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Patient-Specific Tissue Engineered Auricles: Achieving Permanence
Ope A. Asanbe, MD1, Benjamin P. Cohen, BS2, Rachel C. Hooper, MD1, Jennifer L. Puetzer, PhD2, Rachel Nordberg, MEng2, Lawrence J. Bonassar, PhD2, Jason A. Spector, MD, FACS1.
1Weill Cornell Medical College, New York, NY, USA, 2Cornell University, Ithaca, NY, USA.

BACKGROUND: Autologous costal cartilage reconstruction remains the gold standard treatment for microtia. Limitations of this method include donor site morbidity, failure to match auricular cartilage properties, and difficulty recreating the ear morphology of the individual patient. We have previously demonstrated the capacity to fabricate high fidelity patient-specific ear constructs using digital photogrammetry and CAD/CAM techniques. These constructs maintained their topography and formed viable auricular cartilage when implanted in vivo for up to 3 months. We now investigate the fate of constructs implanted in vivo for 6 months.
METHODS: A 5 year-old female ear was imaged using three-dimensional photogrammetry, processed into a continuous surface, and embedded into a virtual block, which was printed as a 7-piece mold. A combination of bovine auricular chondrocytes and 10 mg/mL type I collagen was injection molded to form hydrogel ear constructs with a cell density of 25 x 106 cells/mL. Constructs were subcutaneously implanted into the dorsa of nude rats and harvested after 6 months. Post-harvest, constructs were analyzed by histological, biochemical, and biomechanical testing. Statistical analysis was performed using one-way ANOVA or one-way ANOVA by ranks, with a Tukey or Dunn's, respectively, pairwise comparison and p<0.05 indicating statistical significance.
RESULTS: Engineered auricular constructs retained their gross morphology after 6 months in vivo while forming pliable auricular cartilage with mechanical and biochemical properties similar to those of native auricular cartilage. Histologic analysis demonstrated mature auricular cartilage with a perichondrial surface layer, a proteoglycan rich core, and elastin fiber organization. Mechanically, the equilibrium modulus reached levels similar to those of native auricular cartilage within 3 months with reduced variation after 6 months. Proteoglycan and collagen content was not statistically different from that of native bovine auricular cartilage for constructs implanted for 3 and 6 months.
CONCLUSIONS: High fidelity auricular cartilage constructs were successfully fabricated and remained stable and viable for up to 6 months in vivo by seeding collagen hydrogels with auricular chondrocytes. These engineered constructs maintained their size and aesthetic quality and also displayed similar structural organization, matrix composition, and mechanical properties to native auricular cartilage. Given the stability seen at 6 months we believe these constructs to have achieved effective permanence. Our approach demonstrates the feasibility of fabricating patient-specific, high fidelity tissue engineered ears for patients suffering from microtia or traumatic ear injury. Further work using human auricular chondrocytes is required to show clinical translation of this technology, and alternative cell sources such as mesenchymal stem cells will be investigated.

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