17. Biotribology and Human Tribology

In biotribology and human tribology, tribological theories are applied to biological systems and human interactions, respectively. This chapter focuses on the human tribology fields, slip and fall accidents and hand-object interaction, and the biotribology fields, ocular and oral tribology. Slip and fall accidents are caused by low friction between the shoe and floor surface, frequently due to a fluid contaminant. Experimental methods of evaluating shoe-floor friction are most relevant to human slips when mimicking the dynamics of human stepping and the environmental conditions (using common shoes, floors, and/or contaminants). The tribological mechanisms affecting shoe-floor friction are adhesion, hysteresis, boundary lubrication, and hydrodynamic lubrication. Modeling efforts have shown that certain floor roughness parameters correlate well with shoe-floor friction, that adhesion and hysteresis can be simulated with finite element analysis, and that models using Reynolds equation can simulate the hydrodynamic effects. Skin friction is essential for everyday activities such as gripping and manipulating objects. The friction of the outermost layer of the skin, the stratum corneum, is modulated by hydration allowing the body to optimize skin friction through perspiration. Increasing skin friction leads to improved performance by increasing grip strength and fine motor speed. The tribological interaction in the eye, with or without a contact lens, contributes significantly to comfort. Eye discomfort and the disorder dry eye syndrome occur when abnormalities occur to any of the three tear film layers that protect and lubricate the eye. Low friction is essential to the comfort of contact lens. Experiments and models have implicated that adhesion, hysteresis, boundary lubrication, and elastohydrodynamic lubrication may all contribute to eye lens friction. Tooth wear due to abrasion and corrosion is a major threat to healthy teeth and dental restorative surfaces. Tribological principles such as two-body wear, three-body wear, and corrosion along with innovative modeling and experimental techniques have revealed personal risk factors and the effects of behavior on dental wear. Another application of oral tribology is creaminess perception in the mouth. Creaminess of a food is largely dependent on its ability to lubricate the mouth surfaces. Replication of this sensation using low-fat alternatives to traditional high-fat creamy foods has the potential to achieve reductions in obesity. This chapter demonstrates the applications of tribology to biological systems.