## 4 Conclusions  
The purpose of this study was to determine the feasibility and limitations of additively manufactured polymer gear bearings. The gear bearings were manufactured using PLA with an infill of 15%, and the experiments were designed such that the gear bearings were subjected to loads of 18 N and 45 N and rotational speeds from 250 rpm to 1500 rpm in increments of 250 rpm. PLA was used with an infill of 15% as a lower limit or baseline, and we consider that selecting a material with better mechanical properties combined with an optimal 3D printing technology and an optimized infill pattern and density can only improve the bearing's performance. Although PLA is not a prevalent choice for bearing materials, we embarked on exploring how this type of 3D-printed bearing performs. Common selections for FDM 3D printing include ABS (acrylonitrile butadiene styrene), PET (polyethylene terephthalate) and PEEK (poly-ether-ketone), but these materials are also not typically employed for bearings. In the existing literature, it is evident that polymer bearings are fairly widespread, with numerous manufacturers; however, our focus was on the utilization of 3D printing technology. It is possible that PLA may not become the primary manufacturing choice in the future, but the unique geometry we employed may still have applications. Consequently, our aim was to present our findings, not only from the perspective of using 3D printing technology but also considering the bearing's geometric design. The rapid evolution of additive manufacturing techniques has opened up new ways for the production of complex mechanical components with interesting material properties. In this study, we explore the feasibility of employing 3D-printed polymer materials for the creation of bearing systems. Our research sheds light on the potential of polymer-based bearings to broaden available solutions to industries in which friction reduction and cost-effective manufacturing are concerns. The experiments have shown that at low rpm, the bearing is a feasible alternative for short periods of time, with the longest average lifetime of a gear bearing being 57 h at 250 rpm for a load of 18 N, leading to a number of 855.000 loading cycles. Another factor to take into consideration are the vibrations encountered during testing. These appear because of poor precision in the manufacturing process, as well as dimensional and geometrical tolerances. This issue can be addressed by using other additive manufacturing technologies that can provide better performance or using other types of polymers. An optimization study can address the situation in which the number of gear teeth can improve the lifetime, with more teeth in contact meaning a greater contact surface. Also, an increase in infill density should have a positive impact on lifetime and bearing capacity. Since we now have a baseline after this study, we can extend and optimize designs. The applications of PLA can be chosen based on its advantages: it is non-toxic, environmentally friendly, non-magnetic and can be used in simple 3D printers. On the other hand, its mechanical properties are rather low when compared to steel, ceramics or other polymers. Taking these into consideration, some industries that might benefit from PLA's properties are medical devices, such as custom surgical guides being 3D printed for patientspecific cases (dental, orthopedic or tumor resections), prosthetics, braces, wearable sensors or drug delivery systems for one-time use that can be environmentally disposed of. Also, in the context of MRI-magnetic resonance imaging devices, the non-critical elements involved could use such bearings, for example, adjustable mounts, brackets, fixtures for holding instruments and accessories. Other application industries might be food and beverage, prototyping, education and hobbies, artistic works or the toy industry, which could benefit from the environmental friendliness of PLA.