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Main types of polysaccharides, strategies for killing bacteria and typical fabrication methods.

A significant amount of research has been devoted to developing polysaccharide-based strategies that inhibit bacterial attachment and biofilm formation on surfaces in order to combat antimicrobial resistance, a global threat identified by the United Nations that is a common cause of healthcare-associated infections (HAI) and is responsible for significant costs on healthcare systems. Polysaccharides are a plentiful renewable resource that have drawn a lot of interest because of their remarkable biological properties. Polysaccharide-based coatings have the potential to have a significant global impact if they are developed into effective antibacterial coatings that can be used on a variety of surfaces and applications. This is according to research from Chalmers University of Technology, in the journal Acta Biomaterialia.

What is HAI?

Infections that are contracted while receiving or providing healthcare are known as healthcare-associated infections (HAI), and they can affect both patients and healthcare professionals. Hospitals, long-term care facilities for the elderly, outpatient settings, and even after discharge are all places where HAI can occur, particularly for patients who rely on medical devices like implants, catheters, hernia mesh, wound dressings, and vascular grafts. One of the most frequent adverse events, along with bloodstream infections, pneumonia, gastrointestinal infections, and surgical site infections, is HAI, which puts patients’ safety at risk. It is a significant contributor to rising morbidity, mortality, and financial costs for individuals, families, and healthcare systems around the world. The misuse and overuse of antibiotics, which has been one of the main factors in the spread of antimicrobial resistance, has added to the complexity of HAI by causing bacteria to develop resistance to the majority of common antibiotics, making HAI very challenging to treat. Antimicrobial resistance has been referred to as a global threat by the United Nations as a result.

What are the strategies to prevent HAI?

Bacterial adhesion to the surface of biomaterials and surrounding tissues is the primary cause of HAI. Bacterial adhesion is a complex process that typically involves two stages. Bacterial cells and the surface of the material interact quickly and irreversibly in the first stage. This interaction is typically non-specific and easily broken. Second, adhesion proteins that mediate the interaction with molecules on the material surface are excreted by bacteria. The presence of adhesins on the surfaces of the microbial cells renders this step irreversible (or only marginally reversible). Biofilm formation can improve the interaction between bacteria and the material surface after the adhesion process.

Accordingly, the main approach for designing antibacterial surfaces is to prevent bacteria from adhering to the surface of the material or kill the attached bacteria. Therefore, three strategies to design antibacterial coatings have been proposed: bacteria-repelling, contact-killing, and antibacterial agent release. Bacteria-repelling surfaces can prevent the initial attachment of bacteria in Stage 1. Through contact-killing the cell wall of bacteria is destroyed when in touch with an antibacterial surface. Surfaces embedded with releasable antibacterial agents could kill both adherent and planktonic bacteria efficiently.

Fig. 1. Illustration of the three stages of bacterial adhesion. In Stage 1, the single free-floating bacterium attaches to the material surface and attempts to anchor itself by adhesion structures such as pili and fimbriae; in Stage 2, during the surface colonization the bacteria proliferate into a colony; in the final stage the colony can produce a biofilm to protect growing bacteria.

What are polysaccharides?

Polysaccharides are a group of biomacromolecules composed of different kinds of glycosidic-bonded monosaccharides, and because they are essential building blocks for life they are commonly found in nature from renewable sources. Due to their inherent remarkable biological properties, such as hypoglycemic, hypolipidemic, anticancer, antioxidant, immune-stimulating, antibacterial, etc., polysaccharides have garnered a lot of attention. A polysaccharide-based antibacterial formulation may also significantly affect bacterial biofilms by interfering with quorum sensing, adhesion activity, formation, and efflux pumps, according to some research. Additionally, it has been suggested that polysaccharides may harm bacteria’s cell membrane and cell wall through a variety of mechanisms, such as altering the permeability of the bacterial cell walls and cell membrane, undermining enzyme system integrity in bacterial membrane, impeding cell membrane function, as well as exert antibacterial activities via affecting the nucleic acid and even changing the intracellular metabolic pathways of bacteria.

Table 1. Main polysaccharides considered for antibacterial coatings: structure, properties and origins.

What are the technologies of antibacterial polysaccharide-based coatings?

Polysaccharides present significant potential for antibacterial coating applications combining a broad range of bactericidal strategies and coating technologies. This has been substantiated by a significant number of publications dedicated to the subject, with a broad range of potential applications. However, antibacterial polysaccharides must be compatible with scalable, adaptable, and reasonably priced manufacturing processes to be converted into commercially useful materials. The key to their applicability will be polysaccharide-based antibacterial formulations that can be applied as coatings on the surface of a wide range of substrate materials with any type of shape while also being mechanically and environmentally stable.

Since 2016, chitosan has received the most research attention. The second-most popular polysaccharide is cellulose, which is also prominently featured. However, this is likely due to its availability, which makes it a very attractive material for developing into antibacterial coatings. Although mostly in the context of other polysaccharide formulations, alginate and hyaluronic acid have also been extensively studied. The popular fabrication method for all polysaccharides used in antibacterial coatings is LbL assembly. This demonstrates the adaptability of the LbL method as well as the efficacy of polysaccharides. There are also other fabrication methods such as dip coating, electrospinning, and spin coating, which are also significant for polysaccharides.

Find more information in the scientific journal Acta Biomaterialia: Polysaccharide-based antibacterial coating technologies.