Size-dependent soft epitaxial crystallization in the formation of blend nanofiber shish kebabs

Hierarchical structures called nanofiber shish-kebabs (NFSKs) have been studied as a means to decorate or functionalize electrospun nanofibers. Blending natural and synthetic polymers together into the electrospun fiber NFSK backbones offers the opportunity to design materials with finely tuned mechanical and biological properties. However, it is not known how homopolymer and copolymer kebab formation will be impacted by these blend compositions. NFSKs made from polycaprolactone (PCL) and gelatin blend fibers with PCL homopolymer and PCL-block-poly (acrylic acid) (PCL-b-PAA) block copolymer crystalline kebabs were successfully formed. The blend fibers templated crystal growth on the surface, but with a highly irregular kebab orientation and periodicity that was attributed to the large fiber diameter for the blend. Acetic acid was then incorporated into the fibers and shown to improve the phase mixing between PCL and gelatin, leading to smaller diameter electrospun fibers and more regular and periodic kebab NFSK morphology. The study further confirmed the size-dependent soft-epitaxy mechanism in the formation of crystalline shish kebab structures, with the electrospun nanofiber diameter leading to more oriented PCL chains within the fiber and subsequent orientation of the crystallizing kebab polymer. These NFSKs with multicomponent shish and kebabs have potential to be versatile scaffolds for biomineralization and cellular engineering purposes.