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Introduction to Biopolymers

Gurleen Kaur, Rajinder Kaur and Sukhminderjit Kaur*

Department of Biotechnology, Chandigarh University, Mohali, Punjab, India

Abstract

Biopolymers have engrossed imperative position substantially in every recognizable field of research, manufacturing, and production sector such as pharmaceutical or therapeutic sector, edible industry, textile department, agronomics, cosmetics, and automotive industries due to their biodegradable, biocompatible, and superior resilience demeanor. Chitosan, cellulose, collagen, keratin, pectin, carrageenan, alginate, dextran, curdlan, and starch are the commonly utilized biopolymers by researchers in various fields of interest. Biopolymers can originate from natural sources and can be chemically obtained from biological elements or absolutely synthesized from microorganisms. On the basis of type of origin, polymer backbone, and repeating monomer units, biopolymers can be categorized into three different categories. Biopolymers have been irrefutably acknowledged and accepted in the biomedical region owing to its phenomenal usefulness in wound healing, tissue engineering, drug delivery, medical implants, and gene therapy. Chitosan, cellulose, dextran, alginate, pectin, curdlan, and starch are few commonly used biopolymers. This chapter discusses an introduction to biopolymers, its classification, commonly used biopolymers in different sectors, commercially available biopolymers, and biomedical applications of distinct biopolymers.

Keywords: Biopolymers, biomedical applications, wound healing, tissue engineering, medical implants, gene therapy, drug delivery

1.1 Introduction

Any material made up of long repeating monomer units is termed a polymer. Polymers have been extensively used in human being's routine life for their use in vast applications. Among the polymers, biopolymers or the natural polymers have acquired unique consideration due to inexhaustibility, adaptability, biodegradability, and reasonability. Biopolymers are the larger structures organized from monomeric units synthesized typically from living beings such as microorganisms, herbs, shrubs, and animals with a covalent bond formation in their units [1]. The synthesis of biopolymers has achieved heavier interest in comparison to synthetic polymers like polyethylene, teflon, nylon, polyester, and many more due to distressing surrounding ecological troubles such as non-degradability, global heating, more expenses, burning of nonrenewable synthetic polymers, and unsustainability. Biopolymers are a magnificent substitute for synthetic and chemically synthesized polymers that are invariably being scrutinized to alleviate issues generated by the use of synthetic polymers [2]. One of the most valuable aspects owned by biopolymers is their easy degradation, which can be achieved with the extensive sort of disposal mechanisms such as decomposition in soil, landfill disposition, thermo-mechanical recycling, chemical recycling, microbial degradation, anaerobic digestion, and carbon dioxide neutral incineration [3]. A wide range of applications are associated with the use of biopolymers in the field of medical and pharmaceutical industry, agriculture sector, edible industry, automotive department, cosmetics, and textile industry [47, 51-54] (Figure 1.1).

Over the past few years, biopolymeric substances have enlivened the researchers for its utilization in the biomedical sector including drug delivery, tissue engineering, wound healing, gene therapy, and medical implantation due to their indispensable characteristic features. Biopolymers are being used as film, powders, and hydrogels in cardiac and liver tissue engineering, wound healing, and wound dressing because of its biodegradability and non-destructive behavior. Natural biopolymers such as alginate, chitosan, agar, collagen, casein, carrageenan, and starch have been extensively utilized in injectable and inhalation structures, drug delivery, and scaffold development [4, 5]. Biopolymers demonstrate multifaceted performance in different functionalities within the individual's body like balance the resilience and hydration of skin, development of tissues through cell embracing, further governing the demeanor of cells by sending chemical signals to them, and providing flexibility to the gastrointestinal tract and joints through lubrication [1]. The chapter elucidates about the basic knowledge of biopolymers, classification of biopolymers, preparation of biopolymers, characterization of biopolymers, commercial availability of biopolymers, and their applications in various fields.

Figure 1.1 Applications of biopolymers.

1.2 Classification of Biopolymers

On the basis of type of origin, polymer backbone, and repeating monomer units, biopolymers can be categorized into three different categories as given in Figure 1.2.

1.3 Commonly Used Biopolymers

1.3.1 Chitosan

Chitosan is a derivative of chitin and one of the extensively considered polysaccharides obtained naturally. It is frequently derived from the cell wall of fungi and the firm outer covering of insects and crustaceans. Structurally, chitosan is formed by connecting glucosamine and N-acetyl-glucosamine via ß-1,4 glycosidic linkages. Chitosan is widely employed in tissue engineering scaffold formation and wound dressing [9, 46, 49, 50].

1.3.2 Alginate

Alginate is a significant anionic unbranched linear polysaccharide also referred to as alginic acid. It is predominantly procured from the cell wall of brown algae or seaweeds, especially Laminaria and Ascophyllum species. Alginate can also be extracted in extracellular form from certain bacteria. Alginate is biosynthesized through copolymerization of ß-d-mannuronic acid and a-l-guluronic acid possessing diverse quantities of 1,4 linkages of both monomer acid residues and is able to bind to different molecules having compliant absorptivity, biodegradability, and a biologically functional state [9]. Alginate is principally efficacious for tissue engineering by supporting the repair of liver, cartilage, pancreas, periphery nerve, and blood vessels [10].

Figure 1.2 Classification of biopolymers [6-8].

1.3.3 Cellulose

Cellulose is one of the extensively used existing biopolymers of glucose, allocated in plants as well as fibers like linen and cotton. Acetobacter xylinum is the bacterial species known to synthesize cellulose. Cellulose is made up of numerous hundreds to thousands of D-glucose monomer units linked by ß(14) linear chains. Cellulose is an important biopolymer used in controlled drug delivery. Cellulose ether is utilized in solid tablets that permit the swelling-induced delivery of drug when anatomical fluid forms a communication with the tablet solely [11].

1.3.4 Starch

Starch is the fundamental energy reservoir plant polysaccharide which occurs in the granule form of amylopectin and amylose. Amylopectin is branched glucose polymer with high molecular weight, while amylose is a linear polymer made up of glucose monomers linked through a-D-(1-4) glycosidic bonds. The hydrogel of starch demonstrates resistance against gastric juices; therefore, it has applications in oral drug delivery and site-specific delivery systems. Starch is recognized for tissue engineering also because it assists in cartilage scaffold generation owing to its bone communicating characteristics [12].

1.3.5 Keratin

The protein keratin belongs to the class of polypeptide comprising different amino acids possessing disulphidecysteine intermolecular linkage. Keratin is highly useful in neural tissue regeneration. Keratin is classified on the basis of the presence of sulfur like soft and hard keratin [13]. Soft keratin contains lesser sulfur concentration, organized by cytoplasm filamentous clusters which are packed in unconstrained form, and offers flexibility to the epidermis, while hard keratin contains more sulfur concentration which supports epidermis stiffness comprising intermediate filaments organized in a systematic cluster entrenched in a cross-linked matrix. Two forms of keratin are known, including a-keratin and ß-keratin. a-Keratin is present in hair, wool, and nails, whereas ß-keratin is present in beaks and avian claws [13].

1.3.6 Carrageenan

Carrageenan is a general term assigned to the class of gelatinous and mucilaginous polysaccharide obtained from the class of Rhodophyceaea and red seaweed. Carrageenan is sulfated galactan having a repeated linear chain of d-galactose and 3,6-anhydro-d-galactose. Such polysaccharide possesses an antiviral aspect, by working as an interrupter of numerous enveloped viruses, antithrombotic potential through heparin co-factor II, and anticoagulant property. Kappa-carrageenan is scrutinized as a diabetic wound matrix and in regenerative medicines [9, 11].

1.3.7 Dextran

One of the complex glucans is dextran that is composed of a predominant chain of D-glucose associated through a a-(1,6) link with likely branches of D-glucose of a-(1,2), a-(1,3), and a-(1,4) links. The application of dextran includes gene transfection and nano-scale drug carrier. The generation of dextran takes place by employing a fermentation process using lactic acid bacteria in a...