Micelles based on amphiphilic PCL-PEO triblock and star-shaped diblock copolymers: Potential in drug delivery applications.

In this work, the potential in drug nanodelivery of micelles made from poly(epsilon-caprolactone) (PCL) and poly (ethyleneoxide) (PEO) copolymers with triblock and star-diblock architectures was explored. Linear and 4-arm star-shaped PCL macromers with two or four --OH end groups were prepared by ring-opening polymerization of CL and condensed with alpha-methoxy-omega-carboxy-PEO. The resulting amphiphilic copolymers were characterized by (1)H NMR, size exclusion chromatography, and differential scanning calorimetry. Separate PCL and PEO crystalline phases were observed for both copolymers. Copolymers self-assembled in water giving critical association concentrations in the range 0.010-0.023 mg/mL. Micelles with a size of 32-45 nm were prepared by dialysis and characterized for hydrodynamic diameter and surface charge. Their potential as nanocarriers in drug delivery applications was evaluated too. Micelles were nontoxic to both Red blood cells and HeLa cells. Complement activation experiments indicated that micelles can escape the reticuloendothelial system once intravenously injected. Finally, a different uptake on HeLa cells was found for micelles obtained from triblock and star-shaped copolymers.

Poly(epsilon-caprolactone)-poly(oxyethylene) multiblock copolymers bearing along the chain regularly spaced pendant amino groups.

Poly(epsilon-caprolactone) (PCL) macromers (M(n) = 1.7-3.8 kDa) which contain one Z-protected -NH2 group per chain were synthesized by ring-opening polymerization of epsilon-caprolactone in the presence of Sn(oct)2 using as initiator a diamine prepared by condensation of N-Boc-1,6-hexanediamine and N(alpha)-Boc-N(epsilon)-Z-L-Lysine. The coupling of these macromers with -COCl end-capped poly(oxyethylene) (PEO), M(n) = 1.0 kDa, afforded amphiphilic multiblock poly(ether ester)s (PEEs) which have, along the chain, regularly spaced pendant protected amino groups. Deprotection, accomplished without chain degradation, yielded -NH2 groups available for further reactions. The molecular structure of macromers and PEEs was investigated by 1H NMR and SEC. DSC and WAXS analyses showed that macromers and copolymers were semicrystalline and their T(m) increased with increase in the molecular weight of PCL segments. The inherent viscosity values (0.25-0.30 dL x g(-1)), together with SEC analysis results, indicated moderate polymerization degrees.