## 4 Current Approaches in 3D-Printed Hand Orthotics
### Introduction of Modular Design  
Dynamic orthoses, although complex and challenging to customize, have benefited from 3D printing technologies, enabling more precise and adaptable designs. Innovations like modular components and elastic element-based joints have improved the versatility of usage and customization. Despite advancements in this field, they are still far from being implemented in commercial usage. Future research should focus on developing lighter, more versatile and adaptable devices that can better serve people in rehabilitation and ADL. This sub-section endeavors to bridge this gap by introducing a concept for customizable dynamic orthoses capable of addressing a wide array of conditions and facilitating enhanced hand rehabilitation. The concept was developed by thoroughly understanding the requirements and capabilities of the MEX method, coupled with insights gained from workshops with experts. While AM is primarily employed to tailor the geometry of the orthosis to the patient's hand, this technology also holds significant potential for adapting the functional aspects to specific health conditions. Therefore, the proposed orthosis emphasizes the utilization of this functional adaptation concept. The envisioned orthosis comprises multiple modules that can be interconnected to craft tailored devices for specific conditions--a modular design. This approach capitalizes on universal design principles and identifies commonalities among various orthotic types. The design consists of a base and two module types: an articulating module, and a sensing module (Figure 3). The base serves as the orthosis's structure, enveloping the body part to provide support for the other components. It may consist of one or more parts affixed to the body, featuring both a rigid layer for load transmission and stabilization, and a soft layer for enhanced comfort, which can also function independently under lower loads. Printing the base flat allows printing with continuous fibers and enables subsequent shaping of the structure to match the user's hand after hot water bathing; or if using soft materials exclusively, this step is unnecessary. This process can be repeated multiple times when needed. Moreover, flat printing enables printing with a partially filled infill, thereby incorporating uniformly distributed perforations, which not only promote ventilation but also reduce the print time. Moreover, it simplifies the integration of additional components such as straps, joints, electronics, or actuators. The first module category encompasses articulating joints, which mimic, restrict, or strengthen the movement of specific body joints as necessary. These joints can be subdividedinto three types: those limiting RoM, those providing passive support, and those exerting active force (exoskeletons). Ideally, this is achieved with compliant joints that limit the axial force acting on the joint. The second module category focuses on integrating sensors, enabling the articulating joint to monitor the body joint position, track progress, provide user and therapist feedback, or enhance engagement through gamification. Notably, technologies like those developed by [PERSON] and [PERSON] [85] offer 3D-printed sensors that streamline electronics assembly for medical professionals. Tailoring the configuration of modules to individual needs and directly 3D printing them in clinics enhances the sustainability and accessibility, reducing reliance on lengthy transportation. Such a device can mimic various functions of existing devices, from basic splinting using only a rigid base, to comfortable exoskeletons integrating all module categories. This approach not only provides patients with cost-effective solutions tailored to their needs, but also streamlines the work of medical professionals, reducing manual labor and development time through an automated workflow. By focusing on both geometrical and functional adaptation, modular design allows for the quick reconfiguration of the orthosis over time.