| Material type | Stainless steel, nickel-titanium alloy, cobalt-chromium alloy, titanium alloy, etc. | Zn alloy, Mg alloy, Fe alloy, etc. |
| Property | Inert | Bioactive |
Principle | Support, occupy space, etc., by physical properties to achieve clinical therapeutic effects | Physical properties function in the early stage, then the materials degrade and the target lesion tissue remodels gradually |
Potential source of cytotoxicity | Processing aids, leachables | Processing aids, leachables, degradation products (ions), pH, osmotic pressure, surface energy, etc. |
| Sterilization method | Not limited to ethylene oxide (EO), irradiation sterilization, etc. | Methods with minimal impact on material properties |
| Evaluation endpoint | Morphological evaluation, cell growth ability, and metabolic characteristics (microscopic observation + MTT method, etc.) |
Contact way | Extraction method, direct or indirect contact method can be selected according to the principle of "closest to the application situation". Generally, the extraction method is recommended | Extraction method, direct or indirect contact method can be selected according to the principle of "closest to the application situation" |
Extraction medium | The ability to support cell growth and to extract both polar and non-polar substances | Cell culture medium with serum, generally. The ratio of serum can be adjusted according to the effect of serum on the material |
Extraction condition | Generally (37 ± 1)oC, (24 ± 2) h | The appropriate extraction time can be selected according to the implantation time, degradation rate and degradation products in vivo. Evaluation of multiple extraction times are also necessary to fully understand and assess biological risks |
| Extraction ratio | (Surface area or mass / volume) ± 10% |
| Extraction | Dilution is not recommended generally | Multiple dilutions may be necessary |
| Extraction treatment | Adjustment is not recommended generally | Filtration, centrifugation, pH adjustment, etc., can be used, but treatment should be recorded and evaluated |
Cell line | Suitable cell lines recognized by ISO experts, such as mouse fibroblast CCL1 (L929), mouse embryonic fibroblast CCL163 (Balb/3T3 clone A31), etc. L929 cells are generally used in China | Depending on the application site, sensitivity- or site-specific cells may be required to evaluate their cellular responses more objectively |