The transdisciplinary project, Wireless Metamaterial Interbody Cage for Real-Time Assessment of Lumbar Spinal Fusion In Vivo, could make spinal fusion recovery safer by allowing doctors to track progress remotely and intervene before complications arise.
Each year, as many as a million Americans undergo spinal fusion surgery, which uses a metal cage and a bone graft to fuse two spinal vertebrae, with screws and brackets holding these bones in place.
"After implanting the hardware, we monitor it using X-rays and symptoms presented by the patient," said Agarwal, co-principal investigator and associate professor in the Department of Neurological Surgery School of Medicine with a secondary appointment in the Department of Bioengineering at Pitt's Swanson School of Engineering. "This means patients have to make in-person visits and subject themselves to radiation."
Since doctors and patients cannot easily monitor the spine as it heals, it's not a connected health care experience, explained Agarwal, who also directs Minimally Invasive Spine and Robotic Surgery at UPMC.
While implantable wireless devices that monitor medical procedures are becoming more common and could help allay these issues, the devices require batteries and an electronic component to transmit signals, making them impermanent.
Alavi, principal investigator and an associate professor and B.P. America Faculty Fellow in the Department of Civil and Environmental Engineering, turned to an unexpected place to find a better solution: technology he helped develop to monitor bridge infrastructure.
As a PhD student, Alavi created sensors that produce their own power and send signals indicating changes in the physical properties of bridges. These sensors alert officials to structural weaknesses before more serious damage develops. Alavi thought that the technology could be adapted to work in a patient's spine.
"No batteries, no antennas, no electronics in vivo-no worries!" said Alavi, who also directs the Intelligent Structures and Architected Materials Research and Testing (ISMART) Lab. "By blending metamaterial design with nano-energy harvesting, we create fully battery-free, electronics-free implants that power themselves through contact electrification. They adapt to each patient and wirelessly transmit signals like a mini router inside the body."
Using new, human-developed composites known as metamaterials, Alavi's team has created structures consisting of different sized unit cells. By interweaving conductive and non-conductive materials, they can optimize these structures to harvest energy and transmit signals when pressure is applied to them.
"We're creating cages for spinal fusion surgery that, like human cells, have a natural, built-in intelligence," said Alavi.
These cages are set between two vertebrae and provide stability while also monitoring the healing process.
"If the spine is healing, the bone starts carrying more of the load and the implant's self-generated signal naturally drops," Alavi noted. "Right after surgery, the signal is stronger because the vertebral endplates press harder on the cage, so it generates more energy."
The signals are received through an electrode on the patient's back and transmitted to the cloud, where the signals can be interpreted in real time, allowing for medical intervention before more serious damage occurs.
Alavi also turned to generative AI to generate metamaterial designs unique to each patient's spine, dramatically accelerating the process.
"We can scan the patient's spine and then design and print the cage to fit perfectly. There are different types of porous, patient-specific cages in the market, but ours is a metamaterial system with full control over stiffness and, more importantly, the ability to generate its own power, which we use not only for monitoring but are now working to apply for electrical stimulation as well."
Alavi and Agarwal have tested the cages in vitro, and the technology works. With NIH support, the team will conduct in vivo testing using animal models. "If it works," said Agarwal, "then the next step is human testing."
He added, "By blending the clinical and the bench expertise, we have a better chance of translating the science into patient use, improving safety and outcomes while creating more connected health care."
Research Report:Wireless electronic-free mechanical metamaterial implants
Related Links
Minimally Invasive Spine and Robotic Surgery at UPMC
Space Medicine Technology and Systems
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