Eur. Phys. J. E (2013) 36: 70
https://doi.org/10.1140/epje/i2013-13070-7

Regular Article

Tuning the density profile of surface-grafted hyaluronan and the effect of counter-ions

¹⁹⁸⁸⁴ Science for Life Laboratory, Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, 751 21, Uppsala, Sweden
²⁹⁸⁸⁴ Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 380 42, Grenoble, France
³⁹⁸⁸⁴ Department of Physics and Astronomy: Materials Physics, Uppsala University, Box 516, 751 20, Uppsala, Sweden

^* e-mail: berts@ill.fr

Received: 29 August 2012
Revised: 18 December 2012
Accepted: 19 December 2012
Published online: 16 July 2013

Abstract

The present paper investigates the structure and composition of grafted sodium hyaluronan at a solid-liquid interface using neutron reflection. The solvated polymer at the surface could be described with a density profile that decays exponentially towards the bulk solution. The density profile of the polymer varied depending on the deposition protocol. A single-stage deposition resulted in denser polymer layers, while layers created with a two-stage deposition process were more diffuse and had an overall lower density. Despite the diffuse density profile, two-stage deposition leads to a higher surface excess. Addition of calcium ions causes a strong collapse of the sodium hyaluronan chains, increasing the polymer density near the surface. This effect is more pronounced on the sample prepared by two-stage deposition due to the initial less dense profile. This study provides an understanding at a molecular level of how surface functionalization alters the structure and how surface layers respond to changes in calcium ions in the solvent.