Biopolymer

Source: Wikipedia, the free encyclopedia.
"Biopolymers" redirects here. For the scientific journal, see Biopolymers (journal).
Not to be confused with bioplastics, usually semi-synthetic polymers produced from renewable biomass sources.

Biopolymers are natural

fatty acids), melanin, and polyhydroxyalkanoates (PHAs)
.

In addition to their many essential roles in living organisms, biopolymers have applications in many fields including the

double helix structure
IUPAC definition

biopolymers: Macromolecules (including proteins, nucleic acids and polysaccharides) formed by living organisms. [3]

Biopolymers versus synthetic polymers

A major defining difference between biopolymers and synthetic polymers can be found in their structures. All polymers are made of repetitive units called

polydispersity encountered in synthetic polymers. As a result, biopolymers have a dispersity of 1.[4]

Conventions and nomenclature

Polypeptides

The convention for a

lipids
.

Nucleic acids

The convention for a

polymer chain
, where 5' and 3' refer to the numbering of carbons around the ribose ring which participate in forming the phosphate diester linkages of the chain. Such a sequence is called the primary structure of the biopolymer.

Polysaccharides

Polysaccharides (sugar polymers) can be linear or branched and are typically joined with glycosidic bonds. The exact placement of the linkage can vary, and the orientation of the linking functional groups is also important, resulting in α- and β-glycosidic bonds with numbering definitive of the linking carbons' location in the ring. In addition, many saccharide units can undergo various chemical modifications, such as amination, and can even form parts of other molecules, such as glycoproteins.

Structural characterization

There are a number of

Protein sequence can be determined by Edman degradation, in which the N-terminal residues are hydrolyzed from the chain one at a time, derivatized, and then identified. Mass spectrometer techniques can also be used. Nucleic acid sequence can be determined using gel electrophoresis and capillary electrophoresis. Lastly, mechanical properties of these biopolymers can often be measured using optical tweezers or atomic force microscopy. Dual-polarization interferometry
can be used to measure the conformational changes or self-assembly of these materials when stimulated by pH, temperature, ionic strength or other binding partners.

Common biopolymers

Collagen:[5] 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 silkworm 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 possess anticoagulation 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 consisting of cysteine, and produced by the partial hydrolysis of collagen from bones, tissues and skin of animals.[7] 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 nanoparticles 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.[7]

Starch: Starch is an inexpensive biodegradable biopolymer and copious in supply. Nanofibers 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:

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.

Biopolymer applications

The applications of biopolymers can be categorized under two main fields, which differ due to their biomedical and industrial use.[2]

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.[5] Many 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 bioactivity, and non-toxicity.[8] 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 possess more complex structures, similar to the human body.[citation needed]

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 biopolymers 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.[9] 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.[9]

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 based haemostat reduces blood loss in tissues and helps manage bleeding in organs such as the liver and spleen.

Chitosan is another popular biopolymer in biomedical research.[according to whom?] Chitosan is derived from chitin, the main component in the exoskeleton of crustaceans and insects and the second most abundant biopolymer in the world.[5] Chitosan has many 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 various 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.[10]

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

Chitosan composite for tissue engineering: Chitosan powder blended with alginate is used to form functional wound dressings. These dressings create a moist, biocompatible environment which aids in the healing process. This wound dressing is also biodegradable and has porous structures that allows cells to grow into the dressing.[5] Furthermore, thiolated chitosans (see thiomers) are used for tissue engineering and wound healing, as these biopolymers are able to crosslink via disulfide bonds forming stable three-dimensional networks.[11][12]

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 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

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:

flocculant that only takes a few weeks or months rather than years to degrade in the environment. Chitosan purifies water by chelation. This is the process in which binding sites along the polymer chain bind with the metal ions in the water forming chelates. Chitosan has been shown to be an excellent candidate for use in storm and wastewater treatment.[13]

As materials

Some biopolymers- such as

poly-3-hydroxybutyrate can be used as plastics, replacing the need for polystyrene or polyethylene
based plastics.

Some plastics are now referred to as being 'degradable', 'oxy-degradable' or 'UV-degradable'. This means that they break down when exposed to light or air, but these plastics are still primarily (as much as 98 per cent)

composting.[14]

Biopolymers (also called renewable polymers) are produced from

non food crops
. These can be converted in the following pathways:

Sugar beet > Glyconic acid > Polyglyconic acid

Starch > (fermentation) > Lactic acid > Polylactic acid (PLA)

Ethene > Polyethylene

Many types of packaging can be made from biopolymers: food trays, blown starch pellets for shipping fragile goods, thin films for wrapping.

Environmental impacts

Biopolymers can be sustainable, carbon neutral and are always

carbon neutral
.

Almost all biopolymers are

compostable: they can be put into an industrial composting process and will break down by 90% within six months. Biopolymers that do this can be marked with a 'compostable' symbol, under European Standard EN 13432 (2000). Packaging marked with this symbol can be put into industrial composting processes and will break down within six months or less. An example of a compostable polymer is PLA film under 20μm thick: films which are thicker than that do not qualify as compostable, even though they are "biodegradable".[15] In Europe there is a home composting standard and associated logo that enables consumers to identify and dispose of packaging in their compost heap.[14]

See also

References

  1. ^ Saberi, A.; Bakhsheshi-Rad, H.R.; Abazari, S.; Ismail, A.F.; Sharif, S.; Ramakrishna, S.; Daroonparvar, M.; Berto, F. A Comprehensive Review on Surface Modifications of Biodegradable Magnesium-Based Implant Alloy: Polymer Coatings Opportunities and Challenges. Coatings 2021, 11, 747. https://doi.org/10.3390/coatings11070747
  2. ^
    PMID 33747749
    .
  3. doi:10.1351/goldbook.B00661
    . Retrieved 1 April 2024.
  4. ^ Stupp, S.I and Braun, P.V., "Role of Proteins in Microstructural Control: Biomaterials, Ceramics & Semiconductors", Science, Vol. 277, p. 1242 (1997)
  5. ^
    PMID 26501034
    .
  6. S2CID 137350796. Archived
    (PDF) from the original on 2021-07-15.
  7. ^
    ISBN 978-953-51-4613-1
    .
  8. ISSN 1877-7058
    .
  9. ^
    PMID 26501034
    .
  10. doi:10.1016/j.ejpb.2012.04.007
    .
  11. PMID 32567846
    .
  12. S2CID 135464452
    .
  13. ISSN 1097-0126
    .
  14. ^ a b "NNFCC Renewable Polymers Factsheet: Bioplastics". Archived from the original on 2019-05-22. Retrieved 2011-02-25.
  15. ^ NNFCC Newsletter – Issue 5. Biopolymers: A Renewable Resource for the Plastics Industry

External links

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