Overview of experimental studies of biological effects of medical ultrasound caused by gas body activation and inertial cavitation

Comprehensive assessment of blood-brain barrier opening and sterile inflammatory response: unraveling the therapeutic window

Microbubbles (MBs) combined with focused ultrasound (FUS) has emerged as a promising noninvasive technique to permeabilize the blood-brain barrier (BBB) for drug delivery into the brain. However, the safety and biological consequences of BBB opening (BBBO) remain incompletely understood. This study aims to investigate the effects of two parameters mediating BBBO: microbubble volume dose (MVD) and mechanical index (MI). High-resolution MRI-guided FUS was employed in mouse brains to assess BBBO by manipulating these two parameters. Afterward, the sterile inflammatory response (SIR) was studied 6 h post-FUS treatment. Results demonstrated that both MVD and MI significantly influenced the extent of BBBO, with higher MVD and MI leading to increased permeability. Moreover, RNA sequencing revealed upregulation of major inflammatory pathways and immune cell infiltration after BBBO, indicating the presence and extent of SIR. Gene set enrichment analysis identified 12 gene sets associated with inflammatory responses that were significantly upregulated at higher MVD or MI. A therapeutic window was established between therapeutically relevant BBBO and the onset of SIR, providing operating regimes to avoid damage from stimulation of the NFκB pathway via TNFɑ signaling to apoptosis. These results contribute to the optimization and standardization of BBB opening parameters for safe and effective drug delivery to the brain and further elucidate the underlying molecular mechanisms driving sterile inflammation.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

Efficient ultrasound-mediated drug delivery to orthotopic liver tumors - Direct comparison of doxorubicin-loaded nanobubbles and microbubbles

Liver metastasis is a major obstacle in treating aggressive cancers, and current therapeutic options often prove insufficient. To overcome these challenges, there has been growing interest in ultrasound-mediated drug delivery using lipid-shelled microbubbles (MBs) and nanobubbles (NBs) as promising strategies for enhancing drug delivery to tumors. Our previous work demonstrated the potential of Doxorubicin-loaded C3F8 NBs (hDox-NB, 280 ± 123 nm) in improving cancer treatment in vitro using low-frequency unfocused therapeutic ultrasound (TUS). In this study, we investigated the pharmacokinetics and biodistribution of sonicated hDox-NBs in orthotopic rat liver tumors. We compared their delivery and therapeutic efficiency with size-isolated MBs (hDox-MB, 1104 ± 373 nm) made from identical shell material and core gas. Results showed a similar accumulation of hDox in tumors treated with hDox-MBs and unfocused therapeutic ultrasound (hDox-MB + TUS) and hDox-NB + TUS. However, significantly increased apoptotic cell death in the tumor and fewer off-target apoptotic cells in the normal liver were found upon the treatment with hDox-NB + TUS. The tumor-to-liver apoptotic ratio was elevated 9.4-fold following treatment with hDox-NB + TUS compared to hDox-MB + TUS, suggesting that the therapeutic efficacy and specificity are significantly increased when using hDox-NB + TUS. These findings highlight the potential of this approach as a viable treatment modality for liver tumors. By elucidating the behavior of drug-loaded bubbles in vivo, we aim to contribute to developing more effective liver cancer treatments that could ultimately improve patient outcomes and decrease off-target side effects.

Micro/nanosystems for controllable drug delivery to the brain

Drug delivery to the brain is crucial in the treatment for central nervous system disorders. While significant progress has been made in recent years, there are still major challenges in achieving controllable drug delivery to the brain. Unmet clinical needs arise from various factors, including controlled drug transport, handling large drug doses, methods for crossing biological barriers, the use of imaging guidance, and effective models for analyzing drug delivery. Recent advances in micro/nanosystems have shown promise in addressing some of these challenges. These include the utilization of microfluidic platforms to test and validate the drug delivery process in a controlled and biomimetic setting, the development of novel micro/nanocarriers for large drug loads across the blood-brain barrier, and the implementation of micro-intervention systems for delivering drugs through intraparenchymal or peripheral routes. In this article, we present a review of the latest developments in micro/nanosystems for controllable drug delivery to the brain. We also delve into the relevant diseases, biological barriers, and conventional methods. In addition, we discuss future prospects and the development of emerging robotic micro/nanosystems equipped with directed transportation, real-time image guidance, and closed-loop control.

Mucus-Permeable Sonodynamic Therapy Mediated Amphotericin B-Loaded PEGylated PLGA Nanoparticles Enable Eradication of Candida albicans Biofilm

Background

Candida albicans (C. albicans) forms pathogenic biofilms, and the dense mucus layer secreted by the epithelium is a major barrier to the traditional antibiotic treatment of mucosa-associated C. albicans infections. Herein, we report a novel anti-biofilm strategy of mucus-permeable sonodynamic therapy (mp-SDT) based on ultrasound (US)-mediated amphotericin B-loaded PEGylated PLGA nanoparticles (AmB-NPs) to overcome mucus barrier and enable the eradication of C. albicans biofilm.

Methods

AmB-NPs were fabricated using ultrasonic double emulsion method, and their physicochemical and sonodynamic properties were determined. The mucus and biofilm permeability of US-mediated AmB-NPs were further investigated. Moreover, the anti-biofilm effect of US-mediated AmB-NPs treatment was thoroughly evaluated on mucus barrier abiotic biofilm, epithelium-associated biotic biofilm, and C. albicans-induced rabbit vaginal biofilms model. In addition, the ultrastructure and secreted cytokines of epithelial cells and the polarization of macrophages were analyzed to investigate the regulation of local cellular immune function by US-mediated AmB-NPs treatment.

Results

Polymeric AmB-NPs display excellent sonodynamic performance with massive singlet oxygen (1O2) generation. US-mediated AmB-NPs could rapidly transport through mucus and promote permeability in biofilms, which exhibited excellent eradicating ability to C. albicans biofilms. Furthermore, in the vaginal epithelial cells (VECs)-associated C. albicans biofilm model, the mp-SDT scheme showed the strongest biofilm eradication effect, with up to 98% biofilm re-formation inhibition rate, improved the ultrastructural damage, promoted local immune defense enhancement of VECs, and regulated the polarization of macrophages to the M1 phenotype to enhance macrophage-associated antifungal immune responses. In addition, mp-SDT treatment exhibited excellent therapeutic efficacy against C. albicans-induced rabbit vaginitis, promoted the recovery of mucosal epithelial ultrastructure, and contributed to the reshaping of a healthier vaginal microbiome.

Conclusion

The synergistic anti-biofilm strategies of mp-SDT effectively eradicated C. albicans biofilm and simultaneously regulated local antifungal immunity enhancement, which may provide a new approach to treat refractory drug-resistant biofilm-associated mucosal candidiasis.

Comprehensive Assessment of Blood-Brain Barrier Opening and Sterile Inflammatory Response: Unraveling the Therapeutic Window

Microbubbles (MBs) combined with focused ultrasound (FUS) have emerged as a promising noninvasive technique to permeabilize the blood-brain barrier (BBB) for drug delivery to the brain. However, the safety and biological consequences of BBB opening remain incompletely understood. This study investigates the effects of varying microbubble volume doses (MVD) and ultrasound mechanical indices (MI) on BBB opening and the sterile inflammatory response (SIR) using high-resolution ultra-high field MRI-guided FUS in mouse brains. The results demonstrate that both MVD and MI significantly influence the extent of BBB opening, with higher doses and mechanical indices leading to increased permeability. Moreover, RNA sequencing reveals upregulated inflammatory pathways and immune cell infiltration after BBB opening, suggesting the presence and extent of SIR. Gene set enrichment analysis identifies 12 gene sets associated with inflammatory responses that are upregulated at higher doses of MVD or MI. A therapeutic window is established between significant BBB opening and the onset of SIR, providing operating regimes for avoiding each three classes of increasing damage from stimulation of the NFκB pathway via TNFL signaling to apoptosis. This study contributes to the optimization and standardization of BBB opening parameters for safe and effective drug delivery to the brain and sheds light on the underlying molecular mechanisms of the sterile inflammatory response.

Significance Statement

The significance of this study lies in its comprehensive investigation of microbubble-facilitated focused ultrasound for blood-brain barrier (BBB) opening. By systematically exploring various combinations of microbubble volume doses and ultrasound mechanical indices, the study reveals their direct impact on the extent of BBB permeability and the induction of sterile inflammatory response (SIR). The establishment of a therapeutic window between significant BBB opening and the onset of SIR provides critical insights for safe and targeted drug delivery to the brain. These findings advance our understanding of the biological consequences of BBB opening and contribute to optimizing parameters for clinical applications, thus minimizing potential health risks, and maximizing the therapeutic potential of this technique.

Acoustic radiation force impulse-induced lung hemorrhage: investigating the relationship with peak rarefactional pressure amplitude and mechanical index in rabbits

PURPOSE

The safety of acoustic radiation force impulse (ARFI) elastography, which applies higher acoustic power with a longer pulse duration (PD) than conventional diagnostic ultrasound, is yet to be verified. We assessed the ARFI-induced lung injury risk and its relationship with peak rarefactional pressure amplitude (PRPA) and mechanical index (MI).

METHODS

Eighteen and two rabbits were included in the ARFI (0.3-ms push pulses) and sham groups, respectively. A 5.2-MHz linear probe was applied to the subcostal area and aimed at both lungs through the liver for 30 ARFI emissions. The derated PRPA varied among the six ARFI groups-0.80 MPa, 1.13 MPa, 1.33 MPa, 1.70 MPa, 1.91 MPa, and 2.00 MPa, respectively.

RESULTS

The occurrence of lung hemorrhage and the mean lesion area among all samples in the seven groups were 0/6, 0/6, 1/6 (1.7 mm2), 4/6 (8.0 mm2), 4/6 (11.2 mm2), 5/6 (23.8 mm2), and 0/4 (sham), respectively. Logistic regression analysis showed that derated PRPA was significantly associated with lung injury occurrence (odds ratio: 207, p < 0.01), with the threshold estimated to be 1.1 MPa (MI, 0.5). Spearman's rank correlation showed a positive correlation between derated PRPA and lesion area (r = 0.671, p < 0.01).

CONCLUSION

This study demonstrated that the occurrence and severity of ARFI-induced lung hemorrhage increased with a rise in PRPA under clinical conditions in rabbits. This indicates a potential risk of lung injury due to ARFI elastography, especially when ARFI is unintentionally directed to the lungs during liver, heart, or breast examinations.

An optical and acoustic investigation of microbubble cavitation in small channels under therapeutic ultrasound conditions

Therapeutic focused ultrasound in combination with encapsulated microbubbles is being widely investigated for its ability to elicit bioeffects in the microvasculature, such as transient permeabilization for drug delivery or at higher pressures to achieve 'antivascular' effects. While it is well established that the behaviors of microbubbles are altered when they are situated within sufficiently small vessels, there is a paucity of data examining how the bubble population dynamics and emissions change as a function of channel (vessel) diameter over a size range relevant to therapeutic ultrasound, particularly at pressures relevant to antivascular ultrasound. Here we use acoustic emissions detection and high-speed microscopy (10 kframes/s) to examine the behavior of a polydisperse clinically employed agent (Definity®) in wall-less channels as their diameters are scaled from 1200 to 15 µm. Pressures are varied from 0.1 to 3 MPa using either a 5 ms pulse or a sequence of 0.1 ms pulses spaced at 1 ms, both of which have been previously employed in an in vivo context. With increasing pressure, the 1200 µm channel - on the order of small arteries and veins - exhibited inertial cavitation, 1/2 subharmonics and 3/2 ultraharmonics, consistent with numerous previous reports. The 200 and 100 µm channels - in the size range of larger microvessels less affected by therapeutic focused ultrasound - exhibited a distinctly different behavior, having muted development of 1/2 subharmonics and 3/2 ultraharmonics and reduced persistence. These were associated with radiation forces displacing bubbles to the distal wall and inducing clusters that then rapidly dissipated along with emissions. As the diameter transitioned to 50 and then 15 µm - a size regime that is most relevant to therapeutic focused ultrasound - there was a higher threshold for the onset of inertial cavitation as well as subharmonics and ultraharmonics, which importantly had more complex orders that are not normally reported. Clusters also occurred in these channels (e.g. at 3 MPa, the mean lateral and axial sizes were 23 and 72 µm in the 15 µm channel; 50 and 90 µm in the 50 µm channel), however in this case they occupied the entire lumens and displaced the wall boundaries. Damage to the 15 µm channel was observed for both pulse types, but at a lower pressure for the long pulse. Experiments conducted with a 'nanobubble' (<0.45 µm) subpopulation of Definity followed broadly similar features to 'native' Definity, albeit at a higher pressure threshold for inertial cavitation. These results provide new insights into the behavior of microbubbles in small vessels at higher pressures and have implications for therapeutic focused ultrasound cavitation monitoring and control.

Dual-frequency ultrasound enhances functional neuron differentiation from neural stem cells by modulating Ca2+ dynamics and the ERK1/2 signaling pathway

Our previous study demonstrated that ultrasound is able to promote differentiation on neural stem cells (NSCs), and dual-frequency ultrasound promotes this effect due to enhanced acoustic cavitation compared with single-frequency ultrasound. However, the underlying biological reasons have not been well disclosed. The purpose of this study was to investigate the underlying bioeffects, mechanisms and signaling pathways of dual-frequency ultrasound on NSC differentiation. The morphology, neurite outgrowth, and differentiation percentages were investigated under various dual-frequency simulation parameters with exposure periods varying from 5 to 15 min. Morphological observations identified that dual-frequency ultrasound stimulation promoted ultrasound dose-dependent neurite outgrowth. In particular, cells exposed for 10 min/2 days showed optimal neurite outgrowth and neuron differentiation percentages. In addition, live cell calcium images showed that dual-frequency ultrasound enhanced the internal calcium content of the cells, and calcium ions entering cells from the extracellular environment could be observed. Dual frequency ultrasound exposure enhanced extracellular calcium influx and upregulated extracellular signal-regulated kinases 1/2 (ERK1/2) expression. Observations from immunostaining and protein expression examinations also identified that dual-frequency ultrasound promoted brain-derived neurotrophic factor (BDNF) secretion from astrocytes derived from NSCs. In summary, evidence supports that dual-frequency ultrasound effectively enhances functional neuron differentiation via calcium channel regulation via the downstream ERK1/2 pathway and promotes BDNF secretion to serve as feedback to cascade neuron differentiation. The results may provide an alternative for cell-based therapy in brain injury.

Ultrasound-Mediated Antitumor Therapy via Targeted Acoustic Release Carrier of Carbon Monoxide (TARC-CO)

As one of the most valuable endogenous gas signaling molecules, carbon monoxide (CO) has been demonstrated in numerous studies to show excellent promise in the treatment of diseases, such as cancer. However, for many years, the inherent high affinity of CO for hemoglobin severely impeded the clinical transformation of CO-based treatments. Therefore, the controlled delivery of CO to target tissues has become a common challenge. Herein, an efficient ultrasonic-triggered and targeted CO release strategy was constructed based on a novel targeted acoustic release carrier of carbon monoxide (TARC-CO) that we synthesized in this study. The designed TARC-COs could afford a safe, stable, and ultrasound-guided delivery of CO in vivo by loading a specified dose of CO inside microbubbles, resulting in breast tumor suppression. Taking advantage of the high loading capacity of microbubbles, the unit volume of TARC-CO suspension could encapsulate up to 337.1 ± 8.0 (×10³ ppm) of CO. In addition, the satisfactory ultrasound contrast-enhanced ability of TARC-COs achieved real-time interactive guidance and visual policing of CO delivery. For the in vitro antitumor study, TARC-COs with ultrasonic irradiation were demonstrated to effectively induce mitochondrial dysfunction by reducing mitochondrial membrane potential, leading to the apoptosis of 4T1 cells. In addition, we realized that TARC-CO-based treatment could significantly slow the growth rate of tumors by inducing apoptosis, inhibiting the proliferation of cancer cells, and limiting tumor angiogenesis. In summary, this proof-of-concept study demonstrates the feasibility and tremendous potential of TARC-COs for controlled release of CO, which can be expected to provide new inspirations and a promising perspective for therapy based on active gases.

Ultrasound-mediated blood-brain barrier opening: An effective drug delivery system for theranostics of brain diseases

Blood-brain barrier (BBB) remains a significant obstacle to drug therapy for brain diseases. Focused ultrasound (FUS) combined with microbubbles (MBs) can locally and transiently open the BBB, providing a potential strategy for drug delivery across the BBB into the brain. Nowadays, taking advantage of this technology, many therapeutic agents, such as antibodies, growth factors, and nanomedicine formulations, are intensively investigated across the BBB into specific brain regions for the treatment of various brain diseases. Several preliminary clinical trials also have demonstrated its safety and good tolerance in patients. This review gives an overview of the basic mechanisms, ultrasound contrast agents, evaluation or monitoring methods, and medical applications of FUS-mediated BBB opening in glioblastoma, Alzheimer's disease, and Parkinson's disease.

The promising interplay between sonodynamic therapy and nanomedicine

Sonodynamic therapy (SDT) is a non-invasive approach for cancer treatment in which chemical compounds, named sonosensitizers, are activated by non-thermal ultrasound (US), able to deeply penetrate into the tissues. Despite increasing interest, the underlying mechanisms by which US triggers the sonosensitizer therapeutic activity are not yet clearly elucidate, slowing down SDT clinical application. In this review we will discuss the main mechanisms involved in SDT with particular attention to the sonosensitizers involved for each described mechanism, in order to highlight how much important are the physicochemical properties of the sonosensitizers and their cellular localization to predict their bioeffects. Moreover, we will also focus our attention on the pivotal role of nanomedicine providing the sonodynamic anticancer approach with the ability to shape US-responsive agents to enhance specific sonodynamic effects as the sonoluminescence-mediated anticancer effects. Indeed, SDT is one of the biomedical fields that has significantly improved in recent years due to the increased knowledge of nanosized materials. The shift of the nanosystem from a delivery system for a therapeutic agent to a therapeutic agent in itself represents a real breakthrough in the development of SDT. In doing so, we have also highlighted potential areas in this field, where substantial improvements may provide a valid SDT implementation as a cancer therapy.

Low frequency nanobubble-enhanced ultrasound mechanotherapy for noninvasive cancer surgery

Scaling down the size of microbubble contrast agents to the nanometer level holds the promise for noninvasive cancer therapy. However, the small size of nanobubbles limits the obtained bioeffects as a result of ultrasound cavitation, when operating near the nanobubble resonance frequency. Here we show that coupled with low energy insonation at a frequency of 80 kHz, well below the resonance frequency of these agents, nanobubbles serve as noninvasive therapeutic warheads that trigger potent mechanical effects in tumors following a systemic injection. We demonstrate these capabilities in tissue mimicking phantoms, where a comparison of the acoustic response of micro- and nano-bubbles after insonation at a frequency of 250 or 80 kHz revealed that higher pressures were needed to implode the nanobubbles compared to microbubbles. Complete nanobubble destruction was achieved at a mechanical index of 2.6 for the 250 kHz insonation vs. 1.2 for the 80 kHz frequency. Thus, the 80 kHz insonation complies with safety regulations that recommend operation below a mechanical index of 1.9. In vitro in breast cancer tumor cells, the cell viability was reduced to 17.3 ± 1.7% of live cells. In vivo, in a breast cancer tumor mouse model, nanobubble tumor distribution and accumulation were evaluated by high frequency ultrasound imaging. Finally, nanobubble-mediated low frequency insonation of breast cancer tumors resulted in effective mechanical tumor ablation and tumor tissue fractionation. This approach provides a unique theranostic platform for safe, noninvasive and low energy tumor mechanotherapy.

Ultrasound for Aesthetic Applications: A Review of Biophysical Mechanisms and Safety

Aesthetic ultrasound is used for fat reduction and to improve skin appearance. In this review, the fundamental mechanisms by which ultrasound can alter tissue are outlined. The technologies that are commercially available or under development are discussed. Finally, recommendations are made for safe and effective use of aesthetic ultrasound.

Possible Effects on Health of Ultrasound Exposure, Risk Factors in the Work Environment and Occupational Safety Review

Ultrasonic waves are mechanical waves with a frequency greater than 20,000 Hz. Ultrasonic waves are emitted by devices that are used in industry or that have a medical or aesthetic purpose. There is growing interest in the effect of ultrasound absorption on the human body, since people's exposure to these acoustic waves has increased considerably in recent years. There are more and more devices that emit ultrasounds used for different sanitary procedures, aesthetic treatments and industrial processes, creating more possibilities of ultrasound noise, and therefore an increased risk of occupational hazard and occupational danger. Experiments on animals have shown damage to internal organs from receiving different ultrasonic frequencies. The main task of this work was to organize and summarize recent studies on ultrasound to reflect the current state of this technique and establish a systematic basis for future lines of research. This work has allowed us to better understand the unknown field of these high frequencies of sound, and highlights the need to carry out more studies on the ultrasound emissions that can be absorbed by the human body to determine how this energy could affect humans by calculating the maximum dose of exposure and developing manuals for the use of ultrasound-emitting equipment to protect the health of workers and all people. It is necessary to develop regulations by public administrations to improve the protection of workers, health professionals, patients and all people in general for better occupational safety, indoor environmental quality and environmental health.

Phacoemulsification: Proposals for Improvement in Its Application

A cataract is defined as opacity of the crystalline lens. It is currently one of the most prevalent ocular pathologies and is generally associated with aging. The most common treatment for cataracts is surgery. Cataract surgery is a quick and painless process, is very effective, and has few risks. The operation consists of removing the opacified lens and replacing it with an intraocular lens. The most common intraocular lens removal procedure that is currently used is phacoemulsification. The energy applied in this process is generated by ultrasonic waves, which are mechanical waves with a frequency higher than 20 kHz. A great deal of research on the different ways to perform the stages of this surgical procedure and the analysis of the possible side effects of the operation has been published, but there is little information on the technical characteristics, the intensities applied, and the use of ultrasound-emitting (U/S) equipment for cataract removal. More studies on the method and depth of absorption of ultrasonic waves in our visual system when performing the phacoemulsification procedure are needed. It would be advisable for health authorities and medical professionals to develop guidelines for the handling and use of ultrasonic wave-emitting equipment, such as those that exist for ultrasound and physiotherapy. This could help us to reduce undesirable effects after the operation.

Contrast-enhanced ultrasound: a comprehensive review of safety in children

Contrast-enhanced ultrasound (CEUS) has been increasingly used in pediatric radiology practice worldwide. For nearly two decades, CEUS applications have been performed with the off-label use of gas-containing second-generation ultrasound contrast agents (UCAs). Since 2016, the United States Food and Drug Administration (FDA) has approved the UCA Lumason for three pediatric indications: the evaluation of focal liver lesions and echocardiography via intravenous administration and the assessment of vesicoureteral reflux via intravesical application (contrast-enhanced voiding urosonography, ceVUS). Prior to the FDA approval of Lumason, numerous studies with the use of second-generation UCAs had been conducted in adults and children. Comprehensive protocols for clinical safety evaluations have demonstrated the highly favorable safety profile of UCA for intravenous, intravesical and other intracavitary uses. The safety data on CEUS continue to accumulate as this imaging modality is increasingly utilized in clinical settings worldwide. As of August 2021, 57 pediatric-only original research studies encompassing a total of 4,518 children with 4,906 intravenous CEUS examinations had been published. As in adults, there were a few adverse events; the majority of these were non-serious, although very rarely serious anaphylactic reactions were reported. In the published pediatric-only intravenous CEUS studies included in our analysis, the overall incidence rate of serious adverse events was 0.22% (10/4,518) of children and 0.20% (10/4,906) of all CEUS examinations. Non-serious adverse events from the intravenous CEUS were observed in 1.20% (54/4,518) of children and 1.10% (54/4,906) of CEUS examinations. During the same time period, 31 studies with the intravesical use of UCA were conducted in 12,362 children. A few non-serious adverse events were encountered (0.31%; 38/12,362), but these were most likely attributable to the bladder catheterization rather than the UCA. Other developing clinical applications of UCA in children, including intracavitary and intralymphatic, are ongoing. To date, no serious adverse events have been reported with these applications. This article reviews the existing pediatric CEUS literature and provides an overview of safety-related information reported from UCA uses in children.

Molecular Imaging-Guided Sonodynamic Therapy

Low-intensity ultrasound-triggered sonodynamic therapy (SDT) is a promising noninvasive therapeutic modality due to its strong tissue penetration ability. In recent years, with the development of nanotechnology, nanoparticle-based sonosensitizer-mediated SDT has been widely investigated. With the increasing demand for precise and personalized treatment, abundant novel sonosensitizers with imaging capabilities have been developed for determining the optimal therapeutic window, thus significantly enhancing treatment efficacy. In this review, we focus on the molecular imaging-guided SDT. The prevalent mechanisms of SDT are discussed, including ultrasonic cavitation, sonoluminescence, reactive oxygen species, and mechanical damage. In addition, we introduce the major molecular imaging techniques and the design principles based on nanoparticles to achieve efficient imaging. Furthermore, the imaging-guided SDT for the treatment of cancer, bacterial infections, and vascular diseases is summarized. The ultimate goal is to design more effective imaging-guided SDT modalities and provide novel ideas for clinical translation of SDT.

Ultrasound-Stimulated Microbubbles Inhibit Aggressive Phenotypes and Promotes Radiosensitivity of esophageal squamous cell carcinoma

Ultrasound (US) is reported to improve the delivery efficiency of drugs loading onto large nanoparticles due to the sonoporation effect. Microbubbles (MBs) can be used as contrast agents of US expanding and contracting under low-amplitude US pressure waves. Ultrasound-stimulated microbubbles (USMBs) therapy is a promising option for the treatment of various cancers as a radiosensitizer. However, its role in esophageal squamous cell carcinoma (ESCC) remains unknown. In our study, human ESCC cell lines (KYSE-410, KYSE-1140) were treated with radiation solely, US alone, or radiation in combination with US or USMBs. The migration and invasion abilities of ESCC cells were examined by wound healing and Transwell assays. ESCC cell apoptosis was assessed using flow cytometry analysis and TUNEL assays. The levels of proteins associated with cell apoptosis and angiogenesis were measured by western blot analysis. A tube formation assay was performed to detect the ESCC cell angiogenesis. We found that USMBs at high levels most effectively most efficiently enhanced the effect of radiation, and significant changes in the viability (48%-51%), proliferation (1%), migration (63%-71%), invasion (52%) and cell apoptosis (31%-50%) of ESCC cells were observed compared with the control group in vitro. The ESCC angiogenesis was inhibited by US or radiation treatment and further inhibited by a combination of radiation and US or USMBs. USMBs at high levels most effectively enhanced the inhibitory effect of radiotherapy on ESCC cell apoptosis. Overall, USMBs enhanced the radiosensitivity of esophageal squamous cell carcinoma cells.Graphical abstractUSMBs treatment enhanced the anti-tumor effect of radiation on ESCC cell proliferation, migration, invasion, angiogenesis and apoptosis in vitro.1USMBs enhance the radiation-induced inhibition on ESCC cell growth2USMBs promote the radiation effect on ESCC cell apoptosis3USMBs enhance radiation-caused suppression on ESCC cell migration and invasion4USMBs enhance the suppression of radiation on ESCC angiogenesis[Figure: see text].

Focused ultrasound enhances the anesthetic effects of topical lidocaine in rats

BACKGROUND

High-intensity ultrasound has been used to induce acoustic cavitation in the skin and subsequently enhances skin permeability to deliver hydrophobic topical medications including lidocaine. In contrast, instead of changing skin permeability, pulsed application of low-intensity focused ultrasound (FUS) has shown to non-invasively and temporarily disrupt drug-plasma protein binding, thus has potential to enhance the anesthetic effects of hydrophilic lidocaine hydrochloride through unbinding it from serum/interstitial α1-acid glycoprotein (AAG).

METHODS

FUS, operating at fundamental frequency of 500 kHz, was applied pulse-mode (55-ms pulse duration, 4-Hz pulse repetition frequency) at a spatial-peak pulse-average intensity of 5 W/cm2. In vitro equilibrium dialysis was performed to measure the unbound concentration of lidocaine (lidocaine hydrochloride) from dialysis cassettes, one located at the sonication focus and the other outside the sonication path, all immersed in phosphate-buffered saline solution containing both lidocaine (10 µg/mL) and human AAG (5 mg/mL). In subsequent animal experiments (Sprague-Dawley rats, n = 10), somatosensory evoked potential (SSEP), elicited by electrical stimulations to the unilateral hind leg, was measured under three experimental conditions-applications of FUS to the unilateral thigh area at the site of administered topical lidocaine, FUS only, and lidocaine only. Skin temperature was measured before and after sonication. Passive cavitation detection was also performed during sonication to evaluate the presence of FUS-induced cavitation.

RESULTS

Sonication increased the unbound lidocaine concentration (8.7 ± 3.3 %) from the dialysis cassette, compared to that measured outside the sonication path (P < 0.001). Application of FUS alone did not alter the SSEP while administration of lidocaine reduced its P23 component (i.e., a positive peak at 23 ms latency). The FUS combined with lidocaine resulted in a further reduction of the P23 component (in a range of 21.8 - 23.4 ms after the electrical stimulations; F(2,27) = 3.2 - 4.0, P < 0.05), indicative of the enhanced anesthetic effect of the lidocaine. Administration of FUS neither induced cavitation nor altered skin conductance or temperature, suggesting that skin permeability was unaffected.

CONCLUSIONS

Unbinding lidocaine from the plasma proteins by exposure to non-thermal low-intensity ultrasound is attributed as the main mechanism behind the observation.

Cerebrospinal Fluid Cavitation as a Mechanism of Blast-Induced Traumatic Brain Injury: A Review of Current Debates, Methods, and Findings

Cavitation has gained popularity in recent years as a potential mechanism of blast-induced traumatic brain injury (bTBI). This review presents the most prominent debates on cavitation; how bubbles can form or exist within the cerebrospinal fluid (CSF) and brain vasculature, potential mechanisms of cellular, and tissue level damage following the collapse of bubbles in response to local pressure fluctuations, and a survey of experimental and computational models used to address cavitation research questions. Due to the broad and varied nature of cavitation research, this review attempts to provide a necessary synthesis of cavitation findings relevant to bTBI, and identifies key areas where additional work is required. Fundamental questions about the viability and likelihood of CSF cavitation during blast remain, despite a variety of research regarding potential injury pathways. Much of the existing literature on bTBI evaluates cavitation based off its prima facie plausibility, while more rigorous evaluation of its likelihood becomes increasingly necessary. This review assesses the validity of some of the common assumptions in cavitation research, as well as highlighting outstanding questions that are essential in future work.

Mechanisms and Applications of Neuromodulation Using Surface Acoustic Waves-A Mini-Review

The study of neurons is fundamental for basic neuroscience research and treatment of neurological disorders. In recent years ultrasound has been increasingly recognized as a viable method to stimulate neurons. However, traditional ultrasound transducers are limited in the scope of their application by self-heating effects, limited frequency range and cavitation effects during neuromodulation. In contrast, surface acoustic wave (SAW) devices, which are producing wavemodes with increasing application in biomedical devices, generate less self-heating, are smaller and create less cavitation. SAW devices thus have the potential to address some of the drawbacks of traditional ultrasound transducers and could be implemented as miniaturized wearable or implantable devices. In this mini review, we discuss the potential mechanisms of SAW-based neuromodulation, including mechanical displacement, electromagnetic fields, thermal effects, and acoustic streaming. We also review the application of SAW actuation for neuronal stimulation, including growth and neuromodulation. Finally, we propose future directions for SAW-based neuromodulation.

Characteristic Blood-Perfusion Reduction of Walker 256 Tumor Induced by Diagnostic Ultrasound and Microbubbles

Tumor angiogenesis is characterized by a defective, leaky and fragile microvascular construction, and microbubble-enhanced ultrasound (MEUS) with high-pressure amplitude is capable of disrupting tumor microvasculature and arresting blood perfusion. In this study, we tried to investigate whether the blood perfusion of a malignant tumor can be characteristically interrupted by combining microbubbles and diagnostic ultrasound (US). Twenty-nine Sprague-Dawley (SD) rats with subcutaneous Walker 256 tumors and seven healthy SD rats were included. Fifteen tumors were treated by MEUS, which combined constant microbubble injection and 20 episodes of irradiation by diagnostic US (i.e., acoustic radiation force impulse [ARFI] imaging). The other 14 tumors were treated by ARFI or sham US only. Seven skeleton muscles from healthy SD rats were also treated with MEUS, serving as the control. Contrast-enhanced ultrasound (CEUS) was performed before and after all treatments. The blood perfusion of the tumor MEUS group showed a significant drop immediately after treatment, followed by a quick, incomplete perfusion recovery within 10-20 min. The visual perfusion scoring result was consistent with the quantitative analysis by CEUS peak intensity. However, there were no significant perfusion changes in the tumor control groups or the muscle control group. Histologic examination found severe microvascular disruption and hemorrhage in the MEUS-treated tumors but not in the control groups. Therefore, the treatment combining diagnostic US and microbubbles can specifically decrease or interrupt the blood perfusion of Walker 256 tumors, which could be a potential new imaging method for diagnosing malignant tumors.

Recent advances in ultrasound-triggered drug delivery through lipid-based nanomaterials

The high prescribed dose of anticancer drugs and their resulting adverse effects on healthy tissue are significant drawbacks to conventional chemotherapy (CTP). Ideally, drugs should have the lowest possible degree of interaction with healthy cells, which would diminish any adverse effects. Therefore, an ideal scenario to bring about improvements in CTP is the use of technological strategies to ensure the efficient, specific, and selective transport and/or release of drugs to the target site. One practical and feasible solution to promote the efficiency of conventional CTP is the use of ultrasound (US). In this review, we highlight the potential role of US in combination with lipid-based carriers to achieve a targeted CTP strategy in engineered smart drug delivery systems.

Ultrasound for the treatment of acute kidney injury and other inflammatory conditions: a promising path toward noninvasive neuroimmune regulation

Acute kidney injury (AKI) is an important clinical disorder with high prevalence, serious consequences, and limited therapeutic options. Modulation of neuroimmune interaction by nonpharmacological methods is emerging as a novel strategy for treating inflammatory diseases, including AKI. Recently, pulsed ultrasound (US) treatment was shown to protect from AKI by stimulating the cholinergic anti-inflammatory pathway. Because of the relatively simple, portable, and noninvasive nature of US procedures, US stimulation may be a valuable therapeutic option for treating inflammatory conditions. This review discusses potential impacts of US bioeffects on the nervous system and how this may generate feedback onto the immune system. We also discuss recent evidence supporting the use of US as a means to treat AKI and other inflammatory diseases.

Pharmacokinetic Modeling of Targeted Ultrasound Contrast Agents for Quantitative Assessment of Anti-Angiogenic Therapy: a Longitudinal Case-Control Study in Colon Cancer

PURPOSE

To evaluate quantitative and semi-quantitative ultrasound molecular imaging (USMI) for antiangiogenic therapy monitoring in human colon cancer xenografts in mice.

PROCEDURES

Colon cancer was established in 17 mice by injection of LS174T (N_r = 9) or CT26 (N_n = 8) cancer cells to simulate clinical responders and non-responders, respectively. Antiangiogenic treatment (bevacizumab; N_rt = N_nt = 5) or control treatment (saline; N_rc = 4, N_nc = 3) was administered at days 0, 3, and 7. Three-dimensional USMI was performed by injection at days 0, 1, 3, 7, and 10 of microbubbles targeted to the vascular endothelial growth factor receptor 2 (VEGFR2). Microbubble binding rate (k_b), estimated by first-pass binding model fitting, and semi-quantitative parameters late enhancement (LE) and differential targeted enhancement (dTE) were compared at each day to evaluate their ability to assess and predict the response to therapy. Correlation analysis with the ex-vivo immunohistological quantification of VEGFR2 expression and the percentage blood vessel area was also performed.

RESULTS

Significant changes in the USMI parameters during treatment were observed only in the responders treated with bevacizumab (p-value < 0.05). Prediction of the response to therapy as early as 1 day after treatment was achieved by the quantitative parameter k_b (p-value < 0.01), earlier than possible by tumor volume quantification. USMI parameters could significantly distinguish between clinical responders and non-responders (p-value << 0.01) and correlated well with the ex-vivo quantification of VEGFR2 expression and the percentage blood vessels area (p-value << 0.01).

CONCLUSION

USMI (semi)quantitative parameters provide earlier assessment of the response to therapy compared to tumor volume, permit early prediction of non-responders, and correlate well with ex-vivo angiogenesis biomarkers.

Effect of scattered pressures from oscillating microbubbles on neuronal activity in mouse brain under transcranial focused ultrasound stimulation

Previous studies have indicated that the presence of microbubbles (MBs) during sonication has an impact on neuronal activity, while the underlying mechanisms remain to be revealed. In this study, a model for the scattered pressures produced by the pulsating lipid-encapsulated MBs in mouse brain was developed to numerically investigate the effect of MBs on neuronal activity during transcranial focused ultrasound stimulation. The additional summed scattered pressure (P_{summed_scat}) from the oscillating MBs was calculated from the model. The level of neuronal activity was experimentally verified using an immunofluorescence assay with antibodies against c-fos. The pressure difference (ΔP) between acoustic pressures at which the same level of neuronal activity is excited by ultrasound stimulation with and without MBs was obtained from the experiments. The results showed that P_{summed_scat} accounts for about half of the ΔP when the MBs experience a "compression-only" response. The P_{summed_scat} suddenly increased at a critical acoustic pressure, around which a rapid enhancement of ΔP obtained from experiment also occurred. This work suggested that the additional scattered pressures from pulsating MBs are probably a mechanism that affects neuronal activity under transcranial focused ultrasound stimulation.

Spatiotemporal Assessment of the Cellular Safety of Cavitation-Based Therapies by Passive Acoustic Mapping

Many useful therapeutic bio-effects can be generated using ultrasound-induced cavitation. However, cavitation is also capable of causing unwanted cellular and vascular damage, which should be monitored to ensure treatment safety. In this work, the unique opportunity provided by passive acoustic mapping (PAM) to quantify cavitation dose across an entire volume of interest during therapy is utilised to provide setup-independent measures of spatially localised cavitation dose. This spatiotemporally quantifiable cavitation dose is then related to the level of cellular damage generated. The cavitation-mediated destruction of equine red blood cells mixed with one of two types of cavitation nuclei at a variety of concentrations is investigated. The blood is placed within a 0.5-MHz ultrasound field and exposed to a range of peak rarefactional pressures up to 2 MPa, with 50 to 50,000 cycle pulses maintaining a 5% duty cycle. Two co-planar linear arrays at 90° to each other are used to generate 400-µm-resolution frequency domain robust capon beamforming PAM maps, which are then used to generate estimates of cavitation dose. A relationship between this cavitation dose and the levels of haemolysis generated was found which was comparable regardless of the applied acoustic pressure, pulse length, cavitation agent type or concentration used. PAM was then used to monitor cellular damage in multiple locations within a tissue phantom simultaneously, with the damage-cavitation dose relationship being similar for the two experimental models tested. These results lay the groundwork for this method to be applied to other measures of safety, allowing for improved ultrasound monitoring of cavitation-based therapies.

The AFSUMB Consensus Statements and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound using Sonazoid

The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.

The AFSUMB Consensus Statements and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound using Sonazoid

The first edition of the guidelines for the use of ultrasound contrast agents was published in 2004, dealing with liver applications. The second edition of the guidelines in 2008 reflected changes in the available contrast agents and updated the guidelines for the liver, as well as implementing some nonliver applications. The third edition of the contrast-enhanced ultrasound (CEUS) guidelines was the joint World Federation for Ultrasound in Medicine and Biology-European Federation of Societies for Ultrasound in Medicine and Biology (WFUMB-EFSUMB) venture in conjunction with other regional US societies such as Asian Federation of Societies for Ultrasound in Medicine and Biology, resulting in a simultaneous duplicate on liver CEUS in the official journals of both WFUMB and EFSUMB in 2013. However, no guidelines were described mainly for Sonazoid due to limited clinical experience only in Japan and Korea. The new proposed consensus statements and recommendations provide general advice on the use of Sonazoid and are intended to create standard protocols for the use and administration of Sonazoid in hepatic and pancreatobiliary applications in Asian patients and to improve patient management.

Catalase-based liposomal for reversing immunosuppressive tumor microenvironment and enhanced cancer chemo-photodynamic therapy

Photodynamic therapy (PDT) and chemotherapy has been applied as a prospective approach in tumor therapeutics. However, suffering from the inherent hypoxia status in tumor microenvironment (TME), the anticancer efficiency is enormously restricted, especially PDT. Herein, we develop a unique liposomal encapsulated catalase (CAT), lyso-targeted NIR photosensitizer (MBDP) and doxorubicin (Dox), forming FA-L@MD@CAT, to increase tumor oxygenation by catalyzing intratumoral high-expressed H₂O₂ for enhancing the combination of chemo-PDT. Moreover, the enhanced tumoral oxygenation not only facilitates singlet oxygen (¹O₂) production but also reverses immunosuppressive TME by modulating immune cytokines to favor antitumor immunities, which significantly induce tumor death. Notably, this system also realizes specific tumor recognition to folate receptor upregulated tumors and improves intratumoral accumulation. This work provides an effective strategy to promote tumor therapeutic index, which may possess a promising future in clinical application.

Enhanced neuronal activity in mouse motor cortex with microbubbles' oscillations by transcranial focused ultrasound stimulation

Microbubbles (MBs) are known to serve as an amplifier of the mechanical effects of ultrasound, which combined with ultrasound are widely used in brain. The goal of this study is to investigate the effect of oscillating MBs on the neuronal activity in the central nervous system (CNS) of mammals. The motor cortex of mice brain was subjected to ultrasound stimulation with and without MBs, and evoked electromyogram signals were recorded. A c-fos immunofluorescence assay was performed to evaluate the neuronal activation in the region of ultrasound stimulation. BBB integrity during ultrasound stimulation with MBs was assessed in this study. Moreover, the safety of ultrasound stimulation with MBs was examined. Using ultrasound at 620 kHz, the injection of MBs significantly increased the success rate of motor response from 0.065 ± 0.06 to 0.28 ± 0.10 when stimulation was applied at 0.12 MPa and from 0.38 ± 0.09 to 0.77 ± 0.18 at 0.25 MPa (p < 0.001). The results of the c-fos immunofluorescence assay showed that the mean densities of c-fos⁺ cells were significantly increased from 15.67 ± 3.51 to 53.01 ± 9.54 at 0.12 MPa acoustic pressure. At 0.25 MPa, the mean density of c-fos + cells was 81 ± 10.97 without MBs and it significantly increased to 124.12 ± 25.71 with MBs (p < 0.05). Enhanced neuronal activities were observed with 0.12 MPa ultrasound stimulation with MBs, while the integrity of BBB was not compromised, but 0.25 MPa ultrasound stimulation with MBs resulted in BBB disruption. These findings reveal that the oscillations of MBs can enhance neuronal activity in the CNS of mammals, and may provide an insight into the application of MBs combined with ultrasound in brain.

Normalization of Tumor Vasculature by Oxygen Microbubbles with Ultrasound

Tumor microenvironment influences the efficacy of anti-cancer therapies. The dysfunctional tumor vasculature limits the efficiency of oxygenation and drug delivery to reduce treatment outcome. A concept of tumor vascular normalization (VN), which inhibits angiogenesis to improve vessel maturity, blood perfusion, and oxygenation, has been demonstrated under the anti-angiogenic therapy. The efficiency of drug delivery and penetration is increased by enhancing perfusion and reducing interstitial fluid pressure during the time window of VN. However, anti-angiogenic agents only induce transient VN and then prune vessels to aggravate tumor hypoxia. To repair tumor vessels without altering vessel density, we proposed to induce tumor VN by local oxygen release via oxygen microbubbles with ultrasound. With tumor perfusion enhancement under ultrasound contrast imaging tracing, the time window of VN was defined as 2-8 days after a single oxygen microbubble treatment. The enhanced tumor oxygenation after oxygen microbubble treatment inhibited hypoxia inducible factor-1 alpha (HIF-1α)/vascular endothelial growth factor (VEGF) pathway to improve the morphology and function of tumor vasculature. The pericyte coverage and Hoechst penetration of tumor vessels increased without any changes to the vessel density. Finally, the intratumoral accumulation of anti-cancer drug doxorubicin could be increased 3-4 folds during tumor VN. These findings demonstrate that regulating tumor oxygenation by oxygen microbubbles could normalize dysfunctional vessels to enhance vascular maturity, blood perfusion, and drug penetration. Furthermore, ultrasound perfusion imaging provides a simple and non-invasive way to detect the VN time window, which increases the feasibility of VN in clinical cancer applications.

Histological and blood chemistry examination of the rodent kidney after exposure to flash-replenishment ultrasound contrast imaging

The purpose of this work is to investigate whether imaging sequences of flash-replenishment contrast enhanced ultrasound (CEUS) of the kidney result in chronic or acute bioeffects. Kidneys of female Fischer 344 rats were imaged using the flash-replenishment technique. Animals were separated into four groups (N = 31). Imaging was conducted with a 4C1 probe, driven by an Acuson Sequoia system with Definity microbubbles as the ultrasound contrast agent. During the flash phase of the imaging sequence, one kidney in each animal was exposed to either a mechanical index (MI) of 1.0 or 1.9. For each MI, half of the animals were sacrificed shortly after imaging (4 h) or after 2 weeks. A blinded veterinary nephropathologist reviewed the histopathology of both the imaged and control (non-imaged) kidney. Blood urea nitrogen (BUN) was measured for each animal prior to imaging and at the time of necropsy. Histopathology assessments in both the 1.0 and 1.9 MI groups revealed no signs of hemorrhage at either the 4-h or 2-week time point. BUN showed minor but statistically significant elevations in both the 1.0 and 1.9 MI groups, but no significant difference was present at the 2-week time point in the 1.0 MI group. All BUN levels (at both time points) remained in the normal range. In conclusion, CEUS with flash-replenishment imaging sequences did not result in kidney bioeffects observable with histology at early or late time points. Increases in BUN levels were observed after imaging, but were minimized when using a moderate MI (1.0).

Biomedical Applications for Gas-Stabilizing Solid Cavitation Agents

For over a decade, advancements in ultrasound-enhanced drug delivery strategies have demonstrated remarkable success in providing targeted drug delivery for a broad range of diseases. In order to achieve enhanced drug delivery, these strategies harness the mechanical effects from bubble oscillations (i.e., cavitation) of a variety of exogenous cavitation agents. Recently, solid cavitation agents have emerged due to their capacity for drug-loading and sustained cavitation duration. Unlike other cavitation agents, solid cavitation agents stabilize gaseous bubbles on hydrophobic surface cavities. Thus, the design of these particles is crucial. In this Review, we provide an overview of the different designs for solid cavitation agents such as nanocups, nanocones, and porous structures, as well as the current status of their development. Considering the numerous advantages of solid cavitation agents, we anticipate further innovations for this new type of cavitation agent across a broad range of biomedical applications.

Applications of Ultrasound to Stimulate Therapeutic Revascularization

Many pathological conditions are characterized or caused by the presence of an insufficient or aberrant local vasculature. Thus, therapeutic approaches aimed at modulating the caliber and/or density of the vasculature by controlling angiogenesis and arteriogenesis have been under development for many years. As our understanding of the underlying cellular and molecular mechanisms of these vascular growth processes continues to grow, so too do the available targets for therapeutic intervention. Nonetheless, the tools needed to implement such therapies have often had inherent weaknesses (i.e., invasiveness, expense, poor targeting, and control) that preclude successful outcomes. Approximately 20 years ago, the potential for using ultrasound as a new tool for therapeutically manipulating angiogenesis and arteriogenesis began to emerge. Indeed, the ability of ultrasound, especially when used in combination with contrast agent microbubbles, to mechanically manipulate the microvasculature has opened several doors for exploration. In turn, multiple studies on the influence of ultrasound-mediated bioeffects on vascular growth and the use of ultrasound for the targeted stimulation of blood vessel growth via drug and gene delivery have been performed and published over the years. In this review article, we first discuss the basic principles of therapeutic ultrasound for stimulating angiogenesis and arteriogenesis. We then follow this with a comprehensive cataloging of studies that have used ultrasound for stimulating revascularization to date. Finally, we offer a brief perspective on the future of such approaches, in the context of both further research development and possible clinical translation.

For Whom the Bubble Grows: Physical Principles of Bubble Nucleation and Dynamics in Histotripsy Ultrasound Therapy

Histotripsy is a focused ultrasound therapy for non-invasive tissue ablation. Unlike thermally ablative forms of therapeutic ultrasound, histotripsy relies on the mechanical action of bubble clouds for tissue destruction. Although acoustic bubble activity is often characterized as chaotic, the short-duration histotripsy pulses produce a unique and consistent type of cavitation for tissue destruction. In this review, the action of histotripsy-induced bubbles is discussed. Sources of bubble nuclei are reviewed, and bubble activity over the course of single and multiple pulses is outlined. Recent innovations in terms of novel acoustic excitations, exogenous nuclei for targeted ablation and histotripsy-enhanced drug delivery and image guidance metrics are discussed. Finally, gaps in knowledge of the histotripsy process are highlighted, along with suggested means to expedite widespread clinical utilization of histotripsy.

Advances in acoustic monitoring and control of focused ultrasound-mediated increases in blood-brain barrier permeability

Transcranial focused ultrasound (FUS) combined with intravenously circulating microbubbles can transiently and selectively increase blood-brain barrier permeability to enable targeted drug delivery to the central nervous system, and is a technique that has the potential to revolutionize the way neurological diseases are managed in medical practice. Clinical testing of this approach is currently underway in patients with brain tumors, early Alzheimer's disease, and amyotrophic lateral sclerosis. A major challenge that needs to be addressed in order for widespread clinical adoption of FUS-mediated blood-brain barrier permeabilization to occur is the development of systems and methods for real-time treatment monitoring and control, to ensure that safe and effective acoustic exposure levels are maintained throughout the procedures. This review gives a basic overview of the oscillation dynamics, acoustic emissions, and biological effects associated with ultrasound-stimulated microbubbles in vivo, and provides a summary of recent advances in acoustic-based strategies for detecting, controlling, and mapping microbubble activity in the brain. Further development of next-generation clinical FUS brain devices tailored towards microbubble-mediated applications is warranted and required for translation of this potentially disruptive technology into routine clinical practice.

An in vitro proof-of-principle study of sonobactericide

Infective endocarditis (IE) is associated with high morbidity and mortality rates. The predominant bacteria causing IE is Staphylococcus aureus (S. aureus), which can bind to existing thrombi on heart valves and generate vegetations (biofilms). In this in vitro flow study, we evaluated sonobactericide as a novel strategy to treat IE, using ultrasound and an ultrasound contrast agent with or without other therapeutics. We developed a model of IE biofilm using human whole-blood clots infected with patient-derived S. aureus (infected clots). Histology and live-cell imaging revealed a biofilm layer of fibrin-embedded living Staphylococci around a dense erythrocyte core. Infected clots were treated under flow for 30 minutes and degradation was assessed by time-lapse microscopy imaging. Treatments consisted of either continuous plasma flow alone or with different combinations of therapeutics: oxacillin (antibiotic), recombinant tissue plasminogen activator (rt-PA; thrombolytic), intermittent continuous-wave low-frequency ultrasound (120-kHz, 0.44 MPa peak-to-peak pressure), and an ultrasound contrast agent (Definity). Infected clots exposed to the combination of oxacillin, rt-PA, ultrasound, and Definity achieved 99.3 ± 1.7% loss, which was greater than the other treatment arms. Effluent size measurements suggested low likelihood of emboli formation. These results support the continued investigation of sonobactericide as a therapeutic strategy for IE.

Myocardial contrast echocardiography in mice: technical and physiological aspects

Myocardial contrast echocardiography (MCE) offers the opportunity to study myocardial perfusion defects in mice in detail. The value of MCE compared with single-photon emission computed tomography, positron emission tomography, and computed tomography consists of high spatial resolution, the possibility of quantification of blood volume, and relatively low costs. Nevertheless, a number of technical and physiological aspects should be considered to ensure reproducibility among research groups. The aim of this overview is to describe technical aspects of MCE and the physiological parameters that influence myocardial perfusion data obtained with this technique. First, technical aspects of MCE discussed in this technical review are logarithmic compression of ultrasound data by ultrasound systems, saturation of the contrast signal, and acquisition of images during different phases of the cardiac cycle. Second, physiological aspects of myocardial perfusion that are affected by the experimental design are discussed, including the anesthesia regimen, systemic cardiovascular effects of vasoactive agents used, and fluctuations in body temperature that alter myocardial perfusion. When these technical and physiological aspects of MCE are taken into account and adequately standardized, MCE is an easily accessible technique for mice that can be used to study the control of myocardial perfusion by a wide range of factors.

Low-Intensity Ultrasound-Induced Anti-inflammatory Effects Are Mediated by Several New Mechanisms Including Gene Induction, Immunosuppressor Cell Promotion, and Enhancement of Exosome Biogenesis and Docking

Background: Low-intensity ultrasound (LIUS) was shown to be beneficial in mitigating inflammation and facilitating tissue repair in various pathologies. Determination of the molecular mechanisms underlying the anti-inflammatory effects of LIUS allows to optimize this technique as a therapy for the treatment of malignancies and aseptic inflammatory disorders. Methods: We conducted cutting-edge database mining approaches to determine the anti-inflammatory mechanisms exerted by LIUS. Results: Our data revealed following interesting findings: (1) LIUS anti-inflammatory effects are mediated by upregulating anti-inflammatory gene expression; (2) LIUS induces the upregulation of the markers and master regulators of immunosuppressor cells including MDSCs (myeloid-derived suppressor cells), MSCs (mesenchymal stem cells), B1-B cells and Treg (regulatory T cells); (3) LIUS not only can be used as a therapeutic approach to deliver drugs packed in various structures such as nanobeads, nanospheres, polymer microspheres, and lipidosomes, but also can make use of natural membrane vesicles as small as exosomes derived from immunosuppressor cells as a novel mechanism to fulfill its anti-inflammatory effects; (4) LIUS upregulates the expression of extracellular vesicle/exosome biogenesis mediators and docking mediators; (5) Exosome-carried anti-inflammatory cytokines and anti-inflammatory microRNAs inhibit inflammation of target cells via multiple shared and specific pathways, suggesting exosome-mediated anti-inflammatory effect of LIUS feasible; and (6) LIUS-mediated physical effects on tissues may activate specific cellular sensors that activate downstream transcription factors and signaling pathways. Conclusions: Our results have provided novel insights into the mechanisms underlying anti-inflammatory effects of LIUS, and have provided guidance for the development of future novel therapeutic LIUS for cancers, inflammatory disorders, tissue regeneration and tissue repair.

Ultrasound-Responsive Polymeric Micelles for Sonoporation-Assisted Site-Specific Therapeutic Action

Targeting drug delivery remains a challenge in various disease treatment including cancer. The local drug deposit could be greatly enhanced by some external stimuli-responsive systems. Here we develop pluronic P123/F127 polymeric micelles (M) encapsulating curcumin (Cur) that are permeabilized directly by focused ultrasound, in which ultrasound triggers drug release. Tumor preferential accumulation and site-specific sonochemotherapy were then evaluated. Cur-loaded P123/F127 mixed micelles (Cur-M) exhibited longer circulating time and increased cellular uptake compared to free Cur. With the assistance of focused ultrasound treatment, Cur-M showed tumor-targeting deposition in a time-dependent manner following systemic administration. This was due to enhanced permeabilization of tumor regions and increased penetration of Cur-M in irradiated tumor cells by ultrasound sonoporation. Furthermore, Cur-M self-assembly could be regulated by ultrasound irradiation. In vitro Cur release from mixed micelles was greatly dependent on ultrasound intensity but not on duration, suggesting the cavitational threshold was necessary to initiate subsequent sonochemotherapy. In vivo site-specific drug release was demonstrated in dual-tumor models, which showed spatial-temporal release of entrapped drugs following intratumoral injection. The sonoporation-assisted site-specific chemotherapy significantly inhibited tumor growth and the decrease in tumor weight was approximately 6.5-fold more than without exposure to ultrasound irradiation. In conclusion, the established ultrasound-guided nanomedicine targeting deposit and local release may represent a new strategy to improve chemotherapy efficiency.

Hemocoagulase Combined with Microbubble-Enhanced Ultrasound Cavitation for Augmented Ablation of Microvasculature in Rabbit VX2 Liver Tumors

We investigated a new method for combining microbubble-enhanced ultrasound cavitation (MEUC) with hemocoagulase (HC) atrox. Our goal was to induce embolic effects in the vasculature and combine these with an anti-angiogenic treatment strategy. Fourteen days after being implanted with a single slice of the liver VX2 tumor, rabbits were randomly divided into five groups: (i) a control group injected intra-venously with saline using a micropump; (ii) a group given only an injection of HC; (iii) a group treated only with ultrasound cavitation; (iv) a group treated with MEUC; (v) a group treated with MEUC + HC. Contrast-enhanced ultrasound was performed before treatment and 1 h and 7 d post-treatment to measure tumor size, enhancement and necrosis range. QontraXt software was used to determine the time-intensity curve of tumor blood perfusion and microvascular changes. At 1 h and 7 d after treatment with MEUC + HC, the parameters of the time-intensity curve, which included peak value, regional blood volume, regional blood flow and area under the curve value and which were measured using contrast-enhanced ultrasound, were significantly lower than those of the other treatment groups. The MEUC + HC treatment group exhibited significant growth inhibition relative to the ultrasound cavitation only, HC and MEUC treatment groups. No damage was observed in the surrounding normal tissues. These results support the feasibility of reducing the blood perfusion of rabbit VX2 liver tumors using a new method that combines MEUC and HC.

Mechanical and Biological Effects of Ultrasound: A Review of Present Knowledge

Ultrasound is widely used for medical diagnosis and increasingly for therapeutic purposes. An understanding of the bio-effects of sonography is important for clinicians and scientists working in the field because permanent damage to biological tissues can occur at high levels of exposure. Here the underlying principles of thermal mechanisms and the physical interactions of ultrasound with biological tissues are reviewed. Adverse health effects derived from cellular studies, animal studies and clinical reports are reviewed to provide insight into the in vitro and in vivo bio-effects of ultrasound.

Cytotoxicity control of silicon nanoparticles by biopolymer coating and ultrasound irradiation for cancer theranostic applications

Silicon nanoparticles (SiNPs) prepared by mechanical grinding of luminescent porous silicon were coated with a biopolymer (dextran) and investigated as a potential theranostic agent for bioimaging and sonodynamic therapy. Transmission electron microscopy, photoluminescence and Raman scattering measurements of dextran-coated SiNPs gave evidence of their enhanced stability in water. In vitro experiments confirmed the lower cytotoxicity of the dextran-coated NPs in comparison with uncoated ones, especially for high concentrations of about 2 mg ml^-1. Efficient uptake of the NPs by cancer cells was found using bioimaging in the optical transmittance and photoluminescence modes. Treatment of the cells with uptaken SiNPs by therapeutic ultrasound for 5-20 min resulted in a strong decrease in the number of living cells, while the total number of cells remained nearly unchanged. The obtained data indicate a 'mild' effect of the combined action of ultrasonic irradiation and SiNPs on cancer cells. The observed results reveal new opportunities for controlling the photoluminescent and sonosensitizing properties of silicon-based NPs for applications in the diagnostics and mild therapy of cancer.