How does paw pad of Canine attenuate ground impacts: a micromechanical finite element study

Background. Digitigraded mammals, e.g. dogs and cats, stand or walk on their digits or toes. Their paw pads beneath the digits or toes, rather than the entire sole of the foot, are in contact with the ground surface during locomotion. Digitigrades generally move more quickly and quietly than other animals. So far, little is known about the micro-scale structural characteristics of digitigrades' paw pads and its connection with the superior biomechanical functioning of their feet.

Methods. In this study, we investigated the micro-structure of the paw pad of German shepherd dog (GSD) using SEM and histological examination, and assessed the biomechanical functions of the micro-structured epidermis layer by using dynamic finite element (FE) simulations.

Results. We found that there exists a thick layer of stratified epithelium of a honeycomb like structure with conical protuberances (i.e. dermal papilla) embedded in each cell unit. Our FE simulation analyses revealed that this specially structured layer is capable of effectively attenuating the ground impact across a range of impact velocities. Moreover, this cushioning capacity becomes more pronounced with increased impact velocity. More importantly, this layer can also significantly reduce the mechanical stress transmitting to the soft dermal papillae and dermis by using an off-loading mechanism.

Discussion. This would provide more insights into the biomechanical functioning of the digitigrade's paw pads, and also facilitate the development of bio-inspired ground contacting components of robots and machines, and also the design of footwear and orthotics devices.