Researchers at McGill University, Canada, have built the smallest 3D bioprinter to date. With a nozzle just 2.7 mm in diameter, the device is designed to help surgeons reconstruct tissues removed from the vocal cords in real time during surgery. A study published today in the journal Device reports that the 3D printer was able to accurately repair lesions in surgical models of vocal cords used to train surgeons.
“Our device is designed not only for accuracy and printing quality but also for surgeon usability,” says Swen Groen, PhD student at McGill University and first author of the study. “Its compact and flexible design integrates with standard surgical workflows and provides real-time manual control in a restricted work environment.”
About 18% of people who undergo surgery to remove growths on their vocal cords develop post-surgical fibrosis, which results in stiff vocal cords that can significantly affect the quality of their voice and their ability to speak. Current treatment to prevent these complications consists of injecting soft hydrogels into the vocal cords after surgery to promote healing. These materials are designed to protect new tissue as it grows within the vocal folds, a very delicate organ that is under constant strain due to sound vibrations.
However, injections are not precise enough to ensure that the hydrogels are placed in the right location. The 3D printer could overcome this major limitation by delivering the hydrogel during the procedure with a resolution of 1.22 mm, reconstructing the natural shape and structure of the vocal cords.
While similar devices exist to deliver hydrogels to other organs, such as the colon or the liver, they are too large to be used in vocal cord surgery, where the vocal cords are accessed through the mouth using a laryngoscope. The 3D bioprinter needed to be small enough to fit through the opening without blocking the surgeon’s view of the vocal cords.
“I thought this would not be feasible at first—it seemed like an impossible challenge to make a flexible robot less than three mm in size,” says Luc Mongeau, PhD, professor of mechanical engineering at McGill University and senior author of the study.
The device was inspired by elephant trunks, with the tiny nozzle placed at the end of a flexible “trunk” whose movements are directed through a controller that can be mounted on a standard surgical microscope. This allows the surgeon to control the 3D printing process manually during the procedure.
As a demonstration, the 3D printer was first used to make a variety of shapes on flat surfaces. Then, the team tested it in surgical models used for surgery training, where the printer showed high accuracy repairing small lesions as well as fully reconstructing the vocal folds.
Future work will involve combining manual control of the device with autonomous movement to optimize the deposition process and the accuracy of the hydrogel placement. Going forward, the researchers see potential beyond just vocal cord surgery, as the device could be useful for any other surgeries requiring accurate and minimally invasive hydrogel deposition.
“We’re trying to translate this into the clinic,” says Mongeau. “The next step is testing these hydrogels in animals, and hopefully that will lead us to clinical trials in humans to test the accuracy, usability, and clinical outcomes of the bioprinter and hydrogel.”
