UVA engineers innovate liquid safety cushion technology

The discovery that football players unknowingly suffer permanent brain damage when they hit their heads throughout their professional careers created a rush to design better head protection. One such invention is nanofoam, the material on the inside of a soccer helmet.

Thanks to mechanical and aerospace engineering professor Baoxing Xu at the University of Virginia and his research team, nanofoam has just received a major upgrade and protective sports equipment can too. This newly discovered design integrates nanofoam with “non-wetting ionized liquid”, a form of water that Xu and his research team now know combines seamlessly with nanofoam to create liquid cushioning. This versatile and responsive material will provide better protection to athletes and holds promise for use in protecting car occupants and helping hospital patients use wearable medical devices.

The team’s research was recently published in Advanced Materials.

For maximum safety, the protective foam sandwiched between the inner and outer layers of the helmet can take not one hit but several, match after match. The material should be soft enough to create a soft place for the head to land, but tough enough to bounce back and prepare for the next punch. And the material has to be ductile but not hard, because “hard” hurts the head too. Having one ingredient do all of these things is quite a difficult task.

The team is advancing their work previously published in Proceedings of the National Academy of Sciences, who are beginning to explore the use of fluids in nanofoam, to create materials that meet the complex safety demands of high-contact sports.

“We found that creating liquid nanofoam pads with ionized water instead of plain water made a significant difference in the performance of the material,” said Xu. “Using ionized water in the design is groundbreaking because we discovered an unusual liquid-ion coordination network that allows the creation of more sophisticated materials.”

The liquid nanofoam padding allows the inside of the helmet to compress and disperse impact forces, minimizing the forces being transmitted to the head and reducing the risk of injury. It also regains its original shape after impact, allowing for multiple hits and ensuring the helmet’s continued effectiveness in protecting the athlete’s head during competition.

“An added bonus,” continues Xu, “is that the refined material is more flexible and much more comfortable to wear. The material dynamically responds to external shocks because of the way ionic groups and networks are created in the material.

“Fluid cushioning can be designed as a lighter, smaller, safer protective device,” said professor Weiyi Lu, a collaborator of civil engineering at Michigan State University. “In addition, reducing the weight and size of the liquid nanofoam coating will revolutionize the hard shell design of future helmets. You may be watching a football game one day and wondering how smaller helmets protect the heads of the players. It could be because of our new material.”

In traditional nanofoam, the protection mechanism relies on properties of the material that react when it cracks, or deforms mechanically, such as “collapse” and “compact”. Collapse is just what it sounds like, and compaction is the severe deformation of the foam on strong impact. After collapse and compaction, traditional nanofoam does not recover well due to permanent deformation of the material — making protection a one-time deal. When compared to liquid nanofoam, this property is very slow (several milliseconds) and cannot accommodate “high force reduction requirements”, meaning it cannot effectively absorb and dissipate high-strength impacts in the short timeframes associated with impacts and impacts.

Another downside of traditional nanofoam is that, when subjected to a few minor impacts that don’t damage the material, the foam becomes really “hard” and behaves like a rigid object that can provide no protection. This stiffness has the potential to cause injury and soft tissue damage, such as traumatic brain injury (TBI).

By manipulating the material’s mechanical properties — integrating nanoporous materials with “non-wetting liquids” or ionized water — the team developed ways to create materials that can respond to impacts within a few seconds. microsecond because this combination enables super-fast transport of liquids in a nano-constrained environment. In addition, after being disassembled, namely after the impact, because of its non-wetting nature, the liquid nanofoam pad can return to its original shape because the liquid is expelled from the pores, thus preventing repeated blowing. This dynamic adjustment and reform capability also overcomes the problem of materials stiffening due to micro-impacts.

The same fluid properties that make the new nanofoam safer for athletic gear also offer potential use in other places where crashes occur, such as automobiles, where safety systems and material protection are being reconsidered to embrace the emerging era of electric propulsion and automated vehicles. It can be used to make protective padding that absorbs impact during a crash or helps reduce vibration and noise.

Another purpose that may not be as clear-cut is the role of liquid nanofoam in the hospital environment. The foam can be used in wearable medical devices such as smartwatches, which monitor heart rate and other vital signs. By incorporating liquid nanofoam technology, these watches are able to have a soft, flexible foam-like material on the underside and help improve sensor accuracy by ensuring proper contact with your skin. It can adjust to the shape of your wrist, making it comfortable to wear all day. Also, foam can provide extra protection by acting as a shock absorber. If you accidentally bump your wrist against a hard surface, foam can help cushion the impact and prevent damage to the sensor or your skin.