Читать книгу Biomolecular Engineering Solutions for Renewable Specialty Chemicals - Группа авторов - Страница 43

Any substance that is made up of repeating monomeric units is called as polymer. The polymers that are naturally synthesized by the living organisms are called biopolymers such as proteins, polysaccharides, polyphenols, lipids, polyamides, and polyhydroxyalkanoate (PHA) (spanning from liquid solutions to bioplastics). They are biodegradable hence eco‐friendly. Naturally occurring polymers form the basis for life. Polynucleotides (DNA and RNA) and proteins (amino acids) are present in every living form. Starch is the reserve form of carbohydrate in which plants store food and is the main carbohydrate in the human diet. Lipids store energy and its bilayer acts as a barrier in the living cells. Whereas cellulose is the primary component in the cell wall of plant kingdom providing structural rigidity. Microbial synthesis of biopolymers is known from old age. Louis Pasteur and Van Tieghem, in the mid nineteenth century, discovered that Leuconostoc mesenteriodes synthesize dextran. 40 years after, and PHA reserves were found in B. megaterium, which serves as a basis for bioplastics to date. As stated earlier, understanding in the molecular pathways for synthesis of biopolymers leads to the engineering of microorganism for the production of custom made, altered biopolymers (Rehm, 2010).

Biopolymers have a wide range of application in biomedical, food industry, packaging to cosmetics, electronics, etc. Its biomedical applications are in drug delivery, tissue engineering, wound healing, and medical and dental devices. Porous gelatin, electrospun poly (lactic‐co‐glycolic acid), etc. are used as a scaffold for this purpose (Van Vlierberghe et al., 2007; Zhao et al., 2016). Each biopolymer has a specific characteristic to be used for particular conditions. Poly (D,L‐lactides) scaffolds are used for bone engineering, whereas poly (trimethylene carbonate) scaffolds are used for soft tissue engineering. Poly(L‐lactide‐co‐glycolide) scaffolds provides good adhesion and proliferation (Ulery et al., 2011). Some of the commercially available scaffolds are BioFiber™, an orthopedic scaffold made of a leno weave of P4HB monofilaments (Tornier) for tendon repair, BioFiber®‐CM, an orthopedic scaffold made of P4HB coated with bovine collagen (Tornier) for tendon repair, etc. Use of plastic in packaging industry is growing day by day leading to their disposal problem. Plastic films production takes one‐third portion of the total plastic production. Cellulose and starch are widely used for this purpose after some modifications. The material to be used for packaging should have properties similar to polyethylene terephthalate (PET) i.e. barrier, sealing and thermal properties. Standard cosmetics have nonbiodegradable polymers in them such as polyethylene microparticles in face and body scrubs. These microparticles eventually enter in the ecosystem through waste water stream. Biodegradable poly lactic acid (PLA) powder can be used in exfoliating agents. Chitin absorbs UV light and effectively used in sunscreen lotions. Also, PLA mixed with titanium dioxide and zinc oxide powder shows photocatalytic activity.

Some of the biopolymers having industrial application are highlighted in the section below with their structures shown in Figure 1.2.