A new system for growing heart tissue in the lab may make future heart, liver, and lung repair much easier. University of Toronto scientists have developed asymmetrical honeycomb-shaped 2D meshes of protein scaffolding that stick together like Velcro and imitate the environments in which tissue and muscle cells grow in the body.

The meshes are made from a flexible polymer called POMaC (which is short for this mouthful: "poly(octamethylene maleate (anhydride) citrate)"). T-shaped posts bonded onto the top of the mesh act like the tiny hooks on velcro strips – they loop through the holes in a mesh placed above and lock the two together. The researchers tested with both two and three-sheet-thick mesh scaffolds in a variety of configurations (i.e. with them lined up in different ways).

"As soon as you click them together, they start beating," says project lead Milica Radisic, referring to the way the heart muscle cells contract together and bend the polymer meshes. "And when we apply electrical field stimulation, we see that they beat in synchrony."

The way the scaffold bends and stretches as it "beats" helps the heart cells grow tougher and more robust, which makes them more likely to survive the ravages of life in an actual heart. That's the long-term plan – to get these flexible, modular mesh scaffolds producing artificial tissue that can be used to repair damaged hearts.

"If you had these little building blocks, you could build the tissue right at the surgery time to be whatever size that you require," Radisic says. Surgeons could then graft the scaffold onto the patient's heart, and after a few months the patient would be left with a repaired heart (and no scaffold, as that gradually gets absorbed by the body as harmless waste).

A photomicrograph that shows three sheets of the scaffold layered together(Credit: Radisic Lab)

The scaffolds could also be used for other cell types, such as those found in the liver and lungs, and for drug testing, as artificial tissue grown on them would respond realistically. And they could help scientists learn more about how cells in the body respond to different stimuli or interact with cells in other layers of tissue.

This is not the first time that scientists have attempted to grow artificial heart tissue. One technique used springy, coiled fibers as scaffolding, while another grew the tissue in an injectable hydrogel, and another favored a patterned rubbery gel.

The researchers argue, however, that no prior techniques combined the structural cues needed to get cells self-assembling in an organized fashion with the ability to grow multiple cell types according to position and with 3D tissue assembly and on-demand, minimally-invasive disassembly. (All of which this new technique achieves.)

A paper describing the research was published in the journal Science Advances.

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