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CAD-CAM Tissue Engineering of Auricular Cartilage Scaffolds for Reconstruction of Pediatric Microtia
Alyssa J. Reiffel, MD1, Sherry Zhou2, Sam Chan2, Concepcion Kafka2, Samantha Popa2, Jason A. Spector, MD, FACS1, Lawrence J. Bonassar, PhD3.
1Weill Cornell Medical College, New York, NY, USA, 2Cornell University, Ithaca, NY, USA, 3Cornell University, Department of Biomedical Engineering, Sibley School of Mechanical and Aerospace Engineering, Ithaca, NY, USA.

BACKGROUND: Microtia occurs in approximately 1% of all births. As synthetic implantable prostheses such as porous polyethylene constructs are plagued by infection and implant extrusion, autologous techniques developed by Brent and Nagata are the current gold standard for reconstruction of the microtic ear. However, due to the inherent difficulty involved in sculpting anatomically correct auricular cartilage facsimiles, these approaches are notoriously difficult to perform and may result in suboptimal outcomes in all but few expert hands. Furthermore, the morbidity and pain resulting from harvest of rib cartilage in the pediatric population is well known. We therefore sought to combine digital photogrammetry with computer assisted design/computer assisted manufacturing (CAD/CAM) techniques to develop a biocompatible tissue engineered ear reconstruction that would more closely mimic the normal anatomy of the (patient specific) external ear, as well as the complex mechanical behavior of native tissue, while avoiding the morbidity typically associated with such reconstructions.
METHODS: The three-dimensional structures of representative normal pediatric and adult ears were digitized using Cyberware 3D Digitizer that combined a laser scanner and panoramic camera to obtain rapid (~30 s) high-resolution (~150μm) images of ears without the use of ionizing radiation. Images were converted to virtual solids for mold design using Geomagics Studio, and these virtual images were translated to volume models. Three-dimensional volume molds replicating normal anatomy of the external ear were then fabricated based upon volume models. Image-based synthetic reconstructions of the normal pediatric external ear were fabricated under sterile conditions from alginate and collagen type I hydrogels cast from computer-generated three-dimensional molds.
RESULTS: Constructs effectively mimicked the anatomical features of the external ear including tragus, lobule, helix, and antihelix. Construct texture paralleled the tolerance to large deformation bending of native auricular cartilage while retaining sufficient stiffness to maintain its shape. Constructs were then seeded with 2.5x10^7 primary bovine ear chondrocytes and maintained under standard cell-culture conditions for 8 weeks. Histological analysis demonstrated healthy chondrocytes depositing normal cartilage ECM within the scaffold.
CONCLUSIONS: Digital photogrammetry was successfully combined with imaged-based synthetic techniques to create biocompatible tissue-engineered constructs for the reconstruction of pediatric microtia. Because constructs are based upon imaging data acquired from patient’s own contralateral ear, the construct that is generated has a very high fidelity to specific patient anatomy. Furthermore, such constructs support chondrocyte growth in vitro, thereby allowing for eventual hydrogel replacement with secreted autologous auricular cartilage. Efforts are currently underway to evaluate construct evolution following in vivo implantation in an animal model prior to translation to the clinical realm.


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