Melt electrospinning

A minimum temperature is needed to ensure a molten polymer, all the way to the tip of the spinneret. Spinnerets have a relatively short length, compared to solution electrospinning.

The most significant parameter for controlling the fiber diameter is the flow rate of the polymer to the spinneret - in general, the higher the flow rate, the larger the fiber diameter. While reported flow rates are low, all of the fluid electrospun is collected, unlike solution electrospinning where a great part of the solvent is evaporated.

The molecular weight is important as to whether the polymer can be melt electrospun. For linear homogeneous polymers, a low molecular weight (below 30,000g/mol) can result in broken and poor quality fibers.[7] For high molecular weights (above 100,000 g/mol), the polymer can be very difficult to flow through the spinneret. Many melt electrospun fibers reported use molecular weights between 40,000 and 80,000 g/mol [4] or are blends of low and high molecular weight polymers.[8]

Modifying the voltage does not greatly effect the resulting fiber diameter, however it has been reported that an optimum voltage is needed to make high quality and consistent fibers. Voltages from as low as 0.7kV up to 60kV have been used to melt electrospin.[9][10]

Melt electrospinning is used to process biomedical materials for tissue engineering research. Volatile solvents are often toxic so avoiding solvents has benefits in this field. Melt electrospun fibers were used as part of a "bimodal tissue scaffold", where both micron-scale and nano-scale fibers were deposited simultaneously.[13] Scaffolds made via melt electrospinning can be fully penetrated with cells, which in turn produce extracellular matrix within the scaffold.[17]

Melt electrospinning is also capable to formulate drug-loaded fibers for drug delivery. It is a promising new formulation technique in the field of pharmaceutical technology to prepare amorphous solid dispersions or solid solutions with enhanced or controlled drug dissolution because it can combine the advantages of melt extrusion (e.g. solvent-free, effective amorphization, continuous process) and solvent-based electrospinning (increased surface area).[18][19][20]

The electrified molten jet created via melt electrospinning has a more predictable path, and polymer fibers can be deposited accurately onto the collector. When the collector is moved at sufficient speed (referred to as the critical translation speed), straight melt electrospun fibers can be deposited in a layer upon layer approach. This enables for the fabrication of complex, well-ordered structures.[4] In this respect melt electrospinning writing (MEW) can be considered a class of 3D printing. Melt electrospinning writing has been performed using either a translating flat surface [4] or a rotating cylinder/mandrel.[11] Most polymers that can be melt-electrospun can also be written assuming the parameters can be tuned in such a way as to produce a stable jet. Piezoelectric polymers such as polyvinylidene difluoride (PVDF) have also been shown to be processable via MEW, opening up potential applications in 3d printed sensors, soft robotics, and further applications in biofabrication.[21]