Video: Scientists grow a human ear with new, skin-crawling 3D printing method

“Complications after surgery" is a vague and scary term that refers to secondary conditions, like infection, that develop post-surgery. Studies have shown that these complications affect upwards of 50 million patients worldwide and are more likely to appear in high-income countries like the United States, where surgeries are more common.

For reconstructive and cosmetic surgeries, of which there were 22 million combined in the U.S. in 2018 according to the American Society of Plastic Surgeons, this risk is especially palpable given that they're invasive. But this risk could be revolutionized by a new finding. Using new 3D bioprinting techniques, biomaterial scientists and tissue engineers from China, the U.S. and Belgium have discovered how to non-invasively grow body parts and organs underneath living skin.

Their new approach to 3D bioprinting and allows for non-invasive tissue growth and wound healing. It works through injecting bioink cells, the additive material traditionally used in 3D bioprinting, under the skin and using near-infrared light to penetrate the tissue and transfer customizable building designs -- like an ear or an abstract shape -- to newly injected cells.

The ear began to form in just 20 seconds.

In a new study published Friday in the journal Science Advances, the team explains how their approach stands apart from previous work done in 3D bioprinting.

"Currently, the in vivo application strategies for 3D printed macroscale products are limited to surgical implantation or in situ 3D printing at the exposed trauma, both requiring exposure of the application site," write the authors. "[The need for non-invasive methods] cannot be well met by the existing 3D printing technologies, motivating us to develop non-invasive 3D printing technologies that can non-invasively fabricate the tissue-covered bioink into customized products, including living tissue constructs in situ."

The researchers' non-invasive approach works by first injecting bioink cells under the skin of mice at the site of a wound or future reconstruction. This bioink has no initial shape itself but contains the biological building blocks to be molded into any number of shapes.

After injecting the bioink, the researchers expose the area to near-infrared light that has been passed through a digital chip containing customized building instructions for the bioink. As the light passes through this chip, it picks up the instructions and carries them deep under the skin to the bioink beneath.

Unlike other forms of visible light, even UV light, near-infrared light is capable of penetrating deep into the tissue. This makes it a perfect carrier for delivering the building instructions to the bioink.

Once the bioink has received its instructions, it begins to safely transform underneath the skin and take on the new, customized shape. In the study, the researchers were able to create abstract shapes like a cross and a cake-like structure as well as an approximation of a human ear.

The authors write that the ear began to form in just 20 seconds on the skin of the mouse and maintained its shape for at least a month.

In a video describing the process, the authors say that leftover bioink could be removed from the site to reveal the fully formed new tissue.

In the future, the authors say that an approach like this could be used for personalized and diverse tissue reconstruction in humans as well. They hope that a non-invasive approach like this would allow surgeons to avoid unnecessary and potentially dangerous reconstructive surgeries.

"This work provides the proof of concept for the non-invasive in vivo 3D bioprinting that would open a new avenue for medical 3D printing and advance the minimally invasive or non-invasive medicine," write the authors.

Abstract: Three-dimensional (3D) printing technology has great potential in advancing clinical medicine. Currently, the in vivo application strategies for 3D-printed macroscale products are limited to surgical implantation or in situ 3D printing at the exposed trauma, both requiring exposure of the application site. Here, we show a digital near-infrared (NIR) photopolymerization (DNP)–based 3D printing technology that enables the non-invasive in vivo 3D bioprinting of tissue constructs. In this technology, the NIR is modulated into customized pattern by a digital micromirror device, and dynamically projected for spatially inducing the polymerization of monomer solutions. By ex vivo irradiation with the patterned NIR, the subcutaneously injected bioink can be non-invasively printed into customized tissue constructs in situ. Without surgery implantation, a personalized ear-like tissue constructs with chondrification and a muscle tissue repairable cell-laden conformal scaffold were obtained in vivo. This work provides a proof of concept of noninvasive in vivo 3D bioprinting.