Formation of Core-Sheath Polymer Fibers by Free Surface Spinning of Aqueous Two-Phase Systems

Abstract

Core-sheath fibers have numerous applications ranging from composite materials for advanced manufacturing to materials for drug delivery and regenerative medicine. Here, a simple and tunable approach for the generation of core-sheath fibers from immiscible solutions of dextran and polyethylene oxide is described. This approach exploits the entanglement of polymer molecules within the dextran and polyethylene oxide phases for free surface spinning into dry fibers. The mechanism by which these core-sheath fibers are produced after contact with a solid substrate (such as a microneedle) involves complex flows of the phase-separating polymer solutions, giving rise to a liquid–liquid core-sheath flow that is drawn into a liquid bridge. This liquid bridge then elongates into a core-sheath fiber through extensional flow as the contacting substrate is withdrawn. The core-sheath structure of the fibers produced by this approach is confirmed by attenuated total reflection Fourier-transform infrared spectroscopy and confocal microscopy. Tuning of the core diameter is also demonstrated by varying the weight percentage of dextran added to the reservoir from which the fibers are formed.

Nanofibers with an Adjustable Core-Sheath Structure Constructed from Hyperbranched Polyester for Efficient Loading of ZnO Nanoparticles

“…Further exploration was conducted on the forming mechanism of the core sheath structure. This spontaneous and adjustable formation was attributed to the large difference in the shear viscosity of the two components, which had undergone phase separation during the process of centrifugal spinning . As shown in Figure b, the HBPE solution exhibited an extremely low shear viscosity of merely 0.09 Pa·s, owing to its three-dimensional void structure with few entanglement points.…”

“…This spontaneous and adjustable formation was attributed to the large difference in the shear viscosity of the two components, which had undergone phase separation during the process of centrifugal spinning. 41 As shown in Figure 3b, the HBPE solution exhibited an extremely low shear viscosity of merely 0.09 Pa•s, owing to its threedimensional void structure with few entanglement points. On the contrary, the PAN solution exhibited a high shear viscosity of more than 15.00 Pa•s due to its massive entangled straight-chain structure.…”

Loading and Release of Quercetin from Contact-Drawn Polyvinyl Alcohol Fiber Scaffolds

“…Contact drawing relies on the formation of a liquid bridge that becomes elongated into a rapidly drying filament through extensional flow. 36,52 The formation of the liquid bridge is driven by the process of polymer entanglement. 54 For a polymer solution in the entangled regime, there is a characteristic time scale above which the polymer molecules can escape entanglement and move freely with respect to each other.…”

“…Contact drawing provides a potential route for large-scale production of biomaterial fibers from polymer solutions without the need for elaborate instrumentation, and with minimal process control requirements. The key process control considerations for contact drawing are the formulation of the fiber precursor solution and the speed at which the fibers are drawn from the precursor solution. , Contact drawing also enables blending of a wide array of potential adjuvants into the polymer precursor solution prior to contact drawing, as demonstrated here with quercetin and type I collagen. In addition, it allows one fiber precursor solution to be exchanged for another to fabricate multicomponent fiber scaffolds with a delay of only a few seconds to switch between sets of pins and substrate tools.…”

“…Contact drawing relies on the formation of a liquid bridge that becomes elongated into a rapidly drying filament through extensional flow. , The formation of the liquid bridge is driven by the process of polymer entanglement . For a polymer solution in the entangled regime, there is a characteristic time scale above which the polymer molecules can escape entanglement and move freely with respect to each other. , Thus, an increase in either the polymer concentration or the molecular weight of the polymer is expected to lead to increased entanglement along with fiber formation at slower pull speeds corresponding to longer τ pull values …”