The Bone Foam

The pores in this polymer could let bone cells move in to naturally regrow gaps in people’s bones. Melissa Grunlan/Texas A&M. Millions of people suffer from facial deformities because an injury, surgery, or birth defect left a gap in their bone structure. These bone gaps are too wide for the body’s normal healing process to fix, and surgical solutions like grafts and putties usually fall short of restoring a person’s looks. But a new sponge-like polymer could provide a scaffold that lets bone cells regrow themselves. 

This “bone foam” is made out of a polycaprolactone, a polymer known as PCL that is already used in biomedical applications like sutures and barriers that keep healing tissues separate.

Biomedical engineer Melissa Grunlan of Texas A&M, the foam’s lead researcher, says PCL has two standout properties: It’s malleable at 140° F or above, but stiff at body temperature; and it breaks down slowly and safely in the body. But the real potential comes from combining these properties in a stiff, sponge-like structure, she said here yesterday at the annual meeting of the American Chemical Society.

Grunlan says surgeons would heat a chunk of the polymer in salt water until it becomes pliable, then mold it into the exact shape of the missing bone section. Once in place, the polymer would cool and stiffen. “After the foam is in place, bone cells come in and replace the foam, which is absorbed into the body and naturally excreted,” said Grunlan.

In lab experiments, she and her colleagues coated the PCL with another biodegradable polymer, called polydopamine, that is known to stimulate bone growth. They seeded the polymers with human bone cells, and after a few days saw that the cells were not only multiplying, but producing important bone-forming proteins. 

Currently, Grunlan’s bone foam has only been tested in her lab. She and her research team are currently looking for partners in the biomedical business to help move the product through clinical trials. The next step, she says, is to see how well the polymer can fix bone in a living organism like a mouse.

If it is eventually gains FDA approval, which could be five or 10 years away, this would give doctors a new way to treat cosmetic bone gaps caused by injuries, birth defects, or surgery. Today the most common method is to use reshaped bone harvested from places like the hip. But harvesting bone is risky, and the bone is difficult to shape and can leave the patient with an imperfect fit. Surgeons also have the option of using putties or cements to plug the gap, but these tend to be brittle, and lack pores that would let real bone migrate in and regrow itself.

Because of the rates at which bone grows and PCL breaks down, Grunlan estimates that a person using PCL could fully regrow bone in roughly a year.