In what has been hailed a breakthrough in regenerative medicine, scientists have developed functional ear, bone and muscle structures using 3D-bioprinting technology.
The research team, from the Wake Forest Baptist Medical Center in Winston-Salem, NC, say their novel technology - named the Integrated Tissue and Organ Printing (ITOP) system - and the resulting creations mark "an important advance" in growing replacement tissue and organs for patient transplantation.
Senior study author Dr. Anthony Atala, director of the Wake Forest Institute for Regenerative Medicine (WFIRM), and colleagues explain how they created the 3D-printed body parts in the journal Nature Biotechnology.
In recent years, 3D printing has emerged as a promising strategy for the growth of complex tissues and organs that can replicate those of the human body.
However, Dr. Atala and colleagues note that current 3D printers are unable to produce human tissues and organs that are strong enough to be transplanted in the body or that can survive following transplantation.
The team believes that their ITOP technology, however, could help overcome such problems.
Functional ear, bone and muscle created with ITOP
The researchers have spent the last 10 years developing the ITOP system.
The 3D-printing technology combines a biodegradable, plastic-like material and an optimized water-based gel. The plastic forms the shape of the 3D structure, while the gel contains tissue cells and encourages them to grow.
The 3D prints also consist of micro-channels, which act as a sponge to soak to up the body's nutrients and oxygen after transplantation. This helps the structures survive as they develop a blood vessel system, which they need in order to function in the human body.
In their study, Dr. Atala and colleagues used the ITOP system to build baby-sized human ear structures - around 1.5 in - and implanted them beneath the skin of mice.
Within 2 months after transplantation, the ear structures - the shape of which were well maintained - had formed cartilage tissue and a system of blood vessels.
For comparison, previous research had shown that a 3D-printed tissue structure without a pre-existing blood vessel system needed to be smaller than 200 microns (0.007 in) in order to survive in the human body.
"Our results indicate that the bio-ink combination we used, combined with the micro-channels, provides the right environment to keep the cells alive and to support cell and tissue growth," says Dr. Atala.
The researchers also used the ITOP system and human stem cells to build jaw bone fragments, which the team notes were the size and shape required for human facial reconstruction. Five months after being implanted in rats, the bone fragments had formed blood vessels.
Additionally, the researchers printed muscle tissue and implanted it in rats. The tissue had formed blood vessels and triggered nerve formation in only 2 weeks, and its structural characteristics were maintained.
Technology opens door to personalized tissue regeneration
As well as its ability to support cell growth and keep tissue structures alive, the team says the ITOP system has another benefit: it can use information from computed tomography (CT) and magnetic resonance imaging (MRI) scans to create structures that are individual to each patient.
Talking to BBC News, Dr. Atala uses the example of a patient that has a segment missing from their jaw bone.
"We'd bring the patient in, do the imaging and then we would take the imaging data and transfer it through our software to drive the printer to create a piece of jaw bone that would fit precisely in the patient," he explains.
Commenting on the possible implications of their results, Dr. Atala adds:
"This novel tissue and organ printer is an important advance in our quest to make replacement tissue for patients. It can fabricate stable, human-scale tissue of any shape.
With further development, this technology could potentially be used to print living tissue and organ structures for surgical implantation."
The team's findings build on those from another study they conducted in 2014, in which they created lab-grown vaginas using smooth muscle cells and vaginal epithelial cells, which were successfully transplanted in four females.
Dr. Atala and colleagues noted at the time, however, that such a technique may prove difficult for complex organs such as the liver and kidney. But the team says their latest technology shows that using 3D printing to build more complex tissue is feasible.
"In this study we printed a wide range of tissue strengths - from muscles as a soft tissue to cartilage and bone as a hard tissue showing a whole range of tissue strengths is possible," Dr. Atala told BBC News. "The hope is to continue work on these technologies to target other humans tissues as well."
Earlier this month, Medical News Today reported on a study that reveals how a 3D-printed bone structure enables regeneration of natural tissue.