Diffusion measurements in articular cartilage under compressive loading
A method was devised to characterize the relationship between molecular transport and static compressive loading within normal and enzymatically-treated articular cartilage. To perform loading, a novel method was developed to mechanically load an intact murine humeral head while imaging the loaded cartilage using a confocal microscope. Coupled cellular level measurements of molecule diffusion and strain were collected at the same location in the tissue. Diffusivity of inert molecules was calculated using the fluorescence recovery after photobleaching (FRAP) technique. The collected FRAP data was fit using a developed diffusion model to obtain a representative diffusion constant, D. Tissue strain was calculated using a custom 2 dimensional cross-correlation code.
To test the consistency and reliability of the methodology, three studies were performed. Study I was a sensitivity study to determine how varying FRAP test parameters effect D and to test the efficacy of the diffusion model. The purpose of Study II was to test if the method could detect changes in diffusion rate resulting from enzymatic treatment with collagenase or chondroitinase ABC on compared to normal tissue. In Study III, the goal was to characterize the effect of compression on diffusion in normal and enzymatically treated tissue and to test if the method could detect changes in diffusion as a function of load and strain for each treatment group and changes between groups.
Study I results revealed sensitivities to variations in all parameters and suggested that it is paramount that all parameters be consistent across experiments. In Study II, results showed a decrease in both treatment groups compared to untreated controls. For Study III, in each of the three groups, D decreased with increasing load. With increasing strain, a decrease in diffusion rate for the normal and chondroitinase.