Polyhydroxyalkanoates

Polyhydroxyalkanoates or PHAs are linear polyesters produced in nature by bacterial fermentation of sugar or lipids. More than 100 different monomers can be combined within this family to give materials with extremely different properties.

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They can be either thermoplastic or elastomeric materials, with melting points ranging from 40 to 180 °C. The most common type of PHA is PHB (poly-beta-hydroxybutyrate). PHB has properties similar to those of polypropylene, however it is stiffer and more brittle.

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 'diet' is changed to force the micro-organism to create PHB. Harvested amounts of PHB from the organism can be anywhere from 30% to 80% of the organisms dry weight.

A PHB copolymer called PHBV (polyhydroxybutyrate-valerate) is less stiff and tougher, and it is 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 under unbalanced growth conditions ^[1] 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 ^[2].

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 ^[3].

Some PHAs producers include:

-Metabolix, US

-PHB Industrial SA, or Biocycle, Brazil

-Tianan Biologic Material Co, Ltd Ningbo

-Biomer

References

1. ^  Chen GQ & Wu Q. 2005. The application of polyhydroxyalkanoates as tissue engineering materials. Biomaterials;26:6565-6578.
2. ^  Polyhydroxyalkanoates for tissue engineering
3. ^  Doi Y & Steinbuchel A.2002. Biopolymers. Weinheim, Germany: Wiley- VCH