The most important consideration when choosing a freeze dryer is to ensure the system is fit for both today's applications and future needs. For the sake of this discussion, we will focus on freeze dryers with fluidfilled shelves, which does not include lowend manifold or heatonly shelf freeze dryers.
An understanding of the available features of a freeze dryer can facilitate the choice. The following are some considerations:
The freeze dryer manufacturer will also want to know what space is available for the freeze dryer and what utilities, such as electrical, air, chilled water and air conditioning, are available.The following are a few examples of some of the various options:
Main freeze drying categories
Freeze dryer selection falls into two main categories: laboratory versus production, and non-sterile versus sterile.
Laboratory freeze dryers are used for a large variety of applications, including removal of solvent from a material, Phase I clinical trials and protocol development for scaleup production. A typical laboratory system will have a shelf area of 0.1–1 m2 and a condensing capacity of up to 30 L.
Laboratorystyle systems can be simple freeze dryers with only standard features, such as a pirani gauge for vacuum level measurement and thermocouples for temperature monitoring, or they can incorporate more advanced instrumentation:
Pilot and production systems offer shelf areas from 1 m2 up to more than 40 m2 . Production systems are used for Phases II and III clinical trials, and tend to be used for the same or a limited number of products in high-volume production. Recently, there has been a shift from using 10–50-mL vials, to 2mL and 5mL vials for smaller volume, highpotency biotech and proteinrelated products. The result is smaller freeze dryers with expensive payloads.
The type of processing will determine whether stoppering is required. Bulk applications can have fixedinplace shelves, but vial applications require stoppering where the shelves move and are squeezed together to press the partially inserted stoppers into the vial.
Pharmaceutical and other applications may also need to be sterilised between cycles, which can add significant complications and costs to a freeze dryer. A freeze dryer is normally rated for vacuum and the most common method of sterilisation is pressurized steam, which requires the freezedryer chambers to be certified pressure vessels rated to 2 atm at 131 °C.
An alternative sterilisation technique, which is growing in popularity for laboratory and small production systems, uses hydrogen peroxide (H202). H202 does not require a pressurerated vessel, which helps to minimise costs.