Morphological evolution of nanofibers during electrospinning

Electrospinning is a very useful technique to produce polymeric nanofibers. It involves fast-drawing a polymer fluid into nanofibers under a strong electric filed, and depositing randomly on an electrode collector to form non-woven nanofiber mat in most cases [1]. The fibre stretching during electrospinning is a fast and incessant process which can be divided into three consecutive stages: jet initiation, whipping instability and fibre deposition. From the initial jet to dry fibres, the fibre stretching takes place in milliseconds, so it has been hardly so far to observe fiber morphology changes by any normal methods, such as high speed photography [2-5]. In this study, we used a facile and practical approach to realize the observation of nanofiber morphology changes during electrospinning. Through a special collection device with coagulation bath, newly electrospun nanofibers can be solidified at different electro spinning distances, and by associating the fiber morphology with the electrospinning distance (d), the morphological evolution of nanofibers can be established. We used polyacrylonitrile (PAN) and polystyrene (PS) as two model polymers to demonstrate this method in present research. From experimental results, we found the massive jet-thinning happens at the initial stage of the process. The formation of uniform PAN nanofibers (7%) and the beads structure changes on beads-on-string PAN nanofibers (5%) have also been successful observed. Using the same method, we also observed PS nanofiber (10%) morphology changes to understand the beads formation 011 nanofibers during electrospinning process, and how the beads was eliminated when ionic surfactant is added into the PS solution for electrospinning.

Electrospinning of nanofibres for construction of vital organ replacements

This paper described the production of a novel biosynthetic material using the manufacturing technique of electro spinning for the construction of scaffold for organ replacement. This electrostatic technique uses an electric field to control the deposition of polymer fibres onto a specific substrate to fabricate fibrous polymer constructs composed of fibre diameters ranging from several microns down to 100 nm or less. Two areas of research, in particular, heart valve leaflets and blood vessel will be discussed. Here, a sandwich structure nanofibre mesh was used to construct materials for leaflets of heart valve and blood vessel. In the case of heart valve leaflet, the randomly oriented polyurethane nanofibres were prepared as the first layer, followed by gelatin-chitosan complex layer. Complex nanofibres were initially used to spin on the PU layer with cross orientation to mimic the fibrosa layer. A gelatin and chitosan complex was then spun onto the other side of PU nanofibre mesh to mimic the ventricularis layer. This particular sandwich structure using the PU layer was designed to simulate the mechanical properties of natural tissue. In addition, this design was aimed to provide good biocompatibility and improved cellular environment to assist in adhesion and proliferation. Smooth muscle cells adhered and flattened out onto the surface of the gelatin-chitosan complex as early as 1 day post seeding. There is great potential for this biosynthetic biocompatible nanofibrous material to be developed for various clinical applications.

Electrospinning of continuous nanofiber bundles and twisted nanofiber yarns

Spinning is a prehistoric technology in which endless filaments, shorter fibers or twisted fibers are put together to produce yarns that serve as key element to assemble multifarious structural designs for diverse functions. Electrospinning has been regarded as the most effective and versatile technology to produce nanofibers with controlled fiber morphology, dimension and functional components from various polymeric materials (Dersch et al., 2007, Frenot and Chronakis, 2003, Schreuder-Gibson et al., 2002). However, most electrospun fibers are produced in the form of randomly-oriented nonwoven fiber mats (Doshi and Reneker, 1995, Madhavamoorthi, 2005). The relatively low mechanical strength and difficulty in tailoring the fibrous structure have restricted their applications. With the rapid development in nanoscience and nanotechnology, yarns composed of nanofibers may uncover new opportunities for development of well-defined three dimensional nano fibrous architectures. This chapter focuses on recent research and advancement in electrospinning of nanofiber bundles and nanofiber yarns. The preparation, morphology, mechanical properties and potential applications of these fibrous materials are discussed in details.

Electrospinning of nanofibres with parallel line surface texture for improvement of nerve cell growth

Nanofibres having a parallel line surface texture were electrospun from cellulose acetate butyrate solutions using a solvent mixture of acetone and N,N'-dimethylacetamide. The formation mechanism of the unusual surface feature was explored and attributed to the formation of voids on the jet surface at the early stage of electrospinning and subsequent elongation and solidification of the voids into a line surface structure. The fast evaporation of a highly volatile solvent, acetone, from the polymer solution was found to play a key role in the formation of surface voids, while the high viscosity of the residual solution after the solvent evaporation ensured the line surface to be maintained after the solidification. Based on this principle, nanofibres having a similar surface texture were also electrospun successfully from other polymers, such as cellulose acetate, polyvinylidene fluoride, poly(methyl methacrylate), polystyrene and poly(vinylidene fluoride-co-hexafluoropropene), either from the same or from different solvent systems. Polarized Fourier transform infrared spectroscopy was used to measure the polymer molecular orientation within nanofibres. Schwann cells were grown on both aligned and randomly oriented nanofibre mats. The parallel line surface texture assisted in the growth of Schwann cells especially at the early stage of cell culture regardless of the fibre orientation. In contrast, the molecular orientation within nanofibres showed little impact on the cell growth.

Ultrafine polystyrene nanofibers prepared by electrospinning

Ultrafine polystyrene (PS) nanofibers were prepared via the simple electrospinning technique. Uniform and smooth PS nanofibers were obtained with adding the organic salt BTEAC into the PS solutions and adjusting the concentration of PS solutions. Without the addition of BTEAC, PS fibers with few beads could be achieved with a PS mass fraction of 20%, and the average diameter of the fibers was 280 nm. The addition of the organic salt BTEAC could lower the critical concentration for the fiber formation and reduce the amount of beads on the fibers. Unltrafine PS fibers without any beads were obtained with a PS mass fraction of 10% and an ionic salt mass fraction of 0.5%. The average diameter of the fiber was successfully reduced to 100 nm. The influence of the salt concentration on the morphology and diameter of the PS fibers was also investigated. The viscosity and surface tension changes were measured with changing the concentration of BTEAC. The results show that the changes were so small that these factors could be ignored. It was suggested that variations of the fiber diameter should be mainly resulted from the changes of conductivity and conformation of the polymer chain as the concentration of BTEAC is varied.