Lactic Acid-Induced Colloidal Microrheology of Synovial Fluids.

Area of Science:

• Biomaterials Science
• Rheology
• Biochemistry

Background:

• Synovial fluid (SF) possesses unique viscoelastic properties due to colloidal nanoscaffolds of proteins and hyaluronic acid (HA).
• These nanostructures provide load-bearing capacity and joint lubrication, minimizing wear on cartilage, bone, and muscle.
• Hypoxic conditions, common in joint hyperactivity or arthritis, elevate lactic acid (LA) levels via anaerobic respiration.

Purpose of the Study:

• To investigate the effect of elevated lactic acid (LA) concentrations on synovial fluid (SF) nanoscaffold integrity.
• To understand the transformation of healthy SF from a viscoelastic fluid to a watery liquid under high LA conditions.
• To biosynthesize an artificial SF that replicates the properties of natural SF.

Main Methods:

• Analysis of SF nanoscaffold breakdown under varying LA concentrations.
• Rheological characterization of SF viscosity and elasticity.
• Biosynthesis of artificial SF using proteins and HA.
• Spatiotemporal microscopic imaging to observe nanoscaffold dynamics in artificial SF.

Main Results:

• Elevated LA concentrations (beyond a critical threshold) cause the breakdown of SF colloidal nanoscaffolds.
• This breakdown leads to the precipitation of high molecular weight (MW) proteins and HA, drastically reducing SF viscosity and elasticity.
• Artificial SF, when synthesized, exhibits dynamic cross-linking of proteins and HA, mimicking natural SF behavior, which is absent when LA is mixed with pure HA or proteins alone.

Conclusions:

• Lactic acid plays a critical role in the destruction of synovial nanoscaffolds, compromising joint function.
• Understanding this mechanism is crucial for developing effective artificial synovial fluid.
• The successful biosynthesis of artificial SF demonstrates a promising approach for treating joint-related conditions.