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The versatility of
plasticised PVC for making Medical Devices
Polymers of various types, chemical structures and
configurations are used in medical devices. The
storage of IV fluids, dialysis solutions, blood and
blood products is largely dominated by PVC based
products. This is because of its clarity, strength,
ability to withstand temperatures as low as –40ºC and
as high as +121ºC, steriliasability with steam, ETO
and gamma radiation. A remarkable feature is its
ability to be compounded with a wide range of
plasticsers to give products with a wide spectrum of
characteristics. In addition, PVC can be joined
together by high frequency welding which offers the
possibility of making containers with complex shapes
and with various attachments, thus providing numerous
design possibilities.
PVC bags were first introduced during 1949 and
became very popular by 1960.The most preferred
plasticizer for medical grade PVC is di, (2-ethyl
hexyl) phthalate even though other plasticisers could
be used for specialized applications. DEHP plasticised
PVC containers have been used for the collection of
blood and blood components, for the last 45 years.
DEHP has been shown to have very beneficial effects in
maintaining the viability and long-term storage of
RBCs.
Other components in blood such as platelets have a
higher metabolic rate and so containers for their
storage must have higher permeability to oxygen and
carbon dioxide.
This is achieved by using other plasticisers such
as trimellitates and citrates.
Shortcomings of DEHP plasticised PVC
Plasticizers are not covalently
bonded
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with PVC and so could migrate out
of the containers particularly in the presence of
solubilising lipids, lipoproteins and albumin. Jaeger
and Rubin (1970) showed that DEHP from blood bags
leached into stored human blood. This finding
triggered a spate of studies into the subject.
Concerns have been expressed over the adverse effects
of DEHP leached into blood products and the potential
toxicological hazards. These studies were followed by
a series of excellent reviews of the existing
knowledge.
It is proved that there were shortcomings in
studies made using rats and mice as models since there
are significant differences in the metabolism of DEHP
between rodents and humans. In 1999, a blue ribbon
panel comprising of eminent toxicologists, clinicians
and other scientists and chaired by former US Surgeon
General Dr.C.E. Koop summed up the position. “DEHP is
not harmful to even highly exposed people, those who
undergo certain medical procedures such as regular
haemodialysis or extra corporeal membrane
oxygenation”.
The panel concluded that “DEHP imparts a variety of
important physical characteristics that are critical
to the function of medical devices and eliminating
DEHP in these products could cause harm (1999).
Based on various studies done subsequently: The
Scientific Committee on Emerging and Newly Identified
Health Risks (SCENHIR) has recently published their
Preliminary Report on the Safety of Medical Devices
containing DEHP plasticized PVC or other plasticisers
on neonates or other groups possibly at risk (2007). Dr.C.S.B.Nair is
Consultant, M/s.Terumo Penpol Ltd., Sasthamangalam,
Trivandrum, India. |
The present position regarding
DEHP plasticised PVC in Medical products
Concerns regarding PVC continue to be raised
regarding the toxic effluents produced during the
manufacture of PVC and the generation of hydrochloric
acid and other harmful chemicals during the
incineration of PVC wastes. Other concerns relate to
the environmental hazards of plasticisers used
particularly DEHP which could migrate from refuse
dumps into the soil and thence to water bodies. In
medical products it is the leaching of DEHP into
intravenous solutions or blood and blood products when
stored in PVC containers that is of concern. Hence
concerted efforts are under way to overcome these
problems by developing alternatives to PVC, making
modification to PV and by the development and use of
newer plasticiser to PVC.
1.0 DEVELOPMENT OF ALTERNATIVES TO PVC
The development of metallocene single site catalyst
technology has resulted in the production of poly
olefin resins of very low densities and narrow
molecular weight distribution. Films made with such
resins have high toughness, impact strength, clarity,
elasticity and heat sealability which makes them
suitable for many medical and packaging applications.
Syndiotactic polypropylene and elastomeric
polypropylene are similar in characteristics to thermo
plastic elastomers. They are chemically inert, have
low leaching, have high thermal stability and can be
incinerated or recycled without the production of
toxic products. Metallocene Poly ethylene is mainly
targeted for use in medical packaging because of its
clarity and lower sealing temperature. Metallocene PE
copolymer resins are made with comonomer content of up
to 45%. |
