High-Fidelity Tissue Engineering of Patient Specific Auricles for Reconstruction of Pediatric Microtia

INTRODUCTION: Autologous techniques for the reconstruction of pediatric microtia are plagued by suboptimal aesthetic outcomes and morbidity at the costal cartilage donor site.  We therefore sought to combine digital photogrammetry with computer-assisted design/computer-assisted manufacturing (CAD/CAM) techniques to develop biocompatible tissue-engineered auricular reconstructions that would more closely mimic the normal anatomy of the patient-specific external ear and the complex mechanical behavior of native elastic cartilage, while avoiding the significant morbidity associated with costal cartilage based autologous reconstructions.

METHODS: The three-dimensional structures of normal pediatric ears were digitized using the Cyberware^¨ 3D Digitizer, an apparatus that combines a laser scanner with a panoramic camera to obtain rapid high-resolution images of anatomic structures.  Images were converted to virtual solids using Geomagic Studio^¨ and translated into volume models for mold design.  Image-based synthetic reconstructions of the normal pediatric external ear were fabricated under sterile conditions from collagen type I hydrogels cast from these three-dimensional molds. One group of constructs was seeded with 2.5x10^7 bovine auricular chondrocytes. Cellular and acellular constructs were implanted subcutaneously in the dorsa of nude rats and harvested after 4w.

RESULTS: Post-implantation, cellular constructs effectively maintained the anatomical features of the external ear including tragus, lobule, helix, and antihelix.  Post-harvest weight of cellular specimens was significantly greater than that of acellular specimens (4.2±0.29g v. 0.80±0.12g, p=<0.05). Safranin O-staining revealed that only cellular constructs demonstrated evidence of a self-assembled perichondrial layer and cartilage deposition by lacunar chondrocytes (Figures 1-2).  Verhoeff staining of cellular constructs revealed elastin fibers interspersed among the chondrocytes.  The confined compression modulus of cellular constructs increased significantly from 9.2±1.4kPa pre-implantation to 31±14kPa at 4w (p<0.05).

CONCLUSIONS: We have for the first time successfully combined digital photogrammetry with CAD/CAM techniques to create biocompatible patient-specific human-sized tissue-engineered constructs for ear reconstruction. The cellular constructs' life-like biomechanical properties and maintenance of volume, shape and appropriate topographical characteristics over time can be attributed in part to their unique type I collagen hydrogel composition, which has not yet to our knowledge been described for tissue-engineered auricular scaffolds.  Furthermore, this material chemistry allows for chondrocyte survival and the in vivo deposition of elastic cartilage. We believe our approach to auricular tissue engineering holds tremendous promise for translation to the clinical realm.