When surgeons need to graft bone--for, say, reconstructing someone's face after an accident--they dig it out of another part of the patient's body, usually the pelvis. "It's a painful operation," says John Davies, a dentist and biomedical engineer at the University of Toronto. "And because the patient must undergo essentially two operations, he has to stay on the operating table for a longer time. That's more costly and means a longer recovery time."
Davies and his colleagues have found a way to avoid that first, bone-harvesting operation. They've developed a polymer scaffold that mimics the structure of real bone. In particular, it's designed to work like trabecular bone--the spongy bone beneath the skeleton's hard outer shell. Like trabecular bone, the matrix has countless interconnected pores, each about a millimeter in size. Nestled within those pores are both osteoclasts (bone-eating cells) and osteoblasts (bone-making cells). When the synthetic bone is transplanted, those cells spread and grow new bone, healing the injury.
Researchers have tried to seed bones onto a scaffold before, Davies says, but with little luck. Some groups tried a matrix of calcium phosphate--the mineral that makes up coral. "It works extremely well when it comes to growing cells, but when it's put in the body it's not absorbed. It just stays there. So that's not a very good long-term strategy," he says. Other researchers have tried biodegradable foams, but the pores in the foam are so small that bone cells can't penetrate them. "When they make bone, it's only as a shell formed on the surface," Davies adds.
By tinkering with two manufacturing processes commonly used to make biodegradable foams, Davies has made a foam that has much larger pores--about the same size as the pores in real spongy bone. "When we seed the scaffold with cells, the cells grow right through and penetrate to a depth of up to about half an inch, so they make bone in a three-dimensional configuration," he says. "We haven't gone any deeper than that, and we don't plan to, because when surgeons remove bone for grafting, they only chip out tiny bits of bone, and we are trying to create an alternative." Davies plans to test the synthetic bone in simple dental surgeries within a year.
