Wee-Eong Teo

A review on electrospinning design and nanofibre assemblies.

Although there are many methods of fabricating nanofibres, electrospinning is perhaps the most versatile process. Materials such as polymer, composites, ceramic and metal nanofibres have been fabricated using electrospinning directly or through post-spinning processes. However, what makes electrospinning different from other nanofibre fabrication processes is its ability to form various fibre assemblies. This will certainly enhance the performance of products made from nanofibres and allow application specific modifications. It is therefore vital for us to understand the various parameters and processes that allow us to fabricate the desired fibre assemblies. Fibre assemblies that can be fabricated include nonwoven fibre mesh, aligned fibre mesh, patterned fibre mesh, random three-dimensional structures and sub-micron spring and convoluted fibres. Nevertheless, more studies are required to understand and precisely control the actual mechanics in the formation of various electrospun fibrous assemblies.

Electrospun Nanofibers: Solving Global Issues

Energy and environment will head the list of top global issues facing society for the next 50 years. Nanotechnology is responding to these challenges by designing and fabricating functional nanofibers optimized for energy and environmental applications. The route toward these nano-objects is based primarily on electrospinning: a highly versatile method that allows the fabrication of continuous fibers with diameters down to a few nanometers. The mechanism responsible for the fiber formation mainly includes the Taylor Cone theory and flight-instability theory, which can be predicted theoretically and controlled experimentally. Moreover, the electrospinning has been applied to natural polymers, synthetic polymers, ceramics, and carbon. Fibers with complex architectures, such as ribbon fiber, porous fiber, core-shell fiber, or hollow fiber, can be produced by special electrospinning methods. It is also possible to produce nanofibrous membranes with designed aggregate structure including alignment, patterning, and two-dimensional nanonets. Finally, the brief analysis of nanofibers used for advanced energy and environmental applications in the past decade indicates that their impact has been realized well and is encouraging, and will continually represent a key technology to ensure sustainable energy and preserve our environment for the future.

Technological advances in electrospinning of nanofibers

Progress in the electrospinning techniques has brought new methods for the production and construction of various nanofibrous assemblies. The parameters affecting electrospinning include electrical charges on the emerging jet, charge density and removal, as well as effects of external perturbations. The solvent and the method of fiber collection also affect the construction of the final nanofibrous architecture. Various techniques of yarn spinning using solid and liquid surfaces as well as surface-free collection are described and compared in this review. Recent advances allow production of 3D nanofibrous scaffolds with a desired microstructure. In the area of tissue regeneration and bioengineering, 3D scaffolds should bring nanofibrous technology closer to clinical applications. There is sufficient understanding of the electrospinning process and experimental results to suggest that precision electrospinning is a real possibility.

Electrospun fibre bundle made of aligned nanofibres over two fixed points

Despite recent advances in electrospinning, creating highly ordered structure through the use of electrospun fibres is not possible. This is due to the chaotic motion of the electrospinning jet which means that the deposition location of the fibres covers a few centimetres radius. As a result, applications for electrospun fibres are restricted to applications where precise positioning is not required. However, through the use of steel blades to control the electric field, it is now possible to create a fibre bundle made of highly aligned nanofibres where the ends of the fibre bundle are fixed during electrospinning. The creation of highly ordered structures made of electrospun fibre bundles is now possible since the fibre bundle is robust enough to be handled, and it is also easy to transfer the fibre bundle onto a substrate. More importantly, with the two ends of the fibre bundle known, automating the transfer of the fibre bundle onto a substrate is a possibility.

Porous tubular structures with controlled fibre orientation using a modified electrospinning method

Electrospinning offers an avenue to produce small diameter tubes made out of nanofibres. However, to date, most tubes from electrospun fibres have been either random fibres or from sheets that were rolled into tubes. Although there have been suggestions of getting tubes made of circumferentially aligned fibres, this is the first time that a method used to create a tube made of diagonally aligned electrospun fibres has been described. This tube was formed by depositing fibres on a rotating tube during electrospinning to give a resultant tube with uniform thickness and superior all round mechanical strength without any line of weakness. A knife-edged auxiliary electrode was given a charge that was opposite to that of the charge given to the needle to create an electrostatic field that encouraged fibre alignment on a rotating tube collector. A tubular structure made of nanofibres aligned in a diagonal direction was produced through electrospinning.