Hyaluronic acid adsorption on nanodimaonds: quantitative characteristics and mechanism

Abstract Formation of adsorption complex between hyaluronic acid and detonation nanodiamonds was studied. Nanodiamonds that possess negative and positive zeta-potential in an aqueous suspension were used. To determine the direct amount of hyaluronic acid on the nanodiamond surface tritium label was introduced into the polymer by means of tritium thermal activation method. It was found that hyaluronic acid irreversibly adsorbs on both positively and negatively charged nanodiamonds, but in different quantities. Adsorption of hyaluronic acid on nanodiamonds of positive zeta potential leads to the isoelectric point at the surface coverage close to 100 mg/g, while further increase in surface amount of hyaluronic acid results in the formation of negatively charged particles and the increase of its species diameter comparing with the initial material. In the case of negatively charged nanodiamonds adsorption of hyaluronic acid is also observed, but it was as much as 50 times lower than in the case of positively charged nanodiamonds. Even small amounts of hyaluronic acid adsorbed on nanodiamond surface results in the disaggregation of clusters of nanodiamonds that are formed in an aqueous suspension, while zeta potential was from -50 to -40 mV that is around of the value for non-modified material. On the basis of the experimental data, we can suggest that the adsorption mechanism of complex formation between hyaluronic acid and nanodiamonds includes both electrostatic interaction and formation of hydrogen bonds between surface functional groups and adsorbed water molecules.