Manufacturing and finite element assessment of a novel pressure reducing insole for Diabetic Neuropathic patients

Physical Characterization of Material for the Development of Orthopedic Orthosis for Diabetic Foot

The diabetic foot is characterized by the loss of foot ulcerations and sensitivity. The use of orthopedic orthosis can prevent pathological changes in the diabetic foot. The objective of this study was to characterize materials used for producing orthopedic orthosis: silicone; pre-vulcanized latex of Hevea brasiliensis; Evapod, and Podadur. The Hevea brasiliensis latex material is widely indicated in the literature for biomedical purposes. Physical–mechanical properties were determined (properties of elastic deformation, resistance, durability, lightness, energy absorption, resistance to high temperatures, and chemical composition—ASTM International). In the tensile test, the latex reached 6.02 ± 0.33 MPa, having the best performance among the other materials. In the elastic module, the Podadur stood out, with 28.2 ± 0.89 MPa, compared to silicone with 0.42 ± 0.05 MPa. The most excellent Shore A hardness material was Podadur with 58%. As for the resilience, the Podadur presented a minimum value of 22%, while latex had 63%. Silicone was the densest material, with a density of 1.48 g/cm3, and Evapod and Podadur were the lightest, respectively, at 0.22 g/cm3 and 0.42 g/cm3. Morphologically, Evapod, Podadur, and latex presented open and interconnected cells, characteristics that gave them a more significant water absorption capacity. Silicone was the only material with no empty cells in its structure. In X-ray diffraction, Evapod, Podadur, and silicone materials presented well-defined crystallographic planes, whereas amorphous behavior characterized latex. Thermogravimetry showed weight loss between 240 and 650 °C in the four materials. In the fluorescence test, the presence of metals was observed in the composition of the four materials. Among the materials studied, the Podadur was the material that stood out, with some good properties for the development of orthopedic orthosis.

Effects of Custom-Made Insole Materials on Frictional Stress and Contact Pressure in Diabetic Foot with Neuropathy: Results from a Finite Element Analysis

Offloading plantar pressure in a diabetic foot with neuropathy is challenging in conventional clinical practice. Custom-made insole (CMI) materials play an important role in plantar pressure reduction, but the assessment is costly and time-consuming. Finite element analysis (FEA) can provide an efficient evaluation of different insoles on the plantar pressure distribution. This study investigated the effect of CMI materials and their combinations on plantar pressure reduction for the diabetic foot with neuropathy using FEA. The study was conducted by constructing a three-dimensional foot model along with CMI to study the peak contact pressure between the foot and CMI. The softer material (E = 5 MPa) resulted in a better reduction of peak contact pressure compared with the stiffer material (E = 11 MPa). The plantar pressure was well redistributed with softer material compared with the stiffer material and its combination. In addition, the single softer material resulted in reduced frictional stress under the first metatarsal head compared with the stiffer material and the combination of materials. The softer material and its combination have a beneficial effect on plantar pressure reduction and redistribution for a diabetic foot with neuropathy. This study provided an effective approach for CMI material selection using FEA.

Advanced design and manufacturing of custom orthotics insoles based on hybrid Taguchi-response surface method

Herein, a machining strategy to fabricate custom orthotic insoles with high surface finish and wide fit tolerance is presented. CNC milling was used to machine ethylene-vinyl acetate (EVA) foam for insoles with various surface hardness, and the Taguchi-response surface method (TM-RSM) was adopted to optimize the parameters of the CNC milling process (cutting speed, feed rate, tool path strategy, and step over). EVA foam with varying surface hardness and the tolerance of the wide fit insoles corresponding to the surface roughness were analyzed. Subsequently, a mathematical model was established to determine the optimal CNC milling parameters for a standard milling cutter under dry coolants. The results of the six parameters corresponding to the mean values of surface roughness were initially examined using the signal-to-noise ratio of the Taguchi method (TM). The surface roughness obtained with the TM-RSM was up to 4.13% higher than that obtained with the TM. The EVA foam insole with a surface hardness of 50–60 HRC and a wide fit tolerance of 0.75 mm provided the ideal level of comfort and support for patients with diabetes. The results of this study demonstrated that CNC milling provided a better surface finish of orthotic shoe insoles than other methods, which can serve as guidance in the development of machining strategies for insoles made from EVA foam.

Analysis and Assessment through Mechanical Static Compression Tests of Damping Capacity in a Series of Orthosis Plantar Materials Used as Supports

High plantar pressure is the cause of multiple types of foot injuries and one of the main reasons for patient visits in podiatry and traumatology. Therefore, there is a need to acquire specific tools to address such injuries. The aim of this study was to determine the absorption capacity of selected materials applied as plantar supports and their response to pressure. The study had a cross-sectional design. A total of 21 materials were chosen and different material families were assessed, including ethylene-vinyl acetate, polyurethane foams, and polyethylene foams. Static compression tests were performed to analyze each material. The system is ideally suited for lower-force applications, small components, biomedical applications, and lower-strength materials. Damping was determined using mathematical calculations performed on the study data. It was found that materials with a low Shore A, or soft materials, exhibited worse absorption capacity than harder materials. Ethyl-vinyl acetates had good absorption capacity, polyurethane foams had a poor absorption capacity, and soft materials provided better adaption to impact. The results suggested that damping is not determined by the hardness of the material, and materials within the same family exhibit different damping capabilities.

Designing and fabricating a novel medical insole with universal fluid layer with auto-customizability

Medical insoles play a significant role in pressure reduction, proper stress-strain distribution, and correcting some deformities in the foot. The aim of the present research is to design and fabricate new medical insoles with universal fluid layer. After fabricating two types of insoles including flat silicone insole with shore 17 and flat silicone insole with universal fluid layer (medical silicone with shore 17 and silicone gel with shore 0), PEDAR test using one person in two standing and walking positions in three conditions comprised without the use of medical insole, using of flat medical silicone insole, and flat silicone insole with universal fluid layer was performed. These insoles were also modeled and solved in Abacus software according to the results obtained from mechanical properties testing of silicone and PEDAR test. The results of the finite element analysis showed that absorption of stress and strain in the static state by the silicone insoles with universal fluid layer was 63% and 63%, and in the dynamic state was 84% and 89% more than those obtained by the flat silicone insoles, respectively. The experimental results of the PEDAR system also showed that in the standing state, the silicone insoles with universal fluid layer and the flat silicone insoles had 58% and 30% pressure reduction, respectively, in comparison with without insole condition. Also, in the gait state, the silicone insoles with fluid layer and the flat silicone insole showed 37% and 9% pressure reduction, respectively, in comparison with without insole condition. Eventually, it was found out that the silicone insoles with fluid layer reduce plantar pressure well in comparison to the flat silicone insoles.

Fabrication of medical footwear for suitable distribution of stress and strain and reduction of plantar pressure by numerical and experimental approaches

Medical insoles and orthopedic shoes are responsible for reducing the force exerted by the ground to the plantar region of the feet. This combination is designed to develop a suitable distribution of stress and strain in the plantar region. In the present study, attempts have been made to design a prototype of medical footwear which can provide a proper stress and strain distribution in the plantar region while reducing pressure in comparison with current orthopedic footwear. For this purpose, the hyper-elastic behavior materials, including styrene-butadiene rubber, silicon, Plastazote foam, polyfoam, ethylene-vinyl acetate foam, polyurethane foam, and polyurethane, have been investigated, with different degree of hardness as well as one layer of composite with Kevlar fiber, whose effect is reducing the pressure exerted to the feet. A combination of materials was used to construct an insole sample, and uniaxial pressure tests were performed for testing its mechanical properties. Then, these properties were used in finite element analysis, whereby the best type of insole for the footwear was chosen and fabricated. The results of finite element analysis were validated using Pedar system and after performing the experimental tests both statically and dynamically. Experimental and numerical investigations suggested that the sole material of orthopedic shoe should be selected as styrene-butadiene rubber. The internal layers of styrene-butadiene rubber frame from top to bottom should be comprised of Plastazote-polyurethane with Kevlar fiber-silicon shore A6, which can be a suitable orthopedic boot in terms of proper stress and strain distribution. Generally, it could reduce the pressure exerted to the sole by 79% compared with barefoot.