Chitin and chitosan are biological polymers with promising commercial and biomedical applications. Researchers have long explored the properties and derivative functions of these two polymers. Because of their expansive use, chitin and chitosan are poised to become one of the most important natural resources in the future.
Backgrounder on chitin and chitosan
Chitin is a translucent, pliable, and tough material in its pure and unmodified form. It is abundant in nature because it is a critical component of the exoskeletons of arthropods and insects, beaks and internal shells of cephalopods, and cell walls of fungi.
According to a literature review by Feisal Khoushab and Montarop Yamabhai, French professor Henri Braconnot discovered chitin in 1811. The name came from the French word chitine and Greek word chiton—both mean “covering.”
Today, chitin is the second most important biopolymer in the world according to Marguerite Rinaudo. Shrimps and crabs are the most commonly exploited source because chitin, after all, is actually a waste product of the shrimp canning and crabbing industries.
Khoushab and Yabhai further described chitin as a biocompatible, biodegradable, and bio-absorbable polymer with antibacterial and wound-healing properties. However, despite these characteristics, researcher M. N. V. Kumar noted that chitin remains an underutilised resource.
Chitosan, on the other hand, is a derivative of chitin. Rinaudo noted that this polymer is the most important of other chitin derivatives. Its production involves deacetylation of chitin, particularly by treating the shells of shrimps and crabs, or other crustaceans with sodium hydroxide.
Fertilizer and pesticide in agriculture
Chitin and chitosan have agricultural value. Several studies have pointed out the capacity of chitin and chitosan to induce defense mechanisms in plants, thereby resulting in improve seed germination, plant growth, and yields. Lee A. Hadwiger explored the multiple effects of chitosan on plant systems. Accordingly, when absorbed, chitosan influences the biochemistry and molecular biology of plant cells, thus activating defense responses in plants.
Several chitin-derived agricultural applications have also been patented for commercial use. For example, R. J. Stoner and J. C. Linden invented a micronutrient elicitor for treating nematodes in field crop. This elicitor can be used as a seed coating, a component of irrigation water, or a component of foliar spray. Donald E. Freepons, on the other hand, invented a plant growth regulator made of chitosan and non-phytotoxic acid. When applied as an aqueous solution or as a component of dry blend powders, the substance can influence and regulate plant growth.
Currently, the U.S. Environmental Protection Agency and the U.S. Department of Agriculture, National Organic Program regulate chitin and chitosan or other derivatives for agricultural use, specifically as a bio-pesticide.
Other industrial applications of chitin and chitosan
The same biological polymers derived from shellfishes, insects, and other species have also found their way in several manufacturing processes across different industries.
Chitosan is a non-toxic and biodegradable plastic alternative. In the literature review by S. K. Shukla et al, they described chitosan as a promising material with immense structural possibilities for chemical and mechanical modification needed to produce novel properties and functions. The Wyss Institute at Harvard University has successfully created so-called bio-plastics made from chitosan using traditional casting or inject-molding techniques. This process can be replicated to manufacture components of toys and consumer electronic devices.
Apart from the non-toxic and biodegradable properties of chitosan, using this polymer in manufacturing will promote sustainable industrial practices. Accordingly, the marine environment remains the main source of chitin and chitosan. Thus, these natural resources do not compete against other land resources.
Food manufacturing and processing can also benefit from chitin and chitosan. For instance, a chemically modified chitin can be used as an alternative thickening and stabilising agent in processed foods according to Shahidi, Ararchi, and Jeon. According to a study of Quintela et al, chitosan has also been used as a fining agent in winemaking, specifically in removing ochratoxin—a group of mycotoxins from several species of fungi that could cause acute toxicity in mammalian kidneys coupled with a potential carcinogenic effect in humans.
A more novel application of chitosan is in self-healing coating and paints. Researchers have incorporated chitosan into traditional polymer materials to develop a coating substance to protect paints from scratches. Accordingly, when a scratch damages the structure of the coating, it automatically repairs by itself upon exposure to sunlight as chitosan form chemical chains that bond with other polymer materials.
Researchers from Queen Mary, University of London are also exploring the potential of using chitosan as a cheaper alternative component of solar cells. However, current prototypes have low efficiency to produce electricity.
Biomedical and pharmaceutical applications
The United States and Europe have approved the use of bandages and hemostatic agents that include chitosan as one of the critical components. Accordingly, this biopolymer has several properties that allow rapid blood clotting. A study by Brown, Daya, and Worley involving U.S. Marin Corp revealed that chitosan-based hemostatic products improve the survival from otherwise lethal arterial wounds because of their ability to stop bleeding and thus, reduce blood loss.
There are nonetheless expansive biomedical and pharmaceutical applications for chitin and chitosan. The separate researches from P. K. Dutta, J. Dutta, and V. S. Dutta, and F. Khoushab and M. Yamabhai have enumerated the possible medicinal properties and uses of the biopolymers. These include antitumor, anticholestermic, antioxidant, antimicrobial, or blood cholesterol control, regenerative effects on bones and tissues, and nerve regeneration.
Chitin and chitosan also open newer possibilities for drug administration and other healthcare processes. These include drug delivery and gene delivery using chitin-based nanostructures. Accordingly, the biocompatibility, biodegradability, and non-toxic properties of these polymers, coupled with superior physical and chemical properties make them suitable for engineering new class of pharmaceutical delivery systems.
Further details of the literature review of Khoushab and Yamabhai are in the article “Chitin research revisited” published in 2010 in the journal Marine Drugs. Details of the review study of Kumar are in the article “A review of chitin and chitosan applications” published in 2000 in the journal Reactive and Functional Polymers.
Further details of the review study of Hadwiger are in the article “Multiple effects of chitosan on plant systems: Solid science or hype” published in 2013 in the journal Plant Science. Details of the invention of Stoner and Linden are in the patient information “Micronutrient elicitor for treating nematodes in field crops” published online by Google Patents. Details of the invention of Freepons are in the patent information “Plant growth regulators derived from chitin” published online by Google Patents.
Details of the literature review by S. K. Shukla et al are in the article “Chitosan-based nanomaterials: A state-of-the-art review” published in 2013 in the International Journal of Biological Macromolecules. Details of the Harvard-produced chitosan-based plastic are in the article “Promising solution to plastic pollution” published in 2014 in the Harvard Gazette.
Details of the study of Shahidi, Ararchi, and Jeon are in the article “Food applications of chitin and chitosan” published in 1999 in the journal Trends in Food Science and Technology. Details of the study of Quintela et al are in the article “Ochratoxin A removal from red wine by several oenological fining agents: bentonite, egg albumin, allergen-free adsorbents, chitin and chitosan” published in 2012 in the journal Food Additives and Contaminants.
Further details of the study of Brown, Daya, and Worley are in the article “Experience with chitosan dressings in a civilian EMS system” published in 2006 in The Journal of Emergency Medicine.