By Thomas Gildea, MD
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Three-dimensional (3-D) printing is a hot topic in the news and in the medical community, where the technology is being used to make customizable medical implants. In May 2013, we employed a 3-D printer to fabricate a bioresorbable tracheal splint that saved the life of an Ohio child with congenital tracheobronchomalacia. Computer 3-D rendering, materials science and the ability to construct a device with these 3-D printers are constantly evolving. These are being used in several areas of bronchology. In the Respiratory Institute’s Bronchoscopy Section, we face complex, unique airway challenges and have been investigating the use of 3-D printers to help address our patients’ needs. Currently, the selection of airway stents is extremely limited in the U.S. market. There are only two basic types: silicone-based tube stents and self-expandable metallic nitinol stents and their hybrids. These have only simple tubular shapes and their size range is very limited. Unfortunately, airway diseases don’t just affect the long airways at the midpoint, where the available stents are relatively easily placed. Even in those accessible locations, they can result in airway kinking, bending, conical shapes and problems at branch points.
A look at the technology in action
Following bilateral lung transplant, one of our patients developed an unusual native airway bronchomalacia above the anastomosis and required an airway stent after fighting recurrent pneumonia with trouble clearing secretions. Over time, the limits of existing stents became clinically problematic:
- The anastomotic line was several millimeters smaller than the native airway, causing granulation from improper fit.
- The proper combination of length and diameter was not available.
- The left main bronchus and new lung were not a simple straight tube shape, but a curve with cone-shaped distal end
Despite cutting the proximal end of the stent, it still rode over the main carina and may have migrated proximally. The angle from the main carina to the anastomotic line is curved, not straight, and seems to have some space, but the anastomotic line is clearly smaller than the midpoint. We initially tried metallic stenting, but these quickly failed due to metal fatigue. We tried standard silicone stents, but they did not sit well and developed a biofilm with severe halitosis. We eventually moved to combinations of differing-sized, modified stents, altered to fit the airway as best we could.
3-D printing’s future role
Clearly, there is a role for a custom shaped and sized single-airway prosthesis not currently available. For this patient, we needed a longer-than-available stent that tapers distally. We could cut and shape the proximal end as needed. We were able to employ a technique of making a basic mold with a 3-D printer and pressure-injecting the silicone material around a mandrel to make the basic size and shape we needed. Note the tapered diameter on the left
Another utilization in which 3-D printing has been explored is for medical education. We have identified many respiratory patients with complex anatomical challenges. Printing a 3-D model of each patient’s airway anomaly can provide us an opportunity to try different techniques ex vivo to address the problem. Figure 3 shows a 3-D printed model based on CT scan data. At this point, almost every variation of central airway anomaly can be reproduced except dynamic airway diseases. There are still issues with making 3-D prints from peripheral lung images, as these are subject to the resolution of CT imaging.
We have been collaborating with other institutions to provide these 3-D disease airway models for experimentation with novel materials. Materials scientists can try different deployment systems and techniques to address nonstandard airway shapes and sizes. Dr. Thomas Gildea, Head of the Section of Bronchology and member of the Advanced Lung Disease Section of the Department of Pulmonary Medicine and Transplant Center, can be reached at 216.444.6503 or firstname.lastname@example.org.