Heat and mass transfer phenomena at solid-liquid nanoscale interface in theranostic applications

Nanoparticles show great potential for several biomedical applications. In particular, Superparamagnetic Iron Oxides (SPIOs) have attracted strong interest because of their theranostic features. SPIOs are both excellent T2 Magnetic Resonance Imaging (MRI) contrast agents and nanoparticles for thermal treatments, due to their capability to dissipate thermal energy if excited by alternating magnetic field. However, the understanding of heat and mass transfer phenomena at solid-liquid nanoscale interface is critical for designing specific theranostic particles. For instance, water dynamics is strongly affected by the proximity to solid surfaces, whose nature plays a major role both on the water mobility (hence on the contrast performances of MRI agents), and on the effective thermal transmittance, affecting the localized heat deployment in hyperthermic treatments. In this study, self-diffusion properties of nanoconfined water have been investigated using equilibrium Molecular Dynamics (MD). In particular, a scaling behavior of water self-diffusion coefficient is demonstrated, where a relevant dimensionless variable (expressing the ratio between confined and total water volumes) is suggested for describing water self-diffusivity in various nanoconfined configurations. In addition, non-equilibrium MD computations are performed for predicting temperature relaxation and consequentially for estimating solid/liquid interface thermal resistance, which is known to be the bottleneck in solid/liquid phononic heat conduction. Results show that both particle geometry and non-bonded interactions at the interface modulate heat diffusion in this region. Hence, a few guidelines for a priori design of novel nanoparticles for theranostic purposes are here outlined, based on atomistic simulations and thermodynamics of water under nanoconfined conditions.