3D Printed Motor-Sensory Module Prototype for Facial Rehabilitation

Abstract

This work demonstrates the first 3D printed wearable motor-sensory module prototype designed for facial rehabilitation, focusing on facial paralysis. The novelty of the work lies in the fast fabrication of the first fully soft working prototype, including feedback control, with a focus on the methodology for individual customization. Facial paralysis results from a variety of conditions, and more wearable and modular technologies are needed to address the complexity of facial movement rehabilitation. Smiling muscles are especially important for both expression and eating, and so this work focuses on this motion as an example of how the module can be applied to mimic and support needed muscle movement. A generalized actuator-sensor pair with a feedback control system is created to translate signals from smiling on the healthy side of the face (notably temporal and zygomatic branch) to actuation on the paralyzed side of the face for augmented physiotherapy. Fabric and a sensor fluid are integrated during the silicone printing process to create a multicomponent wearable that is ready to use with minimal postprocessing. The actuators' force and vertical contraction results under a 0.98 and 1.96 N load meet the 1-7 N requirements needed for smiling. It is a challenge to measure soft surface-based force and contraction ratio consistently; therefore, a novel modular surface is designed to simulate the interaction of skin and bone using 3D printed hard plastic (bone) and a silicone sheet (skin). The actuator is tested on top of four different repeatable and standardized surface morphologies, and results reveal that the actuator force application will vary based on topography and hardness of the facial surface. Demonstration of the complete system on the face while collecting sensor and pressure data serves as a proof-of-concept and motivates potential applications in rapid customization of highly specialized soft wearable orthotics, prosthetics, and rehabilitation devices. This unique actuator-sensor combination can have additional applications for wearables due to the (1) customizability, (2) closed-loop control, and (3) unique "grounding" test platform.