Credit: © 2008 Wiley

It is well known that amorphous silica materials can cause haemolysis (or rupture) of red blood cells and this has raised safety concerns over their use in drug delivery. Many explanations for this phenomenon exist, but it is widely agreed that haemolytic activity is due to silanol groups on the surface of the materials. Researchers at Iowa State University now report that certain mesoporous silica nanoparticles rupture red blood cells less easily, even though they have more silanol groups than the conventional amorphous silica.

Victor Lin and colleagues1 mixed rabbit red blood cells with either mesoporous silica particles — containing parallel channels with average pore diameters of 3 nm — or commercially available amorphous silica, and measured the amount of haemoglobin (the oxygen-carrying protein) released from the red blood cells that ruptured. In contrast to amorphous silica, the mesoporous silica did not show any haemolysis at concentrations between 20 and 100 µg cm-3, even though it contained more silanol groups. This suggests that the extent of haemolytic activity is not proportional to the number of silanol groups, as proposed previously. The honeycomb structure of the mesoporous silica is thought to distribute the silanol groups on the surface and inside the pores in such a way that only a small fraction is accessible to the cell membrane for haemolysis.

This new work suggests that the structural effects of certain silica particles may help lower haemolysis.