Development of a model for membrane filtration of long and flexible macromolecules: Application to predict dextran and linear DNA rejections in ultrafiltration

Abstract

a b s t r a c tA model is proposed for predicting the intrinsic rejections of linear flexible molecules, of high molecular dimensions, in microfiltration and ultrafiltration membranes. The developed model is based on the available theory of hindered transport of solutes through narrow pores, assuming that convection is the only relevant transport mechanism. For the application of the model, partition coefficients of the solutes between the solution and the membrane were estimated by a stochastic simulation, assuming suction of the macrosolutes into the pore. In these simulations, the macromolecules were modeled as freely jointed chains. Different methods for the estimation of the molecular dimensions of the solutes are discussed. The validity of the model was tested using dextran T2000 and plasmid pUC19 in its linear isoform, as model solutes; the tests were performed using membranes of different pore size, that include two ultrafiltration membranes previously characterized, having 4.1 and 10.5 nm of pore radius, and two track-etched polycarbonate membranes, having 15 and 40 nm of pore radius. Filtration was performed in a stirred cell, at controlled permeate flux. Different conditions of stirring speed and permeate flux were tested to check the consistency of the model. The results show that very satisfactory predictions are obtained, considering the simplicity of the model, especially in the case of the plasmid.

Plasmid DNA recovery from fermentation broths by a combined process of micro- and ultrafiltration: Modeling and application

“…(12) of [26], respectively, and the gyration radius from r s , using Eq. (6) of [26]. The intrinsic sieving coefficient of linear dsDNA can be predicted in membrane filtration using the FJC approach, like in the case of RNA modeling.…”

“…Under this approach, these molecules are considered to be linear and highly flexible, a property that should explain their ability of permeating through pores of considerable smaller size than their hydrodynamic radii, like in the case of pDNA. Using the FJC model approach, the radius of gyration of the different types of RNA can be approximately estimated as 1.5 times the value of r s [26]. With the r g values and the average pore radii of the membranes studied in this work S m values can be estimated using Eq.…”

“…After the solid/liquid diafiltration operation a second membrane operation was tested to concentrate, and at the same time, purify the plasmid. For this purpose an ultrafiltration membrane was selected, with 100 kDa of molecular weight cut-off in fluoro polymer, FS40PP from DSS/Alfa Laval, which has a pore size of 4.1 nm [26]. Concentration of the permeates from tests MF-A, MF-B and MF-C was performed at the constant pressure of 1 bar to a volumetric concentration factor of 3.0.…”

“…The study included modeling the permeation of the plasmid in the two membrane steps, using a recently published theoretical model [25]. A model for permeation of flexible linear polymers adapted from [26] to include, like in the case of the plasmid, electric charge effects on mass transfer, is used here for the first time to predict the sieving coefficients of the main different types of RNA present in the lysates, and also to interpret experimental results of gDNA removal in the ultrafiltration operation. The study of the effect of the ionic strength on the permeation of pDNA, gDNA, RNA and proteins, in the two membrane steps was also carried out, as well as the effect of CaCl 2 addition to the lysates before filtration.…”

Ultrafiltration of supercoiled plasmid DNA: Modeling and application

“…This phenomenon was attributed to conformational changes of the plasmids with the decrease of electrostatic repulsion between their phosphate groups, as the ionic strength increases, thus becoming more compact molecules [22]. Following an independent approach for explaining the permeation of long flexible molecules through membranes with narrow pores, Morão et al [27] developed a model for the estimation of the solute partition coefficient at the membrane surface, ˚, under the assumption that, besides molecular deformation induced by the flow, it is also required for permeation that the molecule has an adequate molecular conformation and orientation, when approaching the pore. For that purpose, a Monte Carlo method was developed to estimate the probability of permeation under dynamic conditions of filtration, which can be identified with [ 27].…”