Polyhydroxyalkanoates

Polyhydroxyalkanoates or PHAs are linear polyesters produced in nature by bacterial fermentation of sugar or lipids. More than 150 different monomers can be combined within this family to give materials with extremely different properties.ref|Doi-2002

They can be either thermoplastic or elastomeric materials, with melting points ranging from 40 to 180 °C.

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 ref|medicalengineer.

Production

To produce PHB, a culture of a micro-organism such as "Alcaligenes eutrophus" is placed in a suitable medium and fed appropriate nutrients so that it multiplies rapidly. Once the population has reached a substantial level, the nutrient composition is changed to force the micro-organism to synthesize PHB. Harvested amounts of PHB from the organism can be as high as 80% of the organisms dry weight.

Some PHA producers include:

*NatureWorks, LLC PLA
*Metabolix, US
*PHB Industrial SA, or Biocycle, Brazil
*Tianan Biologic Material Co, Ltd Ningbo
*Biomer

Applications

A PHA copolymer called PHBV (poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) is less stiff and tougher, and it may be used as packaging material.

In June 2005, a US company (Metabolix, Inc.) received the US Presidential Green Chemistry Challenge Award (small business category) for their development and commercialisation of a cost-effective method for manufacturing PHAs.

There are potential applications for PHA produced by micro-organisms ref|Doi-2002 within the medical and pharmaceutical industries, primarily due to their biodegradability.

Fixation and orthopaedic applications have included 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, ligament and tendon grafts, ocular cell implants, spinal fusion cages, skin substitutes, dural substitutes, bone graft substitutes, bone dowels, wound dressings, and hemostats ref|Chen-Wu-2005.

External links

* [http://www.epa.gov/greenchemistry/pubs/pgcc/winners/sba05.html Abstract of award for PHAs]
* [http://www.biocycle.com.br/site.htm Biocycle webpage]
* [http://www.natureworksllc.com/ NatureWorks webpage]
* [http://www.metabolix.com/ Metabolix webpage]
* [http://www.tianan-enmat.com/ Tianan webpage]
* [http://www.biomer.de/ Biomer webpage]

References

# Chen GQ & Wu Q. 2005. The application of polyhydroxyalkanoates as tissue engineering materials. Biomaterials;26:6565-6578.
# [http://tissue.medicalengineer.co.uk/Polyhydroxyalkanoates+for+tissue+engineering.php Polyhydroxyalkanoates for tissue engineering]
# Doi Y & Steinbuchel A.2002. Biopolymers. Weinheim, Germany: Wiley- VCH