Regrowing Bone

Lee Chou thinks that implants should provide a comfortable home for bone cells. However, he takes this idea one step further —biodegradable scaffold implants that grow bones where no bones have grown before.

Scientists have traditionally believed that inert materials made the best implants. Since materials such as titanium barely react or change within the body, the body doesn’t react negatively to them. Chou, on the other hand, who specializes in biomaterials and oral medicine at the Goldman School of Dental Medicine, believes an implant made of bioactive, as opposed to inert, materials will coax the body into reacting positively to it.

On a molecular level, no material is completely inert in the body, says Chou. The unique chemical makeup and shape of the surface always causes biological changes, even changing the way genes are expressed. Orthopedists usually use special proteins to induce cell growth on conventional implants. However, says Chou, these genetically engineered proteins change when they come in contact with the implant—the implant and proteins were never designed to work in tandem.

Chou’s approach uses the chemistry and shape of the implanted scaffold to control genes and induce bone growth. He spent several years screening different materials in the research lab before he hit on the right combination of elements.

In addition to the cell-growth-stimulating chemistry of the scaffold, the structure, which looks somewhat like a hard piece of Styrofoam, provides an attractive home for bone cells.The hollow, porous design allows bone cells to grow inside, around, and on the scaffold; and blood vessels to grow through it, in contrast to conventional implants that only allow cells to grow on the surface. Chou also designed the scaffold to dissolve after the bone grows in, leaving only natural bone behind.

Chou implants the scaffold into a body and adds osteogenic cells taken from a chip of the patient’s own bone. He’s had astounding results. One of his patients was born without upper jawbones. Within three months,the scaffold had created useable jawbones, allowing the man to eat normally and flash a smile for the first time in his 26 years.

Astoundingly,although the patient was born with a genetic disease that makes his bones naturally brittle and Chou used cells from his genetically defective bones to seed the scaffold, the structure coaxed them to grow normal, healthy bones — bones even stronger than his natural bones.

At the moment, Chou and his collaborator David Cottrell, chairman of the Department of Oral and Maxillofacial Surgery, are focusing on additional clinical studies for using bone tissue engineering to treat patients with severe bone defects.Although Chou concentrates his research on dental applications, he envisions that his bioactive scaffold will one day be used to grow bones throughout the body.

A man of many interests and talents, Chou also directs a project focusing on the mechanism by which the body takes in the AIDS virus.He also has been recognized for excellence in teaching — in 2002 he received BU’s highest teaching award, the Metcalf Cup and Prize.

For more information about Professor Chou's work, please see: http://dentalschool.bu.edu/research/biomaterials/chou.htm

— Elana Hayasaka

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