Cellulose (CE), a biodegradable and biocompatible biopolymer, can be used as a functional element in systems such as orthotics, where both high strength and flexibility are required. They can also be rapidly produced as embedded flexible sensors that can monitor pressure, strain, humidity and temperature in real time in orthoses produced using patient-specific anatomical data and additive manufacturing. These ‘smart’ orthotic devices not only improve user comfort and treatment outcomes but also align with the growing demand for environmentally friendly healthcare solutions. In this study, the applications of CE as both the main structure and sensor material in reverse engineering and 3D printing applications in medical devices, especially in the design and manufacturing of personalized orthotics are discussed. The promising performance of cellulose-based sensors in experimental settings suggests a bright future for their clinical applications, particularly in rehabilitation, sports medicine, and long-term care.