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The equine hoof wall has outstanding impact resistance, which enables high-velocity gallop over hard terrain with minimum damage. To better understand its viscoelastic behavior, complex moduli were de- termined using two complementary techniques: conventional ( ∼5 mm length scale) and nano ( ∼1 μm length scale) dynamic mechanical analysis (DMA). The evolution of their magnitudes was measured for two hydration conditions: fully hydrated and ambient. The storage modulus of the ambient hoof wall was approximately 400 MPa in macro-scale experiments, decreasing to ∼250 MPa with hydration. In contrast, the loss tangent decreased for both hydrated ( ∼0.1–0.07) and ambient ( ∼0.04–0.01) conditions, over the frequency range of 1–10 Hz. Nano-DMA indentation tests conducted up to 200 Hz showed little frequency dependence beyond 10 Hz. The loss tangent of tubular regions showed more hydration sensitivity than in intertubular regions, but no significant difference in storage modulus was observed. Loss tangent and effective stiffness were higher in indentations for both hydration levels. This behavior is attributed to the hoof wall’s hierarchical structure, which has porosity, functionally graded aspects, and material interfaces that are not captured at the scale of indentation. The hoof wall’s viscoelasticity characterized in this work has implications for the design of bioinspired impact-resistant materials and structures. 

Reference point indentation (RPI) is a novel experimental technique designed to evaluate bone quality. This study utilizes two RPI instruments, BioDent and Osteoprobe, to investigate the mechanical responses of several 3D-printed polymers. We correlated the mechanical properties from a tensile test with the RPI parameters obtained from the BioDent and OsteoProbe. In addition, we tested the same polymers five years later (Age 5). The results show that for Age 0 polymers, the elastic modulus is highly correlated with average unloading slope (r = 0.87), first unloading slope (r = 0.85), bone material strength index (BMSi) (r = 0.85), average loading slope (r = 0.82), first indentation distance (r = 0.79), and total indentation distance (r = 0.76). The ultimate stress correlates significantly with first unloading slope (r = 0.85), average unloading slope (r = 0.83), BMSi (r = 0.81), first indentation distance (r = 0.73), average loading slope (r = 0.71), and total indentation distance (r = 0.70). The elongation has no significant correlation with the RPI parameters except with the average creep indentation distance (r = 0.60). For Age 5 polymers, correlations between mechanical properties and RPI parameters are low. This study illustrates the potential of RPI to assess the mechanical properties of polymers nondestructively with simple sample requirements. Furthermore, for the first time, 3D-printed polymers and aged polymers are investigated with RPI.