Strong material from bacteria

Qiming Wang and researchers at the USC Viterbi School of Engineering are harnessing living bacteria to create engineering materials that are strong, tolerant, and resilient. The research is published in Advanced Materials. “The materials we are making are living and self-growing,” said Wang, the Stephen Schrank Early Career Chair in Civil and Environmental Engineering and assistant professor of civil and environmental engineering in the Sonny Astani Department of Civil and Environmental Engineering (CEE). The researchers work with specific bacteria, S. pasteurii known for secreting an enzyme called urease. When urease is exposed to urea and calcium ions, it produces calcium carbonate, a fundamental and strong mineral compound found in bones or teeth. “The key innovation in our research,” said Wang, “is that we guide the bacteria to grow calcium carbonate minerals to achieve ordered microstructures which are similar to those in the natural mineralized composites.” Wang added: “Bacteria know how to save time and energy to do things. They have their own intelligence, and we can harness their smartness to design hybrid materials that are superior to fully synthetic options.

Combining living bacteria and synthetic materials, Wang said this new living material demonstrates mechanical properties superior to that of any natural or synthetic material currently in use. This is largely due to the material’s bouligand structure, which is characterized by multiple layers of minerals laid at varying angles from each other to form a sort of “twist” or helicoidal shape. This structure is difficult to create synthetically. In order to build the material, the researchers 3-D printed a lattice structure or scaffolding. This structure has empty squares within it and the lattice layers are laid at varying angles to create scaffolding in line with the helicoidal shape. The bacteria are then introduced to this structure. There the bacteria will secrete urease, the enzyme which triggers formations of calcium carbonate crystals. These grow from the surface up, eventually filling in the tiny squares or voids in the 3-D printed lattice structure. Bacteria like porous surfaces, Wang said, allowing them to create different patterns with the minerals. The living materials are relatively lightweight, also offering options for defense applications like body armor or vehicle armor. “This material could resist bullet penetration and dissipate energy from its release to avoid damage,” said Yipin Su, a postdoc working with Wang.

Source: USC news release