A Northwestern engineering research team has developed a 3D-printable ink that produces a synthetic implant capable of rapidly inducing bone regeneration and growth.

This hyperelastic “bone” material, whose shape can be easily customized, could be useful for the treatment of bone defects in children. Bone implantation surgery is particularly painful and complicated for children. Often times bone is harvested from elsewhere in the body to replace the missing bone, which can lead to other complications and pain. Metallic implants are sometimes used but are not a permanent fix for growing children.

“Adults have more options when it comes to implants,” says Ramille Shah, assistant professor of materials science and engineering. “Pediatric patients do not. If you give them a permanent implant, you have to do more surgeries in the future as they grow.”

Shah’s 3D-printed biomaterial is a mix of hydroxyapatite (a calcium mineral found naturally in human bone) and a biocompatible, biodegradable polymer that is used in many medical applications, including sutures. The synthetic “bone” material shows great promise in in vivo animal models, which the researchers attribute to its unusual properties: it is robust, majority hydroxyapatite yet hyperelastic and porous at the nano, micro and macro levels.

Cross-section of a 3D-printed adult human femur. Image credit: Northwestern University.Cross-section of a 3D-printed adult human femur. Image credit: Northwestern University.“Porosity is huge when it comes to tissue regeneration because you want cells and blood vessels to infiltrate the scaffold,” Shah says.

While hydroxyapatite has been proven to induce bone regeneration, it is also notoriously tricky to work with. Clinical products that use hydroxyapatite or other calcium phosphate ceramics are hard and brittle. To compensate for that, previous researchers created structures composed mostly of polymers, but this shields the activity of the bioceramic.

Shah’s bone biomaterial, however, is 90% hydroxyapatite by weight and just 10% polymer by weight and maintains its elasticity because of the way its structure is designed and printed. The high concentration of hydroxyapatite creates an environment that induces rapid bone regeneration.

“Cells can sense the hydroxyapatite and respond to its bioactivity,” Shah says. “When you put stem cells on our scaffolds, they turn into bone cells and start to up-regulate their expression of bone-specific genes.”

Another advantage is that the end product can be customized to the patient. In traditional bone transplant surgeries, the bone—after it is taken from another part of the body—must be shaped and molded to fit the area where it is needed precisely.

Using the new synthetic material, however, physicians would be able to scan the patient’s body and 3D print a personalized product. Alternatively, due to its mechanical properties, the biomaterial could also be easily trimmed and cut to size and shape during a procedure.

Shah imagines that hospitals may one day have 3D printers, where they can print customized implants while the patient waits. “The turnaround time for an implant that’s specialized for a customer could be within 24 hours,” she says.