Ceramic-based ink used to print ‘bone’ with living cells

This is an entirely new technique: it uses a 3D printer to construct bone-like structures from calcium phosphate ink, which harden in minutes when placed in water.

While the idea of using a 3D printer to create bone-like structures is not new, this is the first time it has been executed under convenient conditions: namely, at room temperature, complete with living cells, and without the use of harsh chemicals or radiation. The structure is portable.

“This is a unique technology that can produce structures that closely mimic bone tissue,” said Dr Iman Roohani, from the university’s school of chemistry. “It could be used in 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 or tissue is resected.”

The ability to incorporate living cells incorporated into the structure marks a significant advance on previous efforts to 3D-print bone-like structures.

Until now, these efforts have involved first fabricating the structures in a laboratory furnace, using toxic chemicals. This produces a dry material, which is then moved to a clinical setting, where it is washed thoroughly. Only after that are living cells added to it.

“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,” said Professor Kristopher Kilian. “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. There are currently no technologies that can do that directly.”

The ink was developed in a microgel matrix with living cells, taking advantage of a setting mechanism through the crystallisation of its components in water. This converts the inorganic ink into mechanically interlocked bone apatite nanocrystals. Roohani explains: “In other words, it forms a structure that is chemically similar to bone-building blocks.

“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.”

When combined with a collagenous substance containing living cells, it enables the in situ fabrication of bone-like tissues which could be suitable for bone tissue engineering applications; disease modelling; drug screening, and in situ reconstruction of bone defects. The researchers have already attracted interest from surgeons and the medical technology sector.

Although the technology is at an early stage (the next stage will be performing in vivo tests in animal models to ensure that the structures continue to grow), the researchers hope that this process could open up a whole new way of repairing bone tissue.

“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,” said 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.

“This has the potential to radically change current practice, reducing patient suffering and ultimately saving lives.”