Synthesis of a novel superabsorbent hydrogel by copolymerization of acrylamide and cashew gum modified with glycidyl methacrylate

Novel superabsorbent hydrogels were manufactured using chemically modified cashew gum (CGMA) and acrylamide (AAm) as reactants. The route for the synthesis was feasible due to the incorporation of glycidyl methacrylate (GMA) into structure of cashew gum (CG) to form the cashew gum-methacrylated (CGMA), in an appropriate mixture water-DMSO, as solvent, and using TEMED as catalyst. Thereafter, the CGMA was copolymerized with AAm yielding (CGMA-co-AAm) hydrogels. The main characteristics of raw and the modified materials are reported in this paper. ¹³C NMR, ¹H NMR and FTIR spectroscopies confirmed the incorporation of vinyl groups, from GMA, into CG structure. By the spectrophotometry analyses, it was found that, ca. 82% of GMA was incorporated to the CG after 24 h of reaction. The cross-linking of CGMA or co-polymerization of CGMA with acrylamide leads to a hydrogel formation. Their gelation was characterized by FT-IR analysis. Alkaline hydrolysis at 40 °C for 3 and 4.5 h increased the water uptake (WU) capacity. Hydrolyzed CGMA-co-AAm hydrogels present higher values of WU (up to 1500) and may be classified as water superabsorbent material. Applications in agriculture, as soil conditioner, and in biomedical field, as biomaterial (scaffold) are being investigated.     

Photopolymerization of methacrylated chitosan/PNIPAAm hybrid dual-sensitive hydrogels as carrier for drug delivery

A series of hybrid hydrogels based on glycidyl methacrylated chitosan (CS-GMA) and N-isopropylacrylamide (NIPAAm) were designed and prepared via photopolymerization technology. The hydrogels were characterized by Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC) and optical transmittance. The interior morphology of hydrogels was investigated by scanning electron microscopy (SEM). The swelling experiment results revealed that hybrid hydrogel exhibited combined pH and temperature sensitivities. Acid orange 8 (AO8) and 5-flurouracil (5-Fu) were selected as model drugs for examining their release from hydrogels. The results suggested that hydrogel composition and pH value of buffer solution had great influences on release profiles.     

Immobilization of porcine pancreatic lipase on glycidyl methacrylate grafted poly vinyl alcohol

Graft copolymerization of glycidyl methacrylate (GMA) on to polyvinyl alcohol (PVA) using benzophenone (BP) as initiator was carried out. Grafted PVA was used as carrier for pancreatic lipase immobilization. The effects of GMA and BP concentrations as well as grafting reaction times on grafting yields and activities of the immobilized lipase were determined. The influence of enzyme concentrations was also studied. The optimal conditions for the grafting reaction were: 1 h at 15 mM BP and 2.3 M GMA, the optimum enzyme concentration for immobilization was 1 mg/ml. After optimization of the immobilization process a physical and chemical characterization of the immobilized enzyme was performed. Furthermore, the thermal, pH, storage and operational stability of the immobilized enzyme in comparison to the free form was tested.     

Interpenetrating biopolymer network based hydrogels for an effective drug delivery system

Discovery of hydrogels has resulted in developing competent controlled-release drug delivery systems. Present study describes the synthesis and characterization of novel pH responsive hydrogels of chitosan, hydroxyl ethyl cellulose (HEC) and polyol prepared by physical blending of the three components in different ratios. Vegetable oil derived polyol seems to act as a filler and cross linking agent. The synthesized hydrogels were characterized using FT-IR spectroscopy, thermo gravimetric analysis (TGA), Optical microscopy and scanning electron microscopy (SEM). Equilibrium swelling behavior of hydrogels in water and different buffers with pH values (2, 4, 7.3, and 8) indicated the sustained expansion of the films in different pH solutions.     

Extraction of rifamycin B from native and aqueous solutions]

Optimal conditions for extraction of rifamycin B from aqueous solutions and fermentation broth filtrates at pH values within 2.0-7.0 were determined. When the antibiotic was extracted from the aqueous solutions, the highest yield was obtained at pH 2.0. When the antibiotic was extracted from the fermentation broth filtrates, it was found that chloroform was the most selective solvent with respect to rifamycin B, the chloroform selectivity being increased at pH 3.5-4.0. It was shown that rifamicin B passed from the buffer solutions with a concentration of 3-20 mg/ml to chloroform in amounts of 6-7 mg/ml and to ethylacetate and butanol in amounts of 20 mg/ml. Such conditions of chloroform and butanol (9 : 1) increased the rifamycin B contents in the extract up to 40 mg/ml.     

Synthesis and characterization of hydrogels based on grafted chitosan for the controlled drug release

Temperature and pH-responsive hydrogels based on chitosan grafted with poly acrylic acid (PAAc), poly hydroxy propyl methacrylate (PHPMA), poly (vinyl alcohol) (PVA) and gelatin were prepared for controlled drug delivery. These stimuli-responsive hydrogels were synthesized by gamma irradiation technique. The degree of gelation was over 90% and increased as chitosan, AAc and PVA content increased, while the degree of gelation decrease with the increase of gelatin content. The equilibrium swelling studies of hydrogels prepared in various conditions were carried out in an aqueous solution, and the pH sensitivity in the range of 2–9 was investigated. An increase of swelling degree with an increase in the pH was noticed and showed the highest value at pH 9. Also antibiotic drug Oxttetracycline was loaded into the hydrogels and the release studies were carried out at different pH and temperature. The in vitro release profiles of the drug showed that, the release of the drug increased as the time, temperature and pH increased and reached to maximum after 48 h at pH 9. The prepared hydrogels were characterized by using SEM, FTIR, and DSC.     

One-step synthesis of interpenetrating network hydrogels: Environment sensitivities and drug delivery properties

A novel interpenetrating network hydrogel for drug controlled release, composed of modified poly(aspartic acid) (KPAsp) and carboxymethyl chitosan (CMCTS), was prepared in aqueous system. The surface morphology and composition of hydrogels were characterized by SEM and FTIR. The swelling properties of KPAsp, KPAsp/CMCTS semi-IPN and KPAsp/CMCTS IPN hydrogels were investigated and the swelling dynamics of the hydrogels was analyzed based on the Fickian equation. The pH, temperature and salt sensitivities of hydrogels were further studied, and the prepared hydrogels showed extremely sensitive properties to pH, temperature, the ionic salts kinds and concentration. The results of controlled drug release behaviors of the hydrogels revealed that the introduction of IPN observably improved the drug release properties of hydrogels, the release rate of drug from hydrogels can be controlled by the structure of the hydrogels and pH value of the external environment, a relative large amount of drug released was preferred under simulated intestinal fluid. These results illustrated high potential of the KPAsp/CMCTS IPN hydrogels for application as drug carriers.     

Synthesis of chitosan networks: Swelling, drug release, and magnetically assisted BSA separation using Fe(3)O(4) nanoparticles

Chitosan (CS) nanohydrogel networks were prepared by reaction with glyceroldiglycidylether (GDE) and poly(dimethylsiloxane) (PDMS), as crosslinking agents in an emulsion system. The nanogel content increased with increasing the amount of crosslinkers and reached to a maximum of 90% with GDE. The nanogels structure was characterized by FT-IR, AFM, DSC, and TGA. The average size for CS-GDE and CS-PDMS particles were 59nm and 180nm, respectively. The swelling behavior of nanohydrogels was observed to be dependent on pH, temperature, degree of crosslinking, and on the chemical structure of crosslinker. The equilibrium water content of CS-GDE nanohydrogels reached to a maximum of 600% at neutral pH, and decreased at high and low pH and low temperature. These nanohydrogels were tested for sodium diclofenac (SDF) loading and releasing efficiency. The covalent conjugation of bovine serum albumin (BSA) and magnetic Fe(3)O(4) nanoparticles on the hydrogels were found to hold a potential application in magnetically assisted bioseparation.     

The swelling behavior and network parameters of guar gum/poly(acrylic acid) semi-interpenetrating polymer network hydrogels

Guar gum/poly(acrylic acid) semi-interpenetrating polymer network (IPN) hydrogels have been prepared via free radical polymerization in the presence of a crosslinker of N,N′-methylene bisacrylamide (MBA). The kinetics of swelling and the water transport mechanism were studied as a function of the composition of the hydrogels and the pH of the swelling medium. Hydrogels showed enormous swelling in aqueous medium and displayed swelling characteristics, which were highly dependent on the chemical composition of the hydrogels and pH of the medium in which hydrogels were immersed (ionic strength I = 0.15 mol/L). The semi-INP hydrogels were characterized by evaluating various network parameters such as average molecular weight between crosslinks (M_c) crosslink density (ρ) and mesh size ξ.     

Some chemical and physical properties of nisin, a small-protein antibiotic produced by Lactococcus lactis

Nisin is a small gene-encoded antimicrobial protein produced by Lactococcus lactis that contains unusual dehydroalanine and dehydrobutyrine residues. The reactivity of these residues toward nucleophiles was explored by reacting nisin with a variety of mercaptans. The kinetics of reaction with 2-mercaptoethane-sulfonate and thioglycolate indicated that the reaction pathway includes a binding step. Reaction of nisin at high pH resulted in the formation of multimeric products, apparently as a result of intramolecular and intermolecular reactions between nucleophilic groups and the dehydro residues. One of the nucleophiles had a pKa of about 9.8. The unique vinyl protons of the dehydro residues that give readily identifiable proton nuclear magnetic resonances were used to observe the addition of nucleophiles to the dehydro moiety. After reaction with nucleophiles, nisin lost its antibiotic activity and no longer showed the dehydro resonances, indicating that the dehydro groups had been modified. The effect of pH on the solubility of nisin was determined; the solubility was quite high at low pH (57 mg/ml at pH 2) and was much lower at high pH (0.25 mg/ml at pH 8 to 12), as measured before significant pH-induced chemical modification had occurred. High-performance liquid chromatography on a C18 column was an effective technique for separating unmodified nisin from its reaction products. The cyanogen bromide cleavage products of nisin were about 90% less active toward inhibition of bacterial spore outgrowth than was native nisin. These results are consistent with earlier observations, which suggested that the dehydro residues of nisin have a role in the mechanism of antibiotic action, in which they act as electrophilic Michael acceptors toward nucleophiles in the cellular target.     

Some chemical and physical properties of nisin, a small-protein antibiotic produced by Lactococcus lactis.

Nisin is a small gene-encoded antimicrobial protein produced by Lactococcus lactis that contains unusual dehydroalanine and dehydrobutyrine residues. The reactivity of these residues toward nucleophiles was explored by reacting nisin with a variety of mercaptans. The kinetics of reaction with 2-mercaptoethane-sulfonate and thioglycolate indicated that the reaction pathway includes a binding step. Reaction of nisin at high pH resulted in the formation of multimeric products, apparently as a result of intramolecular and intermolecular reactions between nucleophilic groups and the dehydro residues. One of the nucleophiles had a pKa of about 9.8. The unique vinyl protons of the dehydro residues that give readily identifiable proton nuclear magnetic resonances were used to observe the addition of nucleophiles to the dehydro moiety. After reaction with nucleophiles, nisin lost its antibiotic activity and no longer showed the dehydro resonances, indicating that the dehydro groups had been modified. The effect of pH on the solubility of nisin was determined; the solubility was quite high at low pH (57 mg/ml at pH 2) and was much lower at high pH (0.25 mg/ml at pH 8 to 12), as measured before significant pH-induced chemical modification had occurred. High-performance liquid chromatography on a C18 column was an effective technique for separating unmodified nisin from its reaction products. The cyanogen bromide cleavage products of nisin were about 90% less active toward inhibition of bacterial spore outgrowth than was native nisin. These results are consistent with earlier observations, which suggested that the dehydro residues of nisin have a role in the mechanism of antibiotic action, in which they act as electrophilic Michael acceptors toward nucleophiles in the cellular target.     

Rapid cross-linking of elastin-like polypeptides with (hydroxymethyl)phosphines in aqueous solution

In situ gelation of injectable polypeptide-based materials is attractive for minimally invasive in vivo implantation of biomaterials and tissue engineering scaffolds. We demonstrate that chemically cross-linked elastin-like polypeptide (ELP) hydrogels can be rapidly formed in aqueous solution by reacting lysine-containing ELPs with an organophosphorous cross-linker, beta-[tris(hydroxymethyl)phosphino]propionic acid (THPP) under physiological conditions. The mechanical properties of the cross-linked ELP hydrogels were largely modulated by the molar concentration of lysine residues in the ELP and the pH at which the cross-linking reaction was carried out. Fibroblasts embedded in ELP hydrogels survived the cross-linking process and were viable after in vitro culture for 3 days. DNA quantification of ELP hydrogels with encapsulated fibroblasts indicated that there was no significant difference in DNA content between day 0 and day 3 when ELP hydrogels were formed with an equimolar ratio of THPP and lysine residues of the ELPs. These results suggest that THPP cross-linking may be a biocompatible strategy for the in situ formation of cross-linked hydrogels.     

Synthesis and properties of chitosan hydrogels modified with heterocycles

Preparation and properties of chitosan modified with heterocycles in absence or presence of gluteraldehyde as a cross linker is described. New modified chitosan–heterocyclic hydrogels were prepared from chitosan and heterocyclic compounds such as N,N′-biisomaleimide, N,N′-biisophthalimide, and N,N′-phthalimidomaleimide via a crosslinking reaction. The new hydrogels chemical structure was characterized by spectral analysis (IR), X-ray diffraction, thermal gravimetric analysis (TGA), solubility, and swellability in water and different organic solvents. Evaluation of the efficiency of the new hydrogels to uptake copper and cobalt ions from aqueous systems was carried out and promising results were obtained.     

Entrapment and in vitro release of delta-sleep inducing peptide from polymer hydrogels based on modified polyvinyl alcohol

The aim of this study was to entrap delta-sleep inducing peptide (DSIP) in cross-linked poly(vinyl alcohol)-based hydrogels of different structures and to determine kinetics of the peptide release from these hydrogels using an in vitro model. Isotropic and macroporous hydrogels based on poly(vinyl alcohol) acrylic derivative (Acr-PVA) and also macroporous epoxy groups containing hydrogels synthesized by copolymerization of this macromer and glycidyl methacrylate, have been used in this study. Isotropic hydrogels were prepared at positive temperatures while macroporous ones were obtained by formation in cryo-conditions. The peptide was entrapped into macroporous PVA hydrogels by adding the peptide solution onto preformed matrices, while peptide immobilization on PVA-GMA hydrogels, containing free epoxy groups, was carried out by sorption of peptide from its aqueous solution. In the case of DSIP entrapment into isotropic PVA gel the peptide solution was added into the polymer mixture at hydrogel formation. The kinetics of peptide release from hydrogels was studied by incubating matrices in PBS solution (pH 7.4), in physiological solution (0.9% NaCl) and in water. DSIP concentration in supernatants was determined by reverse-phase HPLC. Incubation of macroporous PVA gels in PBS, 0.9% NaCl, and water for 30 min caused release of 74, 70, and 64% DSIP, respectively, and this processes completed within 3 h. From hydrogel containing epoxy groups the release of neither peptide nor its degradation products was observed even after incubation for 48 h. For freshly prepared isotropic hydrogel the release kinetics was as follows: 27 and 78% DSIP were released within first 30 min and 33 h, relatively. For the lyophilized hydrogel samples the peptide release was 63% after incubation for 30 min, while drying of samples at room temperature for 3 days caused significant peptide loss because of its structure damage.     

Facile synthesis of degradable and electrically conductive polysaccharide hydrogels

Degradable and electrically conductive polysaccharide hydrogels (DECPHs) have been synthesized by functionalizing polysaccharide with conductive aniline oligomers. DECPHs based on chitosan (CS), aniline tetramer (AT), and glutaraldehyde were obtained by a facile one-pot reaction by using the amine group of CS and AT under mild conditions, which avoids the multistep reactions and tedious purification involved in the synthesis of degradable conductive hydrogels in our previous work. Interestingly, these one-pot hydrogels possess good film-forming properties, electrical conductivity, and a pH-sensitive swelling behavior. The chemical structure and morphology before and after swelling of the hydrogels were verified by FT-IR, NMR, and SEM. The conductivity of the hydrogels was tuned by adjusting the content of AT. The swelling ratio of the hydrogels was altered by the content of tetraaniline and cross-linker. The hydrogels underwent slow degradation in a buffer solution. The hydrogels obtained by this facile approach provide new possibilities in biomedical applications, for example, biodegradable conductive hydrogels, films, and scaffolds for cardiovascular tissue engineering and controlled drug delivery.     

Development and validation of a new reversed-phase ion pairing liquid chromatographic method with fluorescence detection for penciclovir analysis in plasma and aqueous humor

A simple, sensitive and reliable HPLC ion-pairing method with fluorescence detection, was developed for penciclovir determination in plasma and aqueous humor, with a Zorbax SB-aq C18 (100 mmx2.1 mm) column. Plasma samples were treated by solid-phase extraction with Oasis MCX (30 mg) cartridges. Ganciclovir, an antiviral drug structurally related to penciclovir, was used as internal standard (I.S.). Aqueous humor samples were directly injected into the chromatographic system. Separation was performed by a gradient elution with a mobile phase consisting of a mixture of acetonitrile and phosphate buffer 50mM containing 5mM of sodium octanesulfonate, pH 2.0, at a flow rate of 0.3 ml/min. The method was validated and showed good performances in terms of linearity, sensitivity, precision and trueness. Quantification limit was obtained at 0.05 microg/ml for aqueous humor and at 0.1 microg/ml for plasma. Finally, the proposed analytical method was used to measure penciclovir in clinical samples for a pharmacokinetic study, after oral administration of famciclovir.     

Reductive alkylation of hyaluronic acid for the synthesis of biocompatible hydrogels by click chemistry

Hyaluronan (HA) based hydrogels have been synthesized combining chemical modification of the polysaccharide by partial oxidation, reductive amination and 'click chemistry'. HA was oxidized by 4-acetamido-TEMPO-mediated reaction, using sodium hypochlorite as primary oxidant and NaBr in buffered pH, so that the produced aldehyde moieties (hemiacetals) were trapped in situ by adding primary amines containing azide or alkyne-terminal groups. The structure of the reaction products, oxidized-HA and primary amines bonded to HA, was elucidated using 2D NMR spectroscopy. SEC-MALLS analysis of the modified substrates showed a negligible degradation of the polysaccharide using this procedure. Furthermore, azido- and alkynyl derivatives underwent cross-linking by click chemistry into hydrogels, which were characterized by NMR, FT-IR, swelling degree and mechanical properties. Possible application of the material as scaffold for tissue engineering was tested by seeding and proliferation of chondrocytes for up to 15 days.     

Cloning and overexpression of a Paenibacillus beta-glucanase in Pichia pastoris: purification and characterization of the recombinant enzyme

Isolation, expression, and characterization of a novel endo-beta-1,3(4)-D-glucanase with high specific activity and homology to Bacillus lichenases is described. One clone was screened from a genomic library of Paenibacillus sp. F-40, using lichenan-containing plates. The nucleotide sequence of the clone contains an ORF consisting of 717 nucleotides, encoding a beta-glucanase protein of 238 amino acids and 26 residues of a putative signal peptide at its N-terminus. The amino acid sequence showed the highest similarity of 87% to other beta-1,3-1,4-glucanases of Bacillus. The gene fragment Bg1 containing the mature glucanase protein was expressed in Pichia pastoris at high expression level in a 3-1 high-cell-density fermenter. The purified recombinant enzyme Bgl showed activity against barley beta-glucan, lichenan, and laminarin. The gene encodes an endo-beta-1,3(4)-D-glucanase (E. C. 3.2.1.6). When lichenan was used as substrate, the optimal pH was 6.5, and the optimal temperature was 60 degrees C. The K(m), V(max), and k(cat) values for lichenan are 2.96 mg/ml, 6,951 micromol/min x mg, and 3,131 s(-1), respectively. For barley beta-glucan the values are 3.73 mg/ml, 8,939 micromol/min x mg, and 4,026 s(-1), respectively. The recombinant Bg1 had resistance to pepsin and trypsin. Other features of recombinant Bg1 including temperature and pH stability, and sensitivity to some metal ions and chemical reagents were also characterized.     

The interaction of glutaraldehyde with poly(α,L-lysine), n-butylamine,and collagen. II. Hydrodynamic,electron microscopic,and optical investigations on the reaction products

Interactions of glutaraldehyde with either n-butylamine, poly(α,L -lysine), or collagen resulted in a fast release of protons in dilute aqueous solutions at various pH values, followed by much slower changes. The latter reactions, which extended over hours and days, were followed spectrophotometrically and revealed the formation of distinct absorption bands in the visible and near-ultraviolet regions in all the above systems. The visible-range bands disappeared upon treatment with sodium borohydride. A qualitative relationship between oxygen uptake by the system n-butylamine–glutaraldehyde and the slow formation of colored products has been established, while the chemical nature of the reaction products has not been determined. Sedimentation velocity, viscosity, and optical rotation measurements on the products of interaction between poly(L -lysine) and glutaraldehyde in aqueous solution indicated large conformational changes in the polyamino acid present in excess (in residues) over the dialdehyde. In particular, the intrinsic viscosity dropped considerably after interaction, indicating intramolecular crosslinking. At molar ratios of 1:1 between polylsine residues and aldehyde groups, intermolecular crosslinking of polylysine was obtained at pH 8.6. Electron microscopic examinations of collagen samples treated by glutaraldehyde at various pH values indicated changes from unordered to more ordered structures upon treatment with glutaraldehyde, in particular at pH 10. The present structural and optical investigations are considered to be relevant to tanning processes of hides and to fixation procedures.     

Novel method using a temperature-sensitive polymer (methylcellulose) to thermally gel aqueous alginate as a pH-sensitive hydrogel

A novel method using a temperature-sensitive polymer (methylcellulose) to thermally gel aqueous alginate blended with distinct salts (CaCl2, Na2HPO4, or NaCl), as a pH-sensitive hydrogel was developed for protein drug delivery. It was noted that the salts blended in hydrogels may affect the structures of an entangled network of methylcellulose and alginate and have an effect on their swelling characteristics. The methylcellulose/alginate hydrogel blended with 0.7 M NaCl (with a gelation temperature of 32 degrees C) demonstrated excellent pH sensitivity and was selected for the study of release profiles of a model protein drug (bovine serum albumin, BSA). In the preparation of drug-loaded hydrogels, BSA was well-mixed to the dissolved aqueous methylcellulose/alginate blended with salts at 4 degrees C and then gelled by elevating the temperature to 37 degrees C. This drug-loading procedure in aqueous environment at low temperature may minimize degradation of the protein drug while achieving a high loading efficiency (95-98%). The amount of BSA released from test hydrogels was a function of the amount of alginate used in the hydrogels. The amount of BSA released at pH 1.2 from the test hydrogel with 2.5% alginate was relatively low (20%), while that released at pH 7.4 increased significantly (86%). In conclusion, the methylcellulose/alginate hydrogel blended with NaCl could be a suitable carrier for site-specific protein drug delivery in the intestine.