Are you using a peristaltic pump to pump shear-sensitive fluids or live cells? Are you using a peristaltic pump head that provides maximum protection for live cells and shear-sensitive fluids? Peristaltic pumps are the golden standard that provides gentle pumping action at low speeds, especially when compared to other positive displacement pumps which use tightly machined gears or high-speed impellers to move liquids. However, when it comes to providing the maximum protection to sensitive fluids and live cells not all peristaltic pumps and pump heads are designed equally.
If you need a solution for this type of application or feel you aren’t getting optimum benefits from your current system, keep reading. (If you read our previous blog on pumping live cells and shear-sensitive fluids with Masterflex® Cytoflow™ Pump Heads, this is the independent test data we promised we would post in the near future.)
Factors impacting shear sensitivity
Many methods are available to compare shear forces within pumps. In this case, hemolysis of blood cells was used to evaluate the sensitivity of several pump designs for live cell circulation. In vitro testing was completed using citrated bovine blood circulated through several peristaltic pump systems and settings to establish optimal conditions. All testing was completed in accordance with ASTM F756-13 (Standard Practice for Assessment of Hemolytic Properties of Materials) and FDA 21 CFR Part 58 (Good Laboratory Practice for Nonclinical Laboratory Studies) by an ANSI-ASQ National Accreditation Board (ANAB)- accredited laboratory.
The performance of each pump system was evaluated against its Average Hemolytic Index (a measure of the percentage of hemolysis of the blood cells) for 180 minutes.
- Pump motor speed
Flow rates in peristaltic pumps are dictated by the rotation speed of the motor, measured in revolutions per minute (rpm). Peristaltic pumps generally present linear flow rates versus rpm with the tubing diameter, number of rollers, and overall occlusion bed size affecting the amount of flow per revolution.
As shown in Chart 1, the motor speed is very dominant in a pump’s ability to maintain cell viability during recirculation.
- Pump head occlusion
In a peristaltic pump head, occlusion refers to the space between the two walls of the tubing as the rollers compress the tubing—full occlusion leaves no space between the walls while partial occlusion does not fully compress the two tubing walls together. In practice, full occlusion generates the highest pressure and flow rates as compared to partial occlusion.
When evaluated for blood cell hemolysis, the pump head occlusion setting was important. Less tubing occlusion allowed
space for the blood cells to shift around the force of the roller which decreased the overall percent of hemolysis. Additionally, in longer circulation times the geometry of the occlusion affects the cell viability.
Peristaltic pumps traditionally have flat rollers. The recent introduction of convex rollers has improved performance in shear-sensitive applications. Flat rollers perform best in most applications, delivering superior dispensing accuracy, maximum pressure capabilities, and higher flow rates. However, convex rollers function similarly to adjustable occlusion pump heads in creating space for cells to move during compression of the tubing (Figure 1). The result is improved cell viability during recirculation with convex rollers.
Chart 2 compares the effect of flat rollers versus convex rollers on pumps running at the same speed. In this case, equipping a pump head with less than full occlusion improves cell viability 10-25%.
Continue reading the entire independent test data shear-sensitive paper to get more helpful information as you read the results when we compare two Masterflex pump heads for pumping live cells and shear-sensitive fluids.