Pennes' bioheat equation vs. porous media approach in computer modeling of radiofrequency tumor ablation

[EN] The objective of this study was to compare three different heat transfer models for radiofrequency ablation of in vivo liver tissue using a cooled electrode and three different voltage levels. The comparison was between the simplest but less realistic Pennes' equation and two porous media-based models, i.e. the Local Thermal Non-Equilibrium (LTNE) equations and Local Thermal Equilibrium (LTE) equation, both modified to take into account two-phase water vaporization (tissue and blood). Different blood volume fractions in liver were considered and the blood velocity was modeled to simulate a vascular network. Governing equations with the appropriate boundary conditions were solved with Comsol Multiphysics finite-element code. The results in terms of coagulation transverse diameters and temperature distributions at the end of the application showed significant differences, especially between Pennes and the modified LTNE and LTE models. The new modified porous media-based models covered the ranges found in the few in vivo experimental studies in the literature and they were closer to the published results with similar in vivo protocol. The outcomes highlight the importance of considering the three models in the future in order to improve thermal ablation protocols and devices and adapt the model to different organs and patient profiles.This work was supported by the Spanish Ministerio de Economia, Industria y Competitividad under "Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad", Grant No "RTI2018-094357-B-C21" and by the Italian Government MIUR Grant No "PRIN-2017F7KZWS".Tucci, C.; Trujillo Guillen, M.; Berjano, E.; Iasiello, M.; Andreozzi, A.; Vanoli, GP. (2021). Pennes' bioheat equation vs. porous media approach in computer modeling of radiofrequency tumor ablation. Scientific Reports. 11(1):1-13. https://doi.org/10.1038/s41598-021-84546-6S113111Chu, K. F. & Dupuy, D. E. 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Oral application of L-menthol in the heat: From pleasure to performance

When menthol is applied to the oral cavity it presents with a familiar refreshing sensation and cooling mint flavour. This may be deemed hedonic in some individuals, but may cause irritation in others. This variation in response is likely dependent upon trigeminal sensitivity toward cold stimuli, suggesting a need for a menthol solution that can be easily personalised. Menthol’s characteristics can also be enhanced by matching colour to qualitative outcomes; a factor which can easily be manipulated by practitioners working in athletic or occupational settings to potentially enhance intervention efficacy. This presentation will outline the efficacy of oral menthol application for improving time trial performance to date, either via swilling or via co-ingestion with other cooling strategies, with an emphasis upon how menthol can be applied in ecologically valid scenarios. Situations in which performance is not expected to be enhanced will also be discussed. An updated model by which menthol may prove hedonic, satiate thirst and affect ventilation will also be presented, with the potential performance implications of these findings discussed and modelled. Qualitative reflections from athletes that have implemented menthol mouth swilling in competition, training and maximal exercise will also be included

Adomian decomposition solution for propulsion of dissipative magnetic Jeffrey biofluid in a ciliated channel containing a porous medium with forced convection heat transfer

Physiological transport phenomena often feature ciliated internal walls. Heat, momentum and multi-species mass transfer may arise and additionally non-Newtonian biofluid characteristics are common in smaller vessels. Blood (containing hemoglobin) or other physiological fluids containing ionic constituents in the human body respond to magnetic body forces when subjected to external (extra-corporeal) magnetic fields. Inspired by such applications, in the present work we consider the forced convective flow of an electrically-conducting viscoelastic physiological fluid through a ciliated channel under the action of a transverse magnetic field. The flow is generated by a metachronal wave formed by the tips of cilia which move to and fro in a synchronized fashion. The presence of deposits (fats, cholesterol etc) in the channel is mimicked with a Darcy porous medium drag force model. The two-dimensional unsteady momentum equation and energy equation are simplified with a stream function and small Reynolds' number approximation. The effect of energy loss is simulated via the inclusion of viscous dissipation in the energy conservation (heat) equation. The non-dimensional, transformed moving boundary value problem is solved with appropriate wall conditions via the semi-numerical Adomian decomposition method (ADM). The velocity, temperature and pressure distribution are computed in the form of infinite series constructed by ADM and numerically evaluated in a symbolic software (MATHEMATICA). Streamline distributions are also presented. The influence of Hartmann number (magnetic parameter), Jeffrey first and second viscoelastic parameters, permeability parameter (modified Darcy number), and Brinkman number (viscous heating parameter) on velocity, temperature, pressure gradient and bolus dynamics is visualized graphically. The flow is decelerated with increasing with increasing Hartmann number and Jeffery first parameter in the core flow whereas it is accelerated in the vicinity of the walls. Increasing permeability and Jeffery second parameter are observed to accelerate the core flow and decelerate the peripheral flow near the ciliated walls. Increasing Hartmann number elevates pressure gradient whereas it is reduced with permeability parameter. Temperatures are elevated with increasing magnetic parameter, Brinkman number and Jeffery second parameter. Increasing magnetic field is also observed to reduce the quantity of trapped boluses. Increasing permeability parameter suppresses streamline amplitudes. Both the magnitude and quantity of trapped boluses is elevated with an increase in both first and second Jeffery parameters

Investigation of Electrical Stimuli for Controlled Drug Release from Chitosan DDS

Controlled drug release is crucial for targeted implantable smart drug delivery system (DDS). In this work, simulations and experiments are conducted to demonstrate drug release mechanism using electrical stimulus. For dyed chitosan beads (diameter 500 um to 900 um), a surface acoustic resonator (SAW) chip cavity which has interdigited electrode on quartz surface was used to provide electrical stimulus. Printed circuit board (PCB) and sputter coated interdigited electrodes were used to provide electrical stimulus on the chitosan film. Two simulation models (SAW resonator and chitosan lm) are developed to explain the physical phenomena of drug release using finite element method (FEM). It is found that drug delivery is nonlinearly increased with applied electric field to the electrodes. The AC electro-kinetic (ACEK) force generated from electrical excitation is a factor influencing this phenomenon. Temperature rise was not significant as demonstrated in both simulations and experiments. Different control and stimulus experiments were performed to show the conceptsof dye release from micro beads using electrical stimuli. Dye release has been identified visually for these experiments. Chitosan films loaded with green food coloring were also fabricated to demonstrate the drug release. Experiments were conducted with different electric fields and frequencies on chitosan film. The spectral absorbance of treated solution after the experiment is measured using a spectrophotometer to quantify the dye release. Verification of the dye release with increased applied voltage was statistically proven with 99% level of significance. This study has shown that application of electric field can be a potential candidate for controlled DDS using both chitosan micro-beads/films

Experimental and Finite Element Studies of Acetabular Cement Pressurisation and Socket Fixation in Total Hip Replacement

PhDWith time, the rate of symptomatic acetabular component loosening accelerates and overtakes that of the femoral component as the principal reason for the revision of total hip replacement. In the femur extensive study has shown that cement pressurisation and good preparation of the bone bed improves the survival rate, but acetabular fixation requires further investigation. Production of cement pressure in the acetabulum is anatomically difficult. Pressurisation with conventional and novel designs of cement pressurisers has been compared to manual techniques and component insertion. The pressurisers increased peak and mean pressures and pressure duration. Finite element modethng of cup insertion showed that flanges and higher insertion rates increased cement penetration into cancellous bone. Per-operatively, one design of pressuriser produced cement pressures comparable to those found in the laboratory. Structural finite element modelling of the natural hip indicated that the subehondral plate and the relatively dense cancellous bone supporting it distribute the joint contact force into the medial and lateral pelvic cortices. A perfectly bonded cemented polyethylene cup stiffened the acetabulum so that more load was transferred directly to the cortices at the acetabular rim, with consequent interface stress concentrations. However, complimentary experimental studies using a dynamic joint simulator and a servo-hydraulic materials testing machine suggested that perfect fixation between cement and bone at the rim was not possible, even under laboratory conditions. Debonding of the cement bone interface at the rim, where dense bone prevents cement interdigitation, allowed micromotion. Since the clinical mechanism of failure of the acetabular component appears to be progressive debonding, from rim to apex, of the cement-bone interface, these studies support the initiation of the failure mechanism by mechanical factors, which may then allow the ingress of wear debris. The experimental studies suggested that the use of pressurisers reduces the amount of micromotion and thus may improve the long term stability of the interface

Biomedical Sensing and Imaging

This book mainly deals with recent advances in biomedical sensing and imaging. More recently, wearable/smart biosensors and devices, which facilitate diagnostics in a non-clinical setting, have become a hot topic. Combined with machine learning and artificial intelligence, they could revolutionize the biomedical diagnostic field. The aim of this book is to provide a research forum in biomedical sensing and imaging and extend the scientific frontier of this very important and significant biomedical endeavor