Biodegradable microspheres having reactive groups prepared from L-lactic acid-depsipeptide copolymers

Poly(L-lactic acid)-based microspheres having chemically reactive groups on their surfaces, MS(LAGA) and MS(LAGL), were prepared from the respective biodegradable L-lactic acid (LA)-depsipeptide copolymers, poly[LA-(Glc-Asp)] and poly[LA-(Glc-Lys)], having low contents of depsipeptide units, by an oil-in-water (O/W) emulsion and solvent evaporation method. The average diameters of the dried microspheres obtained were estimated to be 390–450 nm by scanning electron microscopy (SEM). The amounts of functionalized groups located on their surfaces were found to increase with an increase in the content of depsipeptide units in the used copolymers as determined by a colloidal titration method. The ζ potential values of the MS(LAGA) and MS(LAGL) surfaces increased negatively and positively in proportion to the amount of carboxyl and amino groups, respectively. As one example of the chemical modification of the obtained microspheres, the immobilization of galactose residues onto the surface of MS(LAGA) was demonstrated. Moreover, the entrapment of 1-naphthalenesulfonic acid as a hydrophilic model drug into MS(LAGA) and MS(LAGL), and its release behavior were investigated.