High intensity ultrasound irradiation was used to convert beta-chitin (BCHt) into chitosan (CHs). Typically, beta-chitin was suspended in 40% (w/w) aqueous sodium hydroxide at a ratio 1/10 (gmL(-1)) and then submitted to ultrasound-assisted deacetylation (USAD) during 50min at 60°C and a fixed irradiation surface intensity (52.6Wcm(-2)). Hydrogen nuclear magnetic resonance spectroscopy and capillary viscometry were used to determine the average degree of acetylation (DA‾) and viscosity average degree of polymerization (DPv‾), respectively, of the parent beta-chitin (DA‾=80.7%; DPv‾=6865) and USAD chitosans. A first USAD reaction resulted in chitosan CHs1 (DA‾=36.7%; DPv‾=5838). Chitosans CHs2 (DA‾=15.0%; DPv‾=5128) and CHs3 (DA‾=4.3%; DPv‾=4889) resulted after repeating the USAD procedure to CHs1 consecutively once and twice, respectively. Size-exclusion chromatography analyzes allowed the determination of the weight average molecular weight (Mw‾) and dispersity (Ð) of CHs1 (Mw‾=1,260,000gmol(-1); Ð=1.4), CHs2 (Mw‾=1,137,000gmol(-1); Ð=1.4) and CHs3 (Mw‾=912,000gmol(-1); Ð=1.3). Such results revealed that, thanks to the action of high intensity ultrasound irradiation, the USAD process allowed the preparation of unusually high molecular weight, randomly deacetylated chitosan, an important breakthrough to the development of new high grade chitosan-based materials displaying superior mechanical properties.

The formation of chitosan hydrogels without any external cross-linking agent was successfully achieved by inducing the gelation of a viscous chitosan solution with aqueous NaOH or gaseous NH3. The hydrogels produced from high molecular weight (Mw ≈ 640 000 g mol(-1)) and extensively deacetylated chitosan (DA ≈ 2.8%) at polymer concentrations above ∼2.0% exhibited improved mechanical properties due to the increase of the chain entanglements and intermolecular junctions. The results also show that the physicochemical and mechanical properties of chitosan hydrogels can be controlled by varying their polymer concentration and by controlling the gelation conditions, that is, by using different gelation routes. The biological evaluation of such hydrogels for regeneration of infarcted myocardium revealed that chitosan hydrogels prepared from 1.5% polymer solutions were perfectly incorporated onto the epicardial surface of the heart and presented partial degradation accompanied by mononuclear cell infiltration.

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Chitosan-based thin films were assembled using the layer-by-layer technique, and the axial composition was accessed using X-ray photoelectron spectroscopy with depth profiling. Chitosan (CHI) samples possessing different degrees of acetylation ([Formula: see text]) and molecular weight ([Formula: see text]) produced via the ultrasound-assisted deacetylation reaction were used in this study along with two different polyanions, namely, sodium polystyrenesulfonate (PSS) and carboxymethylcellulose (CMC). When chitosan, a positively charged polymer in aqueous acid medium, was combined with a strong polyanion (PSS), the total positive charge of chitosan, directly related to its [Formula: see text], was the key factor affecting the film formation. However, for CMC/CHI films, the pH of the medium and [Formula: see text] of chitosan strongly affected the film structure and composition. Consequently, the structure and the axial composition of chitosan-based films can be finely adjusted by choosing the polyanion and defining the chitosan to be used according to its DA and [Formula: see text] for the desired application, as demonstrated by the antibacterial tests.

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