Biomedical Engineering Reference
In-Depth Information
performance of rubber articles over time. Metal oxides can be very efficient
acid scavengers. Ions of copper (Cu), iron (Fe), cobalt (Co), nickel (Ni), and
other transition metals that have different oxidation states with comparable
stability are called
rubber poisons
because they are easily oxidized or reduced
by one-electron transfer. They are very active catalysts for hydroperoxide
decomposition and contribute to the degradation of rubber vulcanizates.
Rubber poisons thus requires a specific stabilizer: a metal deactivator, such
as 2,3-bis[[3-[3,5-di-
tert
-butyl-4-hydroxyphenyl]propionyl]]propionohydra-
zide, which binds ions into stable complexes and deactivates them.
As a result of the need to add chemicals to elastomer systems, the extract-
ables in a disposable system can include
• Monomer and oligomers from incomplete polymerization reactions
• Additives and their transformation and degradation products
• Lubricants and surface modifiers
• Fillers
• Rubber curing agents and vulcanizates
• Impurities and undesirable reaction products such as polyaromatic
hydrocarbons, nitrosamines, and mercaptobenzothiazoles
Unexpected additives can also be present in a polymer system because of the
inconsistencies in the process of manufacturing elastomer systems whereby
unpredictable reactions can take place.
Despite the risk in the use of additives added to polymers, the utility of
polymers in disposable bioprocess equipment (and in all medical or phar-
maceutical applications) far outweighs the risks associated with their use.
These risks can be managed well by taking three steps: material selection,
implementation of a proper testing program, and partnering with vendors.
Material Selection
The type of plastic used should match the needed physical and chemical
properties and compatibility of the additives used for the product manufac-
tured. For example, phenolic antioxidants, each with the same active site (the
hindered phenol moiety) but with different nature of the remainder of the
molecule, make them soluble or compatible with a given polymer substrate.
An antioxidant that is compatible with nylon might not be the best choice for
use in polyolefins, as an example.
Ensuring compatibility often lessens the amount of leaching that can
occur. It is also important to select polymers and additives that are approved
for use by the regulatory authorities for the specific use. Such compounds
have already undergone a fair amount of analytical and toxicological testing,
so a good amount of information is often available for them. Because of this,
