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An Israeli experiment holds promise for a solution to organ shortages
The concept of 3D-printed organs has long been touted as a possible solution to the long waiting lists for transplantation. Now scientists in Israel have pumped fresh blood into the idea by printing a miniature “living” heart using a patient’s own tissue as the “ink”.
The Lilliputian organ — about the size of a cherry, while an adult heart is the size of a fist — is living in the sense that it is “vascularised”, meaning it contains blood vessels. It demonstrates that bioprinting can potentially recreate not just the structure of an organ but also the pipework needed for it to function.
“This is the first time anyone anywhere has successfully engineered and printed an entire heart replete with cells, blood vessels, ventricles and chambers,” said Tal Dvir, the Tel Aviv University professor leading the research. The revelation was published last month in the Advanced Science journal. Sceptics point out that this tiny heart cannot pump, and fully functioning bioprinted organs remain a distant hope.
The first step was to create a suitable biological ink. The scientists took a biopsy of fatty tissue and separated it into its cellular and non-cellular components. The cells were reprogrammed to revert to pluripotent stem cells — the most versatile ones — and chemically prompted to turn into heart and endothelial cells (the latter line blood vessels). These were mixed with a “scaffold” gel formed using the non-cellular leftovers, which included collagen.
Guided by computer tomography, or CT, scans of the patient’s heart, the researchers printed this bioink, layer by layer, to build so-called cardiac patches up to a few millimetres thick that matched the individual’s anatomy. They showed the ability to contract.
Printing a larger structure required a support medium, in much the same way that a fruit jelly requires a mould to keep its shape as it solidifies. In this case, a cushioning gel was used to entomb the structure during printing. It was chemically primed to disintegrate afterwards, leaving behind the small printed heart.
The work could augur well for the bespoke creation of spare parts, according to Claudio Capelli, a researcher at University College London who uses clinical scans of children to print 3D plastic models of their hearts. The models, which contain as many as 2,000 layers, help surgeons at Great Ormond Street Hospital to plan complex surgery.
“This raises the possibility of creating cardiac patches which are perfusable,” he said. “If blood can flow, then the patches can become ‘living’. You could replace components of the heart, like a valve or coronary artery, using your own material rather than artificial or animal material.” The virtue of using a patient’s own tissue is that it minimises immune rejection, a serious but treatable complication of transplantation.
Turning out whole hearts is a different order of challenge, Dr Capelli warns, because the way they function is still mysterious: “We don’t yet know the full algorithm of the heart, such as how the conduction system that produces electrical activity develops.”
Another difficulty is image resolution. Mapping finer cardiac structure requires unacceptably high radiation doses for living patients. So to achieve that detail Dr Capelli is collaborating with his UCL colleague Andrew Cook to apply high doses to donated hearts.
Ultimately, fabricated organs could be used in drug screening but the most eye-catching application is transplantation. Scientists can already print skin, cartilage and bone; they are now racing to turn out kidneys, livers, hearts and corneas. There is unquestionably a need: about 6,000 people are on the transplant waiting list in the UK.
Prof Dvir predicts that organ printers could be just a decade away. Dr Capelli is more circumspect: “This work is powerful but it is a long way off from creating a functional beating heart.”