Abstract
The surface of polyethylene was modified by plasma immersion ion implantation. Structure changes including carbonization and oxidation were observed. High surface energy of the modified polyethylene was attributed to the presence of free radicals on the surface. The surface energy decay with storage time after treatment was explained by a decay of the free radical concentration while the concentration of oxygen-containing groups increased with storage time. Horseradish peroxidase was covalently attached onto the modified surface by the reaction with free radicals. Appropriate blocking agents can block this reaction. All aminoacid residues can take part in the covalent attachment process, providing a universal mechanism of attachment for all proteins. The native conformation of attached protein is retained due to hydrophilic interactions in the interface region. The enzymatic activity of covalently attached protein remained high. The long-term activity of the modified layer to attach protein is explained by stabilisation of unpaired electrons in sp2 carbon structures. A high concentration of free radicals can give multiple covalent bonds to the protein molecule and destroy the native conformation and with it the catalytic activity. The universal mechanism of protein attachment to free radicals could be extended to various methods of radiation damage of polymers.
Highlights
E attachment of proteins to polymer surfaces provides a means of modifying the response of an organism to the surface and is an important step for improving the biocompatibility and functionality of medical implant table devices [1]
Structure Changes in Polyethylene Surface Layer Resulting from plasma immersion ion implantation (PIII) Treatment. e effect of ion bombardment during PIII was readily observed as a darkening of the treated polyethylene. e dark colour corresponds to carbonization of the surface layer of polyethylene and increases with ion uence. e dark colour remains a er washing of the modi ed polyethylene surface with water, buffer and the organic solvents toluene, ethanol, and acetone. e carbonization was studied by Raman and UV-vis spectroscopy
E amount of protein attached on a PIII-treated surface is up to 2 times higher than on an untreated surface. e attachment on the PIII-treated surface is through the formation of covalent bonds between the protein molecule and the modi ed surface, while the attachment on the untreated surface is through physical intermolecular interactions
Summary
E attachment of proteins to polymer surfaces provides a means of modifying the response of an organism to the surface and is an important step for improving the biocompatibility and functionality of medical implant table devices [1]. E preparation of polymer surfaces for protein binding can be done using a number of chemical and physical modi cations, such as the attachment of linker molecules to provide covalent binding through speci c active groups [4, 5] plasma treatment [6,7,8,9,10,11,12] UV treatment [13,14,15,16], and ion beam implantation [17,18,19,20]. E present investigation aims to determine the actual mechanism of protein attachment realised one example of polymer surface modi cation ion beam implantation achieved by plasma immersion ion implantation (PIII). Polyethylene when untreated is a representative hydrocarbon polymer with a high hydrophobicity. e modi cation of polyethylene by ion beam implantation [56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72] has been investigated
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