Articular cartilage (AC) tissue lines the ends of articulating joints, withstands high stresses, and provides frictionless movement. Tissue engineering requires the understanding of many factors, yet the role of mechanical properties of chondrocytes in AC development is still largely unexplored. Cartilage mechanical function correlates to the biochemical composition of the extracellular matrix (ECM) which depends on chondrocyte’s mechanical properties, cell-cell interactions, and cell-ECM interactions. The aim of this study was to investigate the mechanical properties of chondrocytes in monolayer culture.

Bovine primary chondrocytes (bAChs) were seeded at 18 k cells/cm² in petri-dishes. Atomic force microscopy (AFM) imaging and force-indentation on cells were performed using the NanoWizard IV (Bruker/JPK) at indicated time points in PBS at 37 C. Silicon nitride tips of 18kHz resonance frequency and a 0.06 N/m nominal spring constant were used. The (8×8 or 10×10) force-indentation profiles collected on a given cell surface were used to individually fit to the Hertz model of contact mechanics to estimate the Young’s modulus of elasticity (E), and to measure adhesion energy using the JPK data processing software. Three independent replicates with n=5 cells were analyzed. A one-way analysis of variance tests (ANOVA) was used to test for significance between time points.

Cells adapted over culture period by a change in phenotype from spherical to flattened cells. Correspondingly, a significant decrease in adhesion energy was seen from day 1 (1.4×10^-16J) up to day 14 (4.9×10^-17J), contrarily a 1.36-fold increase from day 14 to 6.79×10^-17J on day 21 was observed. The elastic moduli was seen to significantly increase from day 1 up till day 14 with a 20-fold increase, while again we see the opposite trend from day 14 to day 21 with a significant 2-fold decrease. The deformability of cells as noted by adhesion energy and the elasticity of cells decreased up till day 14 while cells have an interesting slight increase in elasticity and deformability from day 14 to day 21 possibly attributable to ECM formation at this stage. Our work has the potential to deepen the understanding of cells in development, adaptation, and disease leading to the development of an engineered tissue that is mimicry of a native tissue.

Bernard Van Wie

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