From Prototype to Clinical Workflow: Co-Developing a Wearable Hypomimia System for Parkinson's Disease

Hypomimia, the reduced facial expressiveness commonly seen in Parkinson's disease (PD), is clinically relevant, yet routine assessment usually relies on a single ordinal rating item in major rating scales such as the Unified Parkinson's Disease Rating Scale (MDS-UPDRS). This study aimed to develop and iteratively refine a wearable, cap-mounted device for hypomimia recording during routine inpatient ON/OFF assessments and to examine its usability and technical feasibility. A staged co-development process with four prototypes was conducted. After clinician workflow requirements had been incorporated, Prototype 3 was evaluated during clinical routine using the System Usability Scale (SUS) and short free-text feedback. These findings informed a patient-centered redesign that resulted in Prototype 4. Bench testing confirmed stable operation, robust housing, and reliable closed Wi-Fi streaming. Usability improved from moderate in Prototype 3 (mean SUS 44.7, SD 18.2; n = 15) to good in Prototype 4 (mean SUS 80.0, SD 12.6; n = 50). Mixed-effects regression showed an increase of approximately 33 SUS points for the redesigned device (95% CI 27.7-39.4; p < 0.001). Mean effective sampling rate was 4.79 frames/s (SD 0.33), with face detection in 95.4% of frames. These feasibility and usability results indicate that technical robustness and patient-centered design are critical prerequisites for later clinical validation and support the integration of a wearable hypomimia capture device into routine assessments.