Self-folding straw

image: ANU
25 June 2016

Published in Science Advances: Scientists from the Australian National University have developed a new material that folds itself into a straw-like tube when it comes into contact with a drop of water. The liquid can then move through the tube for up to 15 centimetres.

For the first time the surface tension to fold materials into origami shapes has been used to create tubes of several centimetres.

It has the capacity to rapidly self-assemble into complex shapes, such as bent, curved and splitting channels, and it is compatible with living tissues. This could be used to create cheap fluid distribution systems with potential applications including medical sample analysis, biological sensors of infectious diseases, or micro-robotics.

According to the researchers, who were led by ANU's Associate Professor Antonio Tricoli, the manufacturing process is cheap and non-toxic, and will scale well to industrial levels.

The material is made of two thin layers of nanofibres sandwiched together. The top functional layer, made of polycaprolactone nanofibres, is the water-responsive energy-dense component (superhydrophilic), which draws the material up around the water droplet.

The bottom layer is made of microfibres of polyvinylchloride (PVC) which is strongly water repellent (superhydrophobic) and prevents the water from escaping once the material has rolled into a tube.

While the material rolls up with water, it unrolls again in the presence of ethanol, providing an on/off element of control that could be useful in biological sensors and actuators.

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