Gallium-Based Liquid Metal Materials for Antimicrobial Applications.

The hazards caused by drug-resistant bacteria are rocketing along with the indiscriminate use of antibiotics. The development of new non-antibiotic antibacterial drugs is urgent. The excellent biocompatibility and diverse multifunctionalities of liquid metal have stimulated the studies of antibacterial application. Several gallium-based antimicrobial agents have been developed based on the mechanism that gallium (a type of liquid metal) ions disorder the normal metabolism of iron ions. Other emerging strategies, such as physical sterilization by directly using LM microparticles to destroy the biofilm of bacteria or thermal destruction via infrared laser irradiation, are gaining increasing attention. Different from traditional antibacterial agents of gallium compounds, the pronounced property of gallium-based liquid metal materials would bring innovation to the antibacterial field. Here, LM-based antimicrobial mechanisms, including iron metabolism disorder, production of reactive oxygen species, thermal injury, and mechanical destruction, are highlighted. Antimicrobial applications of LM-based materials are summarized and divided into five categories, including liquid metal motors, antibacterial fabrics, magnetic field-responsive microparticles, liquid metal films, and liquid metal polymer composites. In addition, future opportunities and challenges towards the development and application of LM-based antimicrobial materials are presented.

Flexible Wearables for Plants.

The excellent stretchability and biocompatibility of flexible sensors have inspired an emerging field of plant wearables, which enable intimate contact with the plants to continuously monitor the growth status and localized microclimate in real-time. Plant flexible wearables provide a promising platform for the development of plant phenotype and the construction of intelligent agriculture via monitoring and regulating the critical physiological parameters and microclimate of plants. Here, the emerging applications of plant flexible wearables together with their pros and cons from four aspects, including physiological indicators, surrounding environment, crop quality, and active control of growth, are highlighted. Self-powered energy supply systems and signal transmission mechanisms are also elucidated. Furthermore, the future opportunities and challenges of plant wearables are discussed in detail.

Low-Temperature Triggered Shape Transformation of Liquid Metal Microdroplets.

Shape transformable materials that can respond to external environments have attracted widespread interest over the fields of soft robotics, flexible electronics, and tissue engineering. Among stimuli-responsive materials, liquid metals exhibit rather unique characteristics of versatile morphological changes upon diverse stimuli, including chemicals, electrical field, and mechanical force, etc. Herein, a superfast (few milliseconds), large-scaled (13.8% deformation increase), and fierce (cracks formation) transformation of liquid metal microdroplets (LMMs) with strong impulse expanded force due to liquid-solid phase transition in a dual fluid system composed of LMMs and aqueous solution is reported. When subject to low-temperature stimulus, LMM would transform from ellipsoidal shape to amorphous shape induced by thermal stress, driving the shape morphing. Furthermore, the phase changes of LMMs as well as the formation of surrounding ice crystals are proven to be responsible for this phenomenal behavior. The densification of ice crystals is demonstrated to play a significant role in the transformable behavior. In particular, these nonconductive LMMs in aqueous solutions are discovered to turn into conducive materials with an impedance change of about 105 times. The present discovery is of fundamental and practical significance, and would open new venues in fields such as fluid mechanics, thermal science, flexible electronics, biomedicine, and so forth.

Large-Magnitude Transformable Liquid-Metal Composites.

Most of the existing robots would find it difficult to stretch and transform all parts of their body together due to rigid components and complex actuation mechanisms inside. Here, we presented a highly transformable liquid-metal composite (LMC) that is easy to change shape in large magnitude and resume its original state again according to need. When subject to heating, part of the ethanol droplets embedded in the composite would change phase and then actuate. We demonstrate the flexible transformation of LMC-made octopus from a two-dimensional shape into several predictable three-dimensional shapes freely on a large scale (even up to 11 times its initial height) through remote wireless heating, which needs no sophisticated operating system at all. Further, several designed behaviors, such as movement of octopus and entangling objects of soft robots, are also realized. Theoretical analysis of the heating-induced liquid-vapor transition of the embedded ethanol droplet interprets the mechanisms involved. The present findings open a new way to fabricate functional transformable composites that would find significant applications in developing future generation soft robots.

Computational study of the effects of arterial bifurcation on the temperature distribution during cryosurgery.

BACKGROUND: Thermally significant blood flows into locally cooled diseased tissues and warm them during cryosurgery so that the iceball is often hard to cover the whole diseased volume. This paper is aimed at investigating the effects of large arterial bifurcation on the temperature distribution during cryosurgery through simulation method. METHODS: A parametric geometry model is introduced to construct a close-to-real arterial bifurcation. The three-dimensional transient conjugate heat transfer between bifurcated artery and solid tissues with phase change during cryosurgery is performed by finite volume method. RESULTS: The discussion was then made on the effects of the relative position between cryoprobe and artery bifurcation, the inlet velocity of root artery and the layout of multiple cryoprobes on the temperature distribution and iceball evolution. The results show that the thermal interaction between blood flow and iceball growth near bifurcation is considerable complex. The thermal effects of bifurcation could modulate the iceball morphology, severely weaken its freezing volume and prevent the blood vessel from being frozen. CONCLUSION: The present work is expected to be valuable in optimizing cryosurgery scheme of the situation that the bifurcated artery is embedded into the disease tissue.

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.

Cryobiological Characteristics of L-proline in Mammalian Oocyte Cryopreservation.

BACKGROUND: L-proline is a natural, nontoxic cryoprotectant that helps cells and tissues to tolerate freezing in a variety of plants and animals. The use of L-proline in mammalian oocyte cryopreservation is rare. In this study, we explored the cryobiological characteristics of L-proline and evaluated its protective effect in mouse oocyte cryopreservation. METHODS: The freezing property of L-proline was detected by Raman spectroscopy and osmometer. Mature oocytes obtained from 8-week-old B6D2F1 mice were vitrified in a solution consisting various concentration of L-proline with a reduced proportion of dimethyl sulfoxide (DMSO) and ethylene glycol (EG), comparing with the control group (15% DMSO and 15% EG without L-proline). The survival rate, 5-methylcytosine (5-mC) expression, fertilization rate, two-cell rate, and blastocyst rate in vitro were assessed by immunofluorescence and in vitro fertilization. Data were analyzed by Chi-square test. RESULTS: L-proline can penetrate the oocyte membrane within 1 min. The osmotic pressure of 2.00 mol/L L-proline mixture is similar to that of the control group. The survival rate of the postthawed oocyte in 2.00 mol/L L-proline combining 7.5% DMSO and 10% EG is significantly higher than that of the control group. There is no difference of 5-mC expression between the L-proline combination groups and control. The fertilization rate, two-cell rate, and blastocyst rate in vitro from oocyte vitrified in 2.00 mol/L L-proline combining 7.5% DMSO and 10% EG solution are similar to that of control. CONCLUSIONS: It indicated that an appropriate concentration of L-proline can improve the cryopreservation efficiency of mouse oocytes with low concentrations of DMSO and EG, which may be applicable to human oocyte vitrification.

L-proline: a highly effective cryoprotectant for mouse oocyte vitrification.

Recent studies have shown that L-proline is a natural osmoprotectant and an antioxidant to protect cells from injuries such as that caused by freezing and thawing in many species including plant, ram sperm and human endothelial cells. Nevertheless, this nontoxic cryoprotectant has not yet been applied to mammalian oocyte vitrification. In this study we evaluated the efficiency and safety of the new cryoprotectant in oocyte vitrification. The results indicated that L-proline improves the survival rate of vitrified oocytes, protects mitochondrial functions and could be applied as a new cryoprotectant in mouse oocyte vitrification.

An efficient thermal evolution model for cryoablation with arbitrary multi-cryoprobe configuration.

Cryoablation has been demonstrated powerful in treating of a variety of diseases, especially for the tumor ablation, which destroys the target tissue through the controlled freezing of cryoprobe. The prediction of temperature evolution during cryoablation is of great importance for developing and improving clinical procedure. This paper presented an efficient thermal model to characterize the freezing effect of cryoprobe with arbitrary layout including its size, orientation and number. The key step of the presented model is to establish a boundary heat source method to implicitly characterize the heat transfer from cryoprobe with fixed temperature or convective heat transfer boundary condition, which is furthermore incorporated to a fast parallel alternating direction explicit (PADE) finite difference method for computation acceleration. A novel dynamical and conformal computational region is designed through the shortest distance definition to balance the thermal effect of tissue and computational efficiency. The detailed test cases including a real head tissue demonstrated that the current model can accurately predict the temperature field evolution induced by arbitrary multi-cryoprobe configuration, and achieve significant computational ability due to allowable large time step (100-fold compared with the explicit finite difference method), compact computational region (at least reducing 40% number of voxels) and high parallel efficiency (speedup ratio about 8 for 12 threads) for complex tissue structure.

Personal electronics printing via tapping mode composite liquid metal ink delivery and adhesion mechanism.

Printed electronics is becoming increasingly important in a variety of newly emerging areas. However, restricted to the rather limited conductive inks and available printing strategies, the current electronics manufacture is usually confined to industry level. Here, we show a highly cost-effective and entirely automatic printing way towards personal electronics making, through introducing a tapping-mode composite fluid delivery system. Fundamental mechanisms regarding the reliable printing, transfer and adhesion of the liquid metal inks on the substrate were disclosed through systematic theoretical interpretation and experimental measurements. With this liquid metal printer, a series of representative electronic patterns spanning from single wires to desired complex configurations such as integrated circuit (IC), printed-circuits-on-board (PCB), electronic paintings, or more do-it-yourself (DIY) devices, were demonstrated to be printed out with high precision in a moment. And the total machine cost already reached personally affordable price. This is hard to achieve by a conventional PCB technology which generally takes long time and is material, water and energy consuming, while the existing printed electronics is still far away from the real direct printing goal. The present work opens the way for large scale personal electronics manufacture and is expected to generate important value for the coming society.

Numerical simulations on conformable laser-induced interstitial thermotherapy through combined use of multi-beam heating and biodegradable nanoparticles.

Clinically, precisely heating and thus completely ablating diseased tumor tissue through laser beam is still facing many technical challenges. In this study, numerical simulation of a conformal heating modality based on multi-beam laser along with biodegradable magnesium nanoparticles (Mg-NPs) was put forward to treat liver tumor with large size or irregular shape. Further, a Gaussian-like distribution was proposed to investigate the influence of Mg-NP deposition on the nanoenhanced laser-induced interstitial thermotherapy (LITT). A temperature feedback system was adopted to control the temperature range to avoid overheating. To preliminarily validate the heating enhancement induced by the applied multi-beam laser and Mg-NPs, a conceptual experiment was performed. Both theoretical simulation and experimental measurements demonstrated that multi-beam laser with Mg-NPs could improve efficiency in the conformal heating of tumors with irregular shape or large size. In addition, the distribution and content of Mg-NPs produced significant impact on thermotherapy: (1) The adjustable parameter σ in the Gaussian-like distribution could reflect various practical situations and diffusivities of Mg-NPs; (2) under the premise of the same concentration of Mg-NPs and short time to heat a small-sized target, the whole liver tumor containing Mg-NPs could not improve the efficiency as the nanoparticles limited the photons to be absorbed only around the fibers, while liver tumor partially containing Mg-NPs could improve the thermotherapy efficiency up to 20 %; and (3) the addition of Mg-NPs was rather beneficial for realizing a conformal heating as the residual thermal energy was much less than that without Mg-NPs. This study suggests a feasible and promising modality for planning a high-performance LITT in future clinics.

MRI-based three-dimensional thermal physiological characterization of thyroid gland of human body.

This article is dedicated to present a MRI (magnetic resonance imaging) based three-dimensional finite element modeling on the thermal manifestations relating to the pathophysiology of thyroid gland. An efficient approach for identifying the metabolic dysfunctions of thyroid has also been demonstrated through tracking the localized non-uniform thermal distribution or enhanced dynamic imaging. The temperature features over the skin surface and thyroid domain have been characterized using the numerical simulation and experimental measurement which will help better interpret the thermal physiological mechanisms of the thyroid under steady-state or water-cooling condition. Further, parametric simulations on the hypermetabolism symptoms of hyperthyroidism and thermal effects within thyroid domain caused by varying breathing airflow in the trachea and blood-flow in artery and vein were performed. It was disclosed that among all the parameters, the airflow volume has the largest effect on the total heat flux of thyroid surface. However, thermal contributions caused by varying the breathing frequency and blood-flow velocity are negligibly small. The present study suggests a generalized way for simulating the close to reality physiological behavior or process of human thyroid, which is of significance for disease diagnosis and treatment planning.

Anatomical model-based finite element analysis of the combined cryosurgical and hyperthermic ablation for knee bone tumor.

This paper is aimed at investigating the capacity of using combined cryosurgical and hyperthermic modality for treating knee bone tumor with complex shape. An anatomical model for human knee was constructed and a three-dimensional (3D) finite element analysis was developed to determine temperature distribution of the tissues subject to single freezing (SF), single heating (SH) and alternate freezing-heating (AFH), respectively. The heat fluxes of the probes wall and the ablation volume are particularly tracked to comparatively evaluate the ablation ability of different probe configurations with varied diameter, number and active working length. As example, an effective conformal treatment strategy via one time's insertion while cyclic freezing-heating using multiple probes is designed for a predefined knee bone tumor ablation. Both SF and SH could create large enough ablation volume, while it is hard for them to perform a conformal treatment on irregular and slender knee tumor. As an alternative, AFH could form a flexible and controlled shape and volume of the ablation by changing the size and number of the probes and adjusting their insertion depth. In addition, a thermal protection method is considered to reduce cryoinjury of the health tissue.

Computational study of thermal effects of large blood vessels in human knee joint.

This paper is dedicated to present a comprehensive investigation on the thermal effects of large blood vessels of human knee joint during topical cooling and fomentation treatment. A three-dimensional (3D) finite element analysis by taking full use of the anatomical CAD model of human knee joint was developed to accurately simulate the treatment process. Based on the classical Pennes bio-heat transfer equation, the time evolution of knee joint's temperature distribution and heat flux from large blood vessels was obtained. In addition, we compared several influencing factors and obtained some key conclusions which cannot be easily acquired through clinical experiments. The results indicated that the thermal effects of large blood vessels could remarkably affect the temperature distribution of knee joint during treatment process. Fluctuations of blood flow velocity and metabolic heat production rate affect little on the thermal effects of large blood vessels. Changing the temperature of blood and regimes of treatment could effectively regulate this phenomenon, which is important for many physiological activities. These results provide a guideline to the basic and applied research for the thermally significant large blood vessels in the knee organism.

A new nano-cryosurgical modality for tumor treatment using biodegradable MgO nanoparticles.

A new conceptual modality for nano-cryosurgical ablation of tumors is proposed in this article. The main strategy is to apply MgO nanoparticles (NPs), which are nontoxic, biodegradable, and have few side-effects on the human body, to mediate the freezing procedure effectively. Detailed investigation via animal experiments and nucleation analysis demonstrated that delivery of MgO NPs into the target tissues would significantly improve the cryosurgical outcome. The formation of an iceball during the freezing process is accelerated and enlarged due to the excellent thermal properties of MgO NPs. In addition this method could promote the generation of ice nuclei and thus enhance cryoinjury to the target cells. Therefore, combining the biodegradability and nontoxicity of MgO NPs with their relatively lightweight properties, excellent thermal properties would help develop a high-performance cryosurgery. These findings may lead to methods for safe and targeted nano-cryosurgery and possibly break through the barriers facing current clinical treatments of cancer. FROM THE CLINICAL EDITOR: Cryosurgery is a promising evolving modality to address malignancies. The work presented in this paper may add a novel concept to the field of nanomedicine by demonstrating that MgO nanoparticles enable more efficient ice-ball formation and cryoinjury in the target tissue.

Characterizing ice crystal growth behavior under electric field using phase field method.

In this article, the microscale ice crystal growth behavior under electrostatic field is investigated via a phase field method, which also incorporates the effects of anisotropy and thermal noise. The multiple ice nuclei's competitive growth as disclosed in existing experiments is thus successfully predicted. The present approach suggests a highly efficient theoretical tool for probing into the freeze injury mechanisms of biological material due to ice formation during cryosurgery or cryopreservation process when external electric field was involved.

Complex-anisotropy-induced pattern formation in bistable media.

A construct of anisotropy in bistable media is adopted to characterize the effects of anisotropy on pattern formation by means of anisotropic line tension. A velocity curvature relation is further derived to account for the anisotropic wave propagations. Stability analysis of transverse perturbations indicates that a sufficiently strong complex anisotropy can induce dynamical instabilities and even lead to a breakup of the wave patterns. Numerical simulations show that complex anisotropy can induce rich spatiotemporal behaviors in bistable media. The results of analysis and simulations demonstrate that this method successfully incorporates complex anisotropy into the reaction diffusion model and has general significance.