Binding of Mucin to Water-Soluble and Surface-Grafted Boronate-Containing Polymers

The binding of mucin to water-soluble copolymers of N,N-dimethylacrylamide and N-acryloyl-m-aminophenylboronic acid grafted on the surface of glass is studied. Atomic force microscopy studies show that many graft copolymer islands 20-200 nm in diameter and 50 nm in height occur on the modified surface of flat glass. Owing to the presence of phenyl boronate groups, the copolymer behaves as a weak polyelectrolyte (pK(a) = 9.0) and, in the grafted state in an aqueous solution, experiences reversible transitions between states with higher and lower degrees of ionization. As evidenced by spectral correlation interferometry, this phenomenon brings about a change in the thickness of the grafted layer by approximately 0.5 nm. The ability of phenyl boronate groups to form cyclic esters with diol and polyol groups results in complexation of the soluble copolymer with mucin oligosaccharides and entails the appearance of slowly growing submicron particles formed by similarly charged polymers. The specificity of complexation is confirmed by dissolution of particles in the presence of fructose: a saccharide with a strong affinity for phenyl boronate groups. The binding of mucin to glass, which is chemically modified with the above copolymer, leads to formation of an adsorption layer with a thickness of 1.2-1.8 nm. Thus, boronate-containing copolymers are suitable for preparing carriers with controllable adsorption properties with respect to polyols, including mucinlike proteins of cellular glycocalyxes.