Polylactide containing nanoparticles - new carriers of active compounds (in English)
Polimery 2005, No 7-8, 546
Two amphiphilic block copolymers poly(L-lactide)-b-polyglycidol-b-poly(ethylene oxide) (PLA-b-PGly-b-PEOX) were synthesized: PLA-b-PGly-b-PEOX(I) with Mn equal 6260 (PLA), 510 (PGly) and 6600 (PEOX) and PLA-b-PGly-b-PEOX(II) with Mn equal 3600 (PLA), 500 (PGly) and 5500 (PEOX). Polyglycidol segment in PLA-b-PGly-b-PEOX(II) was modified in reaction with succinic anhydride - the reaction leading to conversion of -CH2OH groups of polyglycidol monomeric units to -CH2OC(O)CH2CH2COOH moieties with carboxyl groups [modified PLA-b-PGly-b-PEOX(II) was denoted as PLA-b-PGly-b-PEOX(IIc)]. Molecules of all three copolymers did self assemble in water into polymeric nanoparticles with number average diameters equal 20.0±0.8 nm [PLA-b-PGly-b-PEOX(I)], 20.9±0.3 nm [PLA-b-PGly-b-PEOX(II)] and 33±1 nm [PLA-b-PGly-b-PEOX(IIc)]. Critical aggregation concentration (CAC - a concentration above which nanoparticles are formed) was equal 1.55 · 10-2, 7.0 · 10-2 and 2.51 · 10-1 g/L for PLA-b-PGly-b-PEOX(I), and PLA-b-PGly-b-PEOX(IIc), respectively. Nanoparticles were formed also in presence of pyrene and partition of pyrene between solution and nanoparticles was determined. For example, for concentrations of PLA-b-PGly-b-PEOX(II) and pyrene equal 1.95 · 10-3 g/L and 4.94 · 10-7 g/L the fraction of encapsulated pyrene was ca. 10% whereas for the same concentration of pyrene but for higher concentration of PLA-b-PGly-b-PEOX(II), above 2.50 · 10-1 g/L, the whole amount of pyrene was incorporated into nanoparticles. Profile of pyrene release from nanoparticles was bi-exponential with the rate constant for fast (kf) component equal 9.5 · 10-2, 3.8 · 10-2 and 1.5 · 10-1 L/h, for PLA-b-PGly-b-PEOX(I), PLA-b-PGly-b-PEOX(II) and PLA-b-PGly-b-PEOX(IIc), respectively, and with the rate constant for slow (ks) component essentially the same for nanoparticles from all terpolymers equal (8.4±0.2) · 10-3 L/h. It has been suggested that fast rate describes the release of pyrene from shells of nanoparticles whereas the slow one describes the release from their cores.
Key words: amphiphilic block copolymers, nanoparticles, pyrene, encapsulation, kinetics of release