Maxim Solovchuk

Nanoscale fluid–ion transport is investigated in biophysical chemistry, drug delivery, protein sequencing, etc. Currently, fast three-dimensional models for fluid–ion transport through biological nanopores are unavailable. This study, therefore, focuses on the simulation and parallelization of nanoscale fluid–ion transport on multiple graphics processing units (GPUs). Nanoscale fluid–ion transport is described through the fourth-order Poisson–Nernst–Planck–Bikerman model coupled with the Navier–Stokes equations. The model incorporates the effect of ionic and non-ionic interactions, ion solvation, nonlocal electrostatics, and the finite size of particles. Governing equations are discretized using the lattice Boltzmann method (LBM). For complex geometries, the immersed boundary method has been incorporated with the LBM. To demonstrate the applicability of the developed model, electro-osmotic flow through a relatively large biological nanopore has been simulated. Parallelization on multiple GPUs has enabled us to perform simulations for a full three-dimensional channel geometry. Results showed a good match with the published data. We captured local variations in concentration and fluid flow in both axial and radial directions. Furthermore, flow circulation around the channel was also observed. The impact of external potential difference and the finite size of the particles on the flow has also been assessed. Using our in-house code, we achieved a performance of 1982 × 106 lattice updates per second on 8 A100 80 gigabyte GPUs. The methodology presented here provides an accurate and fast simulation methodology for characterizing symmetric/asymmetric nanopore properties. This model can help in enhancing the fundamental understanding of nanofluidics and characterization of the nanopores.

High intensity focused ultrasound (HIFU) is very promising new technology that has many therapeutic application, and among them are the treatment of cancer in different organs without major side effects. Some of the limitations of HIFU are the long treatment time and incomplete ablation. High performance computing can help in this regard. Simulation of nonlinear wave propagation in three dimensional geometry is very time consuming process especially when shocks are presented. In the current work, we are going to present three dimensional parallel solver on GPU. Some examples for the simulation in a patient specific geometry will be also presented. The presented results can be used for the optimization of the treatment. For the validation of the results, ex-vivo and in-vivo experiments have been performed. It has been shown that large volume can be ablated within a short period of time.

The objective of the present study is the numerical investigation of the inertial cavitation threshold in soft tissue under different multi-frequency signals of high intensity focused ultrasound (HIFU). For the modeling of bubble dynamics, the Gilmore-Akulichev-Zener model was used. The inertial cavitation threshold was calculated for different criteria, for different signal modes (single-, dual-, and triple-frequency), and for different viscoelastic mediums. Effect of nonlinear wave propagation and mechanical effects of acoustic caviation have been also studied. The obtaining results demonstrated that a criterion, based on bubble size, gives lower threshold values than a criterion using bubble collapse velocity. An increase in the values of viscosity and elasticity leads to a rise in the threshold amplitude. Analyzing threshold values for dual- and triple-frequency signal modes, it can be seen that the inertial cavitation threshold can be sufficiently reduced when a multi-frequency signal with the correct frequency combination is applied. However, the inertial cavitation threshold also depends on the initial bubble size. This dependency was also investigated in the current study.

Fluid-ion transport through a nanochannel is studied to understand the role and impact of different physical phenomena and medium properties on the flow. Mathematically, the system is described through coupled fourth order Poisson–Nernst–Planck–Bikerman and Navier–Stokes equations. The fourth order-Poisson–Nernst–Planck–Bikerman model accounts for ionic and nonionic interactions between particles, the effect of finite size of the particles, polarization of the medium, solvation of the ions, etc. Navier–Stokes equations are modified accordingly to include both electroviscous and viscoelectric effects and the velocity slip. The governing equations are discretized using the lattice Boltzmann method. The mathematical model is validated by comparing the analytical and experimental ion activity while the numerical model is validated by comparing the analytical and numerical velocity profiles for electro-osmotic flow through a microchannel. For a pressure driven flow, the electroviscous and viscoelectric effects decrease the fluid velocity while the velocity slip enhances it. The acidity of the medium also influences the fluid velocity by altering the ζ potential and ion concentration. The finite size of the particle limits the concentration of ionic species, thus, reducing electroviscous effects. As the external concentration decreases, the impact of finite size of particles also reduces. The inhomogeneous diffusion coefficient also influences electroviscous effects as it changes the concentration distribution. The variation in external pressure does not influence the impact of steric and viscoelectric effects significantly. The maximum impact is observed for ΔP = 0 (electro-osmotic flow).