Scale-Dependent Rheology of Synovial Fluid Lubricating Macromolecules

Area of Science:

• Biochemistry
• Biophysics
• Rheology

Background:

• Synovial fluid (SF) lubricates joints via hyaluronic acid (HA) and proteoglycan 4 (PRG4).
• The synergistic interaction and rheological influence of HA and PRG4 remain unclear.
• Understanding SF lubrication is crucial for joint health and diseases like osteoarthritis.

Purpose of the Study:

• To elucidate the microstructural and rheological properties of HA-PRG4 solutions.
• To investigate the interaction between HA and recombinant human PRG4 (rhPRG4).
• To clarify the role of these macromolecules in joint lubrication.

Main Methods:

• Confocal microscopy to examine microstructure.
• Multiscale rheometry to assess rheological properties.
• Analysis of solutions containing recombinant human PRG4 (rhPRG4) and HA.

Main Results:

• PRG4 forms stiff, gel-like aggregates, not an extensive network with HA.
• Aggregate size and stiffness are modulated by the HA matrix's viscoelasticity.
• The system exhibits a disordered, hierarchical network rheology with PRG4 aggregates in an HA phase.

Conclusions:

• PRG4 aggregates, rather than a uniform network, dictate SF rheology.
• Findings offer new insights into cartilage biomechanics and PRG4's lubricating function.
• Results may inform the development of HA-based osteoarthritis treatments.