APPLICATION NOTE

Find detailed information in Application Note 11: Shear Stress/Shear Rates and Flow Rates in ibidi’s Channel Slides

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ibidi FAQs

Find answers to frequently asked questions on cell culture under flow.

What Type of Shear Stress Do You Investigate?

In vivo, several adherent cell types are exposed to mechanical shear stress in biofluidic systems such as blood or lymphatic vessels and nephrons. This mechanical stimulus has a great impact on the physiological behavior and adhesion properties of cells.

For more convenient examination of perfusion assays, ibidi has developed a special pump system, i.e., the ibidi Pump System, and special flow chambers for use in shear stress experiments, i.e., the µ-Slide I Luer Family, µ-Slide VI 0.4 and µ-Slide VI 0.1.


Shear Stress, in General

... is the mechanical force induced by the friction of liquid against the distal cell membrane. Cells are able to countervail deformations caused by shear stress by rearranging their cytoskeleton. Other shear stress dependent effects include changes in metabolism, gene expression, and differentiation. Physiological shear stress values vary from 0.5 to 120 dyne/cm² depending on the vessel type (e.g., artery or vein) and the size of the organism (e.g., mouse, rat, or human).


Unidirectional Laminar Flow

... is encountered in most small healthy biological vessels, such as small arteries and veins. Certain cells, such as endothelial cells and kidney epithelial cells, are in vivo constantly exposed to flow. Experimentally, this is achieved by perfusing medium through low walled channels, and by keeping the flow constant over time for both direction and velocity.

Homogeneous laminar shear stress covers the whole channel area of the slide, except for a thin band on either side of the channel walls and near the reservoirs. The width of these bands is proportional to the channel’s height.

For homogeneous laminar flow experiments the µ-Slide I Luer Family and the µ-Slide VI0.4 are recommended.


Pulsatile Laminar Flow

... is encountered in large arterial vessels due to the fluctuations caused by the heartbeat. Experimentally, this type of flow can be mimicked by employing unidirectional flow with a periodically changing flow rate while keeping the flow direction constant.

The ibidi Pump System is perfectly suited for creating a pulsatile laminar flow. Please find detailed instructions here.

 


Turbulent Flow

... near surfaces is characterized by changes in flow rate and direction. Direction and velocity change over time, thus the flow profile is not constant. In vivo, turbulences are rare and can only be found during pathophysiological processes. In many cases, turbulences are falsely considered to appear around plaque that has developed at the largest branching of the Arteria Carotis.

Note: Due to physical reasons, turbulent flow cannot be achieved in ibidi flow chambers using physiological flow regimes.


Oscillating Flow

... is accepted as a means of simulating turbulences when using flow chambers. Although the flow is laminar, there is no main direction due to the fact that the direction of the flow is changed at regular intervals (often this interval is every 0.5 s). Other than during valve switching, the flow rate is kept constant.

Use the ibidi Pump System to create oscillating flow conditions. Please find detailed instructions here.


Excurse: Non-Uniform Laminar Shear Stress

... occurs in vivo at branching sites and at other regions of disturbed blood flow in vessels. Experimentally, non-uniform laminar shear stress can be achieved by spatially varying flow rates. It can be used for investigating cells at different shear stresses using a single sample. In more complex experiments, it can be used for studying cells and cellular signaling when the cells are exposed to areas of strongly varying shear stress. The µ-Slide y-shaped was designed to help conduct studies of non-uniform shear stress. In the branched region of the slide, the prevalent shear stress is approximately half of that found in the single straight channel regions. Researchers should refer to Application Note 18 for numerical simulations of exact shear stress values at the branching points. Please note that it is experimentally impossible to study turbulences in a µ-Slide y-shaped.


Influence of Shear Stress on Cultured Cells

Human umbilical vein endo-
thelial cells (HUVEC) cultured under flow conditions (20 dyn / cm²) in a µ-Slide I 0.4 Luer over 9 days. The primary cells were transduced with the adenoviral vector rAV CMV-LifeAct-TagRFP 24 hours prior to the experiment.