*2.5. Rheological Properties*

The rheological properties of HA, Ch, and the complex were studied using a Modular Compact Rheometer MCR 92 (Anton Paar GmbH, Graz, Austria), equipped with a 50-mmdiameter cone–plate geometry, with a cone angle of 1◦ . For all tests, the temperature and the gap between the plates were kept constant 20 ◦C and 0.98 mm, respectively.

Viscosity measurements were performed in rotation mode, they were investigated in the range of 0.1–100 s−<sup>1</sup> and ten points per decade were acquired.

The sample viscoelastic behaviour was investigated in the oscillation mode, to determine the storage modulus G'(ω) and the loss modulus G"(ω). First, preliminary tests were conducted to determine the upper amplitude limit of the linear viscoelastic region (LVE), testing the samples over an extended strain field (0.01–100%). Second, after the LVE was determined (2% for HA and HA/Ch and 20% for Ch), the samples were tested by performing a frequency sweep test over the 0.628 rad/s–628 rad/s (i.e., 0.1–100 Hz) frequencies, at a constant strain. Data were elaborated with RheoCompass™ software.

For the analysis, the same solutions as for Zp were tested. Before the analysis, solutions were sonicated to reduce air bubbles.
