The viscoelastic properties of four novel, low molecular weight hyaluronic acid derivatives were investigated and compared to the parent hyaluronic acid compound. Briefly, all derivatives were synthesized by first deacetylating the parent hyaluronic acid. One sample was left as such, while two others were reacytelated. The final compound, of particular interest for its anti-inflammatory properties, was butyrylated. The compounds were dissolved in phosphate buffer solution (PBS) and studied at a concentration of 5 mg/mL. Shear thinning behaviour was observed for all compounds, however, derivative samples had a lower viscosity than the parent compound at high shear rates. Viscoelastic properties were also observed to decrease as a result of the derivative preparation method. It is believed that these changes are primarily caused by a decrease in hyaluronic acid molecular weight. By increasing the concentration of the anti-inflammatory compound, it may be possible to modulate the viscoelastic properties to more closely resemble those of commercial viscosupplements. As a result, an anti-inflammatory derivative of hyaluronic acid may potentially improve upon existing viscosupplements used to treat patients who are susceptible to flare up.

Increased protein concentration has been correlated with decreased shear rheological parameters. Temperature dependence of synovial fluid was also demonstrated and modelled for use in Part 2 of this article.

Appropriate CaBER operating parameters for study of osteoarthritic synovial fluid were identified. No statistically significant correlation was found to exist between protein concentration and extensional rheological parameters. Positive correlations were identified between several shear and extensional rheological parameters. The reported values for extensional viscosity and relaxation times for synovial fluid were found to be within one order of magnitude with a recent study of post mortem synovial fluid.

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