Freeze-Thaw Performance and Robustness Assessment of Celsius FFT 6L

Can this freeze-thaw system handle frozen solutions without compromising container integrity or product quality?
Dec 01, 2009
Volume 22, Issue 12


This article provides data from performance and robustness studies of the Celsius FFT freeze-thaw system for the long-term frozen storage of biopharmaceutical products. In this study, gamma irradiated containers filled with 6 L of colored water solution, were frozen inside a conventional upright freezer and thawed in different conditions (ambient temperature and water bath thawing). Furthermore, frozen containers were submitted to physical challenge to assess their robustness in routine handling and accidental drops. The physical challenge tests concluded that Celsius FFT 6 L is compatible with routine handling in frozen state.

Single-use polymeric bags are successfully used for the storage of biopharmaceuticals in liquid state. Today, bags made of ethylene vinyl acetate (EVA) or low-density polyethylene (LDPE) have been found suitable for the storage and shipping of biological bulks at ambient or cold temperature (2 to 8 °C). However, problems exist in freezing applications with bags as currently configured. At low temperatures, the physical properties of plastic materials may change sufficiently to introduce brittleness that can reduce the capacity of the bag to absorb external forces, i.e., shocks without fracturing. In addition, ice volumetric expansion can cause significant mechanical stress leading to bag, port, tubing, or connector breakage. The incidence of bag damage in freezing applications has not been adequately documented in the biopharmaceutical industry. However, it is well known that current commercially available unprotected bags do not adequately protect frozen products.

To eliminate problems related to bag breakage, Sartorius Stedim Biotech has developed the Celsius FFT concept, which combines a flexible container with a semi-rigid protective shell. The contribution of the protective shell is predominant in the absorption of stresses resulting from processing or handling conditions. Container integrity is maintained throughout its use cycle by providing appropriate support to the bag, by shielding the connectors and ports from impact, and by providing organized and safe tubing stowage.

In addition, the Celsius FFT system is compatible with standard laboratory equipment, facilitating its implementation in existing facilities and eliminating the high capital costs associated with specialized technologies.

Large-scale freezing of liquid in standard laboratory equipment is generally a slow process because of the limiting cooling capacity of the freezing equipment, the low heat transfer coefficient, and the large freezing distance of the container. To circumvent these effects, the Celsius FFT system uses multiple small containers (e.g., 6 L) with a large external surface-to-volume ratio and specific design features to maximize heat transfer.

The objective of this study was to evaluate the freeze-thaw performance of Celsius FFT and to demonstrate if it is well adapted for freezing protein solutions for process development or small-volume manufacturing, when very rapid freezing kinetics is not required.


Figure 1
Celsius FFT 6 L—MPC (Ref. fzb111789) was sourced from Sartorius Stedim Biotech. This integral container is composed of a S71 2-D bag encapsulated inside a protective shell (Figure 1). The S71 bag insures sterile containment of the biopharmaceutical product. The high-density polyethylene (HDPE) semi-rigid shell provides support to the flexible container and protection against impact and vibration. The container is provided ready-to-use because the bag and the shell are factory assembled and sterilized by gamma irradiation.

The S71 film used in the manufacturing of the bag chamber is a multi-layer, co-extruded, high gas barrier film, containing EVA copolymer as fluid contact layer and ethylene vinyl alcohol polymer as gas barrier layer. The film has been extensively characterized for liquid and frozen storage of biopharmaceuticals.

For this study, a Celsius FFT 6 L bag was modified with the addition of a spike port. A T-type thermocouple was introduced in the bag through the septum of the spike port. The thermocouple tip was located 18 cm from the tubing port in the bag center line. Additional thermocouples were placed on the top and bottom faces of the container, between the shell and the bag's external surface. A last thermocouple was used to monitor the temperature of the environment (freezer chamber or water bath). Temperature monitoring was performed with an Almeno 5990-2 (Ahlborn) data acquisition system.

Freezing experiments were performed inside a –86 °C ULT Forma, (621 L) upright freezer (Thermo Scientific) with a –70 °C temperature set point. Two Celsius FFT containers were frozen for each experiment. Thawing experiments were performed in a 20 °C water bath without agitation or at room temperature with exposure to ambient air.

The robustness of the Celsius FFT 6 L under routine operating freeze-thaw conditions and accidental drops was assessed with the following physical challenges.

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