Poly(lactic-co-glycolic acid) (PLGA)
PLGAor poly(lactic-co-glycolic acid) is a copolymer which is used in a host of Food and Drug Administration (FDA) approved therapeutic devices, owing to its biodegradability and biocompatibility. PLGA is synthesized by means of random ring-opening co-polymerization of two different monomers, the cyclic dimers (1,4-dioxane-2,5-diones) of glycolic acid and lactic acid. Common catalysts used in the preparation of this polymer include tin(II) 2-ethylhexanoate, tin(II) alkoxides, or aluminum isopropoxide. During polymerization, successive monomeric units (of glycolic or lactic acid) are linked together in PLGA by ester linkages, thus yielding a linear, aliphatic polyester as a product.
Depending on the ratio of lactide to glycolide used for the polymerization, different forms of PLGA can be obtained: these are usually identified in regard to the monomers' ratio used (e.g. PLGA 75:25 identifies a copolymer whose composition is 75% lactic acid and 25% glycolic acid). All PLGAs are amorphous rather than crystalline and show a glass transition temperature in the range of 40-60 °C. Unlike the homopolymers of lactic acid (polylactide) and glycolic acid (polyglycolide) which show poor solubilities, PLGA can be dissolved by a wide range of common solvents, including chlorinated solvents, tetrahydrofuran, acetone or ethyl acetate.
“Glycolic acid(or hydroxyacetic acid) is the smallest α-hydroxy acid (AHA). This colorless, odorless, and hygroscopic crystalline solid is highly soluble in water. It is used in various skin-care products. Glycolic acid is found in some sugar-crops.” (Wikipedia, Glycolic Acid, 11/29/2011)
“Lactic acid,(2-Hydroxypropanoic acid) also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3. It has a hydroxyl group adjacent to the carboxyl group, making it an alpha hydroxy acid (AHA).”
“In solution, it can lose a proton from the acidic group, producing the lactate ion (to be specific, an anion due to being negatively charged with an extra electron) CH3CH(OH)COO−. Compared to acetic acid its pKa is 1 unit smaller, meaning lactic acid loses its proton ten times as easily as acetic acid does. This higher acidity is the consequence of the intramolecular hydrogen bridge between the α-hydroxyl and the carboxylate group, making the latter less capable of keeping its proton tight.”
Recent Journal Articles
Phase separation of polyphosphazene/poly(lactide-co-glycolide) blends prepared under different conditions
(2448–2457)Polymers for Advanced Technologies 22 #12 (2011)
Cai et al of the Beijing University of Chemical Technology and the Chinese Academy of Science, China, prepared blend films of poly[(alaine ethyl ester)0.62(glycine ethyl ester)0.38]phosphazene/poly(lactide-co-glycolide) (PAGP/PLGA blend) Using a mutual solvent technique,. Compared with dichloromethane and tetrahydrofuran (THF), chloroform was the better solvent to form miscible PAGP/PLGA blend films at relatively anhydrous atmosphere. However, in the humid atmosphere, the hexagonal arrangement of holes appeared on the surface of PAGP/PLGA blend films due to the ordered array of water droplets. A sandwich-liked structure was formed with the hydrophilic PAGP component at the top and bottom, while the PLGA component in the middle. In addition, the surface morphology of PAGP/PLGA blend films was also influenced by the film thickness and the property of the substrate. (RDC 11/25/2011)