To reduce the trial and error in a real clinical scenario, the finite element analysis (FEA) can be effectively used to simulate various effective pad designs and a material selection to reduce and redistribute peak plantar pressure in a diabetic foot with neuropathy. The aim of this study was to investigate the effect of pad design and material stiffness on the reduction in plantar pressure in a diabetic foot with neuropathy using FEA. Three-dimensional foot models with a customized insole (CMI) were created to study the peak contact pressure. Ethylene vinyl acetate, Nora^® Lunalastike, and thermoplastic polyurethane were assigned to the top, middle, and base layers of the CMI, respectively. Two types of pads were proposed: a heel pad and a heel–forefoot pad. Four different materials with different stiffnesses were assigned as pad materials including a void pad. The FEA revealed that pads with soft materials reduced peak plantar pressure more effectively than stiffer pads. The use of a softer heel–forefoot pad reduced the peak plantar pressure at the midfoot and forefoot compared with other pads. The findings suggest that the material and design selection for the fabrication of CMIs with pads are important factors in reducing plantar pressure and may be useful in the management of a neuropathic diabetic foot.

Impact force remains the primary cause of foot injury and general discomfort with regard to footwear. The footwear industry traditionally relies on modified elastomers (including natural rubber) whose properties can be physically adjusted by varying the constituents in the rubber formulations. This work aims to investigate the effect of filler/plasticizer fractions on shock attenuation of natural rubber soles. The statistical response surface method (RSM) was used to optimize the loading of natural rubber, fillers (carbon black and china clay) and a plasticizer (paraffinic oil). A novel predictive equation addressing the effects of additives on the physical and mechanical properties of the shoe sole was successfully created using the RSM. Our results demonstrate how the concentrations of these components regulate final properties, such as impact force absorption and hardness, in the commercial manufacture of shoe soles. While a higher loading level of plasticizer promotes reductions in hardness and impact force, as well as energy dissipation, in these modified elastomers, these properties were improved by increasing the filler content.

Diabetic foot ulcer patients are usually unaware of excessive pressure on their feet due to lost pressure sensitivity. Offloading insoles are used to alleviate foot pain. This study investigated the effect of infill pattern and infill density on plantar pressure reduction for 3D-printed insoles while walking. The study involves five infill patterns: grid, honeycomb, triangle, cubic, and gyroid, along with several infill densities ranging from 14% to 20%. The test 3D-printed thermoplastic polyurethane specimens were assessed for mechanical properties to identify suitable infill patterns for creating prototypes of insoles. The results indicated that the honeycomb infill pattern exhibited the highest maximum compression load at 50% compressive strain and has a significant area under the loading-unloading curve, signifying high energy absorption. Conversely, the gyroid infill pattern exhibited the lowest maximum compression load at 50% compressive strain and minimal energy absorption. Both infill patterns with 20% infill density were applied in 3D-printed insoles and tested on the foot plantar pressure of healthy male volunteers during walking. No statistically significant differences in plantar pressure were observed between the two infill patterns compared to walking without insoles. However, the reduction of plantar pressure at hindfoot region was noticed when using the insoles.

The increased prevalence of unhealthy lifestyles has led to an increase in numerous diseases, especially diabetes mellitus. Hyperglycemia causes peripheral neuropathy, which frequently results in loss of sensitivity in regions such as the plantar foot and increases the risk of diabetic foot ulceration. These ulcers are typically managed with therapeutic insoles designed to reduce plantar pressure. Conventional insoles typically consist of multiple layers of various soft materials. The concept of a 3D-printed insole is introduced in this study, especially regarding infill and infill density. The commercial lattice structures in 3D printers, such as honeycomb, rectilinear, and gyroid, with between 14% and 22% infill density, are considered in this work to study the mechanical behavior in terms of the ability to withstand compressive load and energy absorption capability. The honeycomb pattern with 22% infill density provides good results in comparison to other patterns. This study also verifies that a 3D-printed insole, featuring an optimized infill pattern and density, significantly reduces both the peak and mean plantar pressure in the hindfoot region during the midstance phase of the gait cycle, as observed in both the finite element (FE) model and experimental results. Significantly, this study provides guidelines on the characteristics of energy absorption and the compressive load of infill pattern and density for the 3D-printed structure to develop the orthotic insole in future studies.