Advances in 3-D printing and biomaterials are helping to shape the field of regenerative medicine. Sarah Webb examines the latest developments.
Three years ago, Long Island, NY ear, nose, and throat surgeons David Zeltsman and Lee Smith were searching for a way to treat patients’ tracheal damage. Their main problem was that cartilage in the body doesn’t readily regenerate and is difficult to culture in a 3-D matrix, so they needed to find a new source of tracheal tissue. It was then that the two physicians started to wonder if it might be possible to 3-D bioprint implantable tracheas.
They consulted Daniel Grande’s laboratory at the Feinstein Institute for Medical Research in Manhasset, NY, where researchers were already using 3-D printing to build load-bearing joint cartilage. After early discussions, Todd Goldstein, then a graduate student, decided to take the lead on the trachea project, leveraging his knowledge and skills in biology, engineering, and computers. Goldstein collaborated with another lab to learn how to work with epithelial cells, and within a year, the team had a prototype tracheal tissue. Animal studies showed that the printed tracheal tissue was just as strong as the tracheal tissue found in mammals (1). The researchers are now trying to bring printed tracheas to the clinic, Goldstein says. “Ideally, it’d be nice to do this in the OR on demand.”
The Long Island group is not alone in turning to bioprinting—in fact they are only one of a growing number of interdisciplinary teams that are pairing a knowledge of stem cells and cell culture with 3-D printing techniques to solve problems in regenerative medicine.Precise, reproducible, and scalable
Nearly three decades ago, surgeon Anthony Atala and his team began building novel tissues for regenerative medicine by hand in the laboratory. It was painstaking work, harvesting cells from patients, building structures layer-by-layer, and culturing these handmade scaffolds to produce functional tissues such as skin, bladder, and cartilage.
Although they tested some of these handmade tissues in the clinic, the approach was far too slow and laborious to treat large numbers of patients. So 14 years ago, Atala’s team, now located at the Wake Forest Institute for Regenerative Medicine in Winston-Salem, NC, began to remodel standard desktop inkjet printers to spit out cells. “It really was an automation strategy,” he says. “You’re getting three things. You’re getting precision. You’re getting reproducibility, and you’re getting scalability.”
The precision comes from the use of small nozzles to control the placement of cells and “inks,” the biomaterials printed around the cells that form a structural framework and also provide nutrients and growth factors. Today, a variety of cell printing strategies are available, but two of the most popular techniques are inkjet printing and extrusion-based printing.
Inkjet bioprinting of cells was first demonstrated by Hewlett-Packard in the late 1980s. “It’s a more difficult technology,” says Brian Derby of the University of Manchester in the United Kingdom. Printed inks must be liquid as they’re squeezed through the nozzles in the piezoelectric printing process. But to form and maintain a 3-D structure, those liquid inks must gel quickly as they’re deposited. Even with that challenge, Derby finds the technique more versatile than other approaches because inkjets allow for “color” printing: instead of printing red, blue, green, and black, nozzles in a bioprinter might include, multiple cell types, structural biomaterials, and other chemicals in a single manufacturing process.
Thomas Boland of the University of Texas, El Paso, one of the early developers of inkjet cell printing, emphasizes another advantage of the approach—the method is non-contact, thus avoiding cell contamination. As a result, his team routinely employs 15 different printing modules with various combinations of cells and inks.
In extrusion bioprinting, the nozzles function like tiny syringes, squeezing out ribbons of cells and hydrogel. Inks don’t have to flow as freely. The hydrogels that encapsulate cells can remain relatively stiff—like toothpaste being squeezed out of the tube—as they’re being printed. Bioengineer Lawrence Bonassar of Cornell University uses this strategy for building collagen-based structures. Instead of building layer-by-layer, material is extruded directly. “As soon as the material kind of comes out of the printer and solidifies on the stage, then we’re kind of done,” he says, and the process gives Bonassar and colleagues full control of the assembly in three dimensions.