Dental professional examining a model of a tooth implant under clinic light. (representiational image) sorn340/iStock
Human urine is often dismissed as waste. But in large volumes, it poses serious environmental risks by overloading water systems with excess nutrients.
Now, a team of scientists has found a way to turn this problem into an opportunity by transforming urine into a valuable medical resource.
Researchers from the University of California, Irvine, along with collaborators from U.S. and Japanese institutions, have engineered a synthetic yeast system that converts urine into hydroxyapatite (HAp).
This biocompatible calcium phosphate mineral is widely used in bone and dental implants, archaeological restoration, and biodegradable materials.
Tackling two problems with one process
“This process achieves two goals at the same time,” said co-author David Kisailus, UC Irvine professor of materials science and engineering. “On the one hand, it helps remove human urine from wastewater streams, mitigating environmental pollution and the buildup of unwanted nutrients; and on the other hand, it produces a material that can be commercially marketed for use in a variety of settings.”
Urine’s high nutrient load can damage watersheds if left untreated. The team’s process neutralizes that risk while producing a substance projected to reach a $3.5 billion market value by 2030.
Synthetic yeast mimics natural bone-building cells
In mammals, bone-forming cells called osteoblasts draw calcium phosphate from body fluids to produce HAp. But these natural cells can’t support large-scale production.
To overcome that, the team created “osteoyeast,” a synthetic yeast strain that mimics osteoblast behavior.
These cells break down urea to increase the pH, triggering internal cavities to gather calcium and phosphate.
The material then crystallizes into hydroxyapatite and is secreted outside the cell. The process yields up to 1 gram of HAp per liter of urine.
“This process to yield hydroxyapatite, or bone mineral, takes less than one day,” Kisailus said. “The fact that it uses yeast as a chassis, which is inexpensive and can be placed in large vats at relatively low temperatures – think about beer that’s made via fermentation processes and is well scaled – shows that this can be done easily without major infrastructural needs, and that has the added benefit of making it accessible to developing economies.”
Using yeast also means this system could be deployed in regions where high-tech manufacturing isn’t feasible, making advanced medical materials more accessible.
HAp is known for being lightweight, strong, and durable, which is ideal for implants and restoration. But the team envisions wider use.
“I am continuing to work with Professor Yasuo Yoshikuni from Lawrence Berkeley Laboratory, a corresponding author of this paper, to make other materials using this process, including materials for energy-based applications,” Kisailus said. “We are currently developing strategies to leverage his yeast platform with our 3D printing and structural knowledge to make multifunctional architected materials.”
The project received funding from the U.S. Department of Energy, the Defense Advanced Research Projects Agency, and the Air Force Office of Scientific Research.
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