Printability is not neutral
Five fabrication decisions that shape the conditions inside a living material.
In a living-material project, machine and material settings do more than determine whether something can be printed. They also change the conditions experienced by the organism.
A finer grind can reduce spaces for air. A wider line can increase the distance to its centre. A pH selected for paste stability can alter fungal growth and enzyme activity. A binder can become food. None of these effects is automatically harmful. The problem is that they are often not examined.
For biodesign educators, the practical shift is to treat ingredients, machine settings and geometry as parts of one biological system.
A printed line collapses as it leaves the nozzle
The obvious response is to refine the paste or machine settings: grind the ingredients more finely, add a thickener, increase line width, or adjust the water and acidity until the material extrudes cleanly.
These are sensible fabrication decisions. They are also biological decisions.
The fungus does not experience a category called “printability.” It experiences a wet environment made from particles, water, chemicals, surfaces and spaces.
A change introduced to improve extrusion may close routes for air. A wider line may prevent cracking while making its centre harder to reach. A binder may strengthen the wet paste and provide the fungus with another substance to digest.
The project
Céline Oberholzer, Jennifer Marie Yabut and Ehsan Baharlou investigated whether household waste could be used to produce 3D-printed mycelium panels. Their mixture combined cat litter made from corn and potato with used coffee grounds. The fungus was reishi, or Ganoderma lucidum.
The researchers screened several recipes in dishes, then developed one into a printable paste. During development, the team adjusted several variables to improve extrusion and reduce cracking, bending and separation between layers.
The panels held their shape well enough to become an architectural screen. But after three weeks, the fungus had not grown through their full 2.1-centimetre thickness.
The authors proposed longer growth time as one response.
That may be right. It is also worth asking whether the printing process itself helped create the internal limit.
The fungus was not mixed through the paste. Each panel sat above an inoculated bed, so mycelium had to grow upward into the printed lines. Every question about distance, air and travel in this Reading starts from that arrangement.
Two systems are being designed
A living-material project contains at least two interacting systems. Every major process decision acts on both. It rarely benefits them equally.
Where the blind spot enters
The researchers avoided further changes to the substrate composition, because they were concerned that this could compromise biological viability. They refined the additive-manufacturing process instead.
That distinction sounds sensible. Ingredients belong to biology; machine settings belong to fabrication. But it does not hold inside a living material.
Particle size, line width, layer height and spacing alter air access, moisture distribution, surface contact and the distance the fungus must travel. The ingredient list may look biological while the printer settings look mechanical. The fungus experiences both.
A material that cannot be fabricated is not useful. But fabrication improvements produce rapid, visible feedback, while their biological consequences may take weeks to appear and remain hidden inside the object.
A print can become more stable while its internal habitat becomes harder to colonise.
