Fast nanoparticle rotational and translational diffusion in synovial fluid and hyaluronic acid solutions

Nanoparticles are under investigation as diagnostic and therapeutic agents for joint diseases, such as osteoarthritis. However, there is incomplete understanding of nanoparticle diffusion in synovial fluid, the fluid inside the joint, which consists of a mixture of the polyelectrolyte hyaluronic acid, proteins, and other components. Here, we show that rotational and translational diffusion of polymer-coated nanoparticles in quiescent synovial fluid and in hyaluronic acid solutions is well described by the Stokes-Einstein relationship, albeit with an effective medium viscosity that is much smaller than the macroscopic low shear viscosity of the fluid. This effective medium viscosity is well described by an equation for the viscosity of dilute polymer chains, where the additional viscous dissipation arises because of the presence of the polymer segments. These results shed light on the diffusive behavior of polymer-coated inorganic nanoparticles in complex and crowded biological environments, such as in the joint.

Automated summary

The diffusion behavior of polymer-coated inorganic nanoparticles in synovial fluid can be well described by the Stokes-Einstein relationship, with an effective medium viscosity much smaller than the macroscopic low shear viscosity of the fluid. The additional viscous dissipation in the effective medium viscosity is attributed to the presence of polymer segments, shedding light on the diffusive behavior of these nanoparticles in complex and crowded biological environments such as the joint.