Click to viewAs badass artificial limbs go, it probably doesn't get any better than Rose McGowan's machine gun leg from Planet Terror. But that's probably pretty hard to walk on, so a team from the mechanical engineering department at the Georgia Institute of Technology would suggest you use their artificial bone instead. Professor Andrés García and his collaborators recently managed to create a synthetic bone substitute that mimics the strength and complexity of natural bone — and their material has already carried its weight inside a living organism for several weeks.The major goal for García and his colleagues was to recreate the way natural bone gradually blends into tendons and soft tissue. García and his then-graduate student Jennifer Phillips describe the necessity of their work in a press release from Georgia Tech:
"One of the biggest challenges in regenerative medicine is to have a graded continuous interface, because anatomically that's how the majority of tissues appear and there are studies that strongly suggest that the graded interface provides better integration and load transfer," said Andres Garcia, professor in the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. ... "Every organ in our body is made up of complex, heterogeneous structures, so the ability to engineer tissues that more closely mimic these natural architectures is a critical challenge for the next wave of tissue engineering," said [García's then-graduate student Jennifer] Phillips, who is now working at Emory University as a postdoctoral research fellow in developmental biology.
Using gene therapy, the Georgia Tech researchers were able to artificially engineer that elusive bone-soft tissue interface. They started with a 10-mm scaffold of collagen (pictured above); collagen is the primary protein in the connective tissue of mammals. They then coated this collagen scaffold with a gene delivery vehicle that would encode for a protein called Runx2. At one end of the scaffold, they planned for a high concentration of Runx2 — one that would slowly decrease until it reached the other end. They now had a collagen scaffold with a gradually varying coat of Runx2. After that, they seeded the scaffold with dermal fibroblasts, causing skin cells to sprout uniformly on the Runx2-coated collagen. Skin cells on the area with a high concentration of Runx2 turned into bone, and skin cells at the other end became soft tissue. Voilà — a natural-seeming gradient of bone to tendon was the final result. And they didn't just stop there: García's group went on to implant their collagen scaffold in vivo for several weeks, and successfully. This technology isn't just useful for building artificial limbs; it could also provide major advances in surgery. The Georgia Tech press release had this to say to anybody with aching knees:
Oftentimes, ACL [anterior cruciate ligament] surgery fails at the point where the ligament meets the bone. But if an artificial bone/ligament construct with these types of graded transitions were implanted, it might lead to more successful outcomes for patients.
As someone whose ACL still frequently complains about a seven-year-old injury, this correspondent salutes García, Phillips, and the rest of the Georgia Tech team. Engineers create bone that blends into tendons [EurekAlert!] Engineering graded tissue interfaces [Proceedings of the National Academy of Sciences]