Buffer management has received less attention in process intensification despite the high costs and labor-, space-, time-, and material-intensive nature of this common downstream activity.
By Cynthia A. Challener
Process intensification is a major focus of the biopharma industry, with most efforts targeting upstream cell culture and associated processes. Buffer management has received less attention, despite the high costs and labor-, space-, time-, and material-intensive nature of this common downstream activity. Inline dilution (ILD) combined with inline conditioning (IC) is one of the key ways to intensify downstream processes, according to Avril Vermunt, program manager for connected biomanufacturing at Cytiva.
Large tank farms in biomanufacturing plants occupy expensive real estate that can be put to more productive use in today’s drive to intensify the production environment, agrees Gerard Gach, chief marketing officer for the Bio/Pharma Systems Group of YMC Process Technologies. “The advent of buffer concentrates delivered in single-use (SU) bags combined with automated, compact precision dilution and blending technology allows these tank farms to be repurposed for more productive activities,” he says.
Using concentrated buffer recipes for ILD, or individual buffer component stock solutions that are blended, titrated, and adjusted with IC, it is possible to provide the needed process stream. According to Vermunt, using ILD and IC, Cytiva has shown that the volume of buffer hold tanks can be reduced up to 90% and the total footprint reduced by 40% compared with manual buffer preparation. “Automated buffer preparation methods can lead to a more efficient use of existing resources, including labor and consumable savings, and smaller facility footprints. Eventually, by getting more out from their existing facilities, biomanufacturers can avoid or delay substantial capital investments,” she states.
In addition to freeing up space, optimizing labor, and improving operator safety, these systems can be programmed for use with existing buffers or supplied as end-to-end solutions with concentrates and SU tubing and bag sets, according to Gach.
Secrets of success
This first step in establishing a successful inline dilution solution is to determine the right buffer management approach for the manufacturing facility and process as early as possible. “This assessment tends to take place late, and biomanufacturers are still choosing manual buffer preparation because there is not much time invested in looking at alternatives such as automated solutions and outsourced buffers,” Vermunt observes.
An effective evaluation will include investigation of the total cost of ownership, including space requirements, future expansion plans, labor costs, and quality control, among other factors. “It can be challenging to complete this type of comprehensive assessment, but it helps to understand how resource-heavy buffer preparation really is beyond the straightforward material costs,” comments Vermunt.
Successful implementation of automated solution like IC and ILD then requires selection of the design option best suited for the specific process needs, considering the number of buffers to be used and their concentrations and flow rates. “It is important to compare the different alternatives and understand the pros and cons of each before making the final decision,” Vermunt says. The buffer control strategies must also be understood. She also notes that it is important to recognize that while the upfront costs of ILD are greater, one of the biggest drivers for these solutions is long-term cost savings.
The use of proven technology combined with on-site support and confident buy in from the quality assurance team responsible for buffer quality also contribute greatly to successful implementation, according to Gach. “On-site expert support is an important factor. The systems we supply are pretty much plug-and-play; however, the on-site availability of a vendor with the production site process engineers and operators adds a significant degree of implementation security,” he observes.
Monitoring and control
When looking at the buffer preparation process, the target product profile should be defined first followed by critical quality attributes and critical process parameters, which finally leads to the optimal control strategy. “Typically,” says Vermunt, “each buffer is defined by critical process parameters essential for the process, including pH, conductivity, temperature, and buffer component concentration or molarity. To ensure robust performance, system blending, flow control, and monitoring of critical parameters must be considered,” she asserts.
Another important factor for consideration, according to Vermunt, is the fact that for many buffers, creating a concentrate suitable for ILD is equal to the study and characterization needed for use-strength buffers. “The natural tendency is to assume that a component’s recipe in a concentrate is proportional to the diluted amount. However, especially for a use-strength buffer, which is close to the buffering system’s pKa, the effects of water and dilution can shift the pH,” she explains. This issue must also be considered when ILD is used for chromatography and pH is a key operating parameter. In these cases, concentrate recipes should be characterized to consider the potential pH shift.
Selecting a strategy
A potential deviation during inline buffer dilution can risk the product quality or yield. When choosing a control solution, therefore, it is critical to consider what risk level is acceptable, according to Vermunt.
While quality control of the in-coming concentrates adds a degree of certainty to the blend outcome, paramount is a feedback control that does not drift over time or require regular re-calibration, Gach asserts. “YMC recommends volumetric flow control with pH and/or conductivity monitoring.” Volumetric flow control for blending of buffer constituents, he notes, provides superior, reproducible, buffer composition, and accurate dilution because flow control is less prone to measurement drift than chemical sensors such as pH and conductivity. In addition, pH and conductivity require frequent calibration.
“While our system is also capable of pH and/or conductivity control to adjust the flow rate of the buffer concentrate or diluent based on pre-defined pH/conductivity set points, we have found over many years and numerous installations that this method is not our recommendation for primary control of the dilution process due to the delay in feedback control and potential for these devices to drift over time,” comments Gach. “YMC systems also have an automated function to send to waste or recycle a dilution that may deviate from a customer pre-set band of pH or conductivity, assuring the final buffer falls within the customer’s quality set point.”
Cytiva’s manufacturing-scale systems are typically equipped with three options for ILD control: open-loop flow ratio control, flow feedback control, or conductivity feedback control. All include monitoring of pH, conductivity, or flow to confirm the buffers are in range. “There is no one recommended way to go as all three options have their benefits and challenges,” Vermunt says. For example, open loop is a cheaper option, and it has the simplest design. But if the pH or conductivity goes out of specification, the ratio will not automatically adjust as with inline feedback control.
Accurate blending is also important, according to Gach. He notes that metering pumps, particularly those that are servo controlled, more accurately and consistently blend buffer constituents to the exact molecular ratio that was defined in the original process qualification at the lab scale.
For more advanced control, IC is an option, according to Vermunt, because it enables additional feedback options including pH and pH/conductivity feedback as well as adjustments appropriate for working with corresponding acids and bases or strong-weak interactions.
Advances in automated ILD solutions continued to occur. “Automated systems that provide highly precise and reproducible buffer dilution are available now. Paired with exacting quality control of the buffer concentrates, these technologies are ready to implement in factory-of-the-future schemes,” Gach observes.
YMC has partnered with MilliporeSigma to offer a buffer delivery platform launched at INTERPHEX 2019. The integrated solution consists of a buffer dilution system, buffer concentrates, single-use assemblies, and services. The buffer dilution system was designed, automated, and manufactured by YMC, and together the companies provide documentation, support, and on-site services with a “360-degree buffer dilution solution,” according to Gach.
“A formula that has been successful for us is basing our buffer system design on volumetric control using highly precise industrial (hygienic) metering pumps that have been in use for decades. We innovated on this proven technology by adding digital control to the pumps, adding a proprietary hydraulic design based on a model validated in cooperation with a university engineering team. We also developed an operator control platform that is flexible and familiar to GMP [good manufacturing practice] production environments,” Gach remarks.
The company has also incorporated buffer dilution in-line capability into its chromatography systems. This consolidation of chromatography and buffer in-line dilution reduces two independent systems to a single platform, further saving space and increasing flexibility into the manufacturing environment,” says Gach.
Cytiva has offered a large-scale chromatography system for nearly 15 years that has the ability to perform two-pump ILD. According to Vermunt, this platform is modular and configurable, providing customers with the ability to select the features most advantageous to their processes and manufacturing strategies. For example, a modified system with a three-pump ILD functionality is fairly common. She also notes that the system’s usability and life span can be extended through post-delivery upgrades.
Logical next steps
Vendors of ILD systems such as Cytiva and YMC Process Technologies are not resting on their laurels, however. Demands for process intensification continue to evolve, and advances in technology must occur in tandem. For instance, Vermunt notes that for years there has been a limitation to implementing ILD in SU systems due to a lack of suitable disposable pump and flow sensor technologies. “Today there are new SU pump and flow meter options available that are better-suited to provide ILD. Cytiva has begun to incorporate them into our next-generation SU systems, and we will continue to evaluate new instrumentation for our systems to ensure performance and flexibility,” she says.
Documentation is another area that is evolving, according to Gach. “Linking the concentrate quality documentation to the hardware control/recipe generation and paperless final quality record would be a logical next step. This documentation linked to the buffer dilution system on-board control would further increase quality and reduce cost,” he observes.
IC recipes and flow
In addition to ILD, IC is gaining popularity in the industry mainly due to the additional flexibility and benefits that can be achieved in manufacturing, according to Vermunt. “The system uses different buffer families in one production run to provide all the buffer formulations, affording a high degree of flexibility. Importantly, with IC it is possible to select the feedback mode that best controls the buffer critical process parameters and ensures mass balance,” she adds.
For IC systems, the dynamic control functionality are recipe and flow; pH and flow; and pH and conductivity. With recipe and flow feedback, a known buffer formulation is entered in the system control software, which adjusts the flow rates of the specified stock solutions to achieve the desired formulation. This control mode is useful when the temperature is constant and the stock solutions are accurate.
With pH and flow feedback, the user enters the target pH and the software adjusts the flow rates of the acid and base stock solutions to achieve the desired pH in the final formulation. With pH and conductivity feedback, after the user enters the target pH and conductivity, the dynamic control functionality of the software uses the feedback from flow, conductivity, and pH sensors to adjust the flow rates of the stock solutions to achieve the desired conductivity and pH. In this control mode, both the temperatures and the concentrations of the stock solutions can vary without affecting the accuracy of the final buffer formulation.
IC systems also have the functionality required to operate as a chromatography unit, allowing direct connection to a chromatography column to make it possible to deliver the buffers directly to the process without the need for storage in bags or tanks, according to Vermunt. Waste is therefore only generated during the switch between buffers until the set pH is reached and stable.
Cytiva has conducted a study to address the need for proof that automated buffer formulation meets specifications. In this study, the IC technology was evaluated from a current good manufacturing practice (cGMP) perspective to answer the question: Can we rely on a machine? The results show, according to Vermunt, that automated solutions like inline conditioning can be successfully implemented if the critical process parameters, in this case pH, conductivity, and buffer concentration, are kept under control. The hardware, software algorithms, and chemistry also must work seamlessly together.
“Implementing technologies such as ILD and IC helps streamline the entire buffer preparation process and reduces manual handling by automating several steps, not only reducing the risk of human errors, but also making it possible to reassign personnel to other tasks that provide more value,” Vermunt concludes.