Biomedical Engineering Reference
In-Depth Information
The aseptic connectors once installed cannot be disconnected to maintain
patency of the process.
Pumps
Pumps are used for fluid transfer by creating hydrostatic pressure or by dif-
ferential pressure; the maximum allowed pressure would be determined
by the weakest part of the bioprocess component exposed to the pressure.
Peristaltic pumps, syringe pumps, and diaphragm pumps are all currently
used to provide disposable pumping solutions. All of these are volume dis-
placement pumps, are easy to use, and avoid contact with the product; they
can, however, produce stress on the tubing especially when the operations
are conducted for an extended period of time. It is for this reason that special
peristaltic pump tubes are made available by Saint-Gobain. The stress on the
tube may produce particles from erosion of the tube and contaminate the
fluids being passed through.
High-end peristaltic dispensing pumps have benefited from improved
pulsation-free pump head design, a precise drive motor, and a state-of-the-
art calibration algorithm. They are exceptionally accurate at microliter fill
volumes. Peristaltic pumps that incorporate disposable tubing eliminate
cross-contamination and do not require cleaning because the tubing is the
only part that comes into contact with the product. Similarly, the cleaning
validation of peristaltic pumps with disposable tubing is significantly easier
than for piston pumps. The cost of labor and supplies for writing and execut-
ing protocols, cleaning, and documenting the cleaning process is higher for
a multiple-use piston-pump filling system. Adjusting the flow speed, and
therefore preventing foaming or splashing, is easier for a peristaltic pump
than for a piston pump. Operators can also use a ramp-up and ramp-down
feature to determine how fast a peristaltic pump reaches its fill speed. This
option helps optimize overall fill time and increase throughput.
Many biological drugs are shear-sensitive, and peristaltic pumps protect
them by applying low pressure and providing gentle handling. In contrast, a
piston pump's valve system generates fast flow through small orifices, poten-
tially damaging biological products. Even valveless piston pumps apply high
pressures and high shear factors that could harm a biological product.
On the other hand, viscous products can be problematic for peristaltic
pumps. The pumps apply only approximately 1.3 bar of pressure, and their
accuracy suffers when they handle products more viscous than 100 cP.
A diaphragm pump is a positive displacement pump that uses a combi-
nation of the reciprocating action of a rubber, thermoplastic, or Teflon dia-
phragm, and suitable nonreturn check valves to pump a fluid. Sometimes,
