Chitosan (Chi) is a natural biodegradable cationic polymer with remarkable potency as a vehicle for drug or vaccine delivery. Chi possesses multiple groups, which can be used both for Chi derivatization and for particle formation. The aim of this work was to produce stable nanosized range Chi gels (nanogels, NGs) with different charge and to study the driving forces of complex formation between Chi NGs and proteins or peptides. Positively charged NGs of 150 nm in diameter were prepared from hexanoyl chitosan (HC) by the ionotropic gelation method while negatively charged NGs of 190 nm were obtained from succinoyl Chi (SC) by a Ca²⁺ coacervation approach. NGs were loaded with a panel of proteins or peptides with different weights and charges. We show that NGs preferentially formed complexes with oppositely charged molecules, especially peptides, as was demonstrated by gel-electrophoresis, confocal microscopy and HPLC. Complex formation was accompanied by a change in zeta-potential and decrease in size. We concluded that complex formation between Chi NGs and peptide/proteins is mediated mostly by electrostatic interactions.

The global aquaculture industry faces a number of challenges, including the risk of infection spreading in closed aquatic ecosystems. Since 1942, vaccination has become a mainstream approach in fish cultivation. However, the immune system of cold-blooded organisms differs significantly from that of mammals, which must be taken into account when developing vaccines for aquaculture. Modern technology employs delivery systems for antigens to protect them from degradation in the water and the digestive tract. Packaging the antigen into a biodegradable structure protects the protein or target gene from degradation and enhances antigen delivery to immune cells. The combination of chitosan and alginate is widely used for the development of various types of nano- and microcarriers. New vaccines based on these polysaccharides are more effective, increasing survival rates in some fish species by up to 100% compared to 20% in the control group. However, the correlation between the observed effects and the physicochemical characteristics of the polysaccharides/carriers, and the mechanisms of their action, remains unclear. This review summarizes and analyzes the data on the use of chitosan and alginate in aquaculture vaccines. Particular focus is given to the physicochemical properties and sources of the polysaccharides, and their potential implementation in aquaculture vaccination practices.

Chitosan is a biodegradable and biocompatible polysaccharide widely used in different applications in medicine. The polycationic structure of the polymer provides many possibilities for its modification. One of the most interesting applications of chitosan is the development of nanosized delivery systems for biologically active molecules. The functional properties of these delivery systems depend severely on the structure and properties of nanoparticles. Using dynamic light scattering, atomic force microscopy, and to confocal microscopy, we have shown that both hexanoyl chitosan (HC) and succinoyl chitosan (SC) formed nanoparticles of comparable diameters from 120 to 250 nm. Using several methods of analysis helped us identify a minor fraction with a larger size of 600 to 700 nm formed by nanoparticle aggregates. The determined ζ potential was from −20 to −25 mV for SC nanoparticles and from 30 to 35 mV for HC nanoparticles.