A new synthetic material called hyperelastic bone, or HB, could be "the next breakthrough" in reconstructive surgery, new research shows. The HB can be implanted under the skin as a scaffold for new bone to grow on, or used to replace lost bone matter altogether. Though it hasn’t been tested in humans yet, early experiments on animals appear to have been successful, with "quite astounding" results, according to the researchers.

The hyperelastic bone is flexible and can be easily shaped

The hyperelastic bone, described in a study published today in Science Translational Medicine, is mostly made from a naturally occurring mineral called hydroxyapatite. Hydroxyapatite — a form of calcium found in bone and already used in reconstructive surgeries — is extremely brittle, but the researchers mixed it with a polymer to add flexibility. They then 3D print bone graft from this new, promising material and tested it in various experiments.

"The first time that we actually 3D printed this material, we were very surprised to find that when we squeezed or deformed it, it bounced right back to its original shape," Ramille Shah, one of the study’s authors and an assistant professor of materials science at Northwestern University, said during a press call.

Hyperelastic bone is much more flexible than traditional materials. (Image credit: Adam Jakus)

The hyperelastic bone can be easily cut, rolled, folded, and pressed into areas missing bone material without glue or stitches, Shah said. It is also highly porous and absorbent — which is crucial for bone graft material to encourage the growth of blood vessels into the surgery area. (Without veins and capillaries carrying blood to the target site, the surrounding tissue dies.)

The scientists tested the hyperelastic bone in a range of experiments. They placed human stem cells into a number of scaffolds 3D-printed from hyperelastic bone (the same type of structure that might be used as an implant in surgery). The cells not only grew without any difficulty on the scaffolds, filling up the available space in a matter of weeks, but also ended up producing their own bone minerals.

"It went from a synthetic scaffold to natural minerals being created by the cells themselves," study co-author Adam Jakus, a post-doctoral fellow at Northwestern, said during a press call. In another experiment, the researchers implanted hyperelastic bone under the skin of a mouse. Again, the cells responded well, with the HB "rapidly integrating" with the mouse tissue without any immune responses or inflammation, said Jakus.

Hyperelastic bone can be 3D-printed to make surgical implants tailored to the individual. (Image credit: Adam Jakus)

The researchers also tested the hyperelastic bone in real surgical situations. The HB was used to fuse two vertebrae together in the spine of a rat, and then to replace a section of unhealthy bone in the skull of a rhesus monkey. In both cases, the implant fully integrated with the host tissue, encouraging the growth of blood vessels and even some new bone.

Human testing could happen within five years

However successful, these experiments are still limited in number, and will need to be confirmed and reproduced in large-scale studies with animals. It also obviously has to be tested in humans, which Shah said she hopes to do within five years.

The hyperelastic bone is particularly promising because it’s synthetic, so it’s cheap to produce. It can also be mixed and 3D-printed at room temperature, which simplifies its manufacture. And because the HB is 3D printed, bone grafts made from it can be tailored to individual patients. Finally, it’s easy to package, store, and ship, with an estimated shelf-life of around a year, the researchers say.

It’s ideal for developing countries, "where you could just ship it way ahead of time, have it on the shelf until it's needed rather than having to create a complex biomaterial that needs to be heavily refrigerated or frozen," said Jakus. In developing countries, "those types of facilities may not be accessible, so being able to open a package and to use the material is fantastic."