Researchers at the University of Washington have developed a new system for turning coffee grounds into a paste that can be used to 3D print objects and then using mushroom spores to create a resilient, fully compostable alternative to plastic.
Only 30 per cent of a coffee bean is soluble in water, and many brewing methods aim to extract significantly less than that. So, of the 700 million kilograms of coffee consumed in the USA in a year, more than 500 million kilograms of grounds are knocked from filters into compost bins or end up in landfill.
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While watching the grounds from her own espresso machine accumulate, Danli Luo, a doctoral student in human-centred design and engineering, saw an opportunity. Coffee is nutrient-rich and sterilised during brewing, so it’s ideal for growing fungus, which, before it sprouts into mushrooms, forms a ‘mycelial skin’. This skin, a sort of white root system, can bind loose substances together and create a tough, water-resistant, lightweight material.
Working with a team at UW, Luo created a paste from coffee grounds and used it to 3D print objects. They inoculated the paste with Reishi mushroom spores, which grow on the objects to form that mycelial skin. The skin turns the coffee grounds – even when formed into complex shapes – into a resilient, fully compostable alternative to plastics. For intricate designs, the mycelium fuses separately printed pieces together to form a single object.
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‘We’re especially interested in creating systems for people like small businesses owners producing small-batch products – for example, small, delicate glassware that needs resilient packaging to ship,’ said Luo. ‘So we’ve been working on new material recipes that can replace things like Styrofoam with something more sustainable and that can be easily customised for small-scale production.’
To create the ‘Mycofluid’ paste, Luo mixed used coffee grounds with brown rice flour, Reishi mushroom spores, xanthan gum (a common food binder found in ice creams and salad dressings) and water. Luo also built a new 3D printer head for the Jubilee 3D printer that UW’s Machine Agency lab designed. The new printer system can hold up to a litre of the paste.
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The team printed various objects with the Mycofluid: packaging for a small glass, three pieces of a vase, two halves of a Moai statue and a two-piece coffin the size of a butterfly. The objects then sat covered in a plastic tub for ten days, during which time the mycelium formed a sort of shell around the Mycofluid. In the case of the statue and vase, the separate pieces also fused together.
The process is the same as that of homegrown mushroom kits: keep the mycelium moist as it grows from a nutrient-rich material. If the pieces stayed in the tub longer, actual mushrooms would sprout from the objects, but instead they’re removed after the white mycelial skin has formed. Researchers then dried the pieces for 24 hours, which halts the fruiting of the mushrooms.
The finished material is heavier than Styrofoam – closer to the density of cardboard or charcoal. After an hour in contact with water, it absorbed only seven per cent more weight in water and dried to close to its initial weight while keeping its shape. It was as strong and tough as polystyrene and expanded polystyrene foam, the substance used to make Styrofoam.
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Although the team didn’t specifically test the material’s compostability, all of its components are compostable (and, in fact, edible, although less than appetising).
Because the Mycofluid requires relatively homogeneous used coffee grounds, working with it at significant scale would prove difficult, but the team is interested in other forms of recycled materials that might form similar biopastes.
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‘We’re interested in expanding this to other bio-derived materials, such as other forms of food waste,’ Luo said. ‘We want to broadly support this kind of flexible development, not just to provide one solution to this major problem of plastic waste.’
The research has been published in 3D Printing and Additive Manufacturing.