Equilibrium Swelling Research Articles

Conceptualization and Investigation of Multicomponent Polymer Networks as Prospective Corticosteroid Carriers.

Dexamethasone (DXM) is a highly potent and long-acting synthetic glucocorticoid with anti-inflammatory, anti-allergic, and immunosuppressive effects. However, the systemic application of DXM can cause undesirable side effects: sleep disorders, nervousness, heart rhythm disorders, heart attack, and others. In the present study, multicomponent polymer networks were developed as potential new platforms for the dermal application of dexamethasone sodium phosphate (DSP). First, a copolymer network (CPN) comprising hydrophilic segments of different chemical structures was synthesized by applying redox polymerization of dimethyl acrylamide onto poly(ethylene glycol) in the presence of poly(ethylene glycol) diacrylate (PEGDA) as a crosslinker. On this basis, an interpenetrating polymer network structure (IPN) was obtained by introducing a second network of PEGDA-crosslinked poly(N-isopropylacrylamide). Multicomponent networks obtained were characterized by FTIR, TGA, and swelling kinetics in different solvents. Both CPN and IPN showed a high swelling degree in aqueous media (up to 1800 and 1200%, respectively), reaching the equilibrium swelling within 24 h. Additionally, IPN showed temperature-responsive swelling in an aqueous solution as the equilibrium swelling degree decreased considerably with an increase in the temperature. In order to evaluate the networks' potential as drug carriers, swelling in DSP aqueous solutions of varied concentration was investigated. It was established that the amount of encapsulated DSP could be easily controlled by the concentration of drug aqueous solution. In vitro DSP release was studied in buffer solution (BS) with pH 7.4 at 37 °C. The results obtained during DSP loading and release experiments proved the feasibility of the developed multicomponent hydrophilic polymer networks as effective platforms for potential dermal application.

Accelerated aging behavior and degradation mechanism of nitrile rubber in thermal air and hydraulic oil environments

AbstractThe aging behavior and degradation mechanism of nitrile rubber (NBR) under free and compression states were investigated in simulated air and hydraulic oil environments at various elevated temperatures. The variations in the crosslinking density, volatile components and the chemical structure of NBR during aging were studied using equilibrium swelling testing and dynamic mechanical analysis (DMA), pyrolysis‐gas chromatography–mass spectrometry and attenuated total reflection‐Fourier transform infrared spectroscopy. The migration of additives in different media and the crosslinking density of NBR aged in different conditions were compared. The tensile strength, DMA, and thermogravimetric analysis results were consistent with the changes in the crosslinking density of NBR and the migration of additives. Four effects of the simulated hydraulic system on the thermal aging of NBR were examined. Both the compression stress and the oil medium slowed the aging of NBR. The results can provide new insights into the use of NBR products in lubricating oil environments and NBR lifespan prediction in hydraulic working conditions.

Influence of crosslink on the formation of hydrophobic hydrogels

Recently invented hydrophobic hydrogel is a specific type of soft matter, which is composed of purely hydrophobic networks while maintaining ultra-high water content. Owing to their unique structures, hydrophobic hydrogels manifest various particularities for versatile applications. Therefore, it is essential to reveal the factors that determine the gels’ formation. Until now, the role played by the chemical crosslinks (e.g. crosslink ratio, structure) stays unclear. To figure out the mystery, herein we prepare a series of polyacrylate gels with different crosslinks at diverse crosslinker concentrations. Upon being soaked in water, the gels behave divergently in terms of dynamic swelling behavior. Unlike conventional gels, the maximum swelling degrees of three different hydrophobic hydrogels initially increase and then decrease with raising in crosslink ratio. Similarly, the swelling kinetics significantly vary with the crosslink ratio. From the data, a moderate crosslink ratio is required for the formation of hydrophobic hydrogels as it endows the polymer chain with high mobility and density. In addition, the chemical structure of crosslinks plays a less significant role in the formation of hydrophobic hydrogels but an important role in determining their swelling equilibrium states in water, which ultimately affects their mechanical performance. All these results may help us to uncover the formation mechanism of the hydrophobic hydrogels and establish a general standard for the preparation of such soft matter.

β-Cyclodextrin/chitosan-based (polyvinyl alcohol-co-acrylic acid) interpenetrating hydrogels for oral drug delivery

Gallic acid is an important phenolic compound with extensive applications in the food and pharmaceutical industries due to its health-promoting properties. However, due to its poor solubility and bioavailability, it is rapidly excreted from the body. Therefore, β-cyclodextrin/chitosan-based (polyvinyl alcohol-co-acrylic acid) interpenetrating controlled release hydrogels were developed to improve its dissolution and bioavailability. pH, polymer ratios, dynamic and equilibrium swelling, porosity, sol-gel, FTIR, XRD, TGA, DSC, SEM and structural parameters like an average molecular weight between crosslinks, solvent interaction parameters, and diffusion coefficient affecting release behavior were investigated. The highest swelling and release were observed at pH 7.4. Furthermore, hydrogels showed good antioxidant and antibacterial properties. Hydrogels improved the bioavailability of gallic acid in a pharmacokinetics study in rabbits. In vitro biodegradation showed that hydrogels were more stable in blank PBS than lysozyme and collagenase. Hydrogels were safe for rabbits (3500 mg/kg) without causing hematological or histopathological changes. The hydrogels showed good biocompatibility, and no adverse reactions were observed. Moreover, the developed hydrogels can be used to improve the bioavailability of various other drugs.

Sustained Release of Drug Facilitated Through Chemically Crosslinked Polyvinyl Alcohol-Gelatin (PVA-GE) Hydrogels. A sustainable biomedical approach

Abstract The present study aimed to prepare hydrogel based on polyvinyl alcohol (PVA) and gelatin (Ge) and characterization of PVA/Ge hydrogel for their potential use as a sustained drug delivery system. Polyvinyl Alcohol (PVA) and-Gelatin (Ge) were cross-linked using glutaraldehyde (GA) as a crosslinking agent and hydrochloric acid (HCl) as a catalyst. Different feed polymer ratio and crosslinking agent concentration were used to prepare a series of PVA/Ge hydrogels. The obtained PVA/Ge hydrogels were investigated for dynamic and equilibrium swelling studies. The effect of polymers ratio, degree of crosslinking and pH of the medium on swelling of PVA/Ge hydrogels was investigated. Furthermore, the values of diffusion coefficient (D), volume fraction, polymer-solvent interaction parameter, molecular weight between crosslink and crosslink density were calculated. For swelling studies, 0.05M USP phosphate buffer solutions of different pH (1.2, 5.5, 6.5 and 7.5) were used. For the drug release study, ciprofloxacin HCl was loaded into selected samples as a model drug. The release of drug from these samples was performed for 12 hours in USP phosphate buffers of pH 1.2, 5.5 and 7.5. The release data from these samples were fitted into various kinetic models like zero order, first order, Higuchi and Peppas models to investigate the release mechanism. It was found that by varying the composition of PVA/Ge hydrogel and GA concentration, a significant difference was observed in drug release kinetics. FTIR spectroscopy and X-ray diffraction were used for the characterization of hydrogels. PVA/Ge hydrogel showed sustained release of the model drug at various pH values suggesting its potential use as a sustained drug delivery system.

Formulation of pH-responsive highly swellable hydrogel scaffolds for controlled release of tramadol HCl: characterization and biocompatibility evaluation.

Introduction: The objective of current project was to formulate a system for controlled delivery of Tramadol HCl (TRD), an opioid analgesic used in the treatment of moderate to severe pain. Methods: For this purpose, a pH responsive AvT-co-poly hydrogel network was formulated through free radical polymerization by incorporating natural polymers i.e., aloe vera gel and tamarind gum, monomer and crosslinker. Formulated hydrogels were loaded with Tramadol HCl (TRD) and evaluated for percent drug loading, sol-gel fraction, dynamic and equilibrium swelling, morphological characteristics, structural features and in-vitro release of Tramadol HCl. Results and Discussions: Hydrogels were proved to be pH sensitive as remarkable dynamic swelling response ranging within 2.94g/g-10.81g/g was noticed at pH 7.4 as compared to pH 1.2. Percent drug loading was in the range of 70.28%-90.64% for all formulations. Thermal stability and compatibility of hydrogel components were validated by DSC analysis and FTIR spectroscopy. Controlled release pattern of Tramadol HCl from the polymeric network was confirmed as maximum release of 92.22% was observed for over a period of 24 hours at pH 7.4. Moreover, oral toxicity studies were also conducted in rabbits to investigate the safety of hydrogels. No evidence of any toxicity, lesions and degeneration was reported, confirming the biocompatibility and safety of grafted system.

Gamma Radiation-Induced Advanced 2,3-Dimethylacrylic Acid-(2-Acrylamido-2-methyl-1-propanesulfonic Acid) Superabsorbent Hydrogel: Synthesis and Characterization

Gamma radiation technique for the preparation of pure hydrogels is gaining popularity worldwide. Superabsorbent hydrogels play vital roles in different fields of application. The present work mainly focuses on the preparation and characterization of 2,3-Dimethylacrylic acid-(2-Acrylamido-2-methyl-1-propane sulfonic acid) (DMAA-AMPSA) superabsorbent hydrogel by applying gamma radiation and optimization of the proper dose. To prepare DMAA-AMPSA hydrogel, different doses ranging from 2 kGy to 30 kGy were imparted on the blend aqueous solution of the monomers. The equilibrium swelling increases with increasing radiation dose, followed by decreasing after reaching a certain level, and the highest result is found to be 26,324.9% at 10 kGy. Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy confirmed the formation of co-polymer by showing the characteristic functional groups and proton environment of the gel. X-ray Diffraction (XRD) pattern indicates the crystalline/amorphous nature of the gel. The Differential Scanning Calorimetry (DSC) and Thermogravimetry Analysis (TGA) revealed the thermal stability of the gel. The surface morphology and constitutional elements were analyzed and confirmed by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS). Finally, it can be stated that hydrogels can be usable in metal adsorption, drug delivery, and other relevant fields.

Sodium Salt of Partially Carboxymethylated Sodium Alginate-Graft-Poly(Acrylonitrile): II Superabsorbency, Salt Sensitivity and Swelling Kinetics of Hydrogel, H-Na-PCMSA-g-PAN.

The water absorption measurements of a novel superabsorbent anionic hydrogel, H-Na-PCMSA-g-PAN, has been reported first time in water with a poor conductivity, 0.15 M saline (NaCl, CaCl2, and AlCl3) solutions, and simulated urine (SU) solutions at various times. The hydrogel has been prepared by the saponification of the graft copolymer, Na-PCMSA-g-PAN (%G = 316.53, %GE = 99.31). Results indicated that as compared to the swelling capacity values evaluated in water with a poor conductivity, the ability of the hydrogel to swell in various saline solutions with the same concentration is significantly reduced at all different durations. The swelling tends to be Na+ > Ca2+ > Al3+ at the same saline concentration in the solution. Studies of the absorbency in various aqueous saline (NaCl) solutions also revealed that the swelling capacity decreased as the ionic strength of the swelling medium rose, which is consistent with the experimental results and Flory's equation. Furthermore, the experimental results strongly suggested that second-order kinetics governs the swelling process of the hydrogel in various swelling media. The swelling characteristics and equilibrium water contents for the hydrogel in various swelling media have also been researched. The hydrogel samples have been successfully characterized by FTIR to show the change in chemical environment to COO- and CONH2 groups after swelling in different swelling media. The samples have also been characterized by SEM technique.

Application of plasma modified pyrolytic carbon black in improving mechanical properties of natural rubber composite

AbstractIn this work, the Argon (Ar) plasma technology is adopted for pyrolytic carbon black (CBp) modification and the N330/Modified‐CBp (MCBp) hybrid is then incorporated into the Natural Rubber (NR) matrix. Compared with CBp, the MCBp has smaller particle size, lower ash content, higher specific surface area, and surface activity based on the results of laser diffraction method, transmission electron microscope (TEM), thermogravimetric analysis, gas sorption analysis (Nitrogen), acetone solvent, and X‐ray photoelectron spectroscopy. Among them, Dv (90) is found to have reduced by 20% while the specific surface area increased by 4%. According to the bound rubber content experiments, the equilibrium swelling experiments as well as the temperature and strain sweeps, the bound rubber content, filler‐filler bond strength, and cross‐linking density of NR/N330/MCBp are all superior to those of NR/N330/CBp, resulting in an outstanding comprehensive performance of NR/N330/MCBp composite. In particular, the 300% modulus and the tear strength rise by 43% and 14% respectively, surpassing even the system filled with N330. Finally, the mechanism of mechanical properties improvement in the NR/N330/MCBp composite is proposed: the strong filler‐filler bond is formed between the MCBp and N330 aggregates via molecular chains, and they are anchored on the MCBp and absorbed on the N330 simultaneously.

Transdermal delivery of doxorubicin and methotrexate from polyelectrolyte three layer nanoparticle of graphene oxide/polyethyleneimine/dextran sulphate for chemotherapy: In vitro and in vivo studies

In the present work, novel dual drug loaded - anionic graphene oxide/cationic polyethyleneimine/poly anionic dextran sulfate (GO/PEI/DS) was synthesized by a layer-by-layer self-assembly technique for transdermal anti-cancer drug delivery. Doxorubicin (DOX) was loaded onto folic acid conjugated graphene oxide (GO) and methotrexate (MTX) was loaded onto dextran sulfate (DS). The drug carrier was characterized by fourier transform infrared spectroscopy, x-ray diffraction spectroscopy, dynamic light scattering analysis, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, zeta-potential analysis, drug loading and encapsulation efficiency, equilibrium swelling studies, in vitro drug release studies, hemocompatibility assays, in vitro cytotoxicity assay, skin irritation studies, ex vivo skin permeation studies and in vivo pharmacokinetic studies.The cytotoxicity of synthesized materials was evaluated against MCF-7 breast cancer cells using an MTT assay and apoptosis assay. The synergistic effect of DOX and MTX to inhibit the growth of cancer cells was also confirmed. The final dual drug-loaded carrier showed a cell viability of 36.38 % towards MCF-7 cancer cells while it showed a cell viability of >87.65 % towards normal L929 cell lines. The in vivo pharmacokinetic studies in Wistar rats through oral and transdermal routes of administration, the transdermal route of administration of dual drug-loaded material provided a sustained and prolonged drug existence in the blood circulation system. The mean residence time of drugs in the bloodstream via oral administration was 83.98 ± 3.71 h, while that of the transdermal route of administration was 149.62 ± 6.11 h. The results revealed that the synthesized dual drug-loaded material showed a good pH-dependent controlled and sustained release profile for both DOX and MTX via the transdermal route of administration in comparison with oral delivery.

Hydrogen Bonding Enables Polymer Hydrogels with pH-Induced Reversible Dynamic Responsive Behaviors.

Poly(acrylic acid-co-N-vinylcaprolactam) (PAN) hydrogels containing multiple hydrogen bonds can exhibit pH-induced reversible dynamic responsive behaviors. When placing a transparent hydrogel in an acid bath, as hydrogen bonds between comonomer units involving protonated COOH groups are formed faster than water diffusion, a nonequilibrium light-scattering state is formed to turn the hydrogel opaque, while as the swelling equilibrium is reached over time, the hydrogel regains its transparency. Likewise, when the transparent, hydrogen-bonded hydrogel is subsequently immersed in DI water, faster water absorption occurs in where more COOH groups are deprotonated, which also generates a light-scattering state leading to opacity, while the transparency is slowly recovered after equilibrium. Using such two-way dynamic transparency evolution, a PAN-based hydrogel material is prepared to demonstrate a dynamic memory system for information memorizing-forgetting and recalling-forgetting.

Hydrogen Bonding Enables Polymer Hydrogels with pH‐Induced Reversible Dynamic Responsive Behaviors

AbstractPoly(acrylic acid‐co‐N‐vinylcaprolactam) (PAN) hydrogels containing multiple hydrogen bonds can exhibit pH‐induced reversible dynamic responsive behaviors. When placing a transparent hydrogel in an acid bath, as hydrogen bonds between comonomer units involving protonated COOH groups are formed faster than water diffusion, a nonequilibrium light‐scattering state is formed to turn the hydrogel opaque, while as the swelling equilibrium is reached over time, the hydrogel regains its transparency. Likewise, when the transparent, hydrogen‐bonded hydrogel is subsequently immersed in DI water, faster water absorption occurs in where more COOH groups are deprotonated, which also generates a light‐scattering state leading to opacity, while the transparency is slowly recovered after equilibrium. Using such two‐way dynamic transparency evolution, a PAN‐based hydrogel material is prepared to demonstrate a dynamic memory system for information memorizing‐forgetting and recalling‐forgetting.

Injectable, In Situ Self-cross-linking, Self-healing Poly(l-glutamic acid)/Polyethylene Glycol Hydrogels for Cartilage Tissue Engineering.

Injectable hydrogels have drawn much attention in the field of tissue engineering because of advantages such as simple operation, strong plasticity, and good biocompatibility and biodegradability. Herein, we propose the novel design of injectable hydrogels via a Schiff base cross-linking reaction between adipic dihydrazide (ADH)-modified poly(l-glutamic acid) (PLGA-ADH) and benzaldehyde-terminated poly(ethylene glycol) (PEG-CHO). The effects of the mass fraction and the molar ratio of -CHO/-NH2 on the gelation time, mechanical properties, equilibrium swelling, and in vitro degradation of the hydrogels were examined. The PLGA/PEG hydrogels cross-linked by dynamic Schiff base linkages exhibited good self-healing ability. Additionally, the PLGA/PEG hydrogels had good biocompatibility with bone marrow-derived mesenchymal stem cells (BMSCs) and could effectively support BMSC proliferation and deposition of glycosaminoglycans and upregulate the expression of cartilage-specific genes. In a rat cartilage defect model, PLGA/PEG hydrogels significantly promoted new cartilage formation. The results suggest the prospect of the PLGA/PEG hydrogels in cartilage tissue engineering.

Soaking pretreatment of hydrogel adsorbent in distilled water to enhance efficiency of adsorption onto low concentration dye

AbstractTo address the poor removal rate of low‐concentration dye adsorption, the soaking pretreatment of hydrogel adsorbent in distilled water was suggested. In contrast to the conventional method of directly adding dried particles into dye solution, the purposed procedure involved adding an adsorbent into distilled water before transferring it into the dye solution. A hydrogel adsorbent based on P(AANa/AM) containing COONa groups was fabricated as an example for the hypothesis. The maximum adsorption capacity of P(AANa/AM) hydrogel adsorbent onto MB was 2455.45 mg/g under an initial MB concentration of 1000 mg/L. After two rounds of soaking pretreatment in distilled water, the clearance rate of 20 mg/L MB increased from 97.79% to 99.40%. Considering the hydrophilicity and ionization of COONa group, a high concentration of Na+ was released into solution. Hydrogel soaked multiple times in fresh distilled water induced the continuous release of Na+ into distilled water, although the swelling equilibrium was already achieved in the first soak. In dye adsorption and desorption experiments, the water absorption behavior was observed. Overall, this work revealed that the soaking pretreatment of hydrogel adsorbent in distilled water can enhance the removal rate of low concentration dye through adsorption.

PREPARATION, CHARACTERIZATION AND RELEASING -SWELLING KINETICS OF MYRRH BASED HYDROGEL

In this work, Myrrh gum was used with sodium alginate (SA) to create novel Myrrh-Alginate beads composite. These beads were produced utilizing the ionotropic gelation technique. Methylene blue (MB) was employed as a drug model to evaluate the kinetics of drug release and the capacity of the synthesized beads to function as a drug delivery system. The molecular interaction between sodium alginate and myrrh was confirmed by FTIR spectroscopy. The physical characteristics of the Myrrh-Alginate beads, including drug content, particle size, thermal properties, equilibrium water content (EWC), swelling behavior, and equilibrium swelling ratio (ESR), were studied to establish the hydrogel's response type, as well as the releasing kinetics at 37°C and in Phosphate buffer solution (PBS) at pH = 6.8 and 10. All beads (loaded and unloaded) were analyzed by Differential scanning calorimetry, Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The drug content percentages of the Myrrh-Alginate beads increased with a moderate fraction (5% ) of Myrrh but dropped with a higher Myrrh percentage. The Myrrh-Alginate beads absorbed more water and swelled more than the pure calcium alginate beads (S2) in pH 6.8 and 10 of (PBS). In a pH 6.8 of (PBS), the Myrrh-Alginate beads demonstrated a controlled and regulated style of releasing and demonstrated a high match with the Korsmeyer-Peppas model as they had the maximum values of the correlation factor (R2) in this model.

Effects of polyamide elastomer on the morphology, crosslink density, mechanical, and oil‐resistant properties of acrylonitrile‐butadiene rubber/polyamide elastomer vulcanizates

AbstractPolyamide elastomer (PAE) is a novel material which may improve the performances of acrylonitrile‐butadiene rubber (NBR). This work uses equilibrium swelling and rheological apparatus to study the effects of the PAE content on the overall crosslink densities of NBR/PAE vulcanizate. The presence of PAE significantly increased the overall crosslink density. During the aging stage, the overall crosslink density first increased and then decreased with increasing aging temperature from 25 to 150°C. There was a linear relationship between the tensile strength with the overall crosslink density of the NBR/PAE vulcanizate. Oil resistance of the NBR/PAE vulcanizate was improved with increasing PAE content.

Radiation fabrication of hybrid activated carbon and functionalized terpolymer hydrogel for sorption of Eu(III) and Sm(III) ions

Abstract In this work, a hybrid composite of activated carbon (AC) functionalized with terpolymer hydrogel of polyvinyl alcohol/polyacrylamide/polyacrylic acid (PVA/PAAm/PAA) was prepared by γ-irradiation and used efficiently for sorption of Eu(III) and Sm(III) ions from aquatic solutions. Sewage sludge from the wastewater treatment plant was used to prepare AC, then activated by zinc chloride (ZnCl2) and thermal treatment at 550 °C. The modification of AC by functionalized terpolymer has successfully occurred mainly to limit its precipitation and to increase its adsorption capacity which allowed capable interaction with the metal ions. Different advanced techniques were used to investigate the structure and properties of (PVA/PAAm/PAA)/AC composite before and after the sorption process. Using 20 kGy is sufficient to get gel fraction of 87.5% and equilibrium swelling was 39.1 g/g. The (PVA/PAm/PAA)/AC composite hydrogel showed a pHpzc at pH ∼3. FTIR and EDS confirmed the successful integration of the functional groups and constituent elements of AC into terpolymer hydrogel components. XRD results confirmed the typical diffraction peaks of AC in the composite and the calculated average crystallite size was 167.4 nm. The SEM morphology of AC appeared as grains distributed well into the composite. The effect of synthesized AC, PVA/PAAm/PAA and (PVA/PAAm/PAA)/AC sorbents were tested to uptake of Eu(III) and Sm(III) ions. The highest uptake was noticed for (PVA/PAAm/PAA)/AC composite and it was selected for studying the parameters affecting the sorption process such as pH, shaking time, initial concentration, and adsorbent dosage. Results of the experimental data showed that Langmuir isotherm and Pseudo-second-order kinetic models fit well the sorption process of both Eu(III) and Sm(III) ions with maximum sorption capacities of 173.24 and 160.41 mg/g and uptake percentage of 82.3% and 83.4%, respectively at the optimum conditions of pH 4, 180 min, 100 mg/L metal concentration and 0.01 g adsorbent mass. The thermodynamic parameters indicated endothermic and spontaneous nature of the sorption process. Additionally, the as-prepared composite afford high selectivity and uptake capacity for Eu(III) and Sm(III) ions at pH 4 even in the presence of competing cations; Cd(II), Co(II), Sr(II) and Cs(I). The (PVA/PAAm/PAA)/AC composite was used efficiently as a unique and selective adsorbent for the sorption of Eu(III) and Sm(III) ions.

Determination of the crosslink density of silica-filled styrene butadiene rubber compounds by different analytical methods

AbstractThe crosslink density of rubber compounds has a great effect on the properties of the final product. For this reason, a suitable characterization method is required to understand and optimize the final performance of rubber materials. Four different experimental techniques were used to determine the crosslink density of silica-filled styrene butadiene rubber composites: equilibrium swelling experiments, stress–strain measurements using the Mooney–Rivlin theory, freezing point depression temperature tests and Temperature Scanning Stress Relaxation (TSSR) measurements. The evaluation of these different techniques shows that the results obtained follow a similar trend for all four methods. The results from the Mooney-Rivlin and TSSR measurements correlate the best. These two techniques are the least affected by the presence of fillers and are the less time-consuming ones. Furthermore, they also show the best correlation with the mechanical properties of the studied compounds.

Swelling of Homogeneous Alginate Gels with Multi-Stimuli Sensitivity.

A new two-step method is suggested for the preparation of homogeneous alginate gels. In the first step, alginate chains are weakly bonded by Ca2+ ions in an aqueous solution with a low pH. In the next step, the gel is immersed into a strong solution of CaCl2 to finalize the cross-linking process. Homogeneous alginate gels preserve their integrity in aqueous solutions with a pH ranging from 2 to 7 and ionic strength in the interval from 0 to 0.2 M, at temperatures ranging from room temperature up to 50 °C, and can be used in biomedical applications. The immersion of these gels into aqueous solutions with low pH induces the partial breakage of ionic bonds between chains (treated as gel degradation). This degradation affects the equilibrium and transient swelling of homogeneous alginate gels and makes them sensitive to the history of loading and environmental conditions (pH, ionic strength and temperature of aqueous solutions). As sensitivity to the environmental stimuli is a characteristic feature of polymer networks connected by catch bonds, homogeneous alginate gels may serve as a simple model, mimicking the behavior of more sophisticated structures in living matter.

Development of Tofacitinib Loaded pH-Responsive Chitosan/Mucin Based Hydrogel Microparticles: In-Vitro Characterization and Toxicological Screening.

Tofacitinib is an antirheumatic drug characterized by a short half-life and poor permeability, which necessitates the development of sustained release formulation with enhanced permeability potential. To achieve this goal, the free radical polymerization technique was employed to develop mucin/chitosan copolymer methacrylic acid (MU-CHI-Co-Poly (MAA))-based hydrogel microparticles. The developed hydrogel microparticles were characterized for EDX, FTIR, DSC, TGA, X-ray diffraction, SEM, drug loading; equilibrium swelling (%), in vitro drug release, sol-gel (%) studies, size and zeta potential, permeation, anti-arthritic activities, and acute oral toxicity studies. FTIR studies revealed the incorporation of the ingredients into the polymeric network, while EDX studies depicted the successful loading of tofacitinib into the network. The thermal analysis confirmed the heat stability of the system. SEM analysis displayed the porous structure of the hydrogels. Gel fraction showed an increasing tendency (74-98%) upon increasing the concentrations of the formulation ingredients. Formulations coated with Eudragit (2% w/w) and sodium lauryl sulfate (1% w/v) showed increased permeability. The formulations equilibrium swelling (%) increased (78-93%) at pH 7.4. Maximum drug loading and release (%) of (55.62-80.52%) and (78.02-90.56%), respectively, were noticed at pH 7.4, where the developed microparticles followed zero-order kinetics with case II transport. Anti-inflammatory studies revealed a significant dose-dependent decrease in paw edema in the rats. Oral toxicity studies confirmed the biocompatibility and non-toxicity of the formulated network. Thus, the developed pH-responsive hydrogel microparticles seem to have the potential to enhance permeability and control the delivery of tofacitinib for the management of rheumatoid arthritis.