Creating a new class of spinal fusion cage

Two faculty members are taking the fundamentals of mechanical engineering and applying them in new, life-changing ways. Dana Carpenter and Christopher Yakacki, both assistant professors in the mechanical engineering department, have established the Smart Materials and Biomechanics Lab and are working to discover new biomedical materials and investigate uses for biomedical devices.

Their research interests complement one another: Yakacki studies the materials used to create these devices and Carpenter uses imaging techniques to create models of the devices and test their functionality.

“Our skill sets are different, but we have a lot in common,” says Carpenter. “This makes our projects and proposals a lot stronger.”

Currently the duo is creating a new class of spinal fusion cages. A spinal fusion cage is a prosthesis that is inserted between the vertebrae to maintain the height and decompression features of the spine. Typically, these cages are made with titanium, carbon fiber epoxy or grafted tissue from a donor. However, for this particular prosthesis, Yakacki has found a polymer called polyparaphenylene that maintains a high strength when it’s made into a porous material.

“When you place the device between the vertebrae, the surrounding bone can grow into the pores,” explains Yakacki. “The fact that this material maintains its strength in a porous state is important because it enables us to create new implant designs, increase load sharing and decrease the time it takes for spinal fusion to occur. We really want to make something that challenges the traditional way fusion cages are designed.”

Through digital models of the spine and the device, Carpenter is able to determine load distributions and the distribution of bone density. He then uses the imaging software to insert the device into the modeled spine to see how it will work.

“This is imperative because we can simulate how it will change over time,” says Carpenter. “Through the digital models we’re able to look at load-sharing and the distribution of mechanical force, and adjust the device as needed.”

There are many benefits to the team’s multifaceted research approach. They can test the product without the need for cadaveric testing; they can simulate the amount of bone that will be absorbed into the material, the mechanics of the bone and how it can interact with the device; and they can see how the load distribution will change with the bone over time.

Through collaborations with surgeons from the CU School of Medicine—Vikas Patel and Andriy Noshchenko—the team obtains a clinical perspective on their research.

“It’s invaluable to be able to work with the surgeons,” says Yakacki. “Technically, they’re the end user of the device, so their perspective is key to developing a successful, useful product.”

“Their assessment also helps us to identify limitations and flaws,” says Carpenter. And it gives the team a glimpse into problems with current products and ideas on what would make them better.

“Our overall goal is to improve patient outcomes,” says Yakacki. “We want to develop something that can be used to better people’s lives.” He sees their work as an extension of traditional engineering.

Engineers like to help people. This research embraces that concept to the core.