Quantitative Research On Several Mechanical Properties Of Cells Based On Atomic Force Microscopy

Cancers are among the leading causes of morbidity and mortality worldwide, thus research into the early detection and treatment of cancer is going on in many medical centers throughout the world. Cancer is caused by damage inside the cell. Quantitative study on m echanical properties of cancer cells is a breakthrough approach for early detection and treatment of cancer. The traditional concept of force in physics and engineering is applied to quantitative study of basic biological processes. It has overcome the qualitative but not quantitative limitation of traditional biology methods. Owing to its nanoscopic force sensor, precise operation and physiological environment applicability, atomic force microscopy(AFM) provides scientists with a greater understanding of the microscopic world and makes it possible to study mechanical properties of cells. Studying mechanical property changes of cells is a way to quantitative characterization of intracellular changes and the pathological degree of cells. Due to the wide range of cell mechanical properties, the contents of this thesis is focused on cell mechanical properties that have important influence on basic biological processes.Cancer is a group of diseases involving cells that have abnormal division and the potential to invade or spread to oth er parts of the body. Therefore, cell mitosis is an important starting point to study mechanism of cancer cytopathic. To investigate the equilibrium force, volume and internal pressure of rounding mitosis cells, we combined AFM with optical microscope. The equilibrium force and middle section area of mitosis cells are measured using tipless cantilevers with wedges, then vol ume and internal pressure of cells were calculated. Wedged cantilever improved geometry and mechanical model of cell mitosis properties measurements. We measured the equilibrium force, volume and internal pressure of cells from different cell lines. Results showed that the cells differed significantly from each other and provide a valuable reference for quantitative study of pathologic process.Cell stiffness a biomarker to distinguish cancer cells and normal cells, it is also an aspect to the study of cancer pathology. A real time tracking method based on AFM force-volume mode is used to study the morphology and stiffness changes of cells. Demonstration of the previous cell stiffness measurement theory based on the physical properties of cells, the slope of approaching curve in force-distance curves is defined as cell stiffness. Matlab was used to effective screening and processing the data. Results showed that suspention ephrin-A1 induced morphology change of PC3 cells, but cell stiffness did not significantly change, provide new reference information for quantitative study cell stiffness.Changes of cell adhesion are a precondition for cancer cells to leave the original tumor site and migrate to other parts of the body. Therefore, quantitative research on molecular me chanism of cell adhesion is an important approach to study the metastasis of cancer. To quantitatively determine the interaction strength of cells with extracellular matrix(ECM) proteins under physiological conditions, single cell force microscopy system( SCFS) based on AFM is used. Through analyzing the mechanical principle of SCFS, a relational model expaining cell adhesion force and cell surface molecular bond rupture force was established. A dependence of cell adhesion force and molecular bond rupture force under different experiment conditions were gained. It reveals the cell adhesion mechanism from the molecular perspective, provids reliable experimental evidence for the control of cancer cell invasion and metastasis.In order to overcome the low throughput of single-cell adhesion experiments, segmented polydimethylsiloxane(PDMS) masks were developed. The usability of segmented PDMS masks was tested by photobleaching technique and a sc anning method based on hertz contact model, the utility of these masks in SC FS was also verified. The masks allowing the measurement of cell adhesion to multiple substrates, increased the horizontal comparison of experimental results, improved the throughp ut limitation of single-cell force spectroscopy and reduced the cost. Thereby laying a foundation for e ngineering applications of single cell force microscopy.Regulation of cancer cells adhesion to ECM is closely related to the invasion and metastasis of cancer. By investigating cell adhesion with the use of SCFS instead of more traditional biochemical met hods, we found and quantitatively investigate the mechanisms of ephrin receptors crosstalk to Type I collagen binding integrins in PC3 prostate cancer cells and quantitatively studied the si gnal transduction in PC3 cells. Prostate cancer most commonly metastasizes to the bones, bone is primarily composed of Type I collagen. The effect of ephrin-A1 on PC3 cells suggest that ephrin-A1 may influence prostate cancer bone metastasis.