Metamaterials Make for a Safer Bicycle Helmet
Metamaterials Make for a Safer Bicycle Helmet
Researchers at the University of Gothenburg have developed an improved bicycle helmet.
Safety helmets with high energy absorption are crucial for protecting bike riders from head injuries, and are a significant priority for the sports industry and other commercial/industrial markets. However, conventional foam liners have limitations regarding impact absorption and fit.
To improve helmet safety, researchers at the University of Gothenburg and the University of Isfahan in Iran have created a bicycle helmet manufactured from shock-absorbing materials called auxetic metastructures. These engineered materials expand laterally when stretched and contract when compressed, enhancing properties such as stiffness, energy absorption, and fracture resistance.
Mohsen Mirkhalaf, associate professor in the mechanics and physics of materials at the University of Gothenburg, and his team 3D-printed this material into a specific geometric pattern for the liner, which contracts and absorbs more energy upon impact.
This project originated from Mirkhalaf’s desire to translate advanced materials research into real-world impact. “The ‘aha’ moment came when we started exploring auxetic metamaterials, which have a negative Poisson’s ratio,” he explained. “These materials expand laterally when stretched and offer unusual deformation behavior that can be harnessed to absorb impact more efficiently. The idea of using this in helmets—a product where safety and shock absorption are paramount—was a natural fit.”
The research team tested an innovative design for a mountain bike helmet, featuring an auxetic metastructure made from thermoplastic polyurethane (TPU) for the liner and a thin layer of polyethylene terephthalate glycol (PETG) for the outer shell. A significant challenge was optimizing the material geometry to achieve high energy absorption.
Check This Story Out: Playing it Cool
“We needed to create a structure that could not only distribute forces effectively, but also maintain structural integrity after impacts,” Mirkhalaf said. “Another challenge was prototyping the helmet liner as a one-piece print, and testing in ways that closely mimicked real-world accident conditions.”
A graph demonstrating how the auxetic structure absorbs impacts. Photo: Mohsen Mirkhalaf/University of Gothenburg
The team used SolidWorks software to design the structure of the metamaterial, while impact testing followed per the EN 1078 standard in Abaqus software. A Taguchi design of experiment (DOE) helped uncover the optimal cell geometry of the metastructure and minimize the deceleration during impact tests. This allowed the researchers to identify the optimal geometric configuration to reduce crash forces. A fused deposition modeling (FDM) 3D printer manufactured the entire liner in one print.
After subjecting the manufactured helmet to several different impact test scenarios, a comparison of experimental and finite element results revealed the numerical model’s accuracy. Finite element modeling utilized input data from the compression tests on the 3D-printed TPU specimens.
“Finite element simulations provide valuable information about the structural behavior of the helmet, allowing manufacturers to make informed decisions during the design and manufacturing process,” Mirkhalaf said. “It helps optimize the design, improve performance, and ensure the helmet meets safety standards and requirements and avoids repeating time-consuming and expensive experiments multiple times.”
You May Want To Read: Helmets That Absorb and Respond to Collisions
The shock-absorbing liner was 3D-printed from a flexible, durable polymer. Photo: Mohammad Hossein Zamani
A key surprise for the team was how effectively the auxetic structures dissipated energy compared to traditional helmet materials.
“We expected improvements, but the degree of enhancement in terms of reducing peak acceleration during impact tests exceeded our initial estimates,” Mirkhalaf stated. “Another pleasant surprise was how lightweight the structure could be without compromising on safety—a crucial factor for user comfort.”
The prototype liner shows great promise for enhancing energy absorption and reducing the risk of head injuries.
“Our findings from testing helmets with auxetic metastructure liners can provide valuable insights for helmet manufacturers, researchers, and regulatory bodies,” Mirkhalaf said. “These insights can be used to improve helmet designs and refine manufacturing processes.”
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Mirkhalaf is now looking at how to integrate this material concept into commercially viable helmet designs and collaborating with industrial partners. The team also sees potential in other protective gear—for example, sports, motorcycling, and elder care—where shock absorption and comfort are crucial.
“Further research will focus on refining the design for specific use cases, scaling up manufacturing techniques, and exploring smart material integrations for real-time performance feedback,” Mirkhalaf said.
Possible applications for making innovative products in other fields include automotive crash protection systems, wearable protection paddings, and aerospace needs where weight-to-performance ratios are critical.
Mark Crawford is a technology writer in Corrales, N.M.
To improve helmet safety, researchers at the University of Gothenburg and the University of Isfahan in Iran have created a bicycle helmet manufactured from shock-absorbing materials called auxetic metastructures. These engineered materials expand laterally when stretched and contract when compressed, enhancing properties such as stiffness, energy absorption, and fracture resistance.
Mohsen Mirkhalaf, associate professor in the mechanics and physics of materials at the University of Gothenburg, and his team 3D-printed this material into a specific geometric pattern for the liner, which contracts and absorbs more energy upon impact.
Materials are key
This project originated from Mirkhalaf’s desire to translate advanced materials research into real-world impact. “The ‘aha’ moment came when we started exploring auxetic metamaterials, which have a negative Poisson’s ratio,” he explained. “These materials expand laterally when stretched and offer unusual deformation behavior that can be harnessed to absorb impact more efficiently. The idea of using this in helmets—a product where safety and shock absorption are paramount—was a natural fit.”
The research team tested an innovative design for a mountain bike helmet, featuring an auxetic metastructure made from thermoplastic polyurethane (TPU) for the liner and a thin layer of polyethylene terephthalate glycol (PETG) for the outer shell. A significant challenge was optimizing the material geometry to achieve high energy absorption.
Check This Story Out: Playing it Cool
“We needed to create a structure that could not only distribute forces effectively, but also maintain structural integrity after impacts,” Mirkhalaf said. “Another challenge was prototyping the helmet liner as a one-piece print, and testing in ways that closely mimicked real-world accident conditions.”
A graph demonstrating how the auxetic structure absorbs impacts. Photo: Mohsen Mirkhalaf/University of Gothenburg
The team used SolidWorks software to design the structure of the metamaterial, while impact testing followed per the EN 1078 standard in Abaqus software. A Taguchi design of experiment (DOE) helped uncover the optimal cell geometry of the metastructure and minimize the deceleration during impact tests. This allowed the researchers to identify the optimal geometric configuration to reduce crash forces. A fused deposition modeling (FDM) 3D printer manufactured the entire liner in one print.
After subjecting the manufactured helmet to several different impact test scenarios, a comparison of experimental and finite element results revealed the numerical model’s accuracy. Finite element modeling utilized input data from the compression tests on the 3D-printed TPU specimens.
“Finite element simulations provide valuable information about the structural behavior of the helmet, allowing manufacturers to make informed decisions during the design and manufacturing process,” Mirkhalaf said. “It helps optimize the design, improve performance, and ensure the helmet meets safety standards and requirements and avoids repeating time-consuming and expensive experiments multiple times.”
You May Want To Read: Helmets That Absorb and Respond to Collisions
The shock-absorbing liner was 3D-printed from a flexible, durable polymer. Photo: Mohammad Hossein Zamani
“We expected improvements, but the degree of enhancement in terms of reducing peak acceleration during impact tests exceeded our initial estimates,” Mirkhalaf stated. “Another pleasant surprise was how lightweight the structure could be without compromising on safety—a crucial factor for user comfort.”
Future steps
The prototype liner shows great promise for enhancing energy absorption and reducing the risk of head injuries.
“Our findings from testing helmets with auxetic metastructure liners can provide valuable insights for helmet manufacturers, researchers, and regulatory bodies,” Mirkhalaf said. “These insights can be used to improve helmet designs and refine manufacturing processes.”
Discover the Benefits of ASME Membership
Mirkhalaf is now looking at how to integrate this material concept into commercially viable helmet designs and collaborating with industrial partners. The team also sees potential in other protective gear—for example, sports, motorcycling, and elder care—where shock absorption and comfort are crucial.
“Further research will focus on refining the design for specific use cases, scaling up manufacturing techniques, and exploring smart material integrations for real-time performance feedback,” Mirkhalaf said.
Possible applications for making innovative products in other fields include automotive crash protection systems, wearable protection paddings, and aerospace needs where weight-to-performance ratios are critical.
Mark Crawford is a technology writer in Corrales, N.M.
Researchers at the University of Gothenburg have developed an improved bicycle helmet.
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