Inspired by the infamous animal-shapped sponges that magically grow in water, scientists from the Mayo Clinic have created biodegradable polymer grafts that, when surgically placed in damaged vertebrae, grow to be just the right size and shape to fix one's spinal column.

"The overall goal of this research is to find ways to treat people with metastatic spinal tumors," explained Lichun Lu, one of the study researchers. "The spine is the most common site of skeletal metastases in cancer patients, but unlike current treatments, our approach is less invasive and is inexpensive."

Bone metastasis occurs when cancer cells spread from their original site to a bone. Current procedures of removing extensive spinal tumors require that the entire bone segment and adjacent intervertebral discs be taken out of the infected area. This creates a large void that must be filled to maintain the integrity of the spine and protect the spinal cord. 

Extensive spinal metastases can be treated with one of two surgical procedures. With the more aggressive and invasive approach, the surgeon opens the patient's chest cavity to provide enough room to insert metal cages or bone grafts, which replace the missing fragment. While the less invasive method requires only a small cut in the back or posterior, it uses short, expandable titanium rods that are much more costly. 

So Lu and her postdoctoral fellow, Xifeng Liu, searched for a less expensive material that could be dehydrated down to a size compatible with posterior spinal surgery, and then, once implanted, absorb fluids from the body and expand to replace the missing vertebrae.

"When we designed this expandable tube, we wanted to be able to control the size of the graft so it would fit into the exact space left behind after removing the tumor," Lu said.

Researchers also needed to control the kinetics of the expansion because if the tube were to expand too quickly a surgeon may not have enough time to position it correctly. On the other hand, if the tube were to expand too slowly, it would lengthen the procedure and keep the patient under anesthesia for longer than necessary. 

To time the expansion rate right, researchers tested their polymer grafts under under conditions that mimic the spinal column environment in the lab.

"By modulating the molecular weight and charge of the polymer, we are able to tune the material's properties," Liu added. 

Next, researchers play to study the grafts in cadavers and simulate an in-patient procedure. They hope to start clinical trials within the next few years.

Researchers recently presented their findings at the 251st National Meeting & Exposition of the American Chemical Society.