Effect of extraction vehicles on medical device sensitization testing by LuSens assay

Skin sensitization risk of medical devices (MDs) has to be assessed before their marketing and clinical use. The obligatory methods (ISO 10993-10:2021) include exclusively in vivo tests, however, validated non-animal methods might be utilized after successful verification of their applicability in the specific field of MDs and their extracts. One of the candidate in vitro tests is the LuSens assay (OECD TG 442D), which covers the Key Event 2 (activation of keratinocytes) in the Adverse Outcome Pathway for Skin Sensitization. The aim of this pilot study was to share the experience gained during optimization of this method for testing of real-life MD extracts. We have confirmed that the extraction vehicles recommended in ISO10993-12:2021, could be considered for use in the LuSens assay, as they do not interfere with Luciferase induction. However, the preferred use of culture medium with serum as extraction vehicle for cytotoxicity tests was not optimal, as the fetal bovine serum (FBS) content significantly increased the LuSens cell viability, which biased the sensitization results. The study showed the presence of different content of leachable cytotoxic substances in the extracts depending on the type of extraction vehicle, particularly in case of metallic products. Further research will be necessary to identify the optimal extraction conditions for specific materials or devices.