were first used in packaging and housing materials. Later plastics find their way into medicinal, pharmaceutical and industrial applications. Today, plastics applications have either totally or partly substituted the other materials used previously in industrial applications (on all or some of their parts) such as wood, mud, metals, glass and other materials [35, 36]. Plastic is the best choice in many applications because of its low cost, stability, durability, good mechanical and thermal properties. Those who are interested in the materials produced by biopolymers and are investing funds and arranging resources aimed at commercializing species of biopolymers should identify the areas which lead to the success of the plastic applications. That will enable a successful start for any of the biopolymer application species still out of the market because of the value of the synthetic polymer. Some of the important biopolymer species, such as the bioplastc polyhydroxyalkanoates, gum Arabic, agar, alginate and so on, already exist in the market [28, 35, 37].
2.1.7 Biopolymer Commercialization
As well as plastics and bioplastics, the other types of biopolymer were given more opportunities and many of them were commercialized. Biopolymers have unique properties (there are some exceptions); they are produced and degraded through the biological system, therefore they are non-toxic (mostly); they are bioavailable (mostly); They are diverse, applicable, and renewable. There are many types of classifications which are based on their chemical, biological and physical properties; their source (plant, animal and microbes); their applications (medicinal, pharmaceutical, agriculture, industrial); their economic value; their biodegradability (biodegradable, non-degradable); their bioavailability; their cost and their mechanical properties. In this chapter, the classification which is based on the polymer chemical structure will be used. The main limiting factor in commercializing biopolymers is their production cost. For that this chapter will use the classification which is based on the polymer chemical structure [35].
2.1.8 The Eight Different Biopolymers
The eight types of biopolymers are: (1) nucleic acids (DNA and RNA); (2) polyamides which are polymers containing repeated amide groups (protein poly-(amino acids) such as, gelatine, casein, wheat gluten, silk and wool); (3) polysaccharides, any of a class of carbohydrates whose molecules contain chains of monosaccharide molecules (such as, starch, cellulose, lignin, chitin); (4) organic polyoxoesters (such as poly(hydroxyalkanoic acids), poly(malic acid) and cutin); (5) polyisoprenoides (such as natural rubber or gutta-percha [a whitish rubber derived from the coagulated milky latex of gutta-percha trees; used for insulation of electrical cables]); (6) inorganic polymers such as inorganic polyesters with polyphosphate, (7) polyphenols (such as lignin or humic acids), and (8) polythioesters, for example, poly(3-mercaptopropionate). Polymers from bioderived monomers could be polymerized and might be added as group nine. Additionally, some inorganic elements might show accumulation in the microbial cells in repeated forms but due to their nature they form crystals which are usually different to those made in labs. For example, magnetotactic bacteria show Fe3O4 chains of similar crystals which are unique in their structures. The helical twist of the Fe3O4 series of crystals are not cubes. It might be interesting to report that similar structures are found in goethite in the strengthening of limpet teeth. Other examples are iron, sulphides, pyrite crystals found in some anaerobic bacteria. In fact, more research should be conducted on the nature of the inorganic structures which might be finally classified as biopolymer because they are not crystalline spontaneously but due to the effect of proteins and enzymes. The amazing structure of different diatoms might be a good example [35, 38, 39].
2.2 Biopolymer Type Number 1: Nucleic Acids
Nucleic acids are the genetic code in living cells. DNA and RNA are the most important biopolymers that are located in the nucleotides of the eukaryotic cells and in the cytoplasm of the prokaryotic cells [40, 41]. DNA and RNA are polymers in their nature. They are usually used in various genetic manipulation tools, as well as in some fine technical applications and nanoapplications. DNA is used to generate new protein through mutagenesis, which gives new protein and thus new function or products (protein engineering). RNA is made from polymers of ribose sugar, phosphate and nitrogenous base. DNA is made from polymer of deoxyribose sugar, phosphate and nitrogenous base. DNA was used as a platform based on self-assembled DNA biopolymer for high-performance cancer therapy [42]. DNA novel nanomaterial is designed for applications in photonics and in electronic [43, 44].
2.2.1 Tissue Engineering
Different types of polymers are used in tissue engineering [45]. The existence of the genetic elements in the cells is an essential part of their viability and productivity. Cells aggregate to form tissue: growing free cells in a particular space made of a biodegradable polymer enables their injection or cultivation in a tissue. In a successful process the cells then will differentiate to form or to fill in the target tissue. Upon degrading the polymer and replicating the cells, the new cells become a part of the oriignal repaired tissue, a new technology named “tissue engineering” which offers the possibility to help in regenerating tissues damaged by disease or trauma and, in some cases, to create new tissues. Usually this is achieved through using degradable biomaterials to either induce the surrounding tissue and cell to grow or to serve as temporary scaffolds for transplanted cells to attach, grow, and maintain differentiated functions. In some trials the polymer improves the growth of the cultivated cells. Leucocytes show improvement growth on PHA polymer surface [28].
2.2.2 Gene Therapy and Delivery
Biopolymers were designed in many formulations to either react by themselves or to be used in gene therapy [46–48]. They are used widely in tissue engineering and in genetic cell engineering [49]. They enable the cells to provide biochemical signals [50] which direct cell proliferation and differentiation [51]. The unique criteria in the polymers used in gene therapy, is their biocompatibility, mucoadhesive character, and biodegradability. The biocompatibility of natural polymers allows cells to infiltrate the matrix and transfection can occur as these cells come into contact with the embedded DNA. The biodegradability of the matrices obtained from natural polymers may also assist the release of gene transfer agents into the surrounding environment and thus affect nearby cells [48, 52, 53].
2.2.3 As Biosensor
A biosensor is a molecular device that converts a biological response into a detectable measurable signal. A biosensor is formed from a sensor which could use different types of materials including the polymer and the bioreceptor, such as antibodies, enzymes, nucleic acid, etc., [54], is coupled with the sensor through different immobilizing techniques [54]. Different polymers are used to produce biosensors such as in antibacterial electrospun, dual fluorescence “turn-on” sensors of cysteine and silver ions, chitin nanofiber paper toward optical (bio)sensing applications, click off colorimetric detection of peroxide and glucose etc. [55].
2.3 Biopolymer Type Number 2: Polyamides
2.3.1 Protein (πρώτειος)
The word protein comes from the Greek word πρώτειος (proteios) “primary”. Proteins were first described and named by the Swedish chemist Jöns Jakob Berzelius in 1838. However, the involvement of proteins in living system organisms was correctly understood in 1926, when James B. Sumner showed that urease was a protein defined by the sequence of its related nucleotides and amino acids [56]. The genetic code can include selenocysteine and in certain cases (such as in archaea) pyrrolysine. The residues in a protein are often observed to be chemically modified by post-translational modification, which can happen either before the protein is used in the cell, or as a part of control mechanisms. Proteins can also work together to achieve a particular function, and they often associate to form stable complex functions, such as actin and myosin in muscles and proteins
