To create artificial tissue with functioning vasculature, tissue engineers looked no further than their salad bowls.

By peeling away the cells from a spinach leaf and seeding the cellulose matrix left behind with heart cells, researchers were able to create a beating sheet of human heart tissue—complete with a functional vascular system. The proof-of-concept experiment, appearing in the May issue of Biomaterials, provides an intriguing plant-based approach to generating realistic tissues for grafts and transplants.

Vasculature has been a sticking point for bioengineers. Modern methods for creating artificial tissues and organs, such as 3D printing, haven’t included a good way to recreate the vital conduits. Yet the success (and survival) of any bioengineered tissue or organ hinges on whether it’s equipped with an extensive network of blood-carrying vessels, which drop off oxygen and critical nutrients to cells while flushing away molecular garbage.

Though the vasculature of plants is fundamentally different from that of animals, the structures and cell access are similar. Plus, cellulose—the main organic polysaccharide left standing in de-celled leaves—is known to be biocompatible, that is, it’s safe in humans and already used in other tissue-engineering applications, such as wound healing. This sparked ideas in the study's authors, led by bioengineers at Worcester Polytechnic Institute in Massachusetts.

“When I looked at the spinach leaf, its stem reminded me of an aorta,” Joshua Gershlak, first author on the study and a researcher at WPI, said in a press release. “So I thought, let’s perfuse right through the stem. We weren’t sure it would work, but it turned out to be pretty easy and replicable. It’s working in many other plants."

Basically, the researchers first pumped a detergent solution through the leaves’ veins, which stripped away the plant cells over several days. Then, the researchers pumped in cells that blanket human blood vessels so they could re-line the leaves' pipes. Lastly, the researchers seeded the outside of the leaves with human heart cells, which took to their plant-based skeleton.

Over the course of a 21-day experiment, the heart cells started spontaneously beating, like normal heart tissue. The researchers also found that mock-blood could flow through the system. The researchers did similar experiments with parts of parsley and peanut plants.

This study is simply a first step. The whole process needs optimization and further development to create viable, resilient tissue for transplants. And it’s currently unclear how leaf-shaped tissue sheets could work as graft tissue or combine to create an artificial organ. Still, the researchers are optimistic and are forging ahead with the idea.

“Although further investigation is needed to understand future applications of this new technology, we believe it has the potential to develop into a “green” solution pertinent to a myriad of regenerative medicine applications,” they conclude.

Biomaterials, 2017. DOI: 10.1016/j.biomaterials.2017.02.011 (About DOIs).