Implantation testing is one of several biocompatibility tests, reserved for medical devices that are placed in the body’s internal tissue, bone or cavities. As such, it is an important process for many life-supporting devices, and determines whether the implant causes harmful changes to nearby tissue or bone. Part of the implantation test involves histopathological analysis, so research is done at the cellular and tissue level.
The specifics of implantation testing are defined in ISO 10993, along with other biocompatibility tests that medical device manufacturers use.
Why is Implantation Testing Needed for Medical Devices and Plastics?
If a substance is toxic, it may cause changes to nearby cells long before it produces any symptoms. These changes indicate that the substance could be causing harm, and implantation testing looks for these changes. This gives medical researchers advance warning that a device is not biocompatible, even if no other signs of toxicity or harm are present.
It is critical to note these signs because once an implant is placed, often is a permanent implant or it may be years before it is removed. Implantation testing ensures surgical teams do not have to subject their patients to risky revision procedures.
Which Medical Devices Require Implantation Testing?
Only some devices must pass through implantation testing, depending on how they contact the body and for how long. Here is how ISO 10993 categorizes devices, so manufacturers know if their device requires implantation testing:
- Surface device – Surface devices only make contact with external tissues, including intact or breached skin, or mucosal membranes. They include things like latex gloves, bedpans, compression bandages, some dental devices, dermal patches and a variety of intraintestinal devices, like gastroscopes, colonoscopes and stomach tubes.
- External communicating device – External communicating devices either make contact with the blood path or are connected, to some extent, to the body’s internal tissues. They may not make direct contact, but can affect the health of internal tissues. Some of these devices include vascular catheters, many forms of medical tubing, surgical instruments and temporary life-supporting technologies, like some pacemakers and oxygenators.
- Implant device – Implant devices are placed in the body and maintain direct contact with the body’s internal tissues. Some implants are temporary, but many remain in the body for years or permanently, so they undergo the most stringent testing under the ISO 10993 standard. Some implant devices include artificial joint or heart valve replacements, orthopedic pins and plates and some catheters.
In addition to the above, many PEEK devices, including lumbar and cervical cages, are implants intended to remain in the body forever. As such, they must undergo implantation testing.
Medical devices are further categorized by the duration of contact and placed in one of three classes. They include:
- Class A – Devices that maintain contact with the body for less than 24 hours.
- Class B – Devices that maintain contact between 24 hours and 30 days.
- Class C – Devices that maintain contact for more than 30 days.
According to ISO 10993’s guidelines, all implant devices that contact the blood must undergo implantation testing. Further, all Class B and Class C implants that contact bone or other internal tissues must also pass through testing.
How Do Researchers Perform Implantation Testing?
During implantation testing, a sample of the device is placed in an animal subject, in contact with the tissues the device would contact in a human patient. This could be under the skin, inside the muscle, in contact with bone or anywhere else the implant is expected to go.
Once the implants are placed, the subjects are monitored for several days. Following this, tissue samples are taken from the implant sites and studied by a pathologist under a microscope. This part of the process is similar to what pathologists do with biopsy samples. They look for any changes in nearby cells and tissues, including changes to the cell shape or count, or changes to the cell’s internal structure. These changes are noted in a histopathological report, created by a pathologist specialized in the tested tissues. Additionally, regulatory agencies like the FDA sometime require or are least prefer to see longer term, many weeks, of implantation in an animal to evaluated the overall performance of the device.
Why is the ISO 10993 Standard Important for Medical Device Manufacturers?
Medical device manufacturers reference the ISO 10993 standard when organizing testing because it is the most current and comprehensive resource for biocompatibility research. Its recommended testing guidelines are supported by the FDA and by regulatory agencies around the world, so manufacturers strive to attain ISO 10993 compliance.
Most of ISO 10993’s testing procedures have already been in use for decades among medical researchers, but beyond these procedures, ISO 10993 also helps manufacturers produce usable samples for testing. For example, before a device sample can be used for biocompatibility testing, it must pass through the same processing steps that the final produce would go through, including things like sterilization, packaging and labeling.
Implantation testing is only recommended for devices placed in contact with the body’s internal tissue, bone or cavities. These devices, like PEEK spinal cages, either relieve debilitating pain or are critical life-preserving devices, so their effects on the body must be studied in detail. Implantation testing, because it includes histopathology studies, gives researchers this needed, up-close look.