Anisotropic Microparticles through Periodic Autofragmentation of Amphiphilic Triblock Copolymer Microfibers

Fracture formation due to drying is a common process in a range of systems, from mud cracks to thin polymeric films. Design and control of the fracturing process can be used as a tool for directing the fractures into predefined paths, leading to patterning and controlled fragmentation. In this work, we report the spontaneous periodic fragmentation of polymeric microfibers upon drying. The microfibers are fabricated via electrospinning of amphiphilic triblock copolymers over a glass substrate, and throughout their drying, highly periodic and sharp transverse cracking occurs along the fiber, resulting in the production of anisotropic microparticles (MPs) with a remarkably narrow size distribution. The average length of the MPs depends on the fiber's diameter; hence, by tuning the diameter of the fibers, size control over the MPs is achieved. X-ray scattering measurements reveal the formation of a lamellar arrangement of the copolymers along the fiber, providing a molecular insight into the formation of sharp transverse fractures. Adjusting the lipophilicity of the two terminal hydrophobic dendritic blocks of the triblock copolymers allows tuning the solubility of the obtained MPs in water and the release rate of hydrophobic cargo, opening a new route for the fabrication of anisotropic MPs for controlled release applications.