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Biomaterials

Wicked membranes mimic ultrastretchable spider silk

30 Apr 2018 Anna Demming
Wicked membrane under biaxial compression
Wicked membrane under biaxial compression. Courtesy of the researchers

Take a centimetre of silk spun by an ecribellate spider, stretch it to metres and it won’t rupture, thanks to reserves of excess fibre packed into droplets around the thread. The strategy is replicated in other biological systems such as macrophage cells, which can stretch to five times their surface area to engulf large microbes without rupturing. Now researchers in France have spun synthetic membranes with similar reserves of excess material stored in a venous network so that it stays flat over small areas while drawing on the reserves of material to allow ultrastretchable extensions when pulled. The researchers also show how the reservoir structure allows them to add to the functionality of these stretchable membranes.

A number of studies have sought to replicate some of the extraordinary mechanical properties of biomaterials. Arnaud Antkowiak and colleagues at Sorbonne Université, École Normale Supérieure and Saint-Gobain electrospun a fabric of poly(vinylidene fluoride-co-hexafluoropropylene) with fibres around 300 nm thick. They then infused it with a wetting liquid to form the network of veins made up of ruffles of membrane that provide the excess material for ultrastretchable behaviour. Testing the membrane stretched in planar, cylindrical and spherical geometries, the membrane’s behaviour was similar to a soap film and did not rupture.

“The peculiar behaviour of our wicked membrane stems from its compound nature,” explain the researchers in their report. “Capillarity-induced folds allow it to undergo ample shape changes while remaining taut, while its solid underlying matrix provides mechanical robustness.”

Ultrastretchable and some

The researchers also show that the mechanism behind the stretchable characteristics can be put to use to adjust the chemical functionality of structures, by comparing the wettability of a bare zircon bead with one covered in either a hydrophilic or hydrophobic membrane. They also fix 100 nm gold wires to the membrane surface and demonstrate an elementary electronic circuit that can power an LED while being stretched by a factor of eight.

The work exploits one of the many fascinating features of spider silk in a synthetic product. Antkowiak and colleagues suggest that the material may find use in stretchable electronics, flexible batteries, smart textiles, biomedical devices, tissue engineering, and soft robotics applications.

Full details are reported in Science 10.1126/science.aaq0677 .

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