Design Realization/Detailed Design - Medical Device Design: Innovation from Concept to Market - page 170

8.5.11 Biocompatibility
I do not intend to teach you every term related to biocompatibility. We will meet the
important issues in a moment. However, just because you use stainless steel does not mean
you have considered biocompatibility. If you followed the guidance given in Section 8.5.1
then biocompatibility should not be an issue (all of the hard work has been done for you).
Even if your material is deemed “safe” an eagle eye must be kept pointed at recall notices,
the news channels, and any other sources of “product recall” information - just in case the
material concerned is also used in your device! However, if you intend to use a material that
has not been used before then that is a different ball game!
You must not underestimate the importance placed on biocompatibility. You must be able
to provide evidence that the materials you use comply with the essential requirements for
a medical device. That is why the materials selection pro forma is so important to your
materials selection records.
8.5.11.1 Scope
Biocompatibility comes into play when a device is communicating with tissue. Do not
assume this is only by direct contact; it can also be indirect (it could be by emission or vapor).
If your device communicates with tissue then its biocompatibility must have been tested at
some time. Biocompatibility testing is an expensive, time-consuming business and that is why
following Section 8.5.1 and using the efforts of others helps!
8.5.11.2 Definition(s) and Standards
Initially it was thought that only inert materials were biocompatible, but the definition has
changed due to the increase in using substances that can be implanted into the body that are
not inert (e.g., resorbable implants). There was much debate but the current definition of
biocompatibility states that biocompatibility is
The ability of a material to perform with an appropriate host response in a specific application.
( Williams, 1999 )
This is known as the Williams 2 definition and was adopted by the European Society of
biomaterials. It is brief and to the point. Basically it states that if you have a material
communicating with a host, it should do what it is supposed to do without harming the host -
as in this further definition that expands on the former (not surprisingly, written by Williams):
Refers to the ability of a biomaterial to perform its desired function with respect to a medical
therapy, without eliciting any undesirable local or systemic effects in the recipient or beneficiary
of that therapy, but generating the most appropriate beneficial cellular or tissue response in that
specific situation, and optimizing the clinically relevant performance of that therapy.
( Williams, 2003 )
2 Prof. Williams of Liverpool University, UK. His book The Williams Dictionary of Biomaterials is probably one
you should have on your shelf.