Researchers in Switzerland have developed an ink that could potentially 3D print virtually any shape and gradually mineralize in a few days.

The researchers operate in the Soft Materials Laboratory in the School of Engineering at EPFL Lausanne, also known as the Swiss Federal Institute of Technology Lausanne.

Their 3D printable ink contains Sporosarcina pasteurii. This bacterium, when exposed to a urea-containing solution, triggers a mineralization process that produces calcium carbonate (CaCO₃). The researchers say they can use their “BactoInk” to 3D print a shape that gradually mineralizes over a handful of days.

Among other applications, the bio-composite produced by this process has structure and mechanical properties that mimic those of bone. The team believes this could work in future biomedical applications. They published their findings in the journal Materials Today.

“3D printing is gaining increasing importance in general, but the number of materials that can be 3D printed is limited for the simple reason that inks must fulfil certain flow conditions,” said lab head Esther Amstad. “For example, they must behave like a solid when at rest, but still be extrudable through a 3D printing nozzle — sort of like ketchup.”

How the 3D printed product works

According to Amstad, 3D printing inks contain small mineral particles previously used to meet certain flow criteria. However, resulting structures tend to come out soft or shrink upon drying. This leads to cracking and loss of control over the shape of the final product.

The research team decided to print a polymeric scaffold using the BactoInk instead of printing minerals. This scaffold mineralizes in a second, separate step. After about four days, the process triggered by bacteria in the scaffold leads to a final product with a mineral content higher than 90%. According to the researchers, the process results in a strong, resilient bio-composite. A standard 3D printer and natural materials can produce it without the extreme temperatures often required for manufacturing ceramics.

Final products are submerged in ethanol at the end of the mineralization process and do not contain living bacteria.

“The versatility of the BactoInk processing, combined with the low environmental impact and excellent mechanical properties of the mineralized materials, opens up many new possibilities for fabricating lightweight, load-bearing composites that are more akin to natural materials than to today’s synthetic composites,” Amstad said.