The rheological properties of different GNPs

Rheological analysis can be employed as a sensitive tool in predicting the physical properties of gold nanoparticles (GNPs). Understanding the rheological properties of GNPs can help to develop a better therapeutic cancer product, since these physical properties often link material formulation and processing stages with the ultimate end use. The rheological properties of GNPs have not been previously documented. The present study attempted to characterize the rheological properties of different sizes of GNPs at: 1) fixed temperature and wide range of shear rates; 2) varied temperature and fixed shear rate.

10, 20 and 50 nm GNPs was used in this study. Several rheological parameters of GNPs such as viscosity, torque%, shear stress and shear rate were evaluated using Brookfield LVDV-III Programmable rheometer supplied with temperature bath and controlled by a computer. To measure fluid properties (viscosity as function of shear rate), e.g., to determine whether the flow is Newtonian or non-Newtonian flow behaviour, and viscoelasticity (viscosity as function of temperature), rheological parameters were firstly measured at starting temperature of 37°C and wide range of shear rates from 375 to 1875 s(-1), and secondly at a gradual increase of temperature from 37 to 42°C and fixed shear rate of 1875 s(-1).

The 10, 20 and 50 nm GNPs showed mean size of 9.45 ± 1.33 nm, 20.18 ± 1.80 nm, and 50 nm GNPs, respectively. The 10 and 20 nm GNPs showed spherical morphology while 50 nm GNPs showed hexagonal morphology using the transmission electron microscope (TEM). The relation between viscosity (cp) and shear rate (s(-1)) for 10, 20 and 50 nm GNPs at a temperature of 37°C showed non-Newtonian behaviour. Although the relationship between SS (dyne/cm(2)) and SR (s(-1)) for 10, 20 and 50 nm GNPs was linearly related however their fluid properties showed non-Newtonian behaviour.

The torque%, viscosity (cp) and SS (dyne/cm(2)) of all GNP sizes decreased with increasing the temperature and with decreasing the GNP size (for each fixed temperature value). For each shear rate value, the viscosity of all GNPs decreased with decreasing the GNP size. This study demonstrates that the physical, dimensional and morphological changes of GNPs have effective influence on their rheological properties. To understand and categorize the role of GNPs in drug delivery and cancer therapy, GNPs of varying size, number of particles, shape and surface should be taken into consideration. Moreover, further additional in vivo studies after administration of GNPs in rats should be performed to support this hypothesis.