Complex artificial organs could be created by 3D printing a mold of veins, arteries and capillaries in ice, casting it in organic material and then allowing the ice to melt, resulting in a hollow network and delicate. This leaves space for the complex artificial blood vessels needed for the development of lab-grown internal organs.
Researchers have been working on artificial organs for decades to meet the high global demand for heart, kidney and liver transplants. But creating the networks of blood vessels necessary to keep them alive remains a challenge.
Existing techniques can grow artificial skin or ears, but any flesh or organ dies if it is more than 200 micrometers from a blood vessel, explains Philippe LeDuc at Carnegie Mellon University in Pennsylvania.
“It’s like twice the width of a hair; Once past this stage, if there is no access to nutrients, the cells start to die,” he says. Internal organs therefore require new processes to become cheap and quick to manufacture.
LeDuc and his colleagues had experimented with printing blood vessels with meltable wax, but this requires reasonably high temperatures and can leave residue. “All of a sudden, one day, my student asks, 'Why don't we just use water – the most biologically compatible material in the world?' “, explains LeDuc. “And I'm like, 'oh, yeah.' It still makes me laugh. It's so simple.
They developed a technique that uses 3D printers to create a mold of the inside of an organ's blood vessels in ice. In tests, these were then embedded in a gelatin material that hardens when exposed to ultraviolet light, before the ice melts.
The team used a platform cooled to -35°C and a printer nozzle that dispensed hundreds of water drops per second, allowing structures as small as 50 micrometers in diameter to be printed.
LeDuc says the process is conceptually simple but needs to be fine-tuned: the drops are dispensed too quickly and they don't freeze quickly enough and fail to create the desired shape, but they are printed too slowly and they only form lumps .
The system is also affected by weather conditions and humidity. Researchers are therefore studying the use of artificial intelligence to keep the printer adapted to different conditions.
They also used a version of water in which all the hydrogen is replaced with deuterium, a stable isotope of the element. This so-called heavy water has a higher freezing point and helps create a smooth structure by avoiding unwanted crystallization. Tests have shown that creating artificial organs would be safe because deuterium is not radioactive, unlike some isotopes, LeDuc explains.