## 2 Materials and Methods
### Analysis of Requirements
Independent DOF systems, while offering high movement precision, require a larger number of actuators, resulting in high weight and volume [23]. In contrast, the categories of constrained sliding [5; 12], coupled DOF [13; 16], and cable on glove [20; 21] appear to be more evenly distributed. Among these, cable-based transmission has seen growing adoption in recent years, due to the simple architecture, reduced bulkiness, and improved portability [3]. The assessment of design maturity adopted in this study is derived from [26] to simplify categorization. Specifically, four development stages were considered: (i) concept design (TRL 1-3); (ii) clinical trials (TRL 4-6); (iii) prototype (TRL 7); and (iv) commercial (TRL 8-9). This classification was proposed to provide a clearer understanding of both the technological maturity of each device and its expected performance in real-world environments. For ease of reference, the corresponding development stage is reported in the fourth column of Table 1). Only one rehabilitation device has reached the commercial stage [15], while a single assistive device was found to be in the clinical trial phase [5]. In the case study presented by [PERSON] et al. [17], the feasibility of home use of the pediatric robotic hand orthosis PEXO (see [5] in Table 1) was evaluated in a 13-year-old child with hand impairment following traumatic brain injury. After tailoring the device to the child's needs and providing user training, the child and parent used the PEXO at home over two weeks, showing improved hand function and device acceptance without any safety issues. However, with few exceptions, hand exoskeletons for pediatric users remain underdeveloped, particularly regarding customization to individual patients. A key limitation is the frequent adaptation of designs derived from adult models [21], although such adaptations have demonstrated effectiveness in certain cases. [PERSON] et al. [27] demonstrated the feasibility and positive outcomes of integrating robot-assisted therapy with conventional rehabilitation in a pediatric stroke case, utilizing the Gloreha Sinfonia device--originally designed for adults and adapted for pediatric use--to enhance hand function and daily activity performance. [PERSON] et al. [28] reported similar benefits in a 10-year-old post-stroke patient, highlighting improvements in sensorimotor capabilities and quality of life through the combined use of Gloreha Sinfonia and traditional therapy. Another major challenge observed during the design process is that the interaction with children is inherently more complex than that with adult users [7; 16]. This is due to the fact that children may struggle to follow precise instructions or remain in static positions. These aspects introduce additional constraints to user-centered development, and are currently being investigated through ongoing data collection during user interaction sessions. Moreover, device miniaturization is still an open issue to ensure functional efficacy and reduce overall weight, which are critical aspects when designing for children [2; 7]. Children predominantly employ a three-finger approach when manipulating objects, as reported by [PERSON] et al. [29]. Four of the eight solutions summarized in Table 1 support fingers 1 to 3 and are classified as soft or soft-rigid systems [5; 14; 20; 22]. Among these, two solutions implement cable-driven transmissions, which reduce the weight borne by the hand [20; 22]. Based on these findings, and considering the common issue of mechanical misalignment in rigid-link parallel systems, the present study focuses on the development of a hand exoskeleton incorporating soft-rigid finger modules to support thumb flexion and opposition, as well as index and middle finger flexion, while ensuring passive extension of all involved joints. This system, referred to as the Pediatric Hand EXoskeleton (PHEX), adopts a cable-based transmission to simplify the mechanical architecture, reduce bulkiness, and improve portability.