Researchers at Saarland University are developing smart fracture implants that combine sensing functions with robotic micro-actuation to monitor bone healing and provide mechanical support during recovery.
The project brings together engineers, medical researchers and computer scientists. Professor Paul Motzki’s engineering team is developing shape-memory micro-actuators with integrated sensing capabilities, while Professor Bergita Ganse’s research group is contributing medical expertise in fracture healing. The work is part of Saarland University’s Smart Implants project, which is funded by the Werner Siemens Foundation with €8 million.
The implants are intended to address a limitation in conventional fracture care. At present, clinicians often rely on X-ray imaging several weeks after a fracture to determine whether healing is progressing as expected. The Saarland University team is developing implants that could monitor the fracture site continuously from inside the body and provide data on whether new tissue is forming.
The prototype uses bundles of ultrafine nickel-titanium wires, also known as nitinol, embedded in the implant. The wires function both as micro-actuators and as position sensors. When an electric current passes through the wires, they heat up and contract because of nitinol’s shape-memory properties. After cooling, the wires return to their starting position. This movement allows the implant to adjust conditions at the fracture gap by bringing bone fragments closer together or allowing limited movement when needed.
The system is designed to respond to different stages of bone healing. In the early phase, when a fracture requires firm support, the implant can increase stiffness and stabilize the site. As healing progresses, it can become more compliant. The micro-actuators can also generate controlled motions, including small contractions or vibrations, to stimulate tissue growth at the fracture edges.
Ganse said controlled motion at the fracture site can support healing. “Healing is faster when the fracture gap is subjected to tiny, highly controlled motions and when the tissue at the fracture edges is mechanically stimulated,” she said. She added that oscillating movements with a stroke length of around 100 to 500 micrometres can be sufficient to initiate tissue growth processes.
The implant can also monitor whether healing is progressing by measuring small movements at the fracture edges. As new tissue forms, stiffness at the fracture site increases, and the system can read that change through its measurement data. The same data could indicate when movement is impairing healing, including when a patient places too much weight on an injured leg.
Motzki said nitinol enables strong mechanical performance in a compact structure. “Nickel-titanium alloy has the highest energy density of all known drive mechanisms, so by using nitinol, we’re able to exert a substantial tensile force in very small spaces,” he said.
The sensing function relies on changes in the electrical resistance of the nitinol wires as they deform. Each deformation can be associated with a specific resistance value, allowing the system to infer position and movement. Motzki’s team uses this measurement data to train neural networks to recognize signal patterns and calculate positional information, including when external disturbances affect the data.
In a future clinical setting, the researchers expect data from the implant to be transmitted wirelessly to a smartphone and controlled through the same device. The team is also working to further miniaturize the technology through SmILE, a Horizon Europe project with €21 million in funding.
The Saarland University researchers presentyed the prototype at Hannover Messe, where they are also showing related shape-memory technology applications. The team has established mateligent GmbH to support the transfer of its research into commercial and industrial uses.
Photo credit: Oliver Dietze
