Nature can create biocomposites with high structural complexity and mechanical integrity from a small number of elements. Natural materials have unparalleled mechanical properties due to the unique interplay of hierarchical structure and locally varying composition.

It has an extraordinary talent for making composite materials that are both light and strong, porous and rigid, such as mollusc shells or bone. However, producing such materials in a laboratory or factory is extremely difficult, especially when environmentally friendly materials and processes are used.

Nature provided a solution for researchers in the School of Engineering’s Soft Materials Laboratory. They are the first to develop a 3D printable ink that contains Sporosarcina pasteurii, a bacteria that, when exposed to a urea-containing solution, initiates a mineralization process resulting in calcium carbonate (CaCO3). As a result, the researchers’ ink, called BactoInk, can be used to 3D print virtually any shape, which will then gradually mineralize over the course of a few days.

Lab head Esther Amstad said: “3D printing in general is becoming increasingly important, but the number of materials that can be 3D printed is limited for the simple reason that inks have to meet certain flow conditions.”

“For example, they have to behave like a solid at rest while still being extrudable through a 3D printing nozzle – a bit like ketchup. 3D printing inks with small mineral particles have been used before to meet certain flow criteria. However, the resulting structures tend to soften or shrink on drying, resulting in 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 with our BactoInk, which is then mineralized in a second, separate step. The mineralization process initiated by the bacteria in the scaffold results in an end product with a mineral content of more than 90% after about four days.”

This allows a strong and resilient biocomposite to be made using a standard 3D printer and natural materials, without the extreme temperatures required for ceramic production. The final products are immersed in ethanol at the end of the mineralization process; hence they no longer contain living bacteria.

The procedure was recently described in the journal Materials Today. It describes the first 3D printing ink that used bacteria to induce mineralization.

The concept of the Soft Materials Lab has several potential applications ranging from art and ecology to biomedicine. Amstad believes that BactoInk, which can also be injected directly into a mold or target location – such as a crack in a vase or a chip in a statue – can greatly simplify the restoration of artworks. The ink’s mechanical properties provide the strength and shrinkage resistance needed to repair an artwork while preventing further damage during the restoration process.

Amstad said, “The versatility of 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 current synthetic composites ,”

The environmentally friendly components used in this procedure along with the ability to create a mineralized biocomposite. It is a promising candidate for creating artificial corals to help regenerate damaged marine reefs. Finally, the structure and mechanical properties of the biocomposite are similar to bone, which could make it attractive for future biomedical applications.

The result shows that they were 3D-printable bacteria-loaded microgels that can be converted into macroscopic organic solid/inorganic composites with mineral content by using an energy-efficient MICP process.

Magazine reference:

  1. Hirsch, M., et al. 3D Printing of Living Structural Biocomposites. Materials Today. DOI: 10.1016/j.mattod.2023.02.001