Page 81 - Biodegradable Polyesters

3.8 Application Opportunities of Bacterial Polyhydroxyalkanoates 59

3.8.2
In Material Industry: PHAs as Polymeric Materials

Thanks to their special polymer features, PHAs with diverse structures and prop-
erties have been researched as bioplastics, fibers, biomedical implants, and drug
delivery carriers and so on. Similar to the rapid development of polylactic acid
(PLA) promoted by NatureWork as a bulk bioplastic, the large-scale supply of
PHAs will increase the speed of their development as new plastics with sustainable
properties.

3.8.2.1 PHAs as Biodegradable Plastics and Fiber Materials
Originally PHAs were used to produce articles such as shampoo bottles and pack-
aging materials by Wella AG, Germany. In addition to packaging films mainly for
use as shopping bags, containers, and paper coatings, PHAs were used to pro-
duce disposable items such as razors, utensils, diapers, feminine hygiene products,
cosmetic containers, and cups, as well as medical surgical garments, upholstery,
carpets, packaging, compostable bags, and lids or tubs for thermoformed articles
by P&G, Biomers, Metabolix, and several other companies.
PHB fibers with high tensile strength were prepared by stretching the fibers
after isothermal crystallization close to the glass transition temperature. Increas-
ing the time for isothermal crystallization of PHB fibers resulted in a decrease in
the maximum draw ratio. However the tensile strength of PHA fibers increased
remarkably when the isothermal crystallization time was prolonged to more than
24 h. The tensile strength of low-molecular-weight drawn fibers was higher than
that of high-molecular-weight fibers. PHB fibers stretched after isothermal crys-
tallization had the oriented α-form crystal with a 2(1) helix conformation and the
β-form with a planar zigzag conformation.

3.8.2.2 PHAs as Medical Implant Materials
PHAs including PHB, PHBV, P3HB4HB, P4HB, P3HO (poly-(R)-3-hydroxy-
octanoate), and PHBHHx are commonly investigated for use as sutures, repair
devices, repair patches, slings, cardiovascular patches, orthopedic pins, adhesion
barriers, stents, guided tissue repair/regeneration devices, articular cartilage
repair devices, nerve guides, tendon repair devices, bone marrow scaffolds,
artificial esophagus, and wound dressings. Tepha, a Boston-based company,
specializes in manufacturing pericardial patches, artery augments, cardiological
stents, vascular grafts, heart valves, implants and tablets, sutures, dressings,
dusting powders, and prodrugs; it markets P4HB for medical application under
the name of PHA4400 [62]. Recently, PHBHHx was successfully used as an
osteosynthetic material for stimulating bone growth owing to its piezoelectric
properties, as well as for repairing damaged nerves. Nutritional and therapeutic
uses were found in the oligomers of PHA. It was found that monofilament sutures
made of PHB and PHBV did not cause any in vivo acute vascular reaction at the
site of implantation or any other adverse event for more than 1 year. Compa-
rable phenomena have been found with PHBHHx. One of the most important