Abstract: Scaffolding the Scaffold: 3D-Printed External Biodegradable Cage Mitigates Contraction during Maturation of Elastic Cartilage Constructs

Abstract

INTRODUCTION: Although in previous work we have successfully generated full-scale ear constructs from human auricular chondrocytes (HAuC) and Human Mesenchymal Stem Cells, the main obstacle for clinical translation of the constructs is the shrinkage and loss of topographic definition that occurs during their in vivo implantation/maturation phase. It is known that tension forces generated by skin and other surrounding tissues contribute to the contraction and loss of topography of a collagen hydrogel. We hypothesize that 3D-printing of an external cage to surround our collagen-chondrocyte hydrogel will allow us to study how shielding our auricular scaffolds from naturally occurring external forces has the potential to reduce contraction and preserve topography, while not interfering with neocartilage formation METHODS: HAuCs were isolated from discarded otoplasty specimens and then encapsulated into 8mm disc type I collagen hydrogels with a cell density of 25 million cells/mL. Custom external cages were 3D-printed out of biocompatible polylactic acid (PLA) with high fidelity contour matching to the hydrogel. The hydrogels surrounded by the PLA cages were implanted into the dorsum of nude mice and explanted after 1 month in vivo for analysis. RESULTS: The external PLA cages were able to maintain their shape/strength after 1 month in vivo, providing the protection the hydrogels needed for undisturbed formation of neocartilage. After 1 month in vivo, the discs developed a shiny white cartilage-like appearance, similar to native auricular cartilage. The discs maintained in the external cages contracted on average only 4.17%, which is significantly less contraction than our usual human auricular cartilage constructs, which contract at least 25%. In addition, safranin-o staining shows cartilage formation, proving our design allows sufficient flow of nutrients in vivo for chondrocyte survival and function. CONCLUSION: We have shown that a custom 3D-printed external cage made out of a biocompatible and biodegradable material can be used to mitigate contraction of our auricular chondrocyte scaffolds. We have validated a methodology that not only has the potential to optimize our tissue engineered auricles, but to solve a problem of cartilage contraction well documented in literature that no one has been able to conquer before. The same technique can be applied to create cages that faithfully conform to the contour of full scale auricular scaffolds in order to preserve their complex topography.