Fluid Handling solutions with laboratory pumps

Generally speaking all media/reagents entering/leaving a bioreactor must be sterile. This usually is achieved by autoclaving the liquid itself plus all the contact surfaces between the feed reservoir and the reactor.

Usually the easiest pump type to employ is the peristaltic pump, because here the only contacted surface is the pump tubing which is available in pharmaceutical quality and is autoclaveable. Gear, piston and membrane pumps usually stumble at the first hurdle as they are not autoclaveable but are at best sterilisable/clean-in-place. In addition, strong shear forces are generally attributed to such pumps, which can damage the cells in the pump medium.

Gentle, cell-sensitive pump systems are required at all scales for bioreactor production systems, in the analysis of by-pass streams, reactor inoculation and harvesting. The required flow rate is dependent on the application and reactor size and hence varies considerably. Often cells must be transported using systems not originally designed for this application and hence not usually ideally suited. This results in irreparable cell damage often firstly visible at a later stage in the cultivation.

A comparison between different peristaltic pump systems was made by Ms Fan Sozzi-Guo and Prof Dr Ursula Graf-Hausner of Zürich University of Applied Sciences Winterthur, and Dr. Joanne Laukart of ISMATEC SA. Initial discussions and experiments rapidly established that the higher the number of rollers in the pump head the higher the level of mechanical cell damage.

Further intensive experimentation with two- and three-roller heads then proved that the form of the roller/tube-bed is also a very important parameter responsible for cell damage.

All pump heads were tested with the same tubing diameter to reduce the variation due to shear forces on the tubing walls. The cells are continuously pumped through an external loop at a constant flow rate (1/2 reactor volume/hour = 250ml/h) until identifiable cell death is observed. The experimental target: gentle cell delivery.

Test results showed that cell viability remains high and cell damage remains low.

The pump models tested were MCP Process drive with the following pump-heads: u Pro-280: two convex, non-spring-loaded rollers. u WM5: two straight, spring-loaded rollers. u 380AD: 3 convex, non-spring-loaded rollers. u Easy-Load: three straight, non-spring-loaded rollers.

Thanks to convex rollers and a concave tube-bed, the MCP Process Pro-280 proved to be the gentlest pump system with respect to cell viability and cell concentration.

The pump-head Pro-280 has two convex rollers and the tube-bed is concave. Before the roller totally closes the squeezed tubing, the cells can escape through a gap towards the tubing wall and, hence, are neither squashed nor damaged.

The Pro-280 (mounted either on an MCP or BVP Process drive) is a pump system especially suited for use in biotechnology. It has been tested for use in laboratory scale and small production scale up to 30litres.

Depending on the application, the user can choose from several peristaltic pump models all of them featuring this unique, cell-sensitive pump-head design. But the pump models are different with respect to the functional range, usability, range of flow rates and interfaces (analogue and digital) for remote control.

The MCP Process series, a calibrateable dispensing pump, features a wide functional range. The drive is equipped with four program memories enabling the user to store application sequences programmed in a PC. The pump can run such programs on the spot independently of a PC. In addition, more than 20 different pump-heads are available. Thanks to the bayonet coupling system, pump-heads can be exchanged within seconds if required by a different application. The protection rating IP65 ensures that the drive is dust-tight and protected against water jets from all directions. This makes these pumps ideal for use in a dusty, humid or corrosive environment or for applications carried out in clean room areas. The functional range of the other MCP/BVP pumps is slightly different.

The same cell-sensitive pump principle is also guaranteed by the Ecoline series as well as the Flowmaster for flow rates up to 5.4 or 13litres/min, resp.

Pumps generating a pulsation as little as possible are ideal for continuously dosing a substrate into a bioreactor. Ismatec also offers solutions for such applications ­ both as stand alone as well as panel-mounted pumps. u

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