All products that contain hydrogen bonded to carbon are susceptible to oxidative degradation. For example, foods that we eat and medicines that we take contain hydrogen bonded to carbon. Therefore, foods and medicines are generally stabilized against oxidation by the addition of antioxidants and are labeled with expiration dates.
Many aren’t aware, however, that most plastic products also contain hydrogen bonded to carbon and therefore are also prone to oxidative degradation. As plastics degrade by oxidation, they become brittle and begin to disintegrate and fall apart.
One of the most unstable plastics is polypropylene (PP). Manufacturers of PP plastic resin add antioxidant stabilizers to their plastic before they ship the resin granules to plastic part fabricators. If the resin manufacturers don’t add antioxidant stabilizers to the resin, it would degrade during shipment and be unusable. Therefore, for PP plastic parts to have a reasonable service life, they must be stabilized against oxidation by the addition of antioxidant stabilizers.
Unfortunately, antioxidants are depleted from the surface of plastic parts during use. The mechanism of depletion may include migration from the surface into other material in contact with the part’s surface or chemical degradation of the antioxidant as it performs its antioxidant function.
“If the PP part is very thin, has a high surface area, and is exposed to a highly oxidizing environment, the surface layer of the PP part will rapidly begin to degrade and become brittle."Dr. Duane Priddy, Plastic Expert Group, Founder & CEO
Despite knowing this background information about the propensity of PP to degrade and become brittle, several medical device manufacturers decided to manufacture mesh implants using PP. The mesh/fabric consists of fibers that are woven together. Mesh fibers have an exceptionally high surface area and are under high stress because they are implanted for the purpose of support.
When plastic is under stress, degradation processes are accelerated. Since PP is prone to oxidative degradation and embrittlement, exposure of the mesh to stress in the body causes the mesh to fail after only a few years in the body.
After being in the body for several years, body tissues grow through the pores in the mesh fabric. When the mesh fabric turns brittle and breaks into pieces, removal of the mesh becomes very difficult.
Surgical removal of disintegrated mesh generally leads to significant damage to surrounding tissue and post-surgical infection and pain.
These problems and failures have led to thousands of hernia and surgical mesh lawsuits.
Several PP manufacturers in the US have forbidden the use of their PP resins for the manufacturer of implants and will not sell their PP resin to medical device companies suspected of using their PP for that purpose.
One mesh manufacturer, in an effort to circumvent the PP sourcing problem, imported PP from China and repackaged the PP resin to cover up the fact that they changed their resin supply.
At Plastic Expert Group, our team of professionals have served, and continue to serve, as expert witnesses in ongoing lawsuits involving the failure of PP mesh implants. We have conducted accelerated laboratory testing on several different PP mesh products and have developed laboratory data which predict service lifetime. The data clearly predicts these products will not survive more than a few years, at best, in the body.
We also work with forensic pathologists to examine mesh samples removed from the body. Optical microscope, Transmission Electron Microscope, and Scanning Electron Microscope imaging of the fibers vividly reveal that the surface layer of the fibers has degraded, become brittle, and severely cracked.
If your company needs assistance in making reliable and safe medical devices, we can help advise you on the best material to use. Our team of expert plastics scientists and engineers have decades of experience.
We specialize in material selection and testing, plastic part design, service life prediction, forensic failure analysis, chemical resistance testing, due diligence studies on new plastic technologies, troubleshooting/problem solving in plastic manufacturing, and consulting on new opportunities and uses for existing products.
Our lead expert in this matter, Dr. Duane Priddy, was even recently interviewed for an episode of CBS’ 60 Minutes discussing the problem of gynecological polypropylene vaginal mesh failure: