Agar Hydrogel Research Articles

Aqueous block copolymer–surfactant mixtures—Surface tension, DLS and viscosity measurements and their utility in solubilization of hydrophobic drug and its controlled release

The effects of sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium bromide (DTAB) and polyoxyethylene (10) isooctyl phenyl ether (TX-100) as additives on the association characteristics of an amphiphilic tri-block copolymer P105 (E 37P 56E 37) were monitored by surface tension, dynamic light scattering and viscosity measurements at 303.15 and 313.15 K in water as well as in 200 mM sodium chloride aqueous solutions. The successive addition of surfactants resulted not only in the increase of critical micelle concentration (CMC) of the copolymer and also in CMC/ C 20 values indicating that the adsorption tendency of the copolymer–surfactant complexes at water/air interface is more than the association in the bulk. The experimental CMC data of binary mixtures were analyzed using regular solution theory to calculate the interaction parameter. The mixtures exhibited synergistic interaction behavior. The apparent hydrodynamic radius of copolymer micelles decreased drastically by the addition of surfactants and this destabilization effect has been attributed to the shift of copolymer micelle ↔ unimer equilibrium in favor of latter. Dexamethasone, a drug poorly soluble in aqueous media was solubilized into individual copolymer or copolymer–surfactants solutions followed by their loading onto agar agar hydrogels for its immobilization and dispersion. The drug release profiles were established and drug diffusion coefficients were calculated.

Synergistic performance of cyclodextrin–agar hydrogels for ciprofloxacin delivery and antimicrobial effect

Combination of cyclodextrins (CDs) and agar may render hydrogels that interact with drugs by forming inclusion complexes and/or ionic bonds. Hydroxypropyl-β-cyclodextrin and methyl-β-cyclodextrin (20%) in alkaline solutions containing or not agar (up to 1.5%) were cross-linked with ethyleneglycol diglycidylether at 50°C. Agar increases hardness, compressibility and modulus of deformability, but does not interfere in the loading and release of a probe (3-methyl benzoic acid) with high affinity for CD. Agar notably promoted the loading of the zwitterion ciprofloxacin and endowed the hydrogels with ability to retain the drug in water medium. The release can be triggered by ions or changes in pH, leading to a 12-h sustained delivery. Loading and release profiles were compared to those of maltodextrin-based hydrogels, and the contribution of CDs and agar elucidated. Microbiological tests with Gram-negative and Gram-positive bacteria confirmed the suitability of the “green” CD–agar hydrogels for the development of drug delivery systems with tunable physical and drug loading/release properties.

Agar hydrogel with silver nanoparticles to prolong the shelf life of Fior di Latte cheese

The objective of this work was to evaluate the effectiveness of an antimicrobial packaging system containing active nanoparticles on the quality deterioration of Fior di Latte cheese. To this aim, 3 concentrations of silver montmorillonite embedded in agar were used. The cell loads of spoilage and useful microorganisms were monitored during a refrigerated storage period. Moreover, cheese sensory quality (i.e., odor, color, consistency, and overall quality) was evaluated by means of a panel test. Results showed that the active packaging system markedly increased the shelf life of Fior di Latte cheese, due to the ability of silver cations to control microbial proliferation, without affecting the functional dairy microbiota and the sensory characteristics of the product. The active packaging system developed in this work could be used to prolong the shelf life of Fior di Latte and boost its distribution beyond local market borders.

Chitin Nanowhiskers Mediate Transformation of Escherichia coli by Exogenous Plasmid DNA

A colloidal solution of chitin nanowhiskers containing pUC18 plasmid DNA and cells of Escherichia coli was placed on an agar hydrogel and stimulated by sliding friction applied between the agar hydrogel and polystyrene stir stick, leading to transformation of the bacteria to antibiotic resistance. The combination of chitin nanowhiskers and sliding friction was necessary for genetic transformation, indicating that the chitin nanowhiskers induced the Yoshida effect, resulting in the formation of E. coli cells penetration-intermediates. The pUC18 adsorbed onto the chitin nanowhiskers is presumably taken up through the penetration-intermediates, leading to transformation. The transformation efficiency changed when the number of recipient cells and amount of chitin nanowhiskers were varied. The maximum number of penetration-intermediates acquiring pUC18 DNA was obtained with concentrations of agar hydrogel, chitin nanowhiskers, and recipient E. coli cells of 2.5%, 5.0 ?g/ml, and 4.8 x 108 cells/ml, respectively. Optimal transformation efficiency with pUC18 was achieved with 2.1 x 1066 colony forming units/?g of pUC18. Induction of the Yoshida effect with chitin nanowhiskers represents a simpler alternative for introducing genes into bacteria.

Spray-freeze-drying of nanosuspensions: the manufacture of insulin particles for needle-free ballistic powder delivery

The feasibility of preparing microparticles with high insulin loading suitable for needle-free ballistic drug delivery by spray-freeze-drying (SFD) was examined in this study. The aim was to manufacture dense, robust particles with a diameter of around 50 microm, a narrow size distribution and a high content of insulin. Atomization using ultrasound atomizers showed improved handling of small liquid quantities as well as narrower droplet size distributions over conventional two-fluid nozzle atomization. Insulin nanoparticles were produced by SFD from solutions with a low solid content (<10 mg ml(-1)) and subsequent ultra-turrax homogenization. To prepare particles for needle-free ballistic injection, the insulin nanoparticles were suspended in matrix formulations with a high excipient content (>300 mg ml(-1)) consisting of trehalose, mannitol, dextran (10 kDa) and dextran (150 kDa) (abbreviated to TMDD) in order to maximize particle robustness and density after SFD. With the increase in insulin content, the viscosity of the nanosuspensions increased. Liquid atomization was possible up to a maximum of 250 mg of nano-insulin suspended in a 1.0 g matrix. However, if a narrow size distribution with a good correlation between theoretical and measurable insulin content was desired, no more than 150 mg nano-insulin could be suspended per gram of matrix formulation. Particles were examined by laser light diffraction, scanning electron microscopy and tap density testing. Insulin stability was assessed using size exclusion chromatography (SEC), reverse phase chromatography and Fourier transform infrared (FTIR) spectroscopy. Densification of the particles could be achieved during primary drying if the product temperature (T(prod)) exceeded the glass transition temperature of the freeze concentrate (T(g)') of -29.4 degrees C for TMDD (3331) formulations. Particles showed a collapsed and wrinkled morphology owing to viscous flow of the freeze concentrate. With increasing insulin loading, the d (v, 0.5) of the SFD powders increased and particle size distributions got wider. Insulin showed a good stability during the particle formation process with a maximum decrease in insulin monomer of only 0.123 per cent after SFD. In accordance with the SEC data, FTIR analysis showed only a small increase in the intermolecular beta-sheet of 0.4 per cent after SFD. The good physical stability of the polydisperse particles made them suitable for ballistic injection into tissue-mimicking agar hydrogels, showing a mean penetration depth of 251.3 +/- 114.7 microm.

High-concentration compact agar gels from hydrothermal synthesis

A simple hydrothermal method has been used to prepare for the first time high-concentration, microstructurally compact agar hydrogels (3–30 g agar per 100 ml H2O). These gels reach concentrations unachievable by conventional methods and overcome problems normally associated to them. They feature superior homogeneity, modified and controllable porosity, increased densities and higher strength, thus widening possible applications of this widely used biocompatible polysaccharide.

Syneresis in agar hydrogels

Agar hydrogels exhibit syneresis which creates internal osmotic stress on the physical network. It was observed that such a stress gives rise to characteristic pulsating modes (breathing modes). Experiments carried over a period of 60-day revealed that the network deformations grew monotonously when the solvent released by syneresis was removed periodically from gel surface. However, when the solvent was not withdrawn, the gel exhibited very slowly relaxing breathing modes. The swelling–deswelling dynamics has been discussed in the generalized framework of a dissipative damped oscillator.

Fabrication of PMMA microfluidic chips using disposable agar hydrogel templates

A novel method based on disposable agar hydrogel temples have been developed for the fabrication of PMMA microfluidic chips. Molten agar hydrogel was sandwiched between a glass plate and a PMMA template bearing negative relief of microstructure. After cooling, the negative PMMA template could be easily separated from the solidified agar hydrogel and a layer of agar hydrogel temple bearing high-fidelity positive relief of the microstructure was left on the glass plate. Prepolymerized methyl methacrylate molding solution containing ultraviolet-initiator was subsequently sandwiched between the agar hydrogel template and a PMMA plate and was allowed to polymerize under ultraviolet light to fabricate the PMMA channel plate at room temperature. Complete microchips could be obtained by bonding the channel plates with covers. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of several ions in connection with contactless conductivity detection.

Hierarchical structures in agar hydrogels

Small angle neutron scattering experiments were performed on agar solutions and gels to explore their differential microscopic structures. In solution state, the wave vector, q, dependence of static structure factor, I(q), could be described by I(q)=Igexp(−q2Rg2/3)+IRq−α. Statistical analysis gave: Rg=18nm and α=0.85±0.07 indicating the existence of rod-like rigid structures of length, L=12Rg≈63nm. In gels, I(q)=IGexp(−q2Ξ2)+IFq−β+(IP/q)exp(−q2Rc2/2) which had discernible Gaussian, power-law and Kratky–Porod regimes in the low, intermediate and high-q regions. Regression analysis yielded a characteristic length, Ξ=3.3−4nm for gels with agar concentration, c=0.1−0.3% (w/v). The exponent β=1.2±0.2 and the cross-sectional radius of cylindrical fibres, Rc=1.5±0.3nm remained invariant of agar concentration. This assigned a value 5nm to the persistence length of the fibres in the solution phase that reduced to 3nm in the gel phase indicating differential hydration of the fibres.

High throughput methods to characterize protein permeation and release

Spectroscopic methods have been developed to study protein permeation and release kinetics in multi-well plates. The permeation of bovine serum albumin (BSA) through a membrane, which separated a 96-well plate in two compartments, was characterized. A change in fluorescence intensity was measured corresponding to the permeation of BSA from one compartment to another. The permeation of BSA was influenced by the pore size and pore density size of the membrane. The multi-well plates were also used to study the release of a protein drug, hirudin, from an agar hydrogel. A hirudin formulation was mixed at 60 °C with liquid agar and the mixture turned to a gel by cooling at room temperature. The gel entrapping hirudin was formed inside the wells of a 96-well plate. On top of the 100 μl agar–hirudin gel a volume of 200 μl of 10 mM phosphate buffer pH 7.4, 140 mM NaCl was added. The release kinetics of hirudin from the gel were measured following the changes in the hirudin intrinsic tyrosine fluorescence. The release of hirudin over 12 h was measured at three positions: at the bottom of the agar gel, at the interface of the gel with the solution, and in the middle of the receiver solution. The data presented in this paper indicate that high throughput methods can be applied in the characterization of protein drug release from drug delivery systems using small sample volumes.

Steady-state fluorescence study on release of camptothecin from agar hydrogel

The slow drug release processes from agar hydrogel were studied by steady-state fluorescence (SSF) measurement. An anticancer drug, camptothecin (CPT), was used as the release drug and the fluorescence probe for the real-time monitoring of the release processes by measuring the fluorescence intensity of the probe. The release kinetics of CPT at different temperatures was investigated. The Fickian diffusion model was adopted to fit the results and a good linear relationship could be observed between the logarithmic release fraction and the releasing time. The diffusion coefficients ( D) at these conditions were thus obtained from the slopes of the fitting curves. By plotting D against temperature, the diffusion coefficient of CPT was found to obey the Arrhenius relation and the activation energy was then obtained to be 70.6 kJ mol −1.

Influence of humidity on production of pelleted fungal inoculum

One of the practical problems in scaling-up the production of fungal inocula for environmental applications is how to provide essential humidity for fungal growth. Pelleted solid substrate was used as a fungal biomass carrier. It was coated with alginate or agar hydrogels that contained mycelial fragments of the white-rot fungi Trametes versicolor or Irpex lacteus. To follow fungal growth and formation of mycelial coat over pelleted substrate, the fluorescein-diacetate hydrolysing activity (FDA) assay and visual inspection were used. Both fungi were able to overgrow the pelleted substrate in 5–6 days, at a relative humidity (RH) of 86.3% or higher. The enrichment of alginate hydrogel with nutrients or coating of pelleted substrate with more hydrophilic agar hydrogel enabled I. lacteus to overgrow the pellets at a lower RH of 83.6%. Fungal inocula produced at lower RH possessed lower final moisture contents and had greater mechanical strength. Conditioning of T. versicolor mycelial fragments, by a 3-h incubation in fresh growth medium, enhanced fungal growth over the pelleted substrate. A mathematical model was used to simulate and to explain moisture distribution in a hydrogel-coated pellet and the formation of mycelial coat, for various conditions of fungal inocula production.

Iontophoretically assisted in vitro membrane transport of nicotine from a hydrogel containing ion exchange resins

The iontophoretically assisted transport of nicotine across artificial and human skin membranes from heterogeneous gel vehicles comprising mixtures of ion exchange resins, to which the nicotine had been bound, and agar hydrogel has been investigated. Both strong and weak resins were used and the effects of resin bead size, the degree of cross-linking in the polymer, the medium in which the drug was bound, the drug concentration and the magnitude of the current were determined. The heterogeneous vehicles were shown to have advantages over comparable simple hydrogel vehicles in their versatility, in their capacities to store the drug and to control both its delivery rate and the pH of the vehicle during iontophoresis.

Hydrolytic degradation and mechanical properties of hydrogels prepared from microbial poly(amino acid)s

The thermal hydrolytic degradability of hydrogels prepared from microbial poly(γ-glutamic acid) (PGA) and poly(ɛ-lysine) (PL) by γ-irradiation were measured in excess deionized water. PGA and PL hydrogels were slightly degraded near room temperature and degraded over 60 °C. It was found that PGA and PL hydrogels were hydrodegradable. In addition, the mechanical properties of PGA and PL hydrogels were measured by compression. PGA and PL hydrogels were not very strong and were the same as agar hydrogel (2%).

Studies on irradiation of agar–agar in the solid state: On the changes of thermal property of agar–agar hydrogel produced by irradiation

AbstractSolid agar–agar was irradiated with 60Co gamma‐rays, and effects of radiation on the cross‐links of agar–agar molecule were studied by measuring the melting and setting points of the agar–agar hydrogel at different radiation dose and elapsed time after irradiation.

Preparation of ternary composite hydrogels of agarose, concanavalin A and a glycolipid monolayer, and their permeation properties

Synthetic glycolipids (2C18-de-glu and 2C18-de-gal) form condensed surface monolayers, which have been successfully deposited on the agar hydrogel by the Langmuir–Blodgett (LB) technique. The monolayer-deposited gel membranes were satisfactory for use in the permeation experiments of ammonium salts such as tetramethylammonium bromide or hexyltrimethylammonium bromide over a wide temperature range. The permeability of the salts through the modified gel membranes depends strongly upon the hydrophobicity of the permeants and could be controlled by the phase transition of the deposited monolayers. Concanavalin A (ConA)-bound agar gels were modified with the 2C18-de-glu monolayer, having the α-D-glucopyranosyl head group, but not with the 2C18-de-gal, having the β-D-galactopyranosyl head group, owing to the specific binding ability of ConA. The permeability of the 2C18-de-glu monolayer-deposited ConA-bound agar gel was selectively controlled by the addition of monosaccharides: the permeability was enhanced by the addition of D-mannose, whereas it was hardly changed by the addition of D-galactose, resulting from the high binding constant of D-mannose with ConA.

Permeation Characteristics of a Glycolipid Monolayer-Deposited Agar Hydrogel

Abstract The monolayer film of glycolipid, 2C18-de-MA, containing α-D-glucopyranosyl-D-gluconamide as a hydrophilic head group and two long alkyl chains was successfully formed on an agar hydrogel by Langmuir-Blodgett technique. The permeability of the modified hydrogel membrane thus obtained depended strongly upon the hydrophobicity of permeants and could be controlled by the phase transition of the deposited monolayer.

Studies on irradiation of agar–agar in the solid state: On the changes of water holding capacity of agar–agar hydrogel produced by irradiation

AbstractSolid agar–agar was irradiated with 60Co gamma‐rays, and effects of radiation on the water‐holding capacity of agar–agar molecules were studied by measuring the water content of the agar–agar hydrogel. The effects of postirradiation were also studied. Empirical equations of changes of water holding capacity were obtained.

Studies on irradiation of agar–agar in the solid state: On the changes of melting point of the agar–agar hydrogel and setting point of the agar–agar hydrosol produced by irradiation

Abstract The effects of radiation on the formation of the cross-links of the agar-agar hydrogel were studied by measuring the melting point and setting point, and by calculating the heats of reaction for the cross-linking processes at different radiation doses, times after irradiation and concentrations of added substances (sugar and starch). The empirical equations for the melting point and the setting point were obtained.