Cryoprotection?lyophilization and physical stabilization of rifampicinloaded flower-like polymeric micelles

MORETTON M.A.; CHIAPPETTA D.A.; SOSNIK A.

JOURNAL OF THE ROYAL SOCIETY INTERFACE

ROYAL SOC

Año: 2012 vol. 9 p. 487 - 502

1742-5689

Rifampicin-loaded poly(e-caprolactone)?b-poly(ethylene glycol)?poly(e-caprolactone) flower-like polymeric micelles display low aqueous physical stability over time and undergo substantial secondary aggregation. To improve their physical stability, the lyoprotection?lyophilization process was thoroughly characterized. The preliminary cryoprotectant performance of mono- and disaccharides (e.g. maltose, glucose), hydroxypropyl-bcyclodextrin (HPbCD) and poly(ethylene glycol) (PEG) of different molecular weights was assessed in freeze?thawing assays at -20°C, -80°C and -196°C. The size and size distribution of the micelles at the different stages were measured by dynamic light scattering (DLS). A cryoprotectant factor ( fc) was determined by taking the ratio between the size immediately after the addition of the cryoprotectant and the size after the preliminary freeze?thawing assay. The benefit of a synergistic cryoprotection by means of saccharide/PEG mixtures was also assessed. Glucose (1:20), maltose (1:20), HPbCD (1:5) and glucose or maltose mixtures with PEG3350 (1:20) (copolymer:cryoprotectant weight ratio) were the most effective systems to protect 1 per cent micellar systems. Conversely, only HPbCD (1:5) cryoprotected more concentrated drug-loaded micelles (4% and 6%). Then, those micelle/cryoprotectant systems that displayed fc values smaller than 2 were freeze-dried. The morphology of freeze-dried powders was characterized by scanning electron microscopy and atomic force microscopy and the residual water content analysed by the Karl Fisher method. The HPbCD-added lyophilisates were brittle porous cakes (residual water was between 0.8% and 3%), easily redispersable in water to form transparent systems with a minimal increase in the micellar size, as determined by DLS.