Heat generating electrospun fibers

Electrospun fibers with the ability to generate heat either by passing of electrical currents or under a magnetic field may give rise to some interesting applications. High surface area of the nanofibers allows rapid heat transfer to the immediate environment with low heat retention. Such membrane is also flexible and is transparent if the nanofiber layer is sufficiently thin.

In cancer treatment, one approach is to use hyperthermia where localised heat is applied to the tumor as tumor cells are more sensitive to heat compared to normal tissue cells. Electrospun fibers may be embedded with magnetic particles for heat activation using an alternating magnetic field. Huang et al (2012) loaded polystyrene (PS) solution with iron oxide particles (IOP) before electrospinning to form a nanofibrous membrane. Up to 20wt% IOP may be added to the PS nanofiber without any apparent ill effect on the electrospinning process and fiber morphology. 282 mL of this composite fiber was able to heat 1 mL of water from 23 °C to 83 ° C within 3 minutes under an alternating magnetic field. Ovarian cancer cells attached to the membrane were killed when the membrane was heated to 45&dec;C for 10 minutes.

An interesting potential application of electrospun fibers with loaded magnetic particles is in material bonding. Using an electrospun low melting point polymer containing the magnetic nanoparticles, heat can be generated using alternating magnetic field which causes the fiber to melt. If this fiber is sandwiched between two layers to be bonded, heat generation is localised to the fiber under the magnetic field causing it to melt and bond the materials. Zhong et al (2015) demonstrated this using polycaprolactone (PCL) loaded with Fe₃O₂ nanoparticles. With the heat generated by the magnetic field, the composite fiber melted and the neat PCL nanofibers more than 0.5 mm away was unaffected.

Heat generation by nanofibrous membrane may also be used to activate photochromic dye. Busuioc et al (2016) used electrospinning to produce a thin layer poly(methyl methacrylate) (PMMA) nanofibers membrane such that it exhibits a high level of transparency. Note that the thinner the layer, the greater the transparency. Sputtering was used to coat a layer of silver and gold on its surface for electrical conduction. Thermal treatment was used to melt the PMMA template such that the resultant metallic shell adheres to the base substrate. The study showed that the thinner the fibrous membrane, the greater its resistivity and the electrical energy is converted to heat. Thermochromic ink was painted over the membrane using a small brush. When a voltage is applied, the membrane heats up and the thermochromic ink changes color accordingly.

Images of gold- and silver-covered polymer fiber networks attached to different substrates; these images show the temperature transition of the thermochromic ink for (a) gold on fabric, (b) gold on paper, (c) silver on fabric, and (d) silver on paper. [Busuioc et al Scientific Reports 2016; 6: 34584. This work is licensed under a Creative Commons Attribution 4.0 International.]