Histotripsy: A Method for Mechanical Tissue Ablation with Ultrasound.

Histotripsy is a relatively new therapeutic ultrasound technology to mechanically liquefy tissue into subcellular debris using high-amplitude focused ultrasound pulses. In contrast to conventional high-intensity focused ultrasound thermal therapy, histotripsy has specific clinical advantages: the capacity for real-time monitoring using ultrasound imaging, diminished heat sink effects resulting in lesions with sharp margins, effective removal of the treated tissue, a tissue-selective feature to preserve crucial structures, and immunostimulation. The technology is being evaluated in small and large animal models for treating cancer, thrombosis, hematomas, abscesses, and biofilms; enhancing tumor-specific immune response; and neurological applications. Histotripsy has been recently approved by the US Food and Drug Administration to treat liver tumors, with clinical trials undertaken for benign prostatic hyperplasia and renal tumors. This review outlines the physical principles of various types of histotripsy; presents major parameters of the technology and corresponding hardware and software, imaging methods, and bioeffects; and discusses the most promising preclinical and clinical applications.

Insights from in vivo preclinical cancer studies with histotripsy.

Histotripsy is the first noninvasive, non-ionizing, and non-thermal ablation technique that mechanically fractionates target tissue into acellular homogenate via controlled acoustic cavitation. Histotripsy has been evaluated for various preclinical applications requiring noninvasive tissue removal including cancer, brain surgery, blood clot and hematoma liquefaction, and correction of neonatal congenital heart defects. Promising preclinical results including local tumor suppression, improved survival outcomes, local and systemic anti-tumor immune responses, and histotripsy-induced abscopal effects have been reported in various animal tumor models. Histotripsy is also being investigated in veterinary patients with spontaneously arising tumors. Research is underway to combine histotripsy with immunotherapy and chemotherapy to improve therapeutic outcomes. In addition to preclinical cancer research, human clinical trials are ongoing for the treatment of liver tumors and renal tumors. Histotripsy has been recently approved by the FDA for noninvasive treatment of liver tumors. This review highlights key learnings from in vivo shock-scattering histotripsy, intrinsic threshold histotripsy, and boiling histotripsy cancer studies treating cancers of different anatomic locations and discusses the major considerations in planning in vivo histotripsy studies regarding instrumentation, tumor model, study design, treatment dose, and post-treatment tumor monitoring.

Histological characterization of HIFU lesions.

Background: High intensity focused ultrasound (HIFU) can destroy tissue by thermal ablation which may be accompanied by acoustic cavitation and/or tissue water boiling, but the biological and histological effects of these treatments have not been fully documented. Here, detailed histological analysis over time using well characterized HIFU exposures in in vivo rat livers is described.Methods: Exposures used invoked either (i) thermal, with acoustic cavitation and/or tissue water boiling or (ii) predominantly thermal damage. Cavitation activity was detected using both active and passive methods. Histological assessment involved hematoxylin and eosin (H&E), picrosirius red and immunohistochemical staining.Results: Distinct concentric damage regions were identified after HIFU exposures. The outermost ring showed a red H&E-stained rim that was characterized by hemorrhage. The adjacent inner band appeared white due to increased extracellular spaces. The morphology of the next zone depended on the exposure. Where there was no tissue acoustic cavitation/water boiling, this was the lesion center, in which heat-fixed cells were seen. Where acoustic cavitation/boiling occurred, a centermost zone with irregular holes up to several hundred microns across was seen. Cleaved caspase-3 and Hsp70 staining in the periphery of both types of HIFU exposures was seen within the outermost ring of hemorrhage, where an inflammatory response was also observed. By day 7, a distinct acellular region in the center of the HIFU lesions had been created.Conclusions: These results identify the morphological effects and elucidate the similarities and differences of HIFU-induced thermal lesions in the presence or absence of acoustic cavitation/tissue water boiling.

Computer-Vision- and Deep-Learning-Based Determination of Flow Regimes, Void Fraction, and Resistance Sensor Data in Microchannel Flow Boiling.

The aim of this article is to introduce a novel approach to identifying flow regimes and void fractions in microchannel flow boiling, which is based on binary image segmentation using digital image processing and deep learning. The proposed image processing pipeline uses adaptive thresholding, blurring, gamma correction, contour detection, and histogram comparison to separate vapor from liquid areas, while the deep learning method uses a customized version of a convolutional neural network (CNN) called U-net to extract meaningful features from video frames. Both approaches enabled the automatic detection of flow boiling conditions, such as bubbly, slug, and annular flow, as well as automatic void fraction calculation. Especially CNN demonstrated its ability to deliver fast and dependable results, presenting an appealing substitute to manual feature extraction. The U-net-based CNN was able to segment flow boiling images with a Dice score of 99.1% and classify the above flow regimes with an overall classification accuracy of 91%. In addition, the neural network was able to predict resistance sensor readings from image data and assign them to a flow state with a mean squared error (MSE) < 10-6.

Overcoming the Heat Transfer Paradox: Nano Ridges Induce "Pistol Bubbles" and Reverse the Boiling Curve.

To increase the boiling heat transfer limit, we disrupted the previously nonevaporating region and increased the vaporization activity of "inert" liquid molecules by introducing nano ridges on the boiling surface. This solved the paradox of no heat transfer occurring through the thinnest liquid film in boiling bubbles; thus, the internal heat transfer limit of the bubbles was exceeded. We found that vigorous boiling occurred immediately once the nonevaporating region was activated, and the bubble frequency increased by an order of magnitude, reaching 1186 Hz, which has not been previously reported. With an increase in heat flux, the boiling curve exhibited a "return". We achieved an extremely high bubble frequency by experimentally quantifying the major influence of nonevaporating region disruption on boiling heat transfer. The mechanism behind the generation of the ultrahigh-frequency bubbles was discovered. This study also reveals a new mechanism for the reversed boiling curve.

Heat and mass transfer induced by alternating current during desorption of PAHs from soil using electrical resistance heating.

The transfer of heat and contaminants by alternating current (AC) and the removal mechanism of polycyclic aromatic hydrocarbons (PAHs) in electrical resistance heating (ERH) need further study. The main factors affecting heat transfer and water evaporation in the ERH experiment were studied, and the desorption efficiency, temporal and spatial distribution and kinetic behavior under various conditions were analyzed. The results suggested that moisture content was a necessary condition to ensure effective heating of soil, and soil moisture content above 30% was recommended. Higher voltage intensity and/or ion concentration meant stronger input power, resulting in the rapider heating process and the shorter the boiling time. At a low desorption temperature (about 100°C), the Phe desorption mainly depended on the volatilization of surface Phe and the co-boiling of Phe-water. In ERH, the participation of AC would accelerate the diffusion of pollutants from the internal pores of soil particles and their redistribution with water phase, thus improving the Phe removed by co-boiling. It was noteworthy that AC just greatly promoted solid-liquid mass transfer, but it hardly promoted desorption directly, and the removal still depended on Phe-water co-boiling. The Phe desorption efficiency could be significantly improved from 14.0~18.4% to 59.6~70.8% under the combined action of current strengthening Phe diffusion and co-boiling. Thermogravimetric and product analysis confirmed that no new organic matter was generated, but only Phe entered the gas phase through phase change.

The Relationship Between Molecular Symmetry and Physicochemical Properties Involving Boiling and Melting of Organic Compounds.

OBJECTIVE AND METHODS: The reliable estimation of phase transition physicochemical properties such as boiling and melting points can be valuable when designing compounds with desired physicochemical properties. This study explores the role of external rotational symmetry in determining boiling and melting points of select organic compounds. Using experimental data from the literature, the entropies of boiling and fusion were obtained for 541 compounds. The statistical significance of external rotational symmetry number on entropies of phase change was determined by using multiple linear regression. In addition, a series of aliphatic hydrocarbons, polysubstituted benzenes, and di-substituted napthalenes are used as examples to demonstrate the role of external symmetry on transition temperature. RESULTS: The results reveal that symmetry is not well correlated with boiling point but is statistically significant in melting point. CONCLUSION: The lack of correlation between the boiling point and the symmetry number reflects the fact that molecules have a high degree of rotational freedom in both the liquid and the vapor. On the other hand, the strong relationship between symmetry and melting point reflects the fact that molecules are rotationally restricted in the crystal but not in the liquid. Since the symmetry number is equal to the number of ways that the molecule can be properly oriented for incorporation into the crystal lattice, it is a significant determinant of the melting point.

Understanding of Co-boiling between Organic Contaminants and Water during Thermal Remediation: Effects of Nonequilibrium Heat and Mass Transport.

In situ thermal desorption (ISTD) provides an efficient solution to remediation of soil and groundwater contaminated with nonaqueous phase liquids (NAPLs). Establishing a relationship between the subsurface temperature rise and NAPL removal is significant to reduce energy consumption of ISTD. However, the co-boiling phenomenon between NAPL and water poses a great challenge in developing this relationship due to the nonequilibrium heat and mass transport effects. We performed a systematic experimental investigation into the local temperature rise patterns at different distances from a NAPL pool and under different degrees of superheat by selecting four representative NAPLs (i.e., trichloroethylene, tetrachlorethylene, n-hexane, and n-octane) according to their density and boiling point relative to water. The patterns of temperature rise indicated that the underground temperature field can be divided into three zones: the zone of local thermal equilibrium, the nonequilibrium zone affected by co-boiling, and the zone unaffected by co-boiling. We developed a pattern-recognition-based approach, which considers the effects of local heat and mass transport to establish a qualitative correlation between the temperature rise and NAPL removal. Our results give deeper insights into the understanding of subsurface temperatures in ISTD practice, which can serve as the guideline for more accurate and sustainable remediation.

The histotripsy spectrum: differences and similarities in techniques and instrumentation.

Since its inception about two decades ago, histotripsy - a non-thermal mechanical tissue ablation technique - has evolved into a spectrum of methods, each with distinct potentiating physical mechanisms: intrinsic threshold histotripsy, shock-scattering histotripsy, hybrid histotripsy, and boiling histotripsy. All methods utilize short, high-amplitude pulses of focused ultrasound delivered at a low duty cycle, and all involve excitation of violent bubble activity and acoustic streaming at the focus to fractionate tissue down to the subcellular level. The main differences are in pulse duration, which spans microseconds to milliseconds, and ultrasound waveform shape and corresponding peak acoustic pressures required to achieve the desired type of bubble activity. In addition, most types of histotripsy rely on the presence of high-amplitude shocks that develop in the pressure profile at the focus due to nonlinear propagation effects. Those requirements, in turn, dictate aspects of the instrument design, both in terms of driving electronics, transducer dimensions and intensity limitations at surface, shape (primarily, the F-number) and frequency. The combination of the optimized instrumentation and the bio-effects from bubble activity and streaming on different tissues, lead to target clinical applications for each histotripsy method. Here, the differences and similarities in the physical mechanisms and resulting bioeffects of each method are reviewed and tied to optimal instrumentation and clinical applications.

The thermo-wetting instability driving Leidenfrost film collapse.

Above a critical temperature known as the Leidenfrost point (LFP), a heated surface can suspend a liquid droplet above a film of its own vapor. The insulating vapor film can be highly detrimental in metallurgical quenching and thermal control of electronic devices, but may also be harnessed to reduce drag and generate power. Manipulation of the LFP has occurred mostly through experiment, giving rise to a variety of semiempirical models that account for the Rayleigh-Taylor instability, nucleation rates, and superheat limits. However, formulating a truly comprehensive model has been difficult given that the LFP varies dramatically for different fluids and is affected by system pressure, surface roughness, and liquid wettability. Here, we investigate the vapor film instability for small length scales that ultimately sets the collapse condition at the Leidenfrost point. From a linear stability analysis, it is shown that the main film-stabilizing mechanisms are the liquid-vapor surface tension-driven transport of vapor mass and the evaporation at the liquid-vapor interface. Meanwhile, van der Waals interaction between the bulk liquid and the solid substrate across the vapor phase drives film collapse. This physical insight into vapor film dynamics allows us to derive an ab initio, mathematical expression for the Leidenfrost point of a fluid. The expression captures the experimental data on the LFP for different fluids under various surface wettabilities and ambient pressures. For fluids that wet the surface (small intrinsic contact angle), the expression can be simplified to a single, dimensionless number that encapsulates the wetting instability governing the LFP.

Design and Implementation of a Hardware and Software System for Visual Assessment of Bituminous Coating Quality.

Typically, the quality of the bitumen adhesion in asphalt mixtures is assessed manually by a group of experts who assign subjective ratings to the thickness of the residual bitumen coating on the gravel samples. To automate this process, we propose a hardware and software system for visual assessment of bituminous coating quality, which provides the results both in the form of a discrete estimate compatible with the expert one, and in a more general percentage for a set of samples. The developed methodology ensures static conditions of image capturing, insensitive to external circumstances. This is achieved by using a hardware construction designed to provide capturing the samples at eight different illumination angles. As a result, a generalized image is obtained, in which the effect of highlights and shadows is eliminated. After preprocessing, each gravel sample independently undergoes surface semantic segmentation procedure. Two most relevant approaches of semantic image segmentation were considered: gradient boosting and U-Net architecture. These approaches were compared by both stone surface segmentation accuracy, where they showed the same 77% result and the effectiveness in determining a discrete estimate. Gradient boosting showed an accuracy 2% higher than the U-Net for it and was thereby chosen as the main model when developing the prototype. According to the test results, the evaluation of the algorithm in 75% of cases completely coincided with the expert one, and it had a slight deviation from it in another 22% of cases. The developed solution allows for standardizing the data obtained and contributes to the creation of an interlaboratory digital research database.

Distributed Optical Measurement System for Plate Fin Heat Exchanger.

The acquirement of the flow information in plate-fin heat exchanger (PFHE) is limited by its metal structure and complex flow condition. This work develops a new distributed optical measurement system to obtain flow information and boiling intensity. The system utilizes numerous optical fibers installed at the surface of the PFHE to detect optical signals. The attenuation and fluctuation of the signals reflect the variation of the gas-liquid interfaces and can be further used to estimate the boiling intensity. Practical experiments of flow boiling in PFHE with different heating fluxes have been carried out. The results verify that the measurement system can obtain the flow condition. Meanwhile, according to the results, the boiling development in PFHE can be divided into four stages with the increase in the heating flux, including the unboiling stage, initiation stage, boiling developing stage, and fully developed stage.

Flow Boiling Enhancement Using Three-Dimensional Contact-Line Pinning on Hierarchical Superbiphilic Micro/Nanostructures.

Flow boiling is a promising method for the cooling of sensitive computational and industrial components, facilitating the transportation of large quantities of heat at near-constant temperature and in a small form factor. The prevention of vapor film formation is a fundamental challenge for the enhancement of boiling systems, and an impetus therefore exists for the discovery of new techniques to segregate nucleating bubbles during their formation. Herein, we utilize the strong capillary forces generated by nanostructures to pin the liquid/vapor interface in three dimensions and thereby control the coalescence and flow interactions of developing bubbles. We demonstrate this principle on both symmetrical and asymmetrical superbiphilic microstructures, showing enhancement of peak heat transfer coefficient by 81% and 113%, respectively, when compared to the best superhydrophilic and superhydrophobic analogues. Our approach shows a potential future direction for engineered boiling micro/nanostructures, wherein bubble dynamics are directly manipulated on bespoke, three-dimensional substrates.

Nanomechanical Sensing Using Heater-Integrated Fluidic Resonators.

Micro/nanochannel resonators have been used to measure cells, suspended nanoparticles, or liquids, primarily at or near room temperature while their high temperature operation can offer promising applications such as calorimetric measurements and thermogravimetric analysis. To date, global electrothermal or local photothermal heating mechanisms have been attempted for channel resonators, but both approaches are intrinsically limited by a narrow temperature modulation range, slow heating/cooling, less quantitative heating, or time-consuming optical alignment. Here, we introduce heater-integrated fluidic resonators (HFRs) that enable fast, quantitative, alignment-free, and wide-range temperature modulation and simultaneously offer resistive thermometry and resonant densitometry. HFRs with or without a dispensing nozzle are fabricated, thoroughly characterized, and used for high throughput thermophysical properties measurements, microchannel boiling studies, and atomized spray dispensing. The HFR, without a doubt, opens a new avenue for nanoscale thermal analysis and processing and further encourages the integration of additional functions into channel resonators.

The Impact of Different Cooking Methods on the Flavor Profile of Fermented Chinese Spicy Cabbage.

Chinese spicy cabbage (CSC) is a common traditional fermented vegetable mainly made of Chinese cabbage. In addition to eating raw, boiling and stir-frying are the most common cooking methods for CSC. To identify the impacts of boiling or stir-frying on the quality of CSC, the physicochemical properties, flavor compounds, and sensory properties of CSC were analyzed. A total of 47 volatile flavor compounds (VFCs) were detected by gas chromatography-mass spectrometry. Sulfide was determined as the main flavor compound of CSC, mainly contributed by cabbage, garlic, and onion odors. The content of sulfide decreased significantly after cooking. Nonanal, geranyl acetate, and linalool were newly generated after boiling with odor activity value (OAV) > 1, and contributed fatty, sweet, fruity, and floral odors to BL-CSC. 1-Octen-3-one, 1-octen-3-ol, octanal, nonanal, and (E)-2-nonenal were newly generated after stir-frying with OAV > 1, and contributed mushroom, fatty, and green odors to SF-CSC. Diallyl trisulfide, nonanal, (E)-ß-ionone, ß-sesquiphellandrene, and (E)-2-decenal were considered as the potential key aroma compounds (KACs) to distinguish the CSCs after different heat treatment. After cooking, the total titratable acidity of CSC increased and the sensory properties changed significantly. This study provides valuable information and guidance on the sensory and flavor changes of thermal processing fermented vegetables.

Environmental risks of antibiotic resistance genes released from biological laboratories and its control measure.

Antibiotic resistance genes (ARGs) are a growing global threat to public health. Biological laboratory wastewater contains large amounts of free ARGs. It is important to assess the risk of free ARGs from biological laboratories and to find appropriate treatments to control their spread. The fate of plasmids in the environment and the effect of different thermal treatments on their persistence activity were tested. The results showed that untreated resistance plasmids could exist in water for more than 24 h (the special 245 bp fragment). Gel electrophoresis and transformation assays showed that the plasmids boiled for 20 min retained 3.65% ± 0.31% transformation activity of the intact plasmids, while autoclaving for 20 min at 121 °C could effectively degrade the plasmids and that NaCl, bovine serum albumin, and EDTA-2Na affected the degradation efficiency of the plasmids during boiling. In the simulated aquatic system, using 106 copy/µL of plasmids after autoclaving, only 102 copies/µL of the fragment after only 1-2 h could be detected. By contrast, boiled plasmids for 20 min were still detectable after plunging them into water for 24 h. These findings suggest that untreated and boiled plasmids can remain in the aquatic environment for a certain time resulting in the risk of disseminating ARGs. However, autoclaving is an effective way of degrading waste free resistance plasmids.

Effect of Cooking Method and Enzymatic Treatment on the in vitro Digestibility of Cooked and Instant Chestnut Flour.

Microwave treatment, roasting, boiling, and enzymatic treatment were used to prepare cooked and instant chestnut flour, and the in vitro digestibility were compared. Cooking gelatinized the starch and destroyed the granular and crystal structure, increasing starch digestibility. After enzymatic hydrolysis, starches were degraded by 20~24%, and the reducing sugar content of the instant flours increased by 79~94%. Starch digestibility was reduced after enzymatic hydrolysis, however, the estimated glycemic index (GI) increased to 65.1 ~ 77.7 due to the combined effect of increased reducing sugar and decreased starch hydrolysis in the instant flours. The chestnuts treated by 'boiling + enzymes' are still a medium GI food. These findings give guidance for the development of low GI cooked and instant chestnut flour.

Nucleation Process in Explosive Boiling Phenomena of Water on Micro-Platinum Wire.

The maximum temperature limit at which liquid boils explosively is referred to as the superheat limit of liquid. Through various experimental studies on the superheating limit of liquids, rapid evaporation of liquids has been observed at the superheating limit. This study explored the water nucleation process at the superheat limit achieved in micro-platinum wires using a molecular interaction model. According to the molecular interaction model, the nucleation rate and time delay at 576.2 K are approximately 2.1 × 1011/(µm3µs) and 5.7 ns, respectively. With an evaporation rate (116.0 m/s) much faster than that of hydrocarbons (14.0 m/s), these readings show that explosive boiling or rapid phase transition from liquid to vapor can occur at the superheat limit of water. Subsequent bubble growth after bubble nucleation was also considered.

Laser Interstitial Thermotherapy in Surgical Treatment of Vascular Anomalies.

The effects of subcooled boiling of water and blood in the experimental cuvette and rabbit hepatic vessels under the influence of optical fiber-guided continuous IR laser radiation (1.94 µm) were studied using optical methods and ultrasonic diagnostics near the tip of the laser optical fiber. The liver was chosen as a model of vascular abnormality with a conglomerate of blood vessels. In the proposed approach, modification (obliteration and coagulation) of the vascular anomalies occurred as a result of intense subcooled boiling of the blood with generation of heated submerged jets.

Hot isopropanol quenching procedure for automated microtiter plate scale 13C-labeling experiments.

BACKGROUND: Currently, the generation of genetic diversity for microbial cell factories outpaces the screening of strain variants with omics-based phenotyping methods. Especially isotopic labeling experiments, which constitute techniques aimed at elucidating cellular phenotypes and supporting rational strain design by growing microorganisms on substrates enriched with heavy isotopes, suffer from comparably low throughput and the high cost of labeled substrates. RESULTS: We present a miniaturized, parallelized, and automated approach to 13C-isotopic labeling experiments by establishing and validating a hot isopropanol quenching method on a robotic platform coupled with a microbioreactor cultivation system. This allows for the first time to conduct automated labeling experiments at a microtiter plate scale in up to 48 parallel batches. A further innovation enabled by the automated quenching method is the analysis of free amino acids instead of proteinogenic ones on said microliter scale. Capitalizing on the latter point and as a proof of concept, we present an isotopically instationary labeling experiment in Corynebacterium glutamicum ATCC 13032, generating dynamic labeling data of free amino acids in the process. CONCLUSIONS: Our results show that a robotic liquid handler is sufficiently fast to generate informative isotopically transient labeling data. Furthermore, the amount of biomass obtained from a sub-milliliter cultivation in a microbioreactor is adequate for the detection of labeling patterns of free amino acids. Combining the innovations presented in this study, isotopically stationary and instationary automated labeling experiments can be conducted, thus fulfilling the prerequisites for 13C-metabolic flux analyses in high-throughput.