Natural polymers, such as gelatin, cellulose, alginate, chitin, starch, rubber, and fibrin, are used to develop green nanocomposites. Their use also expands to applications like biosensors, coatings, electronic devices, adhesives, and optical circuits. This article focuses on the applications of different types of natural polymer nanocomposites.
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Natural polymers are often preferred over synthetic polymers due to their non-toxic nature, chemical inertness, and biodegradability. Coupling natural polymers with inorganic nanoparticles fillers helps to improve particular features related to magnetic, electrical conductivity, and antimicrobial activity. Applications of different types of natural polymers nanocomposites are discussed below.
Metal-Cellulose Nanocomposites
Cellulose is a natural polymer composed of a linear chain of β [1 → 4] attached D-glucose units.
Silver-cellulose nanocomposites, which exhibit strong antimicrobial and catalytic activities, can be synthesized utilizing chemical reduction methodologies.
Gold-cellulose nanocomposites have been applied for immobilizing enzymes, such as glucose oxidase and horseradish peroxidase.
These metal-cellulose nanocomposites exhibit superior biocompatibility, conductivity, and large surface area and are used as biosensors to identify various biomolecules, including glucose.
Metal-Alginate Nanocomposites
Alginate is a polysaccharide composed of β-mannuronic acid and αguluronic acid. It is extracted from brown algae, such as Laminaria saccharina and Laminaria digitate. Sodium alginates and calcium alginates are used in wound dressings as they can maintain moisture, stop the bleeding, and relieve pain.
Incorporating silver nanoparticles with alginates has provided an added antimicrobial property for wound dressing.
Notably, silver nanoparticles are effective against antibiotic-resistant bacteria. Furthermore, this nanocomposite is also used for disinfecting drinking water in water treatment plants, where it is packed into the column containing water with bacteria. Alginate coupled with chitosan and gelatin, along with metallic nanoparticles, are suitable for controlled delivery of drugs.
Metal-Chitin Nanocomposite
Chitin is a long-chain polymer of N-acetylglucosamine present in crabs, shrimps, mushrooms, and insects. This polymer is insoluble in conventional solvents for which it is chemically modified.
Modified chitin containing a carboxymethyl group is highly soluble in water, and carboxymethyl chitin-metal nanocomposites are applied in various areas, including medicine, biotechnology, electronics, and catalysis.
Metal-Chitosan Nanocomposites
Chitosan is a natural polymer of N-acetyl glucosamine units of chitin. It is found in mollusks and crustaceans.
Silver-chitosan nanocomposite has been prepared via direct dispersion of silver nanoparticles into chitosan. This nanocomposite exhibits antimicrobial properties. Gold-chitosan nanocomposites coupled with clay nanoplates of opposite charge are used as biosensors for horseradish peroxidase enzyme.
Metal-Starch Nanocomposites
Starch, a semi-crystalline polymer material, has been extensively used in manufacturing foams, papers, adhesives, and textiles.
A stable silver-starch nanocomposite was prepared using a direct chemical reduction method, exhibiting antibacterial properties. Grafting starch onto synthetic polymers results in the formation of novel graft copolymers that can be used for manufacturing nanocomposite hydrogels.
Silver-starch-polyacrylamide hydrogel prepared by grafting starch and acrylamide possesses antimicrobial properties and is used in wound dressings.
Metal-Guar Gum Nanocomposites
Guar gum is a natural polymer obtained from Cyamopsis tetragonoloba (guar) seed. This polymer is composed of β 1,4-D-mannopyranoses and D-galactopyranoses, has been wildly used in textile painting and cement fabrication. Silver-guar gum nanocomposite has been used in catalytic reduction. Silver-chitosan-guar gum hybrid matrix is immobilized with enzymes and used as sensors for detecting glucan and glucose.
Metal-Gelatin Nanocomposites
Gelatin is a natural polymer extracted from animal tissues containing collagen. Gelatin is used for wound dressing because it can absorb exudates and provide the moisture required for a fast healing process. However, one of the disadvantages of using only gelatin for wound healing is that it cannot prevent infection. This limitation has been overcome by incorporating silver nanoparticles, which possess exceptional antimicrobial properties.
Scientists developed silver-gelatin nanocomposite via UV reduction method, which is extensively applied in wound dressing as it contains desirable properties of both gelatin and silver nanoparticles. Gold-gelatin nanocomposite has been used in cancer therapy.
Metal-Dextran Nanocomposites
Dextran is a water-soluble polysaccharide of large molecules of glucose monomers, which is extensively used as an emulsifier and stabilizer in many industrial and medical applications. Silver-dextran nanocomposite is used as an aggregate sensor for glucose. Additionally, this nanocomposite was aggregated by the controlled addition of concanavalin A to study the interaction between proteins and carbohydrates. Silver- N-methylenebisacrylamide- dextran hybrid nanocomposite has been utilized for antibacterial and catalytic applications
Metal-Pectin Nanocomposites
Pectin is a polysaccharide, present in the plant's cell wall, composed of linear chains of α-[1,4]-D-galacturonic acids. Silver-pectin nanocomposite, formed via direct chemical reduction, exhibits antibacterial (e.g., Escherichia coli, and Staphylococcus aureus) and antifungal (e.g., Aspergillus japonicus) activities.
Researchers grafted pectin with copolymer chains, 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylamide, to develop nanocomposite for loading donepezil drug as an implantable and transdermal drug delivery system.
Metal-Rubber Nanocomposites
Rubber is a natural polymer composed of cis-1,4-polyisoprene and is extracted from Hevea brasiliensis. It has wide-ranging applications that include the development of adhesives, condoms, gloves, shoes, tires, and latex-based health care products. Silver-rubber nanocomposite exhibits antimicrobial activities.
Metal-Fibrin Nanocomposites
Fibrin is a blood plasma protein that is essential for clot formation. This protein has been used as an adhesive to improve osteogenesis and deliver drugs, primarily antibiotics, slowly to tissues.
Gold-fibrin nanocomposite can induce the formation of hydroxyapatite, a naturally occurring mineral form of calcium apatite. It is used for perfecting bone at imperfection sites in the presence of hydroxyapatite.
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References and Future Reading
Hosseini, BS (2020) Natural fiber polymer nanocomposites. In Micro and Nano Technologies, Fiber-Reinforced Nanocomposites: Fundamentals and Applications. pp. 279-299. https://linkinghub.elsevier.com/retrieve/pii/B978012819904600013X
Zahran, M. and Marei, HA (2019) Innovative natural polymer metal nanocomposites and their antimicrobial activity. International Journal of Biological Macromolecules. 136. pp.586-596. https://doi.org/10.1016/j.ijbiomac.2019.06.114
Baishya, P. et al. (2017). Natural Polymer‐Based Nanocomposites: A Greener Approach for the Future. Handbook of Composites from Renewable Materials. pp.433-459. https://onlinelibrary.wiley.com/doi/10.1002/9781119441632.ch139
Modi, K. V. et al. (2014) Review on Green Polymer Nanocomposite and Their Applications. International Journal of Innovative Research in Science, Engineering and Technology. 3(11). https://www.scirp.org/html/21051.html
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