Evaluation of agar and agarose gels for studying mechanical impedance in rice roots

Agar and agarose gels were evaluated as systems to mechanically impede roots of rice (Oryza sativa L.). Two-layer gels were used so that seedlings established in a layer of weak gel (0.35% weight/volume) and then grew downwards to encounter a treatment gel of up to 5.0% (w/v). Agarose gels were stronger than agar gels of the same concentration, reaching a maximum penetrometer resistance of 1.2 MPa at a concentration of 5.0%, compared to 0.3 MPa with agar. The 5.0% agar gel stimulated elongation of the seminal axis by 40% in seedlings of variety TN1 (compared with elongation in the 0.2% gel), but decreased it by 15% in the variety Lac 23. Although increasing agarose concentration decreased seminal axis elongation in both varieties, the seminal axis did not reach the lower layer of treatment gel when the concentration of the treatment gel was greater than 2.0%. The decreased root elongation was therefore a non-mechanical inhibition. In experiments conducted using a different batch of agarose, these inhibitory effects were not seen and strong agarose gels stimulated seminal axis elongation. It was concluded that the agar and agarose gel systems studied were unsuitable for studying the effect of mechanical impedance on the elongation of rice roots and that great care should be taken in interpreting the results of experiments using gels as a growth medium. This revised version was published online in June 2006 with corrections to the Cover Date.     

Optimizing sweet potato [Ipomoea batatas (L.) Lam.] root and plantlet formation by selection of proper embryo developmental stage and size,and gel type for fluidized sowing

Potassium starch polyacrylamide, potassium acrylate, a copolymer of potassium acrylate and acrylamide, and hydroxyethylcellulose carrier gels were tested to find a fluid drilling material suited for synthetic seeding of sweet potato (Ipomoea batatas (L.) Lam.) somatic embryos. Somatic embryo developmental stage and size, and maturation (incubation) time were also evaluated to improve plantlet formation. All embryos suspended in the fluidized hydroxyethylcellulose gel were viable after six days and 7% developed into plantlets after two weeks. Up to 97% of the somatic embryos suspended in acrylate and/or acrylamide gels died within six days. Root development was at least 10% and plantlet development at least 30% greater when embryos were subcultured on basal medium for 16 instead of 25 days prior to placement and suspension in hydroxyethylcellulose gel. Up to 25% more plantlets were obtained from embryos at the elongated torpedo stage than those at the cotyledonary or torpedo stages of development. When suspended in hydroxyethylcellulose gel embryo length had no effect on the percentage of plantlets obtained.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog medium (1962) - PC copolymer of potassium acrylate and acrylamide - PSA potassium starch polyacrylamide - PA potassium acrylate - HEC hydroxyethylcellulose - ODR oxygen diffusion rate Florida Agr. Expt. Sta., Journal Series No. R-00253 Mention of proprietary products is for convenience of reader only, and does not constitute endorsement by the University of Florida     

Swelling behavior and controlled release of theophylline and sulfamethoxazole drugs in beta-lactoglobulin protein gels obtained by phase separation in water/ethanol mixture

Physically cross-linked beta-lactoglobulin (BLG) protein gels containing theophylline and sulfamethoxazole low molecular weight drugs were prepared in 50% ethanol solution at pH 8 and two protein concentrations (6 and 7% (w/v)). Swelling behavior of cylindrical gels showed that, irrespective of the hydrated or dehydrated state of the gel, the rate of swelling was the highest in water. When the gels were exposed to water, they first showed a swelling phase in which their weight increased 3 and 30 times for hydrated and dehydrated gels, respectively, due to absorption of water, followed by a dissolution phase. The absorption of solvent was however considerably reduced when the gels were exposed to aqueous buffer solutions. The release behavior of both theophylline and sulfamethoxazole drugs from BLG gels was achieved in a time window ranging from 6 to 24 h. The drug release depended mainly on the solubility of the drugs and the physical state of the gel (hydrated or dry form). Analysis of drug release profiles using the model of Peppas showed that diffusion through hydrated gels was governed by a Fickian process whereas diffusion through dehydrated gels was governed partly by the swelling capacities of the gel but also by the structural rearrangements inside the network occurring during dehydration step. By a judicious selection of protein concentration, hydrated or dehydrated gel state, drug release may be modulated to be engineered suitable for pharmaceutical as well as cosmetics and food applications.     

Characterization of kappa-carrageenan gels used for immobilization of Bacillus firmus.

In this study, aimed at a biochemical and physical characterization of kappa-carrageenan gels used for entrapment of Bacillus firmus NRS 783 (a superior producer of an alkaline protease), effects of carrageenan concentration, gelation temperature, initial cell loading, and strength of the curing agent (KCl) on the properties of cell-free and cell-laden gels were examined. The physical properties of the differently prepared gels that were examined included density, free volume fraction, mechanical strength, and change in gel volume during gel curing. The biochemical characteristics studied included viability of gel-entrapped cells, cell leakage from cell-laden gels, and cell penetration into cell-free gels. For the range of carrageenan contents investigated [between 2% and 5% (w/v)], the mechanical strength of the gels with/without KCl curing was observed to increase with an increase in carrageenan content of gels. The mechanical strength of each gel increased substantially upon extensive curing. Free volume fractions in excess of 0.8 were observed for all gels. Of cells that were viable prior to immobilization, 90-92% remained viable after formation and extensive curing of gels for cell-gel mixtures prepared at 45 degrees C. Attempts at prolonged storage of cell-laden gel beads at 0 degrees C as stock cultures of immobilized B. firmus were unsuccessful due to a significant decline in cell viability during such storage. On the basis of the cell leakage studies, the average pore sizes of 2%, 3%, 4%, and 5% gels were deduced to increase in the following order of carrageenan content (w/v): 4%, 3%, 2%, and 5%. Commensurate with the decrease in the average pore size (or the increased tightness of the gels) with increasing carrageenan content, both the extent of cell leakage and the extent of net cell penetration decreased with increasing carrageenan content for the first three gels. Owing to non-uniform distribution of free space and much larger pores, the extent of net cell penetration in 5% carrageenan gels was considerably low, while the extent of cell leakage in 5% carrageenan gels was an order of magnitude greater than the extents of cell leakage in the other three gels.     

Solution NMR of proteins within polyacrylamide gels: Diffusional properties and residual alignment by mechanical stress or embedding of oriented purple membranes

The diffusive properties of biomacromolecules within the aqueous phase of polyacrylamide gels are described. High quality NMR spectra can be obtained under such conditions. As compared to water, a fivefold reduction in the translational diffusion constant, but only a 1.6-fold decrease (1.4-fold increase) in amide-¹⁵N T₂ (T₁) are observed for human ubiquitin within a 10% acrylamide gel. Weak alignment of the solute macromolecules can be achieved within such gels by vertical or radial compression or by the embedding of magnetically oriented purple membrane fragments. The methods are applied to derive residual dipolar couplings for human HIV-1 Nef and ubiquitin.     

Enhanced Heat-induced Gelation of β-Lactoglobulin by α-Lactalbumin

Heat-induced gelation in a mixed system of α-lactalbumin (La) and β-lactoglobulin (Lg) was studied to elucidate the gelling properties of whey protein. An Lg concentration of 4% (w/v) was required for the formation of a self-supporting gel following heating at 80°C for 30 min in a 100 mM potassium phosphate buffer (pH 6.8). Solutions of La, even up to a protein concentration of 8% (w/v), did not gel under the same conditions. The addition of 6% La to 2% Lg caused a significant increase in the gel hardness, although each protein did not individually form a gel at these concentrations. By adding La to Lg, firmer gels were formed at a lower heating temperature, compared to that from Lg alone. La and Lg interacted to form a soluble aggregate through a thiol-disulfide interchange reaction during gel formation, and such an interaction was critical in the formation and stabilization of the gel network structure. We conclude that the enhancing effect of La on the gel hardness of Lg was due to the formation of a specific soluble aggregate, and that such an interaction between these proteins contributes to the properties of whey protein gels.     

Swelling and de-swelling kinetics of gelatin hydrogels in ethanol-water marginal solvent

Controlled osmotic swelling and de-swelling measurements have been performed on gelatin, a polyampholyte, hydrogels suspended in water-ethanol marginal solvent at room temperature (20 degrees C) where the alcohol concentration was changed from 0 to 100% (v/v). The change in gel mass was monitored as function of time until osmotic equilibrium was established with the surrounding solvent. It was observed that osmotic pressure of polymer-solvent mixing, pi(m)相似文献   

Fluorography--limitations on its use for the quantitative detection of 3H- and 14C-labeled proteins in polyacrylamide gels

The suitability of fluorography for the detection of 3H- and 14C-labeled proteins on polyacrylamide gradient gels has been investigated. It was found that the absorbance of the fluorographic film image produced by a given level of radioactivity decreased as the acrylamide concentration in the gel increased. The use of Coomassie brilliant blue protein dyes to stain the gel prior to fluorography reduced the absorbance of the fluorographic image. It is concluded that quantitative fluorography can only be applied to unstained gels of a uniform acrylamide concentration.     

Photo-cross-linking of type I collagen gels in the presence of smooth muscle cells: mechanical properties,cell viability,and function

The effectiveness of photomediated cross-linking of type I collagen gels in the presence of rat aortic smooth muscle cells (RASMC) as a method to enhance gel mechanical properties while retaining native collagen triple helical structure and maintaining high cell viability was investigated. Collagen was chemically modified to incorporate an acrylate moiety. Collagen methacrylamide was cast into gels in the presence of a photoinitiator along with RASMC. The gels were cross-linked using visible light irradiation. Neither acrylate modification nor the cross-linking reaction altered collagen triple helical content. The cross-linking reaction, however, moved the denaturation temperature beyond the physiologic range. A twelve-fold increase in shear modulus was observed after cross-linking. Cell viability in the range of 70% (n = 4, p > 0.05) was observed in the photo-cross-linked gels. Moreover the cells were able to contract the cross-linked gel in a manner commensurate with that observed for natural type I collagen. Methacrylate-mediated photo-cross-linking is a facile route to improve mechanical properties of collagen gels in the presence of cells while maintaining high cell viability. This enhances the potential for type I collagen gels to be used as scaffolds for tissue engineering.     

Changes of the dynamic properties of tamarind (Tamarindus indica) gel with different saccharose and polysaccharide concentrations

The dynamic properties (storage moduli, G′ and loss moduli, G″) of tamarind gels and the influence of saccharose and polysaccharide concentrations were studied using model rings of 3 mm thickness and 20 mm diameter, prepared with three saccharose (55, 60 and 65% w/v) and three polysaccharide concentrations (1.5, 2.0 and 2.5% w/v). Small amplitude oscillatory measures were taken at 25°C in a PHYSICA LS 100 rheometer with parallel plate geometry. Results for the 9 gels showed the zone of linear viscoelasticity between 0.637 and 6.37 Pa of oscillatory shear stress. The mechanical spectra obtained after 24, 48 and 72 h evidenced the presence of syneresis with an increase in G′ as a function of time. The effects of polysaccharide concentrations on gel viscoelasticity were greater than those of saccharose.     

Lignin gel with unique swelling property

Lignin gels were prepared from acetic acid lignin by use of polyethylene glycol diglycidyl ether as cross-linker. The gels were found to swell in aqueous ethanol solution, in particular 50% (v/v) solution. In addition, they also swelled in alkaline solution and shrank upon heating. A literature search showed that investigation on gel swelling in aqueous ethanol has not been reported so far. Gels prepared from the cross-linker alone and its analogues did not show such swelling characteristics in aqueous ethanol. Therefore, the unique swelling property must be attributable to an intrinsic property of lignin.     

Antimicrobial efficacy of alcohol-based hand gels with a 30-s application

Aims: The objective of this study was to assess the antimicrobial efficacy of alcohol‐based hand gels according to European Norm 1500 (EN 1500). Methods and Results: We assessed the antimicrobial efficacy of 12 alcohol‐based hand gels produced in Brazil, containing 70% w/w or v/v ethyl alcohol as the active ingredient, according to EN 1500, with a 30‐s application. In addition, 70% w/w ethyl alcohol and three alcohol‐based hand rubs commonly used in Europe and effective according to EN 1500 were also tested. Eight of 12 (67%) alcohol‐based hand gels produced in Brazil failed by EN 1500. In contrast, 70% w/w ethyl alcohol and European alcohol‐based hand rubs were approved by EN 1500. Conclusions: In this study, the majority of Brazilian alcohol‐based hand gels showed limited efficacy on hand hygiene within 30 s. Significance and Impact of the Study: The findings of this study may be used as an important argument to motivate Brazilian manufacturers to improve the antimicrobial efficacy of alcohol‐based hand gels, because it is prudent to suppose that alcohol‐based hand gels can be recommended for use in healthcare settings only if they show antimicrobial activity at least similar to that of alcohol‐based liquid preparations, including the traditional 70% w/w ethyl alcohol.     

Impact of the structure of arabinoxylan gels on their rheological and protein transport properties

Water-extractable arabinoxylan (WEAX) gels exhibiting different structural, rheological and protein transport properties were obtained upon laccase treatment of WEAX solutions, by modifying (i) the initial ferulic acid (FA) content of WEAX from 2.3 to 1.6 μg/mg AX or (ii) the AX concentration of the WEAX solution from 0.5 to 2.0% (w/v). WEAX gels with di and tri-ferulic acid (di-FA, tri-FA) contents varying from 6.2 to 3.2 μg/ml gel and from 0.61 to 0.27 μg/ml gel, respectively, were obtained. In parallel, increases in gel mesh sizes from 201 to 331 nm and reduction of G′ of gels from 160 to 12 Pa were observed. The differences in structural and rheological characteristics of WEAX gels were reflected in their capacity to load and release proteins of M_w ranging from 43 to 669 kDa. The possibility of modulating protein release from WEAX gels makes these gels potential candidates for the controlled delivery of proteins.     

Characterization and Stability of Emulsion Gels Based on Acrylamide/Sodium Acryloyldimethyl Taurate Copolymer

Sepineo P 600, a concentrated dispersion of acrylamide/sodium acryloyldimethyl taurate copolymer in isohexadecane, has self-gelling and thickening properties and the ability to emulsify oily phases, which make it easy to use in the formulation of gels and o/w emulsion gels. In this paper, gels were prepared using a Sepineo P 600 concentration between the 0.5% and 5% (w/w), and then emulsion gel was also prepared from the 3% Sepineo gel by adding a specific amount of almond oil. All the prepared systems were analyzed and characterized by oscillation rheology and acoustic spectroscopy. The particle size of the oil droplets and the microrheological extensional moduli (G′ and G″) of the systems were determined from acoustic parameters and used together with the classical oscillatory rheological tests to assess the stability of the systems. Classical oscillatory analysis revealed that the dynamic moduli were very dependent on polymer concentration; as this parameter increased, there was progressive improvement in the sample elasticity. In fact, the mechanical spectra of the 0.5% and 1% (w/w) Sepineo samples were characterized by strong frequency dependence and multiple crossover points, typical of dilute polymer solution with no organized structure. On the other hand, the 3–5% (w/w) concentration systems showed typical gel-like spectra, marked by the absence of crossover points between the dynamic moduli and by weak dependence on frequency. Nevertheless, the elastic properties of the gel-like structure even at elevated polymer concentrations were not strongly long-lasting, as demonstrated by the increase of the viscous contribution in the low frequency range during acoustic spectroscopy analysis. This fact could indicate that the gel structure is characterized by weak polymer–polymer interactions, an advantageous characteristic for topical administration, as the sample is thus easier to rub into the skin. Finally, both rheology and acoustic spectroscopy indicated that addition of the oily phase caused minimal changes to the elastic character of the gel. Thus, Sepineo P 600 gel and emulsion gel are very effective systems for use in topical and other types of applications.     

The superiority of the third-generation catalyst,Rhodococcus rhodochrous J1 nitrile hydratase,for industrial production of acrylamide

As the third-generation biocatalyst for industrial production of acrylamide, the superiority of Rhodococcus rhodochrous J1 nitrile hydratase was demonstrated in comparison with other acrylamide-producing bacteria. R. rhodochrous J1 enzyme is much more heat stable and more tolerant to a high concentration of acrylonitrile than Pseudomonas chlororaphis B23 and Brevibacterium R312 enzymes. The J1 enzyme is peculiar in its extremely high tolerance to acrylamide. The hydration reaction of acrylonitrile catalysed by J1 cells proceeded even in the presence of 50% (w/v) acrylamide. The tolerance of J1 enzyme to various organic solvents such as n-propanol and isopropanol was prominent. Using R. rhodochrous J1 resting cells, the accumulation reaction was carried out by feeding acrylonitrile to maintain a level of 6%. After 10 h incubation, the accumulation of acrylamide was approximately 65.6% (w/v) at 10°C, 56.7% (w/v) at 15°C, and 56.0 (w/v) at 20°C. The high stability, high catalytic efficiency and other outstanding features of the J1 enzyme are analysed and discussed. Correspondence to: T. Nagasawa     

Superiority of cobalt induced acrylonitril hydratase of Arthrobacter sp. IPCB-3 for conversion of acrylonitrile to acrylamide

Summary The activity of cobalt induced acrylonitrile hydratase was found to be 130% higher than the iron induced acrylonitrile hydratase in Arthrobaeter sp. IPCB-3. The activity of cobalt induced hydratase was not affected up to 6% (w/v) acrylonitrile and 25% (w/v) acrylamide. However, iron induced hydratase activity was significantly inhibited even at half the concentration of the above components. Such a higher tolerance for the substrate and the product makes the Arthrobacter sp. IPCB-3 a potential candidate for the commercial production of acrylamide.     

Kinetic models for the dynamical behavior of polyacrylamide (PAAm)–κ-carrageenan (κC) composite gels

A fluorescence method was employed for studying the drying and swelling of PAAm–κC composite gels, which were formed from acrylamide (AAm) and N, N’- methylenebisacrylamide (BIS) with various κ–carrageenan (κC) contents by free radical crosslinking copolymerization in water. Composite gels were prepared at 80 °C with pyranine (Py) as a fluorescence probe. Scattered light, I_sc, and fluorescence emission intensities, I_em, were monitored during drying and swelling of these gels. The fluorescence intensity of pyranine increased and decreased as drying and swelling time are increased, respectively, for all gel samples. The Stern–Volmer equation combined with moving boundary and Li-Tanaka models were used to explain the behavior of I_em during drying and swelling processes respectively. It is found that the desorption coefficient D_d decreased as κC contents were increased for a given temperature during drying. However, the cooperative diffusion coefficient, D_s presented exactly the opposite case. Conventional gravimetrical and volumetric experiments were also carried out during drying and swelling of PAAm–κC composite gels. It was observed that D_d and D_s values measured with the fluorescence method were found to be much larger than they were measured with the conventional methods.     

Unusual cell adhesion and antithrombogenic behavior of citric acid-cross-linked collagen matrices

We have developed a novel biodegradable matrix that has unusual cell adhesion and antithrombogenic properties. The prepared biodegradable matrix was alkali-treated collagen (AlCol) cross-linked with citric acid derivative (CAD), named as AlCol-CAD. The swelling ratio of AlCol-CAD decreased with increasing CAD concentration, but with a further increase of the CAD concentration, the swelling ratio of AlCol-CAD also began to increase; this behavior showed a point where the swelling ratio reached a minimum value before increasing. The highest shrinkage states of 7.5%, 15%, and 30% (w/v) in AlCol-CAD were observed at CAD concentrations of 10, 20, and 40 mM, respectively, and moreover, the residual amino groups in AlCol-CAD were found to decrease with increasing CAD concentration. On the other hand, increases in carboxyl groups of 7.5% and 15% (w/v) in AlCol-CAD were found at CAD concentrations higher than 10 and 20 mM, respectively, whereas, at CAD concentrations from 10 to 40 mM, no significant change of the carboxyl groups was observed in 30% (w/v) AlCol-CAD. Human umbilical vein endothelial cell (HUVEC) adhesion on 15% (w/v) AlCol-CAD increased with increasing CAD concentration up to 20 mM and then slightly decreased. In the case of 30% (w/v) AlCol-CAD, the number of adhered HUVECs on AlCol-CAD increased with increasing CAD concentration. Furthermore, it was observed that HUVECs had excellent cell proliferation on 15% (w/v) AlCol-CAD at CAD concentrations of 20 and 40 mM, after incubation for 7 days. No thrombus formation was observed on 15% (w/v) AlCol-CAD at CAD concentrations above 20 mM. These results suggested that the 15% (w/v) AlCol-CAD at CAD concentrations above 20 mM has both HUVEC adhesion and antithrombogenic properties.     

Cell adhesion and proliferation on poly(N-vinylacetamide) hydrogels and double network approaches for changing cellular affinities

Poly(N-vinylacetamide) hydrogels (PNVA gels) were synthesized to investigate their basic characteristics for biomedical applications such as water contact angles, protein uptake, and mouse fibroblasts (L-929) cell adhesion. Because PNVA gels show hydrophilic features, double network (DN) hydrogels were prepared by the secondary polymerization of N-vinylacetamide (NVA) or acrylamide (AAm) in PNVA gels (NVA/NVA DN gels and NVA/AAm DN gels, respectively), in order to vary PNVA gel features for biocompatibility. Contact angles for both DN gels decreased to around 20 degrees, whereas both PNVA and PAAm gels were over 30 degrees. On the other hand, more protein tended to adsorb to DN gels than single network hydrogels. Compared to PNVA gel, cell adhesion and proliferation on NVA/NVA DN gel were improved with less swelling ratio and much protein uptake, while no significant difference was observed on NVA/AAm DN gel, probably due to more hydrophilic character, supported by lowest water contact angle. These complicated structure change in DN gels would provide a new methodology for tuning the biocompatibility of hydrogels and for controlling surface hydrophilic characteristics and network structures.     

Electrophoresis of small proteins in highly concentrated and crosslinked polyacrylamide gradient gels

A high concentration (40%) of acrylamide plus N,N′-methylenebisacrylamide combined with a high level of crosslinking (12.5%) yielded clear gels capable of restricting the passage of small proteins. This gel composition was chosen in preference to other combinations, in particular those producing opaque gels which have larger pore sizes and which provide a reduced sieving effect. Gradient gels were prepared in which the gel concentration rose from 3 to 40% and the degree of crosslinking increased from 4 to 12.5%. Such gels were suitable for fractionating crude, unreduced, and uncharacterized extracts containing proteins ranging in molecular size from 10,000 to several million daltons under conditions where all proteins are retained on the gel even after prolonged electrophoresis. The gels yielded zones which were of improved sharpness and resolution compared with gels of lower concentration and degree of crosslinking, and can be used to provide an estimate of molecular size. Examples of the use of HX gradient gels included both anodic and cathodic electrophoresis at pH 8.3 and 3.1, respectively, of serum and cereal-grain proteins and a partial enzymic hydrolysate of serum albumin.