## 5 Soft Robotic Exoskeletons for Hand Rehabilitation
### Interactive Experience Features
In soft gloves, soft actuators designed and developed ad hoc are used in most cases. From the analysis of the state-of-the-art technology, it appears that these are soft actuators with very compact and extremely adaptable geometries, which allow soft gloves with high potential in terms of ergonomics and adaptability to be obtained. The feature of transparency, which affects the wearability and safety of the device, is generally very rarely discussed when presenting soft exoskeletons. Only some authors have reported a few cases but without going into detail in the discussion. [PERSON] et al. [92] developed a soft exoskeleton for the fingers and wrist. They considered transparency to be a fundamental feature in the development of wrist actuation. They designed a wrist brace that has adjustable tightness, adapts to the movements of the wrist, is comfortable to wear, and provides good transparency for the soft glove. The fabric-based robotic glove developed by [PERSON] et al. [86] has five finger actuation pockets on the back. As it ensures that there is little mechanical resistance to finger movements and allows kinematic transparency when worn, the glove acts as a compliant interface between the actuators and the hand. In general, many actuator solutions for soft exoskeletons, in particular, actuators made from fabric or with thin artificial McKibben muscles [107], are characterized by their high transparency. Reversibility was never discussed in the examined articles. However, it should be pointed out that, in pneumatic systems with actuators made from flexible materials, reversibility is a feature that the actuation system itself guarantees. The long-lasting performance of soft exoskeletons could be a very important issue to address given the intrinsic compliance properties of the actuators most commonly used in these devices. However, no author has reported on the durability or long-term testing of the developed devices. It must be considered, however, that all of the devices presented in the literature are at the prototype development stage. Finally, regarding the attachment of a soft exoskeleton to the patient's hand, the most commonly adopted solutions are either the use of Velcro straps connected to elements on the back of the hand to which the actuators are attached or the use of gloves to which the actuators are attached. In the case of fabric-based soft actuators, in some cases, the actuators are integrated directly into the glove. The choice of a particular solution has a significant impact on the comfort of wearing the exoskeleton. * _Control possibilities_. Soft glove control can be implemented with different solutions. Model-based control is the most widespread, while control strategies based on the evaluation of EMG signals are growing strongly [93; 108; 109; 110]. EMG signals are collected from the impaired hand and are used to record residual muscle activity for EMG-based control. Sometimes, machine learning algorithms are used to control these devices based on force feedback obtained by measuring EMG signals, as was performed in the paper published by [PERSON] et al. [109]. In this work, the authors developed a soft wearable glove controlled by a machine-learning-based intent detection system applied to closed-loop sensed muscle activity. Soft exoskeletons are often equipped with sensors of various types that provide feedback to control movement. In some cases, these gloves have actuators that generate sensory feedback [111; 112]. Bending sensors are the most common, followed by force or strain sensors, IMUs, pressure sensors, sEMG sensors, as well as soft sensors, often custom-made, which are used to detect motion and to control the device. The widespread use of flex sensors to detect the bending angle of the fingers or force or strain sensors corresponds exactly to the function of a soft glove. In the hand exoskeleton HEXOES [113], control is enabled by flex sensors over the actuated joints and force sensors on the linear actuators.