Adriamycin release from self-assembling nanospheres of poly(DL-lactide-co-glycolide)-grafted pullulan

Poly(DL-lactide-co-glycolide)-graft pullulan (PuLG) was synthesized to produce a hydrophobically modified polysaccharide. Specific pullulan and poly(DL-lactide-co-glycolide) (PLGA) (abbreviated as PuLG) appeared in the peaks of the PuLG spectra on (1)H NMR spectroscopy, suggesting that PLGA was successively grafted to the pullulan backbone. PuLG nanospheres have a round shape with a particle size of about 75-150 nm. From the fluorescence excitation spectra in a fluorescence probe study, the critical association concentration (CAC) values were determined to be 0.017 g/l for PuLG-1, 0.0054 g/l for PuLG-2, and 0.0047 g/l for PuLG-3. The drug contents of the PuLG nanospheres were approximately 20-30% (w/w). As the drug contents of PuLG nanospheres increased, the drug release rate from nanospheres decreased. The drug release rate from PuLG nanospheres was delayed as the molecular weight of PuLG increased. PuLG copolymer with higher graft ratio of PLGA showed slower degradation rate rather than that with lower graft ratio. Since degradation rate of PuLG was taken over 1 month, drug release was governed by diffusion mechanism rather than degradation mechanism.