Biomedical-Grade Chitosan in Wound Management and Its Biocompatibility In Vitro

Abstract

Chitin (┚-1,4-D-linked polymer of N-acetylglucosamine) is a naturally abundant mucopolysaccharide and is second to cellulose in terms of the amount produced annually by biosynthesis. Chitin is visually characterized as a white, hard, inelastic, nitrogenous polysaccharide, and approximately one billion tons are synthesized each year (Peter, 1997). Chitin is a common constituent of the exoskeleton in animals, particularly in crustaceans, mollusks and insects. Commercially sold chitin is usually extracted from shellfish waste (Skjak-Braek et al., 1989; Goosen, 1997). Chitin is structurally similar to cellulose; however less attention has been paid to chitin than cellulose, primarily due to its inertness. Hence, it remains an essentially unutilized resource. Deacetylation of chitin yields chitosan, which is a relatively reactive compound and is produced in numerous forms, such as powder, paste, film and fiber. Chitosan is a poly-(┚-1, 4-D-glucosamine) derived from the N-deacetylation of chitin (Figure 1). It is soluble in dilute aqueous acetic, lactic, malic, formic and succinic acids. Chitosan may be fully or partially N-deacetylated, but the degree of acetylation is typically less than 0.35. The acetylation ratio is defined by a variety of methods, including pyrolysis gas chromatography, gel permeation chromatography and ultra-violet (UV) spectrophotometry, titration, separation spectrometry and near-infrared spectroscopy (Kumar, 2000). Most commercial chitosans have a degree of deacetylation that is greater than 70% and a molecular weight ranging between 100,000 and 1.2 million Da (Li et al., 1997). Chitosans are of commercial interest due to their high percentage of nitrogen compared to synthetically substituted cellulose, rendering them useful for metal chelation and polyoxysalt and film formulations. Chitosan is polycationic at pH< 6 and it readily interacts with negatively charged molecules, such as proteins, anionic polysaccharides (e.g. , alginate and cargeenan), fatty acids, bile acids and phospholipids (Muzzarelli, 1996). Nonetheless, chitosan may also selectively chelate metal ions such as iron, copper, cadmium and magnesium. Wound healing is defined as a tissue restoration and reparative process that is typically comprised of a continuous sequence of inflammation and repair, in which epithelial, endothelial and inflammatory cells, platelets and fibroblasts interact to resume their normal functions. The wound healing process is regulated by cytokines and growth factors and consists of four phases: the process is initialized by inflammation, followed by granulation, matrix remodeling and re-epithelialization. Research is currently being conducted to discover ways for humans to heal via regeneration and the use of a variety of dressing