Researchers on Tunable Stiffness Bone Implant Turn to CIRAS for Technical Help

Iowa State University researchers have designed a new customizable device for optimizing the healing of broken bones—a tunable rod that can be 3D printed and custom matched to the needs of individual patients. 

They formalized the idea only after working with CIRAS to explore the limits of 3D printing technology and confirm that their invention actually could be built via additive manufacturing. 

“CIRAS really made it happen for us,” said Azadeh Sheidaei, assistant professor in the Department of Aerospace Engineering at Iowa State. “We didn’t actually know we could make it until they made it for us.” 

The new device—described in a paper written by Sheidaei; engineering graduate students Mohammad Hashemi and Aaron McCrary; and Karl Kraus, professor in the College of Veterinary Medicine at Iowa State—is designed to eliminate a long-standing difficulty with the healing of broken long bones, such as those found in the leg.  

Significant fractures of long bones currently are treated by attaching metal plates to the outside of the bones or rods through the inner bone canals to provide stability. However, research shows that too much rigidity (the inability of the bones to move while walking) can lead to poor bone growth and a leg that’s more likely to break in the same spot down the road.  

The new device is designed to fit around, rather than alongside, the bone. The center of the hourglass-shaped device can collapse slightly before it becomes rigid, thus providing both motion and support. The idea is that doctors will be able to assess the requirements for each individual patient, then 3D print something that works best in each particular case. 

“The whole idea is that if you’re walking around, it’s going to allow just the right amount of stress on the bone but after that, no more,” Kraus said. “It stops.” 

Kraus described tunable bone stiffness as a “gargantuan” idea that could significantly decrease the healing time from broken bones. 

Researchers have patented this device and hope to begin using the device on large animals sometime later this year. If all goes well, it could be in use for humans by 2023.  

“Additive manufacturing is what enabled us to do this,” Sheidaei said.  

Chris Hill, director of the CIRAS Technology Assistance Program, said CIRAS was “pleased we could help make this challenging part a reality for this important effort.” 

For more information, contact Jake Behrens at or 515-815-5003.