Whisking with robots from rat vibrissae to biomimetic technology for active touch

This article summarizes some of the key features of the rat vibrissal system, including the actively controlled sweeping movements of the vibrissae known as whisking, and reviews the past and ongoing research aimed at replicating some of this functionality in biomimetic robots

Vibrissa-based design of tapered tactile sensors for object sensing

Numerous mammals possess whiskers (tactile hairs, also known as vibrissae) to explore their environment. These complex mechano-sensitive vibrissae are located, e.g. in the snout region (mystacial vibrissae). Because of the deformation of the vibrissa by contact with objects and obstacles, the animal gets additional information about the environment. Despite different morphology of animal vibrissae (e.g., cylindrically or conically shaped, precurved, multi-layer structure), these biological tactile hairs are modeled in a mechanical way to develop and analyze models concerning their bending behavior with a glance to get hints for a technical implementation as a technical sensor. At first, we investigate the bending behavior of cylindrically shaped and tapered rods which are one-sided clamped and are under the load of an external force, using the Euler-Bernoulli non-linear bending theory. Then, a quasi-static sweep of these rods along various obstacle profiles is used for an obstacle profile reconstruction procedure. While scanning the object, the clamping reactions are determined, which are the only observables an animal relies on in biology. In plotting these observables and using them in a reconstruction algorithm to determine the scanned contour, we try to identify special features in dependence on the different geometries of the rods. The clamping reactions tremendously depend on the form and position of the profile which is shown in several numerical simulations

Theoretical and numerical investigations of the parametric resonance of the mechanical vibrissa

In nature, vibrissae are tactile hairs of mammals used as sensor elements for the exploring the surrounding area. These hairs, also known as whiskers, can be found in different locations on an animals body. Mystacial vibrissae are distributed over a whiskerpad on a muzzle. Carpal vibrissae are located on the downside aspect of the forelimbs of mammals. The vibrissal hair has a conical shape and grows from a special heavily innervated hair follicle incorporating a capsule of blood. As the hair itself has no receptors along its length, the vibrissa may be considered as a system for transmitting forces and torques that arise from the contact between the hair and an object to sensory receptors inside the follicle. The present thesis deals with the vibrational motion of vibrissae dur- ing natural exploratory behaviour from the mechanical point of view. The phenomenon of the parametric resonance of the vibrissa is investigated the- oretically and numerically. In the first part of this thesis, two mechanical models of an elastic beam are presented based on findings in the literature. The first model considers a straight beam with the linearly decreasing radius of the circular cross-section. The second model takes into account the circu- lar natural configuration of the cylindrical beam. Within these models, the small transverse vibration of the beam under a periodic following force at the tip are analysed using the Euler-Bernoulli beam theory and asymptotic methods of mechanics. In the second part of the thesis, the numerical analysis of the problems is performed based on the finite element method using ANSYS 16.2 software. For each model, the dynamical response of the system on the parametric excitation is simulated for different frequency values. It is shown theoretically and numerically that at specific ranges of the excitation frequency the phenomenon of the parametric resonance of the beam takes place. That means that the amplitude of vibrations of the beam increases exponentially with time, when it is stimulated within one of the frequency ranges of the parametric resonance. These ranges depend on the geometrical and material parameters of the beam model, as well as the am- plitude of the periodic excitation.Tesi

Modeling an optimal 3D Skin-on-Chip within microfluidic devices for pharmacological studies

Preclinical research remains hampered by an inadequate representation of human tissue environments which results in inaccurate predictions of a drug candidate''s effects and target''s suitability. While human 2D and 3D cell cultures and organoids have been extensively improved to mimic the precise structure and function of human tissues, major challenges persist since only few of these models adequately represent the complexity of human tissues. The development of skin-on-chip technology has allowed the transition from static 3D cultures to dynamic 3D cultures resembling human physiology. The integration of vasculature, immune system, or the resident microbiome in the next generation of SoC, with continuous detection of changes in metabolism, would potentially overcome the current limitations, providing reliable and robust results and mimicking the complex human skin. This review aims to provide an overview of the biological skin constituents and mechanical requirements that should be incorporated in a human skin-on-chip, permitting pharmacological, toxicological, and cosmetic tests closer to reality

Obstacle scanning by technical vibrissae with compliant support

Rodents, like mice and rats, use tactile hairs in the snout region (mystacial vibrissae) to acquire information about their environment, e.g. the shape or contour of obstacles. For this, the vibrissa is used for the perception of stimuli due to an object contact. Mechanoreceptors are processing units of this stimuli measured in the compliant support (follicle sinus complex). We use this behavior from biology as an inspiration to set up a mechanical model for object contour scanning. An elastic bending rod interacts with a rigid obstacle in the plane. Analyzing only one quasi-static sweep of the rod along the obstacle (in contrast to literature), we determine a) the support reactions (the only observables of the problem), and then b) the (discrete) obstacle contour in form of a set of contact points. In doing this, we first assume a stiff support (clamping) of the vibrissa, but in a next step we increase the elasticity of the support in focussing on a bearing with a rotational spring (also to control or delimitate the bending moment at the support). Thereby, we present a fully analytical treatment of the non-linear differential equations emerging from Bernoulli’s rod theory and a representation by Standard Elliptic Integrals

The Functional Diversity of Mammalian Touch Receptors

Humans in the modern world can survive without the Aristotelian senses of vision, hearing, smell or taste, but no one is completely without the ability to sense touch. This sense is essential for everything from basic tasks like tool manipulation to the complex interactions that underlie social bonding, sexual reproduction and pleasure. Touch receptors are embedded in the skin, at the interface of our bodies and the world. A remarkable array of varied receptor types tile our skin to signal different features of the objects we touch and alert us to their shape and texture. An early investigator of the neurological basis of touch, Maximillian von Frey, proposed in 1895 that the morphological diversity of neural endings in the skin could represent functional specificity. It is indeed the evolution of diverse receptor structures that has endowed the sensory organ of our skin with remarkable somatosensory functions. Here I explore the evolution of mechanosensing, and discuss how diversity in form and organization of touch receptors, from the cellular to organismal level, can shape the function of touch reception