Collective Dynamics and Transient Behavior of Partially Hydrophobic Hyaluronic Acid Chains

The unique performance of a partially hydrophobic derivative of hyaluronic acid, HYADD4, bearing 2–3 hexadecylic side chains every 100 repeating units, enables hydrogels based on this polymer to be suitably used as a viscosupplement to replace synovial fluid in stressed or injured articular joints. This contribution addresses: i) as to whether there is a self‐assembly process driving the HYADD4 hydrogel stabilization and ii) what the characteristics of the long‐range dynamics governing the macroscopic viscoelastic behavior are, and to what extent these features are different from those present in the parent polymer (i.e., hyaluronic acid). Mesoscale dynamic and static properties are interpreted in the light of “sticky reptation theory” and evaluated in combination with small‐angle neutron scattering results. Fluorescence recovery after photobleaching shows dramatic differences in the diffusional behavior of hyaluronic acid (HA) and partially hydrophobized hyaluronic acid (HYADD4): in HA, the fluorescence is recovered after about 50 s, whereas in HYADD4 the bleach remains after several minutes. The polymer concentration, Cp = 0.8% (w/v), is the same in both experiments.