Shape-transferred bicycle helmets can redefine the safety of cyclists

In a significant advance in the safety of cycling, researchers have developed a bicycle helmet that contracts when impacted to better absorb the crash force – possibly reducing the severity of head injuries during an accident.

The innovative helmet was created through a collaboration between the University of Gothenburg in Sweden and the University of Isfahan in Iran, and it utilizes a special geometric pattern called the “auxiliary metastructure” in its astonishing water-absorbing lining, which does not act like traditional helmet materials.

“When exposed to energy in impact, lining material contracts, which can improve the absorption of the impact energy, which means that in an accident, the risk of head injury for cyclists is lower,” explains Mohsen Mirkhalaf, associate professor of Materials Mechanics and Physics at the University of Gothenburg.

Traditional bicycle helmets often use extended polystyrene (EPS) foam linings that limit energy absorption and fit. The new design replaces it with a thermoplastic polyurethane (TPU) liner with a well-designed geometry and a thin polyethylene terephthalate (PETG) housing.

What makes this helmet unique is how the material reacts to force. Unlike conventional materials that expand upon compression, the auxiliary structure shrinks from all directions when affected, effectively dispersing energy throughout the material rather than transferring it to the wearer’s head.

The results are promising. In standardized testing for Flat and Kerbstone Anvils (simulating different types of collision scenarios), the prototype helmets performed significantly better than traditional designs.

“We use specific design optimization methods to identify the optimal geometric configuration to minimize impact forces. The geometry of the material structure is a key factor,” Mirkhalaf said.

The protective layer of the helmet is made using a 3D printer, allowing for precise implementation of complex geometries, which are difficult to achieve in traditional manufacturing methods. The researchers chose thermoelastic polymer materials that can undergo significant deformation and restore their original shape, which is crucial to absorbing multiple effects.

In addition to improving safety, the technology offers other benefits. The study, published in the International Journal of Solids and Structures, notes that auxiliary linings can be customized for single head shapes, which is especially valuable for professional athletes or those struggling to find a comfortable helmet.

“The auxiliary metastructure that extends horizontally when stretched has been around for nearly 40 years. However, due to advances in 3D printing technology, the development of different cross-structures has exploded.”

Although the current 3D printing costs outweigh the cost of mass-producing foam linings, researchers expect that this difference will decrease as technology becomes more popular. The potential of personalized protection can justify the additional costs of many cyclists, especially those who are frequent or competitive.

It means more than just riding a bicycle. The study represents a step towards smarter protective devices that can be applied in a variety of impact protection schemes, from other sports to industrial security.

“With further development, this technology could lead to a new generation of bicycle helmets safer, more comfortable and more customizable,” the researchers noted. “In the future, it’s even possible to print personalized helmets on demand to ensure that every rider gets the best protection.”

For about one-third of cyclists who report helmet discomfort as a barrier to consistent use, the possibility of providing a lighter, more comfortable and custom-made helmet may be an advancement that ultimately convinces them to their heads every time they ride.