Medical applications, polylactic acids

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

Lactic acid is an important chemical that has wide applications in food, pharmaceutical, cosmetic, and chemical industries. There are increasing interests in production of lactate esters and biodegradable polylactic acid (PLA) from lactic acid. Lactate esters are a relatively new family of solvents with specific properties. They are considered safe and are biodegradable (1). In many situations they can replace toxic solvents. Their functions vary from that of intermediates in chemical reactions to solvents in ink formulations and cleaning applications (2). PLA has been widely used in medical implants, sutures, and drug-delivery systems because of its capacity to dissolve over time (3-5). PLA also can be used in products such as plant pots, disposable diapers, and textile fabrics. 

Polylactic acid has many potential uses, including many applications in the textile and medical industries as well as the packaging industry. 

Polylactic acid was first discovered in the 1930s when a DuPont scientist, Wallace Caruthers, produced a low molecular weight PLA product. In 1954, DuPont patented Carothers process. Initially the focus was on the manufacture of medical grade applications due to the high cost of the polymer, but advances in fermentation of glucose, which forms lactic acid, has dramatically lowered the cost of producing lactic acid and significantly increased interest in the polymer. 

Polylactic acid is likely to have significant future potential in a variety of applications due to specific advantages compared with conventional petroleum-based polymers. The cost-performance balance of PLA has resulted in its use in many applications, including packaging, fibers, and medicals. The use of PLA as an alternative to petroleum-based polymers will increase demand for agricultural products such as corn and sugar beets, and is an advanced example of sustainable technology. 

Polylactic Acid Polylactic acid (PLA) is a thermoplastic, ahphatic polyester that can be synthesized from biologically produced lactic acid. Currently, the major production of polylactic acid is from the ring-opening polymerization of the lactide [43, 44]. This material has been used extensively in the medical field for sutures, staples, and the like and as such is very expensive. Recently, April 2002, Cargill-Dow has opened a large-scale production facility whereby PLA is being produced at a low cost for nonmedical applications ... 

PLGA (Cutright and Hunsuck, 1971 Athanasiou et al., 1996), which was employed as suture by taking advantage of its biodegradation ability. So far, the medical applications have not changed drastically and the main polymer choices are still the classical types of copolymers based on polylactic acid (PLA) and polyglycolic acid (PGA) as shown in Table 7.6. 

Polylactic acid shows great potential among biopolyesters, particularly for packaging [36-38] and medical applications, and the reason for this fact is its large availability on the market and its relatively low price [34,36-39]. 

On the other hand, a method to obtain biodegradable and less stiff polymers consists in the copolymerization of poly(ethyleneoxide) (PEO) and polylactic acid (PLA). These poly(ether-esters) are characterised by hard semi-crystalline PLLA domains and flexible, elastic and hydrophilic PEO regions. Degradation kinetics suggested a bio-medical application as replacement of soft tissue and drug delivery. 

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