Interaction of IgG and albumin with functionalized silicas

Influence of buffer solutions in the adsorption of human serum proteins onto layered double hydroxide

The adsorption of human immunoglobulin G (IgG) and human serum albumin (HSA) on a non-calcined Mg-Al layered double hydroxide (3:1 Mg-Al LDH) was studied in batch and fixed bed experiments, focusing on the effect of buffer solution and pH over sorbent uptake. Mg-Al LDH was synthesized and characterized by X-ray diffraction (XRD), N₂ adsorption-desorption isotherms at -196°C, X-ray photoelectron spectroscopy (XPS), Zero point charge (pHzpc), particle size distribution and Fourier transform infra-red (FTIR). Batch adsorption experiments were performed in order to investigate the effects of pH on IgG and HSA adsorption with different buffers: sodium acetate (ACETATE), sodium phosphate (PHOSPHATE), 3-(N-morpholino) propanesulfonic acid (MOPS), 4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES) and trizma-hydrochloric acid (TRIS-HCl). Maximum adsorption capacities estimated by the Langmuir model were 239mgg^-1 for IgG and 105mgg^-1 for HSA in TRIS-HCl buffer. On the other hand, the highest selectivity for IgG adsorption over HSA was obtained with buffer PHOSPHATE (pH 6.5). The maximum IgG and HSA adsorption uptake in this case were 165 and 36mgg^-1, respectively. Fixed bed experiments were carried out with both proteins using PHOSPHATE buffer (pH 6.5), which confirmed that IgG was more selectively adsorbed than HSA on Mg-Al LDH and both could be fully recovered by elution with sodium chloride (NaCl).

Heterogeneous surfaces to repel proteins

The nonspecific adsorption of proteins is usually undesirable on solid surfaces as it induces adverse responses, such as platelet adhesion on medical devices, negative signals of biosensors and contamination blockage of filtration membranes. Thus, an important scheme in material science is to design and fabricate protein-repulsive surfaces. Early approaches in this field focused on homogeneous surfaces comprised of single type functionality. Yet, recent researches have demonstrated that surfaces with heterogeneities (chemistry and topography) show promising performance against protein adsorption. In this review, we will summarize the recent achievements and discuss the new perspectives in the research of developing and characterizing heterogeneous surfaces to repel proteins. The protein repulsion mechanisms of different heterogeneous surfaces will also be discussed in details, followed by the perspective and challenge of this emerging field.

Monoclonal antibody interactions with micro- and nanoparticles: adsorption, aggregation, and accelerated stress studies

Therapeutic proteins are exposed to various wetted surfaces that could shed subvisible particles. In this work we measured the adsorption of a monoclonal antibody (mAb) to various microparticles, characterized the adsorbed mAb secondary structure, and determined the reversibility of adsorption. We also developed and used a front-face fluorescence quenching method to determine that the mAb tertiary structure was near-native when adsorbed to glass, cellulose, and silica. Initial adsorption to each of the materials tested was rapid. During incubation studies, exposure to the air-water interface was a significant cause of aggregation but acted independently of the effects of microparticles. Incubations with glass, cellulose, stainless steel, or Fe(2)O(3) microparticles gave very different results. Cellulose preferentially adsorbed aggregates from solution. Glass and Fe(2)O(3) adsorbed the mAb but did not cause aggregation. Adsorption to stainless steel microparticles was irreversible, and caused appearance of soluble aggregates upon incubation. The secondary structure of mAb adsorbed to glass and cellulose was near-native. We suggest that the protocol described in this work could be a useful preformulation stress screening tool to determine the sensitivity of a therapeutic protein to exposure to common surfaces encountered during processing and storage.

Surface modification of polystyrene nanoparticles using dextrans and dextran-POE copolymers: polymer adsorption and colloidal characterization

Hydrophobically-modified dextran (dextran-phenoxy, DexP) and dextran-phenoxy-poly(oxyethylene) (DexP-POE) copolymers have been used to modify the surface properties and the stability of polystyrene nanoparticles. We examined the effect of phenoxy group and POE chain concentrations on their adsorption behaviour. The adsorbed amount was determined by the standard depletion method and the layer thickness of the adsorbed layer by photon correlation spectroscopy and electrokinetic measurements. The results show that the hydrophobic interaction is the driving force during the adsorption while the layer thickness correlates with the interfacial concentration of grafted POE chains. The effects of adsorbed layers on the properties of latex dispersions have been characterized in terms of the stability of the dispersions toward added electrolyte and temperature. The conformation of the adsorbed copolymers is discussed in relation to layer thickness and colloidal stability of suspensions.

Ellipsometric Study of Bovine Serum Albumin Adsorbed onto Ti/TiO(2) Electrodes

The adsorption of bovine serum albumin (BSA) onto relatively hydrophobic TiO(2) surfaces was studied by ellipsometry as a function of pH and BSA concentration. Titanium oxide layers were electrochemically grown on Ti disc electrodes. When fast attachment of BSA onto TiO(2) takes place, the adsorption can be considered as occurring in two different steps. The first step is fast and is the result of the direct adsorption of the protein molecules that attach to the surface without changing their conformation. The second process is slow and lasts for several hours. In this process, the adsorbed amount remains constant, whereas the thickness of the layer increases and its refractive index decreases with time. The changes in this second step are due mainly to rearrangements in the adsorbed layer produced by variations in the conformation and structure of the adsorbed molecules. The main conformational changes take place in the direction normal to the surface because lateral molecule-molecule interactions impede significant lateral expansion. Adsorption from BSA solutions of low concentration does not appear to lead to significant reconformation of the protein layer. Comparison with adsorption on powdered TiO(2) indicates that the adsorbed amount and the effective area occupied by an adsorbed BSA molecule can remain about constant even when strong surface reconformation takes place. Copyright 1999 Academic Press.

Protein adsorption on solid surfaces

The research field of protein adsorption on surfaces appears to be as popular as ever. In the past year, several hundred published papers tackled problems ranging from fundamental aspects of protein surface interactions to applied problems of surface blood compatibility and protein surface immobilization. Although some parts of the protein adsorption process, such as kinetics and equilibrium interactions, can be accurately predicted, other aspects, such as the extent and the rate of protein conformational change, are still somewhat uncertain. The whole field is ripe for a comprehensive theory on protein adsorption.