Comprehensive Biomechanism of Impact Resistance in the Cat’s Paw Pad

Abstract

Cats are able to jump from a high-rise without any sign of injury, which is attributed in large part to their impact-resistant paw pads. The biomechanical study of paw pads may therefore contribute to improving the impact resistance of specific biomimetic materials. The present study is aimed at investigating the mechanics of the paw pads, revealing their impact-resistant biomechanism from macro- and microscopic perspectives. Histological and micro-CT scanning methods were exploited to analyze the microstructure of the pads, and mechanical testing was conducted to observe the macroscopic mechanical properties at different loading frequencies. Numerical micromodels of the ellipsoidal and cylindrical adipose compartments were developed to evaluate the mechanical functionality as compressive actions. The results show that the stiffness of the pad increases roughly in proportion to strain and mechanical properties are almost impervious to strain rate. Furthermore, the adipose compartment, which comprises adipose tissue enclosed within collagen septa, in the subcutaneous tissue presents an ellipsoid-like structure, with a decreasing area from the middle to the two ends. Additionally, the finite element results show that the ellipsoidal structure has larger displacement in the early stage of impact, which can absorb more energy and prevent instability at touchdown, while the cylindrical structure is more resistant to deformation. Moreover, the Von Mises of the ellipsoidal compartment decrease gradually from both ends to the middle, making it change to a cylindrical shape, and this may be the reason why the macroscopic stiffness increases with increasing time after contact. This preliminary investigation represents the basis for biomechanical interpretation and can accordingly provide new inspirations of shock-absorbing composite materials in engineering.

Comparative morphology of the paw pad of the main arboreal Xenarthras from Amazon

“…Likewise, this same stratification can be observed in dogs, cats (Felis catus), anatolian bobcat (Eurasian lynx) and clouded leopard (Neofelis nebulosa) (Ari et al, 2018;Hubbard et al, 2009;Miao et al, 2017;Wu et al, 2019).…”

“…Despite having a different way of locomotion and support of the members on the paw pads, in view of their arboreal habits, the sloths and anteaters showed similar histological constitution to each other and to the skin of the paw pads of domestic animals, with the presence of stratified squamous epithelium keratinized, in addition to the underlying dermis and hypodermis (Konig & Liebich, 2016). Likewise, this same stratification can be observed in dogs, cats ( Felis catus ), anatolian bobcat ( Eurasian lynx ) and clouded leopard ( Neofelis nebulosa) (Ari et al, 2018; Hubbard et al, 2009; Miao et al, 2017; Wu et al, 2019).…”

“…The epidermis of dogs, cats and clouded leopard showed numerous dermal papillae projected into its interior, like that observed in T. tetradactyla , mainly, assuming similar tissue stratification for the most part. However, the guinea pig also has a dome structure inside the dermis of the posterior paw pads of the hand, consisting of hyaline type cartilage, which can act to reduce friction and compression during laying and locomotion (Barbera et al, 2019; Hubbard et al, 2009; Miao et al, 2017; Wu et al, 2019).…”

Hierarchical Structural Engineering of Ultrahigh-Molecular-Weight Polyethylene

“…Fiber reinforcement is another strategy to engineer mechanical performance of a polymer composite, while its structure is dominated by the layer-by-layer fiber array assembly into the polymer matrix . In nature, a feline or canine could safely jump from a great height because of its paw pad structure as a multilayer cushion system to ground impact resistance. ,, Its stratified epithelium layer in the paw pad is the hardest to directly ground impact, and the intermediate dermis layer composed of honeycomb-like patterns with the embedded dermal papillae could effectively attenuate the ground impact, while the internal subcutaneous layer is used for energy absorption . Here, we inherit such bioinspired design into the manufacturing of lightweight UHMWPE composite materials in which we incorporate the vertical Kevlar fiber array into the UHMWPE matrix for the formation of fiber-reinforced polymer composites to mimic a high-impact performance paw pad structure.…”

Cushion Mechanism of Goat Hoof Bulb Tissues

“…The dermal papillae regularly arranged at the inclination angle of 50° are very soft and can effectively reduce the transfer of impact from the epidermal layer to the dermal layer and also disperse the impact in the dermal layer, which avoids the stress concentration and thereby prevents the dermal layer from being destroyed. Based on the foot cushion property research on other animals like the cat's paw, the impact to the ground is usually reduced by the material characteristics of fat [29, 30], whereas the cushion mechanism of the goat hoof is determined by the composite structure and inclined holes, not only the materials. This composite structure with holes can produce more obvious cushion capacity by the coupling methodology (multilayer structure and hole structure).…”