Polyhydroxyalkanoates (PHA), polyesters produced by microorganisms under unbalanced growth conditions (Doi 2002) have potential applications for medical and pharmaceutical purposes. The primary factor is because of their biodegradability. Nevertheless other favorable qualities such as their adaptability to suit the requirements of different applications, non-toxicity and thermoprocessibility properties have propelled their uses as tissue engineering biomaterials. Polyhydoxyalkanoates (PHA) and its composites include poly 3-hydroxybutyrate (PHB), copolymers of 3-hydroxybutyrate and 3-hydroxyvale-rate (PHBV), poly 4-hydroxybutyrate (P4HB), copolymers of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx) and poly 3-hydroxyoctanoate (PHO) (Hrabak 1992).

PHA has been utilized to develop devices like sutures, suture fasteners, meniscus repair devices, rivets, tacks, staples, screws (including interference screws), bone plates and bone plating systems, surgical mesh, repair patches, slings, cardiovascular patches, orthopedic pins (including bone.lling augmentation material),adhesion barriers, stents, guided tissue repair/regeneration devices, articular cartilage repair devices, nerve guides, tendon repair devices, atrial septal defect repair devices, pericardial patches, bulking and.lling agents, vein valves, bone marrow scaffolds, meniscus regeneration devices, liga-ment and tendon grafts, ocular cell implants, spinal fusion cages, skin substitutes, dural substitutes, bone graft substitutes, bone dowels, wound dressings, and hemostats (Chen & Wu 2005).

As PHA composes of various hydroxyalkanoates that are synthesized by as many as 75 different genera of gram-positive and gram-negative bacteria, an extensive group of properties are available (Reddy et al 2003). Non-storage PHA, poly(3HB) have been found in the cytoplasmic membrane and cytoplasm of Escherichia coli, as well as in yeasts, plants and animals. The mechanical and biocompatibility of PHA can also be changed by blending, modifying the surface or combining PHA with other polymers, enzymes and inorganic materials, making it possible for a wider range of applications There are several different pathways for PHA formation. One of which is through the biosynthetic pathway of P(3HB) which consists of three enzymatic reactions catalyzed by three different enzymes; ketoacyl CoA thiolase, NADPH-dependent acetoacetyl-CoA dehydrogenase and P(3HB) polymerase. (Huisman et al.,1989).

Initially PHA was used in the plastic material industry to produce bags and containers as well as disposable items like razors, feminine hygiene products and cosmetic containers. These uses as well as its features like capability to be produced from renewable resources, high degree of polymerization, highly crystalline and insolubility in water made PHA competitive with polypropylene, the petrochemical-derived plastic. But PHA special characteristics like optically active and isotactic (stereochemical regularity in repeating units) (Oeding & Schlegel 1973; Senior & Dawes,1973) has increased the compounds potentiality to be used as biodegradable carriers for drugs, medicines and hormones (Wang & Bakken,1998).

REFERENCES

Doi Y & Steinbuchel A.2002. Biopolymers. Weinheim,Germany: Wiley- VCH

Hrabak O. 1992. 1ndustrial production of poly ?-hydroxybutyrate. FEMS Microbiol Rev;103:251

Chen GQ & Wu Q. 2005. The application of polyhydroxyalkanoates as tissue engineering materials. Biomaterials;26:6565-6578.

Reddy CSK, Ghai R & Kalia VC. 2003. Polyhydroxyalkanoates: an overview. Bioresource Technology; 87: 137-146.

Huisman GW, Leeuwde O, Eggink G & Witholt B. 1989. Synthesis of poly-3-hydroxyalkanoates is a common feature of fluorescent pseudomonads. Appl.Environ.Microbiol;55: 1949-1954.

Oeding V & Schlegel HG. 1973. Beta-ketothiolase from Hydrogenomonas eutropha HI6 and its significance in the regulation of poly-beta-hydroxybutyrate metabolism. Biochem.J; 134: 239-248.

Senior PJ & Dawes EA. 1973.The regulation of poly-beta-hydroxybutyrate metabolism in Azotobacter beirjerinckii.Biochem. J.;134:225.238.

Wang JG & Bakken LR. 1998.Screening of soil bacteria for poly-beta-hydroxybutyric acid production and its role in the survival of starvation. Microb.Ecol.;35:94-101.

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