Our brains are delicate and precious assets. Encased within the thick, bony shell of our craniums, they are largely protected from the damage that our everyday lives might inflict. Inside this armour shielding, our brains are offered further cushioning by several layers of protective membranes and a soup of cerebrospinal fluid.
But sometimes this skeletal saferoom is not enough. Severe blows to the head can crack the bone and damage the brain inside. Heavy impacts can also send the squidgy organ ricocheting around inside the skull, damaging the brain’s soft tissues as it knocks against the hard bone. (Learn more about what happens to the brain during concussion.)
Collisions on the sports field, bike accidents, building site falls and slips and battlefield injuries all present greater threats than we might normally face and call for additional protection for our brains. But helmets cannot simply be thick protective shells. They have to be matched to the activity they are being used for, while offering the best protection possible.
- Why women are more at risk from concussion
- The head injury that turned a man into a maths geniu
- Is humanity about to get stupider?
Advanced new materials and creative thinking are leading to a new generation of protective head gear that promises to keep our delicate brains safer.
Cycling helmets chiefly protect against impacts with the ground. They are rarely needed – but when they are, they can be life-savers. There is an ongoing debate in the cycling community, however, about whether wearing cycling helmets is necessary, with some research suggesting that motorists drive closer to riders with helmets on, while other studies have found that simply wearing a helmet can make cyclists more safety-conscious. Having looked closely at what helmets actually do in the event of an accident, Donal McNally, a bioengineer at the University of Nottingham, is in no doubt.
The busy road environment puts cyclists at risk of a wide range of impacts if they fall or are in a collision (Credit: Alamy)
“I’ve done a fair amount of modelling real-world cycle impacts, and helmets are very protective, especially for children,” says McNally.
Light as they are, most cycling helmets are remarkably effective. The outer shell is a hard material such as carbon fibre or polycarbonate which spreads the blow. This is usually designed to “eggshell”, collapsing on impact, absorbing energy like the crumple zone in a car. Inside this is a layer of expanded polystyrene, a higher-quality version of the ubiquitous packing material. This also permanently deforms and absorbs energy as it does so, further reducing the impact reaching the wearer’s skull.
McNally also has real-world experience of what cycling helmets can do – in 2010 he was struck by a car while cycling and seriously injured. Based on his work, he believes that his injuries would have been much worse without a helmet and now shows pictures of the damaged helmet to students in his lectures.
“That helmet saved my life,” says McNally.
Knockout blows in boxing are more likely to come from the side or below, because these cause the head to rotate
A particular challenge is the rotational motion from an angled impact, which can cause the brain to rotate and, effectively, get twisted briefly out of shape. This is highly damaging. It is why knockout blows in boxing are more likely to come from the side or below, because, unlike a straight punch, these cause the head to rotate.
“In many cases it is not a factor, but for some types of impact, such as being struck by a lorry’s wing mirror, rotational injury can be very significant,” says McNally.
Many newer helmets are now being fitted with a feature known as Mips (for Multi-directional Impact Protection System), which helps to protect against these rotational injuries. Originally developed and tested by Swedish neurosurgeon in 2000, it uses a layer between the shell and liner of the helmet that slips upon impact, deflecting some of the force away from the brain by rotating the outer part of the helmet by around a centimetre.
An alternative approach, known as Wavecel, uses a honeycomb structure. On impact, several layers of material in the helmet liner move and flex independently, absorbing both rotational and impact forces. One set of tests by the technology’s developer suggested that while a standard helmet gives a 59% chance of rotational injury, a Mips-type helmet reduces this to 34% and a Wavecel-type helmet to just 1.2%. These figures are disputed by the makers of Mips, however, and an independent assessment by Virginia Tech found the Mips design gave slightly better protection.
Modern combat helmets are strong enough to stop bullets (Credit: Alamy)
However, while current bike helmets may be highly effective at protecting the skull, facial injuries are another matter. A 2019 statistical study by Hanover Medical School found that 14% of bike accidents involved damage to the face, and that wearing a helmet made no difference. The authors suggest that future bike helmets should incorporate some form of facial protection. At present some extreme off-road cyclists wear helmets with a chinguard or a visor – but, as always, the challenge will be getting the public to wear them.
The yellow hard hats seen on construction sites, and sported by visiting politicians at photo-opportunities everywhere, are designed to protect against impact of falling objects, as well as bumps or scrapes against low beams and similar building site hazards. Hard hats are typically made of thermoplastic or polycarbonate, with suspension bands on the inside giving a thirty-millimetre clearance to reduce the chance of a blow being transmitted to the skull.
But on a sweaty building site, these helmets can get uncomfortably warm, often leading workers to take them off. Adding openings for ventilation can also weaken the shell. A team from the Vellore Institute of technology in Chennai, India, however, hope the solve the problem with some built-in air conditioning. They have designed a helmet that includes a heat sink made of phase-changing material based on paraffin wax. This melts at body temperature, absorbing heat and potentially keeping the wearer cooler for a couple of hours.
Cricket balls can easily cause skull fractures, smash a person’s jaw or cause blindness if it hits them in the wrong place
Another team at the University of Chennai is looking at alternative materials for shock absorption. Hard hats are typically made from a polymer resin reinforced with synthetic fibres such as Kevlar or carbon fibre, but the researchers are looking at replacing these with natural fibres which are more readily available and environmentally friendly to produce. They found that jute fibre, commonly used for sacking, rope, and rugs, shows potential as an alternative way of improving the strength of helmets.
Cricket presents an unusual threat to the human head. Hurtling towards it at up to 100mph (161km/h) is a hard, 160-gram ball. Being hit by one of these can easily cause skull fractures, smash a person’s jaw or cause blindness if it hits them in the wrong place. It can even kill. This means as well as the helmet, a facial cover is also essential. Modern cricket helmets now feature a cage-like faceguard or visor, and a hard cap to protect the skull.
In 2013 a new British Standard introduced projectile testing for faceguards. Now helmet makers like Masuri fire cricket balls at helmets with air cannon to prove their performance. They have reinforced the facial protection, and have found that it is more effective to deflect a ball than try to stop it completely.
"Batters, naturally, move to avoid any impact with the ball,” says Sam Miller, chief executive of Masuri. “A faceguard that sits away from the face, and deflects the ball, protects the wearer from impact – without impairing visibility or mobility.”
They have introduced a double bar grille to their faceguard that sits just below the eyeline, with one bar slightly behind the other. “The rear bar forces the ball upwards, towards the solid part of the peak, deflecting the ball away from the player's face,” says Miller.
This gives a high level of protection without impeding vision, making it popular with international cricketers. But while a reinforced plastic shell protects the skull, there is a need for additional protection from the ball – surprisingly from behind.
Being hit in the head or face by a cricket ball travelling at up to 100mph can lead to life changing injuries (Credit: Getty Images)
In 2014 Australian batsman Phillip Hughes was struck in the neck by a bouncing ball while attempting a hook shot, leading to a brain haemorrhage that would claim his life two days later. His death led to helmets being fitted with neck guards to increase the protection they offer. Masuri’s Stemguard, for example, is an accessory which clips to the back of the helmet grille to protect the stem of the neck. Made from a thermoplastic polyurethane honeycomb material, it also uses crush foam to enhance impact absorption.
But at present such neck protection is an optional extra. Australian batsman Steve Smith did not have a neck guard when he was struck by a 92mph delivery during the recent Ashes, resulting in concussion. This highlights one of the biggest challenges with all types of head protection: they don’t work unless people can be persuaded to wear them.
Perhaps the biggest issue keeping cricketers from wearing a helmet is the heat and humidity. Helmets often have ventilation for cooling, but optimising these is another scientific challenge. Vents can be positioned to try and increase airflow, with some researchers conducting experiments on special “sweating mannikins” to compare different designs. Researchers are now able to embed temperature and moisture sensors into helmets to get real-time mappings of the “hot and wet spots” as the game progresses. Ultimately this should lead to helmets which are cooler, and hence more acceptable on even the hottest days.
Tackling the tackle
Participation in gridiron football has suffered a decline in recent years, partly attributed to studies showing long-term brain damage among players. This is the driving force behind efforts to upgrade to a better type of head protection. Unlike cycling helmets, football helmets tend to be hard shells with foam padding, because they cannot be replaced after each impact.
Energy dissipation is required to reduce the impulse transmitted to the brain – Ellen Arruda
“Most helmets do a good job of reducing the transmitted force. This is why skull fracture is rare in football,” says Ellen Arruda, a mechanical engineer at the University of Michigan. “What they don't do well is dissipate energy. Energy dissipation is required to reduce the impulse transmitted to the brain.”
Arruda’s team is working on a novel helmet design to tackle exactly this problem.
“Our approach considers the entire helmet as a composite structure that includes one or more visco-elastic layers,” says Arruda.
Visco-elastic materials are special because although they are solid, they behave in some ways like a liquid, flowing and dissipating energy. The new helmet will incorporate a synthetic visco-elastic polymer that has been developed specifically to cope with the type of impacts experienced during football.
“Our design mitigates the effect of an impact by reducing both the force and the impulse transmitted to the skull and hence, the brain,” says Arruda.
There are other ways of improving over the traditional design. The Zero1 helmet made by Vicis has a thermoplastic outer shell which is deformable and responds much like hard rubber to take some of the energy of the impact. Inside this is a layer of “columnar elements” resembling springs, designed to absorb shock from different directions. Like the Mips design used in cycling helmets, this helps reduce rotational forces.
There has been a growing discussion about how to protect NFL players from concussion and long term damage to their brains (Credit: Getty Images)
Rotational injuries are a particular risk in American football, but could be reduced by making helmets slippery so that less of the force of an impact is transmitted to the head. One team at Simon Fraser University in Canada are testing stickers that can be applied to the outside of helmets. Composed of several layers of film, a glancing impact causes the outer layer to slide free, reducing the rotational effect by up to 74%. The sticker, however, would need to be replaced after any serious impact.
When two rogue policemen opened fire on a group of US Army soldiers at Camp Maiwand in eastern Afghanistan in 2018, the attack claimed the life of an Army Command Sergeant Major. But another of the soldiers caught up in the ambush could also have lost his life that day.
Staff Sgt Steven McQueen was struck in the back of the head by a round from a machine gun firing at close range from the back of a pick-up truck, knocking him off his feet. Amazingly he was back up again and fighting just seconds later. The round had hit his helmet, which had absorbed the impact and stopped the bullet. The soldier survived largely thanks to the remarkable toughness of his helmet, a type known as the Enhanced Combat Helmet.
Military helmets, like those that wear them, face a unique and ever-changing challenge: small, dense, high-velocity objects, specifically shrapnel and bullets.
UHMWPE is so good at catching bullets because it is stretchy enough to give, but absorbs a lot of energy without breaking
The steel helmets worn by soldiers in the early part of the 20th Century were later replaced by Kevlar in the 1970s and 1980s, but these have now been superseded by polyethylene. This is not the low-density polyethylene of drinks bottles and sandwich wrap, but ultra-high-molecular-weight polyethylene or UHMWP which can stop even large calibre rifle bullets from close range.
“UHMWP is the bees’ knees right now for material going into helmets, because of level of protection it can provide,” says Lt Col Ginger Whitehead, the US Army’s product manager for soldier protective equipment.
UHMWP is made of molecules about a hundred times larger than normal polythene and can be spun into fibre which looks and feels like nylon, but is bulletproof.
“What makes it special is its strength and tenacity,” says Vasilios Brachos, senior manager of defence product development at 3M, who manufacture military helmets for the US.
Tenacity is a technical term combining the force needed to stretch a material with how far it can stretch before it breaks. UHMWPE is so good at catching bullets because it is stretchy enough to give, but absorbs a lot of energy without breaking.
An improved version will be used in the US Army’s next-generation combat helmet being fielded next year, and even better materials are in the pipeline.
Our brains are delicate organs that are kept safe by our hard skulls, but sometimes they need some extra protection (Credit: Science Media Library)
“UHMWP is still relatively young and not wholly taken advantage of,” says Brachos. “We’re only at about 60% of its capability.”
However, even when a helmet stops a bullet, the wearer can still suffer from blunt trauma.
“It is quite similar to other blunt trauma, like being struck with a hammer,” says Marta Polomar, an engineer at Spain’s Universidad Politécnica de Valencia, who adds that in this case the trauma is produced by an object moving at several hundred metres per second.
When a helmet is struck by a bullet it deforms and bends inwards. If the deformation is greater than the distance between the inner helmet surface and the head, the bullet strikes the head through the helmet, and the trauma is correspondingly severe.
The risk of trauma could be reduced if helmets were stiffer and deformed less, but doing so would increase the chance of a bullet getting through.
“From our perspective, resistance to penetration far outweighs any blunt trauma risk,” says Brachos.
Some risk of blunt trauma is seen as the best trade-off. Polomar’s team are working to better understand the dangers and establish standards, including suggesting padding thickness is not reduced when fitting helmets to people with larger heads. Instead, they say the helmet shell should be increased in size proportional to the wearer. Other researchers are developing better shock-absorbing materials to help reduce the damage.
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