Implementing Single-Use Technology in Tangential Flow Filtration Systems in Clinical Manufacturing

Abstract

In a multiproduct cGMP clinical manufacturing facility, flexibility and short processing times are important operating attributes. A critical aspect of a multi-product facility is the procedures used to minimize product cross-contamination. Single-use (SU) technology enables flexibility, short process times, and limited chances for cross-contamination. An SU tangential flow filtration (TFF) system was implemented in a cGMP clinical manufacturing facility. In this article, we evaluate the performance, control of operation, productivity, and overall cost savings of the system.

Improving the time it takes to bring new drugs to the market continues to be an important goal for pharmaceutical companies. There are several approaches that are taken with the overall goal of bringing more drugs into commercialization phase.¹ Single-use (SU) technology is one of the strategies being adopted to reduce overall drug development time. SU technology brings significant advantages of reduced capital costs, faster construction and installation, reduced processing cycle times, and elimination of the need for post-use equipment cleaning and verification.^2,5 Starting with the use of plasticware such as pipettes, petri dishes, and t-flasks, disposable components are being increasingly incorporated in the laboratory environment. With the development of SU bioreactors at the 2,000 L scale (Xcellerex XDR), chromatography systems (GE ReadytoProcess), and systems for micro- and ultrafiltration, disposable equipment continues to replace fixed stainless steel equipment in manufacturing plants.

(JOHNSON & JOHNSON)

Demonstrating that process equipment is adequately cleaned is a critical aspect of any pharmaceutical plant operation. Following some type of post-use cleaning, the presence of residual protein and cleaning agent is typically assessed by subjecting equipment rinse solutions and swab samples to test methods including pH, conductivity, and fluorescamine. These procedures are time consuming and reduce equipment utilization. In a multiproduct facility, when equipment is shared between products with high and low potency, meeting the low acceptance criteria for residual protein can be very challenging.

To meet the demand of reducing production cycle time and improving productivity, a general downstream production process review was performed to identify the bottlenecks that affect the overall process efficiency. This process review identified that an existing stainless steel (SS) ultrafiltration–dialfiltration (UF–DF) system used for an intermediate UF–DF process in the facility was a bottleneck and presented an opportunity to evaluate an SU UF–DF system. The SS UF–DF system was designed for process development and scale-up rather than GMP production and had a limited retentate tank capacity (25 L). Additionaly, the clean-in-place (CIP) and post-CIP swabbing of the SS UF–DF system are very complex and time-consuming.

Criteria for Evaluating SU UF–DF Systems

Currently there are several SU UF/DF systems available. An evaluation was made to choose an appropriate system based on GMP production requirements, operational needs, budget, and timeline. These criteria included:

• Operation: The system should have the capacity to handle 5 m² membrane size, 10–50 L retentate tank working volume, >80 L/h/m² (LHM) feeding flux, and differential pressure (ΔP) and transmembrane pressure (TMP) controls at 0–20 psi. The retentate tank should have a mixing device to avoid localized concentration during the operation.

• Process monitoring, control, and data management: The process should be able to be controlled by constant TMP and ΔP. The pressures, flow rates, process phases, and other process parameters should be able to be monitored and recorded in real time. Data management should meet 21 CFR Part 11 compliance.

• Disposable parts: There should be no or a limited number of bio-compatibility issues for any disposable parts that contact product and process buffers. The levels of leachables and extractables should be in the acceptable safety range for clinical drug substances.

• Equipment availability and vendor support: The product should be readily available. An integrated and off-the-shelf system is preferred because it saves time on equipment validation and meets short project timelines. The manufacturer should have a good record for on-time equipment delivery and reliable technical support. The manufacturer should have the capability to consistently supply high quality accessories and consumable items.

• Cost: The price of the equipment and disposable items should be reasonable to reduce the overall cost of production when implementing a new UF–DF system in a GMP production facility.

The Millipore SU Mobius FlexReady Solution for TFF model TF2 system was selected after comparing three different SU UF–DF systems that are currently on the market. An ultrasonic permeate flow meter and a retentate pressure control valve (PCV) were included to enhance process control. The length of the rods on the cassette holder was extended to increase the holder capacity from 2.5 to 5 m² of membrane.

Operational Performance of the Single-Use System

A typical UF–DF operation includes flow path and membrane installation, pre-use CIP, integrity test, UF, DF, product recovery, and post-use CIP. Figure 1 compares a SS UF–DF system and a single-use UF–DF system. The implementation of the Millipore SU Mobius FlexReady Solution for TFF offers some key advantages over the existing SS UF–DF system in terms of preparation, membrane integrity testing, UF–DF general operation, critical parameters (feed flow rate, efficiency of mixing in retentate tank), and product recovery.

Figure 1. Operation comparison of a stainless steel ultrafiltration–diafiltration (SS UF–DF) system and a single-use (SU) system

Equipment preparation and set up: The disposable flow path is gamma irradiated and ready for use when it arrives. With the SS UF–DF system, cleaning occurs in two steps: the UF–DF system and membrane. The gamma irradiated retentate bag and flow path have eliminated the system pre-use and post-use CIP, rinse samples and protein swabs, and storage steps, however cassette cleaning must still be performed. The disposable flow path is relatively easy to install, and typically can be done in 60 minutes or less. The flow path is discarded after each use, minimizing the potential for product cross-contamination.

Membrane integrity testing: The feed pump on the SS UF–DF system is a rotary lobe pump. An auxiliary peristaltic pump is required to perform membrane integrity testing for the SS UF/DF system. The SU UF–DF system eliminates the need for an auxiliary peristaltic pump for membrane integrity testing.

UF–DF general operation: Four fully automated operations (initial fill, fed-batch, DF, and batch concentration) make the system user friendly. Process parameters are easy to input, and the resulting data are captured in our data acquisition system, eliminating the need to transcribe data into a paper-based GMP batch record. This facilitates trending or comparisons from batch to batch. Electronic data also simplify the technology transfer from pilot plant to commercial manufacturing.

Feed flow rate: One parameter with a significant impact on the UF–DF operation is the feed flow rate. To maximize the permeate flux, UF–DF operations typically require flow rates in the range of 240–360 LHM to maintain specific crossflow characteristics. With the SU Mobius FlexReady Solution, the peristaltic feed pump can achieve 20 L/min with 30 psi back pressure. The feed pump is either controlled by ΔP or fixed pump speed, which is correlated to the flow rate. The flow rate meets our current process feed flow rate specification, and the automated TMP control using the retentate PCV is relatively stable.

Mixing Efficiency: Mixing is critical during the diafiltration step to ensure a homogeneous solution for efficient buffer exchange. With the previous SS UF–DF system, retentate return flow distribution was the only method for mixing in the retentate tank. The SU Mobius TFF system design incorporates flow distribution by a retentate diverter plate and a magnetically coupled agitator for enhanced mixing in the retentate tank. Eliminating dead legs from the flow path is critical to achieving efficient buffer exchange. To this end, the design of the low dead-volume t-connectors for the pressure indicators in the disposable flow path assembly is important. In Figure 2, diafiltration from 1.1 M NaCl to 0.15 M NaCl was performed at a constant-volume diafiltration (50 L) and 9% agitation speed with a 5 m² 30 kD Millipore Biomax membrane. The maximum diafiltration volume with low agitation speed was considered the worst-case scenario. The experimental curve, is comparable to the theoretical curve indicating good mixing.

Figure 2. Constant-volume diafiltration in the Millipore single-use Mobius FlexReady solution for TFF. The solid line is experimental and the dotted line is theoretical: Retentate residue (%) = 100 * e (R–1)*N, where R is the Donnan effect and N is diavolume.

Product recovery: To increase the percent recovery, a buffer flush step was performed to recover product retained in the system and membrane. With the SU Mobius FlexReady TFF system, buffer can be transferred to the retentate tank and weighed directly. This saves time and eliminates the step of weighing the flush buffer, which was required with the previous SS UF–DF system.

System Process Control

To meet the requirement of process control, a retentate PCV was applied for constant TMP control. The retentate PCV position can be selected between 0 and 100% open for feed flow rate control. The 100% open position was chosen for PCV at the start of diafiltration. Table 1 summarizes the performance of constant TMP control at diafiltration phase for six GMP runs with a feed flow rate of 180 LHM. The diafiltration started with the feeding flow rate controlled by the pump speed. Once the feed flow rate was in the recommended operating range (ROP), constant TMP control was applied. The TMP setting was randomly selected in the TMP ROP range (<20 psi). It was found that TMP could be controlled at a narrow fluctuation range with a coefficient of variation (CV) less than 10% in these runs.

The system uses an ultrasonic permeate flow meter to calculate cumulative diafiltration volume (DV), which is used to target the diafiltration process endpoint. During the factory acceptance testing, the accuracy of the permeate flow meter was tested using four solutions with different densities (2 M guanidine HCl, 2 M urea, 100 mM NaCl, and pure water). The results suggest that the solution densities have little impact on the flow meter reading (data not shown).

In GMP production, the accuracy of the flow meter was evaluated by comparing DV values using a flow meter versus those obtained form a weight scale. The comparison of results is summarized in Figure 3, where the dark columns represent DV results obtained from the weigh scale and the light columns represent DV values obtained from the permeate flow meter. The average difference between these two measurements is 3.3%.

Figure 3. Comparison of measuring diafiltration volume by permeate flow meter (light columns) versus by weigh scale (dark columns)

Product Safety

System integration, product quality, and product safety impact factors (leachables, extractables, and biocompatibility) are major concerns. It is beneficial for a company to use a family of SU products from the same manufacturer to save the time and reduce the cost of safety evaluations and validation.

Before introducing an SU UF–DF system to our facility, several other SU systems made by Millipore, including buffer and media mixing tanks and containers, were already evaluated and used in GMP production. The flowpath and associated retentate tank liner for the Millipore SU Mobius FlexReady Solution for TFF are made of the same film and material as those used for the associated containers for the Millipore mixing system, which are widely used in our facility. The risk of leachables and extractables affecting product quality and the compatibility of buffers and protein were previously assessed,^{3, 4} saving both time and cost on those safety evaluations. Unlike SU UF–DF systems, the Mobius FlexReady Solution for TFF is a fully integrated system for operation, process monitoring and control, and data management. In the preliminary evaluation, two systems had the same assessment score based on operation specifications, process monitoring, and control. System integration and product quality and safety impact were the differentiating factors. Ultimately, the Millipore Mobius FlexReady Solution for TFF was chosen because of its better integrated system and the existence of previous safety evaluation assessment.^{3, 4}

Summary and Conclusions

The operation of this single-use system is easier than our existing SS UF–DF systems and the performance is comparable. The disposable flow path pieces can be quickly installed, resulting in short equipment turnaround times. The retentate diverter plate and magnetically coupled mixing device helped avoid the concentration gradients in the retentate tank and improved the UF–DF performance. Product yield and purity of the intermediate UF/DF step using the Mobius FlexReady Solution for TFF are comparable to the results from previous runs (data not shown). Also, the low system hold-up volume (0.6 L) and working volume (2.0 L) allowed for a wider operating range. The strong feed pump maintained a 20 L/m² flow rate even at 30 psi back pressure. Because the whole flow path is disposable, the risk of cross-contamination during product changeover was minimized, and the time and effort for CIP were reduced in our multiproduct facility.

The features of process monitoring, control, and data management enhance the process automation capability and reliability of data recording. The Allen Bradley Controllogix system and the associated human–machine interface (HMI) software were user-friendly. The PID-like display provided real-time information of recipe parameters and process data. The control system was interfaced with our production information management system for data collection and archiving. This feature enables the future implementation of electronic batch records in a GMP production environment. It also enables easy, batch-to-batch comparison for technology transfer.

The PCV and permeate flow meter increased process monitoring and control capabilities. We observed fluctuations of TMP while using the PCV for constant TMP control. It was found that the fluctuations could be reduced to an acceptable level (Table 1) by initiating the operation with feed flow control by pump speed, then switching to constant TMP control by PCV once the feed flow rate is within the ROP range. During the diafiltration, total diafiltration volume target can be preset and monitored with the included permeate flow meter. Although there was a measurement difference of approximately 3% in the total diafiltration volume versus the weight scale measurement, the result is acceptable because the ROP for total diafiltration volume was quite wide and diafiltration completion was primarily based on the conductivity and pH of permeate filtrate.

Table 1. Summary of constant transmembrane pressure control (TMP) control

Implementing this single-use ultrafiltration-diafiltration system doubled the retentate capacity of the intermediate UF–DF system, and therefore shortened the unit process time and improved productivity. By eliminating the six pre- and post-use CIP steps, the usage of water for injection and caustic solutions for CIP also was reduced. Furthermore, the 16 corresponding rinse samples and swab sampling testing for CIP steps were eliminated. The overall cost saving will depend on actual utilization. We found the payback period to be 3.8 years when performing ten campaigns per year.

Acknowledgement

The authors would like to thank the Millipore team for technical and logistic support for introducing this SU UF–DF to our facility. The authors also would like to acknowledge the Centocor pilot plant purification team for their support in implementing the SU UF–DF system for GMP production.

Keqiang Shen is a senior scientist, Be Van Vu is an associate engineer, Nikunj Dani is a senior systems engineer, Bryan Fluke is a senior associate engineer, Lei Xue is a senior manager, and David W. Clark is the global head of supply execution, all in pharmaceutical development and manufacturing sciences at Johnson & Johnson, Inc, Spring House, PA, 215.628.5953, kshen1@its.jnj.com

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