Real-Time Measurement of Cell Traction Force Development with Micropost Arrays during Cell Migration in Three Dimensional Platform


Student thesis: Doctoral Thesis

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Award date21 Jan 2019


This thesis focuses on the real-time measurement of cell traction force on two-dimensional (2D) topographical surfaces and confined three-dimensional (3D) platforms.

To track cell traction force during cell migration under topographical guidance and to dynamically monitor the distribution of cell traction force, micropost sensors with parallel guiding gratings were designed and fabricated using polydimethylsiloxane. MC3T3-E1 mouse osteoblasts were used as the cell model. Traction force in the leading, middle, and trailing regions was measured during forward and reversed cell migration. Traction force showed periodic changes during cell migration and the cell morphology changed from an elongated to contracted shape. The leading region showed the largest traction force among the three regions during unguided cell migration. Under this condition, the traction force of the leading region was 5.8 ± 0.8 nN during cell contraction and 7.1 ± 0.5 nN during cell elongation. Low traction force was obtained during guided cell migration. The traction force in the trailing region decreased from 4.1 ± 0.4 to 2.2 ± 0.2 nN during cell contraction under guided migration. Traction force in the trailing region was 4.8 ± 0.3 nN during cell elongation under guided migration and lowered to 6.0 ± 0.5 nN under unguided migration. Cell migration speed and direction could be related to cell traction force. As the direction of cell migration reversed, the magnitudes of the traction force from the leading to the trailing regions also reversed.

Next, the analysis of cell migration was expanded from 2D to 3D surfaces. To study cell migration under various degrees of confinement and different coating conditions, platforms with micropost arrays and controlled fibronectin (FN) protein coating and top covers were developed. Cells only spread and contacted the top surfaces of microposts with FN coated on top. Cells were trapped between microposts that were fully coated with FN and barely moved (0.05 μm/min) when microposts were separated by 3 μm. As the spacing between microposts increased from 3 to 5 μm, limited cell movement was observed (0.18 μm/min) and cells were more likely to undergo elongation. Cell migration on micropost top was faster (0.40 μm/min) than migration between microposts. The cell nucleus was distorted, and actin filaments were observed around the cellular edges and the sidewalls of microposts that were fully coated with FN. The actin filament signal around microposts (46.6%) emitted by cells between fully FN coated microposts with a spacing of 5 μm was much higher than the actin filament signal (9.4%) around top-coated microposts. The addition of a top cover and the reduction in separation height from 20 to 10 μm increased the cell migration speed to 0.84 μm/min with larger cell migration range. The cell morphology, migration speed, and position of cells were affected by the protein coating and confinement conditions.

To understand the difference between 2D and 3D cell migration, traction force generated by cells on the surrounding 3D extra-cellular matrix (ECM) was measured during cell migration under controlled confinement conditions with different contact area. To monitor the development of traction force, 3D sensing platforms were fabricated with double-sided micropost arrays. Cell traction force was monitored during directional migration under two separation distance of 10 to 15 μm. The density of micropost arrays was modified to investigate the effect of contact area on the development of 3D traction force. Results showed that different 3D confinement conditions and contact areas affect force distribution from the leading to trailing regions of the cell. Specifically, traction force in the leading region increased with separation between the top and bottom micropost layers was small. Summing force vectors on both surfaces revealed that rapidly migrating cells experienced large force imbalance from the leading to trailing regions. The largest traction force of 28.6 ± 2.5 nN on the top microposts and highest migration speed of 0.61 ± 0.07 μm/min were obtained with the densely arranged microposts being separated by a distance of 10 μm. When the density of the top micropost array was decreased, the traction force on the top microposts decreased to 17.8 ± 4.0 nN, and cell migration speed decreased to 0.50 ± 0.08 μm/min. When the separation distance increased to 15 μm, the top traction force and cell migration speed became lower.

These results revealed that the development of cell traction force was related to the cell morphology, migration speed, and directionality during migration on 2D surfaces or 3D ECM under various degrees of confinement. The real-time monitoring and correlation of cell traction force with cell migration could provide useful insights into the mechanisms underlying in vivo cell migration. These information are important to improve the cell migration model that could lead to better understanding of cell migration in tissues.

    Research areas

  • Microfabrication, Biosensors, Cellular force, 2D and 3D cell migration