Study of the transdentinal diffusion of bioactive molecules.

In this work the mass transfer characteristics in a µ-tube that simulates a simplified dentinal tubule geometry are numerically investigated. The aim is to assess the key features that affect transdentinal diffusion of substances and consequently to define the necessary quantitative and qualitative issues related to a specific bioactive agent before its potential application in clinical practice. CFD simulations were performed in an S-shaped tapered micro-tube, while the code was validated using the non-intrusive optical measuring technique Laser Induced Fluorescence (LIF). As the phenomenon is one-dimensional, diffusion dominated and strongly dependent on the molecular size, the time needed for the concentration of released molecules to attain a required value can be controlled by their initial concentration. Thus, we propose a model, which is successfully verified by experimental data using a dentinal disc and which given the type of applied molecules and their critical pulpal concentration is able to estimate the initial concentration to be imposed.

Experimental investigation of the flow of a blood analogue fluid in a replica of a bifurcated small artery.

The scope of this work is to study the pulsatile flow of a blood mimicking fluid in a micro channel that simulates a bifurcated small artery, in which the Fahraeus-Lindqvist effect is insignificant. An aqueous glycerol solution with small amounts of xanthan gum was used for simulating viscoelastic properties of blood and in vivo flow conditions were reproduced. Local flow velocities were measured using micro Particle Image Velocimetry (µ-PIV). From the measured velocity distributions, the wall shear stress (WSS) and its variation during a pulse were estimated. The Reynolds numbers employed are relatively low, i.e. similar to those prevailing during blood flow in small arteries. Experiments both with a Newtonian and a non-Newtonian fluid (having asymptotic viscosity equal to the viscosity of the Newtonian one) proved that the common assumption that blood behaves as a Newtonian fluid is not valid for blood flow in small arteries. It was also shown that the outer wall of the bifurcation, which is exposed to a lower WSS, is more predisposed to atherosclerotic plaque formation. Moreover, this region in small vessels is shorter than the one in large arteries, as the developed secondary flow decays faster. Finally, the WSS values in small arteries were found to be lower than those in large ones.