Thanks to state-of-the-art freeze-drying processes, pharmaceutical products are becoming much more durable and suitable for long-term storage. LyophilizationWorld will accompany you from the beginning to the process design and understanding of the ideal lyophilization system for your needs and applications. This includes get into know the most sensible parts of the equipment and among them, the shelves are extremely complex and vary across manufacturers.
Let’s analyze some key points!
Design
From a manufacturing point of view there are 2 schools of though:
Spot welding: electrical spot welding (or sandwich construction) assures a perfect connection between the bars and plates. Welding assures 100% reliable connection and stiffness.
Brazing: brazing technology allows the use of lighter materials compared to spot welding. The flow path is created using hollow tubes that allow the heat transfer fluid to pass through and around. All tubes must be brazed simultaneously so the distorting effect of uneven heating is eliminated.
In any case, each shelf should:
Pass a pressure hold test at 4.0 bar
Be in accordance with DIN ISO 1101 (better than 1 mm/m)
Pass an helium leak test (better than < 10-7 mbar l/s)
Roughness
Shelves are built in AISI 316 L stainless steel and for maximum vial protection the surface roughness should be Ra = 0,4 μm.
A very interesting point is the origin of the stainless steel: in Europe manufacturers are usually adopting steel from Germany, Sweden, Italy with high standards, documentation and cost. Others manufacturers operate using Chinese or Indian steel.
Temperature accuracy
Commonly in the industry is wide accepted a distribution of +40°C to 40°C with the following deviations:
Per individual shelf ± 1°C
For total shelf system ± 2°C
Some manufacturers claim to be able to validate better performance and get a total deviation along the shelve stack of ± 1°C.
Heating and Cooling
Shelf cooling and heating is carried out by forced circulation of thermal fluid through internal channels in the shelves. The heat transfer fluid is silicone oil, which is suitable for low and high temperature applications. The circuit is closed against atmospheric air to avoid moisture entering. In another article was discussed the risk of Silicon Oil Leak and how to prevent it.
Silicone Oil Hoses
The recirculation throughout the entire shelf stack is arranged by flexible hoses welded to the each shelf and chamber collector. To ensure best flexibility and avoid rupture of the hoses the following criteria should be considered:
Hoses with angle of incidence (vary among the size and number of shelves)
Support of hose movement
Enhanced lateral guidance
Regarding the hoses they can be: non-braided, these are lineal and clean but depending on the size of the freeze dryer they can break quite easily; braided, generally more resistant even though from a GMP point of view could be defined “dirtier”.
Investigations and studies of all these parameters should be carried out due to the relevance of this product contact part (PCP).