Biomechanical properties of single chondrocytes and chondrons determined by micromanipulation and finite-element modelling

Abstract

A chondrocyte and its surrounding pericellular matrix (PCM) are defined as a chondron. Single chondrocytes and chondrons isolated from bovine articular cartilage were compressed by micromanipulation between two parallel surfaces in order to investigate their biomechanical properties and to discover the mechanical significance of the PCM. The force imposed on the cells was measured directly during compression to various deformations and then holding. When the nominal strain at the end of compression was 50 per cent, force relaxation showed that the cells were viscoelastic, but this viscoelasticity was generally insignificant when the nominal strain was 30 per cent or lower. The viscoelastic behaviour might be due to the mechanical response of the cell cytoskeleton and/or nucleus at higher deformations. A finite-element analysis was applied to simulate the experimental force-displacement/time data and to obtain mechanical property parameters of the chondrocytes and chondrons. Because of the large strains in the cells, a nonlinear elastic model was used for simulations of compression to 30 per cent nominal strain and a nonlinear viscoelastic model for 50 per cent. The elastic model yielded a Young's modulus of 14 + 1 kPa (mean + s.e.) for chondrocytes and 19 + 2 kPa for chondrons, respectively. The viscoelastic model generated an instantaneous elastic modulus of 21 + 3 and 27+ 4 kPa, a long-term modulus of 9.3 + 0.8 and 12 + 1 kPa and an apparent viscosity of 2.8 + 0.5 and 3.4 + 0.6 kPa s for chondrocytes and chondrons, respectively. It was concluded that chondrons were generally stiffer and showed less viscoelastic behaviour than chondrocytes, and that the PCM significantly influenced the mechanical properties of the cells.

Cellular contractility and substrate elasticity: a numerical investigation of the actin cytoskeleton and cell adhesion

“…Axial symmetry has been successfully used in previous computational studies to minimize computational cost (Caille et al 2002;Nguyen et al 2010;Ofek et al 2009;Haider and Guilak 2002;Rowat et al 2005). A previous 3D investigation of the role of SF contractility in the compression resistance of cells ,which used the material model employed in the current study, reported similar trends for axisymmetric and polarised cell geometries ).…”

Mechanical confinement regulates cartilage matrix formation by chondrocytes

“…While there have been many mechanical property measurements of viscoelasticity in cartilage 36 , chondrons 37,38 , and chondrocytes 39,40 , this mechanotransduction study examined how the matrix viscoelasticity impacts chondrocyte behavior. Previous studies have found limited proliferation and deposition of cartilage matrix by chondrocytes encapsulated in non-degradable or slowly-degrading hydrogels of PEG 12 , agarose 13 , alginate 41 and hyaluronic acid 22 .…”

Nanobiomechanics of living cells: a review

“…The neo-Hookean (NH) model, also known as the Gaussian model, is one of the most widely used nonlinear elastic (or hyperelastic) models owing to its simplicity. For example, it has been successfully used to model the deformation of single cells in cytocompression tests [66]. For incompressible materials, the NH model has the following energy function [67] …”