Graphical abstractHighlights▶ NP toxicity depends on NP characteristics, administered dose and route. ▶ In vitro toxicity results do not easily translate into in vivo toxicity. ▶ Current research lacks a unifying protocol for the toxicological profiling of NPs.

Stem cell therapies offer great potentials in the treatment for a wide range of diseases and conditions. With so many stem cell replacement therapies going through clinical trials currently, there is a great need to understand the mechanisms behind a successful therapy, and one of the critical points of discovering them is to track stem cell migration, proliferation and differentiation in vivo. To be of most use tracking methods should ideally be non-invasive, high resolution and allow tracking in three dimensions. Magnetic resonance imaging (MRI) is one of the ideal methods, but requires a suitable contrast agent to be loaded to the cells to be tracked, and one of the most wide-spread in stem cell tracking is a group of agents known as magnetic nanoparticles. This review will explore the current use of magnetic nanoparticles in developing and performing stem cell therapies, and will investigate their potential limitations and the future directions magnetic nanoparticle tracking is heading in.

The size and dispersity of nanoparticles (NPs) determine the properties that such particles display. In this study, synthesis of silver nanoparticles in a coaxial flow reactor (CFR) was investigated by confining the reaction and subsequent nucleation to an interface away from the channel wall. Silver NPs were formed at room temperature by reducing silver nitrate with sodium borohydride in the presence of sodium hydroxide, while trisodium citrate was used as the surfactant. The main parameters investigated were flow rate of reagents through the CFR and concentrations of trisodium citrate and silver nitrate.Decreasing the total flow rate resulted in the NP size and dispersity reducing from 5.4 AE 3.4 nm to 3.1 AE 1.6 nm. Increasing surfactant concentration reduced size and dispersity from 8.5 AE 6.9 nm to 4.1 AE 1.1 nm. By tuning the precursor concentration the size and dispersity could be reduced from 9.3 AE 3 nm to 3.7 AE 0.8 nm.