Dynamic Swelling Studies Research Articles

Fabrication and In vitro Evaluation of Carbopol/Polyvinyl Alcohol-based pH-sensitive Hydrogels for Controlled Drug Delivery.

Diclofenac sodium has a short half-life (about 1.5 hours), requiring repeated administration, and as a result, serious complications, such as GI bleeding, peptic ulcer, and kidney and liver dysfunction, are generated. Hence, a sustained/controlled drug delivery system is needed to overcome the complications caused by the administration of diclofenac sodium. This study aimed to fabricate and evaluate carbopol/polyvinyl alcohol-based pH-sensitive hydrogels for controlled drug delivery. pH-sensitive carbopol/polyvinyl alcohol graft-poly(acrylic acid) hydrogels (Cp/PVA-g-PAa hydrogels) were developed for the controlled delivery of diclofenac sodium. The combination of carbopol/polyvinyl alcohol, acrylic acid, and ethylene glycol dimethacrylate was used as polymer, monomer, and cross-linker, respectively. The effects of the formulation's composition on porosity, swelling index, and release pattern of diclofenac sodium from the developed hydrogels were investigated. An increase in porosity and swelling was observed with the increasing amounts of carbopol and acrylic acid, whereas polyvinyl alcohol showed the opposite effect. Due to the formation of a highly viscous system, the drug release decreased with the increasing concentrations of carbopol and polyvinyl alcohol while increased with increasing acrylic acid concentration. The pH-responsive properties of the fabricated hydrogels were demonstrated by dynamic swelling and drug release studies at three different pH values. Higher dynamic swelling and diclofenac sodium (model drug) release were found at high pH values compared to low pH values, i.e., pH 7.4 > 4.6 > 1.2, respectively. Cytotoxicity studies reported no toxic effect of the prepared hydrogels, thus indicating that the prepared hydrogels are safe to be used on clinical basis. The prepared carbopol/polyvinyl alcohol crosslinked hydrogel can be used as a promising carrier for the controlled release of 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, Characterization, and In Vitro Drug Release Study of β-Cyclodextrin-Based Smart Hydrogels.

In this study, novel pH-responsive polymeric β-cyclodextrin-graft-poly(acrylic acid/itaconic acid) hydrogels were fabricated by the free radical polymerization technique. Various concentrations of β-cyclodextrin, acrylic acid, and itaconic acid were crosslinked by ethylene glycol dimethacrylate in the presence of ammonium persulfate. The crosslinked hydrogels were used for the controlled delivery of theophylline. Loading of theophylline was conducted by the absorption and diffusion method. The fabricated network of hydrogel was evaluated by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), and scanning electron microscopy (SEM). The crosslinking among hydrogel contents and drug loading by the fabricated hydrogel were confirmed by FTIR analysis, while TGA indicated a high thermal stability of the prepared hydrogel as compared to pure β-cyclodextrin and itaconic acid. The high thermal stability of the developed hydrogel indicated an increase in the thermal stability of β-cyclodextrin and itaconic acid after crosslinking. Similarly, a decrease in crystallinity of β-cyclodextrin and itaconic acid was observed after crosslinking, as evaluated by XRD analysis. SEM revealed an irregular and hard surface of the prepared hydrogel, which may be correlated with strong crosslinking among hydrogel contents. Crosslinked insoluble and uncrosslinked soluble fractions of hydrogel were evaluated by sol–gel analysis. An increase in gel fraction was seen with the increase in compositions of hydrogel contents, while a decrease in sol fraction was observed. Dynamic swelling and dissolution studies were performed in three various buffer solutions of pH 1.2, 4.6, and 7.4, respectively. Maximum swelling and drug release were observed at higher pH values as compared to the lower pH value due to the deprotonation and protonation of functional groups of the hydrogel contents; thus, the pH-sensitive nature of the fabricated hydrogel was demonstrated. Likewise, water penetration capability and polymer volume were evaluated by porosity and polymer volume studies. Increased incorporation of β-cyclodextrin, acrylic acid, and itaconic acid led to an increase in swelling, drug release, drug loading, and porosity of the fabricated hydrogel, whereas a decrease was detected with the increasing concentration of ethylene glycol dimethacrylate. Conclusively, the prepared hydrogel could be employed as a suitable and promising carrier for the controlled release of theophylline.

Designing of pH-responsive ketorolac tromethamine loaded hydrogels of alginic acid: Characterization, in-vitro and in-vivo evaluation

pH-responsive hydrogels based on alginic acid grafted with acrylic acid and ethylene glycol dimethylacrylate in the presence of ammonium persulfate were developed for controlled delivery of Ketorolac tromethamine. The alginic acid based hydrogels were prepared by free radical polymerization technique. Increase in gel fraction was observed with the increase in alginic acid, acrylic acid, and ethylene glycol dimethylacrylate content. The dynamic swelling and drug release studies were conducted at two different pH values (pH 1.2 and 7.4). Maximum swelling and drug release were observed at pH 7.4. The characterization of prepared hydrogels was carried out by using Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, powder x-ray diffraction, and scanning electron microscopy. Similarly, in-vivo study was performed on rabbits and greater plasma drug concentration was achieved by fabricated hydrogels as compared to drug solution and commercial product Keten. Conclusively, the fabricated hydrogels can be considered as a potential candidate for controlled delivery of Ketorolac tromethamine.

New Formulation and Characterization of Topical Films of Tioconazole and Evaluation of Their Antifungal Therapy

Purpose: New formulation of Scleroglucan (Sclg) films loaded with tioconazole, a medication typically applied for dermal treatments prepared. The feasibility of that treatment relies on the penetration of medications through the target layers of the skin in effective concentrations.
 Methods: Dynamic and mechanical characterization and swelling studies of the novel delivery system were analysed. An aqueous solution of Sclg (Cp=1% w/v) and glycerol (2% w/v) was prepared and kept at room temperature under magnetic stirring for 72 hrs. Tioconazole previously solubilised in Labrasol, was added to the polymer/glycerol solution. 4 ml of solution was poured in a plastic plate. The films were dried at 40°C for 1 hr and then allowed to dry at room temperature (about 25°C) for a week. Translucent films were obtained.
 The fungal strain used to test the film are CO23 sensitive to drugs, CO23 RFLC resistant to fluconazole, CO23 RFK resistant to micafungin, ATCC standard strain.
 Results: The water uptake of the films significantly increased up to 24 hrs. The optical microscope films images show that the presence of the drug did not significantly influence the appearance of the samples. The in vitro studies demonstrated the perceptible fungal activity of the new formulation against Candida albicans infections.
 Conclusion: The patches showed antimicrobial activity against all tested strains. An evident inhibition zone diameter, about 40 mm, for the strains sensitive to azoles (CO23 RFK and CO23) in comparison to strain resistant to fluconazole (CO23 RFLC) was observed. After 48 hours the inhibition zone diameters were reduced of about 6-7 mm in comparison to those observed after 24 hours of incubation.

Preparation and In Vitro Evaluation of Aspartic/Alginic Acid Based Semi-Interpenetrating Network Hydrogels for Controlled Release of Ibuprofen.

Different combinations of polymers, aspartic acid (ASP), alginic acid (AL), and monomer acrylic acid (AA) were crosslinked in the presence of an initiator ammonium peroxodisulfate (APS) and cross-linker ethylene glycol dimethacrylate (EGDMA) to develop aspartic acid/alginic acid-co-poly(acrylic acid) (ASP/ALPAA) (semi-interpenetrating polymer network (SIPN)) hydrogels by the free radical polymerization technique for the controlled delivery of ibuprofen (IBP). Various studies such as dynamic swelling studies, drug loading, in vitro drug release and sol−gel analysis were carried out for the hydrogels. Higher swelling was observed at higher pH 7.4 as compared to lower pH 1.2, due to the presence of carboxylic groups of polymers and the monomer. Hence, pH-dependent swelling was exhibited by the developed hydrogels which led to a pH-dependent drug release and vice versa. The structural properties of the hydrogels were assessed by FTIR, PXRD, TGA, DSC, and SEM which confirmed the fabrication and stability of the developed structure. FTIR analysis revealed the reaction of both polymers with the monomer during the polymerization process and confirmed the overlapping of the monomer on the backbone of the both polymers. The disappearance of high intense crystalline peaks and the encapsulation of the drug by the hydrogel network was confirmed by PXRD. TGA and DSC showed that the developed hydrogels were thermally more stable than their basic ingredients. Similarly, the surface morphology of the hydrogels was analyzed by SEM and showed a smooth surface with few pores. Conclusively, ASP/ALPAA hydrogels have the potential to deliver IBP for a long period of time in a controlled way.

Preparation, Characterization, Swelling Potential, and In-Vitro Evaluation of Sodium Poly(Styrene Sulfonate)-Based Hydrogels for Controlled Delivery of Ketorolac Tromethamine.

The objective of the current study work was to fabricate sodium poly(styrene sulfonate-co-poly acrylic acid) (SPSPAA) hydrogels by using a free radical co-polymerization method for controlled delivery of ketorolac tromethamine (KT). Polymer (sodium poly(styrene sulfonate) (SPS) polymerized with monomer acrylic acid (AA) in the presence of initiator ammonium peroxodisulfate (APS) and cross-linker N′,N′-Methylene bisacrylamide (MBA). Different combinations of polymer, cross-linker and monomer, were employed for development of polymeric hydrogels. Various studies such as sol-gel, drug loading, dynamic swelling, and drug release studies were carried out to know the sol and gel portion of SPSPAA, swelling behavior of hydrogels at different pH media (1.2 and 7.4), quantification of drug loaded by fabricated hydrogels, and amount release of KT at pH 1.2 and 7.4. Higher dynamic swelling was found at pH 7.4 compared to pH 1.2, and as a result, greater percent release of drug was perceived at pH 7.4. Thermal stability, crystallinity, confirmation of functional groups and development of a new polymeric system, and surface morphology were evaluated via Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Powder X-ray Diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) respectively. The results showed that the present work could be used as a potential candidate for controlled delivery of KT.

FABRICATION OF NANO CLAY INTERCALATED POLYMERIC MICROBEADS FOR CONTROLLED RELEASE OF CURCUMIN

Objective: The objective of this study was to formulate and evaluate the Curcumin (CUR) encapsulated sodium alginate (SA)/badam gum (BG)/kaolin (KA) microbeads for controlled drug release studies.
 Methods: The fabricated microbeads were characterized by fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (X-RD), and scanning electron microscopy (SEM). Dynamic swelling studies and in vitro release kinetics were performed in simulated intestinal fluid (pH 7.4) and simulated gastric fluid (pH 1.2) at 37 °C.
 Results: FTIR confirms the formation of microbeads. DSC studies confirm the polymorphism of CUR in drug loaded microbeads which indicate the molecular level dispersion of the drug in the microbeads. SEM studies confirmed the microbeads are spherical in shape with wrinkled and rough surfaces. XRD studies reveal the molecular dispersion of CUR and the presence of KA in the developed microbeads. In vitro release studies and swelling studies depend on the pH of test media, which might be suitable for intestinal drug delivery. The % of drug release values fit into the Korsmeyer-Peppas equation and n values are obtained in the range of 0.577-0.664, which indicates that the developed microbeads follow the non-Fickian diffusion drug release mechanism.
 Conclusion: The results concluded that the CUR encapsulated microbeads are potentially good carriers for controlled drug release studies.

Dual responsive GG-g-PNPA/PIPAM based novel hydrogels for the controlled release of anti- cancer agent and their swelling and release kinetics

This study includes the synthesis of amino acid graft copolymer from N- Acryloyl-L-phenylalanine amino acid and Guar gum polymer through free radical polymerization. Then the dual responsive (pH & temperature) hydrogels are synthesized by employing free radical cross linking polymerization using graft copolymer, N-isopropyl acrylamide and 2-(dimethylamine) ethylmethacrylate using N,N′-methylenebisacrylamide as a cross-linker and ammonium per sulfate as initiator. The structural properties of the hydrogels are evaluated by the determination of various network properties such as mesh size, crosslink density, Flory-Huggins interaction parameter, volume fraction in the swollen state and the average molecular weight of the polymer chain between two neighboring cross links. Dynamic and equilibrium swelling studies of hydrogels are performed in distilled water, pH 1.20 and pH 7.40 solutions at 25 °C and 37o ± 5 °C, swelling capacity in various salt solutions and corresponding swelling kinetic parameters are also calculated. Grafting, cross linking and structural changes are studied by fourier transform infrared and scanning electron microscope, distribution of imatinib mesylate drug in hydrogel is confirmed by X-ray diffraction, differential scanning calorimetry, thermo gravimetric analysis. Drug loading and encapsulation efficiency of Imatinib mesylate in various formulations of the hydrogels are also studied. The in-vitro drug release studies are performed in pH 1.20 and 7.40 phosphate buffer solutions at different amounts of cross linker, monomer and graft copolymer and temperature. The mode of drug release mechanism is analyzed by various kinetic models such as zero order, First order, Higuchi Square root, Hixson-Crowell cube root and Koresmeyer-Peppas equations.

Emerging Novel Drug Delivery System for Control Release of Curcumin through Sodium Alginate/Poly(ethylene glycol) Semi IPN Microbeads-Intercalated with Kaolin Nanoclay

The aim of the present work is fabrication of Curcumin encapsulated microbeads from Sodium Alginate/Polyethylene Glycol/Kaolin using glutaraldehyde as crosslinker by simple ionotropic gelation technique. The developed microbeads were characterized by Fourier transform infrared spectroscopy to confirm the formation of microbeads. Differential scanning calorimetry and X-ray diffraction studies have confirmed uniform molecular dispersion of CUR in the microbeads. Encapsulation efficiency of CUR in microbeads was ranged from 40 to 49%. Dynamic swelling studies and in vitro release kinetics were performed in simulated intestinal fluid (pH 7.4) and simulated gastric fluid (pH 1.2) at 37 oC. The results suggest that both swelling studies and cumulative release studies were depend on pH of the test medium, which might be suitable for intestinal drug delivery. The in vitro release data were analysed by using Korsmeyer peppas equation to compute the diffusion exponent (n); the results suggest that it followed non-Fickian diffusion. Keywords: Sodium Alginate, Polyethylene Glycol, Kaolin, Microbeads, Drug delivery

Synthesis and characterization of dual responsive sodium alginate-g-acryloyl phenylalanine-poly N-isopropyl acrylamide smart hydrogels for the controlled release of anticancer drug

The aim of present study is to design the pH and temperature responsive interpenetrating polymer network (IPN) hydrogels for the controlled release of an anticancer drug, imatinib mesylate. In the course of preparation of these hydrogels, first N-Acryloyl-l-phenylalanine grafted sodium alginate copolymer (NaAla-g-PAPA) was synthesized through free radical polymerization using ammonium persulfate as an initiator. The grafting parameters % grafting, % grafting efficiency, % conversion, % yield, % homopolymer and rate of grafting (Rg) of the reaction were calculated comparatively. The optimum grafting conditions were obtained by alteration of the reaction conditions such as the reaction time, temperature, monomer and initiator concentrations. Then novel dual responsive smart hydrogels were prepared from the graft copolymer (NaAlg-g-PAPA), N-isopropylacrylamide (NIPAM), acrylamide (AAm) by cross linking with N,N′-methylenebisacrylamide (NN-MBA) through free radical polymerization reaction. The hydrogels were characterized by fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) techniques. Various network parameters of hydrogels such as volume fraction in the swollen state (ɸ), the average molecular weight of the polymer chain between two neighboring crosslinks (Mc¯), Flory-Huggins interaction parameter (χ), crosslink density (Ve) and mesh size (ξ) were calculated and explained. Dynamic and equilibrium swelling studies of SAPM hydrgels were performed in distilled water, pH 1.2 and pH 7.4 phosphate buffer solutions. Further, in vitro drug release experiments were conducted in pH 1.2 and pH 7.4 buffer solutions at 25 °C and 37 °C ± 5 °C by taking imatinib mesylate as a test drug. The optimum parameters for maximum % of grafting yield (179) are 240 min of reaction time, 60 °C of reaction temperature, 18.26×10−2 mol/dm3 of APA and 17.54×10−2 mol/dm3 of APS. The in-vitro release studies indicated that the maximum % of IBM release (98 %) was achieved in pH 7.4 buffer at 37 °C within 48 hrs. The swelling data and drug release data were fitted into different empirical kinetic models such as zero order, First order, Higuchi Square root, Hixson-Crowell cube root and Koresmeyer-Peppas equations.

Curing of polyfurfuryl alcohol resin catalyzed by a homologous series of dicarboxylic acid catalysts. II. Swelling behavior and thermal properties

ABSTRACTPolyfurfuryl alcohol (PFA), as a bio‐based resin made from lignocellulosic materials, was crosslinked using a homologous series of dicarboxylic acid catalysts consisting of oxalic, succinic, and adipic acids, which are different in their dissociation constants. Swelling behavior, thermal stability, and non‐oxidative char residue of the resulting networks were characterized as a function of the acids strength and their concentration. Swelling of the networks were investigated at room temperature in eight solvents differing in molecular size and solubility parameter. Using acetonitrile as a solvent, the swelling mechanism was explored by applying kinetic models to the swelling data. Dynamic swelling studies during 16–30 days supported non‐Fickian and anomalous diffusion mechanism in highly crosslinked samples supporting PFA chain rigidity and high crosslinking density of the networks. Polymer–solvent interaction parameter, molecular weight between crosslinks and crosslinking densities were also determined. According to the results, the extent of PFA crosslinking and non‐Fickian behavior of the swelling solvent diffusion through the networks are strongly dependent on the concentration and dissociation characteristics of the catalysts used. Thermal stability studies showed no significant differences between the compositions, up to 900 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45770.

Student Award for Outstanding Research Winner in the Undergraduate Category for the 2017 Society for Biomaterials Annual Meeting and Exposition, April 5–8, 2017, Minneapolis, Minnesota: Development and characterization of stimuli‐responsive hydrogel microcarriers for oral protein delivery

A family of pH-responsive terpolymers composed of methacrylic acid (MAA), N-vinyl pyrrolidone (NVP), and poly(ethylene glycol) monomethylether monomethacrylate (PEGMMA) have been developed and evaluated for their pH-responsive swelling behavior, protein-loading capabilities, and cytocompatibility. These terpolymer hydrogels, designated as P((MAA-co-NVP)-g-EG), were synthesized with varying PEG chain lengths and monomer feed ratios. The incorporation of MAA into the terpolymer structure was quantified with potentiometric titration. Equilibrium and dynamic swelling studies confirmed the pH-responsive behavior of the hydrogel, with the system remaining collapsed/complexed in acidic pH conditions and swollen/decomplexed in neutral pH conditions. The ability of the hydrogels to partition protein into the swollen network was assessed for two model proteins of varying molecular weight: insulin and porcine growth hormone. Finally, the cytocompatibility of the hydrogels in the presence of two model intestinal cell lines was investigated and confirmed minimal cytotoxicity at and below 2.5 mg/mL. The developed P((MAA-co-NVP)-g-EG) hydrogels exhibit unique properties that could potentially be utilized for drug delivery and separation applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1243-1251, 2017.

Effect of ethylene glycol dimethacrylate on swelling and on metformin hydrochloride release behavior of chemically crosslinked pH-sensitive acrylic acid-polyvinyl alcohol hydrogel.

BackgroundThe present work objective was to prepare and to observe the effect of ethylene glycol dimethacrylate on swelling and on drug release behavior of pH-sensitive acrylic acid–polyvinyl alcohol hydrogel.MethodsIn the present work, pH sensitive acrylic acid–polyvinyl alcohol hydrogels have been prepared by free radical polymerization technique in the presence of benzoyl peroxide as an initiator. Different crosslinker contents were used to observe its effect on swelling and on drug release. Dynamic and equilibrium swelling studies of prepared hydrogels were investigated in USP phosphate buffer solutions of pH 1.2, 5.5, 6.5 and 7.5 with constant ionic strengths. Hydrogels were evaluated for polymer volume fraction, solvent interaction parameter, molecular weight between crosslinks, number of links per polymer chain, diffusion coefficient, sol–gel fraction and porosity. To demonstrate the release pattern of the drug, zero-order, first-order, higuchi and korsmeyer-peppas models were applied. Quality and consistency of hydrogels was examined by FTIR and surface morphology of hydrogels was examined by SEM.ResultsDecrease in swelling and in drug release was seen by increasing content of ethylene glycol dimethacrylate. A remarkable high swelling was observed at high pH indicating the potential of this hydrogel for delivery of drugs to intestine. By increasing the concentration of ethylene glycol dimethacrylate, porosity decreased. Order of release was observed first order in all cases and the mechanism was non–fickian diffusion. FTIR confirmed the formation of network. SEM results showed the incorporation of drug.ConclusionThe prepared hydrogels can be suitably used for targeted drug delivery to the intestine.

Diffusion coefficient, porosity measurement, dynamic and equilibrium swelling studies of Acrylic acid/Polyvinyl alcohol (AA/PVA) hydrogels

Objective of the present work was to synthesize hydrogels of acrylic acid/polyvinyl alcohol (AA/PVA) by free radical polymerization by using glutaradehyde (GA) as crosslinkers. The hydrogels were evaluated for swelling, diffusion coefficient and network parameters like the average molecular weight between crosslink’s, polymer volume fraction in swollen state, number of repeating units between crosslinks and crosslinking density by using Flory-Huggins theory. It was found that the degree of swelling of AA/PVA hydrogels increases greatly within the pH range 5-7. The gel fraction and porosity increased by increasing the concentration of AA or PVA. Increase in degree of crosslinking, decreased the porosity and inverse was observed in gel fraction. Selected samples were loaded with metoprolol tartrate. Drug release was studied in USP hydrochloric acid solution of pH 1.2 and phosphate buffer solutions of pH 5.5 and 7.5. Various kinetics models like zero order, first order, Higuchi and Peppas model were used for in vitro kinetic studies. The results showed that the drug release followed concentration dependent effect (First order kinetics) with non-Fickian diffusion. FTIR and SEM used to study the structure, crystallinity, compatibility, thermal stability and morphology of prepared and drug loaded hydrogels respectively.

PH and Thermo Sensitive Superabsorbent Poly (N-Hydroxymethylacrylamide-co-Itaconic Acid) Hydrogels: Synthesis, Characterization and Kinetic Studies

In this study, itaconic acid (IA) was co-polymerized with N-hydroxymethylacrylamide (NHMAA) by free radical solution polymerization to prepare pH and thermo sensitive superabsorbent hydrogels. The polymerization process was carried out at 25°C by using ammonium persulfate (APS) and N,N,N’,N’-tetramethylethylenediamine (TMEDA) as initiating system and ethyleneglycoldimethacrylate (EGDMA) as a crosslinking agent. The effects of copolymer composition, crosslinking agent concentration, pH and temperature on swelling capacity and kinetic parameters were investigated. The copolymer hydrogels were characterized by using swelling studies and FT-IR analyses. The equilibrium degree of swelling of hydrogels was found to increase as pH value of the swelling solution varied from 2 to 12 and temperature from 45 to 25°C. The dynamic swelling studies have showed that, the diffusion exponent(n) and the diffusion coefficient(k) both increase with increasing content of itaconic acid.

PH-sensitive superabsorbent polymers: a potential candidate material for self-healing concrete

Superabsorbent polymers (SAPs) have already found their way in many applications. These ‘smart’ polymers undergo major characteristic changes by small environmental variations. In the present work, copolymer networks composed of acrylic acid, acrylamide and N,N′-methylenebisacrylamide have been synthesized using free radical precipitation polymerization. The polymers obtained have been characterized for their chemical structure, moisture (de)sorption and swelling behaviour using, respectively, attenuated total reflectance-infrared spectroscopy, high-resolution magic-angle spinning NMR spectroscopy, dynamic vapour sorption and swelling studies. The results indicated a remarkable moisture uptake capacity at high relative humidities of more than 90 % the original polymer weight with a negligible hysteresis. The latter implies that the SAPs developed are very promising water reservoir candidates, which become useful in concrete-related applications. Furthermore, the swelling data revealed that polymers with a low cross-linking density result in materials with superabsorbent properties. In addition, these SAPs show a pH-dependent swelling behaviour up to 450 times their original weight at pH 12.

Effect of degree of cross-linking on swelling and on drug release of low viscous chitosan/poly(vinyl alcohol) hydrogels

In the present work, a series of cross-linked LVCS/PVA hydrogels with various feed compositions were prepared using glutaraldehyde as cross-linking agent. The prepared hydrogels were used for dynamic and equilibrium swelling studies. The swelling behavior of these hydrogels was investigated as functions of effect of pH, polymeric compositions and degree of cross-linking. Swelling studies were performed in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing PVA contents in the structure of hydrogels in solutions of higher pH values. This is due to the presence of more hydroxyl groups (–OH) in the PVA structure. On the other hand, by increasing LVCS contents, swelling increased in a solution of acidic pH and it is due to ionization of amino groups (–NH2), but this swelling was not significant. Swelling of hydrogels was decreased with increase in cross-linking ratio due to tighter hydrogel structure. Porosity and sol–gel fraction were also investigated. It was found that with increase in LVCS and PVA contents porosity and gel fraction increased, whereas by increasing glutaraldehyde content gel fraction increased and porosity decreased. Diffusion coefficient (D) and network parameters, i.e., the average molecular weight between cross-links (MC), solvent interaction parameters (χ), polymer volume fraction in swollen state (V2S) and cross-linked density (q) were calculated using Flory–Rehner theory. Selected samples were loaded with model drug diphenhydramine HCl. The release of diphenhydramine HCl was studied for 12 h period in 0.05 M USP phosphate buffer solutions of varying pH 1.2, 5.5 and 7.5. It was observed that drug release increased with increasing PVA contents in the hydrogels, while release of drug decreased as the ratio of cross-linking agent increased in the hydrogel structure owing to strong physical entanglements between polymers. The release mechanisms were studied by fitting experimental data to model equations like zero order, first order, Higuchi and Peppas. Results showed that the kinetics of drug release from hydrogels in buffer solutions of pH 1.2, 5.5 and 7.5 was mainly non-fickian diffusion. Hydrogels were characterized by Fourier transform infrared and X-ray diffraction to confirm the structure and study the crystallinity of hydrogel, respectively.

Preparation and characterization of hybrid pH-sensitive hydrogels of chitosan-co-acrylic acid for controlled release of verapamil

In the present work crosslinked hydrogels based on chitosan (CS) and acrylic acid (AA) were prepared by free radical polymerization with various feed compositions using N,N methylenebisacrylamide (MBA) as crosslinking agent. Benzoyl peroxide was used as catalyst. Fourier transform infrared spectra (FTIR) confirmed the formation of the crosslinked hydrogels. This hydrogel is formed due to electrostatic interaction between cationic groups in CS and anionic groups in AA. Prepared hydrogels were used for dynamic and equilibrium swelling studies. For swelling behavior, effect of pH, polymeric and monomeric compositions and degree of crosslinking were investigated. Swelling studies were performed in USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing AA contents in structure of hydrogels in solutions of higher pH values. This is due to the presence of more carboxylic groups available for ionization. On the other hand by increasing the chitosan content swelling increased in a solution of acidic pH, but this swelling was not significant and it is due to ionization of amine groups present in the structure of hydrogel. Swelling decreased with increase in crosslinking ratio owing to tighter hydrogel structure. Porosity and sol-gel fraction were also measured. With increase in CS and AA contents porosity and gel fraction increased, whereas by increasing MBA content porosity decreased and gel fraction increased. Furthermore, diffusion coefficient (D) and the network parameters i.e., the average molecular weight between crosslinks (M(c)), polymer volume fraction in swollen state (V(2s)), number of repeating units between crosslinks (M(r)) and crosslinking density (q) were calculated using Flory-Rehner theory. Selected samples were loaded with a model drug verapamil. Release of verapamil depends on the ratios of CS/AA, degree of crosslinking and pH of the medium. The release mechanisms were studied by fitting experimental data to model equations and calculating the corresponding parameters. The result showed that the kinetics of drug release from the hydrogels in both pH 1.2 and 7.5 buffer solutions was mainly non-Fickian diffusion.

Biodegradable nano-micro carrier systems for sustained pulmonary drug delivery: (I) Self-assembled nanoparticles encapsulated in respirable/swellable semi-IPN microspheres

Design of appropriate inhaled carriers with adequate aerodynamic properties, drug release, biodegradation and evasion of macrophage uptake is a major challenge for controlled release pulmonary drug delivery. In this study, PEG graft copolymerized onto N-phthaloyl chitosan (NPHCs) was synthesized then characterized using FTIR, EA, DSC and 2D-XRD. The resulting PEG-g-NPHCs copolymers were self-assembled into drug-loaded nanoparticles and encapsulated in respirable/swellable sodium alginate semi-IPN hydrogel microspheres as novel biodegradable carriers for controlled release pulmonary drug delivery. The developed nano-/microspheres carrier systems were formed via spray drying followed by ionotropic crosslinking in mild aqueous medium. The size of the developed self-assembled nanoparticles and the microspheres was measured using dynamic light scattering and laser diffraction, respectively. Morphology, moisture content, in vitro biodegradation and dynamic swelling studies were also investigated for the developed carriers. A model protein was entrapped and the in vitro release profiles were determined in PBS, pH 7.4 at 37 °C. A dry powder aerosolization study was conducted using a Next Generation Impactor (NGI). The developed microspheres had suitable aerodynamic diameters (1.02–2.63 μm) and an excellent fine particle fraction, FPF of 31.52%. The microspheres showed also a very fast initial swelling within the first 2 min and started to enzymatically degrade within the first 2 h. Moreover, the microspheres entrapped up 90% of the model drug and showed promising in vitro sustained release profiles as compared to the control formulation.