Paper summarizes recent advancements in human knee joint assistive devices developed at Wrocław University of Science and Technology, and presents the evolution of the design research process and its findings. It addresses the challenge of mimicking the knee’s motion, combining roll and slide that result in a complex trajectory of instantaneous center of rotation (ICR). Traditional simplified devices frequently struggle to precisely replicate this natural movement. A comprehensive multi-solution approach involved type synthesis, numerical modeling, simulations, 3D design, and prototype construction. This research led to the development of various innovative mechanisms, offering distinct advantages, including linearly and rotationally adjustable 4-bar mechanisms, and cam-based and tie-cam knee mechanisms. The research focused on two successfully constructed prototypes. Specifically, the dampers prototype, based on a linearly adjustable 4-bar mechanism, provides ICR trajectory control through real-time adjustment of its rocker lengths. The cam prototype, featuring easily interchangeable 3D printed cam parts, with profiles derived from fixed and moving centroids, enables highly precise and individualized motion replication. Experimental trials utilized colour markers (visual tracking), as well as IMU sensors to conduct extensive measurements, during both stationary tests and human volunteer trials. The findings confirmed the prototypes’ practical potential, stability and a crucial balance between kinematic accuracy and structural simplicity. By providing personalized knee support, presented research contributed significantly to the field of assistive devices, with potential applications in orthoses, prostheses, motion simulation, and mobile robotics.