Preparation of Polylactide Microspheres Having Positively or Negatively Charged Surfaces

The syntheses of polylactides (PLAs) with branched peptide end groups containing reactive (ionic) moieties such as amino or carboxyl groups are described and were used to prepare PLA-based microspheres (MSs) with positively or negatively charged surfaces. Branched peptides with hydroxyl end groups and four protected amino or carboxyl groups, Boc 4 -K 3 -OH or Bn 4 -E 3 -OH, were synthesized, and the hydroxyl group converted to an alkoxide and was used as the initiation site for the ring-opening polymerization of L-lactide. Subsequent deprotection gave PLAs endcapped with branched peptides having four amino or carboxyl groups, respectively (K 3 -PLA and E 3 -PLA). K 3 -PLA and E 3 -PLA were converted to K 4+ 3 -PLA and E 4- 3 -PLA by acid or base treatment, respectively. MSs with charged surfaces were then prepared using K 4+ 3 -PLA or E 4- 3 -PLA as a surfactant [MS(K 4+ 3 -PLA) or MS(E 4- 3 -PLA)]. The ionic surface state of the MSs was confirmed by colloidal titration and zeta potential analysis.