Design and Characterization of Negative Stiffness Lattice Structures for Diabetic Midsoles

Diabetes mellitus is a chronic condition that often leads to peripheral neuropathy, characterized by pain, tingling, and reduced sensitivity in the lower limbs. These symptoms increase the risk of foot ulcers and amputations, mainly due to elevated plantar pressures from mechanical overload. Standard prevention methods include custom footwear or insoles designed to redistribute weight and accommodate foot de-formities. However, static insoles have limited effectiveness, as plantar pressure points shift over time, requiring frequent adjustments that increase both costs and waiting times. Moreover, static offloading may transfer stress to adjacent areas, potentially triggering new ulcerations. While prior research has introduced cellular metamaterials for dynamic plantar pressure redistribution, this study advances the field by developing a complete, application-oriented workflow for physical prototyping and mechanical validation of such structures. The proposed pipeline leverages Thermoplastic PolyU-rethane (TPU) material extrusion, enabling the fabrication of customized and test-ready prototypes suitable for gait simulation and potential in vivo trials. The cellular unit's compressive behaviour was assessed through theoretical force threshold estimations and experimental compression tests, leading to a data-driven optimization of the unit cell geometry and arrangement for effective dynamic offloading. This study reaches the mechanical validation of the cellular unit under static compression, laying the groundwork for future integration into full-scale orthotic devices and clinical evalua-tion. By bridging the gap between conceptual design and real-world implementation, this work offers a scalable and adaptable solution to improve diabetic foot ulcer pre-vention and supports the development of personalized, next-generation orthotic sys-tems.