First and foremost chemical characterization per ISO 10993-18
Characterize each and every material and alternates
Identify hazards in the materials, additives, processing aids etc
What processing will do to the materials?
What will leach out and what degradants occur?
Establish a clinical use exposure dose?
Review published data?
Chemical Characterization is most useful for limited changes in chemicals within a device, when you have known entities and data is available for the known entities
And if it is easy to do
Useful in targeting biocompatibility studies to specific known effects of compounds present in extracts.
Can be used to calculate rate of elution and subsequent toxicologic safety thresholds