Covalently Attached Thin Coatings Comprising Saccharide and Alkylene Oxide Segments

Abstract

Dextrans of various molecular weights were immobilized on polymer surfaces using a three-step process. In the first step, dextran was oxidized in aqueous solution with sodium periodate, resulting in the release of formic acid. Titration of the formic acid showed that maximal oxidation of the dextran was achieved in 4–5 hours when two moles of periodate were used per mole of glucose subunits. ¹H- and ¹³C-NMR revealed that the oxidized product contained hemialdal moieties when water was present. The hemialdals were capable of reacting with nucleophilic reagents such as fluorescein thiosemicarbazide. In the second step, a radiofrequency glow discharge through an amine-containing vapour was used to place reactive amine groups on the surface of a polymer. In the third step, the oxidized dextran was bound to the surface amine groups; this reaction produced a hydrolytically unstable Schiff-base linkage. The linkage was reduced by sodium cyanoborohydride to a hydrolytically stable secondary amine. The resulting surfaces were highly wettable, as shown by their ability to hold a visually observable, continuous layer of water for several minutes.