Freeze Drying Critical Temperatures

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Freeze Drying Critical
Temperatures
www.lyophilizationtechnology.com
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What is Biopharma Technology?
Biopharma Technology Ltd was set up in 1997 to
provide an international service in all aspects
of freeze-drying technology
Our strength comes from a wealth of experience
and knowledge of product formulation and process
development, particularly in the field of
pharmaceuticals and biotechnology
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Why are Critical Temperatures Important in
Freeze-Drying?

• Freeze-drying above the product critical
  temperature can lead to

Freeze-drying too far below the product critical
temperature can lead to

• Loss of physical structure
• Incomplete drying (high moisture content)
• Decreased solubility
• Reduced activity and/or stability

• Poor efficiency
• High Costs
• Longer cycles than necessary

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Critical Temperatures for Freeze-drying
Collapse Temperature (Tc)
This is the temperature at which the material
softens to the point of not being able to support
its own structure
Eutectic Temperature (Teu)
This is the temperature at which the solute
material melts, preventing any structure forming
after the solvent has been removed
All formulations can be described as having
either a collapse
temperature or a eutectic temperature
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Effect of Formulation Components on Critical
Temperature

• Higher molecular weight components such as
  polymers tend to have higher critical
  temperatures
• Lower molecular weight components such as salts
  and small sugars tend to have lower critical
  temperatures
• Additionally, crystalline / amorphous mix can
  have a major impact on critical temperature
• Lactose NaCl (11) Tc approx. -30C
• Lactose NaCl (10.3) Tc approx. -45C

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Critical Temperature Determination
Using extensive knowledge and experience in the
freeze-drying industry Biopharma Technology has
developed two unique analytical instruments.
These bring scientific understanding and a
rational approach to freeze-drying cycle
development
Lyostat2 Freeze-drying
Microscope
Lyotherm2 DTA Impedance
Analyser
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Critical Temperature Determination
Lyostat2 Freeze-Drying Microscope

• Enables real-time observation of the behaviour of
  your formulation during freeze-drying
• Enables temperature control between -196C and
  125C to an accuracy of 0.1C
• By observing the sample structure during drying
  as the temperature is raised, the exact point of
  collapse or eutectic melt can be observed under
  the microscope

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Critical Temperature Determination
Lyotherm2 DTA and Impedance Analyser

• Provides an integrated Differential Thermal
  Analyser (DTA) and Electrical Impedance analyser
  (Zsinf) capability in one instrument
• Can measure critical events in the frozen
  material that are undetectable by standard
  thermal analysis techniques
• Enables characterisation of the required freezing
  parameters that are essential to a successful
  freeze-drying cycle

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Critical Temperature Application
Cycle Development
From analysis of the product we now know

• The maximum product temperature we can freeze-dry
  at before the product is damaged, allowing us to
  set the primary drying temperature with
  confidence from Lyostat2 analysis
• What events occur in the frozen state that affect
  the freezing stage of the cycle, allowing us to
  add in any thermal treatment steps such as
  annealing from Lyotherm2 analysis

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Case Study
Product Cycle Development
A customer approached BTL with a product that was
being freeze-dried using a cycle borrowed from
another product
They were discarding a high percentage of each
batch due to defects occurring during
freeze-drying
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Case Study
Product Cycle Development

• Step 1 Information was obtained on the critical
  temperatures and thermal behaviour of the
  product using the Lyostat2 and Lyotherm2
  instruments
• Step 2 This data confirmed the lack of
  suitability of the existing freeze-drying cycle
• Step 3 Critical temperature information was
  used to create a first approximation cycle
  tailored to the needs of the product
• Step 4 Data from this cycle was used to design
  a more optimised cycle until a safe and
  efficient cycle was achieved, minimising cycle
  time without jeopardising product quality

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Case Study
Lyostat2 Freeze-Drying Microscopy Analysis
Sample dries well at -50.0C, but collapse starts
as the temperature is increased to -45.7C.
This can be identified by defects appearing in
the dried material
As the temperature increases to -39.6C the
structure continues to weaken and collapse
becomes more evident
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Case Study
Lyostat2 Freeze-Drying Microscopy Analysis
The sample is repeated but this time with an
annealing step frozen and cooled to -50.0C,
warmed to -15.0C and re-cooled to -50.0C before
drying. The sample dries with good structure
until the temperature reaches -31.4C and defects
appear
At -30.8C the sample is too weak to keep any
structure as the water is removed
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Case Study
Lyotherm2 DTA and Impedance Analysis
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2
3
See full labels 1 4 on next slide
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Case Study
Lyotherm2 DTA and Impedance Analysis

• Exotherm in DTA and increase in Impedance
  indicating a stabilisation / rearrangement of the
  frozen structure
• Increase in downward gradient of Impedance curve
  indicating a softening of the frozen material
• Onset of a sharp endotherm consistent with the
  melting of the ice
• Minimum Impedance indicating complete mobility
  within the solute structure

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Case Study
Interpretation of Analysis Results
From the results of these analyses, we could make
the following deductions

• The inclusion of an annealing step resulted in an
  increase in the collapse temperature of the
  formulation from -45.7C to -31.4C, as well
  as increasing ice crystal size and networking
• Therefore, the maximum allowable product
  temperature during sublimation (to avoid
  collapse) was raised by 14.3C by the use of
  annealing, thereby allowing drying to be carried
  out at higher temperatures, for a more efficient
  cycle. The higher the product temperature during
  drying, the faster the drying rate.

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Case Study
Existing Customer Cycle 70 hours
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2
3
20C
A
-15C
-40C
Tc -45.7C
-50C
Shelf Temperature
Product Temperature
Chamber Pressure
1 Freezing 2 Primary Drying 3 Secondary
Drying
A Product at risk of collapse
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Case Study
Modified Cycle Created By BTL 42 hours
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2
3
4
20C
-15C
Tc -31.4C
-35C
-50C
Shelf Temperature
Product Temperature
Chamber Pressure
1 Freezing 2 Annealing 3 Primary Drying
4 Secondary Drying
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Case Study
This graph shows an enlarged section of the
previous graph
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The Sublimation Cooling Effect The
lowering of product temperature caused by the
sublimation of ice
20C
-15C
Tc -31.4C
-35C
-50C
Shelf Temperature
Product Temperature
Chamber Pressure
1 Freezing 2 Annealing 3 Primary Drying
4 Secondary Drying
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Case Study
The Next Steps

• From the previous run we now know
• The extent of sublimation cooling, allowing us to
  increase the shelf temperature / chamber pressure
  as high as possible whilst sublimation cooling
  keeps the product temperature below Tc
• When sublimation was complete in
  temperature-probed samples (when product
  temperature shelf temperature)
• The physical appearance of the cakes produced by
  the cycle
• Residual moisture was measured in the final
  product, in order to establish whether the extent
  of secondary drying was sufficient

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Case Study
End Results
A lyo-cycle with increased efficiency, reduced
costs and no product rejects
Another very happy customer!
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10 years at the forefront of freeze-drying
technology
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