From nanometric to giant polyion complex micelles via a hierarchical assembly of dendrimers

PIC (polyion complex) micelles prepared from oppositely charged block copolymers have typical diameters of about 30-50 nm. Attempts to control their size have proven elusive. Since the presence of a neutral hydrophilic block in the copolymers, such as poly(ethylene glycol) (PEG), allows confining the charged blocks within a core, reducing PEGylation was expected to produce larger micelles to accommodate fewer/smaller PEG chains at the corona.

PIC micelles with variable PEGylation were prepared by tuning the ratio between a PEG-dendritic copolymer/dendrimer pair (% PEG) or the molecular weight (MW) of PEG. The size and core-corona structure of the micelles were studied by dynamic light scattering, electron and confocal microscopies. A model of core-shell spherical particles developed to describe the size variation was validated by static light scattering.

The diameter of PIC micelles can be tuned from 40 nm up to nearly 2 µm by appropriate selection of % PEG and MW of PEG (Eq. (12)). Reducing % PEG produces larger micelles and concomitant reductions in the number and total surface area of particles and PEG density. While smaller PEGs are more effective at templating larger and more densely PEGylated micelles, longer PEG chains fit better into smaller micelles with lower PEG density.