3D printing of mycelium engineered living materials using a waste-based ink and non-sterile conditions

There is an urgent need to change the way society produces and fabricates materials. Among the sustainable processes developed to date, 3D printing enables limited generation of waste. Living materials that are grown by microorganisms is also an interesting approach to fabricate biodegradable materials sustainably. 3D printing of living materials is nevertheless challenged by a high barrier to entry due to stringent sterilization requirements. In this study, the authors use a waste ingredient, coffee grounds, to fabricate mycelium materials using 3D printing in ambient conditions. Mycelium is the vegetative parts of the fungi which forms an interconnected network, covering air-material interfaces with a dense skin. An agar gel was chosen as the printing medium and supplemented with coffee grounds, malt and peptone to double the growth rate and density of the mycelium by Pleurotus ostreatus. Despite the jelly nature of the agar-based ink, 3D printing with a resolution of about 1 mm can be achieved using direct ink writing. The growth of the mycelium embedded in the ink was studied over 28 days and demonstrated that the mycelium was efficient in reinforcing the printed part, doubling its compressive modulus up to 60 kPa. Furthermore, the objects created by this ink exhibit self-healing and can be used for gluing components together. The approach taken in this work could be adapted by the user to accommodate for functionality requirements and the available local resources, thereby addressing some of the most pressing sustainable development goals.