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

The tunable technique is a step towards customizable wood products with little waste

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Scientists predict that the world’s forests could disappear in as few as 100 years, due to deforestation. In an effort to provide an environmentally friendly and low-waste alternative to conventional wood-making, researchers at MIT have developed a tunable technique to generate wood-like, lab-grown plant material, which could enable “growing” a wooden product, like a table, without needing to cut down trees, process lumber, etc.

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

The researchers also show that, by using 3D bioprinting techniques, 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.

The research is still in its early days, but it demonstrates that it is possible to tune lab-grown plant materials to have specific characteristics, which could someday enable researchers to grow wood products with the exact features needed for a particular application. For example, high strength to support the walls of a house, or certain thermal properties to more efficiently heat a room, explained senior author, Luis Fernando Velásquez-García, a principal scientist in 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.

Lab-grown plant material for 3D printing developed by MIT researchers. The tunable technique is a step towards customizable wood.
Grown materials can be produced in forms not naturally available. Selected examples of bioprinted, cultivated plant materials: (a) printed tree-shaped culture in 10 cm-diameter petri dish, standard lighting at 3-months old, (b) stitched, two-channel autofluorescence micrograph of tree-shaped print in which the coincidence of green and blue channels indicates likely presence of lignin, (c) dog-bone structures after transfer to a drying plate (an inverted 10 cm-diameter petri dish), (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 lab-grown plant material

To begin the process of growing plant material in the lab, the researchers first isolate cells from the leaves of young Zinnia elegans plants. The cells are cultured in a 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 the 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.

In a way, these growing plant cells behave almost like stem cells, in the sense that researchers can give them cues to tell them what to become. The researchers use 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. Even with this incubation period, the researchers’ process is about two orders of magnitude faster than the time it takes for a tree to grow to maturity, added Velásquez-García.

Following 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 tunable technique is a step towards customizable wood.
Dual-stained sample cross-sections allow for cell wall and lignin visualization. Light blue coloration indicates cell walls, green coloration indicates lignin as stained using Acriflavine. In dried Zinnia stems, imaged at 10x (a) and 20x (b), lignin is localized to a small bundle of vascular tissue. In Ze-I samples (c) Acriflavine fluorescence is dispersed throughout the sample cross-section. In Ze-M samples, there are no obvious regions of specific Acriflavine fluorescence supporting the expected lack of lignified cells. All scale bars represent 500 micrometers.

Characteristics

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

Another goal of this project 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. The researchers found that higher hormone levels in the growth medium cause 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, the researchers were able to grow plant material in the shape of a tiny evergreen tree.

According to Borenstein, research of this kind is relatively new. “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 added.

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

“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 is going to serve some purpose, there are mechanical expectations to consider. This process is really amenable to customization,” said Velásquez-García.

Now that the researchers have demonstrated the effective tunability of this technique, they want to continue experimenting to better understand and control cellular development, as well as to explore how other chemical and genetic factors can direct the growth of the cells.

The researchers intend to evaluate how their method could be transferred to a new species, considering that Zinnia plants don’t produce wood. If this method were used to make a commercially important tree species, like pine, the process would need to be tailored to that species, added Velásquez-García.

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 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,” said Beckwith.

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

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Edward Wakefield

Edward is a freelance writer and additive manufacturing enthusiast looking to make AM more accessible and understandable.

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