Table 1: Summary of in vitro studies performed in recent years highlighting commonly used assays aimed at investigating toxicity of SPIONs on stem cells and the results.

Particle used Biological polymer Particle size Cells type Particle concentration Toxicity assay Result Reference Feridex (FDA approved) Dextran 80–150 nm rMSC & mMSC 25 μg/mL Live/dead (7 days after labelling) differentiation assays No loss of cell viability observed after 7 days with or without either TA [32] Ferric oxide (noncommercial) Poly-L-lysine 15 nm HUC 20 μg/mL MTT (5 days continued culture) cellular apoptosis—annexin V/PI double stainassay   [19] Noncommercial Silica 110 nm hMSCs 200 μg/mL MTT ( 1 hr and 24 hrs) Trypan Blue No reduction in viability after 1 hour. No reduction in cell proliferation [38] Feridex Dextran 80–150 nm hMSC 100 μg/mL FACS ( fluorescence-activated cell sorting) to evaluate cell death—to determine if iron oxide incorporation affects surface markers expression No reduction in viability after 12 hours [39] Iron fluorescent particle Polystyrene 900 nm pMSC   Trypan Blue MTT Morphological observations Differentiation studies Cells maintained viability and retained label for up to 3 months. Differentiation capacity not altered [22] Manganese oxide nanoparticles Mesoporous silica 65 nm mMSCs   MTS 75% cell viability Limited cell differentiation in the osteogenic lineage [40] Commercially available   1630 nm rMSCs 2.8 μg/mL Trypan Blue Did not affect cell viability [41] Feridex Dextran 150 nm ESCs 50 μg/mL Trypan Blue Did not affect cell viability [42]   HEDP   rMSC 25, 50, 100 μg/mL MTS Cell viability not affected at lower concentrations but viability decreased to 70% at 100 μg/mL [43] Feridex uncoated 80–150 hMSC 50–250 μg/mL Comet assay Did not affect viability [44]

rMSC: rat mesenchymal stem cells; mMSC: mouse mesenchymal stem cell; hMSC: human mesenchymal stem cells; pMSC: porcine mesenchymal stem cells; HUC: human umbilical cells; HEDP: hydroxyethylidene bisphosphonic acid.