Developing separate freeze-drying cycles for each formulation or product is vital to ensure optimum lyophilization conditions and high product quality.
The design of the cycle at each stage of the freeze-drying process (freezing, primary drying, and secondary drying) is influenced by product temperature to equipment capabilities. Manipulating the cycle conditions and monitoring parameters within a freeze-dryer would be quite beneficial for efficiency and reproducibility. The focus in this article is on how formulation data can be utilized to create optimum freeze-drying cycles for a product based on unique Process Analytical Technology (PAT) tools and technologies available in the leading freeze dryer for cycle development, the SP Scientific's LyoStarTM3.
A number of pilot-scale runs were required to develop acceptable recipes for each product in the inception of freeze-drying cycle design. Several criteria were assessed based on parameters, like the physical appearance of the dried product, reconstitution time, residual moisture content, and the active ingredient stability. Sometimes even the same freeze-drying recipe was used for many products in different formats.
On a commercial level, excessive drying times hinder throughput and there is a profound and dramatic, economic effect on the cost the longer the product spends in the freeze dryer. Due to technological advancement, cycle development has analyzed and combined data for various process parameters for efficiency.
The innovative LyoStar 3 uses many innovative PAT tools in the one instrument and proprietary software, defining several drying conditions for the product and combining data with other analytical instruments. With SMARTTM freeze dryer technology, the LyoStar 3 enables the definition of a set of 'framework parameters', automatically adjusts shelf temperature, and then selects chamber pressure so the necessary product temperature profile is achieved and controlled.
The SMARTer Solution for Optimal Freeze-Drying
The LyoStar's SMARTTM freeze dryer technology is based on manometric temperature measurement (MTM), both of which are already the most valuable PAT tools for laboratory enhanced product and process understanding. MTM is a pressure rise measurement where the chamber is isolated from the condenser for 25 seconds. The pressure rise data is recorded to a file, and then raw data is fitted to a non-linear regression model (the 'MTM equation'). From this, all other vital process attributes are derived.
An alternative to the MTM is the LyoFlux200 tunable diode laser absorption spectroscopy (TDLAS) (Figure 1), which is a near-infrared (NIR)-based PAT tool that measures the gas velocity and water vapor concentration in the spool (duct) linking the chamber and the condenser. Using laser diodes with optics transmitters and receivers installed on the spool, the vapor flow inline and online.
Figure 1: LyoFluxTM: Tunable Diode Laser Absorption Spectroscopy (TDLAS) Water Vapor Mass Flow Rate Sensor. Image Credit: SP Scientific
LyoFlux200 can measure and calculate based on water vapor velocity and water vapor concentration, the mass flow rate (dm/dt) in a spool. Steady-state heat and mass transfer contributes to the calculation of product temperature, resistance, and so on, and LyoFlux200 provides comparable information to MTM from the early stage to production equipment.
One of the largest challenges of freeze-drying is the uncontrolled nucleation as a result of the stochastic nature of ice nucleation and corresponding variability in nucleation temperatures. The nucleation temperature dictates the pore size of the ice crystals - the warmer the nucleation temperature, the bigger the ice crystals. Big ice crystals leave, once sublimed, big pores behind in the cake which impose less resistance to water vapor flow during primary drying. This typically saves process time significantly. In contrast, uncontrolled nucleation generates small to intermediate pores in the cake which are not as desirable.
SP Scientific’s Controlled Nucleation (CN) technology (ControLyoTM – Figure 2), available as part of the LyoStar 3, overcomes the limitations of uncontrolled nucleation creating less desirable small to intermediate pores in the cake. With an inert gas such as nitrogen or argon, ControLyo involves pressurization of the freeze dryer chamber followed by the quick depressurization of the chamber, inducing instant nucleation in all vials of the batch at the warmest possible temperature. This yields the largest possible ice crystals. Experts in freeze-drying foresee that most of the newly developed freeze-drying cycles will include a controlled nucleation step in the next ten years (Int. J Pharm. 450 (1–2): 70–78).
Figure 2: Depiction of the effect of ice crystal size on the freeze-drying process performance. Image Credit: SP Scientific
A reliable software package can combine all the data generated using the PAT tools. SP Scientific’s LyoS 2.0 provides process flexibility, data protection, and ease of use for cycle development.
This concept has been expanded to production equipment software for ease of process controls on comparable platforms. This fits well with SP Scientific’s aim of providing a Line of SightTM suite of tools (technologies and equipment) that can allow for better transfer across equipment when scaling-up for commercial development.
The data export function in MS Excel can also combine LyoStar 3 data with other data sets obtained from other PAT tools for rigorous analysis.
A capacitance manometer mounted on the condenser allows the monitoring of the pressure differential between the chamber and condenser. Therefore approximation of mass flow rate can be completed using this instrument as a troubleshooting tool.
There are up to 16 standard thermocouples ports where typically a user can only get 4 —6 in the LyoStar 3. The LyoStar 3 also utilizes best industry practice, such as a Pirani and capacitance manometer convergence monitoring tool, barometric endpoint determination, and pressure rise on-demand in the assessment of primary drying completion.
The Process of Cycle Development
For cycle development in a LyoStar 3, it is best, to begin with conservative low shelf temperatures and moderate pressure proceedings with step changes with a large safety margin. Thus, there is an anchor point for product quality attributes for future development cycles.
Optimization, therefore, starts with 2–3 cycles where only freezing conditions are altered, then primary drying (different chamber pressures and shelf temperatures) and lastly, when freezing and primary drying conditions are defined, secondary drying conditions are optimized, possibly requiring 6–8 cycles with the help of various PAT tools (see Figure 3).
Figure 3: Return on Investment (ROI) illustration of development effort using conventional method vs SMART technology. Image Credit: SP Scientific
In the Quality by Design (QbD) approach, these days companies often evaluate the ‘design space’ or ‘robustness’ of a cycle and the number of cycles could triple without PAT tools. This establishes a design space with defined sets of operating components required for the maintenance of batch consistency and results in a product being a predefined quality. This can require an additional 4–5 cycles to perform.
Figure 4: LyoStarTM 3 with Sample Theif TM Sample extractor. Image Credit: SP Scientific
The last step in development is to upscale to a 'full load'. Up to 200 vials could be used for cycle development for one product needing a minimum shelf area of 0.1-0.5 m2. Allowing lab stability and analytical method development samples to be created in one batch, a standard LyoStar 3 may include 3 or 4 shelves holding around 240 vials of 10 mL per shelf, enabling cycle development on one shelf and the further larger batches of up to 720 (3 shelves) or 960 (4 shelves) 10 mL vials.
Choosing the Best Equipment
Henning Gieseler, GILYOS (Germany), has used different LyoStar generations for cycle development and optimization during the last 15 years. In a recent interview, Dr. Gieseler stated that “A LyoStar 3 equipped with such a combination of high end, highly innovative PAT tools is simply the best piece of equipment for freeze-drying you can get! We could resolve several issues with large scale cycles using the LyoStar 3, only because we could analyze the freeze-drying conditions by having this "orchestra" of PAT tools in place. The special PAT tools, MTM and TDLAS, are even sensitive enough to allow monitoring of atypical product formats, small volumes in microliter plates or capillary tubes.”
The reduction of cycle time, and therefore cost, in freeze-drying is a vital goal in cycle development and optimization, and SP Scientific's LyoStar 3 incorporates SMART-MTM technology, auto-MTM, and LyoF1ux200 PAT tools, and ControLyoTM technology to control ice nucleation. This allows optimal freeze-drying cycle development and reduces drying times.
SP Scientific's Line of Sight suite of tools is optimal for the scaling up and down of product development. Scale-down is also a frequent need in freeze-drying, e.g. if "production problems" on large scale require troubleshooting (you want to mimic the situation on large scale, identify the issue and resolve it).
The LyoStar can also be beneficial in resolving these large scale issues with compatible technologies and PAT tools. SP Scientific's powerful combination of equipment and software allows research and development scientists to accumulate valuable and critical process and product parameters to optimize all freeze-drying process stages.
About SP Scientific Products
SP Scientific is the synergistic collection of well-known, well-established, and highly regarded scientific equipment brands — VirTis, FTS Systems, Hotpack, Hull, Genevac, PennTech, and most recently i-Dositecno — joined to create one of the largest and most experienced companies in freeze-drying/lyophilization, production fill-finish lines, centrifugal evaporation and concentration, temperature control/thermal management, glassware washers and controlled environments.
More than a scientific equipment supplier, SP Scientific represents brands that distinguish themselves by thoroughly assist customers in matching equipment to particular application needs. Fortune 500, pharmaceutical, aerospace, automotive, medical device, diagnostic kit, and biotechnology companies — as well as government facilities, universities, and colleges, are among the organizations served on a daily basis.
SP Scientific is part of SP Industries, Inc., a leading designer, and manufacturer of state-of-the-art laboratory equipment, pharmaceutical manufacturing solutions, laboratory supplies and instruments, and specialty glassware. SP's products support research and production across divers end-user markets including pharmaceutical, scientific research, industrial, aeronautic, semiconductor, and healthcare.
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