Carbonic anhydrase is one of the fastest enzymes in biology. It catalyzes the hydration of carbon dioxide — CO₂ + H₂O → H₂CO₃ — at rates exceeding a million reactions per second. In red blood cells, it converts CO₂ from metabolic waste into a soluble form for transport to the lungs. In kidneys, it regulates acid-base balance. In the stomach lining, it supplies protons for hydrochloric acid production. The enzyme is ancient, ubiquitous, and so unremarkable that it rarely appears outside biochemistry textbooks.
Nima Rahbar's group at Worcester Polytechnic Institute used carbonic anhydrase to make concrete (Wang et al., Matter, 2025). They deployed trace amounts of the enzyme on a polymer scaffold, exposed the scaffold to atmospheric CO₂, and let the enzyme do what it always does: convert CO₂ into carbonate. The carbonate mineralized into solid particles. The particles, bound together under mild conditions, formed a structural material — enzymatic structural material, ESM — that cures in hours rather than weeks.
The environmental arithmetic is striking. One cubic meter of conventional concrete emits 330 kilograms of CO₂, mostly from the calcination of limestone at 1,450°C. One cubic meter of ESM sequesters more than 6 kilograms. The process runs at ambient temperature. Concrete production accounts for roughly 8% of global CO₂ emissions. ESM inverts the sign.
But the structural observation is not about carbon. It is about what the enzyme produces and what the engineer keeps.
In biology, carbonic anhydrase's products are intermediates. The carbonate it generates is consumed — transported, buffered, titrated, recycled. No organism accumulates the mineral output of carbonic anhydrase as a permanent structure. The enzyme's product is transient by design: useful precisely because it flows.
In ESM, the enzyme's product is the structure. The carbonate precipitates, mineralizes, and stays. What biology treats as an intermediate, engineering treats as an endpoint. The enzyme doesn't know the difference — it catalyzes the same reaction regardless of context. But the context determines whether the product is consumed or accumulated. In one context, carbonate is a message (carry this CO₂ to the lungs). In the other, it is a brick.
The general principle: biological mechanisms evolved for throughput, not storage. They produce what the organism needs, when it needs it, in amounts that will be used immediately. Extracting a biological mechanism and repurposing it for accumulation — keeping the product instead of consuming it — converts a metabolic cycle into a manufacturing process. The chemistry is identical. The difference is whether anyone picks up the output.
Concrete has always been mineralization. Portland cement hydrates into calcium silicate hydrate — a mineral. The difference with ESM is not the end product (mineral structure) but the energy path to get there. Limestone calcination requires 1,450°C. Enzymatic mineralization requires an enzyme and ambient CO₂. The organism solved the energy problem billions of years ago. The engineer borrowed the solution and changed what happens to the output.