Evidence has shown that football players have been unintentionally gaining permanent brain damage as they racked up head contact hits throughout their professional careers. A rush to develop improved head protection has led to the application of nanofoam on the interior of football helmets.
Associate Professor Baoxing Xu in the Department of Mechanical and Aerospace Engineering. Image Credit: Tom Cogill
Associate Professor Baoxing Xu at the University of Virginia and his study group have enhanced nanofoam materials, where nanofoam is combined with “non-wetting ionized liquid". This liquid is a type of water that Xu and his study group found to combine perfectly with nanofoam to make a liquid cushion.
This multipurpose and responsive material will improve athletes' safety and is likely to be used in safeguarding car occupants and helping hospital patients use wearable medical devices.
Advanced Materials published the research of the team.
For improved protection, the protective foam packed between the interior and exterior layers of a helmet should not only be able to take one hit but several hits, game after game. The material should be sufficiently cushiony to make a soft place for a head to hit but strong enough to bounce back and be prepared for the next blow.
Also, the material has to be firm but not hard to prevent discomfort.
Earlier work from the group has been published in The Proceedings of the National Academy of Sciences, which explores the application of liquids in nanofoam to make a material that fulfills the complicated protection challenges of high-contact sports.
We found out that creating a liquid nanofoam cushion with ionized water instead of regular water made a significant difference in the way the material performed. Using ionized water in the design is a breakthrough because we uncovered an unusual liquid-ion coordination network which made it possible to create a more sophisticated material.
Baoxing Xu, Associate Professor, University of Virginia
The liquid nanofoam cushion enables the interior of the helmet to compress and disperse the force impacted, reducing the force transferred to the head and minimizing the threat of injury. Also, it regains its original shape after impacted, which allows numerous hits and guarantees the continued effectiveness of the helmet in safeguarding the head of the athlete at the time of the game.
An added bonus is that the enhanced material is more flexible and much more comfortable to wear. The material dynamically responds to external jolts because of the way the ion clusters and networks are fabricated in the material.
Baoxing Xu, Associate Professor, University of Virginia
The liquid cushion can be designed as lighter, smaller, and safer protective devices. Also, the reduced weight and size of the liquid nanofoam liners will revolutionize the design of the hard shell of future helmets. You could be watching a football game one day and wonder how the smaller helmets protect the players’ heads. It could be because of our new material.
Weiyi Lu, Associate Professor and Collaborator, Civil Engineering Michigan State University
In conventional nanofoam, the protection mechanism depends on material characteristics that respond when it gets crunched or mechanically deformed, for example, “densification” and “collapse.” Densification is the extreme deformation of foam on powerful impact and collapse. After densification and collapse, conventional nanofoam does not regain its shape very well due to the permanent deformation of materials, making safety a one-time deal.
In comparison to the liquid nanofoam, such properties are very tedious (a few milliseconds) and cannot fulfill the “high-force reduction requirement,” implying that it cannot efficiently absorb and dissipate high-force blows in the short time duration linked to impacts and collisions.
Another drawback of conventional nanofoam is that, when exposed to several tiny impacts that do not deform the material, the foam gets entirely “hard” and acts as a firm body that cannot offer protection. This rigidness could result in damage and injuries to soft tissues, like traumatic brain injury (TBI).
Through manipulating the mechanical properties of materials—combining nanoporous materials with ionized water and “non-wetting liquid”—the research group developed a method to create a material that could react to impacts in a few microseconds as this integration enables superfast liquid transfer in a nanoconfined environment.
After unloading, i.e., after impacts, owing to its non-wetting nature, the liquid nanofoam cushion can go back to its original form as the liquid is released out of the pores, thus enduring back-to-back blows. This dynamic conforming and reforming potential also remedies the issues of the material getting rigid due to micro-impacts.
The same liquid characteristics that develop this new nanofoam more protective for athletic equipment also provide a likely use in other places where collisions occur, such as cars, whose safety and material protective systems are believed to embrace the developing era of automated vehicles and electric propulsion. It can be employed to make safety cushions that absorb impacts at the time of accidents or aid in reducing noise and vibrations.
Another purpose that may not be as obvious is the part liquid nanofoam can serve in the hospital condition. The foam can be employed in wearable medical devices such as a smartwatch, monitoring the heart rate and other vital conditions. By incorporating liquid nanofoam technology, the watch can have a flexible and soft foam-like material on its underside and enhance the sensors' precision by guaranteeing proper contact with your skin.
It can fit into the shape of any wrist, thereby making it comfortable to wear throughout the day. Besides, the foam can offer added protection by serving as a shock absorber. If someone accidentally bumps their wrist against a hard surface, the foam can aid cushion the impact and avoid any impact to the sensors or skin.
Journal References:
Gao, Y., et al. (2023). Nanoconfined Water‐Ion Coordination Network for Flexible Energy Dissipation Device. Advanced Materials. doi.org/10.1002/adma.202303759.
Gao, Y., et al. (2020). Spontaneous outflow efficiency of confined liquid in hydrophobic nanopores. Proceedings of the National Academy of Sciences. doi.org/10.1073/pnas.2009310117.