Scientists have developed a method that can convert human urine into hard minerals in bone and teeth enamel.
Funded by the US military’s Advanced Defense Research Projects Agency (DARPA), the study uses yeast to break down urine and divides it into hydroxyapatite, a form of calcium used in bone and dental implants.
Also, hydroxyapatite is not useful only for implants. The researcher said the material could be used in archaeological recovery, as a biodegradable alternative to plastics and as a building material for construction projects. They published their findings in the Nature Communications Journal on May 6th.
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“This process achieves two goals at the same time,” said David Kisailus, co-author of Irvine, professor of materials science and engineering at the University of California, in a statement. “On the one hand, it helps to remove human urine from wastewater flows and alleviate environmental pollution and unwanted nutrient accumulation, while on the other hand, it produces materials that can be sold commercially for use in a variety of settings.”
Hydroxyapatite is a strong solid containing charged molecules of calcium, phosphoric acid and hydroxide. It occurs naturally as it is a major component of both bone and teeth. This can be useful in medical implants. This is because it is unlikely to be rejected by the body and can stimulate further growth.
However, synthesis of minerals is expensive, and intermediate chemicals are toxic to the way they do so. In mammals such as humans, hydroxyapatite is secreted by a special cell called osteoblasts that draw calcium phosphate from body fluids. However, these cells do not live too long or divide frequently, making them difficult to utilize on an industrial scale.
Related: Is cavities “contagious”? Dental yeast can pass from mom to baby
To find another way to produce hydroxyapatite, researchers turned to Saccharomyces Boulardii, a type of yeast. Yeast species, found in the skins of tropical fruits like lychee, are commonly used as probiotics.
By applying some genetic adjustments to this yeast, scientists converted it into what they called “osteoy yeast,” breaking down the urea and releasing hydroxyapatite. Urea is a waste that forms when the body breaks down proteins, and is then filtered by the kidneys and excreted in the urine. The process of converting urea produces grams of hydroxyapatite per liter of urine, scientists reported.
“This process of producing hydroxyapatite, or bone mineral, takes less than a day,” says Kisailus. “The fact that yeast is used as a chassis is the fact that it can be placed in a large bat at a relatively low temperature – think of a beer that is made in the fermentation process and is well-expanded – this shows that there is an additional benefit of being able to do it easily without the need for a major infrastructure and allowing access to the developing economy.”
With the methods proven, scientists are now investigating how to make it work on a large scale. They say they want to apply the process to 3D printed hydroxyapatite-based materials for implants, plastics, construction and energy applications.
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