DISSERTATION RESEARCH: Mechanical Properties and Functional Morphology of Mammalian Footpads

脚垫普遍存在于陆生哺乳动物中；然而，在运动过程中，脚垫是如何起作用的，人们知之甚少。在每一步，脚垫被认为是缓冲冲击，稳定脚，并返回弹性能量。为了发挥所有这些作用，衬垫必须具有柔性和刚性、弹性和阻尼的矛盾特性。这项研究提出了一个解决这个明显矛盾的方法——脚垫具有机械各向异性。这一假设已经得到了在运动背景下plantigrade脚垫的结果的支持，并将在两个分别数字化进化的谱系上进行测试：猫和狗。此外，本研究还提出确定解释脚垫在种内和种间观察到的机械变化的形态学决定因素。将比较每个物种的机械和形态参数，以检查脚垫特性是否反映了先前研究中提出的运动习惯。本研究的目标将通过三种方法来实现：(1)研究移动数字化哺乳动物脚垫的运动学和力学作用；(2)测量孤立脚垫的静态和动态压缩和剪切特性；(3)检查脚垫的组成和结构形态。这项研究将首次提供足垫功能机制的实验和比较分析，特别是在运动的背景下。这一综合研究将为今后的研究工作奠定基础，这些工作将重点放在对实验室条件不耐受的动物脚垫的结构和功能，以及哺乳动物足和脚垫的规模、适应、多样性和进化上。

Dr. Virginia L. Roth & Kai-Jung ChiFootpads are found universally in terrestrial mammals; however, how footpads function during locomotion is poorly understood. At each step, footpads are believed to cushion impact, stabilize the foot, and return elastic energy. To perform all these roles, the pad must have the paradoxical properties of being compliant and stiff, resilient and damped. This study proposes a solution to this apparent paradox- the footpad has mechanical anisotropy. This hypothesis has been supported by results on plantigrade footpads in the context of locomotion, and will be tested on two lineages that evolved digitigrady separately: cats and dogs. Furthermore, this study also proposes to identify the morphological determinants that explain footpads' mechanical variation observed both intra- and interspecifically. Mechanical and morphological parameters measured on each species will be compared to examine whether footpad properties reflect locomotor habits as suggested in previous studies. The goals of this study will be achieved by three approaches: (1) Investigation of foot kinematics and mechanical roles of footpads in moving digitigrade mammals, (2) Measurement of compressive and shear properties of isolated footpads both statically and dynamically, and (3) Examination of the compositional and structural morphology of footpads. This study will provide the first experimental and comparative analysis of mechanisms of footpad function, especially in the context of locomotion. Such an integrative study will lay the framework for future work focused on structure and function of pads in animals less tolerant of laboratory conditions, and on scaling, adaptation, diversity, and evolution of mammalian feet and footpads.