Nature makes wood. Could a laboratory improve it?
For all the the way humans have played with nature, the way we cultivate and extract materials from the forest and the fields remains fundamentally unchanged. To get wood, for example, we plant a tree, let it grow, and we cut it down. Wood and other plant-based materials can be renewable resources, but obtaining usable shapes usually requires a lot of transportation, milling, and processing.
Now, a group of researchers at MIT are hoping to dramatically reduce these inefficiencies. The researchers cultivated wood-like plant tissues in the lab, which, if scaled up, might one day lead to the development of wood, fibers and other lab-grown biomaterials aimed at reduce the environmental footprint of forestry and agriculture. Their work is described in a recent Cleaner Production Journal paper.
“The hope is that if this becomes a developed process for producing plant material, you could mitigate some [the] pressures on our farmland. And with those pressures reduced, we hope we can allow more spaces to stay wild and more forests to stay, ”says Ashley Beckwith, lead author of the study and PhD candidate in mechanical engineering at MIT.
Beckwith’s previous research examined using 3D printed microfluidics for biomedical applications such as analysis of tumor fragments. But after spending time working and learning about organic farms, she became interested in more efficient use of agricultural and natural resources.
Plant material grown in the laboratory would not depend on climate, pesticides or arable land for cultivation. And producing only the useful parts of plants would remove bark, leaves and other discarded excess material, the researchers note. “The idea of the next level is to produce goods where they are needed, when they are needed,” says Luis Fernando Velásquez-García, co-author of the study and principal investigator at Microsystems Technology Laboratories at MIT. “Right now we have this model where we produce goods in very few places and then we release them.”
The growth of plant tissue in the laboratory begins with cells, not seeds. Researchers extracted living cells from the leaves of young Zinnia elegans, a species chosen because it grows rapidly and has been well studied with regard to cell differentiation, the process by which cells switch from one type to another. Placed in a culture in nutrient broth, the cells reproduced before being transferred to a gel for further development. “The cells are suspended in this gel scaffold and over time they grow and expand to fill the volume of the scaffold and also transform into cell types that we’re interested in,” Beckwith explains. This scaffold contains nutrients and hormones to support cell growth, meaning the plant-based material grows passively – no sunlight or soil needed.
Still, a concoction of plant cells and gel won’t turn into anything very useful without some tinkering. The researchers therefore tested how the manipulation of the hormonal concentrations, pH and initial cell density of the gel medium, among other variables, influenced development and could affect the properties of the resulting plant tissues. “Plant cells have the ability to become different cells if you give them directions to do so,” says Velásquez-García. “You can persuade the cells to do either thing, and then they get the properties you want.”
To get a wood-like material, the researchers had to trick plant cells into differentiating into vascular cell types, which carry water and minerals and make up woody tissue. As the cells grew, they formed a thickened secondary cell wall reinforced with lignin – a firmness-lending polymer – becoming more rigid. Using fluorescence microscopy to analyze the cultures, the researchers were able to observe which cells were becoming lignified (or turning into wood) and also assess their magnification and elongation.
Once it was time to print them, heating and then 3D bioprinting the gel allowed the resulting material to take almost any shape after cooling and solidifying. The dark green fabric that the research team produced is quite firm, but it would not be structurally strong enough for most construction needs. For now, the thin, rectangular printed structures are only a few inches long and undergo mechanical testing and characterization, Beckwith says, although printing larger versions is possible. (Oh, and the researchers couldn’t resist some fun structures in the form of dog bones and trees.)