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Biomechanically Validated Additive Manufacturing Special Insole For Diabetic Foot

Aug 03, 2020

The United States Centers for Disease Control and Prevention (CDC) reported that in every 1,000 diabetic patients, the rate of lower extremity amputation (LEA) due to complications first appearing in the feet is 18.4%. However, LEA is preventable, and can be prevented and treated through therapeutic shoes or orthopedic insoles. Due to the differences in the individuality of patients' feet, mass-produced orthopedic insoles cannot adapt to every patient, so the use of additive manufacturing can solve this problem.

Recently, researchers at Kocaeli University in Turkey scanned the foot with a three-dimensional scanner, obtained a personalized insole model based on the foot model, and used the fused deposition (FDM) process to manufacture a special insole for diabetic feet. The mechanical properties of the E-SUN polymer wire printed samples used in the FDM process and the traditional ethyl vinyl acetate (EVA) samples were tested, and the insoles printed by the FDM process and the traditional EVA insoles were not synchronized in the walking process ( The finite element analysis and comparison of standing position, heel on the ground, flat sole, standing position, and heel off the ground) were carried out to optimize the FDM printing process to ensure the biomechanical function of the diabetic foot insole under the FDM process.

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Figure 1 Step-by-step additive manufacturing of insoles based on FDM process

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Figure 2 Test results of mechanical properties of ethyl vinyl acetate (EVA) and additive manufacturing samples (filling density of 10-100% respectively), (A) hardness test results and (B) tensile strength test results

Mechanical performance experiments show that the tensile stress of each sample of 3D printing with different filling densities varies between 6.5 and 12.5 MPa. The tensile stress of EVA foam is 2.1 MPa, which is lower than any 3D printed samples.

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Figure 3 Finite element analysis (FEA) results of each printed insole model and traditional EVA foam model in the gait phase
The finite element analysis results show that under the same external force, as the filling density of the insole model increases, the material displacement value decreases at each gait stage, while the equivalent stress increases. The results show that the insole model with a filling density of 30% and the insole model of EVA foam have the same finite element analysis results, thereby ensuring the biomechanical function of the additive manufacturing insole.

The cost of traditional processing insoles is US$31.92, and the processing time is 15 hours. A pair of dedicated insoles manufactured by fused deposition (FDM) cost US$6.88 and the processing time is 8 hours. This method greatly reduces the cost and time.