The effect of finite compressive strain on chondrocyte viability in statically loaded bovine articular cartilage

Abstract

Recent studies have reported that certain regimes of compressive loading of articular cartilage result in increased cell death in the superficial tangential zone (STZ). The objectives of this study were (1) to test the prevalent hypothesis that preferential cell death in the STZ results from excessive compressive strain in that zone, relative to the middle and deep zones, by determining whether cell death correlates with the magnitude of compressive strain and (2) to test the corollary hypothesis that the viability response of cells is uniform through the thickness of the articular layer when exposed to the same loading environment. Live cartilage explants were statically compressed by approximately 65% of their original thickness, either normal to the articular surface (axial loading) or parallel to it (transverse loading). Cell viability after 12 h was compared to the local strain distribution measured by digital image correlation. Results showed that the strain distribution in the axially loaded samples was highest in the STZ (77%) and lowest in the deep zone (55%), whereas the strain was uniformly distributed in the transversely loaded samples (64%). In contrast, axially and transversely loaded samples exhibited very similar profiles of cell death through the depth, with a preferential distribution in the STZ. Unloaded control samples showed negligible cell death. Thus, under prolonged static loading, depth-dependent variations in chondrocyte death did not correlate with the local depth-dependent compressive strain, and the prevalent hypothesis must be rejected. An alternative hypothesis, suggested by these results, is that superficial zone chondrocytes are more vulnerable to prolonged static loading than chondrocytes in the middle and deep zones.

A Novel Macroporous Polyvinyl Alcohol Scaffold Promotes Chondrocyte Migration and Interface Formation in anIn VitroCartilage Defect Model

“…This is likely due to excessive static compression of the cartilage tissue in the transverse direction leading to chondrocyte death. 30 The progression and rate of chondrocyte death can be studied in the future using TUNEL staining and will be a concern in determining the proper scaffold size for different defect sizes. The Ø5.0-mm scaffold demonstrated an interfacial strength that was in between that of the 4-and 6-mm-diameter scaffolds at time zero, but the interface was reinforced with time due to the inward migration of chondrocytes that resulted in a 10-fold increase in interface strength after 42 + days.…”

Special Issue on Cartilage (Part II)

“…They report that immature cartilage exhibits significantly greater amount of cell death compared to mature cartilage, which they attribute to the lower compressive modulus of the immature cartilage in the superficial zone. In a complementary study, Chahine et al (2006) test and reject the hypothesis that cell death in the superficial zone of immature bovine cartilage correlates with the depth-varying strain distribution under static loading; they present results which suggest instead that superficial zone chondrocytes are more vulnerable to prolonged static loading than their middle and deep zone counterparts. Baars et al (2006) explore treatment modalities to help reduce chondrocyte death following injurious loading.…”

Contribution of postnatal collagen reorientation to depth-dependent mechanical properties of articular cartilage

“…The relative fractions of these components and the predominant orientation of the collagen fibrils vary over the tissue depth. Experiments have shown that as a result, the mechanical behaviour of healthy adult articular cartilage is depth-dependent (Buckley et al 2008;Chahine et al 2007;Chen et al 2001a;Choi et al 2007;Erne et al 2005;Guilak et al 1995;Gründer 2006;Laasanen et al 2003;Schinagl et al 1997;Wong et al 1997;Zheng et al 2005). The equilibrium stiffness of AC increases with increasing distance from the articular surface and this is linked to increasing osmotic pressures with increasing distance from the surface (e.g.…”