Electrical Properties Of Human Tissue Research Articles

Highly stretchable dynamic hydrogels for soft multilayer electronics.

Recent progress in the development of synthetic polymer networks has enabled the next generation of hydrogel-based machines and devices. The ability to mimic the mechanical and electrical properties of human tissue gives great potential toward the fields of bioelectronics and soft robotics. However, fabricating hydrogel devices that display high ionic conductivity while maintaining high stretchability and softness remains unmet. Here, we synthesize supramolecular poly(ionic) networks, which display high stretchability (>1500%), compressibility (>90%), and rapid self-recovery (<30 s), while achieving ionic conductivities of up to 0.1 S cm -1. Dynamic cross-links give rise to inter-layer adhesion and a stable interface is formed on account of ultrahigh binding affinities (>1013 M-2). Superior adherence between layers enabled the fabrication of an intrinsically stretchable hydrogel power source, paving the way for the next generation of multi-layer tissue mimetic devices.

Probing underlying biophysical mechanisms of electrical properties change by pathogenesis at the microscopic cellular level

The electrical properties of human tissue have significant potential as biophysical markers in clinical applications, as they can indicate biochemical/biophysical changes occurring at the cellular and extracellular levels. Magnetic resonance electrical properties tomography (MR-EPT) provides a noninvasive approach for extracting pixel-wise electrical properties by processing the B1 field mapping data. However, our current understanding of the biophysical mechanisms underlying changes in electrical properties at the microscopic cellular level during pathogenesis remains incomplete. In this study, an inhomogeneous liver model was developed to establish a linear correlation between fat fraction and electrical properties. We further fit the correlation of liver phantoms with different fat fractions of 0%, 1%, 9%, 17%, 25%, 30%, and 50% (R2 &amp;gt; 0.93). In addition, an inhomogeneous liver phantom was fabricated and measured through MR-EPT at 128 MHz (3 T). The outcomes of this research have the potential to bridge the gap between microscopic lesions and pixel-wise MR-EPT images, offering a feasible method for extracting electrical properties through fat quantification techniques like MRI-Dixon technique.

An Out-of-Phase Wireless Power Transfer System for Implantable Medical Devices to Reduce Human Exposure to Electromagnetic Field and Increase Power Transfer Efficiency.

For the wireless power transfer (WPT) system in implantable medical devices (IMDs), human tissue is positioned between the transmitting and receiving coils which are different from general WPT systems. Because this space is where the strongest electromagnetic field (EMF) occurs, it is essential to reduce the EMF at the interspace to reduce human exposure to the EMF. In this paper, an out-of-phase coupled WPT system for IMDs is proposed to reduce human exposure to EMF. Considering the EMF exposure and power transfer efficiency (PTE) of the proposed system, a design procedure for determining the phase difference of each capacitor is analyzed and presented. Based on the equivalent circuit model analysis of the proposed system, the EMF and PTE characteristics of the WPT system depending on the design variables are comprehensively analyzed. The proposed system is compared with conventional systems through simulation and measurements. It is verified that the proposed system can reduce the EMF by 41.05% and increase the PTE by 9.62% compared to the conventional system. In addition, through simulation, human exposure to EMFs is assessed considering the exposure environment and electrical properties of human tissues. As a result, the current density, induced electric field, and specific absorption rate were reduced by 44.10%, 38.90%, and 63.82%, respectively.

Advance of Electroconductive Hydrogels for Biomedical Applications in Orthopedics

Electroconductive hydrogels (EHs) are promising composite biomaterials of hydrogels and conductive electroactive polymers, incorporating bionic physicochemical properties of hydrogels and conductivity, electrochemistry, and electrical stimulation (ES) responsiveness of conductive electroactive polymers. The biomedical domain has increasingly seen EHs’ application to imitating the biological and electrical properties of human tissues, acclaimed as one of the most effective biomaterials. Bone’s complex bioelectrochemical properties and the corresponding stem cell differentiation affected by electrical signal elevate EHs’ application value in repairing and treating bone, cartilage, and skeletal muscle. Noteworthily, the latest orthopedic biological applications require broader information of EHs. Except for presenting the classification and synthesis of EHs, this review recapitulates the advance of EHs application to orthopedics in the past five years and discusses the pertinent development tendency and challenge, aiming to provide a reference for EHs application direction and prospect in orthopedic therapy.

Proposal of a Lab Bench for the Unobtrusive Monitoring of the Bladder Fullness with Bioimpedance Measurements.

(1) Background: millions of people, from children to the elderly, suffer from bladder dysfunctions all over the world. Monitoring bladder fullness with appropriate miniaturized textile devices can improve, significantly, their daily life quality, or even cure them. Amongst the existing bladder sensing technologies, bioimpedance spectroscopy seems to be the most appropriate one to be integrated into textiles. (2) Methods: to assess the feasibility of monitoring the bladder fullness with textile-based bioimpedance spectroscopy; an innovative lab-bench has been designed and fabricated. As a step towards obtaining a more realistic pelvic phantom, ex vivo pig’s bladder and skin were used. The electrical properties of the fabricated pelvic phantom have been compared to those of two individuals with tetrapolar impedance measurements. The measurements’ reproducibility on the lab bench has been evaluated and discussed. Moreover, its suitability for the continuous monitoring of the bladder filling has been investigated. (3) Results: although the pelvic phantom failed in reproducing the frequency-dependent electrical properties of human tissues, it was found to be suitable at 5 kHz to record bladder volume change. The resistance variations recorded are proportional to the conductivity of the liquid filling the bladder. A 350 mL filling with artificial urine corresponds to a decrease in resistance of 7.2%, which was found to be in the same range as in humans. (4) Conclusions: based on that resistance variation; the instantaneous bladder fullness can be extrapolated. The presented lab-bench will be used to evaluate the ability of textiles electrodes to unobtrusively monitor the bladder volume.

A method for quantitative imaging of electrical properties of human tissues from only amplitude electromagnetic data

The estimation of electrical properties of living biological tissues is relevant to several medical applications ranging from hyperthermia treatment planning to dosimetry and, more in general, is pivotal for a fundamental understanding of bioelectromagnetic interactions. Non-invasive electromagnetic imaging, either based on the processing of electric fields measured via microwave tomography or magnetic fields acquired in magnetic resonance is suitable to pursue this goal. In this framework, the possibility of imaging without the need of phase information would be extremely relevant, as it would enable simpler and more reliable devices and would avoid limiting assumptions typically used in the literature. With reference to the canonical yet significant 2D case, in this paper we propose an inverse scattering approach for tissue characterization from only-amplitude electromagnetic data, which, by virtue of a unified mathematical framework, is viable for both microwave tomography and magnetic resonance imaging. The key feature of the method is the innovative use of morphological maps derived by other medical imaging modalities as prior spatial information. In particular, these images are exploited to define a convenient and effective patient-specific representation of the unknowns. The approach is tested against simulated data derived from anatomically realistic scenarios.

Electrical Characterization of Human Biological Tissue for Irreversible Electroporation Treatments.

Irreversible electroporation (IRE) is a cancer therapy that uses short, high-voltage electrical pulses to treat tumors. Due to its predominantly non-thermal mechanism and ability to ablate unresectable tumors, IRE has gained popularity in clinical treatments of both liver and pancreatic cancers. Existing computational models use electrical properties of animal tissue that are quantified a priori to predict the area of treatment in three dimensions. However, the changes in the electrical properties of human tissue during IRE treatment are so far unexplored. This work aims to improve models by characterizing the dynamic electrical behavior of human liver and pancreatic tissue. Fresh patient samples of each tissue type, both normal and tumor, were collected and IRE pulses were applied between two parallel metal plates at various voltages. The electrical conductivity was determined from the resistance using simple relations applicable to cylindrical samples. The results indicate that the percent change in conductivity during IRE treatments varies significantly with increasing electric field magnitudes. This percent change versus applied electric field behavior can be fit to a sigmoidal curve, as proposed in prior studies. The generic conductivity data from human patients from this work can be input to computational software using patient-specific geometry, giving clinicians a more accurate and personalized prediction of a given IRE treatment.

Comparison of microwave dielectric properties of human normal, benign and malignant thyroid tissues obtained from surgeries: a preliminary study

The aim of this work was to investigate whether there are differences in electromagnetic properties between normal and variously pathological human thyroid tissues. Dielectric properties of normal, diseased and malignant human thyroid tissues have been investigated at microwave frequencies from 200 MHz to 10 GHz; diseased tissues involved goiters, thyroiditis and adenomatous nodules. Measurements were carried out on freshly excised thyroid samples from 14 surgery patients within less than one hour from excision, using the open-ended coaxial probe technique. Complex permittivity values of each measured specimen were fitted to a 2-pole Cole–Cole model. Thyroid samples were classified into five categories according to their final histological examination: normal, struma (nodular goiter), thyroiditis, adenoma and cancer. Data analysis showed that the dielectric constant of a normal thyroid is on average 10% lower than relative permittivity of cancer and less than 8% lower than that of goiter over the entire frequency band. Conductivity for normal samples is from 21% to 8% lower than that for malignant lesions and from 14% to 7% lower than conductivity of goiter (struma) in the band ranging from 0.2 to 2.45 GHz. Above this frequency range no significant difference is found in terms of electrical conductivity. No significant contrast has, however, been found between dielectric properties of cancer and other benign pathologies affecting the gland. These findings are relevant for microwave diagnosis endeavours and for all biomedical applications involving the electrical properties of human tissues.

Frequency‐dependent anisotropic modeling and analysis using mfEIT: A computer simulation study

Electrical properties of human tissues are usually linked with structure of thin insulating membranes and thereby reflect physiological function of the tissues or organs. It is clinically important to characterize electrical properties of tissues in vivo. Electrical impedance tomography is a recently developed medical imaging technique, which has been exploited to characterize electrical properties (conductivity and permittivity) of human tissues by injecting currents and measuring the resulting voltages at boundary electrodes. The electrical characteristic of a majority of human tissues, such as bones, muscles, and brain white matter, exhibits an anisotropic property. The anisotropic phenomenon of human tissues is frequency dependent that vanishes at high frequencies. Previous electrical impedance tomography studies that aimed at the reconstruction of anisotropic subject tissues have been focused on the theoretical analysis of uniqueness up to a diffeomorphism or the establishment of an accurate forward model by using an anisotropic conductivity tensor. However, effects of the current frequency on the accuracy of the reconstructions of anisotropic subjects remain poorly studied. The goal of this study is to examine the feasibility of multifrequency electrical impedance tomography by using it in a simulation study to recover the frequency-dependent anisotropic properties of a phantom subject composed of alternating insulating and conductive layers. The anisotropic properties of the subject were analyzed by an effective admittivity tensor, and the responses of the current flow pathways and voltages were investigated at various applied current frequencies in the forward model. The linear reconstruction was performed following the sensitivity matrix approach at multiple frequencies. Simulation results achieved at various frequencies revealed that the anisotropy of the model was effectively reconstructed at low frequencies and disappeared at high frequencies, from which we validated the feasibility of multifrequency electrical impedance tomography method in reconstructing the anisotropic directions of the considered object.

A Post-Processing Method for Three-Dimensional Electrical Impedance Tomography

Electrical impedance tomography is a modern biomedical imaging method. Its goal is to image the electrical properties of human tissues. This approach is safe for the patient’s health, is non-invasive and has no known hazards. However, the approach suffers from low accuracy. Linear inverse solvers are commonly used in medical applications, as they are strongly robust to noise. However, linear methods can give only an approximation of the solution that corresponds to a linear perturbation from an initial estimate. This paper proposes a novel reconstruction process. After applying a linear solver, the conductivity distribution is post-processed with a nonlinear algorithm, with the aim of reproducing the abrupt change in conductivity at the boundaries between tissues or organs. The results are used to compare the proposed method with three other widely used methods. The proposed method offers higher quality images and a higher robustness to noise, and significantly reduces the error associated with image reconstruction.

PREPARATION OF A HUMAN SKIN-MIMICKING GELS FOR IN VITRO MEASUREMENTS OF THE DUAL-BAND MEDICAL IMPLANT ANTENNA

The purposes of this study are to design of a small size implantable antenna and to present a complementary recipe for a human skin mimicking material for in-vitro testing of implantable antennas operating at MICS (Medical Implant Communications Service, 402–405 MHz) and ISM (Industrial, Scientific, and Medical, 2.4 GHz–2.48 GHz) bands. Approximate electrical properties of human tissues at MICS and ISM bands were obtained by mixing de-ionized water, sugar, NaCl, and Poly(acrylic acid) (PAA or Carbomer) with different content percentages. In the literature Agarose, a polysaccharide polymer material, was widely used to ensure the formation of gel of the mixture and in our study we used Carbomer instead of Agarose for this aim. To test the antenna in-vitro, skin mimicking gels were made that to show electrical properties real skin tissue (relative permittivity ( e r ) and conductivity (σ)) for the operation frequencies of ISM and MICS bands. For the antenna performance evaluations the measurements of the antenna (return loss (S 11 )) have been performed by placing in to the skin mimicking gels. The measurements were taken in the 1 GHz - 5 GHz frequency band. The measurement and simulation results are quite good agreement except some discrepancy in S 11 levels and frequency bands.

A feasibility study of magnetic resonance driven electrical impedance tomography using a phantom

Imaging the electrical properties of human tissue may aid in cancer diagnoses or monitoring organ function. Traditionally, the electrical properties are revealed with electrical impedance tomography, where currents are injected into human tissue and voltages are measured on the surface. This paper focuses on a method of measuring the electrical properties using a magnetic resonance (MR) scanner without current injection. In magnetic resonance driven electrical impedance tomography (MRDEIT), the MR phenomenon is used to induce currents in the body and the complex permittivity map is inversely computed from the difference between the modeled electric field and the actual surface electrode measurements. Computer simulations indicate that with noise level under 20%, the contrast is visually discernible in the reconstruction image. A phantom experiment is demonstrated and this supports results from computer simulation studies. The noise level in electrode measurements is evaluated to be approximately 7.8% from repeated experiments, confirming the potential to reconstruct conductivity contrast using MRDEIT. With further improvements in hardware and image reconstruction, MRDEIT may provide an additional contrast mechanism reflecting the electrical properties of human tissue, which may ultimately be used to diagnose a cancer or assist in electroencephalography.