by Nature has an unusual knack for producing composite materials that are light and strong at the same time, porous and rigid – like shells or mollusc bone. But producing such materials in a laboratory or factory — especially using environmentally friendly materials and processes — is extremely challenging.
Researchers in the School of Engineering’s Soft Materials Laboratory turned to nature for a solution. Contains 3D printable ink Sporosarcina pasteurii: a a bacterium that, when exposed to a solution containing urea, stimulates a mineralization process that produces calcium carbonate (CaCO3). The result is that the researchers can use their ink – called BactoInk – to print almost any shape, which will gradually mineralize over a few days.
“3D printing is of increasing importance in general, but the number of materials that can be 3D printed is limited for the simple reason that inks must meet certain flow conditions,” explains laboratory head Esther Amstad. “For example, they have to behave like a solid when they are at rest, but still be extruded through a 3D printing nozzle – kind of like ketchup.”
Amstad explains that 3D printing inks containing small mineral particles have previously been used to meet some of these flow criteria, but the resulting structures tend to soften, or shrink when dry, leading to cracking and loss of control over the shape of the final product.
“So we came up with a simple trick: instead of printing minerals, we printed a polymer scaffold using our BactoInk, which then mineralized in a second, separate step. After about four days, the mining process inspired by the bacteria resulting in a final product scaffold with a mineral content of over 90%.”
The result is a strong and resilient bio-composite, which can be produced using a standard 3D printer and natural materials, and without the extreme temperatures often required to manufacture ceramics. The final products no longer contain live bacteria, as they are submerged in ethanol at the end of the mineralization process.
The method, which describes the first 3D printing ink that uses bacteria to stimulate mineralization, was recently published in the journal. Topics Today.
Patching art, coral reefs, or bone
The Soft Materials Lab approach has several potential applications across a wide range of fields, from art and ecology to biomedicine. Amstad believes that the restoration of works of art could be greatly facilitated with BactoInk, which can be injected directly into a mold or target location — a crack in a vase or a chip in a sculpture, for example. The mechanical properties of the ink provide the strength and shrinkage resistance necessary to repair artwork, as well as prevent further damage during the restoration process.
Because the method only uses environmentally friendly materials, and its ability to produce a mineral biocomposite, it is also a promising candidate for building artificial corals, which can be used to regenerate damaged marine reefs. Finally, it may be interesting for future biomedical applications because the structure and mechanical properties of the biocomposite mimic bone.
“The flexibility of BactoInk processing, together with the low environmental impact and excellent mechanical properties of the mineralized materials, opens up many new possibilities for making lightweight, load-bearing compounds that are more like natural materials than today’s synthetic compounds, ” Amstad summarizes.
