A two-stage in vivo approach for implanting a 3D printed tissue-engineered tracheal replacement graft: A proof of concept.

ABSTRACT

OBJECTIVES: To optimize a 3D printed tissue-engineered tracheal construct using a combined in vitro and a two-stage in vivo technique. METHODS: A 3D-CAD (Computer-aided Design) template was created; rabbit chondrocytes were harvested and cultured. A Makerbot Replicator™ 2x was used to print a polycaprolactone (PCL) scaffold which was then combined with a bio-ink and the previously harvested chondrocytes. In vitro Cell viability was performed by live/dead assay using Calcein A/Ethidium. Gene expression was performed using quantitative real-time PCR for the following genes Collagen Type I and type II, Sox-9, and Aggrecan. In vivo Surgical implantation occurred in two stages 1) Index procedure construct was implanted within a pocket in the strap muscles for 21 days and, 2) Final surgery construct with vascularized pedicle was rotated into a segmental tracheal defect for 3 or 6 weeks. Following euthanasia, the construct and native trachea were explanted and evaluated. RESULTS: In vitro After 14 days in culture the constructs showed >80% viable cells. Collagen type II and sox-9 were overexpressed in the construct from day 2 and by day 14 all genes were overexpressed when compared to chondrocytes in monolayer. IN VIVO By day 21 (immediately before the rotation), cartilage formation could be seen surrounding all the constructs. Mature cartilage was observed in the grafts after 6 or 9 weeks in vivo. CONCLUSION: This two-stage approach for implanting a 3D printed tissue-engineered tracheal replacement construct has been optimized to yield a high-quality, printable segment with cellular growth and viability both in vitro and in vivo.