Photosynthetic printing material gets stronger with exposure to light
As a seedling matures into a tree, its trunk and branches become stiffer and stronger. Scientists have now replicated this effect in a photosynthesis-assisted 3D-printing ink, made partially from spinach.
Photosynthesis begins with plant cell substructures known as chloroplasts, which absorb sunlight. They use the energy from that light to convert water and carbon dioxide into glucose, which is in turn used to produce cellulose. Because cellulose is the main component of a plant's cell walls, the greater the amount of cellulose that's produced, the stronger the plant gets.
Led by Prof. Qiming Wang, researchers at the University of Southern California's Viterbi School of Engineering set out to copy that process by first using a centrifuge to extract chloroplasts from store-bought spinach. Those chloroplasts were then added to a 3D-printable polymer ink, which was used to print simple three-dimensional structures. When those objects were exposed to full-spectrum white light, the chloroplasts caused cellulose to be produced within the polymer, making the items stiffer and stronger.
The scientists now believe that two to four hours of light exposure could cause the material to become up to six times stronger than its original state. Additionally, by only exposing certain parts of a structure, it can be made stronger in some areas and more flexible in others. What's more, in the same way that a branch becomes stronger when placed under mechanical stress (such as if a weight is hung off of it), the 3D printing material will likewise produce more cellulose in response to external force.
Finally, if one of the 3D-printed objects develops a crack, light exposure will initiate a self-healing process, thus sealing up that crack. And should anyone wish to temporarily halt the spinach chloroplasts' production of glucose (and by extension cellulose), they can do so simply by freezing the material – the chloroplasts become active again when the material warms back up to room temperature.
Among other possible applications for technology, the team envisions custom 3D-printed insoles that mold themselves to the shape of a person's foot, and that can be tuned to different levels of stiffness.
The research is described in a paper that was recently published in the journal Proceedings of the National Academy of Sciences.
Another type of "living" printing material, developed at Harvard University, incorporates algae to deliver oxygen to cells in 3D-printed biological tissue.