Chondrocytes and osteoblasts experience multiple stresses and respectively), such that ? + for small displacements (the linear regime) where is the difference between the cell position (geometric center) when trapped without flow and trapped with flow. deformation parameter (variations in hydrostatic pressure induced from body weight and normal activity constantly act on bone and cartilage cells. These pressure variations are known to play an important role in mechanotransduction. studies performed on osteoblast cultures have shown that mechanical stimulation by hydrostatic compression plays a role in regulating osteoblast metabolism, promoting the synthesis of signaling molecules and other molecules pertinent to new bone formation.15,17,58 Focusing on only the mechanical response, Wilkes and Athanasiou73 have demonstrated that osteoblast-like cells, suspended in media, are incompressible under hydrostatic pressures to up to 7 MPa. Following conventional hydrostatic compression procedures, Smith is buy 877877-35-5 the fluid density (= 103 kg m?3), is gravity (= 9.81 m s?2), and is the height difference (0C20 cm) between the input and output syringes. The laser power was set as low as possible, but sufficient to suspend a cell and position it in the microscope focal plane. For the limited range of hydrostatic pressures examined (0C2 kPa), no Significant volume change was recorded due to a change in hydrostatic pressure. This is not surprising as the pressures applied are quite small when compared to other studies that show no deformation at Significantly higher pressures. With the applied technique, the maximum pressure that can be applied to an optically suspended cell is limited by the structural integrity of the coverslip. The microfluidic interconnects, chip materials (other than the coverslip), and chip bonding methods can withstand pressure in excess of 1.5 MPa. A previous study examining coverslip strength reports coverslip failure at pressures of ~200 kPa.53 At this maximum pressure (200 kPa) it is highly unlikely that a Significant volume change would occur for an optically suspended cell. However, it is still unclear as to the extent small pressure perturbations up to 200 kPa can induce biological responses (Smith = 1 mPa s, a cell radius, = 10 = 30 is the fluid viscosity, is the cell radius, and … As described earlier, trap stiffness is calculated by measuring the cell displacement from its equilibrium, no flow position. Trap stiffness is known to depend, among other parameters, on the properties of the object being trapped. Therefore, trap stiffness may be a source of information to characterize cellular properties. For example, cells could be the same type (for example chondroblasts) but have dissimilar actin filament distributions or orientations, intracellular fluid composition, etc., due to a difference in their location (e.g. different layers of cartilage) or healthy vs. diseased states. buy 877877-35-5 The differences in their intracellular constitution could affect the trap stiffness, and thus provide a means to identify influences on buy 877877-35-5 cell behavior. In this study, eleven chondroblasts extracted at different passages (P2, P3 and P4) and from different layers of cartilage were trapped in a straight flow and their corresponding trap stiffness calculated. The purpose of this study was to determine the reproducibility Mouse monoclonal to PTH of the experiment and the potential range of linear trap stiffness values. Figure 7 shows the trap stiffness is confined within the range of 0.84 and 1.73 pN/m diameters. The trap stiffness (m diameter chondroblast (P2). The experiment was repeated with the same cell to assess the variability due to the measurement technique. The trap stiffness was measured to be approximately 1.2 pN/… Hydrodynamic-Induced Stress: Extensional Flow For uniform flows, the magnitude of fluid induced stresses is limited by the maximum optical trap forces that may be applied without optically damaging the cell. To apply stresses similar to cell monolayer studies, a laser power of ~1 W would be required. As described in the Cell Viability During Optical Tweezing section this would inflict cell damage within ~20 s and cell death after 35 s. Therefore, in order to apply similar fluid induced shear stresses on the cell without inflicting optical damage, flows in which fluid drag is negligible are required. As described earlier, a cross-junction flow geometry creates an extensional flow where the cell is compressed and stretched at the stagnation point. Theoretically, a cell centered at a stagnation point experiences no net drag force and remains there indefinitely regardless of the magnitude of shear/extensional rate. In practice, the stagnation point represents a saddle point, unstable to perturbations in cell position. However, the cell may be maintained at that location by applying small restoring forces (with the OT) to counteract any perturbations. These restoring forces are substantially smaller than the drag force on a cell in a uniform flow with equivalent shear rates. Maintaining the.