Aqueous Agarose Research Articles

Characterization of agarose microparticles prepared by water-in-water emulsification

ABSTRACTMicroparticles have a wide range of applications in various areas. In this study, agarose microparticles (AGM) were successfully prepared by using a water-in-water (w/w) emulsification (WWEM) technique to eliminate the use of a surfactant. An aqueous agarose solution was employed as the dispersed phase, and polyethylene glycol (PEG) was used as the continuous phase. We evaluated how the characteristics of the microparticles were affected by different processing factors, including temperature, agitation speed, stirring time, concentration of agarose, and proportions of the two phases. The agarose microparticles obtained were nearly perfect spheres, and their particle sizes decreased with an increase in the agitation speed. Physicochemical characterization suggested that agarose microparticles, due to their ubiquitous stability, could be applied in most mild environments.

Subdiffusion in a system consisting of two different media separated by a thin membrane

We consider subdiffusion in a system which consists of two media separated by a thin membrane. The subdiffusion parameters may be different in each of the medium. Using the new method presented in this paper we derive the probabilities (the Green’s functions) describing a particle’s random walk in the system. Within this method we firstly consider the particle’s random walk in a system with both discrete time and space variables in which a particle can vanish due to reactions with constant probabilities R1 and R2 defined separately for each medium. Then, we move from discrete to continuous variables. The reactions included in the model play a supporting role. We link the reaction probabilities with the other subdiffusion parameters which characterize the media by means of the formulae presented in this paper. Calculating the generating functions for the difference equations describing the random walk in the composite membrane system with reactions, which depend explicitly on R1 and R2, we are able to correctly incorporate the subdiffusion parameters of both the media into the Green’s functions. Finally, placing R1=R2=0 into the obtained functions we get the Green’s functions for the composite membrane system without any reactions. From the obtained Green’s functions, we derive the boundary conditions at the thin membrane. One of the boundary conditions contains the Riemann–Liouville fractional time derivatives, which show that the additional ‘memory effect’ is created by a discontinuity of the system. The second boundary condition demands continuity of a flux at the membrane. We also derive a new formula describing time evolution of releasing substance from subdiffusive medium. This function coincides well with experimental data presented in Arabski et al. (2009). Confronting the experimental data with the derived formula, we estimate subdiffusive parameters of colistin in gel 1% aqueous agarose solution. We show the subdiffusive character of colistin transport in the gel.

Systematic Study of Functionalizable, Non-Biofouling Agarose Films with Protein and Cellular Patterns on Glass Slides.

Herein we demonstrate a systematic investigation of chemically functionalizable, non-biofouling agarose films over large-area glass surfaces. Agarose films, prepared with various concentrations of aqueous agarose, were activated by using periodate oxidation to generate aldehyde groups at the termini of the agarose chains. The non-biofouling efficacy and binding capabilities of the activated films were evaluated by using protein and cellular patterning, performed by using a microarrayer, microcontact printing, and micromolding in capillaries. Characterization by using a fluorescence slide scanner and a scanning-probe microscope revealed that the pore sizes of the agarose films played an important role in achieving desirable film performance; the 0.2 wt % agarose film exhibited the optimum efficacy in this work.

Magnetic Fluid Hyperthermia of Rodent Tumors Using Manganese Perovskite Nanoparticles

Purpose. To test the antitumor activity of magnetic fluid (MF) on the basis of substituted lanthanum-strontium manganite nanoparticles combined with alternating magnetic field (AMF) in experiments with transplanted tumors. Materials and Methods. MF with a size of nanoparticles of 30–40 nm in aqueous agarose solution was investigated. The ability of MF to heat tumor under AMF (300 kHz, 7.7 kA/m) was tested in vivo with rodent tumors (Guerin carcinoma, Walker-256 carcinosarcoma, and Lewis lung carcinoma (3LL)). Results. Single administration of MF into the tumor at a dose of 150 mg/kg (rats) or 200 mg/kg (mice) followed by AMF within 20–30 min (treatment was repeated 3-4-fold) has resulted in the complete regression of tumor in the 35% of rats and 57% of mice. Administration of MF alone or action of AMF alone has not resulted in tumor growth inhibition. The chemomodifying effect of nanohyperthermia was determined, in particular for cisplatinum: thermal enhancement ratio was 2.0. It was also observed that nanohyperthermia has resulted in the absence of 3LL metastases in 43% of mice. Conclusions. MF on the basis of lanthanum-strontium manganite may be considered as an effective inductor of tumor local hyperthermia.

Physicochemical and rheological properties of agarose/xylans composite hydrogel materials

Agarose (AG)/Xylans [beech (BX) and oat spelt (OSX)] composite hydrogels were prepared by effortless mixing method, using water as solvent. The gelling behavior of the composite hydrogels was investigated by a rheometer fitted with a temperature control facility. Improved gelling properties were observed as a result of incorporation of BX and OSX into the appropriate native aqueous agarose solution. A significant increase in the viscosity and elastic modulus of the parent AG was found with incorporation of xylans. The gelling and melting points of the mixtures resembled that of pure agarose gel, except for 90% xylan concentration. A significant increase in swelling ability of the parent AG was found with incorporation of xylans, while syneresis was reduced on addition of xylans. The physicochemical and rheological properties of seaweed polysaccharide agarose were modified significantly after blending with xylans, allowing their use in new applications. POLYM. COMPOS., 34:978–988, 2013. © 2013 Society of Plastics Engineers

Phase behaviors of agarose gel

We present evidence for the existence of phase separation in the gel state of agarose having the mixture of water and methanol as the gelsolvent. Firstly, the sol-geltransition line and the cloud point line are determined independently as a function of the concentration of agarose as well as the concentration of methanol in the mixed solvent by the quasi-equilibrium cooling of the solutions. Then the spinodal line is determined by quenching the solutions below the sol-geltransition line. We find that the spinodal line appears below the cloud point line and both lines are entirely buried below the sol-geltransition line in the aqueous agarose system. The concentration fluctuations are, therefore, frozen into the polymer network of agarose gel that promotes the opacity of the resultant gel. The structure of agarose gel is observed by the confocal laser scanning microscope (CLSM)imaging technique that reveals that the density fluctuations are grown up to micrometer scale in space. The phase separationboundary is found to shift to the higher temperature region than the sol-geltransition line when the concentration of methanol in the mixed solvent is increased. The results indicate that the position of the phase separation boundary in relative to the sol-geltransition line varies with the quality of solvent.These results are in agreement with the theory of the sol-geltransition in which both the divergence of the connectivity and the thermodynamic instability are taken into account.

Networks of polysaccharides with hydrophilic and hydrophobic characteristics in the presence of co-solute

The present investigation deals with the changing network morphology of agarose and high methoxy pectin when mixed with polydextrose as co-solute at concentrations varying up to high level of solids. Thermomechanical analysis and micro-imaging were performed using small deformation dynamic oscillation in shear, modulated differential scanning calorimetry and environment scanning electron microscopy. Fourier transform infrared spectroscopy and wide angle X-ray diffraction were practised to examine the nature of interactions between polymer and co-solute, and the extent of amorphicity of preparations. We observed a decline in the mechanical strength of aqueous agarose preparations upon addition of high levels of polydextrose, which should be attributed to reduced enthalpic content of the coil-to-helix transition of the polysaccharide network. Glass transition phenomena were observed at subzero temperatures in condensed preparations, hence further arguing for the formation of a lightly cross-linked agarose network with changing solvent quality. High levels of co-solute induce formation of weak pectin gels at elevated temperatures (even at 95°C), which with lowering temperature exhibit increasing strength. This results in the formation of rubbery pectin gels at ambient temperature, which upon controlled cooling to subzero temperatures convert to a clear glass earlier than the agarose counterparts.

New insights into the heating mechanisms and self-regulating abilities of manganite perovskite nanoparticles suitable for magnetic fluid hyperthermia

The heating and self-regulating abilities of La(1-x)Sr(x)MnO(3+Δ) ferromagnetic nanoparticles for magnetic fluid hyperthermia are studied. The samples, synthesized by the Glycine Nitrate Process, present non-agglomerated particles but are partially constituted by polycrystalline nanoparticles, displaying average crystallite diameters ranging from 21 to 31 nm. The strontium content of these nanoparticles, between 0.14 and 0.39, is associated with non-stoichiometry effects in the materials, and both govern their Curie temperatures (T(C)), which range between 13 and 86 °C, respectively. Heating experiments carried out on samples suspended in an aqueous agarose gel and with different alternating magnetic fields derive unexpected maximum temperatures that cannot be explained on the basis of static magnetization data. The measurement of the thermal dependence of the specific absorption rate (SAR) of nanopowders by adiabatic magnetothermia reveals the existence of a dissipation peak just below T(C), which is assigned to a Hopkinson peak. This thermal dependence of SAR, together with a simple thermal model that considers a linear approximation for the heat power losses, is crucial to clarify the behavior observed in heating experiments and also to discuss the possibilities of the samples as self-regulating hyperthermia mediators. This analysis emphasizes that, for the correct design of a self-regulating system, the heat power losses determined by the surrounding conditions must be taken into account as well as the heating capacity of the magnetic nanoparticles.

Spatial Control of Crystal Nucleation in Agarose Gel

Spatial and temporal control of crystal nucleation is demonstrated by nonphotochemical laser-induced nucleation of an aqueous agarose gel prepared with supersaturated potassium chloride. The location of nucleation was controlled by means of an optical mask; crystals were only observed in the area exposed to near-infrared laser radiation. The dependence of nucleation on laser power was measured, and the results suggest that the agarose gel reduces the effective supersaturation of the aqueous potassium chloride.

Effect of Sodium Sulfate on the Gelling Behavior of Agarose and Water Structure Inside the Gel Networks

Agarose hydrogels which constitute a special class of soft matter are undoubtedly one of the most studied biopolymer gels. However, certain issues such as why the sulfate salts and sulfate content in the agarose molecules reduce the gel strength are still not very clear. The present work provides a detailed analysis of structural changes with respect to coil-helix transition or aggregation of helices in the aqueous agarose solutions and hydrogels that accompanied the systematic addition of sodium sulfate. A combined approach which includes the differential scanning calorimetry and temperature-dependent vacuum-ultraviolet circular dichroism measurements permitted the accurate estimates of the energy changes for coil-helix transition and helix-helix interactions. The hydration process of agarose molecule investigated from differential scanning calorimetry and concentration-dependent ultrasonic measurements indicated the loss of both the freeze bound and nonfreezable water molecules with the increase of sulfate content in the solution. Temperature-dependent fluorescence measurements using pyrene as a probe indicated polarity changes when the gel network is created in waters of different salt concentration. Changes in the hydrogen bonding of the water molecules confined in the gel network have been monitored from the intensity ratios of ice-like and liquid-like -OH stretching band of water Fourier transform infrared (FTIR) spectra. Analysis of the -OH stretching band showed the strengthening of hydrogen bonding of water molecules in the gel which tend to weaken with the subsequent addition of sodium sulfate.

Molecular basis of water proton relaxation in gels and tissue

An extensive set of water-1H magnetic relaxation dispersion (MRD) data are presented for aqueous agarose and gelatin gels. It is demonstrated that the EMOR model, which was developed in a companion paper to this study (see Halle, this issue), accounts for the dependence of the water-1H spin-lattice relaxation rate on resonance frequency over more than four decades and on pH. The parameter values deduced from analysis of the 1H MRD data are consistent with values derived from 2H MRD profiles from the same gels and with small-molecule reference data. This agreement indicates that the water-1H relaxation dispersion in aqueous biopolymer gels is produced directly by exchange-mediated orientational randomization of internal water molecules or labile biopolymer protons, with little or no role played by collective biopolymer vibrations or coherent spin diffusion. This ubiquitous mechanism is proposed to be the principal source of water-1H spin-lattice relaxation at low magnetic fields in all aqueous systems with rotationally immobile biopolymers, including biological tissue. The same mechanism also contributes to transverse and rotating-frame relaxation and magnetization transfer at high fields.

Conformal Coating of Mammalian Cells Immobilized onto Magnetically Driven Beads

A novel cell bead system, comprising a magnetic core, a spherical annulus of agarose-immobilized cells, all conformally coated within a synthetic polymer, is proposed as a means of immunoisolating mammalian cells in a system that provides a balance between low total implant volume, retrievability, and diffusion limitations. A successful immunoisolation system could be used to transplant cells without eliciting an inappropriate host response. Chinese hamster ovary (CHO) cells were immobilized at the periphery of large (approximately 2 mm) agarose beads containing inert magnetic cores (< or = 1 mm) and coated in a hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) copolymer by interfacial precipitation. The beads were coated in liquid gradients containing polyethylene glycol 200 (PEG) or bromooctane. Although many cells were adversely affected by the coating process, the cells that did survive (30-50% of those loaded into the beads) remained viable for a period of at least 2 weeks. This viability was much higher than achieved previously because of a number of factors, such as the aqueous agarose, the hydrophobic bromooctane intermediate layer, and faster coating times that minimize the exposure of the cells to organic solvents. Also, a mathematical model was used to describe oxygen transport within the annular agarose beads. These results provide evidence that the proposed geometry and the fabrication approach may be useful for a variety of applications that involve cell encapsulation.

Selective growth and distribution of crystalline enantiomers in hydrogels.

The crystallization of sodium chlorate (NaClO3) is a classic example of spontaneous chirality, since it is achiral in solution but adopts a chiral form in the solid state. While crystal growth of NaClO3 from pure aqueous solutions yields a 50:50 statistical distribution of d- and l-crystals, large enantiomeric excesses of either d- and l-crystals can be achieved by crystal growth in agarose gel, a naturally occurring chiral polysaccharide. The influence of gel density (0.1-0.75 wt %), temperature, and the diffusion of cosolvents on crystal distribution was discerned from statistical data obtained from 752 gel-mediated crystallization experiments yielding 12,384 individual crystals. These studies demonstrate that the magnitude and direction of the bias can be selectively engineered toward either d- or l-forms by changing the gelation conditions. Aqueous agarose gels infused with 48 wt % NaClO3 at 6 degrees C, favored the growth of d-NaClO3 crystals, with ee's reaching 22% at the highest gel concentrations. Crystal growth under methanol diffusion favored deposition of the opposite enantiomorph, l-NaClO3. The bias in the crystal distribution is enhanced at higher temperatures. Aqueous gels at 24 degrees C infused with methanol cosolvent favored l-NaClO3, with ee's reaching 53%. The changing magnitude and direction of the enantiomorph bias can be ascribed to differences in the agarose conformation and intermolecular interactions between the gel and crystal surfaces that inhibit the formation of the two enantiomers to different extents.

Effect of sugars on the mechanical and thermal properties of agarose gels

The present study examines the thermal and mechanical properties of agarose/sugar mixtures using micro-DSC (Differential Scanning Calorimetry) and Dynamic Mechanical Thermal Analyser. In DSC experiments, addition of sugar was reflected in a broad exothermic event compared to sharp transitions generated by the aqueous agarose preparation. At high levels of co-solute, agarose networks show a reduced enthalpic content per gram of the polymer thus arguing for a transformation to a more entropic finely stranded networks of reduced number of junctions zones, the networks exhibited long large deformation properties. At high levels of sugar, agarose samples show a mechanical spectrum that can be modelled according to the WLF/free-volume theory, which requires an entropic lightly cross-linked network.

Diffusion coefficients of retinoids

Purpose. Diffusion coefficients of various retinoids have not been measured previously. It is important to know the diffusion coefficients of the retinoids because this property might be rate-limiting in dark adaptation. Also, retinoid diffusion is important to explore given that rhodopsin regeneration is not impaired in IRBP knockout mice. Methods. Measurements of lateral diffusion coefficients (D) of 9-cis-retinal, all-trans-retinal, and all-trans-retinol were made by Fourier transform pulsed-gradient spin-echo NMR measurements (FT-PGSE NMR) in several solvents. Also, 3 H-all-trans-retinoic acid was used to measure diffusion from an aqueous agarose matrix and absorption into a toluene based scintillation fluid in a biphase assay. Results. In a 1:1 mixture of CD 3 OD:D 2 O the D’s of the retinoids were, 2.4 to 3.0 × 10 -6 cm 2 /s. In the biphase assay, 3 H-all trans-retinoic acid exhibited a diffusion coefficient of 2.3 × 10 -6 cm 2 /s. Conclusions. The lower than expected D for retinoids and our calculations suggest that mechanisms in addition to pure aqueous diffusion may be needed to account for normal rhodopsin regeneration rates in the mammalian retina.

Magnetic field effects on sol-gel phase changes in aqueous polymers

Magnetic field effects were studied on the temperature-induced phase change for the sol–gel systems including the natural high polymer agarose or methyl cellulose. Aqueous agarose and methyl cellulose were set to gel on cooling and heating, respectively. The gel melting temperature T m was observed after the gels were formed under the influence of magnetic fields up 5 T. The magnetic field exposure resulted in 1.0 K rise in T m for agarose gels and 3.5 K lowering in T m for methyl cellulose gels. The magnetic effects became remarkable with the decrease of polymer concentration. The changes in melting temperature saturated at about 3 T. The birefringence for the 0.5 wt.% agarose gels which were formed in different magnetic fields increased with increasing magnetic field but saturated at about 3 T. The exposure of magnetic fields causes the alignment of the polymers and leads to a stable structure of the gels.

Mesoscopic gels at low agarose concentration: perturbation effects of ethanol

Aqueous agarose solutions at low concentrations (0.5 g/liter) were temperature quenched below the spinodal line to form mutually disconnected mesoscopic gels. In the presence of 6% ethanol, these solutions, obtained by quenching at the same temperature depth as in pure water, appear much more fluid, as determined by probe diffusion experiments. We show by static and dynamic light scattering that this can be explained by the solvent-mediated effects of ethanol, leading to a globular shape of mesoscopic agarose gels, rather than to an extended rodlike structure observed in pure water. Our findings show the significant effects of solvent perturbations on particle condensation and, therefore, may be useful in understanding the role of the solvent in the folding of biomolecules.

Dissolution Controlled Drug Release from Agarose Beads

A simple method was used for loading ibuprofen or indomethacin into agarose beads to obtain sustained release. Placebo beads were prepared by a dropwise addition of a hot aqueous agarose solution into a beaker of chilled mineral oil and water. Prior to loading, the aqueous component in the beads was replaced by repeated soakings in ethanol. Loading was accomplished at room temperature using ethanolic drug solutions. Upon drying, the beads shrank to about a third of their original size. The surface morphology of dried placebo and loaded beads was studied using electron microscopy. The release time at 37° C and pH 7.5 increased with drug loading and at 50% loading the release time was 4 hours for indomethacin and 6 hours for ibuprofen. Release of chlorpheniramine from dried and swollen beads was examined to elucidate the release mechanism. From dissolution studies it was concluded that the delay due to swelling is less than 10 minutes, chlorpheniramine release from swollen beads was primarily diffusion controlled, and the release mechanism for indomethacin and ibuprofen has three components: i) swelling of the beads, ii) dissolution of crystallized drug, and iii) diffusion of dissolved drug from the beads.

Using an ultraviolet scanner to determine radiation dose distribution

Aqueous agarose gels containing ferrous ions sustain a radiolytic chain reaction, producing Fe+3. Longitudinal proton magnetic relaxation rates are increased in proportion to ferric production. The distribution of Fe+3, hence the dose, can be revealed as a scanning curve at 304 nm dependent on its extinction, coefficient, permitting visualizing of dose in these gels by a dual wavelength thin layer chromatography scanner. There is a potential for application to radiation therapy treatment planning.

Anion-specific salt effects in aqueous agarose systems. 2. Nuclear spin relaxation of ions in agarose gels and solutions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnion-specific salt effects in aqueous agarose systems. 2. Nuclear spin relaxation of ions in agarose gels and solutionsLennart Piculell and Svante NilssonCite this: J. Phys. Chem. 1989, 93, 14, 5602–5611Publication Date (Print):July 1, 1989Publication History Published online1 May 2002Published inissue 1 July 1989https://doi.org/10.1021/j100351a054RIGHTS & PERMISSIONSArticle Views124Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts