Effect of Mechanical Strain on Solute Diffusion in Human TMJ Discs: An Electrical Conductivity Study

Abstract

This study investigated the effect of mechanical strain on solute diffusion in human TMJ discs (mean cadaver age 77.8) using the electrical conductivity method. The electrical conductivity, as well as small ion diffusivity, of male and female TMJ discs was determined under three compressive strains. In the male group, the average disc electrical conductivity (mean ± sd) at 0% strain was 5.14±0.97 mS/cm, decreased to 4.50±0.91 mS/cm (−12.3%) at 10% strain, and 3.93±0.81 mS/cm (−23.5%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.44±0.08, decreased to 0.40±0.08 (−8.9%) at 10% strain, and 0.36±0.08 (−16.7%) at 20% compressive strain. In the female group, the average disc electrical conductivity at 0% strain was 5.84±0.59 mS/cm, decreased to 5.01±0.50 mS/cm (−14.2%) at 10% strain, and 4.33±0.46 mS/cm (−25.8%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.49±0.05, decreased to 0.43±0.04 (−11.3%) at 10% strain, and 0.39±0.04 (−19.9%) at 20% compressive strain. The results indicated that mechanical strain significantly impeded solute diffusion through the disc. This mechanical strain effect was larger in the female than in the male human TMJ disc. This study may provide new insights into TMJ pathophysiology.

Electrical conductivity and ion diffusion in porcine meniscus: effects of strain, anisotropy, and tissue region

“…This is likely because meniscus composition is most like that of TMJ tissue, which also has a relatively low GAG content as compared to articular cartilage or intervertebral disc (Almarza and Athanasiou, 2004). The strain-dependent behavior of electrical conductivity and relative ion diffusivity found here is similar to results in the literature for other cartilaginous tissues (i.e., meniscus, articular cartilage, intervertebral disc, TMJ), which showed that static compression leads to reduced solute diffusivity and/or electrical conductivity Jackson et al, 2008;Kleinhans et al, 2015;Kuo et al, 2011;Quinn et al, 2000;Quinn et al, 2001;Wright et al, 2013;Yuan et al, 2009). This change is likely due to reduced tissue water content caused by fluid exudation during compression.…”

“…This value is the averaged relative diffusivity of Na þ and Cl À ions, which were assumed to carry the current as the primary ions in PBS solution (Kuo et al, 2011;Wright et al, 2013).…”

“…Due to the low GAG content ( $ 2-3% dry weight) in meniscus compared to other cartilaginous tissues, it was considered an uncharged tissue. The relative diffusivity (D=Do) of NaCl can be related to the conductivity measurements by (Gu et al, 2004;Kuo et al, 2011;Wright et al, 2013):…”

“…The electrical conductivity of several cartilaginous tissues has been investigated, see Table 1. These studies have found that conductivity is directly correlated to tissue water content Gu et al, 2004;Jackson et al, 2009;Kuo et al, 2011;Wright et al, 2013), and is strain-dependent Kuo et al, 2011;Wright et al, 2013). Better understanding of electromechanical properties of tissues, including conductivity and ion transport, and their relationship to tissue composition and relevant loading conditions, can provide essential information about endogenous electrical signals, which play a key role in directing resident cellular activity.…”

“…Electrical conductivity can be used to estimate the relative ion diffusivity in a tissue (Gu et al, 2004;Jackson et al, 2006;Kuo et al, 2011;Wright et al, 2013). Elucidating transport properties in meniscus is important given that much of the adult meniscus is Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com avascular (Makris et al, 2011).…”