| 1. |
- Andersson, M, et al.
(författare)
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Determination of the pore-size distribution in gels
- 1995
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Ingår i: Bioseparation. - 1573-8272. ; 5:2, s. 65-72
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Tidskriftsartikel (refereegranskat)abstract
- A method for determination of the accessible volume fraction in gels as function of the molecular weight of the solutes is presented. The pore-size distribution is determined by measuring the rate of diffusion of a mixture of solutes into a gel using gel filtration for separation. The solutes, of various sizes, are detected by refractive index measurements. Two marker molecules (blue dextran and glucose) were used to determine the gel void and the amount of liquid adhering to the surface. The technique is simple and can easily be adapted to other systems of a porous nature (membranes, catalyst pellets etc.). The method is applied to an N-isopropylacrylamide gel. This gel is sensitive to temperature changes. A considerable increase in volume is obtained when the temperature is decreased. This makes it suitable for use as a separation agent in gel extraction. In order to assess the performance of this unit operation the pore size distribution for the N-isopropylacrylamide gel was determined at 10 degrees C, 20 degrees C and 30 degrees C, using mixtures of different dextrans as well as different polyethylene glycols.
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| 2. |
- Andersson, M, et al.
(författare)
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Diffusion of glucose and insulin in a swelling N-isopropylacrylamide gel
- 1997
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Ingår i: International Journal of Pharmaceutics. - 1873-3476. ; 157:2, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- The diffusional characteristics for poly(N-isopropylacrylamide) (NiPAAm) gel have been investigated. This gel is a critical gel which means that small changes in the environment influence the gel volume considerably. The effective diffusion coefficients for the solutes glucose and insulin were determined in batch experiments with the solutes diffusing out from small cylindrical gel bodies with diameters of 2.4-2.9 mm and at temperatures below the critical temperature: 10, 20 and 30 degrees C. The effective diffusion coefficients were obtained by fitting the experimental data to a mathematical model considering back-mixing and time delay in the experimental set-up, dilution due to the adsorbed liquid on the gel bodies and partition due to the exclusion effect. The effective diffusion coefficient for glucose increases from 2.7.10(-10) to 4.7.10(-10) m(2)/s when the temperature increases from 10 to 30 degrees C, following the Wilke-Chang relationship. This implies that the effect of the network is negligible compared with the effect of the temperature. However, for a solute with a molecular weight of about 6000 the network has a considerable effect. The effective diffusion coefficient for insulin increases from 4.4.10(-10) to 5.9.10(-10) m(2)/s when the temperature increases from 10 to 30 degrees C, which is less than expected from the Wilke-Chang relationship. This indicates an increased resistance for diffusion inside the gel due to shrinking. (C) 1997 Elsevier Science B.V.
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| 3. |
- Andersson, M, et al.
(författare)
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Swelling kinetics of poly(N-isopropylacrylamide) gel
- 1998
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Ingår i: Journal of Controlled Release. - 1873-4995. ; 50:1-3, s. 273-281
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Tidskriftsartikel (refereegranskat)abstract
- In many gel applications the swelling and shrinking kinetics are very important, e.g. in controlled/slow release, where the kinetics determine the rate of out-diffusion of the active component, and in gel extraction where the gel is swollen and shrunk several times. In this study swelling kinetics of poly(N-isopropylacrylamide) gel (NiPAAm gel) was determined by monitoring the swelling process using a stereo microscope and a video camera. The swelling of spherical gel bodies could conveniently be studied after a temperature change. The results obtained were treated according to the approach of Tanaka and Fillmore, in which the swelling and shrinking of a gel is described as a motion of the gel network according to the diffusion equation. This was shown to be valid when the temperature changes are kept below the critical point of the gel. However, the model fails to describe the shrinking process when passing from below to above the critical temperature. The collective diffusion coefficient (D), defined as the osmotic bulk modulus divided by the friction factor, was determined by fitting to the experimental data. D was found to increase with temperature according to the Wilke-Chang relation D=2.0.10(-11)+7.6.10(-17).T/mu. The results were used to simulate the swelling/shrinking process. The simulations show the importance of having sufficiently small gel bodies to achieve a short swelling time. (C) 1998 Elsevier Science B.V.
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| 4. |
- Axelsson, Anders, et al.
(författare)
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Economic evaluation of the hydrolysis of lactose using immobilized beta-galactosidase
- 1990
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 24-5, s. 679-693
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Tidskriftsartikel (refereegranskat)abstract
- A computer program for preliminary cost estimates of free and immobilized enzyme systems has been developed. The cost for the hydrolysis of lactose by β-galactosidase fromAspergillus oryzae has been calculated for a batch tank reactor, with free (BTRF) and immobilized (BTRI) enzymes, a continuously stirred tank reactor (CSTR) and a plug-flow tubular reactor (PFTR), considering the mass transfer behavior and deactivation of the enzyme. Enzyme immobilization is economically feasible, compared with a system with free enzymes, despite a very high cost for the enzyme attachment. At a half-life time of 80 d, the PFTR gives the lowest cost (0.48 SEK/kg lactose), but the cost for the BTRI is just slightly higher (0.66 SEK/kg lactose) and still much lower than the BTRF (2.10 SEK/kg lactose).
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| 5. |
- Axelsson, Anders, et al.
(författare)
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Performance of batch and continuous reactors with co-immobilized yeast and beta-galactosidase
- 1991
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Ingår i: Journal of Chemical Technology and Biotechnology. - : Wiley. - 0268-2575 .- 1097-4660. ; 52:2, s. 227-241
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Tidskriftsartikel (refereegranskat)abstract
- The anaerobic fermentation of deproteinized whey with beta-galactosidase coimmobilized with Saccharomyces cerevisiae in calcium alginate gel beads for the production of ethanol has been studied in a continuous horizontal packed bed reactor (HPBR). The results are compared with batch experiments in a stirred tank reactor. The immobilized yeast cells are exposed to conditions that vary with time and location in the reactor, making a true steady state impossible. In spite of a very low specific growth rate-of the order of 0.01 h-1 in the first section of the HPBR-the yeast cell growth, accompanied by bead expansion in this section, was high enough to create a cell concentration gradient along the reactor. The continuous reactor is preferable to the batch reactor as the galactose conversion is more efficient. The highest volumetric productivity obtained in the HPBR was 125 mol ethanol m-3 h-1 (6 g ethanol dm-3 h-1) at a substrate concentration of 164 mol m-3 lactose (56 g dm-3) and a dilution rate of 0.21 h-1, corresponding to a space velocity of 0.51 dm3 dm-3 gel h-1. The ethanol yield from consumed glucose and galactose was 80%. The ethanol yield from lactose was only 70%, as only 75% of the galactose was consumed while all the lactose and glucose were converted.
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| 6. |
- Axelsson, Anders, et al.
(författare)
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Simulation of batch and continuous reactors with co-immobilized yeast and β-galactosidase
- 1991
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Ingår i: Journal of Chemical Technology and Biotechnology. - : Wiley. - 0268-2575 .- 1097-4660. ; 52:4, s. 481-497
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Tidskriftsartikel (refereegranskat)abstract
- A reaction-diffusion model was used to simulate a co-immobilized system utilizing the numerical method of orthogonal collocation. The production of ethanol from deproteinized whey using beta-galactosidase co-immobilized with Saccharomyces cerevisiae in calcium alginate gel beads was chosen as a model system. Calculated concentrations of lactose, glucose, galactose and ethanol were compared with experimental data for a batch reactor and a continuous horizontal packed-bed reactor. The mathematical model has been used to analyse the influence of internal and external mass transfer for the continuous reactor. The external mass transfer was shown to be of minor importance. The introduction of baffles decreased the backmixing in the horizontal packed-bed reactor. Internal mass transfer was found to be the main cause of the reduction in the apparent reaction rate. Thus, much of the expected increase in reaction rate is diminished by mass transfer hindrance when the cell concentration is increased.
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| 7. |
- Carlsson, F, et al.
(författare)
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Mathematical modelling and parametric studies of affinity chromatography
- 1994
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Ingår i: Computers & Chemical Engineering. - 1873-4375. ; 18:suppl. 1, s. 657-661
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Tidskriftsartikel (refereegranskat)abstract
- In this study a model based on mass transfer and sorption rate constants with physical significance is used for simulation of affinity chromatography, The simulation program has been used to perform a parametric analysis of the adsorption of lysozyme on Cibacron Blue-Sepharose CL-6B. The influence of process parameters as well as physical parameters on the chromatography process was investigated. The external and the internal mass transfer as well as the sorption rate were found to contribute to the control of the overall rate of the system. The most important process parameter was the radius of the beads. The optimum bead size was found to be around 50 mu m.
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| 8. |
- Gustafsson, N O, et al.
(författare)
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Measurement of diffusion coefficients in gels using holographic laser interferometry
- 1993
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Ingår i: Biotechnology Progress. - : Wiley. - 1520-6033 .- 8756-7938. ; 9:4, s. 436-441
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy and precision of holographic interferometry as a method to measure diffusion coefficients in gels are investigated both experimentally and theoretically. The standard deviations in the experimentally determined diffusion coefficient for ethanol in 4% (w/v) agarose gel were 3.3% for diffusion into the gel and 6.1% for diffusion out of the gel. These are in good agreement with the standard deviations obtained using Monte Carlo simulations. Systematic errors derived from an assumption of constant diffusion coefficients were also investigated.
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| 9. |
- Karlsson, David, et al.
(författare)
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Electronic speckle pattern interferometry: A tool for determining diffusion and partition coefficients for proteins in gels
- 2002
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Ingår i: Biotechnology Progress. - : Wiley. - 1520-6033 .- 8756-7938. ; 18:6, s. 1423-1430
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to demonstrate electronic speckle pattern interferometry (ESPI) as a powerful tool in determining diffusion coefficients and partition coefficients for proteins in gels. ESPI employs a CCD camera instead of a holographic plate as in conventional holographic interferometry. This gives the advantage of being able to choose the reference state freely. If a hologram at the,reference state is taken and compared to a hologram during the diffusion process, an interferometric picture can be generated that describes the refraction index gradients and thus the concentration gradients in the gel as well as in the liquid. MATLAB is then used to fit Fick's law to the experimental data to obtain the diffusion coefficients in gel and liquid. The partition coefficient is obtained from the same experiment from the flux condition at the interface between gel and liquid. This makes the comparison between the different diffusants more reliable than when the measurements are performed in separate experiments. The diffusion and partitioning coefficients of lysozyme, BSA, and IgG in 4% agarose gel at pH 5.6 and in 0.1 M NaCl have been determined. In the gel the diffusion coefficients were 11.2 +/- 1.6, 4.8 +/- 0.6, and 3.0 +/- 0.3 m(2)/s for lysozyme, BSA, and IgG, respectively. The partition coefficients were determined to be 0.65 +/- 0.04, 0.44 +/- 0.06, and 0.51 +/- 0.04 for lysozyme, BSA, and IgG, respectively. The current study shows that ESPI is easy to use and gives diffusion coefficients and partition coefficients for proteins with sufficient accuracy from the same experiment.
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| 10. |
- Kempe, Henrik, et al.
(författare)
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Determination of diffusion coefficients of proteins in stationary phases by frontal chromatography
- 2006
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 93:4, s. 656-664
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Tidskriftsartikel (refereegranskat)abstract
- A strategy to determine effective diffusion coefficients of proteins in chromatographic gels is presented in this article. An experimental methodology based on frontal liquid chromatography was combined with a numerical methodology based on a mathematical model describing the chromatographic process including the extra-column dispersion, the dispersion due to the packed bed, the external mass transfer from the bulk phase to the stationary phase, and the diffusive transport within the stationary phase. The methodology has several advantages compared to previously reported methods to determine diffusion coefficients in that no other equipment than an HPLC is required, any class of stationary phases can be investigated as long as the experiments are performed under non-binding conditions, and no modification, e.g., moulding of slabs or membranes, to the stationary phase is required. To show the applicability of the methodology, the effective diffusion coefficients of lysozyme, bovine serum albumin, and immunoglobulin gamma in Sepharose (TM) CL-4B were determined and shown to be comparable with those determined with other methods. (c) 2005 Wiley Periodicals, Inc.
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