Gram Of Gel Research Articles

How the Crosslinker Amount Influences the Final Properties of Hydroxyethyl Methacrylate Cryogels.

The investigation of the mechanical, thermal, and adsorption properties of hydroxyethyl methacrylate (HEMA) cryogels as a function of a reactant ratio is herein reported to better address materials for specific applications. To this aim, cryogels have been synthesized using different monomer/crosslinker (N,N'-methylene-bisacrylamide-MBAA) ratios. The study of SEM images made it possible to identify the trend in the material's macroporosity. As would be expected, the average measured pore width decreased as the amount of MBAA increased while the number of pores grew. Swelling capacity ranges from 8.7 gW/ggel (grams of water per gram of gel) to 9.3 gW/ggel. These values are strictly connected with the pore's size and distribution, revealing that the water uptake for the most crosslinked sample is inferior to other samples. The equilibrium-adsorption capacity (Qe) towards the methylene violet (MV) was also assessed, revealing no remarkable differences after 24 h of a batch test. As expected, thermogravimetric analysis (TGA) also showed no significant changes in stability that ranged from a maximum weight loss temperature (T Max) of 420 °C to 425 °C, which increased as a function of crosslinker content. Conversely, compression strength measurements showed a notable difference of about 50% in modulus (Ec), moving from the higher to the lower HEMA/MBAA ratio. These new comparative results indicate how slight variations in the reactant's ratio can steadily improve the mechanical properties of the HEMA cryogel without affecting its adsorption efficiency. This can be helpful in the design of materials for water and energy purposes. Since swelling properties are needed in the case of biomedical applications, the HEMA/MBAA ratio should be tuned versus high values.

Polyelectrolyte complex gels used for CO2 absorption

AbstractPolymer gels have shown application potential in minimizing gas channeling during CO2 enhanced oil recovery and storage processes, but the pumping pressure of preformed gels was too high, and the in‐situ cross‐linking in reservoirs was uncontrollable. Here we developed polyelectrolyte complex gels through the columbic attraction between sodium carboxymethyl cellulose (NaCMC) and protonated polyethyleneimine (PEI+) by CO2 in the presence of water. Without CO2, the viscosity of polymer complex solution is relatively low; after streaming CO2, the viscosity of the NaCMC‐PEI+ mixture aqueous solution increases significantly, forming a gel. It was also found that the complex solution shows an evolution of “sol–gel‐separated phase” as the polymer concentration increases, which could be attributed to the enhanced electrostatic attraction between CMC− and PEI+. The viscosity of the gel decreases upon increasing salinity owing to the reduced charge repulsion by the introduced inorganic salt. The CMC−‐PEI+ complex can retain its gel behavior until 60°C, after which the complex collapses. The uptake tests show that 11.34 mg CO2 can be absorbed by each gram of gel composed of 0.9 wt% NaCMC and 0.15 wt% PEI at room temperature and ambient pressure. This work provides an inexpensive route to control gas leakoff and improve CO2 absorption.

Novel superabsorbent materials from bacterial cellulose

AbstractA novel process for the production of superabsorbent materials (hydrogels) from bacterial cellulose (BC) was developed. Prior to crosslinking with a water‐soluble polyethylene glycol diacrylate (PEGDA), BC was first carboxymethylated and functionalized with glycidyl methacrylate. The degree of crosslinking influenced the swelling properties of the hydrogels. The use of greater amounts of PEGDA enhanced the formation of a thicker macromolecular network containing fewer capillary spaces in the crosslinked gel. The maximum water retention value of the hydrogels containing 2.5–3.5 mmol of carboxyl groups per gram of gel reached 125 g g−1 in distilled water, and 29 g g−1 in saline (0.9% NaCl solution). The highly porous hydrogel architecture with a pore size of 350–600 µm created a high specific surface area. This enables rapid mass penetration in superabsorbent applications. The superabsorbent hydrogels reached 80% of their maximum water absorption capacity in 30 min. © 2018 Society of Chemical Industry

Potentarea efectului tratamentului cu voltaren gel prin utilizarea ultrasunetelor cu frecvente de 1 MHz

The effects of nonsteroidal anti-inflammatory drugs (NSAIDs) in abarticular conditions are well known. The aim was to compare the efficacy of NSAIDs, of Diclofenac drug class (Voltaren gel, in this case) applied topically, with and without ultrasound, for a period of 10 days in abarticular rheumatic diseases. The following parameters have been aimed at: pain, functional impotence and quality of life index. One gram of gel was applied daily for an area of 100 cm�. The treatment was applied to patients in an outpatient regime. Therapeutic ultrasound frequencies were used. Among the effects of selective warming of the areas exposed to ultrasound, we mention: decreased joint stiffness, increased pain threshold of peripheral nerves and nerve endings, moderate increase of blood flow, increased joint mobility.

Radiation synthesis of biocompatible hydrogels of dextran methacrylate

The aim of this work was to synthesize biocompatible dextran-based hydrogels through crosslinking initiated by ionizing radiation. A series of derivatives of dextran has been synthesized by coupling of methacrylated glycidyl to the structure of this polysaccharide, yielding dextran methacrylate (Dex-MA) of the degree of methacrylate substitution (DS) up to 1.13 as characterised by FTIR and NMR spectroscopy. Chemically crosslinked hydrogels were formed by electron-beam irradiation of Dex-MA in aqueous solution in the absence of low-molecular-weight additives such as catalysts, monomers or crosslinking agents. Crosslinking of Dex-MA in aqueous solutions of 20g/l and above was an efficient process, the gels were formed at doses as low as 0.5 kGy (experiments conducted up to 100 kGy) and were characterised by high content of insoluble fraction (70–100%). Due to high crosslinking density the equilibrium degree of swelling of fabricated gels was controlled principally by the initial concentration of Dex-MA solution subjected to irradiation, and it was in the range of 20 to over 100g of water absorbed by gram of gel. Cytocompatibility of hydrogels was examined using XTT assay through evaluation of the cell viability being in indirect contact with hydrogels. The results indicated that hydrogels of Dex-MA of the average DS below 1 were not cytotoxic. Altogether, our data demonstrate that irradiation of methacrylated dextran in aqueous solution is an efficient method of fabrication of biocompatible hydrogels, which applications in regeneration medicine are anticipated.

Characteristic Swelling–Deswelling of Polymer/Clay Nanocomposite Gels

Swelling behavior of nanocomposite hydrogels (NC gels) having organic polymer/inorganic clay network structures were systematically investigated, focusing on the role of exfoliated clay platelets with sodium counterions in the network and effects of various swelling conditions. NC gels in water exhibited characteristic swelling–deswelling behavior, i.e., initial large swelling, maximum swelling, and subsequent deswelling toward an equilibrium state, under conditions where the water was changed frequently. Effects of swelling conditions, such as the frequency of changing the water, amount of water per unit gram of gel, salt concentration, and pH of the swelling solvent, gel composition (e.g., kind of polymer, clay concentration (Cclay), and polymer concentration (Cp)), swelling temperature, and gel size, were clarified. NC gels with different polymers were all found to exhibit swelling–deswelling behavior except at very low Cclay and high Cp. Spontaneous deswelling of the gels was attributed to the combine...

In vitro release and stability of an artesunate rectal gel suitable for pediatric use

The rectal route is indicated to treat patients with rapidly evolving malaria who cannot take oral medication to prevent progression to severe forms of the disease. Improvement can be made in terms of rectal bioavailability and stability of current formulations. We studied a new two-compartment, muco-adhesive gel formulation of artesunate which is adapted for use in children and storage in tropical climates. The formulation contains 50 mg of artesunate per gram of gel. Because of its instability in aqueous solutions, artesunate is in the dry component of the gel with Carbopol ® and separate from the liquid phase until reconstitution. Artesunate is stable in the dry blend for 6 months at 45 °C and 60% RH. The gel should be used between 1 and 72 h after being reconstituted. Artesunate release was measured by with a rapid, simple and reliable HPLC-UV which allowed the analysis of artesunate and dihydroartemisinin with an analysis time at 3 min. The amount of artesunate released over 6 h was 56 ± 0.97%. Compared to the reference suspension, total release and dissolution efficiency were lower and rate of release was slower (time to 50% dissolution 271 ± 21 min), probably because of the higher viscosity of the gel, but the drug release profiles were similar. The calculated in vitro release exponent ( n) value suggested that artesunate is released from the gel by non-Fickian transport.

Removal of dyes from water by poly(vinyl pyrrolidone) hydrogel

AbstractThe interaction between polymer and dye leading to polymer‐dye complex formation exhibits many interesting and important practical features. For this purpose, a hydrogel was prepared by crosslinking copolymerization of vinyl pyrrolidone with tetraallyl ammonium bromide in aqueous solution, using K2S2O8 as a radical initiator. Dye extraction experiments were carried out simply by contacting wetted gel samples with aqueous dye solutions at room temperature. Capacities were determined by colorimetric analysis of the residual dye contents. The hydrogel swelled in water showing that reasonable high dye sorption capacity (0.71–1.13 g per gram of gel) was achieved. This material is also able to remove the anionic dyes completely even from highly diluted aqueous dye solutions. No trace absorbance was detected in the visible range, after processing. Copyright © 2006 John Wiley & Sons, Ltd.

Kinetics of glucose oxidase immobilized in p(HEMA)-hydrogel microspheres in a packed-bed bioreactor

Glucose oxidase (GO x ) was immobilized via both physical entrapment and covalent linkage to crosslinked poly(hydroxyethyl methacrylate- co-dimethylaminoethyl methacrylate, (p(HEMA-DMEMA)) hydrogel microspheres (20–150 μm in diameter) that were synthesized by inverse suspension polymerization. Loading capacities of 7–8 mg GO x per gram of hydrogel were achieved with physical entrapment, compared to <1.8 mg GO x per gram of gel with the covalent technique. The microspheres containing physically entrapped enzyme were packed into bioreactors and the kinetics of the immobilized enzyme investigated under various flow conditions. Flow rate dependence of K m(app) and C max, when extrapolated to near diffusion-free conditions, resulted in values of 13.2 mM and 2.7×10 −3 mol min −1, respectively, for the immobilized enzyme. Studies of pH-dependence of K m(app) and C max suggest that the imidazolium and sulphydryl groups may be involved at the active site of the immobilized GO x . Studies of the temperature dependence of C and C max confirm lower activation energies for the oxidation of glucose at temperatures >35 °C, suggesting the influence of diffusional limitations within the hydrogel.

Preparation and Release of Ibuprofen from Polyacrylamide Gels

The conditions of preparation of polyacrylamide (polyAC) gels, the incorporation of ibuprofen (IB), and the kinetics of IB release under various conditions have been evaluated. Transparent, opaque, or elastic gels were prepared depending on the concentration of acrylamide (AC) and the cross-linking agent, N,N′-methylenebisacrylamide (BIS). Release studies in media below pH 5.0 resulted in opaque gels. The kinetics of IB release was a function of the AC, BIS, and the pH of the medium, but the optimum composition, in terms of gel integrity and release characteristics, was 7% AC cross-linked with BIS at a 50:1 ratio. Modulation of the release rate was possible with the incorporation of 10% of certain polymers. The amount of IB that could be incorporated per gram of transparent gel was a function of the amount of polymer initiator N,N,N′,N′-tetramethylene diamine (TEMED) used per gram of gel. More than 200 mg of IB could be incorporated per gram of transparent gel by using 100 μl of TEMED. The release of IB obeyed matrix/swelling-controlled kinetics and 70–80% of the IB was released from gels containing 10 to 40 mg IB per gram of gel in 5 hr at pH 7.4 and 37°C.

Enantiomer separation of amino compounds by a novel chiral stationary phase derived from crown ether

A novel chiral stationary phase (CSP-18C6I) was prepared by immobilizing (+)-18-crown-6 tetracarboxylic acid on 3-aminopropylsilanized silica-gel to separate enantiomers of drugs having a primary amino group. The chiral crown ether was combined with 3-aminopropyl silica gel (0.85 mmol of amine per gram of gel) to provide CSP-18C6I having a chiral selector loading of 0.26 mmol per gram of gel. This CSP-18C6I showed good chiral recognition for thirteen out of eighteen dl-amino acids and seven racemic aminoalcohols using a dilute aqueous solution of perchloric acid as the eluent. Afloqualone (a muscle relaxant), primaquine (an antimalarial), and 1-(1-naphthyl)ethylamine (1-NEA) were resolved on the CSP-18C6I. Furthermore, alanine-β-naphthylamide (Ala-β-NA), which is hydrophobic and did not elute within 60 min by the commercially available CROWNPAK CR(+) with 15% methanol and a column temperature of 40°C, was successfully enantioseparated by the novel CSP-18C6I.

A new apheresis system using a copolymer (polyvinyl alcohol triethylene glycol diacrylate) for removal of LDL from dog whole blood.

Studies were undertaken to determine the effectiveness of a copolymer composed of PVA-TEGDA (Poly Vinyl Alcohol TriEthylene Glycol) as a plasma-cholesterol lowering procedure. For a comparative study, five dogs underwent plasmapheresis including the transfusion bag containing gel in the plasma line, while three control dogs underwent the same plasmapheresis without gel. Numerous biological determinations were performed firstly in whole blood circulation before and after treatment over 10 days, and secondly in plasma before and after LDL binding on the gel. In the whole blood circulation, the average significant depletion of cholesterol levels was 31-51% for treated, 0-16% for control dogs and the average significant depletion of LDL cholesterol was 26-75% for treated and 0-3% for control dogs. Gel was therefore able to bind 121-217 mg of total cholesterol and 34-70 mg of LDL cholesterol per gram of gel. Lipid and lipoprotein levels rebounded 3-4 days after treatment. Adverse effects were not observed during all plasmapheresis. No significant differences between control plasmapheresis and gel-plasmapheresis were obtained for blood cell counts while lengthened coagulation times were observed during 24 h. Complement was not significantly activated by the copolymer as shown by a same decreased activity in the blood stream of all dogs: in fact, CH 50 depletion in the gel incubated plasma was due to a protein adsorption on the hydrogel. This new approach for LDL apheresis appears to be a promising new technique.

Bioconversion of Lmalic acid into Llactic acid using a high compacting multiphasic reactor (HCMR)

AbstractBiotransformation of Lmalic acid into Llactic acid was studied in a fluidised bed reactor using cells of Lactobacillus sp. 89 and Leuconostoc oenos ATCC 23278 immobilised in a calcium alginate matrix. The reactor was used in a batch or a continuous manner under a non‐oxidising atmosphere. It was shown that 3 mm diameter beads loaded with 6 and 30 mg dry matter per gram of gel were the best operating conditions for Leuconostoc and Lactobacillus respectively. The optimal working conditions were as follows: pH = 3.0–5.0, temperature = 30°C for Lactobacillus and pH = 3.0, temperature = 25°C for Leuconostoc. No inhibition due to lactic acid was observed and the internal diffusional effects were negligible. The short catalyst life that was initially observed with both strains resulted from a depletion in NAD and Mn2+, two basic cofactors for malolactic enzymes. To prevent this detrimental effect, a regeneration process for biocatalyst was proposed.

One-step purification of trypsin and α-chymotrypsin by affinity chromatography on Eupergit—aprotinin, a novel carrier for purification of serine proteases

Aprotinin isolated from bovine lungs was covalently immobilized on Eupergit C. The highly selective affinity adsorbent was used to purify trypsin and α-chymotrypsin from pancreatic extract in a single step. Sodium dodecyl sulphate—polyacrylamide gel electrophoresis indicated that both enzymes were highly purified. The maximum binding capacity of Eupergit—aprotinin for bovine trypsin was calculated to be ca. 7.5 mg per gram of gel (wet resin).

Fertilizer Salts Reduce Hydration of Polyacrylamide Gels and Affect Physical Properties of Gel-amended Container Media

Hydration of three commercial hydrophilic polyacrylamide gels in deionized water ranged from 340 to 420 g per gram of gel. Hydration was progressively inhibited by fertilizer salt concentrations from 0 to 20 meq·liter-1. Hydration of the gels in the presence of divalent cations (Ca2+ and Mg2+) and monovalent cations (K+ and NH4+) at 20 meq·liter-1 was reduced to ≈10% and 20% of maximum, respectively. The valence of the accompanying anion did not affect hydration. Gel hydration was unaffected by urea over the range of 2 to 20 mm. Sequential rinses of the hydrated gels with deionized water completely reversed the inhibition due to the monovalent, but not the divalent, cations. The electroconductivity (EC) of the external solution increased during gel hydration. In the presence of fertilizer salts, the physical properties of a 2 redwood sawdust : 1 sand (v/v) container mix were unaffected by hydrophilic gel additions of 1.2 and 2.4 kg·m-3 (1 × and 2 × the recommended rate, respectively).

Synthesis of l-Dopa by Escherichia intermedia cells immobilized in a carrageenan gel

Escherichia intermedia cells were immobilized by entrapment in a carrageenan gel and used for l-DOPA synthesis from catechol, pyruvate, and ammonia. A preparation containing 75 mg of cell per gram of gel retained 60–65% of its original activity. The effect of substrate concentrations on the initial rate of l-DOPA synthesis was very similar for free and immobilized cells, and substrate inhibition was observed for the three substrates. In batch reactors, up to 7.8 g l −1 of l-DOPA was obtained in 20 h (productivity 0.39 g l −1 h −1). Cells immobilized in a carrageenan gel showed higher l-DOPA synthesis, in both initial rates conditions and batch reactors, than cells immobilized in a polyacrylamide gel.

Kinetics of immobilized pig heart fumarase

The kinetics of immobilized pig heart fumarase are described and compared with the properties of the enzyme free in solution.1.An analogous pH dependence of initial activity is found for free and immobilized enzyme.2.Immobilized and free fumarase deviate from classical Michaelis-Menten kinetics in the same way. The apparent Km values are three to eight times higher for the immobilized (2 mg/g gel) enzyme.3.The specific activity of immobilized fumarase is dependent on the final enzyme concentration on the gel; normal specific activities are observed when 50 [Symbol: see text]g fumarase is immobilized per gram of gel, whereas the specific activity decreases with increasing enzyme concentration.4.The activation energies for free and immobilized fumarase (50 [Symbol: see text]g/g gel) were found to be identical between 22 and 32‡C and with L-malate as substrate (Ea = 12,290 cal/mol at pH 7.9). Upon increasing the concentration of fumarase on the gel, the activation energy decreases. Our results indicate that the true catalytic properties of fumarase are not affected by immobilization of this enzyme. The slight differences observed when fumarase is immobilized at concentrations higher than 50 [Symbol: see text]g/g gel must be attributed to diffusional limitation at the surface of the Sepharose matrix.