Researchers have developed a method to transform human urine into a solid mineral found in bones and tooth enamel.

In a study funded by the U.S. Defense Advanced Research Projects Agency (DARPA), scientists used yeast to break down urine and produce hydroxyapatite — a calcium-based compound commonly used in bones and dental implants.

Hydroxyapatite isn’t just valuable for medical implants. According to the researchers, the material could also be applied in archaeological restoration, as a biodegradable alternative to plastics, and even as a building material. Their findings were published in the journal Nature Communications.

“This process allows us to achieve two goals at once,” said co-author David Kisailus, professor of materials science and engineering at the University of California, Irvine. “On one hand, it helps remove human urine from wastewater streams, reducing environmental pollution and nutrient overload. On the other, it produces a valuable material that can be sold for use in various applications.”

Hydroxyapatite is a hard substance made up of charged calcium, phosphate, and hydroxide molecules. It naturally occurs as the primary component of both bones and teeth. This biocompatibility makes it ideal for medical implants, as it is unlikely to be rejected by the body and can encourage new tissue growth.

However, synthesizing hydroxyapatite is costly, and some traditional production methods generate toxic intermediate chemicals. In mammals like humans, the mineral is secreted by specialized cells called osteoblasts, which absorb calcium phosphate from bodily fluids. Yet, these cells are short-lived and rarely divide, making them impractical for large-scale industrial use.