P.160 Impact of peritumoral edema during tumor treatment field therapy: a computational modelling study

Background: Tumor treatment fields (TTFields) are an approved adjuvant therapy for glioblastoma. The magnitude of applied electrical field is related to the anti-tumoral response. However, peritumoral edema (ptE) may result in shunting of electrical current around the tumor, thereby reducing the intra-tumoral electric field. In this study, we address this issue with computational simulations. Methods: Finite element models were created with varying amounts of ptE surrounding a virtual tumor. The electric field distribution was simulated using the standard TTFields electrode montage. Electric field magnitude was extracted from the tumor and related to edema thickness. Two patient specific models were created to confirm these results. Results: The inclusion of ptE decreased the magnitude of the electric field within the tumor. In the model considering a frontal tumor and an anterior-posterior electrode configuration, ≥ 6 mm of ptE decreased the electric field by 52%. In the patient specific models, ptE decreased the electric field within the tumor by an average of 26%. The effect of ptE on the electric field distribution was spatially heterogenous. Conclusions: Given the importance of electric field magnitude for the anti-tumoral effects of TTFields, the presence of edema should be considered both in future modelling studies and as a predictor of non-response.

Molecular Dynamics Simulations of Ion Drift in Nanochannel Water Flow

The present paper employs Molecular Dynamics (MD) simulations to reveal nanoscale ion separation from water/ion flows under an external electric field in Poiseuille-like nanochannels. Ions are drifted to the sidewalls due to the effect of wall-normal applied electric fields while flowing inside the channel. Fresh water is obtained from the channel centerline, while ions are rejected near the walls, similar to the Capacitive DeIonization (CDI) principles. Parameters affecting the separation process, i.e., simulation duration, percentage of the removal, volumetric flow rate, and the length of the nanochannel incorporated, are affected by the electric field magnitude, ion correlations, and channel height. For the range of channels investigated here, an ion removal percentage near 100% is achieved in most cases in less than 20 ns for an electric field magnitude of E = 2.0 V/Å. In the nutshell, the ion drift is found satisfactory in the proposed nanoscale method, and it is exploited in a practical, small-scale system. Theoretical investigation from this work can be projected for systems at larger scales to perform fundamental yet elusive studies on water/ion separation issues at the nanoscale and, one step further, for designing real devices as well. The advantages over existing methods refer to the ease of implementation, low cost, and energy consumption, without the need to confront membrane fouling problems and complex electrode material fabrication employed in CDI.

Comparison and calibration of different electroporation models. Application to rabbit livers experiments

Electroporation is a complex phenomenon that occurs when biological tissues are subjected to electric pulses. The clinical interest for the phenomenon has constantly increased for the last decades. Indeed, electroporation makes it possible to either kill directly the cells in the target region (tumor) or to introduce molecules into living cells. However, one of the main limitation of using electroporation in the clinical routine comes from the technical difficulties raised by such therapies, in particular it is difficult to well determine the treated zone. Numerical modeling of the electric field magnitude could provide a powerful strategy to assess the treatment efficacy: thanks to well-designed models, the computation of the distribution of the electric field is achievable, providing a numerical evaluation of the treatment. The main objective of this work is to go further on the patient-adapted numerical modeling of the electric field magnitude by laying the ground of the possible electroporation models - which will be compared qualitatively - and their calibrations. This will be done in the framework of bioelectrical measurements on rabbit livers that come from the literature.

Optimisation of corona ring design for composite insulator strings

PurposeThe purpose of this paper is to propose an optimum design of a corona ring for insulator strings using optimisation techniques, which are gravitational search algorithm (GSA) and imperialist competitive algorithm (ICA).Design/methodology/approachAn insulator string model geometry with a corona ring was modelled in a finite element analysis software, and it was used to obtain the electric field distribution in the model. The design was optimised using GSA and ICA. The variables were the corona ring diameter, ring tube diameter and vertical position of the ring along the insulator string.FindingsUsing optimisation method, the minimum electric field magnitude on the insulator string with a corona ring design is lower than without using optimisation method. GSA yields better results than ICA in terms of the optimised corona ring design.Practical implicationsThe proposed methods can help in improvement of corona ring design in reducing the electric field magnitude on the energised end of insulator strings.Originality/valueA new method to design an optimum corona ring for insulator strings, which is using optimisation methods, has been developed in this work.

Using Shear and DC Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

Manipulating suspended neutrally buoyant colloidal particles of radii a = O(0.1 μm–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the DLVO theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ̇ near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125 nm–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ̇, a scaling consistent with hydrodynamic, vs. electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field or in Poiseuille flow for the same γ̇. Initial results also imply that this force, when repulsive, scales as γ̇1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

Using Shear and Direct Current Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

Manipulating suspended neutrally buoyant colloidal particles of radii a = O (0.1–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ· near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ·, a scaling consistent with hydrodynamic, versus electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field and in Poiseuille flow for the same γ·. Initial results also imply that this force, when repulsive, scales as γ·1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

Time Dependent Polarization and Strain Evolution Around a Circular Hole in Ferroelectrics

The simulation of inhomogeneous creep around a circular hole in the center of ferroelectric plate is presented aiming for understanding the birefringence measurements around the hole. The time dependent fields of strain and polarization around the hole in response to its concentrated electric field effect can be determined using the finite element method. It was found that the electric field concentration factor by a hole can achieve 6 times of the applied loads and shows slightly time dependence; the creep of polarization and strains process is controlled by the local electric field magnitude, which governs the saturation of remnant polarization and strain. The result of geometric principal strain difference contours around the hole agrees with that of birefringence observation. The remnant polarization increased in a power-law relation with electric field magnitude, while the principal strain difference developed quadratically with the total electric displacement. Both experimental and numerical results suggest that the strain distributes around the hole and changes with time, which is controlled by both the local electric field magnitude and the saturation process. Although the inhomogeneities enhance fields locally, the saturated values of strain and polarization decrease with an increase in the defect volume.

Electric Field Manipulation of Cellulose Whiskers in Polyvinyl Acetate

Cellulose whiskers as inclusions have shown a lot of promise due to their potential to enhance mechanical and piezoelectric response of polymers. In addition, CWs are high aspect ratio particles; by aligning them in polymers, improved and anisotropic physical properties could be achieved. In this study, we investigate the effect of AC electric field on the alignment of CWs in a solution of PVAc and DMF. CWs were dispersed as small bundles (<10μm). Alignment and chain formation was found to be a function of electric field magnitude, frequency and time. Dielectric constant of the solutions was studied as a function of applied electric field magnitude, frequency and duration. Significant improvements in dielectric constant were observed for the aligned cases as compared to random case. Optimum properties were achieved at 100 – 200 Vpp/mm and 50 KHz for duration of 20 minutes. Future work will focus on processing thin films with individually dispersed CWs, and improving their alignment to further increase the electrical and mechanical properties.

Gentle Dielectrophoretic Focusing of Yeast Cells in Curved Microchannels

Focusing cells into a tight stream is usually a necessary step prior to counting, detecting and sorting them in, for example, microfluidic flow cytometers. We present herein a simple and gentle cell focusing technique in physiological solutions through a serpentine microchannel using DC-biased AC electric fields. This electrokinetic focusing eliminates sheath flows and in-channel microelectrodes. It results from the cross-stream dielectrophoretic motion of cells induced by the intrinsic channel curvatures. The effects of electric field magnitude, AC to DC electric field ratio, AC field frequency, and cell concentration on the focusing performance of yeast cells will be studied.