Soon, tissue engineers will be able to add bone to their bag of manufactured body parts. For the first time, researchers have created a tissue similar to the growing end of bones. The feat could eventually help children born with genetic defects that make their skeleton grow too slow or too fast.
Bone is difficult to recreate. Many cell types must come together so that marrow is surrounded by a hard, calcified chassis. Blood vessels need to permeate the bone to supply it with oxygen and nutrients. Finally, bone has to stop growing at the right time, which requires careful control of molecular growth signals. While considering how to reconstruct bones, biomedical engineering grad student Eben Alsberg at the University of Michigan, Ann Arbor, suggested to his colleagues that they approach the problem the way the body does, by creating a growth plate--a sheet of tissue at the ends of bones where certain cells make cartilage and other cells harden the cartilage into bone.
Alsberg and colleagues mixed bovine chondrocytes, which fabricate cartilage, and bone-building osteoblasts from rats with a gelatinous matrix that contained a molecular growth signal. Then they injected the concoction into the backs of mice and monitored the growing knob. The two cell types formed structures reminiscent of bone growth plates--cartilage on one side, bone and marrow on the other, they report online 6 September in the Proceedings of the National Academy of Sciences. In addition, blood vessels laced the simulated bone, says Alsberg's adviser, David Mooney. Mooney's group is now trying to control the activity and organization of the tissues so they can be implanted into animals and allowed to grow with them.
The work is a "proof of principle" that researchers can recreate a growth plate, says tissue engineer Anthony Atala of Harvard Medical School in Boston. Most researchers expect that artificial organs will grow normally when implanted into bodies, he says, and this work suggests that bone will too.
The Mooney Lab