Friction studies in biological systems are reviewed, including synovial joints (cartilage, meniscus), eye, pleurae, fat pad, skin, and oral cavity as well as daily activities associated with shaving, brushing, slip, etc. Both natural systems and medical interventions in terms of diagnoses and artificial replacements are considered. Important relevant biomechanical, physiological, and anatomical factors are reviewed in conjunction with friction studies in terms of both methodologies and fricti...

The remarkable ability of geckos to climb and run rapidly on walls and ceilings has recently received considerable interest from many researchers. Significant progress has been made in understanding the attachment and detachment mechanisms and the fabrication of articulated gecko-inspired adhesives and structured surfaces. This article reviews the direct experiments that have investigated the properties of gecko hierarchical structures, i.e., the feet, toes, setae, and spatulae, and the corre...

The application of tribological knowledge is not just restricted to optimizing mechanical and chemical engineering problems. In fact, effective solutions to friction and wear related questions can be found in our everyday life. An important part is related to skin tribology, as the human skin is frequently one of the interacting surfaces in relative motion. People seem to solve these problems related to skin friction based upon a trial-and- error strategy and based upon on our sense for touch...

Many animals have the natural ability to move on various surfaces, such as those having different roughness and slope substrates, or even vertical walls and ceilings. Legged animals primarily attach to surfaces using claws, soft and hairy pads, or combinations of them. Recent studies have indicated that the frictional forces generated by these structures not only control the movement of animals but also significantly increase the reliability of their attachment. Moreover, the frictional force...

The extremely low friction and minimal wear in natural synovial joints appear to be established by effective lubrication mechanisms based on appropriate combination of articular cartilage and synovial fluid. The complex structure of cartilage composed of collagen and proteoglycan with high water content contributes to high load-carrying capacity as biphasic materials and the various constituents of synovial fluid play important roles in various lubrication mechanisms. However, the detailed di...

Steady-state and transient variations in frictional force observed in tribological experiments of mesothelial tissues sliding in lubricant were analyzed with a mathematical model to test the hypothesis that such phenomena are manifestations of elastohydrodynamic lubrication and, importantly, do not require physical contact between the sliding surfaces. The model incorporates three phenomena characteristic of elastohydrodynamic lubrication: thinning of the liquid layer between sliding surfaces...

The femoral condyles of a knee prosthesis articulate with a combination of rolling and sliding on the tibial polyethylene plateau. Little is known about potential polyethylene damage due to rolling motion. Since rolling does not exclude the presence of tangential surface loads, this study sought to investigate the influence of tractive rolling on the wear of polyethylene. A “wheel-on-flat” apparatus, consisting of a metal wheel and a polyethylene flat, mimicked contact conditions present in t...

As green tribology is a new field of tribology still in its infancy, understanding its fundamentals is essential for its further development. In this article, a brief historical retrospective on the emergence of green tribology is introduced first, and then the definition, objectives, and disciplinary features of green tribology are clarified. In particular, the technological connotations of green tribology are expounded comprehensively. Also, the developing directions of this new area are en...