However much it sounds like science fiction, we can envision the day when clinicians will be able to synthesize replacements for almost any part of our bodies using hardware little more complex than an ink jet printer. Already this technology can be used to generate swatches of skin from a patient’s own cells so that the resulting material could be grafted onto a wound with no risk that the body will try to reject it. In much the same way, it might even be possible to construct entirely new organs to stand in for those that are damaged or failing.
As enticing as that vision may be, perhaps nowhere will it be more difficult to realize than in the heart, where hard-working cells beat ceaselessly throughout all the decades of our lives. Replacing even a part of this organ will be a tricky business, with little leeway for allowing synthetic cells to integrate with surrounding tissue. If the replacement cannot stand up to the rigours of the job right away, this intervention could make an individual’s heart problems even worse.
Boyang Zhang began thinking seriously about this challenge when his PhD work took him to Milica Radisic’s University of Toronto laboratory, which is well on the way to creating strings of functional heart cells. Such strings have little practical application and thin cellular meshes would not be sufficiently robust for the task. However, they could be built up to form the necessary strength and stiffness required for healthy heart tissue. “The logical next step is a two-dimensional mesh structure made up of multiple fibres that are just connected together,” says Zhang. These layers of mesh could be stacked on top of each other and the various layers would eventually integrate, he adds.
The resulting three-dimensional structures could then be inserted into a working heart. This kind of flexible arrangement would address some of the greatest challenges that would confront a surgeon trying to repair the heart, where the ultimate shape and structure of the replacement tissue will only be determined once it is in place and actively working. However, the insertion offers little time for the various components to combine into a functional whole, as the heart cannot simply be stopped long enough for this bonding process to take place. Zhang and his colleagues therefore mimicked the intricate design of the material bonding system in Velcro, where extended fibres sticking out from two surfaces link strongly with one another. In this case, each layer of heart cells would be designed with a series of T-shaped hooks that could reach into an adjacent layer and attach firmly. “With this mechanical locking mechanism we link them together,” Zhang says. “Although we grow the cells in each mesh individually, the moment we stack them together and lock them in place as a whole they are immediately functional.”
The ability to assemble and disassemble such meshes with relative ease also offers researchers the possibility of exploring important questions such as how cell viability or gene expression vary with the thickness of the array and other conditions that might be associated with surgical implantation.
This accomplishment, which was published in Science Advances this past August, currently remains at the level of manual production rather than the automated, ink jet printer style of output. Nevertheless, Zhang and Radisic are confident that the idea is worth pursuing as a means of bringing the advantages of tissue engineering to the demanding field of cardiac care. In the meantime, they are left with the additional challenge of what to call their innovation. Although the article uses the term “Tissue-Velcro,” Radisic worries that this will conjure up images of surgeons inserting into their patients the same sort of carpet-like tape that is routinely found in our households. “We’re trying to come up with a better name,” says Radisic, “one that would be uniquely associated with our invention.”