*2.1. Chemicals*

The used chemicals were of analytical grade, and the samples were prepared using deionized water. Highly viscous chitosan powder, from crab shells (with a molecular weight MW of 150,000 and a deacetylation degree ≥75%, Sigma-Aldrich, Milan, Italy) acetic acid (99.9% Sigma-Aldrich, Milan, Italy), and glycerol (+99.5%, Sigma-Aldrich, Milan, Italy) were obtained from Sigma-Aldrich. The same commercial source was adopted for sodium ketoprofen (C16H13NaO3, MW: 276.267 g·mol−<sup>1</sup> Sigma-Aldrich, Milan, Italy), used without further purification. A Kp stock solution with a concentration of 5 mg·L−<sup>1</sup> was prepared. The pH of the various aqueous solutions, when necessary, was adjusted using concentrated HCl and NaOH solutions. Dilutions were performed using deionized water.
