Scientists from the Mayo Clinic in Minnesota have created an expandable polymer that is strong enough to replace bone tissue.
Lichun Lu and Xifeng Lu, scientists at the Mayo Clinic’s college of medicine, have developed special biodegradable polymer bone grafts that will grow to a specific size and shape once surgically placed in the body. The research was presented today at the American Chemical Society’s spring meeting in San Diego.
“We are working on a solution to improve surgical cancer treatments,” Lu said Tuesday. “Removing spinal tumors sometimes requires removing surrounding bone/discs. We’ve created a spongy cage to fill the void in the spine.”
Cancer spreads through the body via a process called metastasis. When cancer spreads to the bones, the spine is the most common skeletal location for it to appear.
When doctors remove spinal tumors, they have to remove significant amounts of bone and even entire intervertebral discs, leaving a significant gap. To ensure the integrity of the spinal cord and maintain the strength of the patient’s spine, doctors have to fill the gaps; however, current methods for doing so are not ideal.
Patients typically have to choose between an aggressive, invasive procedure or one that is incredibly expensive. With the first option, a surgeon would open up the patient’s chest cavity and approach the spine from the front of the body in order to give the surgeon more room to work. Metal spinal cages and bone grafts are surgically implanted in order to fill in the gaps left from the tumor removal. Healing time from this type of procedure is lengthy.
The second option only requires a small incision. A surgeon would then insert short, expandable rods made from titanium to strengthen the spinal column. This procedure is much less invasive, but extremely costly.
Lu’s team is working to develop a third option using a biodegradable polymer as a bone substitute, which will expand after being implanted. The sponge-like implant is made from hydrogel that is dehydrated down to capsule size, allowing the surgeon to implant them just like would the titanium rods. Once inside the body, fluids would cause the polymer to expand and fill the gaps left by the missing vertebrae.
“The cage expands in all directions,” Lu said. “We want it to expand in diameter and length. This way we can control the final dimension of the graft so it can fit the need of specific patients.”
During the procedure, the surgeon would first insert a hollow shell of the graft known as a cage, activate it with sterile saline, initiating the expansion process, and then fill it with stabilizing materials and therapeutic drugs. The researchers worked diligently to perfect the expansion process.
“We’ve engineered the cage expand the way we want it to,” Lu explained during a press conference. “The ideal expansion time is no more than five to 10 minutes.”
The timing of this process had to be just right. If the implant expanded too quickly, the surgeon would not have enough time to properly position it. However, if it expanded too slowly, that would prolong the surgery.
Once implanted in the body, tension would hold the cage the in place until it was filled. After the injection, the graft will be completely secure and eventually surrounding bone tissue will grow into it, anchoring it in place.
Liu described some of the challenges the duo faced. “The most challenging step was finding the right material,” he explained. “We don’t want it to be too soft or too rigid. We believe we now have the most optimal material.”
Preliminary trials with cadavers as test subjects are set to begin soon. The trials will test the feasibility of the techniques, as well as the durability of the polymer. “It needs to support the body weight of the patient,” Liu said. “This polymer is very strong and we believe it will hold up.”
If the cadaver trials are successful, the team expects the first clinical trial with humans to come in the next few years.
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