Lab-grown plant material for 3D printing developed by MIT researchers

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Scientists predict that the world’s forests could disappear within 100 years due to deforestation. In an effort to provide an environmentally friendly, low-polluting alternative to conventional wood manufacturing, MIT researchers have developed a tunable technique to generate lab-grown, wood-like plant material that could “grow “a wooden product, like a table, without the need to cut down trees, process wood, etc.

Researchers have demonstrated that by adjusting certain chemicals used during the wood growth process, they can precisely control the physical and mechanical properties of the resulting plant material, such as its stiffness and density.

Researchers are also showing that by using 3D bioprinting techniques, they can grow plant material into shapes, sizes, and forms that are not found in nature and cannot be easily produced by hand. using traditional farming methods.

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

The research is still in its early stages, but it demonstrates that it is possible to tune plant materials grown in the lab to have specific characteristics, which could one day allow researchers to grow wood products with the exact characteristics needed for a particular application. For example, high resistance to support the walls of a house or certain thermal properties to heat a room more efficiently, explained lead author Luis Fernando Velásquez-García, senior scientist at MIT’s Microsystems Technology Laboratories.

Working on this project, Beckwith and Velásquez-García are joined by Jeffrey Borenstein, a biomedical engineer and group leader at the Charles Stark Draper Laboratory. The research is published today in Materials Today.

Cultured materials can be produced in forms that are not naturally available. Selected examples of bioprinted and cultured plant material: (a) Tree-shaped imprinted culture in a 10 cm diameter petri dish, standard illumination at 3 months of age, (b) two-channel autofluorescent micrograph stitched with a tree-shaped impression in which the coincidence of green and blue channels indicates the probable presence of lignin, (c) dog bone structures after transfer to a drying plate (an inverted petri dish of 10 cm in diameter), (d) bioprinted, cultured and dehydrated samples without growth (top samples) and with growth (dark green, bottom samples). All scale bars represent 2.5 cm.

The process of laboratory-grown plant material

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

Adjusting hormone levels at this stage of the process allows researchers to adjust the physical and mechanical properties of plant cells growing in the nutrient-rich broth.

“In the human body, you have hormones that determine the development of your cells and the emergence of certain traits. In the same way, by changing the concentrations of hormones in the nutrient broth, the plant cells react differently. By simply manipulating these tiny chemical amounts, we can cause some pretty dramatic changes in physical outcomes,” Beckwith said.

In a way, these growing plant cells behave almost like stem cells, in that researchers can give them clues to tell them what to become. Researchers use a 3D printer to extrude the cell culture gel solution into a specific structure in a petri dish and incubate it in the dark for three months. Even with that incubation period, the researchers’ process is about two orders of magnitude faster than the time it takes for a tree to reach maturity, Velásquez-García added.

After incubation, the resulting cell-based material is dehydrated and its properties are evaluated.

Lab-grown plant material for 3D printing developed by MIT researchers.  The tuneable technique is a step towards customizable wood.
Cross-sections of dual-stained samples allow visualization of cell wall and lignin. Light blue staining indicates cell walls, green staining indicates lignin stained with Acriflavine. In dried Zinnia stems, imaged at 10x (a) and 20x (b), lignin is localized in a small bundle of vascular tissue. In Ze-I samples (c), acriflavine fluorescence is scattered throughout the cross section of the sample. In Ze-M samples, there are no obvious regions of acriflavine-specific fluorescence supporting the expected lack of lignified cells. All scale bars represent 500 micrometers.

Characteristics

The researchers found that lower hormone levels produced plant material with more rounded and open cells that have a lower density, while higher hormone levels resulted in the growth of plant material with more cellular structures. smaller and denser. Higher hormone levels also produced stiffer plant material; the researchers were able to grow plant material with a storage modulus (stiffness) similar to that of some natural woods.

Another objective of this project is to study what is called “lignification” in these plant materials grown in the laboratory. Lignin is a polymer that deposits in the cell walls of plants making them stiff and woody. The researchers found that higher hormone levels in the growth medium lead to greater lignification, which would lead to plant material with more wood-like properties.

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

According to Borenstein, research of this type is relatively new. “This work demonstrates the power that a technology at the interface between engineering and biology can bring to address an environmental challenge, leveraging advances originally developed for healthcare applications,” said he added.

Researchers also show that cell cultures can survive and continue to grow for months after printing and that using a thicker gel to produce thicker plant material structures has no impact on the survival rate of cells grown in the laboratory.

Personalization

“I think the real opportunity here is to be optimal with what you use and how you use it. If you want to create an object that will serve a purpose, there are mechanical expectations to consider. This process really lends itself to customization,” said Velásquez-García.

Now that the researchers have demonstrated the technique’s effective tuning ability, they want to continue experimenting to better understand and control cell development, as well as explore how other chemical and genetic factors can direct cell growth.

The researchers intend to assess how their method could be transposed to a new species, considering that Zinnia plants do not produce wood. If this method was used to make a commercially important tree species, such as pine, the process would have to be adapted to that species, Velásquez-García added.

Ultimately, Velásquez-García hopes this work with lab-grown plant materials can motivate other groups to dive into this area of ​​research to help reduce deforestation.

“Trees and forests are a great tool to help us manage climate change, so being as strategic as possible with these resources will be a societal necessity in the future,” Beckwith said.

This research is funded, in part, by the Draper Scholars Program.

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