Cargo Encapsulation In Uniform, Length-Tunable Aqueous Nanofibers With A Coaxial Crystalline And Amorphous Core

Low-dispersity, length-tunable, water-dispersable block copolymer nanofibers with spatially controlled functionalization and a crystalline core have recently become accessible using the living crystallization-driven self-assembly (CDSA) seeded growth method. Unfortunately, a potential obstacle to their use as delivery vectors is that encapsulation within the ordered, crystalline core is expected to be highly problematic. Herein, we address this problem through the design of an ABC triblock copolymer (triBCP) with a crystallizable poly-(fluorenetrimethylcarbonate) (PFTMC) core-forming block (A), a hydrophobic amorphous poly(butyl methacrylate) (PBMA) central block (B), and a hydrophilic poly(N-isopropylacrylamide) (PNIPAM) corona-forming block (C). Living CDSA of the triBCP in polar organic media yielded nanofibers of predetermined and uniform lengths, with a crystalline PFTMC core and a solvated PBMA-b-PNIPAM corona. Transfer to aqueous media led to the collapse of the PBMA block to yield nanofibers composed of an inner crystalline PFTMC core surrounded coaxially by an outer amorphous PBMA core with a solubilizing PNIPAM corona. Performing a solvent switch from organic to aqueous media in the presence of a model hydrophobic cargo, Nile Red (NR), led to efficient encapsulation of the dye in the outer PBMA core, while the reverse solvent switch facilitated NR release. We estimate that only ca. 14% of the core volume is occupied by the crystalline PFTMC leaving 86% available for encapsulation. The results suggest that nanofibers with a coaxial crystalline and amorphous core are promising for the development of tailored, nanoparticle-based drug delivery systems with low dispersity and precise dimensions.