Enter Biocement One such material under development is biocement, produced by living microbes through a process known as “microbially induced calcium carbonate precipitation (MICP) [4].” This process is a biochemical transformation orchestrated by soil bacteria like Sporosarcina pasteurii [5]. Unlike traditional cement, biocement is brewed at room temperature [6] using a blend of bacteria, urea, calcium salts, and a structural base such as sand, crushed stone or gravel [5, 7]. S. pasteurii is a species that grows well under alkaline environment and has a high urease activity [5]. Their cytoplasmic urease breaks down the urea (CO(NH2)2) that is transported or diffused into the cell to ammonia (NH3) and carbonic acid (H2CO3), which is equilibrated to bicarbonate ions (HCO3 -) at physiological pH. Because ammonia is a weak base, it accepts protons (H+) and raises the pH of the environment. By Le Chatelier’s principle, this shifts the carbonate equilibrium to generate carbonate ions (CO3² -) that will be transported out of the cell. In the presence of calcium ions from the added salts, calcium carbonate (CaCO3) crystals precipitate out. The bacterial cell walls act as nucleation sites, growing large-sized and high-strength calcium carbonate Introduction In the past few centuries, we have relied on massive factories for producing cement to build our cities — but did you know that scientists are developing a novel way to manufacture cement with living organisms? What is Cement? Cement is a key component of concrete. When it is brought to building sites and mixed with water, cement paste can act as a binder which binds aggregates (small stones used in building) to form concrete [1]. The manufacture of cement requires large amounts of energy. During the process, raw materials are heated to 1,500°C, and tons of carbon dioxide are generated. The cement industry currently accounts for 5–8% of global carbon dioxide emissions [2]. While urban development continues to push the demand for building materials, researchers began to look toward some more eco-friendly ways to produce cement. A Lesson From Nature: Biomineralization Can we learn from nature? In fact, some of the most durable structural materials in nature are the products of biomineralization [3], which can be defined as “a process by which living organisms produce minerals.” Biominerals include phosphates, carbonates and sulfates, with corals, shells, anthills, tooth enamel and antlers being some common examples [3]. As biological reactions always occur under milder conditions, thus avoiding excessive use of energy, bioengineers are interested in identifying real-world applications of the process. 建造會呼吸的「石屎森林」： A Living Scaffold: Biocement The catabolism of urea: CO(NH2)2 + 2 H2O → 2 NH3 + H2CO3 The carbonate equilibrium: H2CO3 ⇌ HCO3 − + H+ ⇌ CO3 2− + 2 H+
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