Cynthia A. Challener is a contributing editor to Pharmaceutical Technology.

Cynthia A. Challener

The American Chemical Society (ACS) Green Chemistry Institute (GCI) Pharmaceutical Roundtable consists of 15 members, including mostly pharmaceutical companies, but also some suppliers. The Roundtable has defined continuous processing and process intensification as key green-engineering research areas for sustainable manufacturing. In 2012, the group conducted a survey of its members to evaluate the extent to which the industry is interested in and pursuing continuous processing. Peter Poechlauer, principle scientist with DSM Chemtech Center, which is a Roundtable member, spoke with Cynthia Challener, editor of the 

Pharmaceutical Sciences, Manufacturing & Marketplace Report

 about the results of the survey as they relate to chemical manufacturing of pharmaceutical ingredients and APIs.

Pharmaceutical Sciences, Manufacturing and Marketplace Report

: Why did the ACS GCI Pharmaceutical Roundtable define continuous processing and process intensification for API manufacturing as key green engineering research areas?

The mission of the Roundtable is to promote the implementation of green chemistry and engineering practices. The group studied a number of different technologies for their potential benefits, and determined that “process intensification” is very important because it provides for better use of starting materials with reduced byproduct formation and waste generation, a smaller footprint, reduced consumption of water and energy, and lower overall cost.

: What are CMOs/CDMOs doing with respect to continuous processing and the use of microreactor technology?

DSM and others have engaged in continuous processing efforts and have very quickly implemented scaled-up processes and done so in a cost-efficient way. We are very interested in microreactor technology and continuous processing because in some case it makes it easy to scale up reactions that can’t easily be done otherwise due to the nature of the raw materials or the kinetics of the reaction. However, there are uncertainties about scale-up, and managing intellectual property issues must be done carefully, given that in many cases new process chemistry is involved.

: Where is continuous processing most likely to be used in API and intermediate manufacturing and why?

Today, given that most microreactors are laboratory scale, continuous processing is often used early in the development process and can speed up development times and lower costs. It will eventually be used at scale, as well, as the equipment issues are addressed, particularly for reactions that require high temperature and pressure because they can be both hazardous and quite expensive. Ultimately, continuous processing will be beneficial for numerous stages of both GMP and non-GMP primary and secondary manufacturing steps.

: Manufacturers of microreactors and flow-chemistry equipment were identified as important drivers of the adoption of continuous processing, but there are still issues with the technology. What are the main concerns?

One of the biggest issues is scaling up to commercial production levels. Most early equipment for flow chemistry was designed for the laboratory. Chemical manufacturers and pharmaceutical companies, including DSM, have been working with microreactor manufacturers to address this issue, though, and pilot- and small commercial-scale equipment is becoming available, often by “numbering up” and running several microreactors in parallel. One advantage is that modular designs that can be fitted to the specific needs of different reactions are possible. This advantage was taken into consideration when DSM installed its commercial-scale microreactor suite. 

Another issue indirectly related to microreactors is the lack of development of appropriate laboratory-scale models of downstream processing equipment, such as small-scale extractors, distillation units, and crystallizers.

: In addition to actual reactions, what other upstream/downstream processes can be carried out in a continuous manner? What types of equipment are needed? 

Most downstream processes can be easily adapted to run continuously. Extractions, phase separations, and distillations are actually more effective when done continuously. Solids-handling processes, such as filtration and crystallization, present some difficulties, but there are solutions being introduced to the market, such as belt filters and spray-drying, and others will follow.

: How do continuous processes fit in an overall production process that still involves several batch operations? How are the benefits realized?

 Most pharmaceutical companies own large-scale batch production plants and won’t be doing away with them. Continuous equipment like microreactors will be added when needed, and the existing vessels will be modified to serve other purposes, such as hold-up tanks used to define the batch for regulatory purposes.

Typically, API syntheses are multistep processes. In most cases, some steps will benefit from continuous operation while others will not, and thus most pharmaceutical syntheses will continue to be a mix of continuous and batch-manufacturing operations. Mixing continuous and batch processes also enables manufacturers to build in some inventory buffer zones, so that if there is a problem with one part of the process, there will remain some time to fix it without halting the entire production process.

: How can the pharmaceutical industry overcome the hurdles to adoption of continuous processing for API manufacture, such as the reluctance to invest in technology, the uncertainty with respect to the benefits for any given specific process, and the sometimes questionable fit with the pharmaceutical process development process overall?

Our partners in the pharmaceutical industry are in a transition stage and are moving toward integrated solutions. Laboratory chemists consider the environmental consequences of raw materials and processes when developing synthetic routes. Drug manufacturers are also forming closer collaborations with suppliers to explore new technologies and concepts, such as continuous processing and the use of microreactors. Such relationships will help demonstrate the benefits of this approach and ultimately lead to adoption of process intensification when it is the most effective solution.

: What is the role of the regulatory agencies in driving the adoption of continuous processing and the use of microreactor technology?

The regulatory agencies are generally supportive of continuous processing because it provides better process control and thus improved product quality. Process intensification involves a scientific approach to the development of manufacturing processes, including identification of key parameters to monitor and how to react to process changes. Such features are highly appreciated by the regulatory agencies.

Articles

Results of an American Chemical Society Green Chemistry Institute Pharmaceutical Roundtable survey found that there is real interest in continuous processing and the use of flow chemistry, but hurdles remain.

Evaluating the Potential for Continuous Chemical Manufacturing and Microreactor Technology

As quality by design (QbD) has become increasingly adopted in biopharmaceutical manufacturing operations, the need for rapid analytical techniques for the analysis of proteins has also risen. These methods must be robust, easy-to-use, and applicable during product development and on through commercialization. Susan Darling, director of product marketing with ProteinSimple spoke with Cynthia Challener, editor of the 

, about imaged capillary isoelectric focusing (icIEF), a new capillary-based method for protein charge variant analysis that can dramatically reduce analysis times. 

: What are the key attributes of a good protein analysis system used in pharma manufacturing? 

: The ideal protein analysis system is rapid, robust, and reproducible and provides critical information on product quality that is easily transferred across the entire pharmaceutical process.  It should allow biopharmaceutical companies to accelerate product development.

  A good example relates to the analysis of charge variants of therapeutic proteins, because this property is critical for the characterization and monitoring of the quality attributes of proteins. Different types of charge variants include deamidation, formation of N-terminal pyroglutamate, aggregation, isomerization, sialylated glycans, antibody fragmentation, and glycation at the lysine residues. In some cases, such changes affect binding, biological activity, patient safety, and shelf life.

: What performance requirements are needed to ensure effective and efficient analysis throughout the pharmaceutical development process and during commercial manufacture? 

: Methods for charge heterogeneity need to detect small changes reproducibly, but also have to be automated and easy to use.  Newer capillary-based methods, such as imaged capillary isoelectric focusing (icIEF), are becoming increasingly adopted across the biopharmaceutical industry because they provide high resolution separation of charge variants with minimal development and start-up times. 

: How does icIEF work and how is it different from conventional separation/analysis techniques for protein charge variants? 

: The icIEF method involves imaged capillary isoelectric focusing, or isoelectric focusing performed in a capillary. Protein isoforms are separated based on their isoelectric points in an ampholytic pH gradient and detected by a whole column UV absorption detector.   The process takes 15 minutes start to finish and combines the resolution of a traditional gel IEF system with the advantages of quantitation and automation found in standard column-based systems. 

: In addition to high resolution, what other advantages does icIEF provide?

: An additional benefit of capillary-based techniques such as icIEF is that these methods are not product specific.  Given the large pipeline of pharmaceuticals, the ability to use generic methods reduces the time required for analytical method development.  A technique that has these benefits can be implemented across the entire pharmaceutical process, from cell culture development and optimization to commercial quality control (QC) release and stability activities, resulting in an accelerated product development process.  

: What recent advances in protein analysis technology have been made and what need(s) in the marketplace led to their development? 

: Biopharmaceutical manufacturing is evolving from a traditional approach to a QbD strategy. QbD requires determination and measurement of key quality attributes during manufacturing development.  As a result, significantly more samples must be run during process development to set the design space of QbD. High throughput methods are therefore very important for the implementation of a QbD strategy. 

 For example, Simon Briggs, a senior scientist on the in-process analytics team at UCB Pharma, has shown that a process characterization study at his company may generate more than 1000 samples for all of the upstream and downstream processes that must be evaluated. A traditional tool for charge heterogeneity analysis, such as ion-exchange chromatography, which has an average run time of 70 minutes, would require 50 days to analyze all of these samples.  Fortunately, advances in high throughput techniques such as icIEF for the determination of charge heterogeneity have recently been made. At UCB, according to Briggs, by switching to an icIEF method with a 15 minute run time, UCB was able to reduce the analysis time for process characterization studies to 7 days.

 More information on the work at UCB Pharma can be found in a 

 webinar presented by Briggs entitled “Charge Variant Analysis for High Throughput Process Development,” which can be found at: 

http://www.separationsnow.com/details/webinar/13d161c91da/Charge-variant-analysis-for-high-throughput-process-development.html

: What are some of the current issues/limitations that still remain that must be addressed to improve protein analysis? 

: To keep up with the throughput demands of QbD and protein therapeutic development, analysis methods still need to be faster and more sensitive, and ideally, simpler to use. However, proteins aren’t simple. They are complex and highly individual, and post-translational modifications like glycosylation can result in a large number of isoforms. In addition, protein therapeutics are constantly evolving to include fusion proteins, antibody drug conjugates, and bispecific antibodies. Developing protein analysis systems that work robustly with all of these types of molecules and those new ones that haven’t even been developed yet is a major challenge. 

New capillary-based imaging techniques for protein charge variant analysis are reducing development and start-up times for protein-based therapeutics.

Capillary-Based Methods Speed Protein Charge Heterogeneity Determination

Peptoids are not only more stable and easier to synthesize than peptides, their chemical diversity is large. As such, they have attracted significant attention as peptide and protein mimics and are being explored for a vast array of biomedical applications. Kent Kirshenbaum, associate professor in the Department of Chemistry at New York University (NYU), and his graduate student Timothy Craven spoke with Cynthia Challener, editor of the 

, about the advantages of peptoids, their potential as therapeutic agents, and recent developments in the field. 

: What are peptoids and how are they different from peptides/peptidomimetics and other related biologic compounds? 

: Peptoids are oligomers composed of N-substituted glycine monomer units that are sequence-specific heteropolymers, as are many biopolymers, including peptides and nucleic acids. Peptoids are particularly similar to peptides and proteins, in that peptoids are polyamide oligomers with backbone spacing identical to peptides. 
 The major difference is the location of the side-chain variable group. In peptides, the variable group is positioned at the backbone a-carbon. In peptoids, the variable group is positioned at the amide nitrogen. This substitution leads to oligomers linked through tertiary amides, which allow the peptoids to be completely resistant to proteolytic degradation. 

: Why are peptoids of interest to the pharmaceutical industry?

: Many peptoid oligomer sequences have been shown to fold into structures that mimic some of the secondary structure types in proteins, such as polyproline helices. These types of helices are present in many critical signaling, structural, and regulatory events in cell biology. For example, they are the ligands for SH3 and WW domains, and they make up the structural core of collagen fibers. Peptoid oligomers up to 40 monomer units long have been synthesized, potentially allowing the mimicry of more complex protein tertiary structures. 

: Peptoids are typically synthesized using solid-phase protocols following one of two common methods.

A “submonomer” synthesis technique couples bromoacetic acid onto the amino functional end of a nascent resin-bound oligomer, followed by bromide displacement with a primary amine. These steps are repeated iteratively to construct the desired primary sequence. In addition, a “monomer” synthesis has also been demonstrated, which entails coupling of an Fmoc protected N-substituted glycine followed by deprotection with base. 

 The second method is analogous to standard solid-phase peptide synthesis; however, it is limited by the types of Fmoc protected N-substituted monomers that are commercially available. 
 Thus, “submonomer” synthesis with its ease of incorporation of side-chain functionalities, as well as the lack of the need for complex protecting group strategies, makes this method very popular and powerful. More than 200 different peptoid monomers bearing distinct side chains have been reported in the literature.  

: What are the advantages of peptoids compared to conventional peptides and other large-molecule analogs (in terms of their synthesis and applications?

: The main advantage of peptoids is that diverse side chain groups can be readily incorporated into the peptoid backbone without the need for complex protection strategies. Additionally, for applications such as multivalent ligand display, peptoids offer a facile platform for controlling the sequence and fine-tuning the spacing of displayed chemical functionalities. The chemical structure of the oligomeric tertiary amides in the peptoid backbone engenders proteolytic stability to the oligomer. Thus, the peptoid structure has several advantages over peptide-based structures, including sequence diversity, facile synthesis, and proteolytic stability.

: How are peptoids used in biologic formulations? 

: Peptoids are useful in a variety of biological applications, including as the API in drug formulations, as diagnostic tools, as sources of combinatorial libraries for discovery of hit compounds, for drug-delivery applications, and as transfection agents for nucleic acid-based therapeutics. In fact, there are multiple ways in which they may find clinical relevance.  

The folded oligomers themselves may function like peptides as ligands for biomolecular disease targets, such as large surface areas on proteins, to allow modulation of protein-protein interactions and other currently “undruggable” targets.  

Peptoids are also highly effective scaffolds for creating multivalent displays of ligands for enhanced binding interactions to proteins and nucleic acids. 

Peptoids are proving useful as drug-delivery agents. For example, cationic peptoids have been shown to complex with nucleic acids, such as RNA oligonucleotides. This complexation can protect the RNA from degradation and permit efficient intracellular uptake, potentially enabling the development of RNA-interference therapies. 

Specific positions in bioactive peptides can be replaced with peptoid units. These peptoid-peptide hybrid architectures may provide access to new binding modes or display enhanced pharmacological attributes. 

: What are the most recent advances in peptoid technology and what impact will they have?

: There are numerous recent advances in peptoid technology. We believe that some of the most exciting developments include the following: 

Demonstration of potent, broad-ranging, and selective antimicrobial activity by peptoids. 

Extraordinary work by the group of Thomas Kodadek involving the screening of huge libraries of peptoids on-resin in order to identify peptoid sequences that function as protein capture agents.

Identification of peptoid-based multivalent displays for modulation of steroid hormone receptor activity, leading to potential new therapeutic modalities for prostate cancer. 

A broad series of advances by the Zuckermann group at the Lawrence Berkeley Laboratory to create nano-structured peptoid sheets and other peptoids for materials applications. 

The demonstration of rudimentary mimics of protein tertiary structures formed by cross-linked peptoid macrocycles. 

Development of improved computational tools for predicting peptoid structures, enabling the in silico identification of peptoid ligands for protein targets. 

These developments will turbo-charge the discovery of peptoids for use as APIs and speed the identification of peptoids for use in diverse biomedical applications. 

Because peptoids are relatively easy to synthesize, have tremendous sequence diversity, and are more proteolytically stable than peptides and proteins, they have significant potential for use as APIs, drug-delivery agents, and in numerous biomedical applications.

The Promise of Peptoids

Visual inspection of parenterals is critical for ensuring that these drug products meet ever-increasing quality specifications. At the same time, faster production speeds and more complex production processes are presenting challenges. Peter Spinelli, sales director in North America for Bosch Inspection Technology, Emanuele Cudiferro, service manager with Brevetti, and independent consultant John G. Shabushnig, previously a team leader in Pfizer’s Global Quality Operations group, spoke with Cynthia Challener, editor of the Pharmaceutical Sciences, Manufacturing & Marketplace Report, about how advances in technologies for both manual and automated inspection methods are helping address this need in parenteral manufacturing.

Demand for higher quality
Pharmaceutical Sciences, Manufacturing and Marketplace Report:

 What are the key attributes of good visual inspection systems for parenterals manufacturing? What performance requirements are needed for the parenteral formulations that are being developed today and why?

 Parenteral manufacturers are facing increasingly strict quality standards that require them to produce products free of visible particles, reduce process/product variation, and minimize rejects. At the same time, current methodology based on the quality-by- design (QbD) philosophy requires a deep knowledge of the product and its manufacturing process. As a result, automated inspection systems are playing a key role in parenteral manufacturing processes. Efficiency, considered as the reduction of false rejects, and detailed information regarding the cause of rejection are the key attributes that enable improvement of performance.

 Good visual inspection systems for parenterals must adhere to increasingly strict safety regulations all over the world. These regulations require the highest product quality to protect patients from contaminated medicines, which must be achieved at a time of growing parenteral production capacities, greater complexity of manufacturing processes, and higher production speeds.

Parenteral products are typically injected and go directly into the bloodstream, where they might cause adverse reaction due to contamination or the presence of undesired particles. Inspection systems must be able to detect contaminated APIs or foreign matter within the product, as well as cosmetic container defects, such as cracks in syringe flanges or defects in the sealing integrity of ampoules.

 Consistent quality is achieved by good control of critical manufacturing and inspection parameters. For human manual inspection, the method referenced by all of the pharmacopeias, it is important to control the light intensity, contrast (through the use of black and white backgrounds), the speed or pace of the inspection, and the presentation of the container being inspected. This last point involves a swirl or inversion to get particulates in motion to increase their visibility. These same points apply to semi-automated or automated inspection systems as well. Additional requirements for machine inspections are that the resolution of the sensor or camera and the algorithms that are used are appropriate and enable quality decisions based on analysis of images of containers and products.

New light sources, improved analytical tools, and flexibility
Pharmaceutical Sciences, Manufacturing and Marketplace Report:

 What recent advances in automated inspection systems have been made and what need(s) in the marketplace led to their development?

For manual inspection, new light sources, such as florescent lamps with high-frequency ballasts or light-emitting diodes (LEDs), have been introduced and offer several advantages, including stable, flicker-free viewing, which reduces inspector fatigue and variation in light intensity, reduced heat output, and better energy conservation when compared to incandescent lamps.

For automated inspection systems, sensor and camera resolution continue to increase along with image processing speed. These improvements follow the same trend seen in consumer electronics with cell phones, digital cameras, and laptops. For inspection systems, such advances provide the ability to resolve greater detail and “see” smaller defects or inspect a larger area of the container in a single view.

There is also continuing development of commercial X-ray-based imaging systems that permit the detection of denser particles inside opaque containers or products such as suspensions or lyophilized powders.

 Organization of the images acquired during the automatic visual inspection process into digital libraries currently is helping pharmaceutical manufacturers to meet various process requirements. Remote Parametrization & Validation (RPV), recently developed by Brevetti, creates the basis for a deep analysis of the inspection results and makes it possible to reduce the false rejection rate and highlight any possible improvements in the manufacturing process. Importantly, this type of analysis can be easily performed off line without impacting the online productivity.

Flexibility and high output rates are important for new technologies. In addition, compared to manual inspection systems, semi-automated systems are able to perform visual inspection at higher rates while minimizing operator fatigue. As a result, it is possible to achieve optimized inspection of particulates in liquid parenteral products and specks on lyophilized products, as well as the detection of cosmetic container defects.

That is why Bosch Inspection Technology recently launched a computer-bound visual tabletop unit for the inspection of filled or empty pharmaceutical containers such as vials, ampuls syringes, and cartridges. A camera transmits the results directly to the computer, which allows for an especially fast evaluation. It is suitable for containers with diameters from eight to 50 millimeters and is primarily used for research purposes and small batch applications, such as verification of product rejects, particle and defect analyses, and stability surveys. That makes it the ideal starter instrument for companies that plan to switch to fully automated machines in the near future.

Pushing the limits
Pharmaceutical Sciences, Manufacturing and Marketplace Report:

 What are some of the current issues/limitations that still remain that must be addressed to improve automated inspection systems for parenteral manufacturing? 

 Due to the growing number of parenterals, and particularly generic products, manufacturers require ever-faster machines for larger production quantities. Here, manual inspection is quickly stretched to its limits. Even the best-trained human inspector cannot keep up with the high speeds of all production types. Yet, manual and semi-automated visual inspection systems remain very important for inspecting parenterals.

Depending on the size and type of the pharmaceutical product and container, a combination of automated and visual inspection is sure to be the most reliable approach. As an example, during the validation process for fully automated inspection machines, challenge set samples are critical for ensuring that inspection machines maintain their validated state under dynamic conditions. Manual and semi-automated visual inspection tools are particularly well-suited for the inspection of these important samples.

 Inspection by human or machine is still a probabilistic process, thus 100% inspection does not detect all defects. Generally, detectability is size-dependent, with the smallest particles or container defects having the lowest detection probability, and current manufacturing processes and packaging materials do not yield products free of visual defects. A trained inspector using a controlled inspection process or a validated inspection machine can, however, give good sensitivity, delivering safe, high-quality products. 

With respect to automated systems, though, it has been difficult to reach an agreement regarding acceptance specifications for inspector qualification of machine validation. 

 Taking into consideration that leak detection is one of the standard requirements for the industry, the possibility of combining automated visual inspection with the most advanced leak detection technologies represents one of the current challenges for equipment manufacturers.

Continued improvement
Pharmaceutical Sciences, Manufacturing and Marketplace Report:

 What is being done to address these issues? Are there any new technologies under development that could have an impact in the near future?

 To maximize the performance of our visual inspection systems, we recently made available as optional features a high voltage module for the leak detection of liquids and a headspace gas analyzer (HGA) device for the leak detection of freeze-dried products. Importantly, the new modules can be fully integrated into our compact, automatic visual inspection system.

 Machine builders continue to advance inspection technology, offering higher levels of performance. This process is generally an evolutionary one, but there have been significant improvements since these technologies were first introduced over 30 years ago.

The Parenteral Drug Association (PDA) has been offering forums to discuss and advance these issues for many years. There is a Visual Inspection Interest Group that meets in the US and Europe. There is also an annual Visual Inspection Forum dedicated to this topic. In addition, the PDA Training and Research Institute offers training on visual inspection to help the industry achieve consistent inspection results.

In addition, the Expert Panel at USP has published a draft general chapter to better define the conditions for inspection and the acceptance criteria for meeting the current requirement that each lot of injectable product be “essentially free” of visible particles. Draft chapter  has been published for comment and continues to advance through the USP review and publication process.

Any future efforts should balance the need for good inspection practices with prevention. Prevention is certainly preferred for both product quality and process yield. The path forward will rely on both continuous process improvement for the prevention of defects as well as better methods for detecting and rejecting them.

Increasing production efficiency while ensuring high parenteral product quality is the goal of both manual and automated visual inspection systems.

Improving Performance Through Visual Inspection

The choice of possible mixing and blending equipment for the preparation of solid and semisolid dosage formulations is extensive. Therefore, the first step in a successful mixing process is to select the most appropriate equipment. “The choice of mixing equipment is greatly dependent on the products/materials being mixed. Therefore, good blending and mixing equipment will be determined by how suitable the configuration of the blender is for the powders being mixed,” says Wilf Sangüesa, product manager for Quadro Engineering’s IDEX Material Processing Technologies Group.

Specifically, good blending equipment for solid dosage formulations offers a large filling span at constant blending performance and provides homogeneous distribution of the API within the formulation using gentle blending conditions that do not lead to destruction of the particles or granules, according to Tobias Borgers, head of marketing for L.B. Bohle. Adds Pär Almhem, president of ModWave: “The mixer or blender must achieve the specified quality of the final product in a very short time using a very stable and repeatable process and with minimal residual product in the machine and good cleanability.”Some of the different types of mixing equipment used for the preparation of solid and semisolid dosage formulations include ribbon and tumble blenders for dry-powder blends, multishaft mixers for transdermal drug/adhesive mixtures, and double planetary mixers for the processing of wet granulations and viscous gels. “Performance characteristics, such as the shear input, cleanability, ease of discharge, flexibility in terms of batch size and viscosity, vacuum capability, temperature control, and scalability, vary from one mixer design to another and depend on the properties of the particular application as well as the mixing objective itself,” explains Christine Banaszek, an application engineer at Charles Ross & Son Company.

Flexibility is becoming increasingly important as well, notes Sangüesa “The better blending systems are the ones that are able to mix a wide number of powders so that fewer blenders are required in a given facility. Because blending can be a costly and labor-intensive step, equipment also must be efficient and provide the maximum yield possible with few trap points and proper surface finishes that allow the maximum amount of powder to flow out upon completion of the mixing process. Systems also need to readily integrate with upstream/downstream equipment.”

Sangüesa has observed that the drive to reduce the number of components needed to perform a task has been greatly influenced by rising costs for not just capital investment, but also by increasing processing costs, such as cleaning, maintenance, space constraints, safety, product losses, and so on. One solution has been the introduction of blending systems that utilize the same holding recipient (i.e., intermediate bulk container, or IBC) to do both blending and at its completion, product transfer. “In the past,” he says, “powders had to be loaded from an IBC or Supersack to a blender and then, once the mixing was completed , transferred back. Each step adds the potential for powder losses, segregation, operator exposure, higher space needs, and more pieces to clean and maintain. By having the powders inside the IBC, blending them without further handling and then taking the IBC to its next process, many of these concerns and costs are greatly reduced. Companies, such as Matcon have innovative approaches in this area.”

New mixer designs have also been introduced that have also had an impact. For semisolid formulations, for instance, Banaszek points to double planetary mixers with improved mixing efficiency and diminished contamination risk. “We have developed a custom-fabricated and sealed gearbox that protects the drive assembly from all product contact, including solvent vapors. Newer design helical blades also prevent the ‘climbing’ issue commonly experienced with traditional rectangular planetary stirrers. These blades generate a unique mixing action; each sweeping curve firmly pushes batch material forward and downward, keeping it within the mixing zone at all times,” she notes.

Ekato Corp. has also introduced new technology for highly viscous materials, such as those used for the production of softgel and hard shell capsules. “Softgel capsule formulations often undergo several physical property changes during mixing, such as from a liquid to a paste or even a solid-like material and then back to a paste again. Such systems require very powerful mixers,” observes process systems sales engineer Rainer Engenhart. The company has adapted its high-torque, high-viscosity mixers to meet the specific sanitary requirements of the pharmaceutical industry and developed customized solutions that include ergonomic loading of solids materials with a low melting point into a hot vessel, elevated designs that allow for gravity transfer of the finished bulk into transfer tanks, and in-place cleaning systems for quick changeovers from one formulation to another.

Most importantly, the systems address the critical needs for high shear mixing combined with excellent de-aeration in both the shell and fill materials, according to Engenhart. For capsules, if air bubbles remain in the shell material, they can create pinholes that can be sources of potential leaks, while entrapped air in the fill materials can cause fill weight issues. In oral strip products, even a tiny amount of trapped air can lead to the generation of large pores during the drying process. In addition, in capsules, if moisture remains in the fill material, it can migrate from the interior and cause degradation of the water-soluble shell, leading to a loss of integrity.

“We have found that the solution for good de-aeration is to bring the bubbles to the surface while pulling a vacuum on the system to remove the air. Because air bubbles can’t move in the very viscous materials used for the production of softgels, we developed a shear laminar flow impeller that gently moves them to the surface (without breaking them into smaller bubbles), where they are removed under a strong vacuum. “

Other developments have also had an impact on the mixing and blending equipment used for solids and semi-solid formulations. For Borgers, the ability to conduct online analysis of blend homogeneity has helped manufacturers better understand blending behavior and made it possible to detect properly the required blending time. Ekato has found that determination of the end point of mixing using inline techniques such as viscosity, pH, and particle size analysis, but on a bypass loop, enables increased automation. 

Meanwhile, for Almhem and Reiner Lemperle, director of sales with Lödige Process Technology, the shift to continuous processing has been a notable development. “This approach allows the use of smaller equipment, which translates to less expensive production space, reduced product losses, and fewer material surfaces to clean, and eliminates scale-up issues, because the only factor is running time.” Lödige has developed a solution for continuous mixing, granulation, and drying that can be used for continuous mixing with a throughput of up to 200 kg/h, and for granulation and drying from 5 to 30 kg/h.


Despite these advances, there are still numerous ways in which blending and mixing of solid and semisolid formulations can be improved. Engenhart believes that even higher batch size flexibility is needed to increase efficiency and productivity in the mixing and blending of both solid and semisolid dosage forms. Currently, some Ekato mixing systems can efficiently mix batch sizes that are in the range of 10–25% of the maximum batch size that can be processed in a specific size of equipment. Engenhart is confident that these limitations can be pushed further.

For Sangüesa, the main issue is segregation. “Blenders can do a great job to ensure that all the powders, even those with varying densities, particle shapes, flow characteristics, etc., are thoroughly mixed inside the blender. But the moment those powders are either discharged or transferred out, segregation can occur,” he explains. “Depending on the surface finish, for example, some powders will flow better than others, thus negating the very benefits the blender had achieved. As powders flow out, there is always the concern that some of the ingredients will no longer be represented in the same percentage throughout the batch.”

To address issues such as segregation, Borgers would like to see more simulations of blending processes. He believes the ability to effectively simulate different mixing and blending processes will lead to the development of more effective approaches to scale-up of processes and help address equipment transfer questions. “Fortunately, advances are being made in simulation software, and I am thus hopeful that useful software tools will be available in the near future.” 

At the same time, there are a growing number of specialty products and “individual drugs” that are produced in much smaller quantities. “Scaling down production throughput to these small volumes is a challenge. The mixing and blending equipment needed for these niche products looks a lot different than the existing units in use today,” Lemperle notes. To help its customers, Lödige has introduced a mixer designed for batch sizes down to 0.5 kg/batch. Engenhart adds that many of these specialty semisolid formulations, including softgels and oral strip products, involve exceptionally high viscosity materials that require special mixing conditions. 

Furthermore, there is a trend toward the use of non-animal-based shell materials for softgel capsules, and these materials are more challenging to work with, according to Engenhart. In addition to having higher melting temperatures that require an even tighter allowable process parameters during mixing and transfer, these newer shell materials are often of even higher viscosity than conventional materials, and thus higher shear mixing is necessary to adequately disperse some of the solids raw materials.


There are also general challenges related to the selection of appropriate mixing and blending equipment. Because many mixing technologies today overlap in use and function such that certain formulations can be produced in more than one distinct type of mixer, making sure that the mechanical and physical aspects of the equipment enable safe, repeatable, and sanitary mixing is very important, according to Banaszek. “More often than not, there is no all-purpose, off-the-shelf solution,” she says. 

In addition, manufacturers that are using inherited equipment or procedures because they have worked in the past may actually be at a disadvantage and limiting their production capabilities. “With the greater understanding of mixing and blending processes that we have today, combined with the advances in mixing technology and new equipment, it is generally beneficial in such cases to reevaluate the existing mixing strategy to determine if it is efficient,” Banaszek observes. She concludes that, to identify the best mixer or blender for a particular formulation, it helps to partner with a reliable mixer supplier that offers long-term experience, rental, and testing resources. 

Effective blenders provide efficient, homogeneous mixing and de-aeration for a wide range of formulations.

Optimizing the Selection of Mixing Equipment

Many biological APIs are not stable in aqueous solutions, making preparation of shelf-stable sterile formulations difficult or impossible. Removal of the water at low temperature is a gentle method for overcoming this issue. To achieve effective lyophilization processes, careful selection of ingredients and knowledge of their properties and behavior at different temperatures is necessary. Parenteral manufacturers are benefiting from the use of process analytical technology (PAT) and increased automation. High hopes are also placed on controlled ice nucleation technology, with the first commercial product implementations expected soon.

An effective solution for improved stability


For parenterals, the preferred product presentation is a sterile, ready-to-use solution, largely because of ease of use. For many drugs, protein pharmaceuticals in particular, the active ingredient is not stable enough in an aqueous solution to make a sterile solution formulation feasible, according to Steven L. Nail, a senior research scientist at Baxter Biopharma Solutions. Robert Sever, business development manager for life sciences and laboratories at Praxair, also notes that freeze-drying is a relatively gentle method for obtaining the desired shelf life while maintaining the efficacy of the product, which can be more difficult with other options, such as spray-drying.

There are additional benefits as well. “Not only can shelf life be extended from weeks or months to years, but because the product has long-term stability, it can be produced in larger batch sizes, which provides economies of scale,” observes Isobel Cook, a principal scientist at Biopharma Technology. Freeze-dried products also do not require a carefully controlled environment during shipment, which is a cost savings, according to lyophilization consultant Larry Ulfik of Applewood Scientific.

“As importantly,” Ulfik says, “the final product is whole and complete, meaning it can be produced under sterile conditions with dosage accuracy, even when only miniscule amounts of API are required, such as for cytotoxic anticancer formulations and vaccines. The finished lyophilized vial is in its own sterile boundary and protected from environmental gases, moisture, and particulate contamination, and thus remains sterile over the entire expiry period and perhaps even beyond without using antibacterial-mold preservatives.” By freeze-drying parenterals, it is also possible to ensure that the API is in its preferred crystalline or amorphous form and helps speed up the time to market for complex and unstable products.


These benefits only accrue, of course, if the appropriate lyophilization conditions are used. Determining these parameters can be a challenge, though, given the various ingredients found in parenterals formulations. “In general, the composition of the formulation is critical in achieving the desired product quality attributes,” Nail states. “The formulation may include a buffer, a bulking agent, a stabilizer, and (perhaps) a surfactant.” Excipients can also provide stability to complex molecules by replacing the water in the matrix so that the molecular structure of the API is retained after reconstitution, according to Ulfik. For proteins, the stabilizer is generally a disaccharide, which protects against damage to the API, often due to unfolding caused by the stresses associated with freezing, with the drying process, or even reconstitution. 

Excipients can also be added to adjust the critical temperature. “The lower the freezing temperature, the longer the cycle time; excipients are thus often added that can raise the critical temperature,” explains Cook. In fact, the idea is to dry the product at as high a temperature as possible without exceeding the critical, or collapse, temperature where the microstructure established during freezing has the potential to collapse due to viscous flow of solutes during primary drying when the ice is sublimed away. Shorter cycle times are important for controlling costs, which are a major consideration given freeze-drying is a very expensive process, according to Sever.

Knowledge of the formulation and its effect on the API during lyophilization can be obtained using appropriate analytical techniques, such as differential scanning calorimetry, freeze-drying microscopy, Karl Fischer analysis, X-ray diffraction, Raman spectroscopy, infrared spectroscopy, gas chromatography/liquid chromatography analysis, and final inspection via noninvasive methodologies, according to Ulfik. 


Although freeze-drying technology tends to advance at a slow pace, some incremental advances in vial design have been beneficial, according to Cook. Examples include vials that can be stoppered and crimped in the freeze-dryer for improved seal integrity and enhanced glass systems for reduced breakage and cycle times and improved quality.

The use of PAT in recent years has had a significant impact. “Devices that monitor the global moisture levels of drying products to ensure that the process endpoint is reached consistently are an important example,” says Ulfik. Nail points to tunable diode laser absorption spectroscopy (TDLAS), a near-IR-based in-process flow meter that gives an instantaneous reading of the mass flow rate of water vapor during drying. “We use this instrumentation as a part of our quality-by-design approach to freeze-dry process development,” he notes. Nail, however, has found that TDLAS suffers at present from poor quantitative accuracy in large-scale equipment, but expects improvements as the understanding of vapor flow in the freeze-dryer increases.

The implementation of advanced sterile practices enabled by the burgeoning isolator and robotization industries has also allowed automated loading and unloading of freeze-dryers.”With this technology, the product, container, closure, and sealing cap are never exposed or manipulated by operators after sterilization at a cost that is competitive with and less risky than conventional methods in classified facilities,” Ulfik explains. He notes that the important benefit of this isolator technology is an overall improvement in product quality and worker safety.

The technology attracting the most attention, however, is controlled ice nucleation. Using current freezing methodology, ice nucleation occurs randomly and often at very low temperatures. According to Sever, the vial-to-vial nucleation variability leads to heterogeneity in ice structure, which can impact critical product and process attributes, leading to sub-optimal processes and challenges in scale-up.  Very cold nucleation temperatures can significantly reduce the primary drying rate. “The reduction is due to the fact that vials that freeze at lower temperatures have smaller ice crystals, which leave smaller pores behind when they sublime, thus slowing the drying rate.” Praxair has developed a technology that makes it possible to ensure nucleation at not only a specific temperature for all vials, but generally at warmer temperatures than previously possible.  “Such controlled nucleation has the potential to make both the freezing process and the drying process more consistent and efficient,” observes Nail.

Praxair has worked with freeze-dryer manufacturers to make the controlled nucleation technology readily available to the industry. SP Scientific provides laboratory scale freeze-dryers equipped with the new technology; both SP Scientific and GEA Lyophil can provide the technology on new or existing freeze-dryers at pilot and manufacturing scales. Sever notes that the technology has been demonstrated to be effective at manufacturing scales with no scale-up issues. Although no commercial process has yet adopted controlled nucleation, many are looking to implement the technology in the near future. Nail adds that there are several approaches to controlled nucleation that are currently under development that will benefit the industry. 


In addition to ice-nucleation issues, there are several other limitations of the current freeze-drying process that need to be addressed, including protein/nucleic acid stabilization in the solid state, heat transfer, vial-fogging, high-concentration formulations. Improvements are also desired in the reconstitution process, the scale-up process, and characterization and analysis tools. “Each drug formulation has its own unique characteristics, and therefore its own set of issues depending on those properties,” asserts Cook. 

In general, though, Nail sees a real need for better screening techniques to quickly identify the most promising formulations, particularly for protein pharmaceuticals since, in general, solid state stability is very much affected by the composition of the formulation. Nail also believes that the inefficiency of current freeze-drying technology is a serious issue. “Freeze-dryers basically need to be redesigned to make heat transfer more efficient by taking more effective advantage of thermal radiation.” Ulfik notes that there have been improvements in shelf fabrication methodologies that have contributed to increased heat transfer uniformity.

He adds, though, that inexpensive workable, noninvasive methods for measuring product conditions in all areas of the freeze-drying shelf stack are still needed to ensure that the product process envelope can be maintained over each and every product vial in the entire freeze-dryer load. “The shelf position in the dryer can have an effect during processing. Knowing these influences will reduce risks to product efficacy and overall customer safety, and of course save tossing batches if the control system can maintain conditions based upon these individualized measurements,” Ulfik states.

Improvements in technologies for cleaning in place and sterilization are also needed. Ulfik believes that the use of sterilizing gas rather than steam at high pressure is promising and expects that sterilization gases that remain as ideal gases will ultimately replace the use of hydrogen peroxide vapor.


Manufacturers and users of freeze-dryers are also investigating other improvements as well. “Users of lyophilizers want engineered solutions to the problems they face to maintain product process envelopes. That can include tempered jacketed chambers to reduce chamber-heat gain to edge-of-shelf vials, solutions for choked flow during processing, the use of non-hardwired temperature sensors during validation, and non-temperature-based methods for robustly determining process endpoints. Additional improvements include streamlining of the interiors and operation of freeze-drying systems.

With respect to formulating parenterals for freeze-drying, drug manufacturers are exploring different buffer types and concentrations to minimize pH effects on product integrity during freezing and reconstitution, according to Ulfik. The use of more complex excipients, such as amino acids and glass-forming polysaccharides, is also increasing.

Meanwhile, some pharmaceutical companies are entering into what has previously been thought to be forbidden territory and are exploring drying above the critical temperature of the frozen solid. “Drug manufacturers are looking for ways to reduce the cycle time and lower the cost of freeze-drying. Raising the temperature is one way to do so,” Sever explains. “What is most interesting is that it has been found in some cases that the stability and reconstitution properties of the freeze-dried formulations are acceptable despite the potential for collapse of the cake microstructure.”

New characterization technologies are also under development. Baxter is closely following optical coherence tomography, which offers potential improvement over current methodology for freeze-dry microscopy, according to Nail. Biopharma Technology, meanwhile, has investigated headspace moisture analysis. “Moisture analysis is very important in freeze-drying because moisture impacts product quality and storage stability. An approach based on headspace analysis is beneficial because it is both rapid and non-destructive and accurately indicates whether the product is within the specified moisture range, which can be critical for biologics,” Cook says.

Finally, Sever believes that one of the biggest challenges is educating practitioners of freeze-drying technology about recent scientific advances so that they can be put into commercial practice. There has been significant effort to develop effective process modeling  tools and describe robust process design strategies that can help reduce the amount of trial and error needed to optimize lyophilization, but they are not yet widely being used in the industry today,” he says.

As an important method for improving the stability of parenterals, lyophilization is fairly well understood, but can still benefit from several advancements in the technology.