Kirigami-inspired shoe coating for better surface grip

Inspired by the Japanese papercutting technique, Kirigami, researchers from Massachusetts Institute of Technology (MIT), USA, have created a coating for shoe soles to improve grip on potentially dangerous surfaces such as icy pavements.

The friction generated is said to be 20-35% better than on regular soles.

To achieve this, patterns are cut into plastic or metal sheets. These lie  flat on the shoe sole when the wearer is stood still, but then reveal spikes when walking. 

‘The novelty of this type of surface is that we have a shape transition from a 2D flat surface to a 3D geometry with needles that come out. You can use those elements to control friction, because the sharp needles can pop in and out based on the stretch that you apply,’ says Sahab Babaee, Research Scientist at MIT. 

Several patterns, designs, shapes of the spikes – including squares, triangles and curves – as well as different sizes have been tested for stiffness and how the spikes pop out when the material is stretched. 

Friction tests have also been carried out on a variety of surfaces including ice, wood and vinyl flooring – the team reports that the concave curves design has the best results. The coating has also been tested with human volunteers on a selection of footwear such as winter boots and trainers. The researchers explain that although their initial goal is to improve grip on icy surfaces, they expect the coating to work in other environments too, such as wet or oily ones. 

The team is currently working on the best method of attaching the Kirigami material – whether that be embedded into the shoe sole or as a separate unit that can be added to the shoe as and when needed.