Effects of hyaluronic acid on the rheological properties of zinc carboxylate gels

Hyaluronic acid (HyA) and zinc carboxylate gels were synthesized by using L-malic acid (MA) and NaOH solutions. Obtained gels (HyA/Zn/MA gels) had a characteristic with transparency of 12.9 to 48.2% at a wavelength of 500 nm, pH values ranging from 6.8 to 7.1. The polymerization reaction and the formation of network structure were completed within 12 h. Rheological measurements indicated that the storage (G′) moduli were higher than the loss (Gʺ) moduli in all specimens and the elastic moduli were greater than 10,000 Pa, which is higher than gels cross-linked with covalent bonds. Moreover, gel strength values (S calculated from the complex (G*) moduli at 1.0 Hz) were higher than other chemically cross-linked gels. The gel strength increased at zinc concentrations up to 0.45 mol/l, however, decreased at a zinc concentration of 0.5 mol/l with an increasing HyA concentration. The rheological properties of HyA/Zn/MA gels strongly depended on zinc and HyA concentrations.