 Biocompatibility

Biocompatibility is the ability of a biomaterial to function with an appropriate response from the living system in a specified application. It relates the material, its intended function and its biological environment. It is therefore more informative to ask whether a particular finished component is compatible with a particular contact site and duration than to call a substance universally “biocompatible.”^[ref]

Consider the same nominal polymer used as a short-lived skin-contacting film or as part of a long-lived component contacting blood. Its chemistry alone does not specify the biological exposure. Surface treatment, processing residues, final preparation and the length and type of contact can change the relevant response. The FDA’s primary resource emphasizes the final finished device and explicitly identifies contact type, duration and component interactions as assessment variables.^[ref]

A cytotoxicity experiment addresses one part of this question by examining adverse effects on biological cells. In a simple illustrative cell culture comparison, suppose a sample-exposed culture has 900 viable cells and a matched control has 1000 at the same observation time. The relative viable-cell count is $900/1000=0.90$. That ratio is an observation under the chosen conditions, not a complete compatibility verdict: growth rate, exposure preparation, measurement method and repeatability affect its interpretation. A control can distinguish a material-associated effect from an effect of the culture medium or preparation procedure.

Functional compatibility also need not mean that nothing happens at the interface. Some biomaterials are designed to bond to bone, so the desired response differs from that of a material intended merely to remain separated from surrounding tissue. Evidence about cell viability, local tissue organization and the component’s mechanical function answers different questions. A useful experimental account states which response was measured, the biological setting and exposure history, and the uncertainty in the comparison.