Scientists say they have taken an important step forward in creating 3D-printed hearts -- with the ultimate goal of making replacement tissue for organs and body parts damaged by disease or injury.
The 3D printing process builds three-dimensional objects based on a computer model. Unlike traditional printing onto a flat surface, the machines churn out various materials -- plastics, metals, ceramics -- layer by layer.
The technology is used in various industries, and in recent years researchers have been developing an offshoot: 3D "bioprinting." The hope is to eventually have the capacity to produce custom-made replacement tissue, or even whole organs, for patients.
Of course, the human body is far more complicated than a consumer product. Not only does printed tissue need structure, it needs to be permeated by blood vessels, nerves and other elements that keep it alive.
Researchers are years away from bioprinting functional organs that can be transplanted into humans, said lead researcher Andrew Lee.
But he and his colleagues at Carnegie Mellon University in Pittsburgh are reporting a key step on that long road. They've developed a new bioprinting method capable of creating parts of the human heart out of collagen.
Collagen is the most abundant protein in the body, and it's a critical part of the "extracellular matrix" -- a network of molecules that surround your body cells, giving them structure and chemical support.
The new bioprinting strategy helps address a major obstacle: Printing living cells and soft biological material, like collagen, is difficult. Collagen starts out as a fluid, and would just end up in a puddle if bioprinted by itself, the researchers explained. But by supporting the collagen with a gel that can be removed after the bioprinting is done, the collagen has time to solidify.
The technique is dubbed FRESH 2, and with it the researchers were able to reliably print tiny collagen fibers, of 20 micrometers in diameter -- an order of magnitude smaller than the previous 250 micrometers with an earlier version of the technology. The approach also allowed them to solidify the collagen with precise control -- creating tissue "architectures" that can be embedded with living cells.
When the researchers printed the collagen "bioink" with human heart-muscle cells, they were able to build a small model of the heart's left ventricle -- its main pumping chamber. Over a number of days, the ventricles showed the capacity to contract.
The researchers also printed a heart valve that could open and close, and a model of a newborn heart.
"We're nowhere near a functional heart that you can put into a human," Lee stressed. "But this is an important step forward."
That point was echoed by Lauren Black, an associate professor of biomedical engineering at Tufts University, in Medford, Mass.
"This is a pretty significant leap," said Black, who wrote an editorial published with the study in the Aug. 2 issue of Science.
He noted that the approach can not only print collagen, but also other important biological substances, like fibrinogen and hyaluronic acid.
The long-range hope for 3D bioprinting is to generate tissue customized for individual patients. That, Black explained, would be done with the help of a patient's own stem cells: Cells could be taken from the skin and genetically reprogrammed into a state similar to embryonic stem cells -- giving them the potential to mature into any type of body tissue.
Donor organs are in short supply, Black pointed out, and even when a patient receives one, the immune system will reject it without immune-suppressing drugs. 3D bioprinting could help address both of those problems, he said.
But that's a long way off. In the nearer term, Black said, bioprinted human tissue could be used in lab research -- for testing new drugs, and possibly replacing some of the research currently done on animals.
Lee agreed. He also noted that the current study used the heart for "proof of concept." But the FRESH approach could be used to build a range of organ systems, he said.