Additive manufactured tracheal splints provides life-saving support as needed.

Previously, Medical Design Briefs reported on a baby boy whose life was saved using a custom 3D-printed tracheal splint, a groundbreaking procedure pioneered at the University of Michigan. He is now nearly four years old. Since that time, a 14-year-old girl has now joined the list of three baby boys and one baby girl who’ve received novel 3D-printed tracheal splints to treat a congenital breathing condition called tracheobronchomalasia (TBM), which causes tracheal walls to collapse. All five are alive and thriving, thanks to the technology and the surgical procedures that helped their collapsed airways function normally.

Fig. 1 – Shown is an example of a 3D-printed tracheal splint and the actual airways modeled from digital scans of the patient. (Credit: Leisa Thompson, Photography/UMHS)
According to researchers at the University of Michigan who used additive manufacturing (AM) to produce the splints in their laboratory, the first boy’s own tissues have successfully taken over the job of the implant, which has been almost completely reabsorbed by his body.

The engineering and surgical team that designed, built, and implanted the splints is applying for an Investigational Device Exemption from the FDA to treat an additional 10 patients. They are also preparing for a larger clinical trial that will compare the splint’s performance against the traditional solution of keeping a child with TBM on a ventilator.

According to Dr. Scott Hollister, a Professor of Biomedical Engineering who’s part of the design team: “We evolved the design a bit from the very first patient so it’s now pretty automatic to generate an individualized splint design and print it. The whole process only takes about two days now instead of three to five.”

How It Works

Customizing a tracheal splint for an individual patient must be, of necessity, extremely precise. The University of Michigan bioengineering team starts with patient data from magnetic resonance imaging or computed tomography scans to determine the extent of the defect to be repaired and the dimensions of the patient’s existing anatomy. Computer models of this anatomy are then made from the data using commercial as well as custom software to create a model of the splint that best addresses each defect, with circular bellows for support and flexibility, and suture holes so the surgeon can fix the implant in place.

The tem uses polycaprolactone (PCL) for a number of reasons. It has a long resorption time, which is very important for the airway application because the implant should remain in place for at least two years and then resorb. It’s very ductile so if it fails, it won’t produce particles that could puncture tissue. And, PCL could be readily processed for, and fabricated on, the university’s EOS FORMIGA P 100 laser-sintering system, which it purchased in 2006.

The splints are designed with a highly compliant, porous structure of interconnected spaces. The researchers say that in the future these could potentially be infused with biologics to enhance tissue ingrowth and slowly expand along with the maturing airway over time. Topology optimization software draws each complex shape with the least amount of material possible. (See Figure 1)

Next the function of the implant is simulated, as attached to the airway with sutures, with nonlinear Finite Element Analysis to ensure that it will operate properly and stand up to years inside the body. Finally the splint is manufactured via the school’s FORMIGA P 100 system.

Multiples are usually made, or “grown,” of the same device, so they can be put through quality control analysis prior to implantation. After fabrication, the researchers measure the splint dimensions and then mechanically test them (compression, tensile opening, and three-point bending) to confirm that the fabricated splints meet the quantitative design outputs.

Surgery to install a splint, which wraps around the outside of a collapsed airway, usually takes about four to eight hours, depending on the condition of the patient and if there are other issues that must be addressed. The splint-supported trachea expands and is functional right away so that when patients are weaned off oxygen they are able to breathe normally.

Other AM Uses

Hollister’s group is also developing craniofacial, spine, long bone, ear, and nose scaffolds and implants—and producing them all using AM technology solutions from EOS to laser sinter a material with characteristics that promote reconstruction and regrowth following birth defects, illnesses, or accidents. Since tracheal splints are generally needed for fewer than 4,000 patients per year in the US, the university is seeking a regulatory path through the FDA’s humanitarian device exemption.

However, Hollister says, “Even if a market is relatively small, this doesn’t diminish the human need to be treated. Our additive manufacturing process is very efficient, and the cost is the same whether you are making 1 or 1,000 splints.”

His team is already investigating the use of other 3D-printed materials. “If we can expand the number of biomaterials used in laser sintering, we can tackle a tremendous amount of problems currently faced in all field of reconstructive surgery and make enormous strides for patients,” he says. The group has already collaborated with EOS customer Oxford Performance Materials (OPM) to make a non-absorbable tracheal splint out of PEKK material, for patients who have already completed growing.

For more information, visit www.engin.umich.edu .