To prevent contamination between production runs, a clean-in-place (CIP) system is designed into each bioreactor, vessel,
and piping line to remove any residual materials. Sterility assurance at the start of each culture is provided by a steam-in-place
(SIP) system consisting of steam pipes, temperature sensors, and condensate collection piping. These CIP and SIP systems require
extensive validation testing and the valves and piping contained in these systems can create additional validation challenges.
In addition, CIP and SIP systems must be revalidated following significant maintenance or changes to the connecting piping
and valves network.
Recent advances in single-use system technology allow bioprocess engineers to replace most storage vessels and fixed piping
networks with single-use storage systems and transfer lines. Single-use systems reduce maintenance and capital expense by
eliminating expensive vessels, valves, and sanitary piping assemblies. Figure 2 depicts a 10,000-L production suite, which
relies on stainless steel bioreactors, but integrates single-use technology for cell culture media storage and key transfer
Single-use media storage systems are routinely manufactured for volumes ranging from 20 to 2,500 liters. Media storage systems
arrive at the bioprocess facility sterilized by gamma irradiation and often are fitted with integrated filters, sampling systems,
and connectors. Using an SIP connector allows operators to make sterile connections between these presterilized single-use
systems and stainless steel bioreactors for aseptic transfer of media.
Similarly, single-use transfer lines may be used to transfer inoculum between bioreactors using either a peristaltic pump
or head-space pressure for flow rates up to 30 liters per minute. Such transfer lines can reduce the number of reusable valves
required for transfer, and eliminate problem areas for CIP and SIP validation. Terminating each presterilized transfer line
with a single-use SIP connector provides sterility assurance equal to that of traditional fixed piping at lower capital costs.
With the acceptance of single-use bioreactors, some bioprocess engineers are using these systems for both seed trains and
small-scale production. Single-use bioreactors range in volume from 1 to 1,000 liters and use two modes of mixing: rocking
platform and impeller. Rocking platform bioreactors consist of pillow-style bags that are secured to a tray mounted on pneumatic
lifters. Impeller-based single-use bioreactors are based on three-dimensional drum bags fitted with a single-use impeller
before sterilization. These systems are connected to a cell culture media storage bag (either by aseptic welding or aseptic
connectors) using flexible tubing.
Similarly, flexible tubing with aseptic connections are used as transfer lines from one reactor to the next. For production
volumes over 1,000 L, a single-use bioreactor must ultimately seed one or more stainless steel bioreactors. SIP connectors
incorporated into the single-use bioreactor design can link the single-use and stainless section of a seed train. Figure 3
shows a model facility that incorporates single-use media storage and bioreactors, using stainless steel bioreactors for the
two largest vessels of 2,000 L and 10,000 L.
After upstream production, the medium containing protein must be aseptically transferred to a different location in the production
facility for the final filling operation. This suite could be in a room next door or much farther away. Traditional bioprocessing
facilities accomplish this transfer by using stainless steel with piping or reusable hoses as transfer lines. This equipment
requires validated CIP and washing procedures before use and sterilization before each media transfer.
Process engineers are now incorporating single-use transfer lines between the bioreactor in the process suite and the transfer
vessel to simplify this process. By using presterilized connectors and tubing, the medium can be moved from the production
suite to the preparation suite without the need to sterilize stainless steel piping or equipment.
In addition to faster production, these single-use systems also give the manufacturer greater flexibility to determine which
process to run in production suites. The enhanced mobility eliminates many of the restrictions that hard-plumbed piping can
place on the manufacturing facility.