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Although there have been many attempts to build functional beating hearts from scratch, there is still nothing in the pipeline that is ready for the clinic. A big step forward was recently made by University of Toronto researchers who have come up with a promising new way to assemble 2D cellular sheets into 3D cardiac tissues that beat in unison.

Their secret is a new ’tissue-velcro’ system that allows multiple cell types to be cultured separately, and then conveniently zipped together into a scalable mosaic architecture. Led by Milica Radisic, the team had previously demonstrated spontaneously beating “cardiac biowires,” which could be synchronized through electrical stimulation. These one-dimensional hybrid structures were made by seeding human cardiomyocytes (baby heart cells) derived from embryonic stem cells onto teflon tubes with carbon electrons.

Now the team has come up with an improved 2D sheet structure based on an new biodegradable elastomer called POMaC (poly octamethylene maleate anhydride citrate). The injection molded POMaC was photocrosslinked into a honeycomb mesh, where the individual hexagons were longer in one direction. When cardiomyocytes were added, they would preferentially align themselves across the short axis into an organized sheet. The researchers also bonded T-shaped posts to each layer that basically act like the tiny hooks in velcro, enabling the sheets to be reversibly joined together.

The beauty of this arrangement is that tissues of arbitrary thickness, and therefore potential pumping power, can be made to order. The team has already made modular hybrid tissues up to three layers thick that include fibroblasts and endothelial cells in addition to the cardiomyocytes. The polymer base should last several months as it is slowly degraded and replaced by a natural secreted extracellular material.

The next goal is to test the devices out in actual animals to see how they perform. They are not yet meant to be actual heart replacements, but rather supplementary ‘power packs’ that can be slapped on to assist a floundering heart. The ability to customize the orientation and power stroke within each layer means that the integration will be as seamless as possible. Most likely there will still need to be electric synchronizing pulses from some kind of pacemaker device — however, it may not be such a stretch to imagine coaxing endogenous nerves to infiltrate the new tissue. If that can be achieved, then potentially an “all-bio” assist device could be made.

As we have seen recently, minimally invasive surgery to replace heart valves is now possible using advanced catheter technology. In theory, these techniques could be adapted to deposit new contractile material either inside or outside of the heart — giving customers a complete one-stop cardiac tune-up.

Read more http://www.extremetech.com/extreme/213181-tissue-velcro-allows-for-scalable-assembly-of-cardiac-cell-power-units