Scientists have developed a yeast-based system capable of converting human urine from wastewater into hydroxyapatite (HAp), a biocompatible material with a range of applications.

HAp is a valuable substance used in dental and bone implants, the preservation of archaeological artifacts, and various other fields.

A study published in Nature Communications details a techno-economic analysis of this method, which transforms urine-a significant pollutant of watersheds-into HAp, a calcium phosphate mineral. The HAp market is projected to exceed $3.5 billion by 2030.

According to study coauthor David Kisailus, a materials science and engineering professor at the University of California, Irvine, “This process achieves two goals at the same time.”

“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,” Kisailus explains.

The research team, including scientists from Lawrence Berkeley National Laboratory, the University of Illinois Urbana-Champaign, Hokkaido University (Japan), and Tokyo University of Agriculture and Technology, outlined the development and assessment of a biologically inspired system using synthetic yeast cells, called “osteoyeast,” to facilitate the urine-to-HAp conversion.

In mammals, osteoblasts extract calcium phosphate from bodily fluids, processing and secreting it as HAp. Though, the researchers deemed osteoblasts unsuitable for large-scale industrial hap production. Rather, they utilized osteoyeast, which employs enzymes to break down urea and elevate the pH of its surroundings. This process prompts the yeast to accumulate calcium and phosphate within tiny cavities, which are then secreted and crystallized into HAp.

The scientists discovered that their method can yield up to 1 gram of hap per liter of urine.

“This process to yield hydroxyapatite, or bone mineral, takes less than one day,” kisailus states.

Kisailus added, “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.”

Kisailus, whose background includes extensive research into crystal growth mechanisms and the creation of inorganic crystalline materials using biological and bio-inspired techniques, said his primary role was to assess crystallization pathways within the osteoyeast platform.

The researchers noted that HAp composites are lightweight and possess significant mechanical strength, toughness, and durability. Economical, large-scale production of synthetic hydroxyapatite from urine could offer a renewable and biodegradable substitute for materials like plastics and other construction materials.

“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 says.

“We are currently developing strategies to leverage his yeast platform with our 3D printing and structural knowledge to make multifunctional architected materials.”

The US Department of Energy, the Defense Advanced Research Projects Agency, and the Air Force Office of Scientific Research provided financial support for the project.

“This process achieves two goals at the same time…it produces a material that can be commercially marketed for use in a variety of settings.”

Hydroxyapatite: Uses, Benefits, and production

Hydroxyapatite (HAp) is a naturally occurring mineral form of calcium apatite with the formula Ca₅(PO₄)₃(OH). It is indeed a major component of bone and teeth, making it biocompatible and widely used in medical applications. Here’s a closer look: