Pumps & Systems, November 2008
Drug development today is largely focused on biopharmaceuticals rather than chemicals, so the resultant drugs tend to be injectable liquids instead of solids. New drugs are typically designed for specific populations, so batch sizes are smaller. Ongoing pressures in drug development include increased efficiency, reduced costs, minimized risks-including cross-contamination between batches-and reduced time involved in validation procedures, paperwork and man hours. One solution is a peristaltic pump with single-use tubing or tubing sets for biopharmaceutical fill/finish lines.
Fill/finish lines have traditionally used piston pumps, but in today's biopharmaceutical production environment, piston pumps suffer from a number of drawbacks. Piston pumps contain numerous contact parts that must be dismantled, cleaned and sterilized between batches of different product. As batches become smaller, there is a need to shorten changeover times. Even if duplicate pumps are purchased to achieve faster changeovers, each pump still needs to be stripped, cleaned and sterilized; a small risk of cross-contamination between batches always remains. In contrast, the only component of a peristaltic pump that comes into contact with the product is the tubing.
If the tubing is a single-use, pre-sterilized item, the need for cleaning and sterilization is eliminated, as is the risk of cross-contamination. Disposable aseptic fluid path (DAFPA) sets are supplied double bagged and Gamma irradiated ready for use. Various single-use tubing set configurations are available. These include the required pharmaceutical grade silicone tubing for the pump and, depending on the application, a sterile filter, aseptic quick-connect fittings, pre-fillable product bag and filling nozzle.
Production managers switching from piston pumps to peristaltic pumps are often surprised at the high-accuracy, pulsation-free flow that state-of-the-art peristaltic pumps achieve. In addition, sophisticated electronic control of the pump motor enables the flow rate to be ramped up, maximized and ramped down again, reducing aeration and foaming to maintain short cycle times. It is not unusual for peristaltic pumps to be used on filling systems processing up to 150 bottles per minute.
Peristaltic pumps can be fitted with a pump head having two offset sets of six rollers. Product is drawn through two parallel tubes, and after exiting the pump head, the flows are combined via a Y-connector that also combines the pulsation from the two sets of rollers. The resultant smooth flow is comparable with that achieved using piston pumps down to micro fill levels. With appropriately sized tubing, peristaltic pumps can deliver volumes down to 0.5-ml at an industry-standard accuracy of +/-0.5 percent; smaller volumes can be delivered with an accuracy of +/-1 percent. Typical high-speed filling machines use in-process checkweighing to monitor the filling accuracy and, if necessary, the output from this can be used in a closed-loop pump control system.
Varying the pump speed is one way to change the flow rate, but peristaltic pumps can also operate with different sized tubing. This can be beneficial in applications where a facility produces a range of substantially different batches. Although it is an extreme example, a single peristaltic pump can fill volumes between 0.1-ml and 250-ml via different tubing sizes.
Some of today's biopharmaceutical products, such as live vaccines and organisms, are sensitive to shear and high pressure. In micro-filling applications, peristaltic pumps are calibrated to provide a maximum of 1.3-bar pressure. The smooth flow past the pump head rollers means that the liquid is not subjected to shear in the same way as it would be when passing through the valves and small orifices of a piston pump.
Single-use technology is becoming popular in the production of injectable liquid biopharmaceuticals. While it would be impractical to have a single-use piston pump, the only contact part in a peristaltic pump is the tubing. Peristaltic technology fits with the single-use production philosophy without compromising the required pumping characteristics.