Biocompatible Material Enables 3-D Printed Bone Implants

Photo by Adam E. Jakus, Northwestern University.


Photo by Adam E. Jakus, Northwestern University.

Researchers at Northwestern University have developed a 3-D printable ink for producing synthetic bone implants that rapidly induce bone regeneration and growth. The hyperelastic material can be customized easily, the researchers said, which is particularly useful for children who need more adaptable and less painful solutions than grafts from elsewhere in the body.

“Adults have more options when it comes to implants,” said Ramille N. Shah, assistant professor of materials science and engineering and of surgery, who led the research. “Pediatric patients do not. If you give them a permanent implant, you have to do more surgeries in the future as they grow. They might face years of difficulty.”

The material is a mix of hydroxyapatite and a biocompatible, biodegradable polymer used in many medical applications such as sutures. Among other areas of the body, it could be used to replace jawbone lost as a result of periodontal disease or oral cancer.

“We hope that this technology may be able to help with these types of injuries,” Shah said. “Of course, many studies still need to be performed for these particular indications, but it is our hope that our material can replace and help remodel any type of bone defect.”

So far, the researchers say the material shows great promise in in vivo animal models, with its success due to the printed structure’s unique properties. Though it is mostly hydroxyapatite, it is hyperelastic, robust, and porous at the nano, micro, and macro levels.

“Porosity is huge when it comes to tissue regeneration, because you want cells and blood vessels to infiltrate the scaffold,” said Shah. “Our 3-D structure has different levels of porosity that are advantageous for its physical and biological properties.”

Hydroxyapatite has been proven to induce bone regeneration, but it is difficult to work with. Clinical products that use hydroxyapatite or other calcium phosphate ceramics are hard and brittle. Previous researchers have created structures mostly comprising polymers to compensate, but this shields the bioceramic’s activity.

Northwestern’s biomaterial is 90% hydroxyapatite by weight and 10% polymer by weight, yet it still 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, Shah said, can sense the hydroxyapatite and respond to its bioactivity.

“When you put stem cells on our scaffolds, they turn into bone cells and start to upregulate their expression of bone-specific genes,” Shah said. “This is in the absence of any other osteo-inducing substances. It’s just the interaction between the cells and the material itself.”

Other substances could be combined into the ink as well. The 3-D printing is performed at room temperature, so the researchers incorporated other elements into the ink. Adding antibiotics, for example, would reduce the possibility of infection after surgery. The ink could be combined with different growth factors to further enhance regeneration as well.

“It’s really a multifunctional material,” Shah said.

Most importantly, the researchers said, is that the end product can be customized to each patient. Typically, bone taken from other parts of the body must be shaped and molded to fit where it is needed. Using the new material, physicians could scan the patient’s body and 3-D print a personalized product.

And due to its mechanical properties, the biomaterial could be trimmed and cut to size and shape easily during a procedure. This is both faster and less painful than using autograft material, the researchers said. Furthermore, Shah expects that hospitals one day may have 3-D printers to produce customized implants while the patient waits.

“The turnaround time for an implant that’s specialized for a customer could be within 24 hours,” said Shah. “That could change the world of craniofacial and orthopedic surgery and, I hope, will improve patient outcomes.”

Before then, Shah anticipates more preclinical testing in different bone defect applications to further validate efficacy.

“These are necessary steps to get US Food and Drug Administration approval and advance the technology toward human use,” said Shah. “We hope to get to human clinical trials within 5 years, but a lot of biomedical research like this is highly dependent also on getting sufficient funding support to carry out the necessary in vivo studies.”

The study, “Hyperelastic ‘Bone’: A Highly Versatile, Growth Factor-Free, Osteoregenerative, Scalable, and Surgically Friendly Biomaterial,” was published by Science Translational Medicine.

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