Breaks or defects in bones can be tricky and painful to treat, as surgeons often take bone from one region and use that to patch up the fracture. But now researchers have developed a new 3D-printed implant that not only removes this process, but which the body will eventually turn into real bone.

The implants are printed using an ink that is comprised of hydroxyapatite – a calcium mineral that's naturally found in bone – and the natural polymer PLGA. The polymer not only holds the hydroxyapatite together, but also gives the scaffold an incredible degree of flexibility, something the researchers were not expecting. The entire thing can be crushed and yet still spring back to its original shape. This means that during an operation, if the implant is the wrong shape or size, surgeons could alter and manipulate it in the operating room.

The microscopic structure of the implant is designed to mimic that of real bone, which allows the body’s own cells and blood vessels to naturally populate the scaffold. Because the implant is made from hydroxyapatite, it provides the perfect environment for bone regeneration, inducing the cells to begin the process of mineralization. Eventually, the artificial implant will become real bone.

“Cells can sense the hydroxyapatite and respond to its bioactivity,” explains Ramille N. Shah, who led the research published in Science Translational Medicine, in a statement. “When you put stem cells on our scaffolds, they turn into bone cells and start to up-regulate their expression of bone specific genes. This is in the absence of any other osteo-inducing substances. It’s just the interaction between the cells and the material itself.”

This astonishing feat, not unlike another recent study developing synthetic blood vessels, has particularly important applications for children, who often struggle with standard bone implants as their bodies continue to grow, meaning they need frequent and often painful replacements. But there is another advantage to the implants: Doctors can control exactly what goes into the ink, including medicines.

“We can incorporate antibiotics to reduce the possibility of infection after surgery,” says Shah. “We also can combine the ink with different types of growth factors, if needed, to further enhance regeneration. It’s really a multi-functional material.”

So far, the implants have been used to repair the spines of mice and rats, as well as a hole in the head of a monkey. It is expected that after extensive trials, the material will reach clinics in five years, though Shah has grander ambitions. She imagines that hospitals will one day have 3D printers, with which they will use the ink to print hyperelastic bone implants tailored to individual patients within 24 hours.