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Ethylene Vinyl Acetate
Polymers For Advancing Healthcare
IV THERAPY AND EVA
IV therapy is when medicine or fluids are infused directly
into a vein. The majority of IV therapy is for delivery of
nutrition, sodium chloride, potassium chloride or sucrose.
Approximately 80% of hospitalized patients receive some
form of IV therapy. In 1950 Dr. Carl Walter, a Harvard
surgeon and pioneer in kidney transplants,
invented the plastic medical bag (3). This enabled plastic
bags to replace glass bottles thereby reducing breakage,
lowering weight during shipment and enabling safer
handling during dangerous but urgent situations such as a
battlefield or natural disaster, where patients need
immediate attention and are often being moved with IV
lines in place. It is difficult to estimate how many
soldiers’ lives have been saved through the use of rapidly
available plastic IV bags and their contents.
Case Study 1 – Total Parenteral Nutrition and EVA
In 1969 Dr. Stanley Dudrick at the University of
Pennsylvania (4) conducted work that ultimately led to the
foundation for total parenteral nutrition (TPN). In the
1970’s and 1980’s alternatives to PVC plastic IV bags were
sought because the phthalate plasticizer, commonly used in
PVC, was leaching into nutrition fluids including the
lipid components.
EVA was found to be an excellent solution for TPN bags.
EVA offered the ability to have high flexibility without
having to incorporate plasticizers. The simplicity of the
molecular architecture enabled said flexibility by
increasing the content of vinyl acetate comonomer.
The higher VA content, e.g. 18 to 28 percent, also
provides excellent transparency. Film of high quality was
possible due to EVA’s excellent rheology. Of additional
importance was EVA’s ability to be welded for construction
of the bags. For IV nutrition bags, EVA provides excellent
biocompatibility as measured by USP Class VI testing.
STEM CELL THERAPY AND EVA
Stem cell therapy is a very large and promising area for
treating diseases such as Parkinson’s, diabetes, ALS and
heart disease.
Successful therapies for these diseases could enable
treatment for between 100 million to 150 million Americans
(5). Researchers and medical professionals store stem
cells in cryogenic conditions so that they are available
when needed. Case Study 2 – Cell Therapy and EVA.
Consider the lifesaving situation in a 2-year-old toddler
from the UK who received frozen stem cells. She was facing
a rare, lifethreatening form of acute myeloid leukemia
having a 30% life expectancy. She was given a transplant
of frozen stem cells which were originally located in
Tokyo. She made a complete recovery. Which type of medical
packaging is used for storage of these precious cells?
EVA.
Stem cells are stored at temperatures of -156°C to -196°C
(6). Various materials have been used for storage bags,
including EVA and fluorinated ethylene propylene (FEP) or
polytetrafluoroethylene (PTFE). In the USA, EVA is the
material most commonly used for cryocontainers (7). FDA
510K clearances illustrate EVA’s use. If one looks at the
simple molecular structure of EVA it is observed that EVA
can achieve remarkable diversity of properties due to its
two monomer design, ethylene and vinyl acetate. The
reactivity of each monomer is such that the overall
composition of ethylene to VA content in the final
copolymer is approximately the respective feed ratios.
Therefore, one can vary flexibility and glass transition
temperature, Tg, by varying the vinyl acetate content.
For high VA content grades, e.g. 28%, a glass transition
temperature of -30°C is achievable. This provides good
lowtemperature performance with high clarity of the
container. Furthermore, because of the ability to target
desired properties by varying solely the VA content, one
does not need additives such as plasticizers which can
leach into the stored contents, presenting contamination
issues. EVA is easily sterilized by gamma radiation which
is commonly used for sterilization of cryo storage bags.
Gamma sterilization is not recommended for FEP due to its
low tolerance level of 50 kYG. Polytetrafluoroethylene (PTFE)
has a tolerance level of 5 kGY and may disintegrate into
powder with gamma radiation. Also, PTFE may liberate
fluorine gas during gamma sterilization.
Thus, the unique characteristics of EVA have positioned it
to become the leading material in the field of cryogenic
stem cell storage.
CONCLUSION
This article has discussed the evolution of EVA’s usage in
key healthcare applications. From the long history of use
in nutrition bags and expanding the field of IV therapy,
to its importance in the storage of critical products like
stem cells, EVA continues to demonstrate its role as a
highly versatile polymer for a broad range of medical
device and pharmaceutical applications.
REFERENCES
1. Celanese internal data
2. Celanese internal data
3. N. Barsoum and C. Kleeman, Am. J. Nephrol 2002; 22:284
289.
4. Ibid.
5. J. Shaw, Stem Cell Science, Harvard Magazine,
July-August 2004.
6. www.ncbi.nlm.nih.gov/pmc/articles/PMC2075525.
7. Ibid. |
