Indentation protocol to determine viscoelastic properties of cartilage before and after crosslinking

Abstract

Osteoarthritis affects millions of people of different age groups around the world. With very few treatment options and the highly restricted capacity of cartilage to repair, new treatment options are needed. The objective of this thesis was to develop a repeatable cartilage testing protocol, which could be used to test cartilage properties and determine if crosslinking can be used as a potential treatment for osteoarthritis. Previous studies have shown CASPc can be used as a photo-sensitizer to obtain collagen crosslinking through a secondary process. The ability to perform cartilage crosslinking by light-activation, which could be done arthroscopically is especially attractive as this would allow the surgery to be minimally invasive. The indentation protocol developed for a stress-relaxation test was able to achieve 95% repeatability, meaning the error in determining cartilage properties stayed within 5% of the average for tests performed at different times. Results of photo-chemical crosslinking demonstrated no change in cartilage stiffness when compared with control specimens. The spherical indenter chosen to indent the cartilage was suspected to apply less strain on cartilage as a result of its profile, which only compressed the cartilage instead of stretching its surface. The stiffness of CASPc control specimen was observed to be increasing when compared with no-CASPc control, as a result of added viscosity of CASPc solution. This elevated stiffness was observed to diminish over time due to the diffusion of CASPc from cartilage.