Independent and competing roles of fluid exudation and rehydration in cartilage mechanics and tribology
Date
2017
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Articular cartilage is the load bearing and lubricating material of articulating joints. While the exact mechanism/s of joint lubrication still remain a topic of scientific debate it is well accepted that tissue hydration plays a pivotal role in this process. The first part of this dissertation focuses on the development, extension, validation, and application of a tribo-mechanics model to describe the role of interstitial fluid (hydration) in cartilage mechanics and lubrication. The second part of this dissertation details the discovery of a phenomenon termed tribological rehydration (sliding-induced fluid recovery) and attempts to provide mechanistic insights into the governing features. ☐ An analytical tribo-mechanics model was developed to study articular cartilage contacts. The model was developed for rate based sliding and indentation as well as creep loading with a spherical indenter. Each iteration of the original model included additional parameters that were relevant to the physiological condition (substrate effects, strain dependent permeability). Furthermore, each iteration applied different techniques for model validation (comparisons to literature, other testing methods, and other accepted models). The final step in the development of these tribo-mechanics models was to demonstrate their utility by studying the regional variations in cartilage material and tribological properties. ☐ While the analytical models were developed to study the mechanical and tribological effect of fluid exudation, it was discovered that interfacial sliding was capable of driving fluid back into articular cartilage. This novel sliding-induced fluid recovery phenomenon was termed tribological rehydration. Following a series of investigations, it was demonstrated that sliding develops significant hydrodynamic pressures and that the role of the permeable interface is to provide a preferred path for fluid flow into the tissue. This alternate path of fluid flow is capable of restoring cartilage lubricity, load bearing, and its hydrated nature. It was also found that the hydrodynamic parameters: sliding speed; load; contact geometry; and fluid viscosity greatly influence the efficacy of tribological rehydration, suggesting that hydrodynamic forces drive this phenomenon. Finally, by replicating in-vivo experiments ex-vivo it appears that tribological rehydration may play a major role in maintaining normal joint function and health.