Biology and Soft Robotics Towards a Total Artificial Larynx

The larynx is one of the smallest but also one of the most complex organs in the human body, with three main functions: breathing, swallowing (sphincteric), and phonation. Nevertheless, in the case of advanced laryngeal carcinoma, the total laryngectomy remains the gold standard, causing the loss of all three functions, which are replaced with a tracheal stoma and a vocal prosthesis. This clinical practice, however, causes several clinical, psychological, and social problems for the patient. In this work, we present the first soft total artificial larynx, based on biomimetic design and materials, in which the vocal folds are set in motion and able to restore all active and passive laryngeal functions. The larynx of different animal classes has been analyzed to identify the basic structures and movements shared among all the Tetrapoda, obtaining a biomimetic functional design composed of two cartilages, a thin membrane (the elastic cone) that integrates artificial vocal folds, and three intrinsic muscles (the posterior cricoarytenoid, the lateral cricoarytenoid, and the thyroarytenoid), found to be responsible for the movement of the vocal folds, and, hence, the laryngeal functions. The emerging field of soft robotics enables the development of artificial organs that increasingly resemble their anatomical counterparts using soft and flexible materials. In this context, we replicated the laryngeal anatomical structures with materials whose mechanical properties and functional behaviour match those of the natural tissues. The result is a full-scale soft artificial larynx, which not only represents a fundamental step towards the creation of a bioinspired laryngeal model but also contributes to the broader field of artificial organs through the creation of synthetic airway cartilages and mucous-associated membranes. Finally, a hybrid actuation system (fluidic and cable-driven) was integrated into the artificial organ, mimicking the role of the three intrinsic muscles, to guarantee the opening, closing, and tension of the artificial vocal folds, and, therefore, the fulfillment of all three laryngeal functions. The Inverse Pneumatic Artificial Muscles (IPAM) were chosen, as they allow the vocal folds to remain open and, therefore, breathe without constant pressurization of the actuators. Furthermore, in the event of damage, the actuator returns to its resting position, maintaining the vocal folds in an open configuration, thereby preserving normal breathing functionality. Both sphincter and phonatory capacity of the artificial larynx were tested and verified. In their closed configuration, the vocal folds can prevent the passage of water, ensuring complete protection of the lungs, while, during the phonatory phase, they reach an onset pressure and vibration frequency within the human physiological ranges. The realization of an artificial larynx aims to revolutionize the treatment of laryngeal disorders, laying the foundation stone for restoring essential laryngeal functions and significantly improving patients' quality of life. This achievement paves the way for the next generation of laryngeal prostheses, ultimately transforming the landscape of laryngeal healthcare.