its viscosity to achieve filament resolutions and print uniformity approaching that with Pluronic F-127. Gelatin-hyaluronan was also more resistant to plastic deformation than Pluronic F-127, and therefore may be advantageous in situations in which the sacrificial material provides structural support. We expect that this work to establish an economical 3D bioprinter and assess sacrificial materials will assist the ongoing development of vascularized tissues and will help accelerate the widespread adoption 3D bioprinting to create engineered tissues.

Development of Smart Optical Gels with Highly Magnetically Responsive Bicelles.

Hydrogels delivering on-demand tailorable optical properties are formidable smart materials with promising perspectives in numerous fields, including the development of modern sensors and switches, the essential quality criterion being a defined and readily measured response to environmental changes. Lanthanide ion (Ln3+)-chelating bicelles are interesting building blocks for such materials because of their magnetic responsive nature. Imbedding these phospholipid-based nanodiscs in a magnetically aligned state in gelatin permits an orientation-dependent retardation of polarized light. The resulting tailorable anisotropy gives the gel a well-defined optical signature observed as a birefringence signal. These phenomena were only reported for a single bicelle-gelatin pair and required high magnetic field strengths of 8 T. Herein, we demonstrate the versatility and enhance the viability of this technology with a new generation of aminocholesterol (Chol-NH2)-doped bicelles imbedded in two different types of gelatin. The highly magnetically responsive nature of the bicelles allowed to gel the anisotropy at commercially viable magnetic field strengths between 1 and 3 T. Thermoreversible gels with a unique optical signature were generated by exposing the system to various temperature conditions and external magnetic field strengths. The resulting optical properties were a signature of the gel's environmental history, effectively acting as a sensor. Solutions containing the bicelles simultaneously aligning parallel and perpendicular to the magnetic field directions were obtained by mixing samples chelating Tm3+ and Dy3+. These systems were successfully gelled, providing a material with two distinct temperature-dependent optical characteristics. The high degree of tunability in the magnetic response of the bicelles enables encryption of the gel's optical properties. The proposed gels are viable candidates for temperature tracking of sensitive goods and provide numerous perspectives for future development of tomorrow's smart materials and technologies.

Long-lasting Insulin Treatment Via a Single Subcutaneous Administration of Liposomes in Thermoreversible Pluronic® F127 Based Hydrogel.

Repeated administrations of insulin injection on daily basis evoke pain and numerous complications with adverse effects on the diabetic patients' life quality. Moreover, wearing insulin pump is also associated with several problems of diabetic ketoacidosis, catheter site infection, contact dermatitis and high cost. We have developed an in situ gel system, consisting of insulin-loaded liposomes dispersed within a thermoreversible gel (Pluronic® F127 gel), which increases the duration of insulin action for the treatment of diabetes. Vesicular phospholipid gel technique was used to encapsulate the insulin into liposomes. The resulting liposomal gel formulation had a longer drug-release period in vitro than a free insulin solution or liposomes and Pluronic® F127 gel individually. Furthermore, the addition of liposomes to the Pluronic® F127 gel improved the stability of the encapsulated insulin at a physiological temperature. In vivo study was performed to investigate the bioactivity and absorption of insulin released from the liposomal gel and other formulations. The liposomal gel released insulin into the bloodstream continuously for up to 7 days and significantly enhanced drug bioavailability compared to insulin released from liposomes or Pluronic® F127 gel individually. Blood glucose levels were reduced for up to 4 days. Histology data demonstrated excellent biocompatibility of the Pluronic® F127 gel-based delivery systems, with no observable inflammatory response in rat subcutaneous tissues. Obtained results show that the insulin-loaded liposomes dispersed within Pluronic® F127 gel can be used as a long-acting drug delivery system, and replacement for conventional insulin therapy.

Direct 3D Printing of High Strength Biohybrid Gradient Hydrogel Scaffolds for Efficient Repair of Osteochondral Defect

AbstractThe emerging 3D printing technique allows for tailoring hydrogel‐based soft structure tissue scaffolds for individualized therapy of osteochondral defects. However, the weak mechanical strength and uncontrollable swelling intrinsic to conventional hydrogels restrain their use as bioinks. Here, a high‐strength thermoresponsive supramolecular copolymer hydrogel is synthesized by one‐step copolymerization of dual hydrogen bonding monomers, N‐acryloyl glycinamide, and N‐[tris(hydroxymethyl)methyl] acrylamide. The obtained copolymer hydrogels demonstrate excellent mechanical properties—robust tensile strength (up to 0.41 MPa), large stretchability (up to 860%), and high compressive strength (up to 8.4 MPa). The rapid thermoreversible gel ⇔ sol transition behavior makes this copolymer hydrogel suitable for direct 3D printing. Successful preparation of 3D‐printed biohybrid gradient hydrogel scaffolds is demonstrated with controllable 3D architecture, owing to shear thinning property which allows continuous extrusion through a needle and also immediate gelation of fluid upon deposition on the cooled substrate. Furthermore, this biohybrid gradient hydrogel scaffold printed with transforming growth factor beta 1 and β‐tricalciumphosphate on distinct layers facilitates the attachment, spreading, and chondrogenic and osteogenic differentiation of human bone marrow stem cells (hBMSCs) in vitro. The in vivo experiments reveal that the 3D‐printed biohybrid gradient hydrogel scaffolds significantly accelerate simultaneous regeneration of cartilage and subchondral bone in a rat model.

The effect of kappa carrageenan and salt on thermoreversible gelation of methylcellulose

Methylcellulose (MC) and kappa carrageenan (KCG) are widely used in food and pharmaceutical industries as a viscosity modifier, a gelling aid, and a film former due to their reversible thermal gelation properties. Thermoreversible gelation of MC/salt, MC/KCG/water, and MC/KCG/salt mixtures was investigated utilizing dynamic and steady shear rheological measurements. It was found that for the MC/salt mixture, gelation temperatures decreased linearly with increasing salt concentrations independent of valences of cations and molar concentrations of anions. For the MC/KCG blend, double gelation was not observed, and KCG is not influenced or disturbed the gelation properties of MC. Double gelation was observed for the mixture of MC/KCG/KCl for the low concentration of salts of 0.01 M KCl and 0.04 M KCl with the maximum moduli values for the mixture of MC/KCG/0.04 M KCl and then gradually decreased with increasing KCl salt concentration and eventually became similar to the gelation of MC solution. Therefore, KCl concentration played a major role in double gelation properties of MC/KCG/KCl mixture. It was also found that for the MC/KCG/KCl system, gelation transition matrices are linearly depending on salt concentration and independent of KCG and salt type. It was shown that for MC/salt mixture, solution rheology follows the principle of time–temperature superposition (TTS) below the gelation temperature. However, TTS failed above the gelation temperature. TTS also failed for MC/KCG and MC/KCG with low KCl concentration mixtures.

Targeted Local Therapy for Management of Intracranial High-Grade Gliomas.

Systemic chemotherapy of malignant brain tumors has failed to achieve sufficient drug concentrations at the neoplasm site and frequently results in severe toxicities. Therefore, the local application of several anticancer agents, oncolytic viruses and vectors for gene therapy, immune-modifying preparations, and angiogenesis inhibitors has been investigated widely. Various modes of their administration were introduced, including intratumoral injections, implantation of reservoirs or pumps, convection-enhanced delivery, and use of nanocarriers, thermoreversible gels, microchips, and drug-loaded polymers. Many of these therapeutic approaches have shown promising results in management of high-grade gliomas.

Photolithographically assembled polyelectrolyte complexes as shape-directing templates for thermoreversible gels.

Preparation of soft materials with diverse, customized shapes has been a topic of intense research interest. To this end, we have recently demonstrated photolithographic directed assembly as a strategy for customizing polyelectrolyte complex (PEC) shape. This process uses in situ photopolymerization of an anionic monomer in the presence of a cationic polymer, which drives localized PEC formation at the irradiation sites. Here, we show how such photolithographically assembled PECs can serve as structure-directing templates for tailoring the shapes of other soft materials; namely, thermoreversible gels. These templated hydrogels are prepared by adding a thermogelling polymer (agarose) to the anionic monomer/cationic polymer/photoinitiator precursor solutions so that, upon irradiation, custom-shaped PECs form within agarose gel matrices. Once these PECs are formed, the surrounding agarose gels are melted (through heating) and washed away which, upon returning the samples to room temperature, produces interpenetrating PEC/agarose gel networks with photopatterned shapes and dimensions. Dissolution of these sacrificial PEC templates in concentrated NaCl solutions then generates photolithographically templated agarose gels, whose shapes and dimensions match those of their PEC templates. Besides tuning their shapes and sizes, the mechanical properties of these gels can be easily tailored by varying the initial agarose concentrations used. Moreover, this PEC-templated gel synthesis appears to not adversely affect hydrogel cytocompatibility, suggesting its potential suitability for biological and biomedical applications. Though the present study uses only agarose as the model gel system, this PEC-based strategy for customizing gel shape can likely also be applied to other thermoreversible gel networks (e.g., those based on methylcellulose, poloxamers or thermoresponsive chitosan derivatives) and could have many attractive applications, ranging from drug delivery and tissue engineering, to sensing and soft robotics.

Enhancing Antidepressant Effect of Poloxamer/Chitosan Thermosensitive Gel Containing Curcumin-Cyclodextrin Inclusion Complex

Poor solubility and bioavailability are limiting factors for the clinical application of curcumin. This study seeks to develop poloxamer/chitosan thermosensitive gel containing curcumin-cyclodextrin inclusion complex with enhanced brain bioavailability and antidepressant effect. The optimized gel had shorter gelation time and produced sustained release in vitro characterized with non-Fickian diffusion. Pharmacokinetics of gel were evaluated using male Sprague-Dawley rats receiving 240 μg/kg of curcumin and curcumin-cyclodextrin inclusion complex through intranasal administration, compared against a control group receiving intravenous curcumin (240 μg/kg). The intranasal administration of gel provided sustained release by maintaining plasma concentrations of curcumin above 21.27 ± 3.26 ng/mL for up to 8 h. Compared to intranasal administration of the inclusion complex, AUC0–8 h of curcumin from thermoreversible gel in plasma and hippocampus was increased 1.62- and 1.28-fold, respectively. The gel exhibited superior antidepressant activity in mice. The findings reported here suggested that the clinical application of curcumin can be better exploited through an intranasal administration of the thermosensitive gel.

Viscoplastic fracture transition of a biopolymer gel.

Physical gels are swollen polymer networks consisting of transient crosslink junctions associated with hydrogen or ionic bonds. Unlike covalently crosslinked gels, these physical crosslinks are reversible thus enabling these materials to display highly tunable and dynamic mechanical properties. In this work, we study the polymer composition effects on the fracture behavior of a gelatin gel, which is a thermoreversible biopolymer gel consisting of denatured collagen chains bridging physical network junctions formed from triple helices. Below the critical volume fraction for chain entanglement, which we confirm via neutron scattering measurements, we find that the fracture behavior is consistent with a viscoplastic type process characterized by hydrodynamic friction of individual polymer chains through the polymer mesh to show that the enhancement in fracture scales inversely with the squared of the mesh size of the gelatin gel network. Above this critical volume fraction, the fracture process can be described by the Lake-Thomas theory that considers fracture as a chain scission process due to chain entanglements.

Investigation of effectiveness of some extensively used polymers on thermoreversible properties of Pluronic® tri-block copolymers

This investigation presents a study on the effect of various polymers on gelling properties of tri-block (Pluronic®) copolymers and increasing the stability parameter of in situ gelling system by altering their composition. The tri-block copolymers finds their importance in fabrication of in situ gelling system for the delivery of various kinds of drugs, which can be administered by topical, ophthalmic or parenteral routes. Pluronic®, is a category of non-toxic, water soluble, biodegradable poly (ethylene oxide)/poly (propylene oxide)/poly ethylene oxide), tri-block copolymers which have application in formulation of various in situ gelling systems. This formulation undergo thermo-reversible gelation, where it exists as a free flowing liquid at low temperature and gels in the range of body temperature to form stable depot in aqueous environment. Gelling system was prepared according to the 'Cold Method' using different concentration of polymers (15%–20% w/v) and subjected to the determination of gelation temperature (GT), viscosity study and effect of various polymers on the strength of gelation. Overall study on the gelation of system at particular temperature is the important parameter for formulation of in situ drug delivery system. It was established that addition of 0.5% w/v of HPMC K4M into gelling system make it stable for forming gel in the range of body temperature whereas methyl cellulose, carbopol 934P, and HPMC E-50 restrict the gel formation.

Thermoreversible gelation of poly(urethane acyl-semicarbazides) carrying cycloaliphatic moieties and studies on selective adsorption of dyes from wastewater

A series of linear segmented poly(urethane acyl-semicarbazides) of different compositions were synthesized from polypropylene glycol (Mn ∼ 1000 and 2000), hexamethylene diisocyanate and cyclohexanedicarboxylic acid 1,4 dihydrazide. The polymers exhibited thermoreversible gelation at a minimum gelation concentration of 25 mg/mL in DMSO in about 25 min. Among the comparisons of varying NCO/OH ratios, PPG1000 based polyurethanes with NCO/OH ∼ 2.5 and 3 and PPG2000 based systems with NCO/OH ∼ 3.0 and 3.5 exhibited gelation. IR studies on the solutions and gels (in DMSO) revealed the extensive H-bonding between the chains in gel state. Scanning electron micrographs of the xerogel revealed a 3D-network structure – higher hard segment content (P1000-1:3.5) led to a fibrous morphology and lower hard segment content (P2000-1:3) led to a microsphere like architecture. The phase separation induced gelation mechanism of self-assembly and effect of the stoichiometry on the morphology were explained based on the correlation between DSC, WAXS and FE-SEM data. The xerogels of the self-assembled polymers described in this work demonstrate a remarkable ability to remove dye molecules selectively, rapidly and efficiently. The gels retain their original structure and performance even after they are recycled 20 times which was quantified by UV–vis studies.