What is spin-freezing and what are its benefits in freeze-drying?

During spin freezing, the rotation speed can be set between 1,000 – 4,000 rpm. Thanks to spin-freezing, a thin product layer is achieved. This thin product layer results in a up to 40x shorter drying time in comparison to batch freeze-drying (entire process in hours, not days). This reduced drying time enables the possibility to create a continuous production line. This would not be possible without a reduction in drying time. The layer attached to the vial wall also results in improved measurement capabilities. The additional benefit is to have a translucent cake, which assists greatly with automated visual inspection.

The typical thickness of the ice layer is between 0.5 and 2 mm. The cakes are cylinders and
therefore mechanically quite stable. Even in situations where we noticed some cracking or shrinkage, we did not notice destruction of the structure unless applying rather aggressive action.

Shear impact has been evaluated. The shear forces are low. The shear forces are dependent on vial diameter and the ramp up at the start of spin freezing. The calculated maximum shear forces are a magnitude lower than the shear forces you typically have in a filling line. See paper Lammens et al.

“The relevance of shear, sedimentation and diffusion during spin freezing, as potential first step of a continuous freeze-drying process for unit doses.” International journal of pharmaceutics vol. 539,1-2 (2018): 1-10.