Nalgene Nunc's bag management system
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As with stainless steel, disposable bulk containers do have their own set of drawbacks. For example, BPCs and flexible tubing
usually cannot handle more than a few psi of pressure. Temperature limits are also an important detail to consider when companies
are looking for disposable systems or parts. Most disposable systems are validated for operation at standard biopharmaceutical
temperatures, but some BPCs or their connectors and tubing may need additional validation for storage at low temperatures.
For example, certain biotech raw materials such as media or cell lines must be stored at –80 °C, so it is necessary that commercial
manufacturing facilities validate all single-use technologies to ensure compliance with these and other specific temperature
regulations. Although it can be argued that stainless steel vessels are better than single-use systems because they do not
have temperature limits, stainless steel vessels often contain gaskets and elastomers that have different heating and cooling
properties, which can cause leaks and sterility problems.
Operational and Functional Testing
Manufacturers of bulk shipping containers typically put their products through three different types of functional testing:
- shipping and transportation
- drop
- handling.
Shipping and transportation testing includes packaging bioprocess containers into a variety of shipping and support containers
either individually or in groups depending on the type of unit being tested. Frequently, the units are filled with water or
some equal buffer substance at the nominal volume of the container before package testing. The units then undergo trials of
shock and vibration tests to simulate conditions stipulated by the International Safe Transit Association.2 Next, a BPC endures individual drop testing to assess the durability of the unit without the exterior packaging. In this
test, units are dropped from a height of one meter onto a hard concrete surface to simulate the worst-case scenario drop that
might occur in normal shipping operations. Finally, handling tests ensure that the BPCs are operational from the beginning
until the end of the manufacturing process. The units go through a cycle process several times for at least 48 h, in which
they are frozen horizontally at –85 °C, and then incubated at +60 °C.
Mechanical Properties of Film
Along with functional testing, all BPCs must also undergo specific tests to ensure the compatibility and robustness of the
films that will hold the bulk product. Among the specific properties that films are tested for and required to possess include
(but are not limited to):
- tensile properties
- toughness
- elasticity
- puncture resistance
- tear resistance
- flex durability.
Tensile properties describe the ability of a film to stretch when stressed to its limit. A tensile test is described as the
process of elongating a film sample and measuring the strength that results. The moment the film or object breaks is when
elongation is recorded. This number is often recorded as the percent of film elongated compared to its original length. When
a specimen has a high elongation at break, it can endure a large amount of deformation before breaking and is considered a
highly flexible film.
A material's ability not to fracture when stressed is measured as a film's toughness. This describes a film's maximum absorption
of energy before the film rips. Toughness is calculated by finding the area underneath a stress–strain curve, but toughness
and strength do not necessarily mean the same thing. For example, a brittle film material would be one that is strong but
not tough.
The elasticity of a film is measured by Young's Modulus (also known as an elastic or secant modulus). The more rigid a material
is, the higher the elastic modulus is said to be. If the modulus is lower, then the film material is more flexible and easier
to mold. This elastic modulus can be calculated by determining the slope of the line on a stress–strain curve from the origin
of the graph to the strain is held constant at a value of 2%. This provides an estimate for the rigidity or flexibility of
a material.3
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