Researchers Bioengin-Ear Tissue Scaffolds to Human Scale

Some of history’s greatest artists brought slabs of stone to life, sculpting the inert materials to expose hidden human features. As Michelangelo once said, “every block of stone has a statue inside it, and it is the task of the sculptor to discover it.” Plastic surgeons, sculptors of a different kind, depend on a combination of anatomical fluency and artistic talent to reconstruct parts of the human body. Among their most difficult tasks is recreating the structural and biomechanical likeness of the outer part of the human ear, also known as the auricle.¹ Traditional methods rely on sculpting and implanting synthetic materials or cartilage from a patient’s own ribs, but even skilled surgeons find it challenging to carve out the ideal form.^2,3

A team of scientists led by Jason Spector, a plastic and reconstructive surgeon at Weill Cornell Medicine, took a different approach to ear restoration. In addition to surgical know-how, Spector’s understanding of tissue engineering technologies makes him an oracle on auricles. In a proof of concept study published in Acta Biomaterialia, the researchers described how they combined 3D printing, xenografts, and tissue engineering to create full-scale ear scaffolds that support tissue regeneration.⁴ 

“We see in our specialty patients who have ear deformities, called microtia, which can be reconstructed, but it’s a technically challenging operation that I think very few people in the world do well,” Spector said. “If we can engineer an ear, that would be a better approach.”

Spector’s team used 3D printing to create an anatomically accurate template of a human ear from polylactic acid bioink, a biocompatible and biodegradable plastic commonly used for medical implants. The researchers loaded tiny bits of biocompatible sheep rib cartilage into the scaffold and surgically imbedded this 3D human ear template on the backs of rodents, just beneath the skin.

“The study is interesting,” said Jason Burdick, a chemical and biological engineer at the University of Colorado Boulder, who was not involved in the research. “It combines the advantages of a 3D printed synthetic material to control the tissue structure and shape based on the geometry of the patient, with the potential biological signals that are found in the decellularized cartilage pieces that are introduced into the 3D printed material.”

Six months after implantation, the researchers removed the ear construct and found that it acted like a cartilaginous skeleton to support new tissue growth. Animal biology picked up where the 3D scaffold left off. The rodents acted like living bioreactors, providing the biological materials and cellular activity to continue sculpting the human-like ears over time, without rejecting the graft. Instead of chiselling a human likeness from a block of material, Spector’s team created the template and conditions to guide biological sculpting. 

“One of the biggest challenges is printing human sized organs. Culturing a ton of human cells for printing a human scale organ is also very expensive,” said Stephanie Willerth, a biomedical engineer at the University of Victoria, who was not involved in this study. “It’s impressive that the scaffolds persisted for six months and were infiltrated [by cells].”

The ear replicas had the general features and natural flexibility of human ears. For patients with external ear deformities, either congenital or following traumatic injury, this approach holds promise for ear grafts that feel and look more like the real thing. Creating 3D scaffolds from images of human ears also enables personalized ear replicas that reflect the unique contours and patterns of individual auricles, which can vary widely. 

“The body is the best tissue engineer out there. I thought this would be a perfect exploitation of endogenous tissue engineering, the body doing its own work,” Spector said. “I was very pleasantly surprised that tissue formed as well as it did. Do I think this is the definitive approach? Absolutely not. It’s certainly not the same as regular ear cartilage, but there is zero shrinkage and a nice fidelity of the intricate topography of the ear.”

In the future, Spector hopes to test different bioinks that would allow the scaffold to break down faster once implanted, as well as different approaches to support collagen elasticity. While Michelangelo believed that “carving is easy, you just go down to the skin and stop,” in Spector’s case, sculpting realistic ear grafts is more than skin deep.