Synchrotron small-angle X-ray scattering study of cross-linked polymeric micelles

Polymeric micelles of methoxypoly(ethylene glycol)-b-poly(lactide) containing lysine units (mPEG- PLA-Lys₄) were cross-linked by reacting of lysine moieties with a bifunctional bis(N-hydroxysuccinimide ester). The micelles were characterized in aqueous solution using dynamic light scattering, transmission electron microscopy, and synchrotron small-angle X-ray scattering. The mPEG-PLA-Lys₄ was synthesized through the ring-opening polymerization of N⁶-carbobenzyloxy- L-lysine N-carboxyanhydride with amine-terminated mPEG-PLA and subsequent deprotection. The polymeric micelles showed enhanced micelle stability after cross-linking, which was confirmed by adding sodium dodecyl sulfate as a destabilizing agent. The average diameters measured via dynamic light scattering were Delivered 19.1 nm by Ingenta and 29.2 nm for non-cross-linked polymeric micelles (NCPMs) and cross-linked polymeric micelles (CPMs), respectively. The transmission electron microscopy images showed that the size of the polymeric micelles increased slightly due to crosslinking, which was in good agreement with the DLS measurements. The overall structures and internal structural changes of NCPMs and CPMs in aqueous solution were studied in detail using synchrotron X-ray scattering method. According to the structural parameters of X-ray scattering analysis, CPMs with a more densely packed core structure were formed by reacting bifunctional cross-linking agents with lysine amino groups located in the innermost core of the polymeric micelles.