The first technical step in any biological evaluation is categorising the device. The category decides which biological endpoints must be considered, so getting it right shapes the whole evaluation and every test that follows.
Nature of body contact
ISO 10993-1 groups devices by where and how they contact the body:
- Surface-contacting devices: in contact with intact skin, mucosal membranes, or breached or compromised surfaces
- Externally communicating devices: connecting the inside of the body to the outside, for example through the blood path, tissue, bone or dentin, or circulating blood
- Implant devices: placed within tissue, bone or blood
Duration of exposure
Duration is grouped into three bands, and for devices used repeatedly the cumulative exposure counts:
- Limited: up to 24 hours
- Prolonged: more than 24 hours and up to 30 days
- Long-term: more than 30 days
From category to endpoints
Together, contact and duration point to the endpoints that need to be addressed, such as cytotoxicity, sensitisation, irritation, systemic toxicity, genotoxicity, implantation effects and haemocompatibility. A long-term implant needs far more endpoints considered than a surface device used for a few minutes.
Common mistakes
- Categorising the device as a whole when different components have different contact types
- Ignoring indirect contact, such as fluids that pass through the device before reaching the patient
- Underestimating cumulative exposure for devices used daily or repeatedly
- Treating the endpoint list as a test list, instead of deciding how each endpoint is best addressed
Categorisation should be recorded in the Biological Evaluation Plan with the reasoning behind it, so reviewers can follow it and the evaluation can be updated if the device or its use changes.
