In 2015, more than 125,000 organs, mostly kidneys, were transplanted from one human being to another in the United States. Sometimes the donor was a living volunteer. Usually, though, he or she was the victim of a car accident, a stroke, a heart attack, or a similar sudden event that had terminated the life of an otherwise healthy individual. But a lack of suitable donors, particularly as cars get safer and first aid becomes more effective, means the supply of organs is limited. Many people therefore die waiting for a transplant. That has led researchers to study the question of how to build organs from scratch.
One promising approach is to print them. Lots of things are made these days using three-dimensional printing, and there seems to be no reason why body parts should not be among them. As yet, such “bioprinting” remains largely experimental. But bioprinted tissue is already being sold for drug testing, and the first transplantable tissues are expected to be ready for use in a few years’ time.
Bioprinting originated in the early 2000s, when it was discovered that living cells could be sprayed through the nozzles of inkjet printers without being damaged. Today, using multiple printheads to squirt out different cell types, along with polymers that help the structure keep its shape, it is possible to deposit layer upon layer of cells that will bind together and grow into living, functional tissue. Researchers are tinkering with kidney and liver tissues, skin, bones, and cartilage, as well as the networks of blood vessels needed to keep body parts alive. They have implanted printed ears, and also muscles, into animals and watched these integrate properly with their hosts. Last year, a group at Northwestern University even printed working bioprosthetic ovaries for mice. The recipients were able to conceive and give birth with the aid of these artificial organs.
No one is yet talking of printing gonads for people. But blood vessels are a different matter. Sichuan Revotek, a biotechnology company based in Chengdu, China, has successfully implanted a printed section of artery into a monkey. This is the first step in trials of a technique intended for use in humans. Similarly, Organovo, a firm in San Diego, California, announced that it had transplanted printed human-liver tissue into mice and that this tissue had survived and worked. Within three to five years, Organovo hopes to develop this procedure into a treatment for chronic liver failure and for inborn errors of metabolism in young children. The market for such treatments in America alone, the firm estimates, is worth more than $3 billion a year.
Johnson & Johnson is so convinced that bioprinting will transform parts of medical practice that it has formed several alliances with interested academics and biotechnology firms. One of these alliances, with Tissue Regeneration Systems, a firm in Michigan, is intended to develop implants for the treatment of defects in broken bones. Another, with Aspect Biosystems Ltd., a biotechnology company in Canada, is trying to work out how to print parts of the human knee known as the menisci. These are crescent-shaped cartilage pads that separate the femur from the tibia and act as shock absorbers between these two bones. Playing that role causes a lot of wear and tear, so surgical repair is often required.
Bioprinting can help with the development of other treatments. Organovo already offers its kidney and liver tissue for use in testing new drugs for effectiveness and safety. That should please animal rights activists, as such tests cut down on the number of animal trials. It should please drug companies, too—because the tissue being tested is human, the results should be more reliable than those from tests on other species.
With similar motives in mind, L’Oréal, a French cosmetics firm; Procter & Gamble, an American consumer-goods company; and BASF, a German chemical concern, are working on printing human skin. They propose to use it to test their products for adverse reactions. L’Oréal already grows almost 54 square feet of skin each year using older and slower technology. Bioprinting will be faster and also allow different skin types and textures to be printed.
Printed skin might eventually be employed for grafts, repairing burns and ulcers. Plans are also afoot, as it were, to print skin directly onto the surface of the body. Renovacare, a firm in Pennsylvania, has developed a gun that will spray skin stem cells directly onto the wounds of burn victims. (Stem cells are cells that proliferate to produce all the cell types that a tissue is composed of.) If the stem cells in question come from the patient himself or herself, there is no risk that the immune system will reject the new tissue.
The real prize of all this effort would be to print entire organs. For kidneys, Roots Analysis, a medical-technology consultancy, reckons that should be possible in about six years. Livers, which have a natural tendency to regenerate, should also arrive reasonably soon. Hearts, with their complex internal geometries, will take longer. In all cases, though, printed organs would mean that those needing transplants have to wait neither for the altruism of another nor the death of a stranger to provide the means to save their lives.
Next, check out the other cool things 3D printers can make.