# Pressure-Reducing Design of 3D-Printed Diabetic Shoe Midsole Utilizing Auxetic Lattice Structure
## 1 Introduction  
It is estimated that the global prevalence of diabetes will reach 532 million by 2035 [1]. Diabetic patients' hyperglycemia can lead to peripheral neuropathy in areas such as the plantar foot, resulting in diabetes-related foot ulceration (DFU) [2]. The rise in plantar pressure plays a vital role in the development and recurrence of diabetic foot ulcers [3, 4]. Relieving areas of excess plantar pressure is essential to diabetic foot prevention and management [5, 6]. Modern therapeutic footwear has a complex, layered structure including an outer sole, midsole, and insole. Previous research on diabetic footwear has primarily focused on the customized design of insoles to optimize the plantar pressure distribution [7, 8, 9]. However, to enhance the cushioning performance of footwear for diabetic patients, several medical and biomaterials science studies have investigated the relationship between midsole design and plantar biomechanics, exploring their applications in foot protection and disease prevention among diabetic patients. For instance, some researchers utilized 3D-printed lattice structures in shoe midsole design to enhance the energy absorption capacity and elasticity [10]. Other research analyzed changes in plantar pressure and soft tissue stress indiabetic patients with neuropathy using different midsoles, providing a basis for optimizing the structure of protective diabetic footwear [11]. [PERSON] et al. proposed reducing overall plantar pressure in diabetic patients by combining individualized 3D-printed midsoles with self-adjusting insoles [12]. These studies show that in addition to customized insoles, an appropriate shoe midsole design is crucial to reducing plantar pressure in diabetic patients. Materials with a negative or zero Poisson ratio, known as auxetic materials, exhibit exceptional characteristics such as energy absorption and dissipation, pressure reduction, fatigue toughness, and fracture resistance [13; 14; 15]. Compared to diabetic shoes with traditional PU foam heel pads, heel pads with auxetic re-entrant honeycomb structures significantly reduce the peak and average pressures on the heel [16]. Shoe midsoles utilizing mass-tunable auxetic geometry can effectively reduce ground reaction forces compared to traditional midsoles, lowering the risk of foot injuries during intense physical activities [17]. Auxetic midsoles exhibit higher strain energies and greater energy absorption capacities than traditional midsoles, which helps reduce spinal fatigue during walking [18; 19]. Using auxetic midsoles during high-demand activities, such as vertical jumping, can reduce the lumbar load and decrease the risk of musculoskeletal injuries [20]. Previous research proposed applying midsoles with auxetic lattice structures in running shoes to enhance shock absorption; make the shoes lightweight, flexible, and body-conforming; and provide greater tensile strength [21]. Despite existing research recognizing the superior physical properties and benefits of auxetic structures in shoe midsoles, more exploration and validation are needed regarding their application in protecting plantar soft tissue and preventing plantar-related diseases. Therefore, the novelty of this study lies in its verification of the capacity of auxetic lattice midsoles to adapt to foot morphology and their effectiveness in optimizing the plantar pressure distribution through plantar pressure measurements and finite element analysis. This study also analyzed the feasibility of using auxetic midsoles to prevent diabetic foot ulcers or aid in their treatment. Moreover, this research employed a different auxetic lattice structure than those used in similar studies for midsole applications, providing a new reference paradigm for designing pressure-relieving footwear products. This study aimed to investigate the effect of proposed shoe midsoles with auxetic lattice structures on pressure-relieving performance.