_Applied_  
_sciences_  
_Article_  
**Effects of Custom-Made Insole Materials on Frictional Stress and Contact Pressure in Diabetic Foot with Neuropathy: Results from a Finite Element Analysis**  
**[PERSON] 1, [PERSON] 2, [PERSON] 3 and [PERSON] 1,4,*(c)**  
Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
that 85% of all amputations are preceded by foot ulceration and re-ulceration [10; 11] and it can be prevented with appropriate foot care. There are various factors that contribute to the ulcer healing including glycated hemoglobin level and peak plantar pressure. Adequate levels of glycated hemoglobin is an important factor especially during the healing of an ulcer [12; 13; 14]. Other factors, including repetitive high plantar pressure, increased friction between foot and footwear, especially during walking activities, contribute to ulcer formation that can be reduced using appropriate insoles [15; 16; 17]. To prevent ulceration and re-ulceration, the custom-made insole (CMI) is commonly prescribed to redistribute the peak plantar pressure under bony prominences in a diabetic foot with neuropathy [18]. The CMI is considered ideal and is associated with the reduction of peak plantar pressure for a diabetic foot with neuropathy. In experimental studies, plantar pressure sensors have been used to measure the plantar pressure to better understand the biomechanics of the diabetic foot and factors contributing to foot ulcers during gait. However, the experimental procedures are time consuming with varying uncontrolled variables, which has made it difficult for studies to acquire reliable results for a diabetic foot with neuropathy [19; 20]. The prolonged trial and error experimental procedures in a clinical setting with a wide variety of materials for insole fabrication is a challenge for both the clinician and patients. To attain ideal results of CMI, it seems impossible to go through each material and foot complication with all possible age-dependent daily living activities. In comparison with experimental methods, finite element analysis (FEA) is a numerical tool providing solutions to complex mathematical problems to determine various stress, strain, deformation and contact pressure [21; 22]. Nowadays, FEA is a popular tool for studying biomechanics and for evaluating various protocols without prolonged patient involvement. Subject-specific FE foot models offer a huge amount of data that can be beneficial in both clinical application and footwear designs. It also contributes to understanding the behavior of foot biomechanics and the effects of different interventions [23]. Most researchers focused on a single material used to fabricate an insole with varying hardness. Others used inappropriate materials selected for a diabetic foot. In some cases, the thickness of the CMIs was not well controlled and clinically inapplicable [21; 24]. An appropriate material with controlled thickness of CMIs that is clinically prescribed for a diabetic foot with neuropathy is still lacking. Material stiffness, CMI thickness and insole contour to the foot have an effect on plantar pressure distribution [16; 25]. Increasing the material stiffness and thickness of the insole can enhance the stability during gait. However, the cushioning is reduced while increasing the insole stiffness and the stiff insoles are contraindicated towards the diabetic foot [26; 27]. Cushioning is an important factor as it acts as a shock absorber, reducing the impact on the joints, especially the ankle, knee and the lower back [28]. There is a vast variety of commercial materials available claiming to reduce the peak plantar pressure. However, very few materials can be prescribed to the diabetic foot with neuropathy.