Nanofiber, one of the most fascinating nano element, has emerged in recent decades and electrospinning, the most versatile technique for nanofiber production, has increasing attention from many researchers working on diverse fields.
Combining properties from two different materials into one fiber using core-sheath structure extends the versatility of nanofibers and provides new possibilities to be used for many applications such as protective textiles, biomedical, energy, filtration, reinforcement, etc. Coaxial electrospinning is the most versatile technique to produce core-sheath structured micro/nanofibers due to (a) simple and straightforward process; (b) cost effective setup; (c) one-step fabrication of core-sheath structure; (d) large variety of available materials; (e) large surface to volume ratio; (f) no need for vacuum, high temperature, plasma and sophisticated chemistry; etc.
In this dissertation, results related with various applications such as chemically resistive water/oil repellent membranes and controlled drug release scaffolds for tissue engineering have been demonstrated using the versatile coaxial electrospinning. In addition, other interesting results with single nozzle electrospinning are presented for microfluidic immunoassay.
Superhydrophobicity is one of most interesting properties in industry and academia during last decade. We have successfully produced Teflon coated polymer fibers by coaxial electrospinning, which gives extreme superhydrophobic and oleophobic properties. Combining the low surface tension of fibers and the high surface roughness of electrospun non-woven fiber mat provides extreme water repellency in static and dynamic conditions. It also provides an excellent chemical resistance for harsh chemical vapor owing to the Teflon sheath. These coaxial fibers preserve the core material properties as demonstrated with mechanical tensile tests. The fact that a normally non-electrospinnable material such as Teflon AF has been successfully electrospun when combined with an electrospinnable core material indicates the potential of coaxial electrospinning to provide a new degree of freedom in terms of material combinations for many applications.
Core-sheath structured fibers of poly(ε-caprolactone) (PCL) core and gelatin sheath have also been demonstrated using coaxial electrospinning, mimicking natural extracellular matrix (ECM) structure for tissue engineered scaffold. Gelatin sheath provides excellent biocompatibility promoting cell attachment and proliferation, while the synthetic biodegradable polymer core (PCL) provides excellent mechanical strength for scaffold to be handled with no damage. When water-soluble functional drug/dye is loaded in the core, programmable drug/dye release with no initial burst problem has been accomplished.
For microfluidic immunoassay application, the “fold-and-press” electrospun PCL membranes provide excellent immunoassay performance with fast processing time. Initial thin PCL electrospun membrane was first immunoassayed taking advantage of the porous membrane structure. Multiple fold-and-press steps densify immunoassayed electrospun PCL fiber mat, leading to significant fluorescence signal amplification > 120×. Fold-and-pressed electrospun PCL fiber mat shows lower limit of detection (LOD), larger linear detection range and faster processing time than conventional nitrocellulose membranes.
Some preliminary results related to nanoparticle incorporation have also been presented. Functional nanoparticle (NP) embedded fibers provide great potential for integration of various novel functions into one fiber. TiO2 nanoparticle incorporated superhydrophobic fiber mat and Mg(OH)2 nanoparticle embedded nylon6 fiber mat have been successfully produced. Preliminary results show very uniform distribution of TiO2 nanoparticles within the Teflon sheath layer, and fire-retardant behavior of Mg(OH)2 NP embedded fibers.