Protein Adsorption Principles

The classical Langmuir theory for gas adsorption can be applied to adsorption from solution, if the solution is sufficiently dilute 45,46). The surface is considered to consist of sites of about the same area as the projected area of the solute of interest (Fig. 6). 

Let v5 be the number or moles of solute molecules adsorbed per area of surface. The subscript on v refers to the case of adsorption on a solid surface as contrasted with v used in the case of protein-ligand equilibria 4-47 49). Let [A] be the equilibrium solute concentration. 

only one molecule can be adsorbed per site (commonly called the monolayer assumption)  

only one type of site is present (homogeneous surface)  

the adsorption of one molecule does not affect the adsorption energy of other molecules (no lateral interactions or cooperativity)  

---

The tendency of proteins to adsorb at interfaces is determined by many variables, including the pH, the ionic strength, the properties of the protein molecules and the interfaces, and the nature of the solvent and other components present. The process of protein adsorption is complicated, and despite the great volume of work over the past decades, a unified theory is still far ahead. Yet, some principles may be indicated. 

Discussing principles of protein adsorption may start from general trends observed for the adsorption of more simple flexible, highly solvated polymers, in particular, polyelectrolytes. 

Antrade, J. D., Principles of protein adsorption, In Surface and Interfacial Aspects of Biomed ical Polymers Antrade, J. D., Ed. Plenum Press, New York, 1985, Vol. 2... 

The general principles of protein adsorption are beginning to be identified and understood. New techniques and methods are now available which, together with well-established methods, allow one to thoroughly probe the adsorption process. 

We will briefly outline the principle thermodynamic considerations that comprise the underlying key issues of protein adsorption on surfaces. Subsequently, we will describe strategies that have been followed for the design of protein-repellent surface coatings. For details on protein adsorption, as well as further discussion on this particular topic, the reader is referred to more comprehensive reviews [31, 32],... 

Compared to systems that rely on protein adsorption for spatially guided cell adhesion, reports on cell chips based on peptide-mediated adhesion are less frequent, but emerging. In principle, identical methods to those used for the microstructuring of proteins can be employed for peptides, although reports on direct patterning (controlled deposition of peptides) prevail. 

The separation principle in capillary gel electrophoresis (CGE) is the same as that of slab gel electrophoresis. Most often CGE is used in a denaturing mode with the incorporation of SDS and is referred to as SDS-CGE. As such, separation is based on the protein s molecular mass and, due to the sieving mechanism of the gel, smaller proteins migrate past the detector first. The use of a gel material and SDS decreases the EOF and eliminates protein adsorption to the capillary walls further ensuring that migration is based on molecular mass. This precludes the need for additives and coated capillaries. 

The studies of protein adsorption to biomaterials undertaken so far have shown that the process is understandable in terms of the principles of surface activity, mass action, surface chemistry, and transitions in the structure of proteins. Furthermore, cells with receptors for certain of the adsorbed proteins are likely to respond to surfaces in proportion to the amount of this protein on the surface, although other processes involving... 

Whereas these reviews encompass general principles, methodologies, and applications of TIRF, this review focuses mainly on protein adsorption characteristics that have been studied in this laboratory. 

In this limiting case protein adsorption should not depend on the surface tension of the substratum and, in principle, should be zero if no other effects, such as electrostatic interactions, come into play (28-31). Thus the model suggests that the surface tension of not only the substrates and the adsorbing protein but also of the suspending liquid medium is an important parameter in determining protein adsorption yet this important physico-chemical property is seldom reported or even considered. 

The postulate of Vroman addresses only one variable, namely concentration, that may be expected to influence a protein s adsorption competitiveness. From known adsorption principles we may reasonably assume that protein affinity for the surface (free energy of adsorption), protein-protein interactions in the layer, and kinetic factors such as activation energy of adsorption will also influence competitive adsorption. The idea of a sequenced based at least partly on concentration seems reasonable, since initially difTusion would ensure relatively high concentrations of the abundant proteins, and only later would the true relative affinities of the proteins for the surface be expressed. This idea raises tantalizing questions such as whether all surfaces end up with the same protein layer or whether the sequence stops at different points on different surfaces. 

The advantages of ion-exchange chromatography are its straightforward adsorption principle that is based on the Coulomb interaction that can be adjusted according to the isoelectric point (pl) of the proteins to be separated. The binding mechanism can be tuned over a wide area of conditions by choosing different types... 

In the present paper, we review the totality of these data and attempt a synthesis of our current knowledge of this system. Such a synthesis relates both to the fundamental aspects of the interaction and to its relationship to blood-material interactions, incorporating both our own work and that of others. In the context of the present Symposiun this paper will serve the additional purpose of Illustrating some of the principles of protein adsorption discussed in the paper of Andrade (this volume). 

The study of proteins adsorption on MNPs was performed using ESR-spectroscopy of spin labels. The stable nitroxide radical used as spin label is presented in Fig. 3. Spin labels technique allows studying adsorption of macromolecules on nano-sized magnetic particles in dispersion without complicated separation processes of solution components [14]. The principle of quantitative evaluation of adsorption is the following. Influence of local fields of MNPs on spectra of radicals in solution depends on the... 

The topics discussed in this chapter are divided into three sections physical characterization, chemical analysis, and the characterization of biointerfacial events. In each section, the principles behind the most commonly used characterization methods are presented, the techniques are described, and typical measurements are illustrated with examples. The emphasis is on methods to quantify and characterize protein adsorption on thin films, which precedes host biological responses. 

---