Protein adsorption theory

The most possible reason may be in the higher free energy of the protein adsorption on PolyPROPYL A materials. Chemisorbed neutral poly(succinimide) of molecular weight 13000 apparently forms a diffuse interface as predicted by theory (see Sect. 2.2). Controversially, a short polyethyleneimine exists on a surface in a more flat conformation exhibiting almost no excluded volume and producing... 

Roth, CM Lenhoff, AM, Electrostatic and van der Waals Contributions to Protein Adsorption Comparison of Theory and Experiment, Langmuir 11, 3500, 1995. 

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. 

LTI pyrolytic carbon is one of the very few synthetic materials generally accepted as suitable for long-term blood contact applications (1 ). Although a number of hypotheses have been formulated with respect to the blood tolerability of materials, a general theory or mechanism is not yet available. Nyilas, et al., ( ) have shown that in certain situations the local hemodynamics can play a predominant role, while in most cases the solid-blood interfacial properties have been shown to be equally important (2, 3). It is assumed that understanding the plasma protein adsorption processes on solids used for blood-contact applications will lead to a better understanding of solid-blood interactions (, 2, ... 

Adsorption kinetics and isotherms. The rate of protein adsorption onto solids is usually much slower than that predicted from the diffusion theory [85-87]. For various protein-adsorbent systems, the period of time required to obtain maximum adsorption ranges, as a rule, from several tens of minutes [10,12,14,88] to several hours [11,12,14,63,65,66,79,81,84,89,90]. More rarely, the adsorption terminates after several minutes [67,91] or continues for 24 h and longer [92,93], It cannot be excluded, however, that the initial adsorption rates should be transport limited, as has been shown by Norde et al. [94] for adsorption of lysozyme, RNase, and myoglobin on glass. The importance of diffusion is also obvious at the first step of adsorption from protein mixtures [95]. In this case the interface accommodates initially the protein molecules with the largest diffusion coefficients, and afterwards these molecules may be displaced by other molecules with higher affinity to the surface. 

Therefore, complete unfolding of the polypeptidic chain at the interface leading to a train-loop-tail model, similar to the conformation of copolymers at interfaces, is to be considered as a limiting case only. Even for a disordered and uncross-linked protein such as /3-casein, this type of conformation at air-water or oil-water interface may not in fact be totally realistic [200]. It provides however a convenient basis to derive a thermodynamical analysis of protein interfacial layers from polymer theories [201-203]. Recent specular neutron reflectance studies on protein adsorption layers at the air-water interface [204] show that the protein density profile normal to the interface is qualitatively similar for /3-casein and BLG and consists of a protein-rich layer, about 15 A thick, close to the interface, and a... 

Surveying the literature, it appears that the interfacial behavior of proteins is a controversial subject. The main reason is that many studies have been performed under insufficiently defined conditions and/or that conclusions have been drawn on the basis of too scanty experimental evidence. Furthermore, the theoretical description of adsorbed layers of simple, flexible polymers is still in its infancy (5,6). As the structure of proteins is much more complex than that of those simple polymers, theories of polymer adsorption need to be greatly extended to become applicable to proteins. Clearly, our current knowledge of protein adsorption mechanisms and of the structure of the adsorbed layer is far from complete. 

Blood plasma is a concentrated protein solution, and the adsorption behavior onto material surfaces may be estimated from the amount and the type of adsorption for major plasma proteins in dilute solution, where the adsorption theory for a monomolecular layer is applied. 

There is no unified theory to explain the process of mucoadhesion. The total phenomenon of mucoadhesion is a combined result of all these theories. First, the polymer gets wet and swells (wetting theory) followed by the noncovalent (physical) bonds created within the mucus-polymer interface (electronic and adsorption theory). Then, the polymer and protein chains interpenetrate (diffusion theory) and entangle together to form further noncovalent (physical) and covalent... 

Salad dressings and mayonnaise can be stabilized by ionic surfactants, which provide some electrostatic stabilization as described by DLVO theory, or by nonionic surfactants which provide a viscoelastic surface coating. The protein-covered oil (fat) droplets tend to be mostly stabilized by steric stabilization (rather than electrostatic stabilization) [34,126,129], particularly at very high levels of surface protein adsorption, in which case the adsorption layer can include not just protein molecules but structured protein globules (aggregates). In some cases, lipid liquid crystal layers surround and stabilize the oil droplets, such as the stabilization of O/W droplets by egg-yolk lecithins in salad dressing [34,135]. 

The thermodynamics of snrface adsorption has been extensively described by Gibbs adsorption theory (Chattoraj and Birdi, 1984 Spaull, 2004 Zhou, 1989). Further, Gibbs adsorption theory has also been applied in the analyses of diverse phenomena (snch as solid-liqnid or Uqnidj-liqnidj, adsorption of solute on polymers, etc.). In fact, in any systan where adsorption takes place at an interface the Gibbs theory will be applicable (such as solid-liquid protein molecnle-solntion with solutes that may adsorb). 

Brusatori and Van Tassel [20] presented a kinetic model of protein adsorption/surface-induced transition kinetics evaluated by the scale particle theory (SPT). Assuming that proteins (or, more generally, particles ) on the surface are at all times in an equilibrium distribution, they could express the probability functions that an incoming protein finds a space available for adsorption to the surface and an adsorbed protein has sufficient space to spread in terms of the reversible work required to create cavities in a binary system of reversibly and irreversibly adsorbed states. They foimd that the scale particle theory compared well with the computer simulation in the limit of a lower spreading rate (i.e., smaller surface-induced unfolding rate constant) and a relatively faster rate of surface filling. 

Even the van Oss-Good theory has been criticized, e.g. due to the very high basic values, but despite that it has found wide applicability in describing interfacial phenomena (interactions) involving polymers, paints, proteins and other complex systems (like polymer surface characterization, CMC determination of surfactants, protein adsorption, cell adhesion, enzyme-substrate interactions). 

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