## 6 Hybrid Soft-Rigid Robotic Exoskeletons for Hand Rehabilitation
### Functional Features  
The present section involves an analysis of the available literature in terms of the key trends in functional features and the link between the accepted actuation solutions and functional needs in the process of developing a hybrid robotic exoskeleton. These developments and requirements are discussed in relation to the previous state-of-the-art section.  
* _Actuated movements_. The main goal in the development of devices that integrate both flexible and rigid components involves facilitating the articulation of all fingers of the human hand. While tendon actuation is the prevailing method, there are instances where pneumatic is employed in conjunction with innovative design choices, as reported in [121; 128]. In addition to the control of finger flexion and extension, a few studies integrate methodologies for thumb rotation (pronation and supination), hence enhancing the adaptability of the system to various rehabilitation approaches for users and operators [126; 129]. Furthermore, the design of the device has been the subject of several studies, with particular emphasis on its portability and lightweight nature [130]. The device developed by [PERSON] et al. focuses on one finger, unlike the others, adding an additional degree of rotation of the index finger, mainly related to patients in post-stroke rehabilitation treatments [124].
* _Range of motion_. The ROM is one of the main parameters for device evaluation. Across different authors, ranges have been reported with a variety of values. Many studies have provided overall results without specifying variations between joints. Othershave noted and validated specific thumb or finger ranges. This shortcoming stems from the different technologies adopted by the authors, both for the development of the device and the aim of the study. Some works do not indicate a specific movement range, other than the force values taken as a reference from the literature. Table 6 outlines the parameters of the ROMs for each of the developed devices examined.
* _Force._ The limited availability of force-related data in the publications examined in this section, which specifically investigated hybrid exoskeletons for rehabilitation purposes, highlights the distinctive difficulties presented by these novel technologies. The following papers present novel combinations of pliable and inflexible materials, including the complex integration of technical principles and biomechanical concepts. The evaluation and characterization of these hybrid exoskeletons, resulting from the unusual fusion, introduce additional levels of complexity to the investigation. The selected studies focus on examining the complex elements of exoskeleton functionality and its ability to support various types of movement. The focus placed on this matter is perceptive, since it acknowledges that the quantification of force in isolation fails to encompass the entirety of the case.  
Figure 5: Examples of hybrid hand exoskeletons. (**a**) The device consists of pneumatic actuation, combined with rigid armor. Source: [PERSON] et al. [121]. (**b**,**c**) Global and bottom view, respectively, of a hybrid assistive hand exoskeleton for stroke patience: a rigid structure with flexible joints. Source: [PERSON] et al. [127].