which differ significantly from the PHASCL, such as P(3HB). Particularly with respect to the melting temperature and the extension to break value the two types of PHAs showed, mainly because of the lower crystallinity of PHAMCL, striking differences. PHAs have been processed into fibers, which were then used to construct materials such as non-woven fabrics [229]. Moreover P(3HB) and P(3HB-co-3HV) were described as hot-melt adhesives [230]. They are considered for several applications in the packaging industry, medicine, pharmacy, agriculture and food industry or as raw materials for the synthesis of enantiomerically pure chemicals and the production of paints [231]. Possible applications of P(3HB) and copolymers are as packaging materials or agricultural foil [232]. As in the BiopolTM recovery process, the fermentor contents are heat treated to break down the nucleic acids, and proteases and detergents are added to solubilize the cells. Subsequent washing (i.e., removal of the solubilized cell material) and concentration of the resulting PHA latex is established by cross-flow microfiltration. To produce a coating, the PHA latex is sprayed onto a substrate such as paper. After evaporation of the water, the PHA latex particles readily coalesce into a film [218]. Due to the relatively high cost of PHA production, it is wise to apply PHAs for some cost-effective applications like medicinal instruments. PHAs were proved to be biocompatible in tissue engineering, implantations, etc. Many prokaryotic and eukaryotic organisms are able to produce LMW PHB molecules that are complexed with other biomolecules such as polyphosphates and that are present at low concentrations [233]. Over recent years, PHAs were used to develop many devices and material useful for clinical purposes such as suture fasteners, meniscus repair devices, rivets, tacks, staples, screws, (including interference screws), bone plates and bone plating systems, surgical mesh, repair patches, orthopedic pins (including bone filling augmentation material), adhesion barriers, stents, guided tissue repair regeneration devices, articular cartilage repair devices, nerve guides, tendon repair devices, pericardial patches, bulking and filling agents, vein valves, bone marrow scaffolds, meniscus regeneration devices, ligament, tendon grafts, ocular cell implants, spinal fusion cages, skin substitutes, dural substitutes, bone graft substitutes, bone dowels, wound dressing and hemostats [234–240]. Many biochemical engineering, molecular biology experiments and other tools were used to change the end products of the polyhydroxyalkanoate or to produce copolymers. To assess the biocompatibility of PHB, the structural organization of cellular molecules involved in adhesion was studied using osteoblastic and epithelial cell lines. On PHB, both cell lines revealed a rounded cell shape due to reduced spreading. The filamentous organization of the actin cytoskeleton was impaired. In double immunofluorescence, analyses the co-localization of the fibronectin with the fibril actin was demonstrated [241]. The investigated properties of PHB and PHB-co-PHV films proved to be fundamentally similar [242–246]. PHB-co-PHV film was chosen as a temporary substrate for growing retinal pigment epithelium cells as an organized monolayer before their subretinal transplantation. The surface of the PHB-co-PHV film was rendered hydrophilic by oxygen plasma treatment to increase the reattachment of D407 cells on the film surface. The cells were also grown to confluency as an organized monolayer suggesting PHB-co-PHV film as a potential temporary substrate for subretinal transplantation to replace diseased or damaged retinal pigment epithelium [247]. Tesema et al. and Malm et al. implanted PHB non-woven patches as transannular patches into the right ventricular outflow tract and pulmonary artery in 13 weanling sheep [248–250].
PHB non-woven patches can be used as a scaffold for tissue regeneration in low-pressure systems. The regenerated vessel had structural and biochemical qualities in common with the native pulmonary artery [250]. PHAs were used in tissue engineering, as antibiotic carriers, and many other medicinal applications [238, 251, 252]. Chen and Wu recently reported that PHAs possesses the biodegradability, biocompatibility and thermo-processibility for not only implant applications but also controlled drug release uses. PHAs show a promising future in pharmaceutical application such as drug delivery, which open a new approach. The many possibilities to tailor-make PHAs for medical implant applications have shown that this class of materials has a bright future as tissue engineering materials [253]. Different types of mutagenesis were applied for changing the substrate specificity, study the catalytic residues and to overproduce the PHAs [254–257].
2.6 Biopolymer Type Number 5: Polyisoprenoides
2.6.1 Natural Rubber
Natural rubber is a cis-1,4-polyisoprene-based biopolymer that has good resilience and damping behavior, but poor chemical resistance and processing capacity. It is collected from the milky secretion (latex) of individual trees, but the Hevea brasiliensis tree is the only important commercial source of natural rubber (sometimes called Pará rubber). Guayuleule is the only other plant under cultivation as a commercial source of rubber (Parthenium argentatum). Tyres, computer components, gloves, toys, shoe soles, elastic bands, flippers, erasers and athletic equipment are well-known uses of natural rubber. It is typically used for applications that need resistance to abrasion/wear; elastic resistance and properties that absorb damping or shock. In the production of synthetic rubber, oil is one of the necessary substituents. Natural rubber has enjoyed a rising market share due to the cost of oil and has become an attractive replacement for synthetic rubber. Since natural rubber has better properties compared to other synthetically manufactured rubber, rubber industries usually use it to enhance properties and extend applications of other rubber materials by blending. A very low level of adherence to other materials has also been documented. Natural rubber blended with virgin and recycled ethylene-propylene-diene monomer has been reported by Hayeemasae et al., the curing rate of natural rubber vulcanization was decreased. This was due to the incompatibility of these materials with natural rubber being cured. However, the maximum torque for the recycled material was increased with the addition of both virgin and recycled EPDM and was even higher. This was due to the higher density of cross-linking implemented by EPDM. Natural rubber is an economically important biopolymer with unparalleled performance characteristics, such as high elasticity, durability and efficient heat dispersion [258, 259]. Normal rubber is poly (cis-1,4-isoprene) 300 to 70000 isoperene molecules are coupled to form an irregular structure that cannot crystallize under normal conditions that mediate the amorphous rubber texture. Normal rubber is poly (cis-1,4-isoprene). Currently, the major rubber producing countries are Thailand, Indonesia, Malaysia, India and the People’s Republic of China, which together account for 89% of the world’s 9.33 million tons of the global rubber production.
2.7 Biopolymer Type Number 6: Inorganic Polyesters with Polyphosphate
The polyanhydride present in all living cells is inorganic polyphosphate. Commercial bacterial polyphosphate generation has not yet succceeded for economic reasons. Polyphosphates may have two cell regions as granules within the cytoplasm and related to the inner layer within the periplasmic space, the latter place being primarily related to the use of polyphosphate chemicals such as transport types. The chemical composition is that of a direct inorganic phosphate anhydride that changes in chain length from three to more than 103 units and consists more often than not of mixtures of distinct atomic sizes. Cations are attached to them. The polyphosphate increases particularly when a supplement lopsidedness occurs within the vicinity of phosphate overabundance. The Mg2+-dependent polyphosphate kinase that moves the terminal phosphoryl group of ATP to polyphosphate is a second direct mechanism. The enzyme is found in various bacteria that are aerobic, anaerobic and facultative. Harland Wood and his colleagues studied Propionibacterium shermanii polyphosphate kinase and have shown that this monomeric enzyme (Mr 83000) catalyzes a strictly processive reaction [260]. Polyphosphate glucokinase, which makes the formation of glucose 6-phosphate without the intervention of ATP, has a fairly widespread distribution: (P)n + Glucose ~ (P)n-t + Glucose 6-P. The distribution of the enzyme is of taxonomic concern, being limited to a limited group of species (Actinomycetes, Propionibacteria, Micrococci, Brevibacteria and related species). Recently, Wood and colleagues made several major developments with the P. shermanii enzyme [260]. Polyphosphate glucokinase is four times more active in P. shermanii than the ATP glucokinase, illustrating the role of polyphosphate in this organism’s metabolism. Some Acinetobacter species contained in sewage treatment plants using the active sludge process have the capacity, under suitable conditions,
