Layer protein-repellent

When poly(ethylene oxide) (PEO) silane was grafted onto oxidized PDMS stamps it acts as a protein repellent layer. This property was utilized to design a flat stamp with regions that can attract proteins (nonmodified PDMS) and regions modified with PEO that have protein-repellent properties. The local modification of native PDMS was conducted by oxidation in 02-plasma with the application of a metal mask (areas that were covered by the mask were not oxidized and not modified). Proteins (immunoglobulin G, IgG) were transferred successfully to the glass substrates... 

Finally, we note that in a very recent work Heuberger et al. investigated protein-resistant copolymer monolayers of PEG grafted to poly(L-lysine) (PLL) (PLL-g-PEG) in terms of the role of water in surface grafted PEG layers [159], interaction forces and morphology [160], compressibility, temperature dependence and molecular architecture [161], PEG is often used in biomedical applications in order to create protein-resistant surfaces but the mechanisms responsible for the protein-repelling properties of PEG are not fully understood. 

Measurement of interfacial forces thus offers the potential to study the factors involved in protein repellence or adsorption. Force measurements on adsorbed and grafted PEG layers have been reported, using both the surface forces apparatus (SFA) and the colloid-probe atomic force microscopy (AFM) technique. - Adsorbed PEG layers show responses due to relaxation processes,... 

Block copolymers containing poly(ethylene oxide) (PEO) have attracted attention, mainly due to the high hydrophilicity of this polymer and its biocompatible and protein-repellent properties. However, to promote formation of aggregates or mono-layers, PEO has to be combined with a hydrophobic block. 

The same system was used to study the interactions between the polymer mono-layer and a water-soluble protein, bovine serum albumin (BSA) [54]. As could be expected, an increasing amount of PLA in monolayers considerably hindered BSA adsorption, as did the increase of PEO length in the block copolymers. However, many points of this study remain unclear, for example the details of polymer-protein molecular interactions and the protein concentration dependence. No proof was presented that the protein was actually integrated into the monolayer, rather than the interaction being unspecific adsorption (despite PEO-protein repellence), and there was no discussion on the diffusion limit of protein integration. 

There are some qualitative difficulties when the specific ion effects are explained via the dispersion forces of the ions. Particularly the anions, for which the dispersion coefficients / , are large, affect the double layer interactions. However, experiments on colloid stability [6] or colloidal forces [11] revealed strong specific ion effects especially for cations. Furthermore, the ions which affect most strongly the solvating properties of the proteins are those from their vicinity, since they perturb mostly the structure of water near the proteins. However, the van der Waals interactions of ions predict that the cations remain in the vicinity of an interface, and the anions are strongly repelled, while Hofmeister concluded that anions are mainly responsible for the salting out of proteins. 

The method of preparation significantly affects the ability of bentonite to remove wine or juice proteins. Bentonite is made up of small platelets that are separated by a layer of water molecules. During hydration, the charged platelets repel each other and pop apart. As this occurs, swelling begins. Water molecules partially neutralize... 

Using experimental results on ovalbumin, Nystrom [165] deduced that the charge on the protein rather than the difference in charge between the membrane and the protein, determines the degree of protein deposition on membrane surface. When the protein is charged, the solubility (protein stability) increases and the affinity for the membrane material decreases. Where the membrane charge is opposite to that of the protein, initial adsorption may result in a thin modified layer of charged proteins on the membrane surface that then repels further deposition as quasi-steady flux is attained [165]. 

However, at this pH, highly acidic proteins (pi 3 or less) carry a net negative charge and are repelled from the dextran layer. It is not possible to reduce the pH to accommodate the immobihzation of highly acidic proteins because the dextran on the chip surface will protonate and become resistant to activation by EDC/NHS. In order to immobilize highly acidic proteins by amine couphng, it is necessary to modify the standard immobihzation protocol. Some options are now described. 

Electrodes are sometimes coated with protective layers to prevent fouling from larger molecules (e.g., proteins). A layer of cellulose acetate, for example, will allow the small H2O2 molecule to pass but not the larger ascorbic acid molecule present in biological fluids, which is oxidized at the same potential. Anionic Nafion membranes repel anions and allow cations to pass. 

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