The performances of poly(lactic-co-glycolic acid) drug delivery systems are affected by the molecular interactions established between the drug and the polymer matrix as well as by the physical state of the drug embedded. Indeed, the drug may induce polymer plasticization with a drastic change in the release kinetics and medicinal product performances. The aim of this study was to better understand the interactions between poly(lactic-co-glycolic acid) and ketoprofen, the latter known to plasticize hydrophilic and hydrophobic polymers. Ketoprofen interacts with poly(lactic-co-glycolic acid) exerting a maximum plasticizing effect at weight fractions around 0.25. Higher ketoprofen amounts form heterogeneous mixtures with the non-soluble molecules dispersed in the matrix as crystals or amorphous domains, depending on the preparation method. Unexpectedly, the amorphous ketoprofen dispersed in the poly(lactic-co-glycolic acid) matrix was remarkably stable. H-bonding seems responsible for the glass transition temperature reduction and the limited solubility. Brillouin spectroscopy and molecular dynamics simulation data suggest that ketoprofen solubility increases with temperature and non-polar interactions are responsible for this phenomenon.
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