Protein Adsorption Kinetics Research Articles

Zeolite inorganic supports for BSA immobilization: Comparative study of several zeolite crystals and composite membranes

Zeolites due to their low toxicity and high compatibility are considered new biomaterials for medical applications. The surface adsorption behaviour of zeolite crystals and composite membranes was discussed in this research. The zeolite materials were synthesized by hydrothermal syntheses using different reaction gels to modulate the Brönsted acidity of the microporous structures. Spectrophotometric analyses were used to evaluate protein adsorption on these surfaces. This study revealed that zeolite chemical composition and structure influenced the kinetics of protein adsorption. Zeolite Y surface adsorbed greater amount of BSA than the other structures. The percentage of adsorption increases with temperature and depends on the pH of the solution, being highest at the p I of the protein. The influence of the membrane configuration on the protein adsorption was studied using different zeolite structures and crystallization types. It seems that the observed differences could depend on the type of hydrothermal crystallization inside the inorganic support.

Protein adsorption kinetics of mixed-mode adsorbent with benzylamine as functional ligand

Adsorption kinetics of bovine serum albumin (BSA) to mixed-mode adsorbent with benzylamine ligand was studied via stirred-batch uptake experiments. The effects of liquid-phase conditions, such as salt concentration and pH, on the uptake rates of BSA were evaluated by effective pore diffusivity ( D e ) derived from the pore diffusion model (PDM). The results indicated that when electrostatic attractive interactions exist between protein and ligand, D e increases firstly with increasing salt concentration and then turns to decreasing after reaching the maximum. When there are electrostatic repulsion protein/ligand interactions, it seems that the adsorption process is patch controlled, and the specific salt concentration to result in a minimum adsorption capacity could be found. The value of D e showed a similar tendency to the change of adsorption capacities. With the increase of salt concentration, the increase in D e value was considered due to the decrease of electrostatic repulsion interactions and increase of hydrophobic interactions between BSA and ligand. Since BSA has the most compact structure at the isoelectric point, which leads to lower hydrodynamic forces, it is reasonable that the maximum of effective diffusion coefficient could be found around the isoelectric point.

Miscibility of Binary Monolayers at the Air−Water Interface and Interaction of Protein with Immobilized Monolayers by Surface Plasmon Resonance Technique

The miscibility and stability of the binary monolayers of zwitterionic dipalmitoylphosphatidylcholine (DPPC) and cationic dioctadecyldimethylammonium bromide (DOMA) at the air-water interface and the interaction of ferritin with the immobilized monolayers have been studied in detail using surface pressure-area isotherms and surface plasmon resonance technique, respectively. The surface pressure-area isotherms indicated that the binary monolayers of DPPC and DOMA at the air-water interface were miscible and more stable than the monolayers of the two individual components. The surface plasmon resonance studies indicated that ferritin binding to the immobilized monolayers was primarily driven by the electrostatic interaction and that the amount of adsorbed protein at saturation was closely related not only to the number of positive charges in the monolayers but also to the pattern of positive charges at a given mole fraction of DOMA. The protein adsorption kinetics was determined by the properties of the monolayers (i.e., the protein-monolayer interaction) and the structure of preadsorbed protein molecules (i.e., the protein-protein interaction).

Determination of the Quantitative Relationships between the Synthesis Conditions of Macroporous Poly(styrene-co-divinylbenzene) Microparticles and the Characteristics of Their Behavior as Adsorbents Using Bovine Serum Albumin as a Model Macromolecule

The adsorption properties of macroporous polymeric microparticles are dependent on their porous structure, which, in turn, is dependent on the synthesis conditions of the adsorbent material. In the present work, we have investigated whether it is feasible to find a quantitative relationship between the synthesis conditions of macroporous poly(styrene-co-divinylbenzene) adsorbent microparticles and their behavior in the adsorption of a protein of intermediate size. For this purpose, 10 types of such microparticles were synthesized from reactive mixtures with different divinylbenzene (cross-linker) and n-heptane (diluent) contents, and the equilibrium isotherms and adsorption kinetics of a model protein (the bovine serum albumin (BSA) protein) were studied. The results allowed us to determine some quantitative relationships that, within the limits of this research, permit the synthesis of adsorbents with predetermined adsorption properties. Thus, the model obtained, relating the synthesis conditions of the ...

Regulation of the biological properties of medical polymer materials with the use of a gas-discharge plasma and vacuum ultraviolet radiation

The mechanisms of the interaction of a gas-discharge plasma and vacuum ultraviolet (VUV) radiation with medical polymers were considered. Various techniques were proposed for the use of plasma-chemical and photochemical processes for enhancing the biocompatibility of medical polymers. The plasma-chemical and photochemical processes for the surface functionalization and regulation of the biological characteristics of medical polymers by the immobilization of proteins, biologically active compounds, and liquid-crystal biosensors were described. The relationships of the surface processes that occur in the VUV photolysis of polymers with the kinetics of protein adsorption and the adhesion of blood cell components were analyzed.

Use of polysaccharides to control protein adsorption to the air–water interface

In order to understand foaming behaviour of mixed protein/anionic polysaccharide solutions, we investigated the effect of β-lactoglobulin/pectin interaction in the bulk on β-lactoglobulin adsorption to the air–water interface. Adsorption kinetics were evaluated by following surface pressure development in time of several pure protein solutions and of mixed protein/polysaccharide solutions using an automated drop tensiometer (ADT). It was found that complexation of proteins with polysaccharides can slow down the kinetics of surface pressure development by at least a factor 100, and greatly diminish foam formation. In contrast, a five times acceleration in the increase of surface pressure was observed in other cases. We propose a mechanism for protein adsorption from mixed protein/polysaccharide solutions. Effects of ionic strength, pH and mixing ratio on this mechanism were studied for mixtures of β-lactoglobulin and low methoxyl pectin, whereas other proteins and anionic polysaccharides were used to explore the role of protein and polysaccharide charge density and distribution. Whereas the possibilities to change system parameters like ionic strength or pH are limited in food related systems, selecting a suitable combination of protein and polysaccharide offers a broad opportunity to control protein adsorption kinetics and with that foam formation.

Adsorption kinetics of proteins at the solution/air interfaces with controlled bulk convection

The adsorption kinetics of β-casein, β-lactoglobulin and HSA is studied at solution/gas interface with and without forced convection. It is shown that, in spite of a significant difference in the adsorption rates for these two experiments by one order of magnitude, the equilibrium surface tension values are virtually the same. This leads to the conclusion about the thermodynamic reversibility of protein adsorption at the solution/gas interface, in contrast to the kinetic irreversibility of the process.

Fate of Prions in Soil: Adsorption Kinetics of Recombinant Unglycosylated Ovine Prion Protein onto Mica in Laminar Flow Conditions and Subsequent Desorption

Prions can be disseminated in soils. Their interaction with soil minerals is a key factor for the assessment of risks associated with the transport of their infectivity. We did not examine here the infectivity itself but the adsorption kinetics of an ovine recombinant prion protein (ovine PrPrec), as a noninfectious model protein, on muscovite mica, a phyllosilicate with surface properties analogous to soil clays, in conditions of laminar flow through a channel. The protein was labeled with (125)I, and its adsorption examined between pH 4.0 and 9.0. At wall shear rate 100 s(-1), we found the process to be controlled mainly by transport at the beginning of the adsorption process. Additional experiments at 1000 s(-1) (pH 5 and 6) determined that the diffusion coefficient was in accordance with the hydrodynamic radius measured by size exclusion chromatography. The pseudo-plateau of the interfacial concentration with time was compatible with more than a monolayer and suggests the presence of aggregates. Desorption was not observed in the presence of buffer between pH 4 and 9 and sheep plasma, while the addition of alkaline detergent or 10(-1) M NaOH allowed an almost complete removal from the interface. The ensemble of results suggests that the largely irreversible adsorption of the ovine PrPrec onto mica is mainly due to electrostatic attraction between the protein and the highly negatively charged mica surface. Possible consequences for the mode of dissemination of prion proteins in soils are indicated.

Kinetics of Protein Adsorption and Desorption on Surfaces with Grafted Polymers

The kinetics of protein adsorption are studied using a generalized diffusion approach which shows that the time-determining step in the adsorption is the crossing of the kinetic barrier presented by the polymers and already adsorbed proteins. The potential of mean-force between the adsorbing protein and the polymer-protein surface changes as a function of time due to the deformation of the polymer layers as the proteins adsorb. Furthermore, the range and strength of the repulsive interaction felt by the approaching proteins increases with grafted polymer molecular weight and surface coverage. The effect of molecular weight on the kinetics is very complex and different than its role on the equilibrium adsorption isotherms. The very large kinetic barriers make the timescale for the adsorption process very long and the computational effort increases with time, thus, an approximate kinetic approach is developed. The kinetic theory is based on the knowledge that the time-determining step is crossing the potential-of-mean-force barrier. Kinetic equations for two states (adsorbed and bulk) are written where the kinetic coefficients are the product of the Boltzmann factor for the free energy of adsorption (desorption) multiplied by a preexponential factor determined from a Kramers-like theory. The predictions from the kinetic approach are in excellent quantitative agreement with the full diffusion equation solutions demonstrating that the two most important physical processes are the crossing of the barrier and the changes in the barrier with time due to the deformation of the polymer layer as the proteins adsorb/desorb. The kinetic coefficients can be calculated a priori allowing for systematic calculations over very long timescales. It is found that, in many cases where the equilibrium adsorption shows a finite value, the kinetics of the process is so slow that the experimental system will show no adsorption. This effect is particularly important at high grafted polymer surface coverage. The construction of guidelines for molecular weight/surface coverage necessary for kinetic prevention of protein adsorption in a desired timescale is shown. The time-dependent desorption is also studied by modeling how adsorbed proteins leave the surface when in contact with a pure water solution. It is found that the kinetics of desorption are very slow and depend in a nonmonotonic way in the polymer chain length. When the polymer layer thickness is shorter than the size of the protein, increasing polymer chain length, at fixed surface coverage, makes the desorption process faster. For polymer layers with thickness larger than the protein size, increases in molecular weight results in a longer time for desorption. This is due to the grafted polymers trapping the adsorbed proteins and slowing down the desorption process. These results offer a possible explanation to some experimental data on adsorption. Limitations and extension of the developed approaches for practical applications are discussed.

Predictive modeling of protein adsorption along the bed height by taking into account the axial nonuniform liquid dispersion and particle classification in expanded beds

Expanded bed adsorption (EBA) is a special chromatography technique with perfect classification of adsorbent particles in the column, thus the performance of protein adsorption in expanded beds is particular, obviously nonuniform and complex along the column. Detailed description of the complex adsorption kinetics of proteins in expanded bed is essential for better analyzing of adsorptive mechanisms, the design of chromatographic processes and the optimization of operation parameters of EBA processes. In this work, a theoretical model for the prediction of protein adsorption kinetics in expanded beds was developed by taking into account the classified distribution of adsorbent particles along the bed height, the nonuniform behaviors of axial liquid dispersion, the axial variation of local bed voidage as well as the axial changes of target component mass transfer. The model was solved using the implicit finite difference scheme combining with the orthogonal collocation method, and then applied to predict the breakthrough behaviors of bovine serum albumin (BSA) on Streamline DEAE and lysozyme on Streamline SP along the bed height in expanded beds under various conditions. In addition, the experiments of front adsorption of BSA on Streamline DEAE at different axial column positions were carried out to reveal the adsorption kinetics of BSA along the bed height in a 20 mm I.D. expanded bed, and the influences of liquid velocity and feed concentration on the breakthrough behaviors were also analyzed. The breakthrough behaviors predicted by the present model were compared with the experimental data obtained in this work and in the literature published. The agreement between the prediction and the experimental breakthrough curves is satisfied.

Adsorption kinetics of plasma proteins on solid lipid nanoparticles for drug targeting

The interactions of intravenously injected carriers with plasma proteins are the determining factor for the in vivo fate of the particles. In this study the adsorption kinetics on solid lipid nanoparticles (SLN) were investigated and compared to the adsorption kinetics on previously analyzed polymeric model particles and O/W-emulsions. The adsorbed proteins were determined using two-dimensional polyacrylamide gel electrophoresis (2-DE). Employing diluted human plasma, a transient adsorption of fibrinogen was observed on the surface of SLN stabilized with the surfactant Tego Care 450, which in plasma of higher concentrations was displaced by apolipoproteins. This was in agreement with the “Vroman-effect” previously determined on solid surfaces. It says that in the early stages of adsorption, more plentiful proteins with low affinity are displaced by less plentiful with higher affinity to the surface. Over a period of time (0.5 min to 4 h) more interesting for the organ distribution of long circulating carriers, no relevant changes in the composition of the adsorption patterns of SLN, surface-modified with poloxamine 908 and poloxamer 407, respectively, were detected. This is in contrast to the chemically similar surface-modified polymeric particles but well in agreement with the surface-modified O/W-emulsions. As there is no competitive displacement of apolipoproteins on these modified SLN, the stable adsorption patterns may be better exploited for drug targeting than particles with an adsorption pattern being very dependent on contact time with plasma.

Mucin at solution/air and solid/solution interfaces

In this paper the surface activity of protein mucin at solution/air interface has been studied. The experiments of the adsorbed protein at solution/air interface have been carried out with a range of protein concentrations at a defined pH. The adsorption of the protein to solid surfaces and the degree of hydrophobicity at solid/solution interface of mucin have been evaluated at different pH and in the presence of Hofmeister electrolyte. The results from these studies have been further substantiated by surface potential measurements of mucin covered surface on stainless steel. Quartz crystal microbalance (QCM) has been used to follow the protein adsorption kinetics from solution to solid surface. The results from these measurements show that the adsorption behavior has a remarkable dependence on the degree of maximum coverage and is almost independent of the ionic strength. Other characteristic features such as maximum adsorption values at the protein isoelectric point (IEP4.7) and low-affinity isotherms that showed surface saturation even under unfavorable electrostatic conditions have been observed. The amount of mucin adsorbed in the presence of electrolytes has been estimated using electron spectroscopy for chemical analysis (ESCA). The study clearly shows that there exists an inverse relationship between the hydrophobicity and surface tension of the protein and also on the hydrated radius of Hofmeister electrolyte used.

Equilibrium and Dynamic Characteristics of Protein Adsorption Layers at Gas-Liquid Interfaces: Theoretical and Experimental Data

Within the framework of a nonideal two-dimensional solution model, equations are derived for the state of a surface layer, adsorption isotherms, and the distribution function of adsorbed protein molecules with respect to their states characterized by different molar surface areas. The derived equations satisfactorily describe the known experimental dependences obtained for equilibrium adsorption layers of some proteins (serum albumin, β-casein, and β-lactoglobulin): the dependences of the surface pressure on concentration and adsorption, the surface layer thickness on adsorption, and the limiting high-frequency elastic modulus of an adsorption layer on the surface pressure. All dependences for a given protein are described by the same set of parameters of the theoretical model. It is shown that the kinetics of protein adsorption studied by dynamic tensiometry, ellipsometry, and the radiotracer technique is consistent with the diffusion model comprising the Ward-Tordai equation and the set of equations describing the equilibrium. The kinetics of protein desorption from the adsorption layer at a liquid-fluid interface is analyzed. The kinetics of β-lactoglobulin desorption is shown to be described by the barrier mechanism.

Two-component protein adsorption kinetics in porous ion exchange media

This work provides a theoretical analysis of multicomponent adsorption kinetics for conditions typical of protein adsorption in porous ion exchangers as well as experimental results for the adsorption of lysozyme/cytochrome c mixtures in the cation exchanger SP-Sepharose-FF. The theory predicts the formation of overshoots in the intraparticle concentration profiles and in the total amount adsorbed for the more weakly adsorbed component. An analytical solution valid for the case where the isotherms are rectangular is developed and found to be in good agreement with the limiting behavior of the general numerical solution of the model equations. The experimental results show that the two proteins are competitively adsorbed and that an overshoot of adsorbed cytochrome c occurs during simultaneous adsorption. Model predictions based on the assumption that the adsorption isotherms are rectangular and that lysozyme completely displaces cytochrome c are in qualitative and quantitative agreement with the experimental kinetics suggesting that the overshoot phenomena observed with multicomponent systems in these resins can be explained with a diffusion model without the need to account for flux coupling or electrophoretic contributions to transport.

Dynamics of protein adsorption at the oil–water interface: comparison with a theoretical model

A novel procedure of analysis of protein adsorption at liquid interfaces is proposed in terms of the steady state (equilibrium) surface pressure–concentration curves and also the dynamic interfacial tension–time curves obtained for each individual protein concentration. The analysis is performed on the basis of a thermodynamic model that has been recently extended to the study of adsorption dynamics. The procedure presented is based on the modification of the area values given to the protein at the oil–water interface with respect to those used at the air–water interface. This is done in order to account for the differences inferred from the experimental data. In this manner, and in view of the excellent correlation found between theory and experiment, the model substantially deepens the understanding of the adsorption process in two steps. Firstly, the fitting of the equilibrium isotherm provides a set of characteristic parameters that quantifies the interfacial structure adopted by the protein at the oil–water interface in terms of the partial molar area. Subsequently, the optimal set of parameters obtained by this procedure is also used in the fitting of the dynamic curves and similarly the area parameters changed according to experimental findings. Such practice yields as a conclusion a direct relationship between the degree of interfacial unfolding attained by the protein at the tetradecane–water interface and the bulk concentration, representing an innovative quantification of the kinetics of protein adsorption.

Protein adsorption in static microsystems: effect of the surface to volume ratio

A numerical model for the adsorption kinetics of proteins on the walls of a microchannel has been developed using the finite element method (FEM) to address the coupling with diffusion phenomena in the restricted microchannel volume. Time evolutions of the concentration of one species are given, both in solution and on the microchannel walls. The model illustrates the adsorption limitation sometimes observed when the microdimensions of these systems induce a global depletion of the bulk solution. A new non-dimensional parameter is introduced to predict the final value of the coverage of any microsystem under static adsorption. A working curve and a criteria (h/K[Gamma](max) > 10) are provided in order to choose, for given adsorption characteristics, the value of the volume-to-surface ratio (i.e. the channel height h) avoiding depletion effects on the coverage (relative coverage greater than 90% of the theoretical one). Simulations were compared with confocal microscopy measurements of IgG antibody adsorption on the walls of a PET microchannel. The fit of the model to the experimental data show that the adsorption is under apparent kinetic control.

In situ determination of adsorption kinetics of proteins in a finite bath

A method for fast in situ measurement of adsorption kinetics based on a finite bath was developed. We modified the conventional finite bath by replacing the external loop by a dip probe which enables in situ measurement of the concentration change in the contactor. Deposition of adsorbent particles on the reflection surface of the dip probe compromised measurements. Different membranes, a polyamide, a polypropylene and a nylon membrane were tested to protect the internal reflection surface of the dip probe from fouling with adsorbent particles. The nylon membrane provided efficient protection and high mass transfer evaluated by response time experiments. Unspecific adsorption of the model protein on the membrane could also be excluded. To corroborate the measurements of the dip probe the results were compared to a conventional finite bath and to a shallow-bed. The uptake curves for human polyclonal IgG at different concentrationes (0.1–3 g/l) on rProtein A Sepharose FF and MabSelect were used as model system. The effective diffusion coefficients were determined using a pore diffusion model. These values were in good agreement for all methods.

A 3-zone model for protein adsorption kinetics in expanded beds

The adsorption behavior of expanded beds is more complex than that of fixed beds, since the adsorbent particle size, local bed voidage and liquid axial dispersion will vary axially with expanded height. Models applicable to fixed beds maybe not adequately describe the hydrodynamic and adsorption behavior in expanded beds. In this paper, a 3-zone model is developed, in which the model equations are written for the bottom zone, middle zone, and top zone of the column, respectively, and the model parameters, such as the adsorbent particle diameter, bed voidage and liquid axial dispersion coefficient, are zonal values. In-bed breakthrough curves are predicted by the 3-zone model, and tested against literature data for lysozyme adsorption on Streamline SP in an expanded bed. Model parametric sensitivity is analyzed. The effects of film mass transfer resistance, liquid axial dispersion and adsorbent axial dispersion on the breakthrough curves are weaker than that of protein intraparticle diffusion resistance for stable expanded beds. Adsorbent particle size axial distribution and bed voidage axial variation significantly affect in-bed breakthrough curves, therefore, model parameters should not be assigned uniform values over the whole column; instead the model should account for the adsorbent particle size axial distribution and bed voidage axial variation.

Fluidics-resolved estimation of protein adsorption kinetics in a biomicrofluidic system

Protein adsorption on surfaces is a complex phenomenon that is described by the balance of convective/diffusive transport of the protein species to the surface and its adsorption/desorption at the surface. The extent of binding depends on a variety of factors such as protein/surface interactions, availability of binding sites, localized concentrations of protein near biomaterial surfaces and flow characteristics of the protein in that region. Factors such as time-varying flows, complex device geometries, presence of multiple competitive species, or possible denaturing of proteins when they attach to the surface make it extremely difficult to quantitatively analyze protein interactions with surfaces. Adsorption/desorption rate constants are often inferred using simplistic models which neglect mass transport and have limited use across different microfluidic systems and flow protocols. In this work, we have developed and demonstrated a fluidics-resolved model that evaluates protein adsorption, accounting for both the fluidic transport and the biochemical kinetics in complex biomicrofluidic devices. The model is valid for both flow and static conditions. An automated procedure was also developed to extract the “intrinsic” mass-transport-independent adsorption kinetic rate constants from experimental data using a least squares optimization method. The automated data extraction methodology is applied to two proteins (alkaline phosphatase and glucose oxidase) that have been brought into contact with poly(etheretherketone) and Teflon capillaries. The applicability of the procedure in analyzing flow and adsorption in complex microfluidic structures is also demonstrated.

Dynamic Surface Tension and Adsorption Kinetics of β-Casein at the Solution/Air Interface

A diffusion model is proposed to describe the adsorption kinetics of proteins at a liquid interface. The model is based on the simultaneous solution of the Ward-Tordai equation and a set of recently developed equations describing the equilibrium state of the adsorption layer: the adsorption isotherm, the surface layer equation of state, and the function of adsorption distribution over the states with different molar areas. The new kinetics model is compared with dynamic surface tensions of beta-casein solutions measured with the drop/bubble profile and maximum bubble pressure methods. The adsorption process for low concentrations is governed by the diffusion mechanism, while at large protein concentrations this is only the case in the initial stage. The effective diffusion coefficients agree fairly well with literature data. The adsorption values calculated from the dynamic surface tension data agree very well with the used equilibrium adsorption model.