Table 2 Summary of the material properties

General

Hydrophilic pyrogenic^a

Hydrophilic pyrogenic^a

Specific surface area

200 m²/g^a

380 m²/g^a

Purity

≥99.9%^b

≥99.8%^a

Primary particle size

10-25 nm^a

7 nm^a

SEM size distribution

At least 61% of the material was <100 nm.^c (Figure 1E)

At least 78% of the material was <100 nm.^c (Figure 1E)

XPS

Si: 25.0 ± 0.3 at%^b

Si: 29.8 ± 0.5 at%

O: 72.1 ± 0.4 at% ^b

O: 68.1 ± 0.6 at%

C: 2.9 ± 0.6 at% ^b

C: 2.1 ± 0.6 at%

EDX

Presence of carbon on the surface (Figure 1F).

Presence of carbon on the surface (Figure 1F).

FTIR

Large peak between 1000–1130 cm^-1 and a peak at ~800 cm^-2 corresponding to Si-O bonds in a pattern characteristic for amorphous fumed silica.

Large peak between 1000–1130 cm^-1 and a peak at ~800 cm^-2 corresponding to Si-O bonds in a pattern characteristic for amorphous fumed silica.

Some C-H stretching vibrations at ~3000 cm^-1, indicating the presence of organic material on the surface.

(HDC)-ICP-MS

79.6 ± 20.7 mg silica/g feed, ~100% between 5–200 nm

80.5 ± 20.9 mg silica/g feed, ~40% between 5–200 nm

SEM-EDX

Presence of carbon on the material surface before and after in vitro digestion.

Presence of carbon on the material surface before and after in vitro digestion.

Presence of salts (e.g. Ca and P, likely in the form of CaPO₄) on the material surface after in vitro digestion_.

Presence of salts (e.g. Ca and P, likely in the form of CaPO₄) on the material surface after in vitro digestion_.

(Additional file 1: Figure S1)

(Additional file 1: Figure S1)

(HDC)-ICP-MS

81, 81, 97% (low, medium and high group respectively) of the material has a size between 5–200 nm

55, 106, 54% (low, medium and high group respectively) of the material has a size between 5–200 nm

Dissolution

~15-20 wt% or less dissolves after in vitro digestion.

~15-20 wt% or less dissolves after in vitro digestion.