BACKGROUND: Patients with large segment tracheal disease from benign processes or cancer (thyroid or squamous cell) have limited treatment options. Reconstruction of large-segment tracheal defects is difficult, and allograft transplantation with the requisite immunosuppression is not an option in patients with active malignancy. Regenerative medicine may offer a viable alternative. In 2008, a trachea was grown in an experimental bioreactor from a patient’s own stem cells and successfully transplanted. Problems encountered with this process include inability to sterilize the bioreactor, implementation barriers of scale, and potential cross-contamination between repeated use the bioreactor vessel.
The purpose of this study was to design a second-generation bioreactor that could potentially be implemented in a wide variety of end-user clinical locations.

METHODS: We used computer aided design / computer aided manufacturing (CAD-CAM) coupled with a custom-built 3-D printing device capable of directly fabricating design components to construct a prototype second-generation bioreactor. Essential design elements included the following: 1) A two chamber system allowing for separate growth media conditions for the luminal (epithelial cells) and external (chondrocytes) graft surfaces. 2) Controlled rotation at 1 RPM to induce optimal fluid shear forces to induce chondrogenic differentiation and growth. 3) Continuous carbon-dioxide and oxygen gas exchange. 4) Single-use modular design, where the bioreactor vessel can be pre-sterilized and individually packaged. 5) Easy media exchange if required during graft culturing. The bioreactor prototype was constructed using polylactic acid (PLA), to minimize any potential biocompatibility issues.

RESULTS: The CAD-CAM system allowed rapid turnaround time (2-7 days) between iterative design changes. We successfully fabricated a final prototype bioreactor meeting all design requirements. The prototype uses a novel “rock-tumbler” based approach where the sterile chamber is essentially a modular, single use cylinder-in-cylinder that can be pre-sterilized separate from the motor and gas exchange connectors.

CONCLUSION: Our next-generation bioreactor model has the potential to allow hollow-tube organ production at large scale. The ability to test in nearly real-time, the effects of various modifications was a unique advantage of using the 3D printing system. While initially designed for growth of stem-cell seeded trachea, it can easily be modified for future use in a variety of other applications, such as esophageal or vascular grafts. Owing to the modular design and “single-use cartridge” approach, use of stem-cell mediated regenerative techniques may eventually be feasible at a much broader range of clinical settings than previously thought possible.