Researchers at the Massachusetts Institute of Technology (MIT; Cambridge, Massachusetts) have developed a new accordion-like honeycomb scaffold that they say may one day be used to repair, well, broken hearts.

The MIT team believes that living heart cells or stem cells seeded onto such a scaffold would develop into a patch of heart tissue that could be used to treat congenital heart defects or to help repair tissue damaged by a heart attack. The biodegradable device would be gradually absorbed into the body, leaving behind new tissue, the researchers say.

The scaffold, reported in the Nov. 2 online edition of Nature Materials, is designed to more closely match the structural and mechanical properties of native heart tissue than traditional scaffolds, according to George Engelmayr Jr., lead author of the paper and a postdoctoral fellow in the Harvard-MIT Division of Health Sciences and Technology (HST).

Engelmayr told Medical Device Daily that traditional "off-the-shelf" scaffolds have basically been adapted for myocardial repair but not specifically designed for this application. He said such scaffolds have been structurally incompatible with recapturing cardiac anisotropy. Heart tissue has to be flexible enough to change shape as the heart contracts, but strong enough to withstand the forces generated by the contractions.

The objective of Engelmayr's team's research was to create a scaffold designed explicitly for hearts, unlike current scaffolds, which are made out of synthetic materials.

The MIT team seeded small patches of the scaffold with heart cells from newborn rats and grew them for one week. They found that the mechanical and electrical properties of the engineered tissue varied in different directions. When the cells were lined up parallel to an electric field, for instance, they beat in sync more readily.

Engelmayr and his colleagues used microfabrication techniques to create the accordion-like honeycomb microstructure in poly(glycerol sebacate), which yields porous, elastomeric 3-D scaffolds with controllable stiffness and anisotropy.

The accordion-like honeycomb scaffold has three key advantages over traditional cardiac tissue engineered scaffolds, Engelmayr said: First, its mechanical properties closely match those of native heart tissue. For example, it is stiffer when stretched circumferentially as compared to longitudinally. Surprisingly though, the new scaffold "turned out to be a better match for the right ventricle rather than the left ventricle," Engelmayr told MDD.

Engelmayr found that he could essentially "dial in" specific mechanical properties for the polymer scaffold by varying the time it is allowed to set, or cure. He noted that with this ability, coupled with the flexibility of the laser technique, "we might be able to come up with even better pore shapes with better mechanical properties."

Second, the MIT team demonstrated heart cell contractility inducible by electric field stimulation with directionally dependent electrical excitation thresholds. Heart muscle, Engelmayr explained, is directionally dependent – meaning its cells are aligned in specific directions. Third, his team saw greater heart cell alignment on the accordion-like honeycomb scaffolds than isotropic control scaffolds.

"Prototype bilaminar scaffolds with 3-D interconnected pore networks yielded electrically excitable grafts with multi-layered neonatal rat heart cells," the MIT researchers noted. "Accordion-like honeycombs can thus overcome principal structural–mechanical limitations of previous scaffolds, promoting the formation of grafts with aligned heart cells and mechanical properties more closely resembling native myocardium."

The National Institutes of Health, National Aeronautics and Space Administration, and Draper Laboratory sponsored the research.

"At this point we have not done any in vivo studies yet, but this is certainly on the horizon," Engelmayr said.

The MIT team believes its general approach also has applications to other types of engineered tissues. "In the long term we'd like to have a whole library of scaffolds for different tissues in need of repair," said Lisa Freed, corresponding author of the paper and an HST principal research scientist. She said each scaffold could be tailor-made with specific structural and mechanical properties. "We're already on the way to a few other examples," Freed said.