Background

Articular cartilage(AC) is a connective tissue that is constantly subject to mechanical loading and relative motion of contacting surfaces. In this regard the science of tribology has a lot to offer when it comes to understanding the causes of functional disorders associated with it such as osteoarthritis and offering solutions to such disorders. Our research efforts in this project are targeted at characterizing AC for its mechanical and tribological properties and finding the correlation between these properties and the structural composition of AC.

Figure 1. Cross sectional porcine cartilage sample

Research Overview

The mechanical behaviour of AC is governed by its biphasic and poroviscoelastic nature. Three of the major properties necessary to characterize this type of behaviour are shear or elastic modulus, drained Poisson’s ratio and diffusivity. In order to measure these properties, we carry out relaxation and creep experiments by using the Hysitron TI-950 triboindenter located in the Materials Science Center. Extraction of material properties from relaxation and creep curves is then carried out by the help of poroviscoelastic theories present in the literature. Porcine and human AC samples characterized in this way undergo MRI imaging in the Department of Radiology to quantify the amount of water, collagen and proteoglycans in them. Eventually the results of these two types of measurements  are correlated with each other to trace the effects of structural composition on the tribological and mechanical performance of AC.

AC, especially the depth, is a highly anisotropic material and there are researchers trying to incorporate this important characteristic of AC into the already existing poroviscoelastic models. In this context we work on the characterization of spin-coated transversely isotropic multilayered PDMS structures again by using nanoindentation as the main method. Our measurements are intended to serve as a guideline for researchers working on the development of new mechanical models such that they can check the validity of their numerical models through a comparison to our experimental measurements.

                                              Figure 2. A representative force relaxation curve