Researchers at the Massachusetts Institue of Technology said they have pioneered a tunable technique to generate wood-like plant material in a lab, which could enable someone to “grow” a wooden product like a table without needing to cut down trees and process lumber.

While the research has focused on an annual flower, the researchers believe the technique can be used on different types of lumber.

By adjusting certain chemicals used during a tree’s growth process, the researchers said they can precisely control the physical and mechanical properties of the resulting plant material, such as its stiffness and density.

Using 3D bioprinting techniques, the researchers believe they can grow plant material in shapes, sizes, and forms that are not found in nature and that can’t be easily produced using traditional agricultural methods.

“The idea is that you can grow these plant materials in exactly the shape that you need, so you don’t need to do any subtractive manufacturing after the fact, which reduces the amount of energy and waste. There is a lot of potential to expand this and grow three-dimensional structures,” said lead author Ashley Beckwith, a recent PhD graduate.

Luis Fernando Velásquez-García senior author of the paper and a principal scientist in MIT’s Microsystems Technology Laboratories, said that lab-grown plant materials can be tuned to have specific characteristics, which could someday enable researchers to grow wood products with the exact features needed for a particular application, like high strength thermal properties.

Joining Beckwith and Velásquez-García on the paper is Jeffrey Borenstein, a biomedical engineer and group leader at the Charles Stark Draper Laboratory. The research, funded in part, by the Draper Scholars Program, was published in Materials Today.

Planting cells

To begin the process of growing plant material in the lab, the researchers first isolate cells from the leaves of young Zinnia elegans,  annual flowes. The cells are cultured in liquid medium for two days, then transferred to a gel-based medium, which contains nutrients and two different hormones.

Adjusting the hormone levels at this stage in the process enables researchers to tune the physical and mechanical properties of the plant cells that grow in that nutrient-rich broth.

“In the human body, you have hormones that determine how your cells develop and how certain traits emerge. In the same way, by changing the hormone concentrations in the nutrient broth, the plant cells respond differently. Just by manipulating these tiny chemical quantities, we can elicit pretty dramatic changes in terms of the physical outcomes,” said Beckwith.

The researchgers used a 3D printer to extrude the cell culture gel solution into a specific structure in a petri dish, and let it incubate in the dark for three months. Following incubation, the resulting cell-based material is dehydrated, and then the researchers evaluate its properties.

Wood-like characteristics

Lower hormone levels yielded plant materials with more rounded, open cells that have lower density, while higher hormone levels led to the growth of plant materials with smaller, denser cell structures. Higher hormone levels also yielded plant material that was stiffer; the researchers were able to grow plant material with a stiffness similar to that of some natural woods.

Another goal of this work is to study what is known as lignification in these lab-grown plant materials. Lignin is a polymer that is deposited in the cell walls of plants which makes them rigid and woody. They found that higher hormone levels in the growth medium causes more lignification, which would lead to plant material with more wood-like properties.

The researchers also demonstrated that using a 3D bioprinting process, the plant material can be grown in a custom shape and size. Rather than using a mold, the process involves the use of a customizable computer-aided design file that is fed to a 3D bioprinter, which deposits the cell gel culture into a specific shape. 

For instance, they were able to grow plant material in the shape of a tiny evergreen tree.
Research of this kind is relatively new, Borenstein said.

“This work demonstrates the power that a technology at the interface between engineering and biology can bring to bear on an environmental challenge, leveraging advances originally developed for health care applications,” he adds.

The researchers also show that the cell cultures can survive and continue to grow for months after printing, and that using a thicker gel to produce thicker plant material structures does not impact the survival rate of the lab-grown cells.

Customization

Velásquez-García said the opportunity of the process is to optimize what is used and how. “If you want to create an object that is going to serve some purpose, there are mechanical expectations to consider. This process is really amenable to customization,” he said.

The researchers want to continue experimenting so they can better understand and control cellular development. They also want to explore how other chemical and genetic factors can direct the growth of the cells.

They hope to evaluate how their method could be transferred to a new species. Zinnia plants don’t produce wood, but if this method were used to make a commercially important tree species, like pine, the process would need to be tailored to that species, Velásquez-García said.

Ultimately, he is hopeful this work can help to motivate other groups to dive into this area of research to help reduce deforestation.

“Trees and forests are an amazing tool for helping us manage climate change, so being as strategic as we can with these resources will be a societal necessity going forward,” Beckwith added.