# Pressure-Reducing Design of 3D-Printed Diabetic Shoe Midsole Utilizing Auxetic Lattice Structure
## 4 Discussion
### Effects of Auxetic Structural Design on Midsole Deformation and Plantar Contact Area  
When compressing auxetic lattice-structured midsoles, pressure is converted into displacement and deformation of the lattice, thereby reducing plantar stress. The auxetic 60\({}^{\circ}\) lattice structure allows for more significant elastic deformation of the midsole under the same load conditions, which can reduce foot deformation and plantar pressure. This is consistent with findings from existing research on auxetic structures. Auxetic materials can conform to curved surfaces, such as surfaces of the human body, through the formation of synclastic curvatures [51]. Increases in the plantar contact area are associated with less load per unit in each plantar region [52; 53]. The deformation of the auxetic lattice structure in  
Figure 8: Comparison of maximal displacement and contact area in each region of shoe midsoles: (**a**) walking state, (**b**) running state.  
the shoe midsole may increase the plantar contact area, thereby reducing the peak pressures in various plantar regions.  
Figure 9 illustrates the differences in the lattice structures at the center of pressure in the HF region for the A60 and N90 midsoles. The midsole of the A60 shoe features a honeycomb structure with re-entrant elastic rods that exhibit varying degrees of bending, with the inner rods bending more significantly than the outer rods. This variance in bending results in the tilting of the bridging beam. Consequently, the shoe's tensile structure is better able to conform to the curved surface of the sole, thereby generating a larger contact area. Unlike the auxetic lattice with re-entrant units, the rods of the non-auxetic 90\({}^{\circ}\) structure are not V-shaped, which imparts additional rigidity to the structure. Consequently, the non-auxetic 90\({}^{\circ}\) structure deforms less under the same load, resulting in a smaller contact area between the plantar foot surface and the insole than with the V-shaped configuration.  
The A60 midsole, with its superior compliance with the plantar foot surface and better redistribution of plantar stress, is a testament to the potential of scientific research. Its exceptional plantar pressure reduction and conformity characteristics make it a valuable tool for preventing pressure ulcers in diabetic patients during physical activities. Moreover, this lattice structure has applications in specialized footwear such as military boots designed for prolonged walking [54; 55], protective shoes for the aged [56], and therapeutic shoes for alleviating chronic metatarsalgia [57; 58]. With the advancement of parametric design and additive manufacturing, 3D printing technology is not just a tool but a game-changer. It enables the production of midsoles that meet diverse individual needs based on the design of filled two-dimensional or three-dimensional patterns. Traditional manufacturing typically involves cutting and shaping from larger material blocks, resulting in considerable scrap. Unlike traditional manufacturing methods, 3D printing's high precision significantly reduces material waste and improves the stability of the sole structure [59]. Thus, applying 3D printing technology and utilizing auxetic lattice structures to recover or maintain foot health represent a scientific design concept that aligns with green manufacturing, significantly contributing to sustainability.