Hydroxyethyl Cellulose Solutions Research Articles

Biomedical application of a superabsorbent hydrogel for body water elimination in the treatment of edemas

A novel system of body water elimination to be used for the treatment of edemas, based on superabsorbent cellulose derivatives able to absorb large amounts of water and water solutions, has been investigated. Hydrogels have been synthesized starting from water solutions of carboxymethylcellulose sodium salt and hydroxyethylcellulose, chemically crosslinked with divinylsulphone. Polyelectrolyte hydrogels displayed high sensitivity in sorption capacity to variations of the ionic strength and pH of the external solution, which is a key parameter for the application under investigation. Further, swelling properties have been modulated acting on the degree of crosslinking of the macromolecular network, and a direct method for the measurement of this parameter based on NMR solid-state analysis has been provided. The hydrogel biocompatibility has been studied in terms of its capacity either to induce nitric oxide and lactate dehydrogenase release by macrophages or influence their viability. The eventual release of toxic substances from the hydrogel was also investigated using Swiss 3T3 fibroblasts. The results obtained from the biocompatibility studies carried out in this work are consistent with the hypothesis that this gel may represent an alternative to diuretic therapies in those pathologic conditions in which edemas occur.

Evaluation of the degree of cross‐linking of cellulose‐based superabsorbent hydrogels: a comparison between different techniques

AbstractThree different techniques have been applied to the evaluation of the degree of cross‐linking of superabsorbent cellulose‐based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross‐linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate‐based superabsorbents on the market. A 13C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross‐linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross‐linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress‐deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross‐linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross‐linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.

Radiation crosslinking of methylcellulose and hydroxyethylcellulose in concentrated aqueous solutions

The effects of ionizing radiation on aqueous solutions of cellulose ethers, methylcellulose (MC) and hydroxyethylcellulose (HEC) were investigated. The well-established knowledge states that cellulose and its derivatives belong to degrading type of polymers. However, in our study intermolecular crosslinking initiated by gamma rays or electron beam leaded to the formation of insoluble gel. This is an opposite effect of irradiation to the degradation. Paste-like form of the initial specimen, i.e. concentration 20–30%, when water plasticizes the bulk of polymer; and a high dose rate were favorable for hydrogel formation. Gel fraction up to 60% and 70% was obtained from solutions of HEC and MC, respectively. Produced hydrogels swell markedly in aqueous media by imbibing and holding the solvent. Radiation parameters of irradiation, such as yields of degradation and crosslinking and the gelation dose, were evaluated by sol–gel analysis on the basis of Charlesby–Rosiak equation. Despite of the crosslinked structure, obtained hydrogels can be included into the group of biodegradable materials. They undergo decomposition by the action of cellulase enzyme or microorganisms from compost.

Effect of Steam Sterilization on the Rheology of Polymer Solutions

The effect of steam sterilization (dwell@121°C) on the apparent viscosity of solutions of carbomer 940P, guar gum, hydroxyethylcellulose (HEC), and xanthan gum was studied. Guar gum and carbomer 940P could be steam sterilized for 30 min without any change in the apparent viscosity. Steam sterilization of HEC and xanthan gum resulted in a substantial decrease in the apparent viscosity and the desirable shear-thinning rheology. The addition of sodium chloride to either polymer prior to steam sterilization diminished the effect of sterilization on the rheology. The apparent viscosity of xanthan solutions was not significantly affected if the solution was made isotonic with sodium chloride (0.15 M). The addition of sodium chloride to xanthan gum after steam sterilization resulted in full recovery of the initial rheological properties. Carbomers, guar gum, and xanthan (in 0.15 M NaCl) are candidates for use in pharmaceutical solutions/suspensions that are subjected to steam sterilization.

Adsorption of Hydroxyethyl Cellulose Selenium Nanoparticles during Their Formation in Water

Two previously unknown phenomena were observed in studying the reduction of selenious acid with ascorbic acid in an aqueous hydroxyethyl cellulose solution: (1) formation of nanoparticles of amorphous Se0 with uniform particle size distribution and mean particle radius of 15 ± 4 nm and (2) adsorption of more than 3000 macromolecules on these nanoparticles with formation of spherical nanostructures.

Shear thinning and thixotropy of HMHEC and HEC water solutions

Steady state viscosity and thixotropy of hydrophobically modified hydroxyethyl cellulose (HMHEC) and nonassociative cellulose water solutions are studied. Although all the samples are shear thinning, only the HMHEC is thixotropic, since the migration of hydrophobes to micelles is controlled by diffusion. The Cross model fits steady state curves. The Mewis model, a phenomenological model that proposes that the rate of change of viscosity when the shear rate is suddenly changed is related to the difference between the steady state and current values of viscosity raised to an exponent, fits structure construction experiments when the exponent, n, is estimated to be around 2. The Newtonian assumption used by Mewis cannot be used here, however. This seems to be related to the fact that the thickening is due to bridged micelle formation, which is a slow process, and also to topological constraints and entanglements, which are rapid processes. The kinetic parameter was redefined to kn in order to make it independent of initial conditions. So, kn depends only on how the shear affects the structure. kn reaches a plateau at shear rates too low to produce structure destruction and decreases at higher shear rates.

Shear and extensional rheology of solutions of modified hydroxyethyl celluloses and sodium dodecyl sulfate

This work reports on the rheology of aqueous solutions of hydroxyethyl cellulose (HEC) and three derivatives, in the presence of sodium dodecyl sulfate (SDS). The polymers employed were: a hydrophobically modified hydroxyethyl cellulose (HMHEC) containing hexadecyl grafts, a cationically modified hydroxyethyl cellulose (cat-HEC), containing glycidyl-trimethyl-ammonium grafts, and a polymer with both modifications (cat-HMHEC). Rheological measurements were performed in simple shear flow, oscillatory shear flow, opposed-jets flow and flow through porous media. The addition of surfactant increases intermolecular interactions between HMHEC molecules due to the formation of mixed micelles that bridge hydrophobic side groups from different polymer chains. These interactions lead to phase separation in an intermediate SDS concentration range and, at higher surfactant concentrations when a homogeneous phase was obtained, to higher shear and apparent extensional viscosities. Further surfactant addition eventually inhibits hydrophobe interactions due to electrostatic repulsion between micelles, leading to shear viscosities that are even lower than that of the original polymer solution. Hydrophobe interactions are inhibited by the relatively strong nature of flow in opposed-jets. The addition of cationic side groups confers the polymer a polyelectrolytic nature, which translates into higher shear and apparent extensional viscosities. Interchain interactions are strengthened by the presence of surfactant by the formation of intermolecular cross-links between polymer chains.

Comparison of RNA, single-stranded DNA and double-stranded DNA behavior during capillary electrophoresis in semidilute polymer solutions

We present a study of the separation of RNA, single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) in semidilute linear hydroxyethylcellulose (HEC) solution. Our results strive to provide a better understanding of the mechanisms of nucleic acid migration during electrophoresis in polymer solutions under native and denaturing conditions. From a study of the dependence of mobility on chain length and applied electric field, we found that RNA and ssDNA show better separation and higher resolution over a larger range of sizes compared to dsDNA. In addition, RNA reptation without orientation extends to longer chain lengths in comparison to ssDNA, possibly as a result of different type of short-lived secondary structure formations. Such a comparative study between nucleic acid capillary electrophoresis helps to optimize RNA separation and provides better understanding of RNA migration mechanisms in semidilute polymer solutions under denaturing conditions.

Rheological behavior of hydrophobically modified hydroxyethyl cellulose solutions: A linear viscoelastic model

The rheological behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC), an associative thickener, was studied and compared with that of hydrophobically modified ethoxylated urethanes (HEURs) and nonassociative celluloses. In contrast to HEURs, a simple Maxwell model does not fit the linear viscoelastic behavior of HMHEC. Differences are attributed to the stiffness and comb structure of HMHEC. A generalized Maxwell model with a logarithmic distribution of relaxation times is proposed, and another parameter that includes Rouse-like relaxation is added to fit behavior at high frequencies. Four parameters are needed to describe HMHEC viscoelasticity: a mean relaxation time, λM; its corresponding standard deviation, σ; a plateau modulus, GN; and a viscosity at infinite frequency, η∞. Satisfactory fitting is obtained for all concentrations and temperatures in the range of frequencies studied. The sharp increase of GN with concentration indicates loop-to-bridge transitions. Temperature does not influence GN, since the reduction in the number density of elastically effective chains caused by Brownian motion masks the direct effect of temperature. The dependence of λM on temperature follows the Arrhenius equation, as does the relaxation time of HEURs, but it does not change with concentration, presumably because the comb structure of HMHEC prevents the formation of long superchains.

The impact of urea on viscosity of hydroxethyl cellulose and observed mobility of deoxyribonucleic acids.

The influence of urea on the viscosity of hydroxyethyl cellulose (HEC), and the state and separation of double-stranded DNA, was studied by viscometry, fluorometry, and capillary electrophoresis. The results show that double logarithm plots of specific viscosity against the volume fraction of HEC in very dilute polymer solutions are linear, the slopes of which decrease from 0.96 in 0M to 0.29 in 7M urea. The linear regression plots converge at 0.0029 g/mL, the entanglement threshold of HEC. The inclusion of urea in HEC solution thus provides an accurate method of determining its entanglement threshold from such plots. Above the entanglement threshold of HEC, urea has no effect on the specific viscosity of HEC. Results also show that urea has no effect on double-stranded DNA. No change in fluorescence was observed when increasing amounts of urea were added to a fixed concentration of DNA. To examine the influence of urea on the migration of DNA in HEC, the separation of DNA was carried out by polymer-solution capillary electrophoresis in HEC solutions containing 0 or 7M urea using unmodified capillary. Observed mobilities were used in data reduction. It was found that a parallel relationship exists between the observed mobilities and the true mobilities. In buffers containing no urea, the pseudo-free solution mobility appears to be independent of the DNA size. It was also observed to be independent of the electric field below 300 V/cm, but relates exponentially to it in 7M urea. The pseudo-retardation constants obtained by Ferguson-like plots were observed to be positive for smaller DNA molecules below 300 V/cm and increasing linearly with electric field in 0M urea, but nearly constant in 7M urea.

Light scattering experiments on aqueous solutions of selected cellulose ethers: contribution to the study of polymer-mineral interactions in a new injectable biomaterial.

Hydroxypropylmethylcellulose (HPMC) is used as a ligand for a bioactive calcium phosphate ceramic (the filler) in a ready-to-use injectable sterilized biomaterial for bone and dental surgery. Light scattering experiments were usually used to study high water-soluble polymers and to determine the basic macromolecular parameters. In order to gain a deeper understanding of polymer/mineral interactions in this type of material, we have investigated the effect of divalent and trivalent ions (Ca(2+), PO(4)(3-)) and steam sterilization on dilute solutions of HPMC and hydroxyethylcellulose (HEC). The sterilization process may cause some degradation of HEC taking into account its high molecular weight and some rigidity of the polymer chain. Moreover, in the case of HPMC, the changes in the conformations rather than degradation process are supposed. These effects of degradation and flocculation are strengthened in alkaline medium. Experimental data suggested the formation of chelate complexes between Ca(2+) and HPMC which improve its affinity to the mineral blend and consolidate the injectable biomaterial even in the case of its hydration by biological fluid.

Separation of polymerase chain reaction amplified bird genes by capillary electrophoresis.

Female birds possess one Z and one W chromosome, whereas male birds possess two identical Z chromosomes. Thus, the presence of a W genetic marker is diagnostic of the female sex. Capillary electrophoresis with buffer containing an entangled solution of hydroxyethylcellulose was used to separate the polymerase chain reaction (PCR) amplified bird sexing genes CHD-Z and CHD-W. The relative standard deviations (RSD) were less than 0.6% for the male genes and less than 0.4% for the female genes for six runs and detection limits of 0.1 ng/microL were obtained with laser-induced fluorescence (LIF) detection. Using a DNA ladder and theoretical models for DNA separation in sieving media, the sizes of the two bird genes were determined.

Capillary electrophoresis of DNA in uncrosslinked polymer solutions: Evidence for a new mechanism of DNA separation

The electrophoretic separation of DNA molecules is usually performed in thin slabs of agarose or polyacrylamide gel. However, DNA separations can be achieved more rapidly and efficiently within a microbore fused silica capillary filled with an uncrosslinked polymer solution. An early assumption was that the mechanism of DNA separation in polymer solution-capillary electrophoresis (PS-CE) is the same as that postulated to occur in slab gel electrophoresis, i.e., that entangled polymer chains form a network of "pores" through which the DNA migrates. However, we have demonstrated that large DNA restriction fragments (2.0-23.1 kbp) can be separated by CE in extremely dilute polymer solutions, which contain as little as 6 parts per million [0.0006% (w/w)] of uncrosslinked hydroxyethyl cellulose (HEC) polymers. In such extremely dilute HEC solutions, far below the measured polymer entanglement threshold concentration, pore-based models of DNA electrophoresis do not apply. We propose a transient entanglement coupling mechanism for the electrophoretic separation of DNA in uncrosslinked polymer solutions, which is based on physical polymer/DNA interactions.

High performance capillary gel electrophoresis as a method to separate plasmid-DNA cloning vectors with very high resolution (below 100 bp) and its application in molecular biology

A novel high resolution method for the separation of, both, linear and supercoiled circular plasmid DNA in the range of 3000–5600 bp is described. Employing ultradilute solutions of hydroxyethylcellulose (0.070–0.100% w/w) containing no intercalating agent, we were able to resolve plasmids as well as linear fragments with a size difference of about 100 to 55 bp (R=0.5), depending on their size, at a limit-of-detection of about 3 ng (UV/VIS 260 nm, absolute amount). The effect on the separation efficiency of varying polymer and buffer concentration, capillary coating, salt additives and applied voltage has been investigated. The main issue of this study is to explore the applicability of high performance capillary gel electrophoresis (HPCGE) to molecular cloning and related purposes. Our results demonstrate that this method allows convenient monitoring of cloning procedures. It is superior to conventional agarose gel electrophoresis with respect to, both, sensitivity and resolution. Hence, it is especially useful for manipulations which result in only a small difference in fragment length or provide only limited quantities of sample DNA. To summarize, the method described in this paper allows to determine the size, concentration, and purity of plasmid DNA simultaneously in one single step. ©2000 John Wiley & Sons, Inc. J Micro Sep 12: 75–86, 2000

High performance capillary gel electrophoresis as a method to separate plasmid-DNA cloning vectors with very high resolution (below 100 bp) and its application in molecular biology

A novel high resolution method for the separation of, both, linear and supercoiled circular plasmid DNA in the range of 3000–5600 bp is described. Employing ultradilute solutions of hydroxyethylcellulose (0.070–0.100% w/w) containing no intercalating agent, we were able to resolve plasmids as well as linear fragments with a size difference of about 100 to 55 bp (R=0.5), depending on their size, at a limit-of-detection of about 3 ng (UV/VIS 260 nm, absolute amount). The effect on the separation efficiency of varying polymer and buffer concentration, capillary coating, salt additives and applied voltage has been investigated. The main issue of this study is to explore the applicability of high performance capillary gel electrophoresis (HPCGE) to molecular cloning and related purposes. Our results demonstrate that this method allows convenient monitoring of cloning procedures. It is superior to conventional agarose gel electrophoresis with respect to, both, sensitivity and resolution. Hence, it is especially useful for manipulations which result in only a small difference in fragment length or provide only limited quantities of sample DNA. To summarize, the method described in this paper allows to determine the size, concentration, and purity of plasmid DNA simultaneously in one single step. ©2000 John Wiley & Sons, Inc. J Micro Sep 12: 75–86, 2000

Synergistic blends from aqueous solutions of two cellulose derivatives

Homogeneous blends of two solutions of carboxymethylcellulose and hydroxyethylcellulose (HEC) were studied with respect to viscosity properties at different blending ratios, shear rates and temperatures. The blends exhibited viscosity synergism at all blending ratios, as well as improved shear and temperature stability. Maximum synergism was observed for the blend containing 67% of HEC. The UV and IR spectra showed that the hydrogen-bonding interaction between the blended components is the main reason for the synergism.

Comparative Conformational Dynamics of Supercoiled Plasmids and Linear DNA during Capillary Electrophoresis

The electrophoretic migration of 40 and 90 kbp supercoiled (sc) double-stranded (ds) plasmid DNA in dilute and entangled solutions of linear hydroxyethyl cellulose (HEC, Mn = 438 800) was visualized by video fluorescence microscopy at 60−222 frames/s. The sc-DNA molecules migrated as elastic rods with stretch−contraction cycles directed along the electric field axis. The elastic rod electrophoretic behavior of sc-DNA is completely different from the familiar random coil electrophoretic dynamics of linear ds-DNA. Extension−contraction cycles were more periodic for sc-DNA than for linear ds-DNA. The consequences of the different sc-DNA and linear ds-DNA electrophoretic dynamics on mobility dispersion are discussed.

Temperature effect on the separation of DNA fragments by capillary electrophoresis in hydroxyethyl cellulose solution

Temperature effect on the separation of DNA fragments by capillary electrophoresis in hydroxyethyl cellulose solution

Temperature effect on the separation of DNA fragments by capillary electrophoresis in hydroxyethyl cellulose solution

Temperature effect on the separation of DNA fragments by capillary electrophoresis in hydroxyethyl cellulose solution

A theory for the electrophoretic separation of DNA in polymer solutions.

We present a mathematical model of DNA capillary electrophoresis in polymer solutions based on nonentangling collisions between DNA and polymer molecules. Using videomicroscopy images of DNA migrating through polymer solutions, we propose a modified transient entanglement coupling mechanism for DNA separations that includes nonentangling DNA/polymer collisions. We show that a mathematical model based on individual nonentangling DNA/polymer collisions is able to predict the mobilities of DNA in solutions of low molecular mass polymer. We compare the model predictions to mobility data for separations of DNA in a range of concentrations for solutions of both hydroxypropylcellulose (Mw 100,000) and hydroxyethylcellulose (Mw 139,000). The model relies on one fitted parameter, the time constant for the interaction between the DNA and polymer molecules, which is based on the physical properties of DNA and polymers.