Hydrophobically modified PEG-driven morphology control in thermo-responsive biosourced 12-hydroxy-stearic acid...

We have recently shown that mixing green fatty acid 12-hydroxystearic acid (12-HSA) molecules with a low amount of various end-capped polyethylene glycol (PEG) chains (mono- or di-functionalized by 12-HSA or stearic acid (SA) moieties) provides a straightforward one-pot route to design PEGylated self-assemblies, either vesicles or multilamellar tubes. Tuning the concentration of end-capped PEG chains offers a simple strategy to precisely control the morphology of these PEGylated architectures.

Four types of 4 kDa end-capped PEG chains, functionalized at one or both ends with either 12-HSA or SA, were mixed with 12-HSA over a wide range of ratios between PEG-borne fatty acid moieties and free 12-HSA molecules. The detailed structure of the resulting self-assemblies was investigated by Small-Angle Neutron Scattering with contrast variation at 20 °C and 45 °C.

For both mono-functionalized PEGs, PEGylated multilamellar tubes are obtained, with a PEG brush density controlled by polymer content. Di-functionalized 12-HSA PEG chains yield PEGylated unilamellar vesicles whose diameter decreases with increasing PEG concentration due to curvature changes. Di-functionalized SA PEG chains form PEGylated multilamellar tubes coexisting with telechelic polymer flowers located within the interlayer at low PEG content and both inside and outside the tubes at higher concentrations. All architectures transform into small PEGylated ellipsoidal micelles between 20 and 45 °C. This dual control over structure and dimensions provides a versatile platform for designing nanocarriers adapted to specific drug-delivery requirements.