Electric and magnetic fields
James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney in Basic Introduction to Bioelectromagnetics, 2018
Permittivity is often represented by the Greek letter epsilon (ε); its units* are farads per meter (F/m). The permittivity of free space (no charges present) is called ε0, and in the International System of Units, ε0 = 8.854 × 10−12 F/m. Relative permittivity is defined as εr = ε/ε0; it is the permittivity relative to that of free space and is unitless. Conductivity† is often represented by the Greek letter sigma (σ); its units are siemens per meter (S/m), which is the same as 1/ohm-m. Permeability is usually represented by the Greek letter mu (μ); its units‡ are henrys per meter (H/m). The permeability of free space is μ0 = 4π × 10−7 H/m, and relative permeability is defined as μr = μ/μ0; it is unitless. For most applications, the human body is so weakly magnetic that we can assume μ = μ0, so μr = 1. Appendix A discusses the electrical properties of specific human tissues in more detail.
Nanoparticles for Cardiovascular Medicine: Trends in Myocardial Infarction Therapy
Harishkumar Madhyastha, Durgesh Nandini Chauhan in Nanopharmaceuticals in Regenerative Medicine, 2022
Metallic nanoparticles are nanosized clusters of metals, often prepared to be modifiable with functional chemical groups to allow binding of ligands or drugs. Metallic nanoparticles allow for a broad range of application in CVD therapeutics, including modalities that other nanoparticles lack, such as catalyst enzyme-like activities, imaging by MRI and magnetisation for guided delivery. Another advantage of metallic-based materials is their innate conductivity of electrical charge. Major challenges in repair of MI are how to increase electrical behaviours of implanted biomaterials and how to maximise electrical interactions between cells and scaffolds. Dong et al. utilised the distribution of electrically and biologically active gold nanoparticles throughout tissue regeneration-conducive ECM/silk fibroin scaffolds (Dong et al. 2020). The supply of gold nanoparticles within ECM matrices can provide corrugation of cardiac cells and the effective organisation of electrical coupling with cells (Somasuntharam et al. 2016; Nair et al. 2017). The researchers used different ratios of ECM, silk fibroin, and gold nanoparticles to investigate changes in morphology, mechanical properties, and cell compatibility with MSCs. The optimised composite scaffolds containing gold nanoparticles, or cardiac patches, supported MSC survivability and promoted myocardium regeneration in MI cryo-injury rat models. The researchers concluded that their developed heart patches were conducive to supporting cardiomyocyte cell behaviour, essential to myocardial function.
Instrumentation
Clive R. Bagshaw in Biomolecular Kinetics, 2017
Although not as widely used as temperature jumps, electric-field jumps provide an important perturbation for examining very fast reactions involving ionic equilibria and reactions coupled to them. The method was the basis of the classic studies of Eigen and colleagues (Figure 8.9) for characterizing protonation and hydration reactions [383,384,463]. As with joule-heating temperature jump (Figure 7.15a), an electric field is applied to the sample using discharge from a capacitor or coaxial cable, but the field is switched off after a few tens of microseconds using a second spark gap to minimize discharge through the sample and the associated heating [49]. The conductivity is measured during the brief application of the charge and reflects changes in the concentration of ionized species. Sample heating is also minimized by working at low ionic strength, although modifications to the apparatus allow measurements under physiological conditions with a limited (1°C) change in temperature [457].
Study of enhanced radiofrequency heating by pre-freezing tissue
Published in International Journal of Hyperthermia, 2018
Kangwei Zhang, Jincheng Zou, Kun He, Lichao Xu, Ping Liu, Wentao Li, Aili Zhang, Lisa X. Xu
The thermal damage in tissue is closely related to temperature transients, namely the thermal history experienced by the tissue. The pre-freezing significantly changes tissue properties that would influence the temperature rise in tissue during the RF heating. Thus, it is essential to study the tissue property changes and temperature transients that occur during the thermal treatment, for the purpose of more effective surgical planning in clinical applications. In this study, both ex vivo and in vivo experiments were performed to compare the heating patterns in tissues with or without pre-freezing. Histopathological analysis of in vivo tissue was carried out to observe the ablation volume and the histological changes. To investigate the main cause of the heating pattern change, three parameters closely related to the RF heating were studied, namely the electrical conductivity, thermal conductivity, and perfusion [19,20]. The electrical conductivity was experimentally measured. A finite element model was developed to numerically study both the thermal conductivity and blood perfusion rate. The spatial and temporal temperature profiles of RF heating pattern in in vivo tissue undergone pre-freezing process were obtained and the volume of the heated tissue quantified.
Transient blood–brain barrier disruption is induced by low pulsed electrical fields in vitro: an analysis of permeability and trans-endothelial electric resistivity
Published in Drug Delivery, 2019
Shirley Sharabi, Yael Bresler, Orly Ravid, Chen Shemesh, Dana Atrakchi, Michal Schnaider-Beeri, Fabien Gosselet, Lucie Dehouck, David Last, David Guez, Dianne Daniels, Yael Mardor, Itzik Cooper
The numerical model calculated the electric field distribution between the electrodes. First the model was solved without conductivity changes. The results of the constant conductivity model demonstrated that in the center of the TW insert, the electric field between the electrode is relatively uniform and can be approximated as voltage-to-distance ratio. Around the edge of the electrodes, higher electrical fields are developed. In order to incorporate the changes in conductivity, the electric field of for each voltage was considered uniform and was calculated as the voltage-to-distance ratio. The time constant of the function describing the dependence of the change in TEER in the pulse voltage was modified accordingly (divided by 0.68 cm) and the equation was multiplied by the conductivity of the initial cells to account for the changes. The conductivity was thus described as: σ0 is the initial conductivity and E is the electric field.
Sodium N-lauryl amino acids derived from silk protein can form catanionic aggregates with cytarabine as novel anti-tumor drug delivery systems
Published in Drug Delivery, 2020
Meng Zhang, Shu-Xiang Zhao, Biao Ding, Yu-Qing Zhang
The conductivity of the aggregate solution at 25 °C and 37 °C is shown in Figure 3(a). The temperature has a significant effect on the conductivity of the aggregate solution, and the conductivity of aggregates at a high temperature is obviously higher than that at a low temperature. The reason for this phenomenon is the accelerated migration rate of ions at high temperatures. At the same time, the change in the conductivity trends for samples at different temperatures is similar. At the same temperature, with an increase in X1, the conductivity decreases until X1 = 0.2, and then the conductivity gradually increases until X1 = 1. The conductivity of the solution is mainly determined by the strength of charged aggregates and free ions. With the constant addition of cationic drugs, the anions in the solution are neutralized to form a vesicle structure, resulting in a decrease in the conductivity of samples with X1≤0.2. However, the vesicle structure begins to change toward the micelle structure as the cationic drug continues to increase, the particle size decreases, the migration rate increases and the conductivity increases for sample solutions with X1>0.2.
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