EXPERIMENTAL AND NUMERICAL INVESTIGATION OF STRAIN-RATE DEPENDENT MECHANICAL PROPERTIES OF SINGLE LIVING CELLS
Yuan Tong Gu1, Trung Dung Nguyen2
1Queensland University of Technology, Australia;
2University of North Dame
Living cells are the basic structural units existing in all known living organisms. It is well known that cells are sensitive to variation in their mechanical and physiological environments. Physiological loads are usually applied at varying rates to achieve optimal biomechanical and biochemical outcomes in the body. In this study, living chondrocytes, which are the mature cells in cartilage tissues, are target cells. The understanding of the strain-rate-dependent behaviour of single cells is arguably a significant contribution that would provide insight into chondrocyte health in particular and cartilage dysfunction in general. Therefore, this study aims to investigate the mechanical properties and relaxation behaviour of chondrocytes subjected to different strain-rates. Chondrocytes were collected, cultured, and prepared before AFM testing. The porohyperelastic(PHE) continuum mechanical model was used. Using the experimental results, the inverse FEA procedures were used to determine the model parameters. It has observed that the cells’ stiffness increased with increasing of strain-rates. It was demonstrated that the intracellular fluid governs the behaviour of the cells at high strain-rates whereas the cytoskeleton plays an important role. In relaxation study, there were two phases in the force–time curves. In the first phase, a sudden drop of applied force. In the second phase, the applied force gradually reduces and reaches an asymptotic value. It can be explained that the intracellular fluid was blocked within the cells at high loading rates due to low permeability of the cells. When the cells were allowed to relax, the fluid started to exude out from the cells caused by fluid pressure gradient leading to the significant reduce of the applied force at the end of the transient phase. As a result, it can be concluded that the PHE model is suitable for capturing the behaviour of living chondrocytes.