Ultrasound-assisted preparation of size-controlled chitosan nanoparticles: Characterization and fabrication of transparent biofilms

The use of biodegradable natural polymers is a suitable alternative for the preparation of more environmentally- friendly plastics and biocompatible nanoparticulated systems. Chitosan is an abundant and inexpensive candidate. However, its transparent films present poor mechanical response and high sensitivity to moisture. Moreover, the findings made by different researchers on the effects of molecular mass and degree of deacetylation (DD) on these properties are still controversial. This paper aims to unveil the separate effects of these parameters on biofilm properties. For these purposes, two aqueous solutions of chitosan (DD = 90 and 95%) were submitted to controlled fragmentation by ultrasonication. The resulting solutions were characterized by rheological techniques and the nanoparticles formed were studied ex-situ by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Irrespective of DD, the application of longer sonication times reduced the viscoelasticity of the solutions and yielded nanoparticles with lower size (and molecular mass). The mechanical strength and stiffness of transparent biofilms fabricated from these solutions, without plasticizers, were determined in stress tests. Sensitivity to moisture was also evaluated through water vapor permeability measurements and water sorption isothermal data. The results showed a significant decrease in the permeability with decreasing the molecular mass. However, the mechanical properties were adversely affected. These findings may be useful for the future design of bioplastics with improved properties but also for the development of biocompatible nanoparticles with tunable size and molecular mass. [Display omitted] Chitosans with different degree of deacetylation (DD) were fragmented under ultrasonic irradiation and characterized by rheological techniques. Then, the roles played by molecular mass and DD on the structural characteristics, moisture sensitivity, and mechanical properties of transparent plastic films of pure chitosan could be unveiled without interferences of plasticizers. ► Chitosans with different degree of deacetylation were fragmented under ultrasonic irradiation. ► Viscoelastic properties were characterized by rheological techniques. ► Particle morphology was studied by Atomic Force Microscopy and Scanning Electron Microscopy. ► Transparent chitosan films were produced without the incorporation of additive or plasticizer.