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March 23, 2017

Spinach Wears a Heart on Its Leaves

  • WPI research team shows spinach leaves stripped of plant cells can become a vascular network to deliver blood, oxygen, and nutrients to grow human tissues like cardiac muscle to treat heart attack patients. This green solution may solve the major problem now limiting the regeneration of large section of human tissues, bone, even whole organs to treat disease or traumatic injuries.

     

  • It’s a pretty safe bet that when Popeye was eating his spinach to gain superhuman strength to fight off bullies he wasn’t thinking about using the plant to regenerate human heart tissue. Yet, that is exactly what a team of researchers, led by investigators at Worcester Polytechnic Institute (WPI), have just reported on in a new study published in the journal Biomaterials.

    Researchers often face a fundamental challenge as they seek to scale up human tissue regeneration: how to establish a vascular system that delivers blood deep into the developing tissue. Findings from the new study—published in an article entitled “Crossing Kingdoms: Using Decellularized Plants as Perfusable Tissue Engineering Scaffolds”—address the problems that current bioengineering techniques, including 3D printing, can't fabricate, which is creating the branching network of blood vessels down to the capillary scale required to deliver the oxygen, nutrients, and essential molecules required for proper tissue growth.

    "Plants and animals exploit fundamentally different approaches to transporting fluids, chemicals, and macromolecules, yet there are surprising similarities in their vascular network structures," the authors wrote. "The development of decellularized plants for scaffolding opens up the potential for a new branch of science that investigates the mimicry between kingdoms, e.g. between plant and animal." 

    For the current study, the scientists cultured beating human heart cells on spinach leaves that were stripped of plant cells. They flowed fluids and microbeads similar in size to human blood cells through the spinach vasculature, and they seeded the spinach veins with human cells that line blood vessels. These proof-of-concept studies open the door to using multiple spinach leaves to grow layers of the healthy heart muscle to treat heart attack patients.

  • Click Image To Enlarge +
    In this sequence, a spinach leaf is stripped of its plant cells, a process called decellularization, using a detergent. The process leaves behind the leaf's vasculature. Researchers at Worcester Polytechnic Institute (WPI) were able to culture beating human heart cells on such decelluralized leaves. [Worcester Polytechnic Institute]

    "We have a lot more work to do, but so far this is very promising," notes senior study investigator Glenn Gaudette, Ph.D., professor of biomedical engineering at WPI. "Adapting abundant plants that farmers have been cultivating for thousands of years for use in tissue engineering could solve a host of problems limiting the field."

    The research team was able to develop an effective process for removing plant cells from spinach leaves by flowing or "perfusing" a detergent solution through the leaves' veins. "I had done decellularization work on human hearts before and when I looked at the spinach leaf its stem reminded me of an aorta,” explained lead study investigator Joshua Gerslak, a graduate student in Dr. Gaudette's laboratory. “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."

    When the plant cells are washed away what remains is a framework made primarily of cellulose, a natural substance that is not harmful to people. "Cellulose is biocompatible and has been used in a wide variety of regenerative medicine applications, such as cartilage tissue engineering, bone tissue engineering, and wound healing," the authors penned.

    Amazingly, in addition to spinach leaves, the team successfully removed cells from parsley, Artemesia annua (sweet wormwood), and peanut hairy roots. They expect the technique will work with many plant species that could be adapted for specialized tissue regeneration studies. The authors commented that “the spinach leaf might be better suited for a highly vascularized tissue, like cardiac tissue, whereas the cylindrical hollow structure of the stem of Impatiens capensis (jewelweed) might better suit an arterial graft. Conversely, the vascular columns of wood might be useful in bone engineering due to their relative strength and geometries."

    Using plants as the basis for tissue engineering also has economic and environmental benefits. "By exploiting the benign chemistry of plant tissue scaffolds, we could address the many limitations and high costs of synthetic, complex composite materials,” the authors pointed out. “Plants can be easily grown using good agricultural practices (GAP) and under controlled environments. By combining environmentally friendly plant tissue with perfusion-based decellularization, we have shown that there can be a sustainable solution for pre-vascularized tissue engineering scaffolds."

    The investigators were excited by their findings and are looking to optimize the decellularization process and further characterize how various human cell types grow while they are attached to, and are potentially nourished by, plant-based scaffolds. In addition to the researchers at WPI, this study was made possible through the collaborative efforts of scientists the University of Wisconsin–Madison, and Arkansas State University–Jonesboro. "This project speaks to the importance of interdisciplinary research," Dr. Gaudette concluded. "When you have people with different expertise coming at a problem from different perspectives, novel solutions can emerge."

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