ORLANDO -- Sixteen-month-old Garrett Peterson's airways collapsed daily.
Peterson was born with bronchomalacia, weak cartilage in the walls of the bronchial tubes, and had spent his entire life at the University of Utah Hospital on a high-pressure ventilator to keep him alive.
Meanwhile, at the University of Michigan, biomedical engineer Scott Hollister had developed a 3D printed splint that could absorb into the body over time but could hold open airways in newborns for two to three years; it was enough time for the bronchial cartilage to reform into healthy airways.
While still a risk, Garrett's parents -- Jake and Natalie -- had their baby flown by an intensive care unit plane to the University of Michigan. After a successful operation, their son was able to be taken off the ventilator and go home.
The biomedical splint is just one example of how 3D printing -- with either lab-generated tissue or biomaterials -- can now be used to create implantable devices to correct medical conditions.
The technology is known as 4D printing because the implants can change shape and conform over time as the body moves or grows, according to Dr. Robert Morrison, a resident otolaryngology-head and neck surgeon at the University of Michigan.
Originally, "4D printing" referred to 3D printed objects that used "smart materials" that could then self-assemble. Now, the term covers 3D printed objects that can change shape and conform to their environment.
Morrison and Hollister spoke about the science behind 4D printing at the RAPID 3D Printing and Manufacturing Conference here today.
To date, the engineering and surgical staff at the University of Michigan have successfully implanted the stints in four babies, all of whom were able to go home just weeks after their surgeries.
The stints are made by first performing a CT scan of a patient, creating a virtual model of the trachea. Then medical imaging software called Mimics from Belgium-based 3D printer maker Materialise NV is used to model the virtual stint onto the tracheal image.
Next, that image is uploaded to a Formiga P100 3D printer from Munich-based EOS, which uses laser sintering to bind layers of polycaprolactone (PCL), a biomaterial, layer by layer into the shape of a specific trachea.
The splint must then be cryogenically milled -- or frozen and grinded - microns at a time until it's a perfect fit.
While the process of creating customized splints may seem arduous, it takes only a day. And, up to 200 splints can be printed at a time, according to Hollister.
The splints must be biocompatible with a patient's immune system and able to resist external compression from surrounding tissue in the body, allow for flexibility, radial expansion or growth, and must last two to four years.
To date, the splints have met all the criteria as successful medical implants, and even begin deteriorating as planned after just six months. Once absorbed by surrounding tissue, the biomaterial is simply excreted from the body, Hollister said.
Hollister, Morrison and other researchers believe 4D biomaterials will some day go far beyond helping only babies with respiratory issues; they are already exploring their use on adults to correct skeletal applications, such as facial reconstruction or rebuilding ears with biomedical scaffolds that hold tissue in place.
What is needed to advance 4D printing are more academic and industrial partnerships that could enable the development of new materials and methods for creating implants.
"Being able to print a much broader range of soft materials for these types of reconstructions is important," Hollister said.
The researchers believe, however, that the 4D biomedical printing field will explode as new uses evolve.
"I think in the next five years, we will see an explosion of clinicians coming to table with new ideas for the use of this," Morrison said.