Groundbreaking Liquid Cushioning Technology Transforms Safety Gear

A state-of-the-art nanofoam substance presents enhanced protection and comfort for sports gear, while also offering potential uses in automotive safety systems and wearable medical equipment. This pioneering material transcends the constraints of conventional nanofoam, delivering a flexible and comfortable solution that can endure multiple impacts. This image depicts an artist’s conception of the “liquid” safety cushion.

A major breakthrough in material engineering brings hope for football players, vehicle occupants, and hospital patients.

A significant development in protective gear technology has come following the revelation that football players were inadvertently suffering irreversible brain damage due to repeated head impacts over their professional careers. This discovery sparked a desperate search for improved head protection alternatives. Among these innovations is nanofoam, a material found in football helmets.

Thanks to Baoxing Xu, an associate professor of mechanical and aerospace engineering at the University of Virginia, and his research team, nanofoam has now received a significant upgrade that could transform protective sports gear. The new design combines nanofoam with “non-wetting ionized liquid”, a type of water that blends seamlessly with nanofoam to form a liquid cushion. This adaptable and responsive material could offer better protection for athletes, and holds potential for use in safeguarding car passengers and aiding patients through wearable medical devices.

The team’s research was recently featured in the journal Advanced Materials.

A diagram demonstrating how a liquid nanofoam cushion responds to an impact. Credit: B. Xu.

Refined Nanofoam: Progress and Prospects

Optimal safety calls for protective foam situated between a helmet’s inner and outer layers to withstand not just one but multiple hits, match after match. The material should provide a soft landing spot for the head, yet be robust enough to rebound and prepare for the next hit. It must be resilient without being hard, as hardness also presents a risk to the head. Having a single material meet all these requirements is indeed challenging.

The team built upon their prior work published in the Proceedings of the National Academy of Sciences, which began exploring liquid use in nanofoam. They created a material that accommodates the complicated safety needs of high-contact sports.

“We discovered that creating a liquid nanofoam cushion with ionized water instead of regular water significantly affected the material’s performance,” said Xu. “Incorporating ionized water into the design is a breakthrough as we discovered a unique liquid-ion coordination network that enabled us to create a more advanced material.”

Associate Professor Baoxing Xu in the UVA Department of Mechanical and Aerospace Engineering. Credit: Tom Cogill.

Superior Performance and Comfort

The liquid nanofoam cushion lets the helmet’s interior compress and spread the impact force, reducing the force transferred to the head and minimizing injury risk. It also recovers its original shape post-impact, allowing for multiple hits and ensuring the helmet continues to protect the player’s head throughout the game.

“An added benefit,” Xu continued, “is that the improved material is more flexible and considerably more comfortable. The material dynamically reacts to external shocks due to the way the ion clusters and networks are structured within the material.”

“Furthermore, the liquid cushion can be engineered as lighter, smaller, and safer protective devices,” said Weiyi Lu, an associate professor from civil engineering at Michigan State University and a collaborator on the project. “The decrease in weight and size of liquid nanofoam liners will transform future helmet designs. You may be watching a football game one day, wondering how the smaller helmets protect the players’ heads. It could be because of our new material.”

Overcoming Conventional Nanofoam Challenges

Conventional nanofoam’s protective mechanism depends on material properties that respond when compressed or mechanically distorted, such as “collapse” and “densification”. Following a collapse and densification, the traditional nanofoam struggles to recover due to permanent material deformation, offering protection only once. When compared to liquid nanofoam, these properties are very slow (milliseconds) and cannot meet the “high-force reduction requirement,” meaning they can’t effectively absorb and dissipate high-force impacts within the short time window associated with collisions.

Another drawback of traditional nanofoam is that, when exposed to several small impacts that don’t deform the material, the foam becomes entirely “hard” and acts as a rigid body, offering no protection. This rigidity could potentially cause injuries and damage to soft tissues, such as traumatic brain injury (TBI).

By altering the mechanical properties of materials—integrating nanoporous materials with “non-wetting liquid” or ionized water—the team developed a material that can respond to impacts in a few microseconds. This combination facilitates superfast liquid transport in a nanoconfined environment. Also, after impacts, due to its non-wetting nature, the liquid nanofoam cushion can return to its original form as the liquid is ejected from the pores, thereby withstanding repeated impacts. This dynamic conforming and reforming ability also solves the problem of the material becoming rigid from micro-impacts.

Wider Applications of Liquid Nanofoam

The same liquid properties that make this new nanofoam safer for athletic gear could also be employed in other collision-prone areas, such as cars. The safety and material protective systems in vehicles are currently being reconsidered to adapt to the emerging era of electric propulsion and autonomous vehicles. The material could be used to create protective cushions that absorb impacts during accidents or help reduce vibrations and noise.

Another less obvious application is in hospitals. The foam could be incorporated into wearable medical devices like a smartwatch, which monitors vital signs. By integrating liquid nanofoam technology, the watch could feature a soft, foam-like material on its underside, improving sensor accuracy by ensuring proper skin contact. It could conform to the shape of your wrist, making it comfortable for all-day wear. Additionally, the foam could provide extra protection by acting as a shock absorber. If you accidentally knock your wrist against a hard surface, the foam could cushion the impact, protecting the sensors and your skin.

Reference: “Nanoconfined Water-Ion Coordination Network for Flexible Energy Dissipation Device” by Yuan Gao, Mingzhe Li, Chi Zhan, Haozhe Zhang, Mengtian Yin, Weiyi Lu and Baoxing Xu, 6 July 2023, Advanced Materials. DOI: 10.1002/adma.202303759

Frequently Asked Questions (FAQs) about Liquid Nanofoam Technology

More about Liquid Nanofoam Technology

• Research on Advanced Materials
• Baoxing Xu’s Research Profile
• Mechanical and Aerospace Engineering at the University of Virginia
• Nanoconfined Water-Ion Coordination Network for Flexible Energy Dissipation Device – Study
• About Nanofoam Technology