Using the knitted moulds as a flexible framework or 'formwork', the scientists created a composite called 'mycocrete' which is stronger and more versatile in terms of shape and form, allowing the scientists to grow lightweight and relatively eco-friendly construction materials.
"Our ambition is to transform the look, feel and wellbeing of architectural spaces using mycelium in combination with biobased materials such as wool, sawdust and cellulose," said Dr Jane Scott of Newcastle University.
To make composites using mycelium, scientists mix spores with grains they can feed on and material that they can grow on. This mixture is packed into a mould and placed in a dark, humid, and warm environment so that the mycelium can grow, binding the substrate tightly together.
Once it's reached the right density, but before it starts to produce fruiting bodies such as mushrooms, it is dried out. This process could provide a cheap, sustainable replacement for foam, timber, and plastic, the researchers said.
Mycelium needs oxygen to grow, which constrains the size and shape of conventional rigid moulds and limits current applications. Knitted textiles offer a possible solution: oxygen-permeable moulds that could change from flexible to stiff with the growth of the mycelium.
"Knitting is an incredibly versatile 3D-manufacturing system," Scott said. "It is lightweight, flexible and formable. The major advantage of knitting technology compared to other textile processes is the ability to knit 3D structures and forms with no seams and no waste."
Samples of conventional mycelium composite were prepared by the scientists as controls, and grown alongside samples of mycocrete, which also contained paper powder, paper fibre clumps, water, glycerin and xanthan gum.
This paste was designed to be delivered into the knitted formwork with an injection gun to improve packing consistency: the paste needed to be liquid enough for the delivery system, but not so liquid that it failed to hold its shape.
Tubes for their planned test structure were knitted from merino yarn, sterilised, and fixed to a rigid structure while they were filled with the paste, so that changes in tension of the fabric would not affect the performance of the mycocrete.
Once dried, samples were subjected to strength tests in tension, compression and flexion. The mycocrete samples proved to be stronger than the conventional mycelium composite samples and outperformed mycelium composites grown without knitted formwork. In addition, the porous knitted fabric of the formwork provided better oxygen availability, and the samples grown in it shrank less than most mycelium composite materials do when they are dried, suggesting more predictable and consistent manufacturing results could be achieved.
The team were also able to build a larger proof-of-concept prototype structure – a complex freestanding dome constructed in a single piece without joins that could prove to be weak points, thanks to the flexible knitted form.
"The mechanical performance of the mycocrete used in combination with permanent knitted formwork is a significant result, and a step towards the use of mycelium and textile biohybrids within construction," said Scott.
