Chitosan is a biodegradable natural polymer with many advantages such as nontoxicity, biocompatibility, and biodegradability. It can be applied in many fields, especially in medicine. As a delivery carrier, it has great potential and cannot be compared with other polymers. Chitosan is extremely difficult to solubilize in water, but it can be solubilized in acidic solution. Its insolubility in water is a major limitation for its use in medical applications. Chitosan derivatives can be obtained by chemical modification using such techniques as acylation, alkylation, sulfation, hydroxylation, quaternization, esterification, graft copolymerization, and etherification. Modified chitosan has chemical properties superior to unmodified chitosan. For example, nanoparticles produced from chitosan derivatives can be used to deliver drugs due to their stability and biocompatibility. This review mainly focuses on the properties of chitosan, chitosan derivatives, and the origin of chitosan-based nanoparticles. In addition, applications of chitosan-based nanoparticles in drug delivery, vaccine delivery, antimicrobial applications, and callus and tissue regeneration are also presented. In summary, nanoparticles based on chitosan have great potential for research and development of new nano vaccines and nano drugs in the future.

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Polymer-based nanoparticles have good solubility, stability, safety, and sustained release,which increases the absorption of loaded drugs, protects the drugs from degradation, and prolongs their circulation time and targeted delivery. Generally, we believe that prevention and control of infectious diseases through inoculation is the most efficient measure. However, these vaccines including live attenuated vaccines, inactivated vaccines, protein subunit vaccines, recombinant subunit vaccines, synthetic peptide vaccines and DNA vaccines have several defects, such as immune tolerance, poor immunogenicity, low expression level and induction of respiration pathological changes. All kinds of biodegradable natural and synthetic polymers play major roles in the vaccine delivery system to control the release of antigens for an extended period of time. In addition, these polymers also serve as adjuvants to enhance the immunogenicity of vaccine. This review mainly introduces natural and synthetic polymer-based nanoparticles and their formulation and properties. Moreover, polymer-based nanoparticles as adjuvants and delivery carriers in the applications of vaccine are also discussed. This review provides the basis for further operation of nano vaccines by utilizing the polymer-based nanoparticles as vaccine adjuvants and delivery systems. Polymer-based nanoparticles have exhibited great potential in improving the immunogenicity of antigens and the development of nano vaccines in future.

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