Nature and Technology: Walls That Can Grow Plants

The relationship between architecture and nature is complex. If, on the one hand, we enjoy framing nature as art in our homes; on the other hand, we try at all costs to avoid the presence of obstructive “real” nature in our walls and structures, which can be damaged by roots and leaves. At the same time, we use green roofs, vertical gardens and flower boxes to bring cities closer to nature and improve people’s wellbeing; but we also construct buildings with materials that are completely dissociated from fauna and flora. Although the advancement of biomaterials and new technologies is gradually changing this, we should nevertheless ask ourselves whether the structures and buildings we occupy need to be separated from the nature that surrounds them. This was the question that led researchers at the University of Virginia (UVA) to develop geometrically complex 3D-printed soil structures on which plants could grow freely.

The team developed a method for 3D printing with bio-based materials, incorporating circularity into the process. Instead of traditional concrete or plastic materials, the raw material used is the soil itself and local plants mixed with water and inserted into the printer to form walls and structures. By combining the speed, cost efficiency, and low energy demands with locally-sourced bio-based materials, the process of additive manufacturing can evolve and create 3D-printed structures that are completely biodegradable, returning to the earth at the end of its useful lives.

The team consisted of Ji Ma, Assistant Professor of Science and Material Engineering at the School of Engineering and Applied Science at UVA; David Carr, Research Professor at the Department of Environmental Sciences at UVA; and Ehsan Baharlou, Assistant Professor at the UVA School of Architecture, as well as Spencer Barnes, a student at the University. Barnes conducted experiments on the most conducive mixtures for printing, through two approaches: printing soil and seeds in sequential layers or mixing seeds with the soil before printing. Both approaches worked well.

As Ji Ma points out in this article published by the University, “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.”

David Carr, in turn, was responsible for finding the ideal composition of the soil for printing and the most conducive plant species. These findings would ensure that the plants could prosper within the structure and the soil could accumulate organic matter and collect necessary nutrients. He proposed plants that grow naturally in areas that seem to be on the outer limits of life – native plants that grow practically on naked rocks. The chosen species was Sedum (Stonecrop), commonly used in green roofs. The physiology of this species is similar to the cactus and it can survive with very little water, and can even dry up to some extent in order to recover.

The team published their first results earlier this year in the paper entitled 3D Printing of Ecologically Active Soil Structures. Research around the technology has continued and the next steps include soil “ink” formulations for larger structures with at least one floor, seeking to anticipate problems such as soil breakage in larger tensions. In addition, researchers have also experimented with various layers within a wall panel in order to isolate the inner wall and maintain the moisture of the outer wall. Although it is just a start, it can be a step towards keeping nature closer to human manufacturing.