3D printed cycling helmet contracts for superior protection

Wearing a cycling helmet has been shown to dramatically reduce the risk of head injuries in bike accidents, with one notable study finding a 60% reduction in serious head injuries. This figure alone is enough to convince anyone of the importance of wearing a helmet, but no one would deny that there is room for improvement in helmet design to get that rate even higher. On that front, an international research team from the University of Gothenburg in Sweden and University of Isfahan in Iran is developing a cycling helmet optimized for shock absorption thanks to a 3D printed geometry.

The 3D printed helmet increases shock absorption through its design, which integrates what is known as an auxetic metastructure. This geometric metastructure, known as re-entrant honeycomb, is engineered to contract bilaterally on impact, which translates to less shock reaching the cyclist’s head. This is a more effective approach than traditional foam helmet liners, which compress upon impact to dissipate shock.

“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,” explained Mohsen Mirkhalaf, Associate Professor in the mechanics and physics of materials at the University of Gothenburg. “We used a specific design optimization method to identify the best possible geometric configuration to minimize crash forces. The geometry of the material structure is a key factor.”

The auxetic metastructures were created using digital design and underwent computer simulations and optimization to enhance performance. This geometry was then iterated physically using FDM 3D printing. The 3D printed helmet liner was made from TPU, a polymer known for its hyperelastic properties, and was encased in a 3D printed PETG shell.

The 3D printed helmet was then subject to controlled impact scenarios, such as drop tests, and results were compared to existing safety standards for cycling helmets. According to this comparison, the helmet with the auxetic metastructure “has the potential to enhance energy absorption and reduce the risk of head injuries”.

“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,” added Mirkhalaf, whose research paper was recently published in the International Journal of Solids and Structures.

Beyond its superior impact absorption, the 3D printed geometry also has other benefits, including a more lightweight structure, which will be more comfortable for cyclists. While not specifically cited as a benefit by the research team, we can also imagine that superior ventilation would also be a bonus, as it has been with other 3D printed foam-replacement applications.

On top of that, there is the potential to customize these cycling helmets, which could improve protection even more and enhance comfort. “With further development, this technology could lead to a new generation of bicycle helmets that are safer, more comfortable and more customizable,” he added. “Although 3D printing technology currently is more expensive than mass-produced foam liners, costs are expected to fall as the technology becomes more widely used. In the future, it may even be possible to have personalized helmets printed on demand, ensuring that each rider receives the best possible protection.”

Helmets for various sports have been a growing application for 3D printing in recent years. For example, a number of American football helmet manufacturers are now integrated 3D printed lattices to improve player protection. In cycling as well, there have been a handful of 3D printed helmets, including the KAV Portola helmet made from a custom carbon-fiber-reinforced nylon material, which was named by Time Magazine as one of the “best inventions of 2022”.