The shock-absorbing layer of a bicycle helmet has a geometric structure that absorbs crash forces better than today’s helmets. Photo: Mohammad Hossein Zamani
The shock-absorbing layer of a bicycle helmet has a geometric structure that absorbs crash forces better than today’s helmets. Photo: Mohammad Hossein Zamani
In a significant advance for cyclist safety, researchers have developed a bicycle helmet that contracts upon impact to better absorb crash forces – potentially reducing the severity of head injuries during accidents.
The innovative helmet, created through a collaboration between the University of Gothenburg in Sweden and the University of Isfahan in Iran, utilizes special geometric patterns called “auxetic metastructures” in its shock-absorbing liner that behave unlike conventional helmet materials.
“When exposed to energy from an impact, the liner material contracts, and this improves the absorption of impact energy, which means lower risks of injuries to a cyclist’s head in an accident,” explains Mohsen Mirkhalaf, Associate Professor in the mechanics and physics of materials at the University of Gothenburg.
Traditional bicycle helmets typically use expanded polystyrene (EPS) foam liners, which have limitations in energy absorption and fit. The new design replaces this with a thermoplastic polyurethane (TPU) liner featuring a carefully engineered geometric structure and a thin polyethylene terephthalate glycol (PETG) outer shell.
What makes this helmet unique is how the material responds to force. Unlike conventional materials that expand when compressed, the auxetic structure contracts from all directions when impacted, effectively dispersing the energy throughout the material rather than transferring it to the wearer’s head.
The results are promising. In standardized testing against both flat and kerbstone anvils – simulating different types of crash scenarios – the prototype helmet performed significantly better than traditional designs.
“We used a specific design optimisation method to identify the best possible geometric configuration to minimise crash forces. The geometry of the material structure is a key factor,” says Mirkhalaf.
The helmet’s protective layer was manufactured using a 3D printer, allowing for precise implementation of the complex geometry that would be difficult to achieve with traditional manufacturing methods. The researchers selected hyperelastic polymer materials that can undergo significant deformation and return to their original shape, critical for absorbing multiple impacts.
Beyond improved safety, the technology offers additional benefits. The study, published in the International Journal of Solids and Structures, notes that the auxetic liner can be customized to individual head shapes – particularly valuable for professional athletes or those who struggle to find comfortable helmets.
“The knowledge of auxetic metastructures that expand laterally when stretched has been around for almost 40 years. However, development of different metastructures has exploded due to the advancements in 3D printing technology,” Mirkhalaf notes.
While current 3D printing costs exceed those of mass-produced foam liners, the researchers anticipate this differential will decrease as the technology becomes more widespread. The potential for personalized protection could justify the additional expense for many cyclists, especially those who ride frequently or competitively.
The implications extend beyond cycling. The research represents a step toward smarter protective equipment that could be applied in various impact-protection scenarios, from other sports to industrial safety.
“With further development, this technology could lead to a new generation of bicycle helmets that are safer, more comfortable and more customisable,” the researchers state. “In the future, it may even be possible to have personalised helmets printed on demand, ensuring that each rider receives the best possible protection.”
For the approximately 1 in 3 cyclists who report helmet discomfort as a barrier to consistent use, the possibility of a lighter, more comfortable, and customized helmet that provides superior protection could be the advancement that finally convinces them to protect their heads on every ride.
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