To say there’s a wrinkle in Dr Ken Phillips’ motorcycle helmet design would be no exaggeration. But rather than being an unfortunate error, the wrinkle in question is built into the design of his Phillips Head Protection System (PHPS), now being exploited commercially by Belgian motorcycle helmet maker Lazer Helmets SA.
Phillips, a medical doctor, has spent 16 years developing his idea – “a skin to cover a motorcycle helmet, which mimics the action of the skin on the skull,” into a technological reality. With such a covering, the wrinkling absorbs/deflects some 67 percent of the rapid and highly damaging rotational force which can cause both damage to the blood vessels running between the skull and the brain, as well as, “severe and untreatable damage to tiny blood vessels and to nerve fibres in the brain,” said Phillips, in an 18 March telephone interview from his base in the London suburb of Pinner.
Such damage is not necessarily fatal — sufferers can recover – but there is no treatment guaranteed to repair the injury, he said.
The figure of 67-percent energy absorption came from a digital study on Lazer’s Superskin helmets with PHPS technology, carried out at the French National Scientific Research Centre (CNRS) at the Louis Pasteur University (ULP) in Strasbourg, France.
Researchers, led by CNRS’s Prof Remy Willinger, used computerised recreations of head injuries to assess the effect of the Superskin solution. With the skin, the risk of intra-cerebral shearing in the event of a head impact is cut by two thirds, the scientists concluded.
Willinger’s work followed a detailed European Union study published in 2001 – called COST 327 – which evaluated the head and neck injuries caused by a group of well documented motorcycle accidents in Germany and Scotland, in terms of the protection given by motorcycle safety helmets (see box below).
A long project
In developing his idea into reality, Phillips struggled – not with the problem of how to prevent or reduce such rotation, he knew that. You could say the idea came to him when he was scratching his head one day, because the basic concept behind the PHPS is that simple: cover a hard helmet with a skin that wrinkles — just as the human scalp wrinkles on the skull and protects it from injury.
What took Phillips, and technological partner Industrial Design Company (IDC) of Datchett in the UK, so long was identifying a polymer for the skin with the appropriate combination of strength, durability, elongation and chemical inertness.
Phillips said that it then took a long time to deduce a combination of skin material and lubricant that would do the job.
Eventually, in cooperation with Bayer MaterialScience, the team came up with a thermoplastic polyurethane (TPU) skin which would fit the role, coupled with a lubricant layer to provide the right degree of slippage to prevent rotation.
Working with IDC, Phillips assessed a great many combinations of lubricant and skin material before settling on a polymer gel made “from a custom organic compound,” for the lubricant.
Phillips’ European Patent Specification EP1404189B1, granted in April 2008, says that, for the outer layer, designed to mimic the behaviour of the scalp, he first aimed for a material which was “substantially inelastic in shear but elastically compressible in the normal direction.” But testing showed that an “outer layer which was substantially elastic both in shear and when subject to forces in the normal direction was also effective.” A wide range of possibilities
Potential skin materials listed in the patent include thermoplastic elastomers in a solid or foamed form, thermoset elastomers including PU types, High Q rubber from Astron, Sorbothane, a shock-absorbing viscoelastic PU elastomer, and others.
This layer may be reinforced with highstiffness, low-elongation fibres such as glass, carbon or aramid to reduce its elasticity.
Compatibility between the lubricant gel and TPU was also crucial to ensuring long term performance of the skin.
The lubricant is not a thick semi-solid gel, said Phillips, it is almost a molecular layer, simply there to allow the covering to slip.
Meanwhile the tough TPU is only 1mm thick before it is applied, and perhaps 0.8 mm thick when stretched over the helmet structure, Phillips said.
In his patent, the outer layer is glued to the lower edge of the helmet shell, but it can be fixed by conventional mechanical means.
The rest of the outer layer is unattached and free to move relative to the shell, so as to mimic the protective movement of the scalp. The lubricant reduces friction and aids relative movement between the two layers.
Damaging rotational injuries
Phillips said the effects of rotational injury are now well known and were first identified in the 1940s. Rotational force on the head can cause tearing of blood vessels between the brain mass and the skull wall, as a result of rotation of the head around the neck. This causes bleeding — known as a sub-dural haematoma.
Meanwhile, Phillips explained, sudden rotation of the head can also set up shear forces within the soft brain itself, causing “differential movement of brain parts or intracerebral shearing” resulting in neurological lesions and further damage. This is known as “diffusional axonal injury” (DAI), he said.
As Lazer literature notes, the critical time for brain injury is in the first 15 milliseconds of the impact. This is when the road surface “bites into a conventional helmet and causes rotation, while the Superskin slides on the lubricant.” Videos of an oblique drop test onto an anvil – a standard helmet test, show this clearly. A Superskin helmet with PHPS rotates only about 20 degrees compared with over 90 degrees for a conventional type – a reduction of three quarters. Rotational acceleration is also reduced by two thirds, Phillips said. The tangential impact force is reduced by 60 percent, the test results showed.
Phillips was keen to stress that the Superskin tests were performed at much higher speeds than those required by the current standard – UN ECE 22.05. Helmet tests, he said, conventionally use speeds of 8 m/s, while the PHPS concept has been tested at speeds of 10- 12 m/s. At the lower speed, a reduction of 70 percent in damage is seen, while at 12 m/s this is reduced to 35 percent, he said, indicating that higher speeds give a much more realistic assessment of what happens in an accident.
Current motorcycle helmets are made of a hard thermoplastic such as ABS (acrylonitrilebutadiene- styrene) with an inner protective layer of a cushioning foam – often expanded polystyrene), which gives some protection against direct linear impact forces.
In Phillips’ patent, he says that the hard shell mimics the skull by offering a solid surface for energy dissipation — and also allowing a degree of compression or crushing to facilitate increased energy absorption.
Suitable shell materials include polypropylene, polycarbonate, ABS, polycarbonate/ABS blends, carbon-fibre or aramid fibre composites.
This structure protects against the force of a linear impact – the type of force which tends to cause skull fractures.
But as Phillips pointed out, most impacts in an accident are a mixture of direct and rotational forces.
Lazer launched its Superskin helmet in 2009, using what the company calls an, “anti-rotational synthetic membrane with exceptional characteristics,” which it said weighs 100 g, and is thermoformed over the lubricated shell. Describing the membrane as tough and programmed to give about 800 percent elongation when stretched, Lazer said it can be cut by sharp objects, and points out that after any accident, motorcyclists should always replace their helmets.
All motorcyclists can benefit from use of such a helmet, according to Phillips. Lazer puts the cost of adding the TPU skin at only €150 ($200) more than for a conventional helmet.
List prices of the Lazer Superskin are about Euro 250.
The cost of MC accidents
As we’re all aware, motorbike riders are at high risk on the roads and it’s their heads — and more importantly what’s inside them — that are most likely to suffer trauma.
Set up in the mid -1990s, the extensive EU COST (Cooperation in the field of Science and Technology) 327 study on motorcycle helmets reported 4700 fatalities a year among 8.6 million motorcycle users in Europe (15 EU countries at the time, data from 1996-1998).
This represented 16 percent of all road deaths.
COST 237 also noted that head injuries cause three quarters of all fatalities amongst motorcyclists, who are “typically the most vulnerable of road users.” From analysis of 253 accidents, assessed for the severity of head injury and accident speed, the study concluded that, with head injuries above a certain level of severity (AIS — Abbreviated Injury Scale – level 2 or higher) “rotational motion is considered to be the cause of over 60 percent of the injuries and linear motion of 30 percent.” During the project, the participants estimated that fatal and serious head injuries could be reduced by “at least 20 percent with an achievable increase in helmet performance.” That would save 1000 lives each year, the study said.
To achieve this, COST said, helmets must meet tests for impact resistance at higher speeds, of 8.5 m/s rather than the 5.5 – 6 m/s used then.
More potential elsewhere
While his initial aim was to lessen brain damage in motorcycle accidents, Phillips stresses that there is also “a huge market for other uses for helmets” using PHPS, in sports but also in industry and construction.
Lazer has exclusive rights to the technology for motorcycle helmets in Europe, which leaves scope for other fields and geographic regions.
Phillips intends to license the patented technology to expert companies in specific fields and take royalties on his invention.
At the time of this interview, he was about to fly to the US to talk to an ASTM committee on head injuries in sport, and promote the concept of PHPS in activities such as American football and ice hockey, where head injuries are common. In such sports, concussion seems to be an accepted occupational hazard, but Phillips says “you only have to look at the long-term effects of such injuries on professional boxers such as Mohamed Ali,” to see the risks involved.
Huge potential market also lies in industrial hard hats, where there is “a massive incidence of head injury,” Phillips said. In some 30 percent of construction incidents, a swinging piece of equipment simply knocks the hat off. Another 30 percent of injuries involve falls from a height, again where the relatively flimsy helmets tend to fly off, offering no protection.
Military and police uses, as well as skiing, are other uses with potential, Phillips said.
Meanwhile US equestrians number up to 30 million, said Phillips, and only half-a-million of them wear protective headgear.
Phillips also noted that material and manufacturing costs for the skin are only about $7— so that a low-cost solution for cyclists and construction uses, for example, may be feasible.
One Swiss manufacturer is already interested in developing a cycle helmet using the membrane, Phillips noted.
