## 1 Introduction  
Ankle foot orthoses (AFOs) are medical devices prescribed to support the foot of patients suffering from weakness of the ankle plantar/dorsiflexion muscles. This can be due to damage to the central or peripheral nervous system, such as peroneal nerve injury and spinal cord disorders. In the older population, about 20% of stroke survivors develop a drop-foot [1], whereas cerebral palsy, either hemiplegic or diplegic, is one of the main causes in children [2]. AFOs provide stability to the ankle and prevent the foot from dropping in the swing phase of gait, thus limiting stumbling and falling injuries. Passive AFOs--those not fitted with actuators or other active devices--are classifiable into two main groups: (1) solid or rigid and (2) dynamic. Rigid AFOs are characterized by stiff shells that prevent ankle movement in any anatomical plane, whereas passive-dynamic AFOs (PD-AFOs) are more compliant in the sagittal plane and allow for some dorsi/ plantarflexion movement. The latter are characterized by energy absorption/release during the stance phase of gait and are most indicated for less severe drop-foot patients. Although off-the-shelf PD-AFOs are suitable for most patients, they are sold in limited sizes and do not always address other leg and foot morphological alterations. Advancements in additive manufacturing allow obtaining custom PD-AFOs in different plastic and composite materials of virtually any shape [3]. In general, custom PD-AFOs are customized to fit the patient's foot and leg morphology. While personalization of the mechanical properties can be obtained by adjusting the calf or ventral shell bending stiffness [4; 5; 6], no clear or standard methods to establish the correct bending stiffness with respect to the patient's weight, physical impairment, and functional demand have been reported to date. The decision on the optimal AFO flexibility often relies on the orthotist experience and/or on the patient's feedback on perceived comfort, donning easiness, and subjective feeling during walking trials [7; 8].  
The use of hinge joints fitted with precompressed springs between the calf shell and footplate has also been proposed to provide a stiffness-controlled dynamic response to flexion/extension movements [5; 9]. However, the most common designs include a posterior leaf spring (PLS) that allows the ankle joint some dorsi/plantarflexion motion. Thermoplastic, such as polypropylene, or a combination of thermoplastics and metals are the most widely used materials for PD-AFOs [10; 11; 12; 13]. Carbon-fiber-reinforced plastics have been considered for their high mechanical properties [8; 14; 15; 16]. Alternatively, fiberglass-reinforced plastics appear to be potentially suitable materials for PD-AFOs. In fact, while carbon fiber reinforcement ensures excellent strength-to-weight properties for components undergoing small deformation, fiberglass reinforcement may be more appropriate for dynamic large-deflection bending such as that occurring in PLS PD-AFOs. One of such composite materials, a fiberglass-reinforced polyamide (Windform\({}^{\copyright}\) GT, CRP Technology, Modena, Italy), has thus far been used to manufacture light, flexible, and stiff parts for the motor and aerospace industry. In this study, it was hypothesized that this composite material could be suitable also to manufacture PD-AFOs.  
This is the first study describing the overall procedure for the design and manufacturing of a PD-AFO made of fiberglass-reinforced polyamide. The feasibility and reliability of the proposed procedure were evaluated in a case study.