## 4 Discussion
These modifications provide comfort by reduction of peak contact pressure, especially at the forefoot and provide stability to the foot, which is similarly found in the previous studies with an improvement in gait [51; 52]. The FE modeling allowed a systematic analysis of the CMI fabricated from various materials and their combinations on peak contact pressure in a diabetic foot with neuropathy. The unique aspect of this work is to compare the frictional stress among different materials and their combinations that are useful for clinical practice toward diabetic foot with neuropathy. The peak plantar pressure is frequently addressed in the subjects with foot complications. However, the measurement of frictional stress using in-shoe pressure sensors is rarely addressed and are still challenging in real clinical scenarios. The high rate of ulceration is related to abnormal plantar pressure distribution and frictional stresses under bony prominences. These frictional stresses lead to callus formation and ulceration. Previous studies focused on the attachment of a sensor to the callus sites to measure the forces that cause the callus formation [53; 54]. In our current study, a real scenario representing a balanced standing position without CMI in a comparison with different CMI materials was analyzed. FEA is a powerful tool that can provide insights for the clinician to select appropriate insole materials and their combinations for the diabetic foot with neuropathy to reduce the frictional stresses between the foot and CMI. The repetitive maximum frictional stresses lead to callus formation, causing ulceration under the metatarsal heads. These ulcerations can be prevented with the use of CMI as it shows a remarkable reduction of frictional stress with CMI compared to without CMI. The maximum frictional stress is reduced especially under the first metatarsal head using soft material. However, due to rigidity of the base layer, the addition of a stiffer base layer with softer material increased the maximum frictional stress. As a result, maximum frictional stress can be identified as the secondary factor causing ulceration as the primary causative factor is considered as the imbalance ratio between forefoot and hindfoot in a diabetic foot with neuropathy [55]. Our previous experimental study demonstrated how CMI material and its variations dramatically reduced the peak contact pressure at the forefoot and hindfoot, includinga contact pressure shifting to the midfoot [16]. Furthermore, the combination of multi-density materials to fabricate CMI provides comfort and stability to the diabetic neuropathic foot. The information from the FE results is to shorten the trial and error process for the podiatrist, but the clinical consideration should be made after a detailed foot examination of each case. Some limitations were presented in the current study in investigating the use of CMI materials. At present, only a one-foot model was simulated with different types of CMI, and the foot model was simplified and assigned with linear elastic material properties obtained from the literature. The Achilles tendon was the only muscle force considered while other intrinsic and extrinsic muscle forces were not simulated. Moreover, the validation was not done on the same subject as the experimental study, but the plantar pressure measurement was obtained with a subject of similar weight and age.