Controlling Ice Nucleation During the Freezing Step of Lyophilization - Pharmaceutical Technology

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Controlling Ice Nucleation During the Freezing Step of Lyophilization
Lyophilization technologies for controlled nucleation.

Pharmaceutical Technology
Volume 37, Issue 5, pp. 36-40

Depressurization technique

For successful controlled nucleation, each vial of product must experience the same conditions at the same time. "ControLyo technology is based on pressure and each vial, regardless of shelf location or tray position, experiences exactly the same conditions at exactly the same time," says Thierfelder. "For this reason, ControLyo technology is successfully used from laboratory to manufacturing scale."

ControLyo Nucleation On-Demand technology was developed by Praxair and licensed to SP Scientific exclusively for use on dryers with shelf areas of less than 1.0 m2 and nonexclusively on larger dryers. This technology allows users to select the temperature at which they want to nucleate. The selected temperature must be below the true freezing point of the product and above the temperature at which stochastic nucleation starts. Thierfelder explains that by selecting a temperature above the stochastic nucleation temperature, supercooling can be minimized, the freeze-drying chamber can remain warmer, and overall energy consumption and cycle time can be reduced.

"SP Scientific introduced the Lyostar 3 pilot freeze dryer with ControLyo technology approximately three years ago. It was the first commercially available freeze dryer with the capability to control nucleation," says Shon.

"ControLyo technology provides advantages in product quality and yield as well as in manufacturing cost and capacity," says Thierfelder. Benefits that have been observed include:

  • Ice crystal size: Nucleation at warmer temperate creates larger ice crystals with reduced resistance to mass transfer and decreases drying time. Cycle time reductions of up to 40% have been reported (7–9).
  • Product appearance: Nucleation behavior can have a pronounced effect on the cosmetic quality and structure of the final freeze-dried product. Cake cosmetic defects such as cracks, stratification, glazing, and color heterogeneity in many cases owe their origin to problems in freezing. Controlled nucleation may be a useful tool for adjusting freezing behavior to optimize cake elegance.
  • Protein aggregation: Larger ice crystals also result in lower overall ice crystal surface area. Protein aggregation (i.e., clumping of short strands of proteins) tends to occur on the surface of ice crystals and is synonymous with yield loss and potential adverse effects. ControLyo users have reported a reduction in protein aggregation (14).
  • Reduced vial cracking: Some lyophilized products have an amorphous structure and some have a crystalline structure. Others, such as those formulated with mannitol, can freeze in either an amorphous or crystalline structure. Upon initial freezing, certain products with the ability to form amorphous or crystalline structures will orient in an amorphous structure. During an annealing cycle (i.e., freeze, warm, and refreeze), the product is forced into its crystalline structure. In the absence of annealing, some products may randomly transition during processing, resulting in vial cracking. Vial cracking is costly and disruptive. In general, it has been observed that cracking problems can be substantially mitigated using ControLyo technology to induce nucleation at warmer temperatures (18).

"A number of studies have been conducted where we have scaled-up ControLyo technology to a production dryer," says Shon. "It does not require that the dryer be manufactured with the capability to perform the controlled nucleation." Shon explains that it is relatively easy to retrofit a commercial freeze dryer that has steam-in-place (SIP) capability with the manifolds and controls to do the pressurization/depressurization required for ControLyo technology. "In the largest scale-up study to date, we collaborated with Fresinius-Kabi and performed a retrofit on a 28-m2 production dryer (19). The dryer was fully loaded with 100 mL, 50 mL, 30 mL, and 20 mL vials with 5% mannitol solution. Nucleation was controlled and every vial was visually inspected to confirm complete nucleation. In total, 8701 vials were nucleated (19)."


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