Wardle sums up the benefits: “A lot of parts are bottlenecked by the autoclave process. This technique absolutely gets you to a lighter infrastructure and much lighter, flexible and robust manufacturing processes.”
Healing Broken Bones with CFRP
Project: Braided carbon fiber tubes and polymer cement
School: The University of Arizona
Location: Tucson, Ariz.
Principal Investigators: Hamid Saadatmanesh and Ehsan Mahmoudabadi
Structural engineers at the University of Arizona are adapting a CFRP process used to reinforce ailing infrastructure columns to repair broken bones. “When supporting a structure – whether it is a bridge or the body of a person – the mechanics are more or less the same,” says Hamid Saadatmanesh, professor of structural engineering.
Saadatmanesh, who has focused on composite-reinforced infrastructure projects for decades, hadn’t considered biomedical applications until a cardiologist asked him to examine the viability of CFRP heart valves. That sparked another idea: “It came to me that we could make a direct transfer from this proven civil engineering technique that has worked well for bridges and convert the technology for use in the human body,” he says.
To repair degraded concrete and steel supports on bridges, piers and highways, a braided CFRP tube is inserted into the hollow column and filled with polymer concrete, creating a new structural column inside the existing form. Saadatmanesh believes surgeons could stabilize broken bones in the same way, by aligning broken bones, inserting a braided CFRP tube into the bone cavity and filling it with bio-compatible polymer. As the polymer fills the CFRP sleeve, it would expand and take the form of the bone’s cavity. “The whole system works like steel-reinforced concrete,” says Ehsan Mahmoudabadi, professor of structural engineering. “But here we have carbon fiber as the tensile material and polymer concrete as the compression part.”
The hope is that the new technique will allow patients to avoid either invasive repair surgeries to implant plates, rods, wires and screws or external frames with steel pins drilled into the bone. In contrast, the new technique is expected to require two small incisions – one to insert the CFRP tube and another to pull it through the bone cavity. The inherent antioxidant properties of carbon may also promote faster healing than titanium or other metal implants. “We want to minimize the healing period and the trauma and make it as non-invasive as possible,” says Saadatmanesh.
Current research is focused on 4- to 5-millimeter diameter, multiaxial braided CFRP tubes that are manufactured to specifications by an outside vendor. The tubes are pre-impregnated with zinc phosphate or resin modified glass ionomer (RMGI). While it was easy to locate a manufacturer to produce the tubes, finding the right polymer to fill the sleeve presented a challenge. The team is investigating multiple bio-grade polymers – or “bone cements” – that are already approved for use in the human body.