Methods: A one-dimensional steady-state diffusion experiment was designed and performed to measure strain-dependent diffusivities of glucose and lactate in TMJ disc tissues. Specimens with diameter of 6mm and average height of 0.6mm were prepared from 5 regions of porcine TMJ discs. Specimens were confined in a chamber between two solution wells containing phosphate buffered solution (PBS) mixed with 20 mg/mL D-glucose and 10 mg/mL L-lactate in the upstream and osmotic balanced PBS in the downstream. Samples were tested at 0, 10, and 20% compressive strain and solute diffusivities were compared statistically.
Results: Average glucose diffusivity at 0% strain was 5.62x10-11 m2/sec, decreased to 5.20x10-11 m2/sec (-7.5%) at 10%, and 4.04x10-11 m2/sec (-28%) for 20%. The average lactate diffusivity was 8.93-11 m2/sec, 8.50x10-11 m2/sec (-4.7%) and 6.95x10-11 m2/sec (-22%) for 0, 10, and 20% strains, respectively. Diffusivity for both solutes was found to be significantly higher in the intermediate and medial regions as compared to the anterior, intermediate, and posterior regions.
Conclusion: Compression of the sample significantly impeded solute diffusion at 20% strain suggesting potential difficulty for nutrient transport and metabolite removal during sustained or pathological loading. Glucose diffusion occurred at 60% the rate of lactate diffusion and was a function of molecular weight or size of the solute. The regional variation is potentially related to the inhomogeneous distribution of collagen fibers and glycosaminoglycan molecules. This study further confirmed that compressive strain induced by mechanical loading may impact disc nutritional supply and serve as a possible cause of TMJ pathologies. (Supported by NIH F31DE020230, T32DE017551, and R03DE018741.)
Keywords: Biomechanics, Cartilage, Joint dysfunction, TMJ and masticatory muscles and Tissue engineering
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