Comprehensive Biomechanism of Impact Resistance in the Cat's Paw Pad.

Xueqing Wu,Yan Hao,Yuyang Pei,Baoqing Pei,Wei Wang,Kaiyuan Zhou

doi:10.1155/2019/2183712

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.

Highlights

Cats are generally acknowledged to have excellent athletic ability, especially in jumping, achieved through natural selection
Alexander et al [13] conducted the numerical simulation and vitro dynamic compression tests on the paw pads of some mammals, and the results show that the paw pads should have a variable mechanical property, so as to prevent the excessive ground peak reaction force and enhance stability and robustness under vibration
It is logical to argue that the pads must not be too stiff for stability when the paws first touch the ground, and the subsequent gradual increase in stiffness can improve their compliance with the ground, preventing chattering

Summary

Introduction

Cats are generally acknowledged to have excellent athletic ability, especially in jumping, achieved through natural selection. They can land smoothly, without any injury, though they are subjected to large impact forces, as high as several times their body weight [1, 2]. It is believed that the paw pads play a protective and loadbearing role during landing since they are the only body parts that touch the ground. Most sporty members of the Felidae family (including cats, tigers, leopards and so on) are extant representatives of the padded foot. The cat paw pad consists of digital and metacarpal pads, which are usually located beneath distal interphalangeal joints and metacarpophalangeal joints, respectively [3]. It is logical to argue that cats mainly rely on the metacarpal pads to absorb impact energy because they have relatively long carpals and tarsals as well as large metacarpal pads

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Conclusion