Jose-Maria Fullana

Behaviour of silica nanoparticles in dermis-like cellularized collagen hydrogels

A model of the fate of colloidal silica in the dermis was designed based on the diffusion of fluorescent silica nanoparticles through collagen hydrogels. The diffusion process was found to depend on particle size (10-200 nm) and surface charge, as well as on collagen concentration (1.5-5 mg mL-1). The presence of human dermal fibroblasts within the hydrogels also significantly impacted on the behaviour of the particles. In particular, the simultaneous monitoring of particulate and soluble forms of silica showed that both the hydrogel network and the cellular activity have a strong influence on the solubilization process of the silica particles, through a combination of surface sorption, uptake and intracellular dissolution. Interactions between silica and collagen in 3D environments also lower the cytotoxicity of 10 nm particles compared to traditional 2D cultures. The results emphasize the complexity of silica chemistry in living tissues and specifically indicate the need for further investigations of the in vivo behaviour of its soluble forms.

Blood Flow Arterial Network Simulation with the Implicit Parallelism Library SkelGIS

Implicit parallelism computing is an active research domain of computer science. Most implicit parallelism solutions, to solve partial differential equations and scientific simulations, are based on the specificity of resolution methods where the user has to call specific functions which embed parallelism. This paper presents the parallel implicit library SkelGIS which allows the user to freely write its resolution method in a sequential programming style in C++. This library relies on four concepts that are applied to the specific case of network simulations. SkelGIS is evaluated on the real-case simulation of the blood-flow in an arterial network. Benchmarks have been performed to compare the SkelGIS simulation to an OpenMP code and to show its scalability on a cluster using 1024 cores.

Effect of viscoelasticity of arterial wall on pulse wave: a comparative study on ovine

Pulse waves of pressure and flow rate in the arterial system can be well captured by 1D models of blood flow. In the 1D models, the mechanics of the arterial wall is taken into account to close the governing equations. Although the viscoelastic behaviour of the wall has been recognised as a fundamental factor for a long time, most 1D simulations in the literature adopted elastic models for simplicity. A recent in vitro study (Alastruey et al. 2011) showed that viscosity has considerable influence on the pulse waves, especially at the peripheral part of the arterial network. However, the vessels in the study were made of polymers which are actually much less viscous than the real arterial wall. There are also some other studies on in vivo conditions, such as Reymond et al. (2009). But the estimation of the wall viscoelasticitywas done by interpolation of limited available data. In this paper, the coefficients of the viscoelastic model were estimated from in vivomeasurements. The pulse wave in an arterial treewas simulated by a nonlinear 1Dblood flow model. The effect of viscoelasticity of the arterial wall on the pulse wave was investigated.

Boundary conditions in arterial flows and evaluation of reflection indices.

The numerical simulations were performed using the COMSOL software (COMSOL, Inc., Burlington, MA, USA). This tool is based on a finite element method and numerically simulates partial differential equations. For the fluid part, COMSOL solves the Navier–Stokes equation inside the computational domain. The fluid is assumed incompressible, Newtonian of dynamic viscosity h 1⁄4 5 £ 10 Pa s and density r 1⁄4 1060 kg/m. For the fluid domain, the inlet and outlet boundary conditions are expressed as follows in COMSOL: the pressure is imposed as a function of time at both ends of the computational domain. Depending on models (see below), these functions can be directly given as inputs or can be obtained through an ordinary differential equation relating pressure and flux. In addition, a no slip condition is imposed on the artery wall. We assume, in the solid solver, the flexiblewall to be nearly incompressible. It is made of an isotropic linearly elastic solid which is thus defined only by its YoungmodulusE and its Poisson’s ratio np. For the solid, the boundary conditions read as: the arterial wall is assumed to move only radially, which is generally well admitted in haemodynamics. The inlet is held fixed and the outlet portion of the solid is free to move radially under the pressure forces (Table 1). We propose below an approach based on the idea that proper boundary conditions should enable a unidirectional wave to cross the outward boundaries without being reflected. The new conditions are thus introduced and based on properties of specific propagative unidirectional solutions coupled with an integral formulation. Let us consider the z-component of the linearised Navier–Stokes equation in which one assumes axial derivatives to be negligiblewith respect to radial derivatives (such hypotheses are justified for blood flow since artery radius is much smaller than characteristic wavelength). When integrated over a section at constant z, this equation reads as: