Characterization of 3D printed re-entrant midsole structure with various infill density and print direction

This study focused on manufacturing 3D printed conductive re-entrant (RE) midsoles with two slicing directions (horizontal and vertical) and three infill densities. Optimal 3D printing conditions were assessed through analyses of slicing processes, morphology, compressive and electrical properties, electromechanical property, and plantar pressure analysis. The analysis of the RE midsole was further divided into three parts: Meta (MT), Midfoot (MF), and Heel (HL). As results, horizontal direction (HD) layers were stacked horizontally, while vertical direction (VD) layers were deposited vertically, with VD being 1.5 times more rigid than HD. For VD, rigidity decreased in the order of MF > HL > MT, while for HD, it was HL > MF > MT. Both slicing directions showed similar electrical properties, with conductivity improving with higher infill density. The 50% infill density demonstrated the best electrical and electromechanical properties. Plantar pressure analysis revealed that HD provided a wider pressure area and better pressure distribution. Overall, HD midsoles with 50% infill density exhibited softer compressive property and superior electrical property during compression, offering better stability by distributing plantar pressure more effectively.