A study published recently in the journal Nanotechnology sets out to understand the morphology of NFES fibres and establish the criteria for probing their elastic and electric properties.

Right ink for the job

To perform fibre deposition and electrode patterning, a composite solution of carbon nanotubes (as the conducting filler, up to 20% loading) and polyethylene oxide (a good matrix material for electrospinning), was fine-tuned for its viscosity and solvent evaporation characteristics. The long, thin carbon nanotubes provide good electrical percolation throughout each composite fibre. A fibre conductivity of around 5 S/m was obtained, which is superior to many conducting polymer fibres fabricated by far-field electrospinning.

Direct deposition of electrodes on a rough PDMS surface significantly extended the reversible fibre extension from 2% (the intrinsic elastic limit of a free-standing fibre) to an effective 20%, for which no electrical degradation is observed. There are two key reasons for the improvement. The NFES composite fibres are deposited on the target substrate in the semi-liquid state, which preserves the intrinsic mechanical compliance of individual fibres; furthermore, it allows the fibre array to follow the topography of the substrate surface.

Flexible bio-interface

Room temperature deposition and patterning of circuitry may circumnavigate the need for conventional energy- and time-intensive fabrication of conducting materials. It is also a requirement if components need to interface with biological tissues.

A unique advantage of the approach is that the mild processing conditions permit direct writing of conducting elements on soft bio-compatible substrates, which are mostly gel-like in nature.

The technique can be used to form precise conducting patterns with line widths ranging from sub-micron to tens of microns – feature sizes that are well suited to common biological cells.

The new electrode deposition method also provides a way to incorporate less-deformable polymeric components in flexible electronics, through integrated design of circuits on an insulating, elastically stretchable substrate.

More information can be found in the journal Nanotechnology.