(EDMONTON) As the song goes, the head bone is connected to the neck bone. Testing how sports helmets protect brains means you have to look beyond both head and helmet. You have to account for the unsung factor in head injury: the delicate-looking and flexible apparatus that is the human neck. And that’s where mechanical engineering master’s student Megan Ogle is training her focus.
“Basically, the biomedical community has found that the rotation of your head on your neck is a primary factor for concussion in sports,” she says.
Ogle is in the lab, pointing to a dummy head that is attached to a tower, which runs floor-to-ceiling. The model head is designed to measure impact when dropped from different points on the tower. “The dummy head is attached to the tower with a neck that is supported by a stiff metal rod,” she says. “It’s the only artificial neck that labs use right now—it’s built for crash test dummies, which is not that helpful in this application,” Ogle says.
She explains that, when you take a hit, your head doesn’t just move stiffly back to front or side to side, but moves with your neck, a factor that shows how well your helmet is protecting you. Under the co-supervision of Chris Dennison and Jason Carey, Ogle set about studying cadaveric necks and designing an artificial one that mimics natural, human flex and stretch.
The necks she has been designing are based on a typical North American man in the 50th percentile for height and weight. “Once we demonstrate that it works, we can customize for women and children, too,” Ogle says.
In the meantime, her average guy’s test neck is flexible and does have a range of motion that is eerily lifelike. Made of putty-coloured silicone, inside there are simplified vertebrae made of aluminum, and intervertebral discs made of 3D-printed rubber. Steel cables run through these and out the end of the model. The silicone represents the tissues of the neck. “Right now we’re building based on cadaver data,” she days, “which tells us the minimum bending requirements.”
The silicone neck is durable and can be used on the test tower many times—Ogle has used her current one in 50 tests and counting. Two more necks are in the works. She shows me an earlier prototype made of clear ballistic gel. It has the advantage in that the inner workings are visible. But this earlier prototype didn’t stand up as well, and each neck could only be used five or six times before the quick-setting gel started to break down.
Ogle is testing the silicone neck, dropping it so it reaches speeds ranging from two metres per second to 5.5 metres per second. “The reason for that is that hockey helmets are tested at speeds of up to six metres per second,” Ogle says, “so if my neck holds out at those speeds it will be useful for testing those helmets.”
The solution that Ogle’s human-like neck brings is that it allows engineers to quantify concussions so they can better test and design equipment. “It introduces a component to testing that allows other people to explore impact,” she says. And hopefully it will teach medical personnel and designers alike a little more about the mechanics of concussion.