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| Issue date:01/04/2008 |
| ATA Journal for Asia on Textile & Apparel - Apr 2008 Issue |
| Source:Journal for Asia on Textile & Apparel |
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Newly developed biodegradable fibers provide solutions to various medical applications as they promise improved performance and functionality at a more competitive price level.
by Liu Xiangyang and Staff Reporters
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.jpg "Biocompatible polymers are increasingly used in surgery (Photo source: the University of British Columbia)") |
| Biocompatible polymers are increasingly used in surgery (Photo source: the University of British Columbia) |
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Medical fiber is currently a growing industry as the world sees its applications mainly in medical implants and sutures to ease problems from organ dysfunction to tissue defects.
The United States annually conducts about eight million operations of tissue and organ restoration at a cost of more than US$40 billion, representing half of the country's aggregate medical expenses and a quarter of it is being spent on related fiber materials and products.
Biodegradable fibers used as medical implant materials must deliver reliable properties such as good levels of biocompatibility, durability and biodegradability. They are among the highest value medical products as they directly contact with human body, playing a vital role in the success and safety of medical operations and procedures. Thus, biodegradable fiber is a high potential field in the global medical market.
Extensive applications for polyvinyl alcohol
Polyvinyl alcohol (PVA) -- obtained by the hydrolysis of the polymer called poly vinyl acetate -- is a water-soluble high-molecule polymer widely used in diverging fields.
PVA has good film forming and adhesive properties. It resists oil, solvent and abrasion with high flexibility, and it is also a high oxygen barrier. Soluble PVA is soluble in water, and it is more readily soluble in higher water temperature; however, it is barely solved by organic solvents.
Textile-grade PVA is either a fully or a partially hydrolyzed polymer. Fully hydrolyzed PVA is cold water soluble, while partially hydrolyzed PVA is cold water insoluble. Hence, the polymer solution can be done by the means of water, and PVA can be spun in a dry or wet way.
Medical PVA fibers consist of such specifications as PVA05-88, PVA17-88 and PVA-124. The degree of alcoholysis for the first two specifications is (88 ?2)(mol)% and their average degree of polymerization are 500-600n and 1,700-1,800n respectively. The degree of alcoholysis for PVA-124 is 98-99(mol)% and its average degree of polymerization is 2,400-2,500n.
PGLA polymers bring economic benefits
Polyglycolide lactide (PGLA) produces absorbable medical sutures, thereby eliminating the need to remove them after surgery. It is particularly suitable for medical operations inside a human body, such as an anastomosis operation of liver, spleen, intestines and stomach, as well as for obstetrics and other surgical procedures of plastic surgery, ophthalmology and general surgery.
Scanning electron microscopy of a fiber-based polymer scaffold consisting of a nonwoven mesh of PGA fibers (Photo source: Middle East Technical University) |
Bringing substantial social benefits in the current medical science, this product has a high economic value.
PGLA, at a cost of no more than RMB 50,000 per kilogram, has a market value of RMB 300,000 after being processed as absorbable sutures.
In developed countries, absorbable sutures are widely adopted in the medical suture market, up to an 85% market share in the US, for example. In such less developed countries as China, catgut sutures are used, although they are increasingly replaced by sutures made of Polyglycolic acid (PGA) and PGLA.
Plant-based PLAs are fully commercialized
Polylactic acid (PLA) has become a popular polymer for academic and commercial research in the US and Japan for its extensive applications and potentials. NatureWorks LLC (formerly known as Cargill Dow Polymers LLC) in the US and Toray Industries in Japan are some pioneers in the PLA field. Toray Industries acquired Kanebo Gohsen's biodegradable (polylactic acid) fiber business in 2005.
Fully biodegradable, PLA is a plant-based polymer manufactured by polymerizing lactic acid produced by fermenting starch contained in sweet corn and other plants.
According to Toray, the eco-friendly PLA has a great potential with its "carbon neutral" feature that helps control greenhouse gases and conserve the depleting oil reserves.
In response to the rising oil prices, PLA gains increased attention for its potential as a low-cost raw material in the future and companies have looked for ways to intensify its applications in wide-ranging fields.
Toray itself kicked off full-scale commercialization of polylactic acid film, namely Ecodear, in 2006, targeting an annual capacity of 5,000 tons at its South Korean subsidiary. Ecodear is marketed as the group's universal PLA brand.
PLA polymers offer good functional performance, making them suitable for a wide variety of market applications. Similar to polyethylene terephthalate (PET), PLA polymers are non-toxic and non-irritative with a high degree of biocompatibility and bioavailability.
PLA is used in medical applications, including surgical sutures, sustained-release capsules in drug delivery systems, and reinforcing materials for bone fractures.
For example, bioabsorbable PLA can perform as a carrier of bone morphogenetic protein (BMP). Histological examinations revealed that while new bones were forming, PLA was gradually absorbed and completely disappeared within a certain period of time and were replaced by connective tissue. No negative influence was found and PLA was considered a suitable and promising material in medical applications.
PCL has excellent biocompatibility
With outstanding biocompatibility, memory and biodegradability, polycaprolacton (PCL) is extensively used for medical and general applications such as braces, sutures, bandages and degradable plastics.
PCL polymers are crystalline and degrade more slowly. They degrade in two phases. First, they constantly decrease in molecular weight without deforming. In the second stage, when molecular weight continues to drop, the polymers start breaking down into fragments, followed by absorption and excretion of human body.
PHA scaffolds with good mechanical properties
Polyhydroxyalkanoate (PHA) is a biodegradable material with good biocompatibility and polyhydroxybutyrate (PHB) is a popularly used material in the PHA family.
Being water insoluble, biodegradable, biocompatible and exhibiting thermo-plastic properties, PHAs and PHA-based composites can be used in an array of biomedical and tissue engineering applications. It has the potential to replace some uses of metal-based scaffolds and components, which do not degrade.
Metabolix is a US company pioneering in the commercialization of polyhydroxyalkanoates (PHAs).
According to Metabolix, PHAs are based on a biocatalytic process that uses renewable feedstocks, such as cornstarch, cane sugar and vegetable oils. These natural PHA plastics are highly versatile, have a broad range of physical properties, and are practical alternatives to synthetic petrochemical plastics. PHAs range from rigid to highly elastic, have very good barrier properties, and are resistant to hot water and greases.
Replacement of petrochemical plastics with PHAs can also have significant economic benefits. Producing 50 billion pounds of PHA natural plastics to replace about half of the petrochemical plastics currently used in the United States would reduce oil imports by over 200-230 million barrels per year, according to the company.
Polydioxanone promises safety and reliability
PDS (polydioxanone suture), a new synthetic absorbable suture, does not need to be removed but retains tensile strength for longer than other absorbable sutures. The tensile strength of PDS lasts 60 to 90 days and absorption takes 130-180 days.
PDS has little tissue drag and induces minimal tissue reaction. It is often used in areas where additional support is required for prolonged periods and high-tension areas such as the back.
Liu Xiangyang is a senior engineer in the Chinese textile industry.
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
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