October 15, 2016 (Vol. 36, No. 18)
Eric Isberg Bioprocess Business Development Director Entegris
Michael W. Johnson Life Sciences Development Engineering Manager Entegris
Mark McElligott Principal/Partner SU Process Engineer PDS Sandbox
Single-Use Fluoropolymer Bag Mitigates Risk in Frozen Bioprocess Applications
The promise of single-use technologies is still being unveiled. While much more widely adopted today than just five years ago, developers of single-use products and systems are well aware of remaining challenges—specifically technology roadblocks that continue to leave a chasm to providing the ultimate in effectiveness and efficiency. One bottleneck, if you will, is in the area of materials for products that store, transport, and protect valuable bioprocess fluids.
According to BioPlan Associates’ “Twelfth Annual Report and Survey of Biopharmaceutical Manufacturing Capacity and Production,” published in April 2015, breakage of bags and loss of production material is the top concern of the survey respondents (Figure 1).
One of the survey conclusions is that new materials need to be developed—particularly novel and improved plastic materials—to enable design innovations. Fluoropolymer plastics appear promising. Fluoropolymers are a special class of materials designed for durability, purity, cleanliness, and universal chemical compatibility. They are well suited for addressing the challenges facing the biopharmaceutical single-use industry.
Interestingly, fluoropolymer plastics appear to have the widest temperature profile of any plastic traditionally used in single-use systems, from +200 to -200°C. They have been shown experimentally to remain flexible and have no negative effects even after submersion in liquid nitrogen at -196°C (Figure 2).
Comparative freeze-thaw cycles and frozen drop tests are commonly performed by end users to help decide which products are best in frozen applications. They are good indicators of durability. One experiment, to test the effects of repeated temperature cycling and frozen material durability of single-use bags, was executed by PDS Sandbox—a process engineering solutions provider. The purpose was to show whether or not single-use products marketed and sold for cryogenic applications are suitable for use under real-world conditions in a pilot-scale manufacturing environment.
One bag in the test performed very well. As a newer market entry, and one made from fluoropolymer film, it provided a unique opportunity for a broader comparison test of existing product-grade films. It was the Aramus™ bag from Entegris (Figure 3), made from a high-grade, gamma-stable fluoropolymer material. Unlike layered films, the single-layered construction of Aramus film certainly ensured against material failure due to delamination, but performance levels for other factors were also encouraging.
An additional and rigorous cold crack temperature test was performed specifically on the fluoropolymer film to see if it would hold up to cryogenic temperatures. Standard ISO 8570 protocol was used for that testing.
What follows are the test methods and test results for the two experiments, one on a group of bags/films, and the other targeted to the performance of the fluoropolymer film technology.
Freeze/Drop Test Method
For this test, the product must be able to withstand a specific number of freeze/thaw cycles where the bag is filled to the rated volume capacity; the temperature and number of cycles chosen often models actual usage conditions. It must also be able to withstand single or multiple drops at room temperature and also when frozen; it is common to use lab counter height (e.g. 36”) or higher for this testing. Any breach in the integrity of the bag during testing is noted; including pin holes, rips, tears, broken seams, fractured connectors, delamination issues, or other fluid leaks.
During the PDS testing, frozen bag assemblies made from materials that included LDPE, Polyolefin, EVAM, FEP and Fluoropolymer were exposed to multiple changes in temperature—from ambient environment conditions to harsh temperatures—and impact to the bags were noted. Temperature tests included 2 – 8°C, -20°C and -85°C.
In the second part of the PDS test, frozen bag assemblies were dropped at a 45° angle from various heights onto a solid surface, immediately upon removal of the frozen bags from the freezer. Impact to the bags as a result of the drops were also noted.
Freeze/Drop Test Result Summary
Aramus bags with the fluoropolymer film received excellent results from PDS Testing with all bags passing all tests to a temperature of -85°C—with no failures. It is interesting to note that all other bags failed some aspect of testing, even though they are also marketed for cold- temperature applications (Figure 4).
Cold Crack Test Method
For this test, specimens were prepared as follows:
Cut the 100 mm X 100 mm sheets into 60 mm X 15 mm strips. For each temperature, 10 specimens were taken. Specimens were taken 150 mm from the edge of the roll. The specimens were cut into strips and bowed in the form of a loop then six of them were mounted in the specimen holder (test fixture). The strips were conditioned for four hours at 18°C +/-2°C.
The impact device was placed in the freezer at the test temperature until equilibrium was reached. The impact mass was released then reset to its initial position. The platen was taken out of the freezer, and the specimens removed (strips) and inspected. If no specimen (strip) was damaged or broken, the temperature was lowered by 5°C. The test was then repeated with fresh specimens and continued until a temperature was reached at which 50% of the specimens (strips) were broken or damaged.
Cold Crack Test Result Summary
The fluoropolymer film passed the cold crack test at 5°C temperature intervals down to a temperature of -85°C. It was then tested to a temperature of -188°C, which is the limit of the ability to cool the test fixture. In this test, the entire fixture and attached film samples were immersed in liquid nitrogen. The result was zero material failures.
This learning is an indication that fluoropolymer film is suitable for cryogenic applications. There are, perhaps, few suitable films for bioprocess applications—especially of the single-layer variety—that can withstand this test.
As we continue to look for new ways to address materials challenges, the tests and results outlined here have likely defined a benchmark for the industry with respect to one aspect of materials performance. It is clear that, given the materials that were tested, the fluoropolymer-based option has proven most reliable in comparative temperature testing, delivering on its promise of a wider temperature viability range.
This article also illustrates how the Aramus bag could be an example of the kind of material innovation the industry (according to the BioPlan report survey) agrees it would like to see delivered. With continued investigation in this area, perhaps other materials will emerge to help ensure safer, more reliable films for protecting bioprocess fluids and products.
Eric Isberg ([email protected]) is bioprocess business development director and Michael W. Johnson ([email protected]) is life sciences development engineering manager at Entegris; Mark McElligott is principal/partner SU process engineer at PDS Sandbox ([email protected]). Websites: www.EntegrisLifeSciences.com, www.pds-sandbox.com, www.workwithpds.com. Entegris and Aramus™ are trademarks of Entegris. BioPlan Associates and PSD Sandbox are names owned by their respective companies.