Aggrecan is a major component of cartilage extracellular matrix (ECM). It has a bottlebrush shape and a semi-rigid character. Aggrecan molecules form aggregates by interacting with hyaluronic acid (HA). In cartilage, the aggrecan-HA aggregates are interspersed in a collagen mesh. The negatively charged aggregates possess a high osmotic pressure that withstands compressive loads. From a chemical viewpoint aggrecan-HA complexes are charged polysaccharides. The viscoelastic behavior of polyelectrolyte solutions is governed by the chain architecture, the fixed charge density, the molecular weight of the polymer, and the thermodynamic interaction between the polymer and the solvent. Changes in the ionic environment (ion concentration and ion valence) significantly affect the dynamic response and stability of typical linear polyelectrolyte (polyacrylic acid, DNA, etc.) solutions. We report a systematical study of the viscoelastic properties of solutions of aggrecan and aggrecan-HA aggregates. We determine the concentration dependence of the storage (G’) and loss (G”) moduli of aggrecan solutions in different ionic environments. The data show that ions have a relatively weak effect on the viscoelastic behavior of aggrecan solutions. In the presence of HA, aggrecan bottlebrushes form supramolecular aggregates (aggrecan-HA complex). In these gel-like assemblies approximately 100 aggrecan monomers are attached to a linear HA molecule. Measurements of the kinetics of complexation indicate that HA significantly increases the storage modulus of the aggregates.

Viscoelastic behavior of aggrecan-hyaluronic acid complexes

250th National Meeting (2015)

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