Zone-specific micromechanical properties of the extracellular matrices of growth plate cartilage.

Growth plate cartilage demonstrates a unique capacity for cell proliferation and matrix synthesis while sustaining mechanical stresses. To test the hypothesis that the extracellular matrices along various depth of growth plate cartilage have different elastic properties, microindentation by atomic force microscopy was applied to en bloc dissected rabbit cranial base growth plate samples from the reserve zone to mineralizing zone in 50-microm increments. The average elastic modulus upon transverse indentation orthogonal to the long axis of the growth plate showed a gradient distribution, increasing significantly from the reserve zone (0.57 +/- 0.05 MPa) to mineralizing zone (1.41 +/- 0.19 MPa). Longitudinal indentation of the reserve zone along the long axis of the growth plate revealed an average elastic modulus of 0.77 +/- 0.12 MPa, significantly different from the same zone upon transverse indentation. Thus, the extracellular matrix of growth plate cartilage seems to be inhomogenous in its capacity to withstand mechanical stresses.