Freeze drying (lyophilisation) is a stabilisation method that is widely used in the pharmaceutical industry for drugs, vaccines, antibodies and other biological material. Freeze drying can be a complex process to manage effectively but despite improvements in analytical and process science a number of misconceptions persist.

This is part 2 / 2 in this series – click here for part one.

Lower chamber pressure means faster freeze drying

“A higher vacuum (lower pressure) will suck the water out faster and speed up processing”

The vacuum within a freeze drying chamber is intended only to create the necessary conditions for the moisture to sublime directly from ice to vapour. The moisture is not “sucked out” of the product and in fact chamber pressures that are unnecessarily low will slow freeze drying.

When moisture sublimes from ice to vapour, the product temperature will drop due to an effect known as “sublimation cooling”. As the product cools, sublimation will slow and the process will lengthen. In order to counter this effect energy (heat) needs to be continually added.

Heat enters the product by conduction and by radiation but also convection from the remaining air molecules. As the pressure in the chamber drops, the effect of convection decreases. Control of the pressure/vacuum in the chamber is therefore one way of influencing the overall speed of the process.

The driving force of freeze drying is the vapour pressure differential between condenser and the product in the drying chamber, not simply the pressure or the flow of gas created by a vacuum pump.

Condenser overloads

“Why does the condenser overload or by-pass when we’re processing far less than its stated overall capacity?”

If vapour is being created at a rate faster than the condenser can trap it, the vapour will bypass the condenser and exit to the vacuum pump. Known as an overload, this can cause vapour to condense in the pump, damage the pump and can also be an indication that there is a problem with the particular processing step or recipe.

Performance figures for freeze dryer condensers are most commonly given as overall capacity (at a particular ice thickness) and deposition rate over 24 or 48 hours – the latter being a particularly important figure. These figures are often quoted for comparison with other systems and it’s important to note that both of these measurements are based on a number of standardised parameters that may not be applicable to a particular scenario. Factors such as the processing temperature, the container type and the batch size can all affect the rate at which a quantity of vapour is generated and careful consideration of drying conditions is important.

Graph 1: Condenser trapping rate and condenser load

 Vapour will not be given off at an even rate throughout the cycle (see graph 1 above). Drying is often much faster at the start of primary drying, when there is less impedance to the migration of vapour. The condenser’s performance may match the requirements when they are taken as an average over 24 or 48 hours, but it may be that the majority of this vapour is being generated early on in too large a volume for the condenser to trap and the condenser will overload or by-pass.

Application of too much energy at the start of the drying process can lead to high vapour generation which in turn can lead to vacuum pump failure and risk a rise in condenser temperature as it tries to cope with condensing too much vapour. This is a particular design consideration when specifying benchtop or production systems and correctly sizing the condenser’s capacity and operating temperature to ensure the particular solvent will condense is important to long term reliability.

 Shelf spacing requirements

“I have 10 ml vials with a height of 45mm plus stopper at 8mm for a total height of 53mm. Why can’t I specify a dryer with 55mm shelf spacing to maximise batch capacity?”

Vials loaded with good shelf spacing

Shelf spacing calculations are made to ensure that not only can we easily load product onto shelves, but that there is also sufficient space above the drying vials ( or other container types ) to allow unhindered vapour escape. Vapour can leave the drying vials at a high rate and with insufficient space for that vapour to escape above the vials it is possible to set up local drying conditions in the centre of a shelf, for example, with different drying conditions than those vials nearer the edge of a shelf.

There are various formulas available for determining the shelf spacing required. In the example given above, our own calculations suggest that a spacing of 65mm (loaded with a removable bottom tray, so no extra allowance for tray thickness) would be more acceptable. In practice, we may also consider the dimensions of the shelf and vial shoulder design when making recommendations. It would be possible to complete drying at reduced spacing but it’s likely an extended cycle would be required to reduce possible vapour load and the risk of localised drying conditions.

On larger production dryers, it is increasingly common to employ automated loading and unloading systems (ALUS) and shelf spacing also needs to accommodate mechanisms of such equipment.

Vacuum pumps are all the same

“I have a vacuum in the lab that works fine, I’ll use that one”

“I’ll just connect the dryer to our house vacuum system”

“I want to put the vacuum pump at the other end of the bench”

“What is the gas ballast function?”

Many pumps often found in the lab – central vacuum systems, single stage pumps or diaphragm pumps – are not suited for freeze drying as they cannot achieve the required vacuum or maintain performance, having no pumping speed capability at typical freeze drying operating vacuum. The system must achieve a vacuum lower than the vapour pressure of ice at the frozen product temperature in order to begin the sublimation process.

Most commonly, a two stage, oil sealed, rotary vane vacuum pump is sufficient for most freeze drying applications. With the pump’s ultimate achievable vacuum typically of the order of <1mtorr (measured directly at the pump according to pump manufacturer data), this provides near 100% of the pumping speed performance across the typical working range of freeze drying vacuum requirements. If the freeze drying system is specified correctly then the condenser will trap all condensable vapours and the pump will provide initial pull down and maintain set vacuum in the case of minor vacuum fluctuations and control by gas bleed.

In all vacuum applications, it is useful to site the pump as close as possible to where performance is required as long length, small bore tubes have a significant effect on reducing vacuum pump performance.

Dry vacuum pump technology has improved in recent years and is more affordable. Dry pumps potentially offer reduced maintenance through no oil changes and certain designs can be more tolerant to agressive vapours, liquids and particulates. Although ultimate performance does not match “wet” oil sealed pumps, pumping speed characteristics have improved and such dry pumps are now successfully employed in freeze drying applications.

Typical rotary-vane vacuum pump (left) and dry pump (right) used in freeze drying applications.

“Gas ballast” is normally a two position valve – on /off – that allows a small amount of air to be introduced at the final compression stage of the pump. The effect is to increase the pump’s tolerance to pumping water vapour and also to raise the pump’s operating temperature so degassing and cleaning up the oil of any solvent contamination. It is good practice to operate gas ballast for 10-15 minutes after a freeze drying run before switch off. Remember to turn the gas ballast off as oil carryover to the exhaust can be measured in significant cc/hr and will eventually drain the pump, potentially causing damage.

Vacuum pump maintenance is one of the more important day to day tasks that users can complete simply and easily to ensure the long term performance of the freeze dryer generally.

Freeze drying equipment doesn’t need maintenance

“No-one ever services my fridge/freezer.”

Freeze drying equipment can be very complicated, often operating daily at both high temperatures and very low temperatures in the same system as well working to negative and positive pressures. Changes in the batch quality, degradation in performance characteristics and system alarms may indicate that maintenance is required.

Problems in the refrigeration system can cause the shelf and/or condenser to cool more slowly or not to a low enough temperature. The amount of refrigerant in the system is important and both under- and over-charge can cause the system to function incorrectly. Other problems include moisture or air contamination and mechanical faults. Refrigeration problems should only ever be investigated by qualified engineers in accordance with EU legislation.

Refrigerating systems such as freeze dryers work best if they are run regularly as the refrigerants and system lubricants will pool and settle if left to stand even for a few months, so when bringing an old system out of storage or purchasing a second hand unit it’s important to consider that the system will not simply switch back on again and run as it used to. Freeze dryers should always be stored upright and should never be tilted or stored lying down.

As a vacuum system a freeze dryer is complicated and there are a lot of valves, gaskets and joints where leaks can develop. As well as reducing the vacuum that can be achieved this can also let moisture and contaminated air in to the chamber. However the most common cause of loss of vacuum is a problem with the vacuum pump which is relatively easy to service or even replace.

Control systems, CIP / SIP systems and instrumentation can also develop faults which will cause the freeze dryer to operate incorrectly or not at all.

Faultfinding can be time-consuming. Regular scheduled maintenance is the best way to ensure that the system continues to work as required with a minimum of downtime.

Links & More information

5 Misconceptions (Part 1) >>

Download this article as a pdf>>

Freeze dryer maintenance services>>

New to freeze drying? Request a free copy of our Introduction to Freeze Drying or learn about our Training Courses.

Our popular free one-day event, “Emerging Technologies in Freeze Drying”, is set to visit Carrigaline, co Cork, this September.

This will be the third year we have run this popular event. Speakers from industry and academia will present a variety of subjects about technology, advances and applications in the field of freeze drying. As well as BTL’s Kevin Ward and Isobel Cook there will be presentations from SP Scientific and Genzyme with more speakers to be confirmed shortly.

More details including the timetable will be announced shortly. For more information please contact us – sales@biopharma.co.uk

Emerging Technologies in Freeze Drying

Location: FAS, Carrigaline, Co Cork

Date: 3rd September 2013

Cost: FREE

Registration: Opening soon

About Lyosolutions

Lyosolutions Ltd is a specialist research and development company, with particular expertise in pharmaceutical product development and freeze-drying. Originally started in 2003 by Gerald Adams, the running of Lyosolutions was taken over by Peter Riggs in 2006. Wanting to scale down to retirement, Peter recently began to look for ways to ensure continuity of service for his existing customers.

About BTL

Biopharma Technology Ltd (BTL) was established in 1997 to provide contract research and development services, training and advanced instrumentation in the field of freeze drying. BTL offers a uniquely comprehensive service covering all aspects of freeze-drying from pre-formulation through to full-scale production and dried product analysis. Over 1000 different products have been successfully processed on behalf of clients in industries including pharmaceutical, biotechnology, regenerative medicine, diagnostics and defence.

BTL and Lyosolutions

Lyosolutions and BTL are based a mere 30 miles apart. Lyosolutions founder Dr Gerald Adams was a former head of R&D at BTL, working with our now-Director Dr Kevin Ward. Given this shared history and love of lyo a partnership between the two came as the ideal solution.

We are pleased to announce that from April 2013 Lyosolutions Ltd has been incorporated into BTL. Peter Riggs will continue to consult on behalf of BTL for the next two years while the Lyosolutions brand is retired. Peter can be reached through his existing details or through BTL on +44 1962 841092, btl@biopharma.co.uk.

All future work will be conducted at BTL’s laboratories in Winchester, which customers are welcome to visit by appointment. All existing agreements with Lyosolutions will be taken on by BTL unless they are specifically renegotiated – please contact Andrew Cowen to discuss.

Future business will be handled by BTL and interested parties should contact BTL’s sales department – contact details are given below.

 Products and Services

Products and services offered by BTL include:

• -Product characterisation and development of formulations for freeze drying
• -Freeze drying cycle development and optimisation for production
• -Scale-up and technology transfer
• -Training courses
• -Analytical instruments

 Freeze Drying Equipment and Servicing

 Our sister company, BPS, provides freeze drying equipment and technical services for customers in the UK, Ireland and France. The equipment ranges from simple benchtop systems, sophisticated research and scale-up models, to full-scale production. Technical services include installation and validation and maintenance. For more information please click here or contact Peter Williams at sales@biopharma.co.uk, +44 962 841092.

 Contacts

Switchboard: +44 1962 841092  |  btl@biopharma.co.uk

For sales enquiries, please contact Dr Laura Ciccolini.

For more information on existing CDAs and other agreements please contact Andrew Cowen.

Peter Riggs can also be reached via BTL.

Biopharma Process Systems (BPS) is pleased to be representing Avestin Liposome Extruders and High Pressure Homogenisers within the UK and Ireland.

Avestin Homogenisation Technology

Avestin C5 High Pressure Homogeniser

Avestin is the leading manufacturer of high pressure homogenizers suitable for high-pressure applications such as pharmaceuticals and biotechnology. Founded in 1991, Avestin’s focus on quality of engineering and design led to the development of a unique design that eliminates all o-rings and gaskets in the product path. This means less risk of contamination, easier cleaning and no risk of leakage. All face seals are precision-machined metal-to-metal or metal-to-ceramic for optimal durability and efficiency.

Avestin’s laboratory homogenisers are capable of processing samples as small as 3ml with both electrically-powered and pneumatically-driven models available. Research and production systems scale all the way up to 1000 litres/hour. All Avestin’s systems are capable of achieving controllable pressures up 30,000psi, more than enough for disrupting cells such as ecoli and yeast, with options for 45,000psi on some models. The most popular laboratory scale systems are often available from local stock.

Unique Homogenising Valve

Avestin’s unique dynamic homogenising valve is proven on over 2000 installations world-wide and self regulates once set. Submicron particles or droplets <50nm can be achieved. The valve has been designed to be easily disassembled for cleaning or inspection.

Options include filter/extruder for applications such as liposomes or sterile filtration, automatic homogenising pressure control  and precision pressure measurement with electronic data recording.

Avestin systems are suitable for a whole range of cell disruption, emulsification, homogenising and particle size reduction applications. They are CIP-(able) and all wetted parts are also suitable for SIP or autoclave. They can be used in cleanrooms and for GMP manufacturing where required.

All Avestin systems are fully supported for service and spares in the UK & Ireland by BPS’ in-house service department.

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High pressure homogenisers>>

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The new VirTis BenchTop Pro freeze dryer range from SP Scientific has been designed to be highly affordable, yet meet the needs of the most demanding research laboratories. Each system can be configured to meet both present and future needs.

Built-In Flexibility

Condenser refrigeration packages of -55°C, -75°C, -85°C and -103°C enable processing of aqueous or solvent based formulations. Systems can be configured for smaller sample volumes or to process a relatively heavy workload, with condenser sizes of 3 litre, 8 litre or 9 litre.

Manifolds are available in a variety of easily interchangeable styles. Acrylic manifolds are available for applications where aqueous products are being processed or it is important to ensure visibility of the product. For applications involving organic solvent, stainless steel manifolds provide superior corrosion resistance.

Hot-gas defrost minimises time losses traditionally incurred from lengthy condenser defrost and clean-up procedures.

Intuitive Controls

Designed for both the occasional user and freeze drying expert, the Benchtop Pro Omnitronics Controller simplifies freeze drying and makes the system easy to operate. One touch start-up and shut down ensure that your product and freeze dryer are protected from inadvertent operational errors. An intuitive graphic display provides users with at-a-glance understanding of the status of the freeze dryer and whether or not appropriate freeze drying conditions exist. Audible alarms help notify the user of potential problems with the system and hence, with the product. All Omnitronics controllers come complete with a trending screen that allows critical parameters to be monitored throughout the process if required. An optional Ethernet control allows the freeze dryer to be connected to a network, so that it can be monitored and controlled remotely. The Ethernet option also allows printout in a batch record, alpha-numeric, type report.

Advanced Benchtop Freeze Drying

The BTPro series updates and replaces the popular Benchtop “BTK” series.

More information

Contact us>>

Benchtop Pro freeze dryers>>

Introduction to freeze drying>>

The US National Institute for Occupational Safety & Health (NIOSH) has published studies describing the external contamination of chemotherapy drug vials. Several studies evaluated the external contamination of drug vials with cyclophosphamide and ifosfamide. Cytotoxic drugs may be mutagenic, carcinogenic and can be teratogenic. To keep employees safe, human involvement with any processing stage should be kept to a minimum. Decontaminating the outside of vials is a process that should also be automated wherever possible.

Recently, a US-based Biotech company asked Penntech to help them solve a major vial contamination problem. The task was to clean extremely dirty vials at 400 containers per minute and to dry them completely when exiting the machine. The most contaminated part was the bottom of the vial. The product was particularly difficult to shift, and even a high pressure water-jet did not give satisfactory results.

The only way to remove the contamination was by mechanical means: brushes driven by submersible servomotor. After weeks of testing with different brushes at different speeds and at different angles, the ideal combination was discovered.

Only one question remained: How do you dry the vials in less than two seconds? The answer Venturi air-amplifiers in combination with vacuum.

Benefits of Penntech’s external vial washer:

• Completely sealed cap (no water trapped in flip-off-cap)
• Completely exposed vial body, including bottom
• Automatic vial height adjustment as part of recipe
• Automatic spray nozzle adjustment for each vial format
• Tool-less vial changeover in 5 minutes (2 timing screws)
• Suitable for both 13mm and 20mm flip-off caps with no change parts required

Links

External Vial Washer>>

Rotary Vial Washer>>

Sterilising Oven>>

A QbD approach to freeze drying will help produce repeatable, robust results.

Quality by Design (QbD) is a systematic approach to development that begins with the defined objectives and emphasizes science and quality risk management in order to achieve those goals. QbD ensures that the quality of the product is built into production processes from the outset, rather than being tested after development has already commenced.

In practice this means gaining an understanding of the product and each process involved: the requirements of the product and effect of any changes to it, the various process steps involved and the robustness within these steps, as well as robustness of the end product. This enables tolerances for each stage to be established.

This approach requires us to gain a greater knowledge of the processes and identify the key points related to achieving and maintaining product quality. Once we have this information we can focus on investigating how these critical product quality attributes are derived and the specification range that is acceptable.

QbD in Freeze Drying : Defining Objectives

The goal of freeze drying is produce a shelf-stable product with good levels of activity. Therefore stability and activity of the product immediately after processing and over time will be two of the most important goals to define. However depending on the product and its ultimate usage a number of other “Quality Attributes” may also be important, for example:

• Appearance (especially for consumer products such as foods)
• Ease and speed of reconstitution (for injectable formulations)
• Pore size and distribution (for example, collagen scaffolds)
• Stability with respect to different storage conditions, for example light and heat
• Survival rates (for example, live bacteria)
• Location and mobility of residual moisture within the dried product
• Batch / unit process costs – time, energy, manpower

Each of the relevant parameters must be identified and tolerances must be defined that are stringent enough to produce the best possible product, while remaining practically achievable.

Designing in Quality from the Start

The balance of excipients within a formulation will define its process parameters.

Freeze drying formulations are, in general, complex mixes of excipients that benefit the active ingredient or the product as a whole. Various additives are available that offer protection for different processing stresses, and formulation development aims to create a balance of these that results in the best possible final product. However, the exact constitution of a formulation is what defines the subsequent process parameters and for this reason formulation and cycle development should ideally be conducted together.

The Quality Attributes will most likely include cost of production. The lower the critical temperatures of a product, the slower, longer and more expensive freeze drying will be. Process efficiencies may be gained through process optimisation but reformulation can also radically alter the thermal characteristics of a product. The difference of a few degrees of process temperature can result in a loss or gain of hours of process time and therefore both product and process should be developed with efficiency of manufacture as a goal.

Identification of Formulation Parameters

Many of the parameters for cycle development can be determined mechanistically: for example, freeze drying microscopy enables the determination of freezing and collapse temperatures, DTA/Impedance analysis identifies frozen-state mobilities, and there are various PAT techniques in-process montoring. “Design of Experiment” (DOE) testing will be applicable to other areas, for example, evaluating the effects of changes in formulation on thermal characteristics or post-process variables.

Variables and Risk Identification

One of the key elements of QbD is the identification of potential risks in advance. Understanding the impact of each of these will enable the definition of tolerances and implantation of controls to prevent failure. The nature and number of these variables will depend on the specific product and processes involved, some of which may not be directly freeze-drying related. Each of these variables must be evaluated using a formalised risk assessment procedure to find the “edges of failure” and therefore define the acceptable range.

Process variables before loading into the freeze dryer may include:

• The individual material components of the formulation, both API and excipients – for example purity and consistency
• Preparation of the formulation – procedures, equipment controls and atmospheric requirements, preparation time and stability of the formulation at each stage
• Container – tolerances for shape, glass thickness, pre-treatment

Process variables during freeze-drying may include:

• Freeze dryer specification and tolerances
• Product loading temperature and freezing time
• Shelf temperature ramp rates for both cooling and heating
• Shelf temperature control, including temperature variances across and between shelves
• Product temperature throughout the process – controlled by shelf temperature and chamber pressure
• Length of each process stage
• Batch size, with respect to the capabilities of the freeze dryer and the effect different batch sizes may have on sublimation and deposition

Scaling up to production

Where development for research and pilot scale has been undertaken from a QbD perspective, many of the Quality Attributes will also be applicable to production although the tolerances should be re-evaluated with the different equipment and handling in mind.

Establishing a Design Space

A Design Space is a multidimensional combination and interaction of input variables and process parameters that have been demonstrated to provide assurance of product quality. A successful and detailed study into all the product and process variables will allow us to establish a Design Space that provides repeatable, consistent and provable results.

Quality at BTL

BTL’s experience with hundreds of products makes us ideal to assist with implementing QbD. We can help identify and define the Quality Attributes that are relevant for your product, including characterising the product and process requirements. We are also familiar with the capabilities of freeze drying equipment and how the different specifications of temperature variation and process control can impact on final product quality. We can help you devise a way forward to maximise your design space, limit product losses due to process variations and maximise efficiency.

Contact us>>

Along with Tc and Teu, Tg’ (glass transition) is one of the most important thermal events in freeze drying. Identification of these events and understanding the behaviour of the product throughout the lyophilisation cycle is important to ensure that the product dries properly and therefore maintains stability and activity.

In this paper, Dr Paul Matejtschuk of NIBSC looks at the importance of glass transition to freeze drying and discusses several methods of determination including freeze drying microscopy, DSC, and impedance / DTA (Lyotherm2).

>>Read more (pdf)

BPS are pleased to welcome new Sales Support Executive Melvin Jose to the team.

Melvin joins us having completed masters in Biotechnology, Bioprocessing and Business Management from the University of Warwick. He has laboratory experience in the biological, chemical and biochemical settings as well as a BSc (Hons) in Biochemistry from the University of Nottingham.

With specialisms in both science and business, Melvin will be working alongside the BPS team. His responsibilities include business development, marketing, and project and sales support.