Smart soft fingers rehabilitation hands represent a significant advancement in upper limb rehabilitation technology. These devices address the complex challenge of restoring hand functionality by combining soft robotics and sensor technology. Unlike rigid rehabilitation devices, smart soft fingers utilize compliant materials and structures to enhance patient safety, comfort, and adaptability. This paper reviews the design considerations for soft finger mechanisms, focusing on materials, mechanical principles, and the integration of sensors and actuators. Emphasis is placed on selecting skin-safe materials, mechanical compliance, and the need for accurate motion tracking and feedback. Various sensor types, including pressure, force, and tactile sensors, are explored for their roles in capturing finger motion and contact forces. Actuation mechanisms range from simple motors to sophisticated pneumatic and artificial muscle systems, each with distinct advantages and limitations. Integrating these components into a functional rehabilitation hand requires strategic sensor placement and advanced control systems to manage force and movement effectively. Challenges such as sensor accuracy, device robustness, and Scalability are discussed alongside potential future directions for incorporating machine learning and enhancing user customization. The paper concludes by highlighting the progress and ongoing efforts to refine smart soft fingers rehabilitation hands to improve outcomes and patient engagement.