Novel device measures stiffness and stickiness of red blood cells

Researchers have created a versatile device that measures two important properties of red blood cells that are relevant for sickle cell and other diseases: deformation and adhesion.

The team, from Case Western Reserve University (CWRU) in Cleveland, OH, describes the innovative device - a microfluidic platform with a computer algorithm that does the math - in a paper published in the journal Technology.

Sickle cell disease is a group of inherited red blood cell disorders. People with the disease have abnormal hemoglobin - the protein that carries oxygen - in their red blood cells. The abnormal hemoglobin is called sickle hemoglobin.

Red blood cells containing normal hemoglobin are flexible and shaped like a doughnut with a thin flat area in the middle instead of a hole. This allows them to squeeze round bends in blood vessels and through smaller ones to deliver vital oxygen to tissues and organs.

However, sickle hemoglobin has a tendency to form stiff rods inside the red blood cell - changing it into the crescent or sickle shape that gives the disease its name.

Red blood cells containing sickle hemoglobin are less flexible than normal red blood cells and also tend to be stickier. These two features increase the risk that they will cause a blockage in a blood vessel and impede the delivery of oxygen to nearby tissues and organs.

When such a blockage occurs, it causes a sudden and severe attack of pain - called a pain crisis - that is typical of sickle cell disease. Pain crises occur without warning and often require hospitalization for effective treatment.

In extreme cases, the blockage of blood vessels in sickle cell disease can lead to widespread organ damage and early death.

Currently, the only way to cure sickle cell disease is with a stem cell transplant. But unfortunately, most patients are either too old for a transplant or do not have a relative with a good enough genetic match to receive transplantable stem cells from.

Effective treatments exist and these can reduce symptoms and prolong life. Early diagnosis and regular monitoring to prevent complications also helps.
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Potential monitor of disease progression

By assessing the extent of stiffness and stickiness, or the "dynamic deformability and adhesion," of red blood cells, the new microfluidic device offers great potential as a way to monitor progression of sickle cell disease, note the researchers.

They say the device could also help with research and developing new treatments for sickle cell disease.

Other ways to measure stiffness and stickiness in red blood cells - such as atomic force microscopy and optical tweezers - do exist, but they do not lend themselves to working with whole blood in a clinical setting, say the researchers.

They note their device can assess the stiffness of a single red blood cell, and also, by mimicking blood vessel properties, assess the stickiness of red blood cells from whole blood of sickle cell patients.

Lead investigator Umut Gurkan, an assistant professor in CWRU's Department of Mechanical and Aerospace Engineering, says:

"The microfluidic system developed here has the potential to be used in a high-throughput manner with an integrated automated image processing algorithm for measurement of RBC [red blood cell] deformability and adhesion in patients' blood."

The authors explain that healthy red blood cells undergo reversible deformation when they circulate around the body in blood vessels. They respond to "fluid shear stresses" extremely fast - they can bend and regain their shape in the space of 100 milliseconds.
'Interplay between dynamic deformability and increased adhesion'

To assess dynamic deformability of red blood cells, the researchers used what they call a dynamic deformability index (DDI), which they define as "the time-dependent change of the cell's aspect ratio." Essentially, a cell's DDI is a measure of how quickly it springs back to its normal shape after experiencing flow shear stress.

In their paper, the team describes a range of tests where they measured the DDI of deformable and non-deformable red blood cells.

The researchers also compared adhesion of deformable and non-deformable red blood cells from blood samples taken from sickle cell patients. They tested the stickiness of the cells under different flow shear stresses - both within and outside ranges experienced in normal blood vessels.

They found that at flow shear stresses "well above the physiological range," non-deformable sickle red blood cells were much stickier than deformable sickle red blood cells, "suggesting an interplay between dynamic deformability and increased adhesion" of red blood cells when blood vessel blockage occurs.

The team suggests the device may also be useful for studying the deformation of cells that could be relevant in other diseases - such as diabetes, malaria and the bone marrow disorder polycythemia vera.

The researchers plan to study red blood cell stiffness and stickiness in more sickle cell disease patients so they can link the two properties with other disease and patient characteristics.

As the technology for making them becomes cheaper and more widely available, more and more researchers are using microfluidic devices in all kinds of ways to investigate, diagnose and perhaps even treat disease.

For example, Medical News Today recently learned how an "IVF chip" incorporating microfluidics with imaging techniques enabled researchers to film a single sperm fusing with an egg cell.

And in May 2015, another article described how scientists are using microfluidic technology to develop new immunotherapy vaccines. Using microfluidic technology, they can squeeze immune system B cells so their membranes develop temporary holes through which antigens that program specific immune responses can be inserted.

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