Salt Formation of Lactic Acid Oligomers as Matrix for Sustained Release of Drugs

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Abstract
The calcium and sodium salts of l- and d, l-lactic acid oligomers were obtained by immersion of the oligomer powders (weight average mol. wt 3000–10000) in aqueous solutions of CaCl2 and NaCl, respectively, at room temperature (22°C). The salt formation was analysed by atomic absorption measurement. The thermal properties, including glass transition temperature, melting temperature, and softening temperature, were altered by conversion of the terminal free acid of the oligomer to its salt. An in-vitro release test of an anti-cancer drug from the oligomer beads showed that the drug was released more rapidly from the beads prepared from the non-converted oligomers than those prepared from the salts when the release test was carried out in media containing no calcium and no sodium ions.