Polylactide limitations

Polyesters, specifically polylactides and poly(lactide-co-glycolide)s have played a critical role in the development of polymer-based CR technologies. The biocompatibility and the well-established safety profiles of PLA and PLGA polymers have made them the polymer of choice for CR applications. However the off-patent status of these polymers makes them freely available for research in industry as well as academia. This has led to a vast number of patents covering various applications of these polymers within the drug delivery sector. Due to these issues, very limited scope remains to utilize these polymers to reformulate generic, off-patent drugs. 

DL-Polylactic acid, for the most part, was found to erode in about 12 months. Slow degradation of DL-polylactic acid often becomes a limitation on its use. This rate can be accelerated appreciably by copolymerizing with up to 50 mol% glycolide to yield complete erosion in as fast as 2 to 3 weeks. Incorporation of glycolide into the polylactide chain alters crystallinity, solubility, biodegradation rate, and water uptake of the polymer. 

At the time of writing, the applications of biodegradable polymers are confined mostly to the field of agriculture, where they are used in products with limited lifetimes, such as mulch films and pellets for the controlled release of herbicides. The synthetic polyesters used in medical applications, principally polylactide and poly(lactide-co-glycolide), while claimed to be biodegradable, are degraded in the body mainly, if not entirely, by chemical hydrolysis. There is little evidence that the hydrolysis of these polyesters of a-hydroxyacids can be catalyzed by hydrolase or depolymerase enzymes. 

Bourges et al. studied the kinetics of polylactide (PLA) nanoparticle (NP) localization within the intraocular tissues and to evaluate their potential to release encapsulated material. Environmental scanning electron microscopy (ESEM) showed the flow of the NPs from the site of injection into the vitreous cavity and their rapid settling on the internal limiting membrane. Histology demonstrated the anatomic integrity of the injected eyes and showed no toxic effects. A mild inflammatory cell infiltrate was observed in the ciliary body 6 h after the injection and in the posterior vitreous and retina at 18-24 h. The intensity of inflammation decreased markedly by 48 h. Confocal and fluorescence microscopy and immunohistochemistry showed that a transretinal movement of the NPs was... 

Polylactide (PLA), a biodegradable aliphatie polyester, can efficiently be produced by the ROP of LA using metal-alkoxides, whereas enzymatic ROP of LA has had limited success. Laetide is a hiorenewable monomer derived from corn, sugar beets and wheat, and ean he obtained as either l- or d-LA single enantiomers, racemic mixture (rac-LA) or meso (meso-LA). The PLA microstructures (isotactic, syndiotactic, heterotactic and atactic) depend on both the type of LAs used and the catalysts selected, and influence the PLA s physical properties (Scheme 6.1)." ... 

The flexibility will limit the applications of pure PBS polyester however, the disadvantage can be overcome by blending it with starch or polylactide. Blending with these rigid plastics will improve the modulus of the final products. 

Aliphatic polyesters are biocompatible and biodegradable polymers that are widely used in biomedical applications. Within these, polylactides and poly(s-caprolactone) are two of the most studied ones (Fig. 2). These polyesters can be synthesized via ring-opening polymerization of the corresponding cyclic esters (s-caprolactone and lactide) and via polycondensation of lactic acid. In material science, both pure aliphatic polyesters and natural polysaccharides have limitations in some specific applications. These limitations can be overcome by the introduction of hydrophilic groups (carbohydrate compounds) into the aliphatic polyesters and modifications of natural polysaccharides with hydrophobic polyesters. 

While the chemical hydrolysis of PLA has been widely studied other information concerning the chemical stability or resistance of PLA is rather limited. Stability and possible migration from polylactide to food simulants has been evaluated in a few studies (36). The stability in water, 3% acetic acid and isooctane has been shown to be adequate. However, large mass losses were reported in contact with alcoholic food stimulants such as 95% ethanol. Migrants... 

PLA, also known as polylactide (i.e. polymerization of cyclic lactic acid, also called lactide), originally is a brittle material with lower impact strength and elongation at break, similar to another relatively brittle polymer—polystyrene (PS). However, its tensile strength and modulus are comparable to polyethylene terephthalate (PET). This is shown in Table 5. 2 as reported by Anderson et al (2008). Poor toughness limits its usage in... 

Nowadays, certain blend of polylactide and polycaprolactone are extensively used for packaging of vegetable oils. These blend exhibit comparable tensile strength, brittleness, and rigidity as packaging material derived from polypropylene or polyethylene derivative. The PLA and PCL shows improved barrier properties and prevents aroma losses but only limitation of using this blend as packaging material is its inefficient gas permeability. 

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