Researchers 3D-print walls that can grow plants
Image credit: Tom Daly
University of Virginia researchers have invented a method of 3D printing with seed-impregnated soil, which could be used to build walls and roofs where plants can grow.
By combining soil and seeds into 3D-printable "soil inks", the University of Virginia scientists believe greenery could be built into the very fabric of architectural features rather than just layered on top.
To build these green walls, the UVA research team is combining additive manufacturing’s speed, cost efficiency and low energy demands with locally resourced, bio-based materials. The team has already had success covering these materials in greenery, leading the team to compare the prototypes to "oversized Chia Pets".
This construction material has the potential to reduce the need for more emissions-intensive building materials and replace them with a circular alternative, which the researchers say can be can be reused again and again.
"We are working with local soils and plants mixed with water," said Ehsan Baharlou, an assistant professor at UVA's School of Architecture. "The only electricity we need is to move the material and run a pump during printing. If we don't need a printed piece or if it isn't the right quality, we can recycle and reuse the material in the next batch of inks."
This solution could pave the way for carbon-neutral buildings as their plant covering would draw down carbon dioxide from the atmosphere.
Moreover, building elements such as green walls and roofs could be constructed using this method, bringing benefits like natural insulation, flood prevention and green spaces for people, pollinators and other animals, according to UVA.
“Why do we have to make it so that the structure or building is separate from the nature it sits in?” asked Ji Ma, an assistant professor of materials science and engineering at UVA’s School of Engineering and Applied Science.
Initially, the UVA researchers used their method to create a series of small, self-supporting structures that resemble beehives. After this was done successfully, the team moved to build more complex structures, such as domes.
Barnes conducted experiments with soil-based inks, supported by a University of Virginia Harrison Grant. Using a desk-sized 3D printer, he explored two approaches, printing soil and seed in sequential layers and mixing seed and soil before printing. Both approaches worked. Barnes produced a cylindrical prototype, about the size of a soda can, which looked a bit like a Chia pet.
These collective efforts revealed that 3D-printed soil structures can support plant growth but would likely be limited to plants that can survive with little water.
“3D-printed soil tends to lose water more quickly and keeps a stronger grip on the water it has,” Ma said. “Because 3D printing makes the environment around the plant drier, we have to incorporate plants that like drier climates. The reason we think this is the case is because the soil gets compacted. When the soil is squeezed through the nozzle, air bubbles are pushed out. When the soil loses air bubbles, it holds onto water more tightly.”
To determine which plants can be grown in 3D-printed soil, Barnes explored the relative availability of water held in soil over time, in combination with the number of energy plants needed to extract the water.
The team settled on using stonecrop as a good candidate for 3D-printing soil structures. Stonecrop, formally known as genus sedum, is commonly used in green roof settings. Stonecrop’s physiology is similar to the cactus. It can survive on very little water, dry out and desiccate to some degree, and then recover.
The researchers' prototypes begin to resemble ordinary raw-earth structures. However, they sprout and become covered in greenery after a few days.
The findings of the experiment were published in the journal Additive Manufacturing.
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