Dynamic kirigami shoe grip designed to reduce risks of slips and falls

August 20, 2020

Losing your balance and falling does not just happen during icy Boston winters. The slip resistance of your shoes can determine how well you walk on different surfaces without losing balance. Shoe grips increase friction by engaging with the walking surface, helping to increase stability. In a recently published study, investigators from Brigham and Women's Hospital and the Massachusetts Institute of Technology (MIT) presented a bioinspired assistive shoe grip based on kirigami, the Japanese art of paper cutting. Kirigami can be used to create highly flexible surfaces that buckle from a flat sheet to a three-dimensional textured surface. The new kirigami-based shoe sole is intended to reduce the risks of slips and falls by adjusting as a person steps, increasing friction with pop-up spikes as necessary. In Nature Biomedical Engineering, the team reports the results of friction testing on a range of surfaces, including ice, finding that the kirigami shoe soles increased friction with the ground to get a better grip on slippery surfaces.

"What we developed is a dynamic shoe sole that can give you grip when you need it, which is when you are actually walking and moving," said co-corresponding author Giovanni Traverso, MB, BChir, PhD, a gastroenterologist and biomedical engineer in the Division of Gastroenterology at the Brigham and MIT. "The key is that it is dynamic and has the capacity to tune friction as you take a step. Current solutions like cleats have spikes that are always present, so a dynamic shoe grip that could adjust itself with movement would be a more ideal way to mitigate falling."

To learn more about dynamic ways of modulating friction, the researchers looked to nature for inspiration, examining how animals have scales or claws that selectively increase friction in certain situations. They recognized that by applying change in the shape of the sole, they could control the popping up of the spikes and modulate friction with the surface due to the flexible, buckling nature of kirigami. To identify the set of shapes that would best accomplish this, the team modeled each shape's performance on how it popped up under certain strains.

The buckling-induced kirigami patches were constructed using steel and attached to shoe soles, enabling the dynamic tuning of the walking surface's frictional properties. Traverso and colleagues tested the soles by creating flat or popped-up versions and measured the friction on different surfaces including ice, vinyl and hardwood to identify the optimal conformation. They initially tested the pop-up designs in the form of a sheet that was dragged across different surfaces. Then the team tested the designs on three human subjects by placing the sheets on shoe soles and having the subjects walk on a block of ice that was placed on a surface that measured the amount of force. By having the subjects walk on the ice both with and without the soles, the team could get a sense of the mechanics behind the design.

The results showed that the kirigami shoe grips were able to enhance the frictional properties between the soles and the walking surface, mitigating slips and falls. The team reports that use of the kirigami shoe grip could achieve a greater friction than that observed with standard winter boots by two- to three-fold. Although the initial designs were constructed using stainless steel for proof of concept, the researchers are now applying the concept to other materials that are more commonly used today. They are also focusing on creating prototypes where the grip is already built into the shoe as opposed to being added on.

"We are now working towards applying and incorporating the grips into different shoes," said Traverso. "The grips could be useful in the sporting shoe industry, in standard shoes used in day-to-day settings, and in occupational health situations where there might be an increased risk of slippage."
Funding for this work was provided by a start-up grant from the Department of Mechanical Engineering, MIT, to Giovanni Traverso. Katia Bertoldi received support from the National Science Foundation (DMR-1420570, EFRI C3 SoRo 1830896). Ahmad Rafsanjani received support from a grant from the Swiss National Science Foundation (P300P2-164648). Two co-authors of the paper are inventors on a patent application (patent no. US2019/0232598A1) describing buckling-induced kirigami. Other co-authors, including Traverso are co-inventors on a provisional patent application (no. 62913419) for the technology described.

Complete details of all relationships for profit and not-for-profit for Traverso can be found at the following link: https://www.dropbox.com/sh/szi7vnr4a2ajb56/AABs5N5i0q9AfT1IqIJAE-T5a?dl=0.

Paper cited: Babaee, S. et al. "Bioinspired kirigami metasurfaces as assistive shoe grips" Nat Biomed Eng DOI: https://doi.org/10.1038/s41551-020-0564-3

Brigham and Women's Hospital

Related Walking Articles from Brightsurf:

Why walking to work may be better for you than a casual stroll
Walking with a purpose -- especially walking to get to work -- makes people walk faster and consider themselves to be healthier, a new study has found.

Spinal cord gives bio-bots walking rhythm
Miniature biological robots are making greater strides than ever, thanks to the spinal cord directing their steps.

These feet were made for walking
Many of us take our feet for granted, but they have a challenging job in the biomechanics department.

Walking sharks discovered in the tropics
Four new species of tropical sharks that use their fins to walk are causing a stir in waters off northern Australia and New Guinea.

Micro implants could restore standing and walking
Researchers at the University of Alberta are focused on restoring lower-body function after severe spinal injuries using a tiny spinal implant.

Walking changes vision
When people walk around, they process visual information differently than at rest: the peripheral visual field shows enhanced processing.

Virtual walking system for re-experiencing the journey of another person
Virtual-reality researchers have developed a virtual-walking system that records a person's walking and re-plays it with vision and foot vibrations.

A large study indicates how cities can promote walking for travel
Coinciding with the European Mobility Week, a study performed in seven European cities focuses on walking for travel, a strategy to increase physical activity in cities.

Robotic cane shown to improve stability in walking
By adding electronics and computation technology to a simple cane that has been around since ancient times, Columbia Engineering researchers have transformed it into a 21st century robotic device that can provide light-touch assistance in walking to the aged and others with impaired mobility.

Water walking -- The new mode of rock skipping
Utah State University's Splash Lab not only reveals the physics of how elastic spheres interact with water, but it also lays the foundation for the future design of water-walking drones.

Read More: Walking News and Walking Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.