Grafted ionomer complexes and their effect on prot

Authors: Agata M Brzozowska Arie de Keizer Christophe Detrembleur Martien A Cohen Stuart Willem Norde

Publish Date: 2010/09/26

Volume: 288, Issue: 16-17, Pages: 1621-1632

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Abstract

We have studied the formation and the stability of ionomer complexes from grafted copolymers GICs in solution and the influence of GIC coatings on the adsorption of the proteins βlactoglobulin βlac bovine serum albumin BSA and lysozyme Lsz on silica and polysulfone The GICs consist of the grafted copolymer PAA28coPAPEO22 polyacrylic acidcopolyacrylate methoxy polyethylene oxide with negatively charged AA and neutral APEO groups and the positively charged homopolymers P2MVPI43 polyNmethyl 2vinyl pyridinium iodide and PAH∙HCl160 polyallylamine hydrochloride In solution these aggregates are characterized by means of dynamic and static light scattering They appear to be assemblies with hydrodynamic radii of 8 nm GICPAPEO22/P2MVPI43 and 22 nm GICPAPEO22/PAH∙HCl160 respectively The GICs partly disintegrate in solution at salt concentrations above 10 mM NaCl Adsorption of GICs and proteins has been studied with fixed angle optical reflectometry at salt concentrations ranging from 1 to 50 mM NaCl Adsorption of GICs results in high density PEO side chains on the surface Higher densities were obtained for GICs consisting of PAH∙HCl160 16 ÷ 19 chains/nm2 than of P2MVPI43 06 ÷ 15 chains/nm2 Both GIC coatings strongly suppress adsorption of all proteins on silica 90 however reduction of protein adsorption on polysulfone depends on the composition of the coating and the type of protein We observed a moderate reduction of βlac and Lsz adsorption 60 Adsorption of BSA on the GICPAPEO22/P2MVPI43 coating is moderately reduced but on the GICPAPEO22/PAH∙HCl160 coating it is enhancedIn order to effectively suppress protein adsorption on surfaces primary adsorption 1 by a polymer brush coating the brush should be sufficiently dense to prevent penetration by protein molecules Relatively high brush densities can be obtained by timeconsuming and laborious methods ie chemical grafting of polymer chains to the surfaces “grafting to” and “grafting from” methods or by adsorption of grafted block copolymers also called comb copolymers 2 3 4 instead of the linear polymers Using such polymers the density of the neutral brush forming chains is partly predetermined by the density of their chemical grafting to the backbone Grafted copolymers have been shown to be effective in suppressing protein adsorption on various surfaces 2 5 Surface modification with comb copolymers can be obtained in two ways the grafted copolymers can be adsorbed at solid–liquid interfaces 2 or mixed into a casting melt eg during the production of antifouling membranes 6 7 however simple adsorption of such chains on a solid–liquid interface may result in low surface coverage due to the steric repulsion from earlier adsorbed chains and hence in a low overall brush density Comb copolymers used as additives to the casting melt consist of hydrophilic and hydrophobic blocks During the membrane preparation precipitation in a waterbased coagulation bath hydrophilic blocks segregate and position themselves in the membrane–liquid interface 6 7 The degree of reduction of protein adsorption depends on the structure of the grafted copolymers ie the grafting density 1 the length of the grafted chains 8 the size of the protein molecules ionic strength and surface charge 9As indicated previously 19 formation of micelles with grafted copolymers has severe consequences for the resulting structure of the aggregate ie there may not be a distinguished core–corona structure characteristic of C3Ms More likely attraction between individual oppositely charged chains will dominate resulting in low aggregation numbers To distinguish these aggregates from regular C3Ms we introduced the term “grafted ionomer complexes” GICsHomopolymers used in this study are polyallylamine hydrochloride and polyNmethyl 2vinyl pyridinium iodide These polyelectrolytes differ in length 160 and 43 monomers respectively and properties Polyallylamine hydrochloride was extensively studied for its ability to form stable polyelectrolyte multilayers 20 21 22 also at low salt concentrations which are considered for many applications eg to enhance the tensile strength of paper 23 encapsulation 24 drug delivery 25 or corrosion protection 26 The derivatives of polyvinyl pyridine are applied in eg catalysis 27 28 29 removal of heavy metals 30 31 32 33 and organic pollutants 34 35 36 water purification and disinfection 34 37 38 39 or production of materials with antibacterial properties 40 41 42 43

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