Integrating Single-Use Connection Components into Filter Integrity Testing Reduces Manufacturing Risk

Abstract

Biopharmaceutical manufacturers and engineers are implementing filter integrity testing procedures that incorporate single-use systems both upstream and downstream in the manufacturing process to improve their processes and reduce risks associated with product contamination. This article addresses how single-use components can be incorporated into manufacturers' filter integrity testing procedures. Specific examples include post filtration integrity testing for a media and buffer, a pre-filtration addition point (application), and filtrations between purification and formulation steps.

Biopharmaceutical manufacturers are striving to improve processes, increase production efficiencies, and launch new products faster. One way manufacturers can do this is to conduct filter integrity testing. Process fluids during testing and also throughout the bioprocess, from upstream culture media and buffer preparation to purification, formulation, and final fill, bioprocess fluids are filtered to achieve and maintain sterility. Testing the condition of these filters both before and after key production steps allows manufacturers to identify potential breaches in sterility and re-run a batch process if necessary to minimize product loss.

Sartorius Stedim Biotech

Introducing single-use components into these filter integrity test systems reduces the risk of contaminating in addition to improves process flexibility. This implementation is aided through the incorporation of single-use connection technologies.

Overview of Filter Integrity Tests

Filter integrity testing verifies that the filters used in a bioprocess are functioning properly and are capable of removing a minimum particle size from filtrate. These tests can be conducted pre- or post-filtration, or both, and are primarily non-destructive. The standard non-destructive testing methods are bubble-point, gas diffusion, and pressure decay tests.

The first step in all three tests requires that the filter membrane be thoroughly wetted with a flush solution. During testing, the filter inlet is sealed while controlled pressure, typically in the form of compressed air or other gas, is applied to the proximal side of the filter membrane. Excess filtrate is allowed to exit the filter outlet to a flush bag or collection vessel.

In the bubble-point test, pressure is gradually increased until bubbles are observed exiting the filter outlet. The pressure at which the bubbles are observed indicates whether or not the filter is functioning correctly. This is the simplest test to perform and requires the highest pressure.

The gas diffusion test uses lower pressure and measures gas as it diffuses through a filter membrane to determine integrity. During the test, a calibrated gas flow meter is attached to the filter outlet, potentially compromising sterility. Both the bubble-point and gas diffusion tests typically are conducted post-filtration.

Pressure decay tests do not compromise sterility, are performed at low pressure, and are widely used for in-process testing. A calibrated pressure gauge is used on the proximal side of the filter rather than using visual observations or an outlet flow meter as in the other tests. Filter integrity is determined by the rate of pressure decay across the filter; excessive pressure decay indicates failure.

In addition to non-destructive testing, destructive testing can be conducted post-filtration for the final formulation and fill process. Rigorous bacterial challenge testing passes a known quantity of challenge bacterium into a filter. The resulting filtrate is aseptically transferred to growth-promoting medium to confirm that all bacterial cells were retained in the filter. Bacterial growth indicates filter failure.

Single-use Systems for Filter Integrity Testing

Bioprocessing facilities historically conducted filter integrity tests using hard-plumbed systems with replaceable filter elements in stainless steel filter housings that required time consuming set-up, validation, and post-production cleaning. Modern operations use stand-alone single-use systems or single-use components in combination with stainless steel processing equipment to reduce costs, maximize production efficiencies, and increase facility flexibility. Extending the use of single-use components to filter integrity testing is an additional way manufacturers can streamline the bioprocess and get product to market faster.

Single-use components used in filtration and filter integrity testing include disposable capsule filters, bags, tubing, clamps, and connectors. Connectors are a vitally important interface between the components in these filter systems. They also provide quick and easy integration of the subsystem into the larger production process. There is a wide range of connection technologies available, including:

• standard connections used to quickly connect bioprocess fluid sources to filter assemblies

• aseptic connectors that allow process technicians to connect two or more single-use systems together without introducing contaminants

• aseptic disconnects that feature in-line valves to prevent contaminant ingress and fluid egress on disconnection

• single-use steam-in-place (SIP) connectors that can be used to make sterile connections between single-use systems and stainless process equipment.

These single-use connections offer engineers flexibility in process design to minimize equipment downtime, and are particularly beneficial in multi-product facilities.

Post-filtration Testing for Upstream Processes and Buffer Preparation

In traditional stainless steel facilities, the ingredients for culture media or buffer are combined with water and mixed in a mixing tank. The media or buffer are then pumped through stainless steel filter housings containing sterilizing filter elements with pore sizes of 0.2–0.1 μm and directly into sterile hold tanks.

Single-use components and systems can replace some or all of the stainless steel equipment used for culture media and buffer preparation (Figure 1). Single-use tank liners or specialty mixing bag systems can substitute for fixed mixing tanks. Bag systems with integrated capsule filters can replace both stainless filter housings and sterile hold tanks.

Figure 1. Single-use components that can replace some of the stainless steel equipment used in cell culture media and buffer preparation

After the process fluid has been filtered into the sterile hold bag, the filter can be quickly and easily detached for post-filtration integrity testing using valved quick-disconnect couplings. The resulting aseptic disconnection allows technicians to confidently remove the filter without the risk of contaminating the contents stored in the holding bag, while also keeping the filter wetted for integrity testing. After removal, filters may be tested using automated equipment by bubble-point, gas diffusion, or pressure decay methods. After testing confirms filter integrity, the stored cell culture media may be released for continued processing.

In-process Pre-filtration Testing Between Purification Steps

Because of the high value of biopharmaceutical proteins, preventing product contamination is crucial when testing during downstream processes, such as between purification steps. In-process pre-filtration integrity testing verifies that filters are capable of removing biological contaminants before product filtering begins, allowing replacement of failed filters before processing. This additional step helps manufacturers avoid costly product loss or reprocessing.

Adopting single-use technology in the pre-filtration testing environment offers many of the same benefits as described in the post-filtration example. However, designing single-use filtration systems to facilitate pre-filtration testing requires additional components, including a flush collection bag and an optional flush solution supply bag.

Figure 2 illustrates a single-use filter assembly that allows in-process pre-filtration integrity testing. To ensure that no product is lost during testing, a compatible filter flush solution is used to wet the filter. Opening the flush clamps allows the solution to enter the tubing line to the filter; the flow clamps remain closed during the pre-filtration testing. After it is wetted, an automated test system pressurizes the non-sterile side of the filter membrane to verify its integrity through pressure decay. During testing, excess flush solution is captured in a collection bag.

Figure 2. A single-use filter assembly

If the integrity test fails, the entire filter assembly may be replaced before processing. After a successful test, the flush clamps are clamped off and the filter assembly is connected to the process equipment using standard connections. The filter is then connected to the sterile hold bag using an aseptic connector. The flow clamps are then opened and filtering can begin.

Combined Pre- and Post-filtration Testing—Formulation and Fill

Product safety concerns and overall product value are highest during final formulation and dose filling. To address product quality and reduce waste, pre- and post-filtration integrity testing may be combined during final production stages (Figure 3). To conduct pre-filtration testing, the filter assembly is connected to the sterile hold tank using an aseptic connector. After it is connected, the filter is wetted using product formulation instead of flush solution to prevent dilution of the active drug. At this point, pre-filtration testing can be performed.

Figure 3. Combined pre- and post-filtration integrity testing set up

After filter integrity is confirmed, the line to the flush bag is clamped off and the filter assembly is connected to the vial filling system using an SIP connection, ensuring final product sterility. The flow clamp is then opened for filtration to begin. After filtration is complete, the filter can be removed from the assembly using aseptic disconnects to maintain the sterility of the filter until post-filtration integrity testing can be performed. This can be an automated non-destructive or destructive test such as a bacterial retention test. By conducting both pre- and post-filter integrity tests, operators are assured that product purity has been maintained in the final drug formulation and is ready for release.

Conclusion

Using single-use systems in filter integrity testing is a cost-effective solution to ensure product purity, increase process flexibility, and reduce contamination risk. The examples above illustrate the benefits of incorporating appropriate single-use connection technologies as part of an overall filter integrity testing strategy. As manufacturers seek to maximize every step in the bioprocess, the integration of single-use components into filter integrity testing protocols will continue to increase.

John Boehm is the bioprocess business unit manager at Colder Products Company, St. Paul, MN, 651.645.0091 john.boehm@colder.com