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Introduction (revised)
Biopolymers are natural polymers produced by living organisms; in other words, they are polymeric biomolecules derived from cellular or extracellular matter. Biopolymers contain monomeric units that are covalently bonded to form larger structures. There are three main classes of biopolymers, classified according to the monomeric units used and the structure of the biopolymer formed: polynucleotides, polypeptides, and polysaccharides. More specifically, polynucleotides, such as RNA and DNA, are long polymers composed of 13 or more nucleotide monomers. Polypeptides or proteins, are short polymers of amino acids and some major examples include collagen, actin, and fibrin. The last class, polysaccharides,are often linear bonded polymeric carbohydrate structures and some examples include cellulose and alginate. Other examples of biopolymers include rubber, suberin, melanin and lignin.

Biopolymers have various applications such as in the food industry, manufacturing, packaging and biomedical engineering.

Common Biopolymers (to add)
Collagen: Collagen is the primary structure of vertebrates and is the most abundant protein in mammals. Because of this, collagen is one of the most easily attainable biopolymers, and used for many research purposes. Because of its mechanical structure, collagen has high tensile strength and is a non toxic, easily absorbable, biodegradable and biocompatible material. Therefore, it has been used for many medical applications such as in treatment for tissue infection, drug delivery systems, and gene therapy.

Silk Fibroin: Silk Fibroin (SF) is another protein rich biopolymer that can be obtained from different silk worm species, such as the mulberry worm Bombyx mori. In contrast to collagen, SF has a lower tensile strength but has strong adhesive properties due to its insoluble and fibrous protein composition. In recent studies, silk fibroin has been found to posses antiagulation properties and platelet adhesion. Silk fibroin has been additionally found to support stem cell proliferation in vitro.

Gelatin: Gelatin is obtained from type I collagen comprising of cysteine, and produced by the partial hydrolysis of collagen from bones, tissues and skin of animals. There are two types of gelatin, Type A and Type B. Type A collagen is derived by acid hydrolysis of collagen and has 18.5% nitrogen. Type B is derived by alkaline hydrolysis containing 18% nitrogen and no amide groups. Elevated temperatures cause the gelatin to melts and exists as coils, whereas lower temperatures result in coil to helix transformation. Gelatin contains many functional groups like NH2, SH, and COOH which allow for gelatin to be modified using nonoparticles and biomolecules. Gelatin is an Extracellular Matrix protein which allows it to be applied for applications such as wound dressings, drug delivery and gene transfection.

Starch: Starch is an inexpensive biodegradable biopolymer and copious in supply. Nano fibers and microfibers can be added to the polymer matrix to increase the mechanical properties of starch improving elasticity and strength. Without the fibers, starch has poor mechanical properties due to its sensitivity to moisture. Starch being biodegradable and renewable is used for many applications including plastics and pharmaceutical tablets.

Cellulose: Cellulose is very structured with stacked chains that result in stability and strength. The strength and stability comes from the straighter shape of cellulose caused by glucose monomers joined together by glycogen bonds. The straight shape allows the molecules to pack closely. Cellulose is very common in application due to its abundant supply, its biocompatibility, and is environmentally friendly. Cellulose is used vastly in the form of nano-fibrils called nano-cellulose. Nano-cellulose presented at low concentrations produces a transparent gel material. This material can be used for biodegradable, homogeneous, dense films that are very useful in the biomedical field.

Alginate: Alginate is the most copious marine natural polymer derived from brown seaweed. Alginate biopolymer applications range from packaging, textile and food industry to biomedical and chemical engineering. The first ever application of alginate was in the form of wound dressing, where its gel-like and absorbent properties were discovered. When applied to wounds, alginate produces a protective gel layer that is optimal for healing and tissue regeneration, and keeps a stable temperature environment. Additionally, there have been developments with alginate as a drug delivery medium, as drug release rate can easily be manipulated due to a variety of alginate densities and fibrous composition.

Poly(e-Caprolactone) (PCL): PCL is a biodegradable, biocompatible polyester which is a type of polymer that has an ester functional group for their main chain. PCL is used vastly in the biomedical field. It is used to create scaffolds to be used in cell and tissue engineering and can support a lot of cell types. PCL is especially useful for tissue engineering applications because under physiological conditions it is degraded but hydrolysis if its ester linkages. This property makes it ideal for long term implantable biomaterials due to the low degradation rate.

Biomedical
Because one of the main purposes for biomedical engineering is to mimic body parts to sustain normal body functions, due to their biocompatible properties, biopolymers are used vastly for tissue engineering, medical devices and the pharmaceutical industry. Lots of biopolymers can be used for regenerative medicine, tissue engineering, drug delivery, and overall medical applications due to their mechanical properties. They provide characteristics like wound healing, and catalysis of bio-activity, and non-toxicity. Compared to synthetic polymers, which can present various disadvantages like immunogenic rejection and toxicity after degradation, many biopolymers are normally better with bodily integration as they also posses more complex structures, similar to the human body.

More specifically, polypeptides like collagen and silk, are biocompatible materials that are being used in ground breaking research, as these are inexpensive and easily attainable materials.Gelatin polymer is often used on dressing wounds where it acts as an adhesive.Scaffolds and films with gelatin allow for the scaffolds to hold drugs and other nutrients that can be used to supply to a wound for healing.

As collagen is one of the more popular biopolymer used in biomedical science, here are some examples of their use:

Collagen based drug delivery systems: collagen films act like a barrier membrane and are used to treat tissue infections like infected corneal tissue or liver cancer. Collagen films have all been used for gene delivery carriers which can promote bone formation.

Collagen sponges: Collagen sponges are used as a dressing to treat burn victims and other serious wounds. Collagen based implants are used for cultured skin cells or drug carriers that are used for burn wounds and replacing skin.

Collagen as Haemostat: When collagen interacts with platelets it causes a rapid coagulation of blood. This rapid coagulation produces a temporary framework so the fibrous stroma can be regenerated by host cells. Collagen bases haemostat reduces blood loss in tissues and helps manage bleeding in cellular organs like the liver and spleen.

Chitosan is another very popular biopolymer in biomedical research. Chitosan is the main component in the exoskeleton of crustaceans and insects and the second most abundant biopolymer in the world. Chitosan has a lot of excellent characteristics for biomedical science. Chitosan is biocompatible, it is highly bioactive, meaning it stimulates a beneficial response from the body, it can biodegrade which can eliminate a second surgery in implant applications, can form gels and films, and is selectively permeable. These properties allow for a lot of biomedical applications of Chitosan.

Chitosan as drug delivery: Chitosan is used mainly with drug targeting because it has potential to improve drug absorption and stability. in addition Chitosan conjugated with anticancer agents can also produce better anticancer effects by causing gradual release of free drug into cancerous tissue.

Chitosan as an anti-microbial agent: Chitosan is used to stop the growth of microorganisms. It preforms antimicrobial functions in microorganisms like algae, fungi, bacteria, and gram positive bacteria of different yeast species.

Chitosan composite for tissue engineering: Blended power of Chitosan along with alginate are used together to form functional wound dressings. These dressings create a moist environment which aids in the healing process. This wound dressing is also very biocompatible, biodegradable and has porous structures that allows cells to grow into the dressing.

Industrial
Food: Biopolymers are being used in the food industry for things like packaging, edible encapsulation films and coating foods. Polylactic Acid (PLA) is very common in the food industry due to is clear color and resistance to water. However, most polymers have a hydrophilic nature and start deteriorating when exposed to moisture. Biopolymers are also being used as edible films that encapsulate foods. These films are can carry things like antioxidants, enzymes, probiotics, minerals, and vitamins. The food consumed encapsulated with the biopolymer film can supply these things to the body.

Packaging: The most common biopolymers used in packaging are polyhydroxyalkanoate (PHA), polylactic acid (PLA), and starch. Starch and PLA are commercially available biodegradable making them a common choice for packaging. However, their barrier properties and thermal properties are not ideal. Hydrophilic polymers are not water resistant and allow water to get through the packaging which can effect the contents of the package. Polyglycolic acid (PGA) is a biopolymer that has great barrier characteristics and is now being used to correct the barrier obstacles from PLA and starch.

Water Purification: A newer biopolymer called chitosan has been used for water purification. Chitosan is used as a flocculant that only takes a few weeks or months rather then years to degrade into the environment. Chitosan purify's water by Chelation when it removes metals from the water. Chelation is when binding sites along the polymer chain bind with the metal in the water forming clelates. Chitosan has been used in many situations to clean out storm or waste water that may have been contaminated.