Three-dimensional printing of living material

Unlike conventional synthetic materials, which degrade over time, biological materials such as silk, cellulose, and wood can grow, regenerate, and adapt to their environment. For nearly two decades, that fact has inspired the creation of novel synthetic materials. By combining material-producing microorganisms and abiotic building blocks, researchers have made self-healing concretes, antibiotic-releasing surfaces, and other custom-engineered materials.

André Studart of ETH Zürich, Kunal Masania of Delft University of Technology, and their colleagues have developed a new approach for making living materials: by three-dimensionally printing hydrogel “inks” loaded with mycelia, the rootlike structures of a fungus that absorbs nutrients from the soil. The printing process provides a mechanism for building a grid-like architecture into any geometry of choice, and the fungal mycelia in the hydrogel encode the biological machinery needed for the hydrogel to grow or regenerate. To harness that potential, Studart, Masania, and coworkers printed mechanically robust lattice structures, in which water and nutrients had been incorporated in the hydrogel for fungal growth. The implanted fungi grew through open air gaps in the lattice and formed a network of elongated cells, each called a hypha, in the printed object.

In the researchers’ experiments, the hyphae were able to grow across macroscopic defects in the lattice—cracks up to 2 mm across. And so long as the fractured parts of the lattice had sufficient nutrients, the mycelial film healed into stronger and stiffer structures. On each piece, the front of the hypha grew across the lattice at a rate of 0.6–0.7 mm/day. Besides self-healing, the researchers demonstrated that the growth of their mycelium network could be used to merge differently printed hydrogels into a single, more complex object. The confocal microscopy images here illustrate the potential of the mycelium-laden hydrogels. The third object is formed by combining the first two. And the fourth object in the set shows a robotic gripper. (S. Gantenbein et al., Nat. Mater. 22, 128, 2023 .)