Durability and offloading performance of 3D-printed multilayer lattice for accommodative insoles

Custom accommodative insoles fabricated from multilayer foams are the standard of care (SoC) for offloading elevated plantar pressures in individuals with diabetes at risk of foot ulceration. While SoC insoles have demonstrated short-term effectiveness, they are prone to permanent material deformation over time, reducing their offloading efficacy. Recent work has shown that 3D-printed multilayer lattice structures using elastomeric polyurethane (EPU) can match the mechanical properties of SoC foams and is effective in reducing plantar pressures. However, their long-term pressure offloading performance and durability have not been investigated. In this pilot study, 3D-printed EPU multilayer lattice pucks and SoC multilayer foam pucks, with and without designed offloading regions, underwent one million cycles of sinusoidal compressive loading under both uniform and uneven loading conditions. Peak pressure (PP), pressure time integral (PTI), residual thickness, and elastic modulus were assessed at multiple timepoints throughout testing. Under uniform loading, both materials maintained stable PPs below the 200 kPa clinical threshold across one million cycles. Under uneven loading, SoC pucks exhibited progressive pressure increases and residual thickness reductions of up to 36%, while 3D-printed pucks maintained structural integrity with thickness reductions of 3% or less and demonstrated reduced PP over time. Both materials with designed offloading regions effectively maintained PPs below 150 kPa throughout testing. These results from bench testing are promising and show the potential for 3D-printed multilayer lattice materials as a durable and effective long-term strategy for pressure reduction.