# Anatomical-Based Customized Cervical Orthosis Design in Automation
## 4 Discussion
This study developed a customized two-piece orthosis consisting of a rigid front and back support structure made of PLA. The soft material, thermoplastic polyurethane (TPU), can also be used in 3D printers. Compared to TPU material, the PLA is less elastic but has more support and immobility and is strong enough to bear the load. It was also considered that TPU can easily cause allergies, which makes it unsuitable to have contact with the skin for hours. The orthosis was fabricated by an affordable 3D printing machine (D-force V2, 3 DPW, Taiwan). We set the printing parameters with an infill of 20%, a printing layer of 0.2 mm, a printing speed of 200 mm per second, and an external thickness of 0.8 mm. The contact surfaces are lined with a layer of soft material to distribute loads evenly. Typically, 3D-printed orthoses were fixed using elastic nylon straps [24]. Since these straps were single use, they were better suited for orthoses that do not require frequent removal. This study uses elastic straps with Velcro to secure the front and back pieces of the cervical orthosis. This operation was convenient and easy to put on and remove the orthosis. Studies provide various input sources, designs, and materials for customized cervical orthoses [4; 5; 6; 7; 8]. The input sources for the neck surface in these articles were computed tomography [5; 7], 3D scanners [4; 6], and specific layouts of commercial sensors [8]. We used a handheld 3D scanner with a resolution of 0.5 mm to obtain body geometric models. These studies used FDM 3D printers for manufacturing, as this study did, but with different materials. The materials used include Hemp Bio-Plastic(r), Boulder, CO, USA, composed of PLA and hemp shives [5; 8], acrylic styrene acrylonitrile [4], acrylonitrile butadiene styrene [7], and thermoplastic elastomer flex material [6]. This study used PLA to fabricate the designed cervical orthosis. When designing cervical orthoses, ensuring comfort and adequate ventilation is crucial. [PERSON] et al. used elliptical holes in their flexible neck orthosis design, significantly improving air circulation and reducing heat buildup [6]. Similarly, [PERSON] et al. found that an elliptical pattern reduces stress concentrations, making the orthosis lighter and more breathable [5]. Their subsequent study refined their approach with a Voronoi pattern, achieving better ventilation and thermal comfort [8]. [PERSON] et al. optimized material distribution using a reaction-diffusion algorithm for improved ventilation [4]. [PERSON] et al. used topology optimization to create specific holes for ventilation, ensuring adequate airflow and enhancing overall comfort [7]. Except for the designs mentioned above, as shown in Figure 1, our orthosis only covers regions that pass through vital anatomical features, providing maximum ventilation while maintaining necessary support. The material utilized in this study is assumed to be isotropic for finite element analysis, although the material properties of a 3D-printed material are generally considered anisotropic. The isotropic assumption is based on the testing data obtained by [PERSON] et al. [25], who conducted tensile testing on PLA and concluded that the variation in elastic modulus on different orientations is insignificant. The measurement data reported by [PERSON] and [PERSON] [19] also agree with this conclusion. Thus, the isotropic assumption in the finite element model can be accepted. This study has certain limitations. First, the finite analysis simulations were conducted using a model of only one subject with different thicknesses, which may not fully capture the variability in human anatomy. Second, the duration of custom orthosis manufacturing was time-consuming, requiring approximately one working day for a low-cost 3D printer to complete. However, future advancements in 3D printing technology are expected to address these limitations by increasing printing speeds and offering a more comprehensive selection of materials with vibrant colors.