Chitosan is a naturally originating product that can be applied in many areas due to its biocompatibility, biodegradability, and nontoxic properties. The broad-spectrum antimicrobial activity of chitosan offers great commercial potential for this product. Nevertheless, the antimicrobial activity of chitosan varies, because this activity is associated with its physicochemical characteristics and depends on the type of microorganism. In this review article, the fundamental properties, modes of antimicrobial action, and antimicrobial effects-related factors of chitosan are discussed. We further summarize how microorganisms genetically respond to chitosan. Finally, applications of chitosan-based biomaterials, such as nanoparticles and films, in combination with current clinical antibiotics or antifungal drugs, are also addressed.

Antimicrobial Actions and Applications of Chitosan

Coronavirus 19 Disease (COVID-19) originating in the province of Wuhan, China in 2019, is caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), whose infection in humans causes mild or severe clinical manifestations that mainly affect the respiratory system. So far, the COVID-19 has caused more than 2 million deaths worldwide. SARS-CoV-2 contains the Spike (S) glycoprotein on its surface, which is the main target for current vaccine development because antibodies directed against this protein can neutralize the infection. Companies and academic institutions have developed vaccines based on the S glycoprotein, as well as its antigenic domains and epitopes, which have been proven effective in generating neutralizing antibodies. However, the emergence of new SARS-CoV-2 variants could affect the effectiveness of vaccines. Here, we review the different types of vaccines designed and developed against SARS-CoV-2, placing emphasis on whether they are based on the complete S glycoprotein, its antigenic domains such as the receptor-binding domain (RBD) or short epitopes within the S glycoprotein. We also review and discuss the possible effectiveness of these vaccines against emerging SARS-CoV-2 variants.

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SARS-CoV-2 Vaccines Based on the Spike Glycoprotein and Implications of New Viral Variants.

Currently, the treatment and care of diabetic wounds, which generally possess the characteristics of a high amputation rate, high recurrence rate and high mortality, has developed into a worldwide challenge. Wound dressings have been playing an important role in diabetic wound treatment and continuously innovated to obtain many amazing properties. Among them, hydrogel dressings have become one of the most attractive and promising wound dressings because of their considerable moisture retention, biocompatibility and therapeutic properties. In recent years, with the in depth understanding of the pathogenesis of diabetic wounds, various functionalized hydrogel dressings have been reported and shown encouraging results, which has brought great benefits to the improvement of diabetic wounds. In this work, we will systematically and comprehensively summarize the advances of hydrogel dressings in diabetic wounds, aiming to provide not only theoretical support for hydrogel dressing devising but also inspiration for diabetic wound treatment.

Advances of hydrogel dressings in diabetic wounds.

Augmentation of immunogenicity can be achieved by particulate delivery of an antigen and by its co-administration with an adjuvant. However, many adjuvants initiate strong systemic inflammatory reactions in vivo, leading to potential adverse events and safety concerns. We have developed a synthetic vaccine particle (SVP) technology that enables co-encapsulation of antigen with potent adjuvants. We demonstrate that co-delivery of an antigen with a TLR7/8 or TLR9 agonist in synthetic polymer nanoparticles results in a strong augmentation of humoral and cellular immune responses with minimal systemic production of inflammatory cytokines. In contrast, antigen encapsulated into nanoparticles and admixed with free TLR7/8 agonist leads to lower immunogenicity and rapid induction of high levels of inflammatory cytokines in the serum (e.g., TNF-a and IL-6 levels are 50- to 200-fold higher upon injection of free resiquimod (R848) than of nanoparticle-encapsulated R848). Conversely, local immune stimulation as evidenced by cellular infiltration of draining lymph nodes and by intranodal cytokine production was more pronounced and persisted longer when SVP-encapsulated TLR agonists were used. The strong local immune activation achieved using a modular self-assembling nanoparticle platform markedly enhanced immunogenicity and was equally effective whether antigen and adjuvant were co-encapsulated in a single nanoparticle formulation or co-delivered in two separate nanoparticles. Moreover, particle encapsulation enabled the utilization of CpG oligonucleotides with the natural phosphodiester backbone, which are otherwise rapidly hydrolyzed by nucleases in vivo. The use of SVP may enable clinical use of potent TLR agonists as vaccine adjuvants for indications where cellular immunity or robust humoral responses are required.

Adjuvant-carrying synthetic vaccine particles augment the immune response to encapsulated antigen and exhibit strong local immune activation without inducing systemic cytokine release

Absorption, distribution, metabolism and excretion of the biomaterials used in Nanocarrier drug delivery systems.

Chitosan is a product of the deacetylation of chitin, which is widely found in nature. Chitosan is insoluble in water and most organic solvents, which seriously limits both its application scope and applicable fields. However, chitosan contains active functional groups that are liable to chemical reactions; thus, chitosan derivatives can be obtained through the chemical modification of chitosan. The modification of chitosan has been an important aspect of chitosan research, showing a better solubility, pH-sensitive targeting, an increased number of delivery systems, etc. This review summarizes the modification of chitosan by acylation, carboxylation, alkylation, and quaternization in order to improve the water solubility, pH sensitivity, and the targeting of chitosan derivatives. The applications of chitosan derivatives in the antibacterial, sustained slowly release, targeting, and delivery system fields are also described. Chitosan derivatives will have a large impact and show potential in biomedicine for the development of drugs in future.

https://www.mdpi.com/1422-0067/21/2/487/pdf

Chitosan Derivatives and Their Application in Biomedicine.

Abstract 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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Applications of polymer-based nanoparticles in vaccine field

An overview of biodegradable nanomaterials and applications in vaccines.

Water-soluble N-2-Hydroxypropyl trimethyl ammonium chloride chitosan enhanced the immunogenicity of inactivated porcine parvovirus vaccine vaccination on sows against porcine parvovirus infection

Mo Zhou

Papers

Chitosan Derivatives and Their Application in Biomedicine.

Applications of polymer-based nanoparticles in vaccine field

An overview of biodegradable nanomaterials and applications in vaccines.

Water-soluble N-2-Hydroxypropyl trimethyl ammonium chloride chitosan enhanced the immunogenicity of inactivated porcine parvovirus vaccine vaccination on sows against porcine parvovirus infection