Studies On The Preparation Of Polymeric Helical,Superhelical Microfibers And Helical Tubes Via Microfluidic Spinning

Helix and superhelix play critical roles in the achievement of tissue functions.These fascinating structures have attracted increasing interests due to their potential bio mimicking applications.Recently,substantial elegant achievements have been made in microfluidic spinning helical microfibers via liquid rope coiling effect within the microchannels.However,the helical fluids in these microchannels need to be rapidly gelated or solidificated to maintain their helical shape,and thus these helical microfibers were mainly restricted to the Ca-alginate rapid cross-linking system.So the application of these helical fibers is limited due to the restricted availability of materials.Additionally,the amplitude of these helical fibers mainly depended on the inner dimension of the collection tube,and thus could not be adjusted once the device was made.On the other hand,superhelical structure,which is a hierarchical structure in which a helix is further folded to produce a more ordered helix,is another higher order and more sophisticated structure from natural creatures.Superhelical structures also play important roles in a number of biological processes.However,there are few reports on the preparation of superhelical structures.Up to now,continuous and controlled fabrication of these structures,especially the superhelical structures,from various polymers for different practical applications still remains a big challenge.This thesis mainly aims to the preparation of helical,superhelical microfibers of various polymers and helical tubes using simple single emulstion capillary microfluidic technique.The detailed research contents are as follows:1.Based on the synergy effect of the mass-transfer between the dispersed inner and the continuous outer phase and the widening of collection tube of a simple single emulstion capillary microfluidic device,a novel and versatile microfluidic spinning strategy was presented for controllable and consecutive generation of helical microfibers from various polymers,such as hydrophilic carboxylated chitosan(CCS)and poly(vinyl alcohol)(PVA),hydrophobic ethylene-vinyl alcohol(EVOH)and amphiphilic polyurethane-urea(PUU3-12)copolymers.The diameter,wavelength and amplitude of these microfibers could be highly controlled.Tensile experiments showed that the helical microfibers have excellent elongation properties.2.By simply connecting a even wider collection tube to the end of the above mentioned single emulstion microfluidic device,superhelical microfibers of hydrophilic carboxylated chitosan(CCS)and poly(vinyl alcohol)(PVA),hydrophobic ethylene-vinyl alcohol(EVOH)and amphiphilic polyurethane-urea(PUU3-12)copolymers could also be continuously and controllably prepared.The wavelength and amplitude of these superhelical microfibers can be precisely controlled by simply adjusting the flow rates of the internal and external phase.These results,once again,further confirmed the synergistic effect of mass transfer and channel widening induced formation and holding of the helical and superhelical structures.3.PUU3-12 based helical tube was prepared using a simple single emulsion capillary microfluidic device.The obtained helical tube was further surface coated by simply immersing in viscous PUU3-12 solution,yielding even stable bioinspired artificial blood-vessel structure.This opens up a new way for the preparation of small-sized bionic vascular structures.