(Invited) Shear-Induced Fabrication of Multiple Parallel Gel Filaments Using Aqueous Two-Phase Separation

Abstract

Macroscopic structures of gel fibers have been prepared by control of the polymer solution properties and by design of the nozzle and flow path of the microfluidic device. In this research, we investigated a method to simultaneously fabricate hundreds to thousands of gel filaments simply by flowing the polymer solution inside the capillary without spinneret. An aqueous two-phase separation (ATPS) can be induced by adjusting their concentration in certain combinations of two polymers. The respective polymer concentration in each phase can be determined from the phase diagram, whereas an assembly of heterogeneous polymers generate in each phase. Hydrodynamic properties of pre-gel solution can be controlled by inducing such heterogeneous polymer assemblies. A co-axial flow double capillary was used to fabricate gel filaments, where an inner capillary (inner diameter 0.7 mm) was fixed at the insert position of an outer capillary. To induce ATPS, an ionic strength for the aqueous solution of sodium alginate (Alg) / polyethylene glycol (PEG) mixture was controlled by NaCl addition. The pre-gel Alg/PEG solution was flown as an inner flow of glass double capillaries, where a crosslinker solution (Ca2+ soln.) was flown as a sheath flow. The obtained gel was composed of multiple parallel gel filaments with a diameter of several micrometers, while a single gel without filament structure was obtained from the homogeneous solution without NaCl addition. In aqueous solution, the Alg chain has a structure with few entanglements because of its rigidity. The rigid assembly of alginate is mainly caused by guluronic acid block, that is stabilized by diaxial linkages via intramolecular hydrogen bonds. The shear stress generated by flowing the aqueous Alg solution inside the capillary cannot induce deformation of its rigid assembly, results in the single thick gel filament. By complexation with PEG, destruction of regular hydrogen bond was responsible for breaking the rigid structure of Alg. Thus, deformation of Alg/PEG assembly was enabled to elongate as the fibrous structure by the shear stress, followed by gelation in contact with Ca2+ ions at the outlet of the inner capillary. Such shear-induced deformation of the Alg/PEG assembly was studied by measuring viscoelastic properties with a spindle viscometer. Besides, Alg/PEG assembly generation in each phase was determined by size-exclusion chromatography with a multi angle light scattering detector. This presentation will discuss a simple technique for preparing multiple gel filaments simply by passing a polymer solution through a capillary.