Popeye was fond of cramming cans of spinach to beef up his cartoon biceps. Now scientists say the leafy green really could help build a real-world muscle, only this time, it's the human heart.

A team of U.S. researchers found a way to use the veins of the spinach leaf to build a miniature version of a beating heart muscle.

Their discoveries offer a potential solution a major challenge confronting biomedical engineers: how to repair and regenerate damaged organs and tissues.

If proven to work, scientists could use the spinach treatment to grow layers of healthy heart muscle to treat heart attack patients, the group said in a proof-of-concept study published this month in the journal Biomaterials.

Existing bioengineering techniques, including 3-D printing, can't fabricate the branching network of blood vessels down to the capillary scale.

That tiny scaffolding is key to delivering the oxygen, nutrients and essential molecules tissues need to properly grow, said Joshua Gershlak, a study co-author and graduate student at Worcester Polytechnic Institute (WPI) in Massachusetts.

"The major limiting factor for tissue engineering ... is the lack of a vascular network," Gershlak said in a video describing the study. "Without that vascular network, you get a lot of tissue death."

In a series of experiments, the team took single spinach leaves and flowed a detergent solution through the veins to remove all the plant cells.

"What we're left with is the structure that keeps those cells in place," Glenn Gaudette, professor of biomedical engineering at WPI and corresponding author of the paper, said in the video.

Next, they flowed fluids and microbeads similar in size to human blood cells through the spinach's veiny network. Then they "seeded" the spinach veins with human cells that line blood vessels. The result? A tissue that mimics the heart muscle, replete with veins and arteries.

Along with spinach leaves, the team also removed cells from parsley, sweet wormwood (an herb) and hairy roots of peanuts. Researchers said they suspect the spinach leaf might be best for heart tissue, with its complex vascular network, while the vascular columns in wood might be useful in bone engineering.

Still, human testing remains years away.

"We have a lot more work to do, but so far this is very promising," Gaudette said in a statement.

"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," he said.