Nanomechanical properties of individual chondrocytes and their developing growth factor-stimulated pericellular matrix
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Appendix (Supplementary Material) Appendix A. Experimental quantification of the ratedependence of indentation hysteresis of individual chondrocytes Freshly isolated cells were probed with the nanosized and micron-sized tips at indentation rates of 200nm/s, 500nm/s, 1μm/s, 3μm/s, and 5μm/s. The area enclosed by the hysteresis loop (e.g., Fig. 6) is related to the strain energy dissipated during cyclic loading of the cell, which is most likely associated with viscoelastic and/or poroelastic cell behavior (Leipzig and Athanasiou 2005). The hysteresis loop area was calculated by fitting the loading and unloading curves to polynomials, integrating, and subtracting the area under the unloading from that of the loading curve. Hysteresis was seen at all rates and normalized to the area obtained at 1μm/s (Fig. A1). In this study, an increase in hysteresis was not seen between 200nm/s to 1μm/s indentation rates, indicating a pseudo-steady state within this loading regime, giving an estimated relaxation time constant of ~1s (based on a rate of 1μm/s). A previous study involving cytoindentation of single adult bovine chondrocytes reported a time relaxation constant of 1.32s (Koay et al., 2003). Similar hysteresis behavior was reported previously for skeletal muscle cells for
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Nanomechanical properties of individual chondrocytes and their developing growth factor-stimulated pericellular matrix.
The nanomechanical properties of individual cartilage cells (chondrocytes) and their aggrecan and collagen-rich pericellular matrix (PCM) were measured via atomic force microscope nanoindentation using probe tips of two length scales (nanosized and micron-sized). The properties of cells freshly isolated from cartilage tissue (devoid of PCM) were compared to cells that were cultured for selected...
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