A team of architects and chemists from the University of Cambridge has designed super-stretchy and strong fibers which are almost entirely composed of water, and could be used to make textiles, sensors and other materials. The fibers, which resemble miniature bungee cords as they can absorb large amounts of energy, are sustainable, non-toxic and can be made at room temperature.
This new method not only improves upon earlier methods of making synthetic spider silk, since it does not require high energy procedures or extensive use of harmful solvents, but it could substantially improve methods of making synthetic fibres of all kinds, since other types of synthetic fibers also rely on high-energy, toxic methods. The results are reported in the journal Proceedings of the National Academy of Sciences.
Spider silk is one of nature’s strongest materials, and scientists have been attempting to mimic its properties for a range of applications, with varying degrees of success. “We have yet to fully recreate the elegance with which spiders spin silk,” said co-author Dr Darshil Shah from Cambridge’s Department of Architecture.
The fibers designed by the Cambridge team are “spun” from a soupy material called a hydro-gel, which is 98% water. The remaining 2% of the hydro-gel is made of silica and cellulose, both naturally available materials, held together in a network by barrel-shaped molecular “handcuffs” known as cucurbiturils. The chemical interactions between the different components enable long fibers to be pulled from the gel.
The fibers are pulled from the hydro-gel, forming long, extremely thin threads – a few millionths of a meter in diameter. After roughly 30 seconds, the water evaporates, leaving a fiber which is both strong and stretchy.
“Although our fibers are not as strong as the strongest spider silks, they can support stresses in the range of 100 to 150 megapascals, which is similar to other synthetic and natural silks,” said Shah. “However, our fibers are non-toxic and far less energy-intensive to make.”
The fibers are capable of self-assembly at room temperature, and are held together by supra-molecular host-guest chemistry, which relies on forces other than covalent bonds, where atoms share electrons.
“When you look at these fibers, you can see a range of different forces holding them together at different scales,” said Yuchao Wu, a PhD student in Cambridge’s Department of Chemistry, and the paper’s lead author. “It’s like a hierarchy that results in a complex combination of properties.”
The strength of the fibers exceeds that of other synthetic fibers, such as cellulose-based viscose and artificial silks, as well as natural fibers such as human or animal hair.
In addition to its strength, the fibers also show very high damping capacity, meaning that they can absorb large amounts of energy, similar to a bungee cord. There are very few synthetic fibers which have this capacity, but high damping is one of the special characteristics of spider silk. The researchers found that the damping capacity in some cases even exceeded that of natural silks.
“We think that this method of making fibers could be a sustainable alternative to current manufacturing methods,” said Shah. The researchers plan to explore the chemistry of the fibers further, including making yarns and braided fibers.
This research is the result of a collaboration between the Melville Laboratory for Polymer Synthesis in the Department of Chemistry, led by Professor Oren Scherman; and the Centre for Natural Material Innovation in the Department of Architecture, led by Dr Michael Ramage. The two groups have a mutual interest in natural and nature-inspired materials, processes and their applications across different scales and disciplines.
The research is supported by the UK Engineering and Physical Sciences Research Council (EPSRC) and the Leverhulme Trust.
William Waterway on 10 Jul 2017
Source:Cambridge University News
Yuchao Wu et al. ‘Bioinspired supramolecular fibers drawn from a multiphase self-assembled hydrogel.’ Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1705380114