## 1 Introduction  
Healthy human hands are incredibly versatile, enabling us to hold, grasp, manipulate objects, interact with the environment, protect ourselves, and communicate. This versatility stems from the hand's complex structure, which, however, complicates healthcare due to the multitude of conditions requiring diverse treatments, primarily rehabilitation. The need for accessibility of medical care keeps increasing due to the growing aging population, who are often more vulnerable to various types of health conditions, leading to the desire to find new solutions for improved treatment [1]. Orthoses are a commonly used device for the treatment of hand conditions. Orthoses can be prescribed for short-term use during acute recovery phases or for long-term wear to manage chronic conditions. However, the effective use of orthoses requires individualization to achieve better therapy outcomes. The need for customization poses significant challenges in traditional fabrication, including high costs, lengthy customization times, the requirement for skilled clinicians, and limited access to advanced technologies [2]. One potential solution to these challenges is additive manufacturing (AM), commonly known as 3D printing. AM addresses these issues by enabling cost-effective production,reducing manual labor through automation, and allowing for the creation of complex structures tailored to individual needs. This technology not only overcomes the traditional barriers to orthosis fabrication but also provides a similar rehabilitation effectiveness, making it a promising alternative in both acute and chronic care settings [3]. It is possible thanks to layer-wise object fabrication from a digital model. There are several types of AM processes, including stereolithography (SLA), selective laser sintering (SLS), multi-jet fusion (MJF), and several material extrusion (MEX) methods, with the widely used fused filament fabrication (FFF). SLA uses UV light to cure photopolymer resins, producing detailed, smooth parts, but requiring extensive post-processing and being limited to single-material production. SLS fuses powder with a laser, creating high-quality parts without support structures, but sharing similar limitations, with the added drawback of a high hardware cost. Commercial 3D-printed devices usually utilize MJF technology, which binds powder particles with a binder. This process allows the production of large quantities of pieces at a low cost and in a short time, while offering good and reliable quality. However, this technology faces limitations, such as a narrower range of compatible materials and higher equipment costs [4]. Consequently, alternatives need to be explored. Conversely, despite its infrequent commercial use in this field, MEX technology stands out for its accessibility, affordability, and versatility, allowing for the use of various thermoplastic materials, as well as multi-material settings and multi-axis manufacturing possibilities, making it suitable for the production of cost-effective, personalized medical products directly within clinics and whenever required [5]. At the same time, 3D-printed orthoses are comparable to conventional products and often provide additional advantages [2]. However, there have not yet been many long-term studies proving their effectiveness [6]. However, integrating MEX methods into orthopedic practice is still an ongoing development process, due to the need for further research to optimize the design, material selection, and manufacturing techniques for orthotic devices, as well as compliance with regulatory requirements to ensure the safety and quality of these devices [7; 8]. To overcome these challenges, there is a growing need to utilize design for additive manufacturing (DfAM) principles, which focus on designing products specifically for the AM process, thereby enhancing their performance, functionality, and manufacturability [9].