A U-Shaped Dual-Frequency-Reconfigurable Monopole Antenna Based on Liquid Metal.

This study presents a U-shaped dual-frequency-reconfigurable liquid-metal monopole antenna. Eutectic Gallium-Indium (EGaIn) was used as a conductive fluid and filled in the two branches of the U-shaped glass tube. A precision syringe pump was connected to one of the branches of the U-shaped tube by a silicone tube to drive EGaIn, forming a height difference between the two liquid levels. When the height of liquid metal in the two branches met the initial condition of L1 = L2 = 10 mm, and L1 increased from 10 mm to 18 mm, the two branches obtained two working bandwidths of 2.27-4.98 GHz and 2.71-8.58 GHz, respectively. The maximum peak gain was 4.00 dBi. The initial amount of EGaIn also affected the available operating bandwidth. When the liquid metal was perfused according to the initial condition: L1 = L2 = 12 mm, and L1 was adjusted within the range of 12-20 mm, the two branches had the corresponding working bandwidths of 2.18-4.32 GHz and 2.57-9.09 GHz, and the measured maximum peak gain was 3.72 dBi. The simulation and measurement data corresponded well. A series of dual-frequency-reconfigurable antennas can be obtained by changing the initial amount of EGaIn. This series of antennas may have broad application prospects in fields such as base stations and navigation.

A Gravity-Triggered Liquid Metal Patch Antenna with Reconfigurable Frequency.

In this paper, a gravity-triggered liquid metal microstrip patch antenna with reconfigurable frequency is proposed with experimental verification. In this work, the substrate of the antenna is quickly obtained through three-dimensional (3D) printing technology. Non-toxic EGaIn alloy is filled into the resin substrate as a radiation patch, and the NaOH solution is used to remove the oxide film of EGaIn. In this configuration, the liquid metal inside the antenna can be flexibly flowed and deformed with different rotation angles due to the gravity to realize different working states. To validate the conception, the reflection coefficients and radiation patterns of the prototyped antenna are then measured, from which it can be observed that the measured results closely follow the simulations. The antenna can obtain a wide operating bandwidth of 3.69-4.95 GHz, which coverage over a range of frequencies suitable for various channels of the 5th generation (5G) mobile networks. The principle of gravitational driving can be applied to the design of reconfigurable antennas for other types of liquid metals.

The Design and Manufacturing Process of an Electrolyte-Free Liquid Metal Frequency-Reconfigurable Antenna.

This communication provides an integrated process route of smelting gallium-based liquid metal (GBLM) in a high vacuum, and injecting GBLM into the antenna channel in high-pressure protective gas, which avoids the oxidation of GBLM during smelting and filling. Then, a frequency-reconfigurable antenna, utilizing the thermal expansion characteristic of GBLM, is proposed. To drive GBLM into an air-proof space, the thermal expansion characteristics of GBLM are required. The dimensions of the radiating element of the liquid metal antenna can be adjusted at different temperatures, resulting in the reconfigurability of the operating frequency. To validate the proposed concept, an L-band antenna prototype was fabricated and measured. Experimental results demonstrate that the GBLM in the antenna was well filled, and the GBLM was not oxidized. Due to the GBLM being in an air-proof channel, the designed liquid metal antenna without electrolytes could be used in an air environment for a long time. The antenna is able to achieve an effective bandwidth of over 1.25-2.00 GHz between 25 °C and 100 °C. The maximum radiation efficiency and gain in the tunable range are 94% and 2.9 dBi, respectively. The designed antenna also provides a new approach to the fabrication of a temperature sensor that detects temperature in some situations that are challenging for conventional temperature sensing technology.

Liquid metal bath as conformable soft electrodes for target tissue ablation in radio-frequency ablation therapy.

BACKGROUND: Radio-frequency ablation has been an important physical method for tumor hyperthermia therapy. The conventional rigid electrode boards are often uncomfortable and inconvenient for performing surgery on irregular tumors, especially for those tumors near the joints, such as ankles, knee-joints or other facets like finger joints. MATERIAL AND METHODS: We proposed and demonstrated a highly conformable tumor ablation strategy through introducing liquid metal bath as conformable soft electrodes. Different heights of liquid metal bath electrodes were adopted to perform radio-frequency ablation on targeted tissues. Temperature and ablation area were measured to compare the ablation effect with plate metal electrodes. RESULTS: The recorded temperature around the ablation electrode was almost twice as high as that with the plate electrode and the effective ablated area was 2-3 fold larger in all the mimicking situations of bone tumors, span-shaped or round-shaped tumors. Another unique feature of the liquid metal electrode therapy is that the incidence of heat injury was reduced, which is a severe accident that can occur during the treatment of irregular tumors with plate metal boards. CONCLUSIONS: The present method suggests a new way of using soft liquid metal bath electrodes for targeted minimally invasive tumor ablation in future clinical practice.

Chemothermal therapy for localized heating and ablation of tumor.

Chemothermal therapy is a new hyperthermia treatment on tumor using heat released from exothermic chemical reaction between the injected reactants and the diseased tissues. With the highly minimally invasive feature and localized heating performance, this method is expected to overcome the ubiquitous shortcomings encountered by many existing hyperthermia approaches in ablating irregular tumor. This review provides a relatively comprehensive review on the latest advancements and state of the art in chemothermal therapy. The basic principles and features of two typical chemothermal ablation strategies (acid-base neutralization-reaction-enabled thermal ablation and alkali-metal-enabled thermal/chemical ablation) are illustrated. The prospects and possible challenges facing chemothermal ablation are analyzed. The chemothermal therapy is expected to open many clinical possibilities for precise tumor treatment in a minimally invasive way.

A review of hyperthermia combined with radiotherapy/chemotherapy on malignant tumors.

Therapeutic hyperthermia is a procedure that involves heating tissues to a higher temperature level, typically ranging from 41 degrees C to 45 degrees C. Its combination with radiotherapy and/or chemotherapy has been performed for many years, with remarkable success in treating advanced and recurrent cancers. The current hyperthermia strategies generally include local, regional, and whole-body hyperthermia, which can be implemented by many heating methods, such as microwave, radiofrequency, laser, and ultrasound. There are several hyperthermic treatment modalities in conjunction with radiotherapy/chemotherapy. Numerous studies have attempted to explain the mechanisms of thermosensitization from radiation and chemotherapy; however, a generalized standard for determining an optimal hyperthermia modality combined with radiotherapy/chemotherapy has not been established, so more research is needed. Fortunately, phase II/III clinical trials have demonstrated that hyperthermia combination therapy is beneficial for local tumor control and survival in patients with high-risk tumors of different types. The aim of this article is to present a comprehensive review of the latest advances in tumor hyperthermia combined with radiotherapy and/ or chemotherapy. We specifically focus on synergistic cellular and molecular mechanisms, thermal dose, treatment sequence, monitoring and imaging, and clinical outcomes of the combination therapy. The role of nanoparticles in sensitization during radio-/chemotherapy is also evaluated. Finally, research challenges and future trends in the related areas are presented.

Nano-cryosurgery: advances and challenges.

In clinics, the minimally invasive freezing therapy, commonly known as cryosurgery, has been increasingly used for the controlled destruction of tumor tissue. However, there are still many bottlenecks to impede the success of a cryosurgery. One of the most critical factors has been that insufficient or inappropriate freezing will not completely destroy the target tumor tissues, which as a result may lead to tumor regenesis and thus failure of treatment. In addition, the surrounding healthy tissues may suffer from serious freeze injury due to unavoidable release of a large amount of cold from the freezing probe. To resolve these challenges, we recently proposed a new strategy, termed as nano-cryosurgery, to improve freezing efficiency of the conventional cryosurgical procedure. The basic principle of this protocol is to deliver functional suspension of nanoparticles with favorable physical and/or chemical properties into the target tissues, which then serve as adjuvant or drug carrier either to maximize the freezing heat transfer process, regulate freezing scale, modify ice-ball formation orientation or prevent the surrounding healthy tissues from being frozen. In addition, introduction of nanoparticles during cryosurgery could also help better image the edge of a tumor as well as the margin of the iceball. The new therapy raised many critical fundamental as well as practical issues for solving. This review is dedicated to present a comprehensive review on multiscale fundamental phase change heat transfer issues thus involved. Attentions would span from micro-scale heat transfer in cellular scale to tissue level. Some related thermal physical effects of nanoparticles on the freezing process such as ice nucleation enhancement, water transport during freezing of a single cell will be discussed. Cryosurgical thermal management of using nanoparticles to modify thermal properties of the tissue-particle components, regulate the growth orientation and strength of an ice ball, enable a conformal tumor destruction in tissues with or without large blood vessels, etc. will be illustrated. Meanwhile, the fundamental issue for the transport of nanoparticle and its assisted drug delivery will be summarized. Theoretical modeling as well as experimental approaches for studying the micro/nano-scale heat transfer throughout the tissue or cell domain during nano-cryosurgery will be suggested. Some potential applications and possible challenges when nanotechnology meets cryosurgery will be outlined. The nano-cryosurgery is expected to help expand the boundary of the emerging frontier of nano-biomedical engineering.

[Deeply cooled far-infrared thermal imaging strategy for early tumor diagnostics].

This paper is dedicated to evaluate the thermal behavior of skin surface embedded with tumor tissue through construction of three-dimensional heat transfer model of the human body. It was found that the far-infrared imaging equipment could not yet get the accurate results for diagnosis of tumors developed in early stage or located deeply in the human body, because of limited resolution and accuracy in the current system. Conceptual experiments with a thermal imaging system under various cooling levels were performed to confirm this issue. A dual cooling cavity was proposed to realize ultra-low-temperature so as to improve the cooling of the current infrared equipment and thereby to enhance its image precision and accuracy. This study is expected to be of significant reference value for realizing an early diagnosis of cancers through medical image.

Minimally invasive thermotherapy method for tumor treatment based on an exothermic chemical reaction.

In tumor thermotherapy treatment, it is very difficult to achieve the objective of exactly killing the tumor while minimizing the injury of healthy tissues or organs surrounding the tumor. In this study, we describe a new minimally invasive thermotherapy protocol for tumor treatment using heat released from an exothermic chemical reaction, which can safely deliver a totally localized and uniform heating to exactly kill the tumor. Both in vitro and in vivo experiments were performed to test the feasibility of this thermotherapy method based on an exothermic chemical reaction. After injection of only a small amount of matched reactants into the target tissue by medical syringes, an exothermic reaction takes place, and then releases tremendous heat to elevate the temperature to its thermally lethal value. Compared with most of the currently existing thermotherapy strategies, this heating is highly localized, completely safe and uniform, which will remarkably reduce the thermal damage and mechanical trauma to the surrounding healthy tissues. This study opens the clinical possibilities for tumors to be treated in a minimally invasive way by a thermotherapy treatment based on an exothermic chemical reaction.

Feasibility study on using an infrared thermometer for evaluation and administration of cryosurgery.

Successful performance of cryosurgery relies heavily on a quick, efficient, safe and economic imaging way to monitor the surgical advancement and then to evaluate the curative effect. However, there is currently a lack of such an imaging modality. As for the commonly adopted imaging devices such as X-CT, MRI and PET, in addition their high cost and complexity in operation, they often induce additional scathe to the patients due to their potential radiation effects. Besides, in cryosurgery, the most important parameter - temperature - can not be directly detected by these methods. Considering the above factors, infrared thermography (IRT), a rather useful yet often neglected functional imaging technique in clinics, is proposed in this paper as an efficient tool for the quick evaluation and administration of a cryosurgical treatment of tumors. Based on skin surface temperature mapping, the degree of damage to the target tissue site caused by different freezing/heating protocols, as well as the states of blood circulation and metabolic heat generation within the treated region can possibly be identified. Further, through recording the temperature variation feature at the skin surface before and after cryosurgery, IRT would help to quickly evaluate the curative effect, which is very beneficial for later treatment planning. By detecting the surface infrared image and analyzing its digital values, the patient's invisible focus and abnormal physiological states, e.g. inflammations or pneumothorax, often accompanied by cryosurgical output yet difficult to determine via conventional imaging, could also possibly be diagnosed. To test the above concepts, both typical animal and clinical experiments were performed to demonstrate the feasibility and advantages of IRT-guided cryosurgery. This study may help push forward a novel, low-cost and non-contact way for an efficient performance of cryosurgery.

Numerical simulation of selective freezing of target biological tissues following injection of solutions with specific thermal properties.

Recently, we proposed a method for controlling the extent of freezing during cryosurgery by percutaneously injecting some solutions with particular thermal properties into the target tissues. In order to better understand the mechanism of the enhancement of freezing by these injections, a new numerical algorithm was developed to simulate the corresponding heat transfer process that is involved. The three-dimensional phase change processes in biological tissues subjected to cryoprobe freezing, with or without injection, were compared numerically. Two specific cases were investigated to illustrate the selective freezing method: the injection of solutions with high thermal conductivity; the injection of solutions with low latent heat. It was found that the localized injection of such solutions could significantly enhance the freezing effect and decrease the lowest temperature in the target tissues. The result also suggests that the injection of these solutions may be a feasible and flexible way to control the size of the ice ball and its direction of growth during cryosurgery, which will help to optimize the treatment process.

Enhancement of thermal diagnostics on tumors underneath the skin by induced evaporation.

Infrared imaging has frequently been used in clinics to detect changes in skin surface temperature associated with some superficial tumors. In order to accurately detect and diagnose tumors (especially in their early stages) using infrared thermography, enhancement of thermal expression on the skin over the tumor is desired. This study proposed a novel approach to effectively enhance the skin thermal expression of tumor by induced evaporation on skin surface. To illustrate its feasibility, numerical calculation was first applied to simulate the corresponding heat transfer process, from which the three-dimensional transient temperatures of the biological bodies subjected to induced evaporation were theoretically predicted. Further, preliminary infrared imaging experiments on human forearm were also performed, in which water and 75% (V/V) medical ethanol were particularly chosen to be respectively sprayed on the skin surface. Both the numerical and experimental results indicate that the induced evaporation can significantly enhance the sensitivity of temperature mapping on skin surface over the tumor. The results also suggest that the induced evaporation method can be used to improve the diagnostic accuracy of infrared thermography, especially for tumors at early stages and/or deeply embedded.

Effect of configuration between cryoprobe and large blood vessels on the tissue freezing during cryosurgery.

For accurate predictions of the tissue temperature distribution during cryosurgery a thermal model should incorporate the individual impact of large blood vessels. In presence of large vessel, configuring cryoprobe becomes very important because misplacement of cryoprobes may result in either inadequate cooling temperatures in the target tissue due to the heating nature of large vessels or undesired damage to the downstream healthy tissues and organs as a result of arresting of key vessels. In this article, typical vascular models are applied to investigate the effects of large blood vessels and cryoprobe configurations on the transient temperature profiles of cooled tissues during cryosurgery. The thermal model describing heat transfer to or from large vessels is based on heat transfer coefficient derived from analytical solutions of forced convection in cylindrical ducts. A finite difference algorithm developed in our previous study is used to solve this complex problem with phase change heat transfer in biological tissues embedded with large blood vessels. Numerical computations are then performed to predict the transient temperature distributions of tissues under three different configurations of cryoprobe. The results indicate that different configurations of cryoprobe can produce significantly different temperature profiles and blood vessel heating in cooled tissues. Results of this study should be considered in the strategy for an optimal placement of cryoprobes when performing cryosurgical treatments in the vicinity of large blood vessels.

3-D numerical study on the induced heating effects of embedded micro/nanoparticles on human body subject to external medical electromagnetic field.

Advancement of the recent micro/nanotechnology stimulates the renaissance of using magnetic micro/nanoparticles embedded in tissues for the target tumor hyperthermia. However, there is a strong lack of quantitative understanding of the temperature profiles thus induced by the applied external electromagnetic (EM) field, which may impede the successful operation of this therapy. In the current study, the three-dimensional quasi-steady-state EM field and transient tissue temperature behavior induced by two planar electrodes were numerically investigated. Detailed computations indicated that nanoparticles exhibit an extraordinary highly focused heating on target tumor tissue, which is much stronger than that in the surrounding areas. This heating effect depends heavily on the properties of the magnetic nanoparticles, which may vary appreciably for different samples depending on their particle sizes and microstructures. The effect of micro/nanoparticle concentration, heating area, and the frequency and strength of the external alternating EM field were also tested. Moreover, a criterion to determine the appropriate particle concentration thermally important for medical treatment was established. Given accurate thermal and EM parameters for cancerous tissue embedded with nanoparticles, the current model could possibly be applied in the hyperthermia treatment planning and help optimize the surgical procedures.

Addition of cryoprotective agent into biological tissue through minimally invasive injection.

In this article, a minimally invasive injection method to enhance the addition of cryoprotective agent into the target biological tissues or organs to be cryopreserved was studied. Compared with the traditional treatment through immersion and permeation, direct injection could be much more effective and faster. To illustrate the benefit of this approach, a mathematical model for the addition of cryoprotective agent was established and experiments were performed to test the differences given by the two methods. Both the theoretical and the experimental results demonstrate that the minimally invasive injection method for enhancing the addition of cryoprotective agent is a promising substitution for the commonly used immersing method.

Mathematical modeling of temperature mapping over skin surface and its implementation in thermal disease diagnostics.

In non-invasive thermal diagnostics, accurate correlations between the thermal image on skin surface and interior human pathophysiology are often desired, which require general solutions for the bioheat equation. In this study, the Monte Carlo method was implemented to solve the transient three-dimensional bio-heat transfer problem with non-linear boundary conditions (simultaneously with convection, radiation and evaporation) and space-dependent thermal physiological parameters. Detailed computations indicated that the thermal states of biological bodies, reflecting physiological conditions, could be correlated to the temperature or heat flux mapping recorded at the skin surface. The effect of the skin emissivity and humidity, the convective heat transfer coefficient, the relative humidity and temperature of the surrounding air, the metabolic rate and blood perfusion rate in the tumor, and the tumor size and number on the sensitivity of thermography are comprehensively investigated. Moreover, several thermal criteria for disease diagnostic were proposed based on statistical principles. Implementations of this study for the clinical thermal diagnostics are discussed.

Sinusoidal heating method to noninvasively measure tissue perfusion.

Noninvasively measuring the tissue blood perfusion has been an important however difficult problem in the biomedical engineering field. Based on the newly developed phase-shift principle, an improved sinusoidal heating method to estimate the perfusion was proposed in this paper to replace the original heating algorithm. The phase shift between the sinusoidal heat flux and the surface temperature response was both theoretically and experimentally revealed to be a time-dependent value which however will approach a constant value after a sufficiently long time. Only using this constant phase shift can the perfusion be properly estimated. Following the theory, an instrument consisting of low-frequency sinusoidal signal generator, power amplifier, heating plate, temperature and heat flux monitoring unit, as well as the data-acquisition system was carefully constructed. It allows generating a high-quality sinusoidal heat flux whose frequency and magnitude can be easily regulated. An auxiliary heat-conducting plate was introduced to simultaneously measure the surface temperature and the heat flux, which are hard to do otherwise. Experiments on human bodies were performed and the forearm perfusion was estimated and then validated through a constant surface heating experiment. Several issues related to the instrument integration and perfusion measurement were discussed. The instrument was also tested through experiments on nonperfused materials and good results were obtained. These efforts will help to build a compact device for noninvasively measuring the human perfusion, which may have significant applications in future clinics.

Analytical study on bioheat transfer problems with spatial or transient heating on skin surface or inside biological bodies.

Several closed form analytical solutions to the bioheat transfer problems with space or transient heating on skin surface or inside biological bodies were obtained using Green's function method. The solutions were applied to study several selected typical bioheat transfer processes, which are often encountered in cancer hyperthermia, laser surgery, thermal comfort analysis, and tissue thermal parameter estimation. Thus a straightforward way to quantitatively interpret the temperature behavior of living tissues subject to constant, sinusoidal, step, point or stochastic heatings etc. both in volume and on boundary were established. Further solution to the three-dimensional bioheat transfer problems was also given to illustrate the versatility of the present method. Implementations of this study to the practical problems were addressed.