Table 2.

Overview on relevance and major challenges related to methods measuring surface properties with reference to regulatory documents.

Area	Subcategories	Relevance	Challenges	Gaps
Surface properties [[6], [7], [8], [9], [10], [11], [12], [13],22,23]	Coating analysis (amount, chemical composition, homogeneity)	Impact on the interaction with proteins, biomolecules, immune cells	Most of the existing methods are not standardised	– Limited technological solutions for soft nanomaterials, and/or for surface properties in solution– No methods for the heterogeneity of surface coatings
	Hydrophobicity
	Surface area