Spontaneous formation of polylactide stereocomplex microspheres containing metal ions

Abstract

Linear poly(l‐lactides) (PLLAs) and poly(d‐lactides) (PDLAs) with Mn in the range 2000 − 4300 containing a different number and placement of carboxyl groups were obtained via cationic ring‐opening polymerization and post‐polymerization functionalization. PLA stereoisomers (PLLA‐(COOH)x and PDLA‐(COOH)x, where x = 1 − 3) were used for the investigation of stereocomplexation in solution performed in the presence of metal cations such as Ca2+, Mg2+, Zn2+, Fe3+. Spherical microparticles with a diameter in the range 0.7 − 3.0 µm were obtained in all cases which was confirmed on the basis of scanning electron microscopy (SEM) analysis. The microsphere size and homogeneity were analyzed depending on the stereocomplexation conditions and the molecular weight as well as the number of carboxyl end groups in the PLLA and PDLA used for stereocomplexation. The PLA microspheres obtained were analyzed by Fourier transform IR spectroscopy, wide angle X‐ray spectroscopy and energy‐dispersive X‐ray spectroscopy methods which confirmed the presence of metal cations inside. The application of regular microspheres with metal ions as drug delivery systems is considered. © 2016 Society of Chemical Industry

Encapsulation of hydrophobic vitamins by polylactide stereocomplexation and their release study

“…Stereocomplexes in the form of microparticles with an average diameter of 1–1.5 µm precipitated spontaneously from THF solution after mixing of PLLA and PDLA solutions containing dispersed calcium oxide. Calcium ions were present inside the resulting microparticles as we proved earlier …”

“…Preceding the microsphere formation in a solution containing PLLA/PDLA/Ca 2+ (also PLLA/PDLA/Ca 2+ /vitamin) the pre‐organization of PLA macromolecules proceeds due to cooperative interactions between ionized carboxyl end‐groups and the encapsulated compound with metal cations and PLA stereocomplexation, as discussed by us earlier …”

“…Microparticles of PLA stereocomplex were prepared according to the procedure described by us earlier . Polylactides PLLA and PDLA containing one hydroxyl and one carboxyl terminal group used for stereocomplexation were synthesized via bulk cationic polymerization initiated by glycolic acid .…”

“…Among the papers concerning the preparation of (nano)microparticles using the phenomenon of PLA stereocomplexation, with potential applications as drug carriers, there are also papers from our group . These contributions concern the stereocomplexation of medium molecular weight PLAs containing ionic end‐groups.…”

“…Spontaneous PLA stereocomplexation leads to hydrophobic microparticles built only from the PLA stereocomplex; thus the method of encapsulation by PLA stereocomplexation was expected to give a positive effect in the case of the entrapment of fat‐soluble vitamins such as D 3 (cholecalciferol), A (retinol) and E (α‐tocopherol). The additional justification for undertaking this study is the fact that carboxyl groups at the PLA chain end can be ionized by calcium ions . Calcium ions (Ca 2+ ) play a vital role in the physiology and biochemistry of organisms and the cell.…”