In agriculture, chitosan is typically used as a natural seed treatment and plant growth enhancer, and as an ecologically friendly biopesticide substance that boosts the innate ability of plants to defend themselves against fungal infections. The natural biocontrol active ingredients, chitin/chitosan, are found in the shells of crustaceans, such as lobsters, crabs, and shrimp, and many other organisms, including insects and fungi. It is one of the most abundant biodegradable materials in the world. Degraded molecules of chitin/chitosan exist in soil and water. Chitosan applications for plants and crops are regulated by the EPA, and the USDA National Organic Program regulates its use on organic certified farms and crops. EPA-approved, biodegradable chitosan products are allowed for use outdoors and indoors on plants and crops grown commercially and by consumers.
Chitosan active biopesticides represent a new tier of cost-effective biological control of crops for agriculture and horticulture. The biocontrol mode of action of chitosan elicits natural innate defense responses within plant to resist insects, pathogens, and soil-borne diseases when applied to foliage or the soil. Chitosan increases photosynthesis, promotes and enhances plant growth, stimulates nutrient uptake, increases germination and sprouting, and boosts plant vigor.
Agricultural applications of chitosan can reduce environmental stress due to drought and soil deficiencies, strengthen seed vitality, improve stand quality, increase yields, and reduce fruit decay of vegetables, fruits and citrus crops. Horticultural application of chitosan increases blooms and extends the life of cut flowers and Christmas trees. The US Forest Service has conducted research on chitosan to control pathogens in pine trees and increase resin pitch outflow which resists pine beetle infestation.
A natural chitosan elicitor solution for agriculture and horticultural uses was granted an amended label for foliar and irrigation applications by the EPA in 2009. Given its low potential for toxicity and abundance in the natural environment, chitosan does not harm people, pets, wildlife, or the environment when used according to label directions. The US Forest Service tested chitosan as an ecofriendly biopesticide to prearm pine trees to defend themselves against mountain pine beetles.
Chitosan can also be used in water processing engineering as a part of a filtration process. Chitosan causes the fine sediment particles to bind together, and is subsequently removed with the sediment during sand filtration. It also removes phosphorus, heavy minerals, and oils from the water. Chitosan is an important additive in the filtration process. Sand filtration apparently can remove up to 50% of the turbidity alone, while the chitosan with sand filtration removes up to 99% turbidity. Chitosan has been used to precipitate caseins from bovine milk and cheese making.
Chitosan is also useful in other filtration situations, where one may need to remove suspended particles from a liquid. In combination with bentonite, gelatin, silica gel, isinglass, or other fining agents, it is used to clarify wine, mead, and beer. Added late in the brewing process, chitosan improves flocculation, and removes yeast cells, fruit particles, and other detritus that cause hazy wine. Chitosan combined with colloidal silica is becoming a popular fining agent for white wines, because chitosan does not require acidic tannins (found primarily in red wines) with which to flocculate.
Bioinspired materials, a manufacturing concept inspired by natural nacre, shrimp carapace or insect cuticles, has led to development of bioprinting methods to manufacture large scale consumer objects using chitosan. This method is based on replicating the molecular arrangement of chitosan from natural materials into fabrication methods, such as injection molding or mold casting. Once discarded, chitosan-constructed objects are biodegradable and non-toxic. The method is used to engineer and bioprint human organs or tissues.
Pigmented chitosan objects can be recycled, with the option of reintroducing or discarding the dye at each recycling step, enabling reuse of the polymer independently of colorants. Unlike other plant-based bioplastics (e.g. cellulose, starch), the main natural sources of chitosan are from marine environments and do not compete for land or other human resources.
Winemaking and fungal source chitosan
Chitosan has a long history for use as a fining agent in winemaking. Fungal source chitosan has shown an increase in settling activity, reduction of oxidized polyphenolics in juice and wine, chelation and removal of copper (post-racking) and control of the spoilage yeast Brettanomyces. These products and uses are approved for European use by the EU and OIV standards.
Potential industrial uses
Scientists have developed a polyurethane coating that heals its own scratches when exposed to sunlight. The self-healing coating uses chitosan incorporated into traditional polymer materials, such as those used in coatings on cars to protect paint. When a scratch damages the chemical structure, the chitosan responds to sunshine by forming chemical chains that bond with other materials in the substance, eventually smoothing the scratch. The process can take less than an hour.
The polymer can only repair itself in the same spot once, and would not work after repeated scratches. Whether this technology can be applied to industrial materials, however, depends on a number of factors, such as long-term persistence of the repair, stiffness and heat resistance of the coating.
Chitosan’s properties allow it to rapidly clot blood, and has recently gained approval in the United States and Europe for use in bandages and other hemostatic agents. Chitosan hemostatic products have been shown in testing by the U.S. Marine Corps to quickly stop bleeding and to reduce blood loss, and result in 100% survival of otherwise lethal arterial wounds in swine. Chitosan hemostatic products reduce blood loss in comparison to gauze dressings and increase patient survival. Chitosan hemostatic products have been sold to the U.S. Army and are currently used by the UK military. Both the US and UK have already used the bandages on the battlefields of Iraq and Afghanistan. Chitosan is hypoallergenic and has natural antibacterial properties, which further support its use in field bandages. Chitosan’s hemostatic properties also allow it to reduce pain by blocking nerve endings
Chitosan hemostatic agents are often chitosan salts made from mixing chitosan with an organic acid (such as succinic or lactic acid). The hemostatic agent works by an interaction between the cell membrane of erythrocytes (negative charge) and the protonated chitosan (positive charge) leading to involvement of platelets and rapid thrombus formation. The chitosan salts can be mixed with other materials to make them more absorbent (such as mixing with alginate), or to vary the rate of solubility and bioabsorbability of the chitosan salt. The chitosan salts are biocompatible and biodegradable making them useful as absorbable haemostats. The protonated chitosan is broken down by lysozyme in the body to glucosamine and the conjugate base of the acid (such as lactate or succinate) are substances naturally found in the body. The chitosan salt may be placed on an absorbable backing. The absorbable backing may be synthetic (for instance made from existing absorbable suture materials e.g. Tephaflex polymer) or natural (e.g. cellulose or gelled/solidified honey). In addition to salts, hydrogel-based chitosan bandages have been developed to treat burn wounds. Burns are similar to other wounds, but are problematic because they are associated with membrane destabilization, energy depletion, and hypoxia, all of which can cause severe tissue necrosis if not treated properly or quickly enough. Chitosan-gelation bandages using nanofibrin have been shown to be more durable than ointments, while still allowing gas exchange at the cell surface.
In 2016 researchers announced a chitosan-based plastic wrap that doubles the shelf life of some foods. The plastic also included grapefruit seed extract, which has antibacterial and antifungal properties, and is an antioxidant, antiseptic and anti-viral. The film blocked the transmission of ultraviolet light — slowing oxidation and photochemical deterioration. The plastic can use raw ingredients that would otherwise be discarded, and biodegrades once discarded.