An amphiphilic
hyaluronic acid (HA) derivative has been obtained by the amidation of the carboxylic group of the
glucuronic acid. This derivative, HYADD4-G (HY4), is the hexadecylamide of 500-730 kDa
hyaluronic acid, derived from Streptococcus equi at about 2% degree of substitution (2 mol
hexadecylamine per 100 mol hexuronic
acid). Its viscoelastic properties, at a concentration of 5 mg/mL in
phosphate buffer saline, have been compared with those solutions of native HA, having the same molecular weight. Changes in the viscoelastic properties of equine synovial fluid (SF) when mixed with HY4 over a series of volume ratios-viz 1:2, 1:1, 3:1, and 7:1-have been evaluated. HY4 is able to associate into aqueous
solution, and its rheological behavior is typical of a weak gel. Throughout the frequency range investigated (0.1-10 Hz), the elastic modulus G' is higher than the viscous modulus G'', and both moduli are frequency independent, and G' value is about two orders of magnitude higher than that of a comparable
solution of native HA. The addition of HY4 to equine synovial fluid (SF) increased its viscoelasticity at all the SF:HY4 ratios tested. These results demonstrate that HY4 is able to integrate with SF, increasing the synovial fluid rheology, and could be an interesting new option in
viscosupplement therapy of
osteoarthritis, particularly considering its low degree of chemical modification from native HA.