Materials and methods
2.1. Materials
2.1.1. Purification
The sample of chitosan, produced from squid pens, was purchased by Mahtani Chitosan (batch No. 114). To obtain a high-purity material, chitosan was dissolved at 0.5% (w/v) in the presence of an amount of acetic acid necessary to achieve the stoichiometric protonation of the –NH2 sites. After complete dissolution, it was filtered successively on 3, 1.2, 0.8 and 0.45 μm membranes from Millipore. Then, dilute ammonia was added to fully precipitate the polymer. The latter was repeatedly rinsed with distilled de-ionized water and centrifuged until a neutral pH was achieved, then lyophilized.