Good as bone

Australian scientists have 3D-printed bone-like structures containing living cells, which may create a whole new way for surgeons to treat and repair bone tissue.

The new study, published in Advanced Functional Materials, describes a unique 3D printing technique. It uses a special ceramic-based ink to produce a soft structure that closely mimics bone tissue – and when placed in water or exposed to body fluids, it hardens within minutes.

While other bone-mimicking structures have previously been 3D printed, this is the first time that such a material has been created at room temperature without the use of harsh chemicals or radiation. It also incorporates living tissue into the structure and is portable.

Co-lead researcher Kristopher Kilian, from the University of New South Wales (UNSW), explains that until now, fabricating a piece of bone-like material was an involved process requiring high-temperature furnaces and toxic chemicals in a laboratory setting. Living tissue was added later, when the replacement piece was taken into a clinical setting.

“The cool thing about our technique is you can just extrude it directly into a place where there are cells, like a cavity in a patient’s bone,” Kilian says. “We can go directly into the bone where there are cells, blood vessels and fat, and print a bone-like structure that already contains living cells, right in that area.”

This is currently the only technology that can directly achieve this.

The technique is known as ceramic omnidirectional bioprinting in cell-suspensions (COBICS). It mimics the natural bone formation process – called ossification – in which specialised connective tissues secrete a gelatinous substance called osteoid. Inorganic salts are then deposited on it to form hard, mineralised bone.

The fabrication process uses ink made up of calcium phosphate that transforms into a structure chemically similar to bone-building blocks – a microgel matrix with living cells – which then “sets” by crystallising in aqueous environments.

“The ink is formulated in such a way that the conversion is quick, non-toxic in a biological environment and it only initiates when ink is exposed to the body fluids, providing an ample working time for the end-user, for example, surgeons,” explains Iman Roohani, the other lead researcher also from UNSW.

Roohani foresees “clinical applications where there is a large demand for in-situ repair of bone defects such as those caused by trauma, cancer, or where a big chunk of tissue is resected”.

Surgeons of the future may even have 3D printers in the operating theatre.

“This advance really paves the way for numerous opportunities that we believe could prove transformational – from using the ink to create bone in the lab for disease modelling, as a bioactive material for dental restoration, to direct bone reconstruction in a patient,” says Kilian.

“I imagine a day where a patient needing a bone graft can walk into a clinic where the anatomical structure of their bone is imaged, translated to a 3D printer, and directly printed into the cavity with their own cells.”

The next step is to perform in vivo tests in animal models, to see whether the living cells in the printed structure continue to grow after being implanted.

The Royal Institution of Australia has an Education resource based on this article. You can access it here.