Spinning webs sustainably

HYDROGEL fibres similar to spider silk have been spun at room temperature, and researchers say it could offer a sustainable low-energy alternative to current manufacturing methods.

Fibre materials impact our lives every day, with common uses including textiles and functional reinforcements in composites. Much research has been undertaken into creating synthetic fibres that mimic spider silk, which is one of nature’s lightest, strongest and most elastic materials.  However, conventional techniques such as wet-, dry-, gel-, and electro-spinning are limited by high energy input, laborious procedures, and intensive use of organic solvents.

 Now, researchers from University of Cambridge, UK, have developed a new technique capable of spinning environmentally-friendly “supramolecular fibres” at room temperature.

Their method uses a supramolecular polymer–colloidal hydrogel (SPCH) made from 98 wt% water. The remaining 2 wt% is composed of functionalised polymer-grafted silica nanoparticles and a semicrystalline hydroxyethyl cellulose derivative held together by barrel-shaped molecular ‘handcuffs’ known as cucurbiturils. When pulled, the fibres undergo self-assembly to form the SPCH, facilitated by host–guest interactions at the molecular level, and nanofibril formation at colloidal-length scale. After roughly 30 seconds, the water evaporates, leaving a ~6 μm-thick fibre which is both strong and stretchy.

The fibres exhibit a unique combination of stiffness and high damping capacity of 60–70%. This latter property means the fibres can absorb very large amounts of energy, and there are few synthetic fibres capable of doing so.

Shah believes that the method could be a sustainable alternative to existing fibre manufacturing methods. He said: “We are currently working on altering the chemistry of the hydrogels to produce, at room temperature, a family of supramolecular fibres with a whole range of tunable properties.”

The group has already had talks with major fibre producers, specifically of regenerated cellulose and Viscose Rayon, to improve their processes, which currently use high temperatures and harmful solvents.

Regarding the next steps to commercialisation, Shah said: “We are also working on processing methods and upscaling strategies; for all conceivable applications, we would need to process them into some form of bundles, yarns or braided materials. For this we are working on a robotic device to extrude multiples fibres through a spinneret and simultaneously twist or braid them into yarns, for example.”

They envisage exploring a range of applications in the fields of technical textiles, sensors, composite reinforcements and biomedicine. Products benefitting from the high energy absorption could range from blast-proof military clothing and helmets for cycling to medical devices for back, spine or neck injury – as the fibres are fully biocompatible.

Concerning their use in sensors, Shah said: “By altering the chemistry and introducing tiny amounts of other materials, we can use these fibres for sensing applications and ‘health monitoring’ which is an important field in engineering to ensure safety, reliability and functionality of a structure.”

Proceedings of the National Academy of Sciences: http://doi.org/b9jm