Study On The Application Of Unelectrosinnable Sheath Fluid In The Formation And Functionalization Of Electrospun Nanofibers

This thesis developed modified coaxial/triaxial electrospinning processes for manipulating the nanofibers'morphology,inner structure,and endowing them functions.These processes were characterized by the effective applications of unspinnable solvent or solution as the sheath working fluids.Aimed to the specific applications in the fields of drug delivery and environment,the following topics were investigated in details:?1?Firstly,the fabrication of medicated nanofibers for potential colon-targeted drug delivery using a modified coaxial electrospinning was reported,in which salt?NaCl?solutions were exploited as shell fluids to facilitate the preparation processes.A homemade concentric spinneret with an indented core capillary was developed to conduct the coaxial processes.Optical observations and scanning electron microscopic results demonstrated that the shell-to-core fluid flow rate ratio was a key parameter,which exerted a significant influence on the electrospinning processes and could be exploited to control the fibers'morphology and diameters.A scaling law of=0.173-0.531?2=0.9976?was built,by which the nanofibers'sizes can be predicted and manipulated easily.X-ray diffraction and attenuated total reflected FTIR tests verified that the medicated nanofibers were essentially a polymeric nanocomposite and the guest drug diclofenac sodium?DS?had fine compatibility with the host polymer.All the drug was encapsulated in the filament-forming carrier.In vitro dissolution experiments demonstrated that the medicated nanofibers could free the drug in a neutral condition,suggesting potential colon-targeted drug delivery applications.Ex vivo tests demonstrated that the medicated fiber mats could enhance the transmembrane of DS.?2?Secondly,based on the modified coaxial processes,the possibility oftri-axial electrospinning with only one of the three fluids being electrospinnable was investigated.Using an electrospinnable middle fluid of Eudragit S100?ES100?with pure ethanol as the outer solvent and an unspinnable lecithin-diclofenac sodium?PL–DS?core solution,nanofibers with linear morphology and clear core/shell structures can be fabricated continuously and smoothly.X-ray diffraction proved that these nanofibers are structural nanocomposites with the drug present in an amorphous state.In vitro dissolution tests demonstrated that the formulations could preclude release in acidic conditions,and that the drug was released from the fibers in two successive steps at neutral pH.The first step is the dissolution of the shell ES100 and the conversion of the core PL–DS into sub-micron sized particles.This frees some DS into solution,and later the remaining DS is gradually released from the PL–DS particles through diffusion.Ex vivo permeation results showed that the composite nanofibers give a more than twofold uplift in the amount of DS passing through the colonic membrane as compared to pure DS;74%of the transmitted drug was in the form of PL–DS particles.The new tri-axial electrospinning process developed in this work provides a platform to fabricate structural nanomaterials,and the core–shell polymer-PL nanocomposites we have produced have significant potential applications for oral colon-targeted drug delivery.?3?Thirdly,the influences of different sheath solvents on the formation cellulose acetate?CA?nanofibers based on the utilization of a modified coaxial electrospinning were studied.With a solution of 11%w/v CA in a mixed solvents as the core electrospinnable fluid,and solvents including acetone,ethanol and dimethylformamide as the sheath working fluids,the modified coaxial processes were run smoothly and continuously.Scanning electron microscopic observations demonstrated that the size of CA nanofibers?D?is closely related to solvent boiling point?T?.A scaling law of D=490.33-2.42 T?R²=0.9906?can be achieved.With suitable selection of the sheath solvent,homogeneous and fine polymeric nanofibers can be generated using the modified coaxial electrospinning processes.Then with the TiO₂ suspension as the sheath fluid and 11%w/v CA in a mixed solvents as the core electrospinnable fluid,we prepared nanofibers with TiO₂ particles loaded on it.The composite nanofibers which TiO₂ loaded on the surface of fibers using the modified coaxial processes showed better mechanical properties and improved photocatalytic properties on the degrations of organic dye pollutant methylene blue than that nanofibers using single fluid electrospinning.