## 4 Discussion
This simplification has also been used in other studies, since with a larger number of contacts, the computational time increases [29; 67]. However, [PERSON] et al. [60] showed that the use of a common mesh has little effect on the results of plantar pressure distribution when the soft tissue is assigned hyperelastic material properties. Therefore, this simplification will only have a minor impact on our results. The material assignment for the plantar tissue was carried out with a hyperelastic material for the reasons mentioned before. For this purpose, the material properties according to [PERSON] et al. [56] were used, which were also used for a subject with healthy plantar tissue and a similar age to that of the subject in this study. It was also experimentally shown that the plantar tissue has a hyperelastic property [55]. Furthermore, the normally multilayered soft tissue was defined as a homogeneous structure. However, according to [PERSON] et al. [68], this may have had little effect on plantar pressure in the FE simulation, although stresses in the soft tissue cannot be used for investigation in this case. A further material simplification was made for the bone tissue. Only one linear elastic material was chosen for the normally inhomogeneous bone consisting of cancellous and cortical bone. This simplification was used because material assignment for an inhomogeneous bone structure is a time-consuming procedure in the FE method [69]. The linear elastic bone property introduced by [PERSON] et al. [52] used in this FE model has also been applied in most studies [27; 35; 36; 56; 70]. However, it should be noted that the characteristics of the tissue and also of the bone vary from individual to individual. Here, age or diseases of the foot also have an influence [71]. People suffering from diabetes in particular usually have stiffer plantar tissue, which additionally increases the occurrence of ulcers [72]. This must be taken into account when fitting diabetes-adapted insoles. The additively manufactured insole was initially considered homogeneous in the FE model as it was made from one material, one infill, and one filler structure. However, additively manufactured components generally exhibit inhomogeneous and anisotropic properties [73]. Furthermore, the structural material of the insole was additionally wrapped with an edge, top, and bottom layer. To prevent the influence of the envelope layers, the insole could be designed without an envelope, as done by [PERSON] et al. [34]. The friction coefficient between the insole and the foot was chosen as 0.5. In the literature, different coefficients of friction have been defined for the contact between the insole and foot, which range from 0.3 [34] to 0.6 [35]. Therefore, the influence of the friction coefficient on the plantar pressure was examined in a sensitivity study. It was shown that friction coefficients showed a minor influence on the pressure distribution pattern and the maximum pressure values. These results are in agreement with the sensitivity analysis according to [PERSON] et al. [26]. Due to this, the friction coefficient of 0.5 used in this work was not considered further in the result analysis. In order to enable the calculation of the individual plantar pressure values, subject-specific boundary conditions were used for the FE model [74]. In most studies, elaborate muscle forces have been applied via muscle connectors and/or ground reaction forces. To generate the FE model as efficiently as possible in this study, subject-specific ankle reaction forces and moments were used. For this purpose, data from the subject's 3D gait analysis was imported into a musculoskeletal multi-body model. The results of the musculoskeletal model showed good agreement with data in the literature [75]. Since only five markers were placed on each foot, inaccuracies may have occurred in the calculation. More markers could be used to record the movement of the foot more accurate in further studies [76].