After vocal cord surgery, many patients develop stiff vocal folds that impact their ability to speak. Hydrogels can help prevent this by promoting healing, but delivering hydrogels to the vocal cords is difficult. Publishing October 29 in the Cell Press journal Device, a team of biomechanical engineers and surgeons have developed a 3D-printing soft robot that can accurately deliver hydrogels to the vocal cord surgical site to reconstruct tissues removed during surgery. The robot's printhead is only 2.7 mm in size—the smallest bioprinter reported to date.
"Our device is designed not only for accuracy and printing quality but also for surgeon usability," says first author and biomedical engineer Swen Groen of McGill University. "Its compact and flexible design integrates with standard surgical workflows and provides real-time manual control in a restricted work environment."
Between 3% and 9% of people develop voice disorders during their lifetime due to cysts, growths, or cancers on the vocal cords. These growths are usually removed surgically, but many patients develop fibrosis post-surgery, which stiffens the vocal cords and makes speaking difficult. To prevent fibrosis, surgeons usually inject hydrogels into the throat tissues, but it's difficult to deliver hydrogels accurately via injection.
To enable more accurate hydrogel delivery, the researchers set out to design a miniature 3D printer that could be integrated into the surgical procedure. Similar bioprinting devices have been designed to deliver hydrogels to the colon and liver, but those devices are too large to use during vocal cord surgery, which is performed through the patient's open mouth using a laryngoscope. To be compatible with the surgical procedure, the printhead needed to be small enough to fit inside a patient's throat without obscuring the surgeon's view of the vocal folds.
"I thought this would not be feasible at first—it seemed like an impossible challenge to make a flexible robot less than 3 mm in size," says senior author Luc Mongeau, a biomedical engineer at McGill University.
The device's design was inspired by elephant trunks. The printhead consists of a nozzle at the end of a flexible "trunk" that is connected via tendon-like cables to a control module that can be mounted on a surgical microscope. The device can be manually controlled in real time and functions by delivering a hyaluronic acid-based hydrogel in 1.2 mm lines. The researchers programmed its movements to be precise, accurate, and repeatable within a 20 mm working range.
To demonstrate the printhead's ability to deliver hydrogels with precision, the researchers used it to manually "draw" shapes including 2D spirals, heart shapes, and letters on a flat surface. Then, they used the device to deliver hydrogels to simulated vocal folds used to train surgeons. The device was able to accurately reconstruct the vocal fold geometry in these models, which represented tissue defects, including a cavity left after a lesion was removed and a vocal fold that required complete reconstruction.
"Part of what makes this device so impressive is that it behaves predictably, even though it's essentially a garden hose—and if you've ever seen a garden hose, you know that when you start running water through it, it goes crazy," says coauthor Audrey Sedal, a biomedical engineer at McGill University.
Currently, the device is controlled manually, but the researchers are working to develop a system that combines autonomous and manual control.
"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."
