Monodisperse stereocomplex block copolymer micelles were obtained through the self-assembly of equimolar mixtures of poly(ethylene glycol)-block-poly(l-lactide) and poly(ethylene glycol)-block-poly(d-lactide) in water. These micelles possessed partially crystallized cores and mean hydrodynamic diameters ranging from 31 to 56 nm, depending on the lactide content. They exhibited kinetic stability and redispersion properties superior to micelles prepared with isotactic or racemic polymers alone. This study demonstrates the advantages of stereocomplex formation in the design of stabilized water-soluble nanoparticles.
Glasses made from compounds of low molecular weight are useful materials with many attractive features, including well-defined compositions. At present, there are no reliable ways to identify molecules that will form long-lived glasses, and efforts to design them have tended to rely on crude principles, such as avoiding small, symmetric, and relatively inflexible molecules that engage in strong intermolecular association. We have found that it is possible to make glasses from such molecules by turning to the dark side of crystal engineering and by making small but carefully selected structural modifications specifically designed to thwart established patterns of crystallization.
New low-molecular-weight gelators can be discovered by an approach that integrates classical methods for identifying potential gelators with strategies recently developed by crystal engineers to build porous molecular networks. This hybrid approach has yielded a potent new class of selective gelators based on salts of 4,6-bis(arylamino)-1,3,5-triazine-2-carboxylic acids. These compounds lack the high degree of conformational flexibility and long alkyl chains typical of classical gelators, and Na + and DMSO play specific roles in the mechanism of gelation. Scanning electron microscopy and atomic force microscopy showed that the resulting gels consist of elemental nanofibers that are approximately 30-100 nm in width, and X-ray diffraction yielded the structure of needle-shaped crystals of a gelator obtained directly from its gel. The crystals are constructed from bilayers, with the hydrophobic aryl groups of the gelators interacting intermolecularly to form the core of the bilayers and polar triazinecarboxylate headgroups aligned on the surface. The polar surfaces then stack in a process directed by the formation by multiple intermolecular hydrogen bonds and chelation of Na + . The hybrid approach that led to the discovery of these gels promises to yield other new molecular materials at the boundary between gels and crystalline solids.
Poly(ethylene oxide)-block-poly(styrene oxide) (PEO-b-PSO) and PEO-b-poly(butylene oxide) (PEO-b-PBO) of different chain lengths were synthesized and characterized for their self-assembling properties in water by dynamic/static light scattering, spectrofluorimetry, and transmission electron microscopy. The resulting polymeric micelles were evaluated for their ability to solubilize and protect the anticancer drug docetaxel (DCTX) from degradation. The drug release kinetics as well as the cytotoxicity of the loaded micelles were assessed in vitro. All polymers formed micelles with a highly viscous core at low critical association concentrations (<10 mg/L). Micelle morphology depended on the nature of the hydrophobic block, with PBO- and PSO-based micelles yielding monodisperse spherical and cylindrical nanosized aggregates, respectively. The maximum solubilization capacity for DCTX ranged from 0.7 to 4.2% and was the highest for PSO micelles exhibiting the longest hydrophobic segment. Despite their high affinity for DCTX, PEO-b-PSO micelles were not able to efficiently protect DCTX against hydrolysis under accelerated stability testing conditions. Only PEO-b-PBO bearing 24 BO units afforded significant protection against degradation. In vitro, DCTX was released slower from the latter micelles, but all formulations possessed a similar cytotoxic effect against PC-3 prostate cancer cells. These data suggest that PEO-b-P(SO/BO) micelles could be used as alternatives to conventional surfactants for the solubilization of taxanes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.