Cavitation microstreaming and stress fields created by microbubbles

Rapid synergistic thrombolysis of ischemic stroke guided by high-resolution and high-speed photoacoustic cerebrovascular imaging

Thrombosis is the major cause of ischemic stroke and poses a serious health burden globally. Current thrombolytic strategies, such as systematic administration of recombinant human tissue plasminogen activator (rt-PA), are challenged by limited thrombolysis efficiency due to low targeting ability and a short plasma half-life. Here, we report a rapid synergistic strategy that integrates sonothrombolysis and rt-PA mediated pharmacological thrombolysis to achieve accurate and efficient treatment of ischemic stroke. The strategy (PLPA@PFP) uses a platelet-biomimetic membrane as a carrier to deliver both perfluoropentane (PFP) and rt-PA, prolonging half-life and effectively accumulating at the thrombus within 0.5 hours. Upon exposure to focused ultrasound, PFP-based cavitation effects significantly enhance thrombus breakdown and rt-PA penetration, enabling synergistic sono/pharmacological thrombolysis both in vitro and in vivo. High-resolution photoacoustic (PA) imaging provides direct assessment of vascular reperfusion following therapeutic intervention in a murine model of ischemic stroke, offering important guidance for clinical treatment.

Evaluation of focused ultrasound modulation of the blood-brain barrier in gray and white matter

RATIONALE

Focused ultrasound (FUS) in combination with intravenous microbubbles is being studied clinically for modulation of the blood-brain barrier. Contrast-enhanced MRI can be used to visualize the enhanced permeability resulting from the treatment. However, contrast enhancement in the white matter (WM) are inconsistently observed compared to the gray matter (GM). Intrinsic tissue differences are believed to result in reduced treatment efficacy and insufficient drug delivery to the WM. In this study we evaluate the deposition of MRI contrast and clinically relevant antineoplastics in GM and WM tissues following single and repeated FUS and microbubble treatments.

METHODS

The brains of Fischer-344 rats (n = 24) and Yorkshire pigs (n = 6) underwent FUS (rats: 580 kHz; pigs: 220 kHz) treatments targeting the internal capsule and thalamus, repeated at 30-min intervals. Definity microbubbles (rats: 20 μL/kg bolus; pigs: 4 μL/kg/5-min infusion) were administered intravenously for each sonication with MRI contrast to measure gadolinium-mediated signal change. Feedback-controlled algorithms were used to monitor treatments and modulate the pressure based on emitted microbubble signals to ensure safe and effective exposures. The delivery of methotrexate (MTX; 454.4 Da) and bevacizumab (BVZ; 149 kDa) was evaluated via immunofluorescence microscopy in rats, and respectively quantified via liquid chromatography mass spectrometry and enzyme-linked immunosorbent assay in pigs.

RESULTS

Repeated FUS exposures successfully increased the vascular permeability of both gray and white matter tissues to MRI contrast and drugs of both small and large molecular sizes. In rats, single treatments showed statistically significant higher enhancements in the GM (23.5 ± 4.3 %; WM: 4.68 ± 3.75 %), however following a second sonication there were no between-tissue differences (GM: 38.0 ± 6.4 %; WM: 34.0 ± 8.7 %). In pigs, the smaller focus size relative to the brain enabled separate targeting of GM vs WM and the treatment controller used higher average power level in the WM to achieve the same cavitation dose. This resulted in no difference in gray and white matter permeability levels (to both contrast and pharmacological agents) after a single sonication. Repeated treatments sustained MRI enhancements for a longer time and enhanced drug deposition (MTX increased 6.5 and 8.3 folds after single and repeated treatment; BVZ increased 6.8 and 20.4 folds respectively).

CONCLUSIONS

Feedback-controlled algorithms and the possibility to individually target gray and white matter highlighted the impact of tissue composition on treatment outcomes. Repeated FUS-mediated modulation of the brain microvasculature achieved higher levels of permeabilization to contrast and pharmacological agents in both gray and white matter.

Ultrasound modulation of melatonin release from pineal glands in vitro

OBJECTIVES

In this study, we aim to investigate whether therapeutic ultrasound can modulate the release of melatonin from the pineal gland-either increasing or decreasing its levels-and to assess the safety of this technique. This research could address a significant clinical need by providing a noninvasive method to potentially regulate sleep and circadian rhythms through the targeted modulation of melatonin.

METHODS

Rat pineal glands were placed in a well with a Krebs Ringer Buffer solution. Ultrasound was applied to the glands using unfocused transducers set at an average intensity of 1 W/cm2 and three different frequencies (400, 600, and 800 kHz) with continuous exposure for 5 min. Fluid samples were collected from the well before (t = 0 min), immediately after (t = 5 min), and 30 min post-ultrasound treatment (t = 30 min). Melatonin release was subsequently measured using an ELISA kit and analyzed statistically. In addition, histological analysis was completed to determine any structural abnormalities due to ultrasound application.

RESULTS

In the 600 kHz group there was a statistically significant decrease from t = 0 min to t = 5 min. No other statistically significant differences were observed. In addition, no histological changes were observed in the pineal glands due to ultrasound application.

CONCLUSIONS

This study indicated that ultrasound may be able to modulate melatonin release, however follow-up studies are necessary to determine optimal ultrasound parameters for this application.

Ultrasound-Assisted Blood-Brain Barrier Opening Monitoring by Photoacoustic and Fluorescence Imaging Using Indocyanine Green

OBJECTIVE

The blood-brain barrier (BBB) is a selectively permeable membrane that restricts drug delivery to the central nervous system. Focused ultrasound (FUS) combined with microbubbles (MBs) is a promising technique to transiently open the BBB, enabling therapeutic delivery. However, real-time monitoring of BBB permeability changes remains challenging. This study investigated the use of indocyanine green (ICG) as a bi-modal contrast agent for photoacoustic and fluorescence imaging to assess BBB opening and closure dynamics.

METHODS

BALB/c mice underwent FUS-mediated BBB opening with different doses of MBs and ICG administration. Photoacoustic and fluorescence imaging were performed at various time points post-FUS to evaluate ICG extravasation dynamics. Magnetic resonance imaging (MRI) with gadolinium contrast was used as the gold standard for BBB permeability assessment. The effect of MB dose and injection timing on BBB closure kinetics was analyzed.

RESULTS

Photoacoustic imaging provided reliable BBB monitoring within the first hour post-FUS, whereas fluorescence imaging was more effective at detecting ICG extravasation at 24 h. A strong correlation was observed between fluorescence intensity and MRI-based contrast enhancement, confirming BBB opening dynamics. BBB closure followed an exponential decay model, with a half-closure time of approximately 81 min. The degree of BBB opening was proportional to the MB dose administered.

CONCLUSION

ICG-based photoacoustic and fluorescence imaging provide a non-invasive and cost-effective alternative to MRI for monitoring FUS-induced BBB opening. These techniques offer complementary temporal windows for assessment, improving the precision of BBB permeability evaluation in preclinical and potentially clinical applications.

Nanoscale Ligand Spacing Regulates Mechanical Force-Induced Cancer Cell Killing

Cancer cells sense and respond to the extracellular environment, with differences in nanoscale ligand spacing affecting their behavior. Emerging reports show that stretch/ultrasound-mediated mechanical forces promote apoptosis (mechanoptosis) by increasing myosin contractility. Since myosin contractility is critical for nanoscale-ligand spacing-regulated cell behavior, we study the effect of ligand spacing on mechanoptosis. Gold nanoparticle arrays were created with 35, 50, and 70 nm spacings and functionalized with cyclic-RGD peptide. Interestingly, the highest level of apoptosis was observed on 50 and 70 nm ligand spacing, where increased myosin contractility and peripheral Piezo1 channel localization causing calcium influx were observed. Perturbing cell-matrix interactions by nanomolar doses of Cilengitide (cyclic RGD pentapeptide) increases mechanoptosis on 35 nm ligand spacing to similar levels observed on 50 and 70 nm. Thus, nanoscale-level changes in binding domains regulate mechanoptosis through cell-matrix mediated mechanotransduction, and the synergistic action of ultrasound and Cilengitide can ultimately be applied to enhance tumor treatment.

Advancements in Acoustic Cavitation Modelling: Progress, Challenges, and Future Directions in Sonochemical Reactor Design

This review provides a comprehensive overview of ultrasonic wave propagation, with a primary focus on high-power ultrasound systems where cavitation bubbles are likely to occur. The review is structured to guide readers through the historical development of cavitation models, from early works such as the Rayleigh-Plesset equation to more advanced numerical approaches. It explores the dynamics of cavitation bubbles, their physical effects, and the key factors influencing bubble formation, growth, and collapse. In addition to bubble-induced cavitation, the review addresses nonlinear wave propagation in the absence of bubbles, highlighting phenomena such as harmonic generation and shock wave formation. A detailed discussion on the numerical modelling of ultrasonic systems follows, covering linear and nonlinear approaches, boundary conditions, and the challenges of accurately simulating cavitating systems. The review concludes with an analysis of recent developments, emerging trends, and future directions in computational modelling for ultrasonic applications. By presenting a structured overview of both the theoretical and practical aspects of ultrasonic wave propagation, this work aims to provide a foundation for future research and design improvements in sonochemical and acoustic systems.

Reversible Ca2+ signaling and enhanced paracellular transport in endothelial monolayer induced by acoustic bubbles and targeted microbeads

Ultrasound and microbubble mediated blood brain barrier opening is a non-invasive and effective technique for drug delivery to targeted brain region. However, the exact mechanisms are not fully resolved. The influences of Ca2+ signaling on sonoporation and endothelial tight junctional regulation affect the efficiency and biosafety of the technique. Therefore, an improved understanding of how ultrasound evokes Ca2+ signaling in the brain endothelial monolayer, and its correlation to endothelial permeability change is necessary. Here, we examined the effects of SonoVue microbubbles or integrin-targeted microbeads on ultrasound induced bioeffects in brain microvascular endothelial monolayer using an acoustically-coupled microscopy system, where focused ultrasound exposure and real-time recording of Ca2+ signaling and membrane perforation were performed. Microbubbles induced robust Ca2+ responses, often accompanied by cell poration, while ultrasound with microbeads elicited reversible Ca2+ response without membrane poration. At the conditions evoking reversible Ca2+ signaling, intracellular Ca2+ release and reactive oxygen species played key roles for microbubbles induced Ca2+ signaling while activation of mechanosensitive ion channels was essential for the case of microbeads. Trans-well diffusion analysis revealed significantly higher trans-endothelial transport of 70 kDa FITC-dextran for both integrin-targeted microbeads and microbubbles compared to the control group. Further immunofluorescence staining showed disruption of cell junctions with microbubble stimulation and reversible remodeling of many cell junctions by ultrasound with integrin-targeted microbeads. This investigation provides new insights for ultrasound induced Ca2+ signaling and its influence on endothelial permeability, which may help develop new strategies for safe and efficient drug/gene delivery in the vascular system.

Experimental investigation on the effect of concentration on the resonance frequency of lipid coated ultrasonically excited microbubbles

This study presents an experimental investigation of the influence of MB concentration on the resonance frequency of lipid-coated microbubbles (MBs). Expanding on theoretical models and numerical simulations from previous research, this work experimentally investigates the effect of MB size on the rate of resonance frequency increase with concentration, a phenomenon observed across MBs with two different lipid compositions: propylene glycol (PG) and propylene glycol and glycerol (PGG). Employing a custom-designed ultrasound attenuation measurement setup, we measured the frequency-dependent attenuation of MBs, isolating MBs based on size to generate distinct monodisperse sub-populations for analysis. The resonance frequency of MBs was determined by identifying the attenuation peak in the broadband attenuation ultrasound attenuation measurements. Our experimental findings confirm that larger MBs (≈2.1μm) demonstrate a more significant shift in resonance frequency (≈ 5 MHz, ≈ 40%) as a function of MB concentration. In contrast, smaller MBs (≈1.3μm) show a minor shift in the resonant frequency (≈ 1.8 MHz, ≈ 8%), underlining the importance of size in determining acoustic behavior compared to changes in the lipid shell properties. Additionally, we observed that resonance frequency increase with concentration reaching a saturation point at higher concentrations. This plateau occurs at higher concentrations for larger MBs (≈2.1μm), while smaller MBs (≈1.6μm and ≈1.3μm) reach this saturation point at lower concentrations. Furthermore, the study highlights the small effect of bubble-bubble interactions on the resonance frequency of MB populations, particularly at lower MB concentrations and for smaller MBs. This insight is important for applications utilizing MB clusters, such as contrast-enhanced ultrasound imaging and MB-mediated therapies. While both size and lipid shell composition influence resonance frequency, MB size has a more significant effect. In conclusion, our findings affirm the need to consider both MB size and concentration when utilizing MBs for clinical and industrial ultrasonic applications.

Effect of Microbubble Size, Composition, and Multiple Sonication Points on Sterile Inflammatory Response in Focused Ultrasound-Mediated Blood-Brain Barrier Opening

Blood-brain barrier opening (BBBO) using focused ultrasound (FUS) and microbubbles (MBs) has emerged as a promising technique for delivering therapeutics to the brain. However, the influence of various FUS and MB parameters on BBBO and subsequent sterile inflammatory response (SIR) remains unclear. In this study, we investigated the effects of MB size and composition, as well as the number of FUS sonication points, on BBBO and SIR in an immunocompetent mouse model. Using MRI-guided MB + FUS, we targeted the striatum and assessed extravasation of an MRI contrast agent to assess BBBO and RNaseq to assess SIR. Our results revealed distinct effects of these parameters on BBBO and SIR. Specifically, at a matched microbubble volume dose (MVD), MB size did not affect the extent of BBBO, but smaller (1 μm diameter) MBs exhibited a lower classification of SIR than larger (3 or 5 μm diameter) MBs. Lipid-shelled microbubbles exhibited greater BBBO and a more pronounced SIR compared to albumin-shelled microbubbles, likely owing to the latter's poor in vivo stability. As expected, increasing the number of sonication points resulted in greater BBBO and SIR. Furthermore, correlation analysis revealed strong associations between passive cavitation detection measurements of harmonic and inertial MB echoes, BBBO, and the expression of SIR gene sets. Our findings highlight the critical role of MB and FUS parameters in modulating BBBO and subsequent SIR in the brain. These insights inform the development of targeted drug delivery strategies and the mitigation of adverse inflammatory reactions in neurological disorders.

Sonothrombolysis in Patients With ST-Elevation Myocardial Infarction With Electrocardiographic No-Reflow After Percutaneous Coronary Intervention: A Randomized Controlled Trial

BACKGROUND AND AIMS

Approximately 50% of patients with ST elevation myocardial infarction (STEMI) treated with percutaneous coronary intervention (PCI) experience microvascular no-reflow. Pre- and post-PCI sonothrombolysis has been shown to decrease infarct size and improve left ventricular (LV) systolic function in STEMI patients receiving urgent PCI. The aim of this study was to investigate whether post-PCI sonothrombolysis alone in STEMI patients with persistent ST elevation could reduce no-reflow and infarct size.

METHODS

Patients with STEMI with symptoms <12 hours who had persistent ST elevation (≤70% ST resolution) after primary PCI were randomized to sonothrombolysis or control. The primary end point was summed (Σ) ST elevation 60 minutes after study intervention. Secondary end points included infarct size, myocardial perfusion score, LV ejection fraction on cardiovascular magnetic resonance imaging at 2 months follow-up, and clinical outcome at 6-month follow-up.

RESULTS

Sixty-seven STEMI patients with persistent ST elevation after PCI were randomized (49 left anterior descending, 18 right coronary/left circumflex artery). No difference was observed in Σ ST elevation 60 minutes after study intervention (mean difference, 0.6 mm; 95% CI, -1.1 to 2.2, P = .50). Complete ST resolution occurred in 14 (40%) of patients treated with sonothrombolysis compared to 6 (19%) of controls (P = .16). Myocardial perfusion score index (1.5 ± 0.3 vs 1.5 ± 0.3, P = .93), infarct size (18.0% ± 10% vs 16.8% ± 11%; P = .29) and LV ejection fraction on cardiovascular magnetic resonance (46% ± 8% vs 47% ± 11% in the control group; P = .86) were comparable. Incidence of all-cause death, acute coronary syndrome, and hospital admission for heart failure at 6-month follow-up was similar between the groups (sonothrombolysis, 2; control, 5).

CONCLUSIONS

In STEMI patients with persistent ST elevation after PCI, post-PCI sonothrombolysis did not result in more ST resolution or smaller infarct size compared to control subjects. The incidence of the combined clinical end points was remarkably low in this high-risk patient population.

A compact and low-frequency drive ultrasound transducer for facilitating cavitation-assisted drug permeation via skin

Low-frequency sonophoresis has emerged as a promising minimally invasive transdermal drug delivery method. However, effectively inducing cavitation on the skin surface with a compact, low-frequency ultrasound transducer poses a significant challenge. This paper presents a modified design of a low-frequency ultrasound transducer capable of generating ultrasound cavitation on the skin surfaces. The transducer comprises a piezoelectric ceramic disk and a bowl-shaped acoustic resonator. A conical slit structure was incorporated into the modified transducer design to amplify vibration displacement and enhance the maximum sound pressure. The FEM-based simulation results confirmed that the maximum sound pressure at the resonance frequency of 78 kHz was increased by 1.9 times that of the previous design. Ultrasound cavitation could be experimentally observed on the gel surface. Moreover, 3 min of ultrasound treatment significantly improved the caffeine permeability across an artificial membrane. These results demonstrated that this transducer holds promise for enhancing drug permeation by generating ultrasound cavitation on the skin surface.

Safety, feasibility and efficacy of sonothrombolysis with micro boluses of perfluoropropane as a point of care therapy for patients with acute ST-elevation myocardial infarction

BACKGROUND

Despite advances in timely revascularisation of ST elevation myocardial infarction (STEMI) patients, there are several practical and unavoidable delays. Sonothrombolysis (administered during micro boluses of Perfluoropropane) initiated bedside as a point-of-care therapy during the initial evaluation of the patient may potentially mitigate this by producing early culprit vessel revascularisation.

METHODS

This was a prospective, single-centre study on hemodynamically stable patients presenting within 12 hours of a first STEMI who consented for study participation.

RESULTS

Fifteen patients were recruited over a 1-month period. Eleven were male. Nine patients had anterior wall STEMI and left anterior descending as culprit vessel. There were no significant changes in safety outcomes. Median First Medical Contact (FMC)-Sono time was 12 min (10-15). Median duration of sonothrombolysis was 14 min (12-16). FMC-device time was 97 min (79-128). Six patients had culprit vessel recanalisation before primary percutaneous coronary intervention (PPCI) which was consistent with the reference rates of therapy-associated recanalisation (p = 0.535).

CONCLUSION

Micro bolus sonothrombolysis maybe safely initiated as a point of care therapy adjunctive to PPCI in hemodynamically stable STEMI patients with reasonable efficacy. Further randomised trials are needed to ascertain its applicability in various geographical and clinical settings.

Effect of Ultrasound on Thrombus debris during Sonothrombolysis in a Microfluidic device

Microbubble-mediated sonothrombolysis has been proven to be a non-invasive and efficient method for thrombolysis. Nevertheless, there is a potential risk that the thrombus debris generated during the dissolution of the original thrombus are too large and can lead to hazardous emboli. Using a sonothrombolysis microfluidic platform, we investigated the effects of ultrasound power, thrombolytic agent and microbubble concentration on the size of thrombus debris with the example of microbubble-mediated sonothrombolysis of arterial thrombus. Additionally, we studied the effects of ultrasound power on the size and shape of thrombus debris produced by acute and chronic arterial sonothrombolysis. In acute arterial sonothrombolysis, ultrasound power has significant effect on the size of thrombus debris and steadily increases with the increase of ultrasound power. Conversely, in chronic arterial sonothrombolysis, the size of thrombus debris is minimally affected by ultrasound power. Using the sonothrombolysis microfluidic platform, the relationship between ultrasound power and the safety of sonothrombolysis has been illustrated, and the sonothrombolysis microfluidic platform is demonstrated to be a promising tool for further studies on the process of sonothrombolysis.

Histotripsy and Catheter-Directed Lytic: Efficacy in Highly Retracted Porcine Clots In Vitro

OBJECTIVE

Standard treatment for deep vein thrombosis (DVT) involves catheter-directed anticoagulants or thrombolytics, but the chronic thrombi present in many DVT cases are often resistant to this therapy. Histotripsy has been found to be a promising adjuvant treatment, using the mechanical action of cavitating bubble clouds to enhance thrombolytic activity. The objective of this study was to determine if histotripsy enhanced recombinant tissue plasminogen activator (rt-PA) thrombolysis in highly retracted porcine clots in vitro in a flow model of occlusive DVT.

METHODS

Highly retracted porcine whole blood clots were treated for 1 h with either catheter-directed saline (negative control), rt-PA (lytic control), histotripsy, DEFINITY and histotripsy or the combination of rt-PA and histotripsy with or without DEFINITY. Five-cycle, 1.5 MHz histotripsy pulses with a peak negative pressure of 33.2 MPa and pulse repetition frequency of 40 Hz were applied along the clot. B-Mode and passive cavitation images were acquired during histotripsy insonation to monitor bubble activity.

RESULTS

Clots subjected to histotripsy with and without rt-PA exhibited greater thrombolytic efficacy than controls (7.0% flow recovery or lower), and histotripsy with rt-PA was more efficacious than histotripsy with saline (86.1 ± 10.2% compared with 61.7 ± 19.8% flow recovery). The addition of DEFINITY to histotripsy with or without rt-PA did not enhance either thrombolytic efficacy or cavitation dose. Cavitation dose generally did not correlate with thrombolytic efficacy.

CONCLUSION

Enhancement of thrombolytic efficacy was achieved using histotripsy, with and without catheter-directed rt-PA, in the presence of physiologic flow. This suggests these treatments may be effective as therapy for DVT.

Real-Time Cavitation Monitoring During Optical Coherence Tomography Guided Photo-Mediated Ultrasound Therapy of the Retina

OBJECTIVE

Photo-mediated ultrasound therapy (PUT) is a novel antivascular therapeutic modality based on cavitation-induced bioeffects. During PUT, synergistic combinations of laser pulses and ultrasound bursts are used to remove the targeted microvessels selectively and precisely without harming nearby tissue. In the current study, an integrated system combining PUT and spectral domain optical coherence tomography (SD-OCT) was developed, where the SD-OCT system was used to guide PUT by detecting cavitation in real time in the retina of the eye.

METHOD

We first examined the capability of SD-OCT in detecting cavitation on a vascular-mimicking phantom and compared the results with those from a passive cavitation detector. The performance of the integrated system in treatment of choroidal microvessels was then evaluated in rabbit eyes in vivo.

RESULTS

During the in vivo PUT experiments, several biomarkers at the subretinal layer in the rabbit eye were identified on OCT images. The findings indicate that, by evaluating biomarkers of treatment effect, real-time SD-OCT monitoring could help to avoid micro-hemorrhage, which is a potential major side effect.

CONCLUSION

Real-time OCT monitoring can thus improve the safety and efficiency of PUT in removing the retinal and choroidal microvasculature.

High-Speed Optical Characterization of Protein-and-Nanoparticle-Stabilized Microbubbles for Ultrasound-Triggered Drug Release

OBJECTIVE

Ultrasound-triggered bubble-mediated local drug delivery has shown potential to increase therapeutic efficacy and reduce systemic side effects, by loading drugs into the microbubble shell and triggering delivery of the payload on demand using ultrasound. Understanding the behavior of the microbubbles in response to ultrasound is crucial for efficient and controlled release.

METHODS

In this work, the response of microbubbles with a coating consisting of poly(2-ethyl-butyl cyanoacrylate) (PEBCA) nanoparticles and denatured casein was characterized. High-speed recordings were taken of single microbubbles, in both bright field and fluorescence.

RESULTS

The nanoparticle-loaded microbubbles show resonance behavior, but with a large variation in response, revealing a substantial interbubble variation in mechanical shell properties. The probability of shell rupture and the probability of nanoparticle release were found to strongly depend on microbubble size, and the most effective size was inversely proportional to the driving frequency. The probabilities of both rupture and release increased with increasing driving pressure amplitude. Rupture of the microbubble shell occurred after fewer cycles of ultrasound as the driving pressure amplitude or driving frequency was increased.

CONCLUSION

The results highlight the importance of careful selection of the driving frequency, driving pressure amplitude and duration of ultrasound to achieve the most efficient ultrasound-triggered shell rupture and nanoparticle release of protein-and-nanoparticle-stabilized microbubbles.

High-Intensity Focused Ultrasound Enhances Drug Penetration into the Human Skin in the Franz Diffusion Cell

Purpose

High-intensity focused ultrasound (HIFU)-assisted drug delivery is a non-invasive tool to deliver drugs to targeted areas, currently used mainly for treating cancer and cardiovascular diseases. However, in terms of transdermal drug delivery, HIFU technology is still poorly understood. Accordingly, this study sought to investigate the effectiveness of HIFU on drug penetration into the skin using human skin tissues.

Methods

Gel-type drugs whose ingredient is glutathione were labelled with fluorescein isothiocyanate, in turn the drugs were allowed to penetrate to the human skin tissue in the Franz diffusion cell for 24 hours in control and HIFU treatment groups, and their fluorescence intensity was measured using a multiple microplate reader at one, two, six, and 24 hours after drug application. In addition, tissue slice analysis was performed in each tissue slice at 24 hours post-drug application. The % area, fluorescence intensity per area, and penetration depth of the drug were measured using a fluorescence microscope.

Results

The fluorescence intensity increased with time in all groups. Specifically, at 24 hours after drug application, the fluorescence intensity (a.u). of the 10-shot HIFU treatment group was significantly enhanced compared to that of the control group (p < 0.05). The tissue slice analysis demonstrated that the % area of fluorescent drug and the fluorescence intensity per area (a.u.) were all significantly increased in both HIFU treatment groups compared to the control group (p < 0.05, p < 0.001). In addition, the penetration depth (μm) also markedly rose in both HIFU treatment groups compared to the control group (p < 0.01, p < 0.05).

Conclusion

It was demonstrated for the first time that HIFU significantly facilitated topical drug penetration into the human skin, strongly implying that HIFU can be a useful option for transdermal drug delivery.

Effect of Microbubble Size, Composition and Multiple Sonication Points on Sterile Inflammatory Response in Focused Ultrasound-Mediated Blood-Brain Barrier Opening

Blood-brain barrier opening (BBBO) using focused ultrasound (FUS) and microbubbles (MBs) has emerged as a promising technique for delivering therapeutics to the brain. However, the influence of various FUS and MB parameters on BBBO and subsequent sterile inflammatory response (SIR) remains unclear. In this study, we investigated the effects of MB size and composition, as well as the number of FUS sonication points, on BBBO and SIR in an immunocompetent mouse model. Using MRI-guided MB+FUS, we targeted the striatum and assessed extravasation of an MRI contrast agent to assess BBBO and RNAseq to assess SIR. Our results revealed distinct effects of these parameters on BBBO and SIR. Specifically, at a matched microbubble volume dose (MVD), MB size did not affect the extent of BBBO, but smaller (1 μm diameter) MBs exhibited a lower classification of SIR than larger (3 or 5 μm diameter) MBs. Lipid-shelled microbubbles exhibited greater BBBO and a more pronounced SIR compared to albumin-shelled microbubbles, likely owing to the latter's poor in vivo stability. As expected, increasing the number of sonication points resulted in greater BBBO and SIR. Furthermore, correlation analysis revealed strong associations between passive cavitation detection measurements of harmonic and inertial MB echoes, BBBO and the expression of SIR gene sets. Our findings highlight the critical role of MB and FUS parameters in modulating BBBO and subsequent SIR in the brain. These insights inform the development of targeted drug delivery strategies and the mitigation of adverse inflammatory reactions in neurological disorders.

Smart Nanocarriers for the Treatment of Retinal Diseases

Retinal diseases, such as age-related macular degeneration, diabetic retinopathy, and retinoblastoma, stand as the leading causes of irreversible vision impairment and blindness worldwide. Effectively administering drugs for retinal diseases poses a formidable challenge due to the presence of complex ocular barriers and elimination mechanisms. Over time, various approaches have been developed to fabricate drug delivery systems for improving retinal therapy including virus vectors, lipid nanoparticles, and polymers. However, conventional nanocarriers encounter issues related to the controllability, efficiency, and safety in the retina. Therefore, the development of smart nanocarriers for effective or more invasive long-term treatment remains a desirable goal. Recently, approaches have surfaced for the intelligent design of nanocarriers, leveraging specific responses to external or internal triggers and enabling multiple functions for retinal therapy such as topical administration, prolonged drug release, and site-specific drug delivery. This Review provides an overview of prevalent retinal pathologies and related pharmacotherapies to enhance the understanding of retinal diseases. It also surveys recent developments and strategies employed in the intelligent design of nanocarriers for retinal disease. Finally, the challenges of smart nanocarriers in potential clinical retinal therapeutic applications are discussed to inspire the next generation of smart nanocarriers.

Bubble oscillations at low frequency ultrasound for biological applications

Bubbles oscillating in the presence of ultrasound is commonly employed in biomedical applications for drug delivery, ultrasound enhanced thrombolysis, and the transport and manipulation of cells. This is possible because bubbles tend to interact with the ultrasound to undergo periodic shape changes known as shape-mode oscillation, concomitant with the generation of liquid agitation or streaming. This phenomenon is examined both experimentally and theoretically on a single bubble at a frequency of (45 ± 1) kHz. Effects of ultrasonic frequency and power on the flowfield were explored. Experiments revealed different trends in the development of liquid streaming velocities at different acoustic forcing conditions (5.53, 6.80 and 7.02 Vpp), with lowest (0.5 mm/s) and highest (1.1 mm/s) values of time-averaged mean streaming velocity occurring at 6.80 Vpp and 7.02 Vpp, respectively. Simulations captured the simultaneous evolution of bubble-shapes that helped create flow vortices in the liquid surrounding the bubble. These vortices collectively responsible in generating signature patterns in the liquid for a dominant shape-mode of the bubble, and could also generate localised shear stresses for practical application. The velocity and pressure profiles in the liquid around the bubble confirmed the connection of the applied and reflected soundwaves in driving this phenomenon.

Mechanisms underlying the influence of skin properties on a single cavitation bubble in low-frequency sonophoresis

As a safe and effective method for systemic transdermal drug delivery (TDD), sonophoresis has drawn much attention from researchers. Despite numerous studies confirming cavitation as the main reason for sonophoresis, the effect skin has on cavitation bubble dynamics remains elusive due to the difficulty of experimental challenges. For a start, we reveal how single cavitation bubble (SCB) dynamics are affected by skin properties, including elasticity, hydrophilicity and texture. We use polydimethylsiloxane (PDMS) to simulate human skin and record the temporary evolution of SCBs with synchronous ultrafast photography. The influences of skin properties on SCBs are concluded: 1) SCBs collapse later near walls with better elasticities and generate microjets with higher speed; 2) SCBs collapse later near hydrophilic walls with slower microjets; and 3) the existence of a texture structure on walls also delays the time of bubble collapse near them and slows the velocities of microjets (v) during collapses.

Mechanobiological Strategies to Augment Cancer Treatment

Cancer cells exhibit aberrant extracellular matrix mechanosensing due to the altered expression of mechanosensory cytoskeletal proteins. Such aberrant mechanosensing of the tumor microenvironment (TME) by cancer cells is associated with disease development and progression. In addition, recent studies show that such mechanosensing changes the mechanobiological properties of cells, and in turn cells become susceptible to mechanical perturbations. Due to an increasing understanding of cell biomechanics and cellular machinery, several approaches have emerged to target the mechanobiological properties of cancer cells and cancer-associated cells to inhibit cancer growth and progression. In this Perspective, we summarize the progress in developing mechano-based approaches to target cancer by interfering with the cellular mechanosensing machinery and overall TME.

Ultrasonics and sonochemistry: Editors' perspective

Ultrasonic waves can induce physical and chemical changes in liquid media via acoustic cavitation. Various applications have benefitted from utilizing these effects, including but not limited to the synthesis of functional materials, emulsification, cleaning, and processing. Several books and review articles in the public domain cover both fundamental and applied aspects of ultrasonics and sonochemistry. The Editors of the Ultrasonics Sonochemistry journal possess diverse expertise in this field, from theoretical and experimental aspects of acoustic cavitation to materials synthesis, environmental remediation, and sonoprocessing. This article provides Editors' perspectives on various aspects of ultrasonics and sonochemistry that may benefit students and early career researchers.

Experimental assessment of cardiovascular physiology in the chick embryo

High resolution assessment of cardiac functional parameters is crucial in translational animal research. The chick embryo is a historically well-used in vivo model for cardiovascular research due to its many practical advantages, and the conserved form and function of the chick and human cardiogenesis programs. This review aims to provide an overview of several different technical approaches for chick embryo cardiac assessment. Doppler echocardiography, optical coherence tomography, micromagnetic resonance imaging, microparticle image velocimetry, real-time pressure monitoring, and associated issues with the techniques will be discussed. Alongside this discussion, we also highlight recent advances in cardiac function measurements in chick embryos.

Radiation combined with ultrasound and microbubbles: A potential novel strategy for cancer treatment

Cancer is one of the leading causes of death worldwide. Several emerging technologies are helping to battle cancer. Cancer therapies have been effective at killing cancer cells, but a large portion of patients still die to this disease every year. As such, more aggressive treatments of primary cancers are employed and have been shown to be capable of saving a greater number of lives. Recent research advances the field of cancer therapy by employing the use of physical methods to alter tumor biology. It uses microbubbles to enhance radiation effect by damaging tumor vasculature followed by tumor cell death. The technique can specifically target tumor volumes by conforming ultrasound fields capable of microbubbles stimulation and localizing it to avoid vascular damage in surrounding tissues. Thus, this new application of ultrasound-stimulated microbubbles (USMB) can be utilized as a novel approach to cancer therapy by inducing vascular disruption resulting in tumor cell death. Using USMB alongside radiation has showed to augment the anti-vascular effect of radiation, resulting in enhanced tumor response. Recent work with nanobubbles has shown vascular permeation into intracellular space, extending the use of this new treatment method to potentially further improve the therapeutic effect of the ultrasound-based therapy. The significant enhancement of localized tumor cell kill means that radiation-based treatments can be made more potent with lower doses of radiation. This technique can manifest a greater impact on radiation oncology practice by increasing treatment effectiveness significantly while reducing normal tissue toxicity. This review article summarizes the past and recent advances in USMB enhancement of radiation treatments. The review mainly focuses on preclinical findings but also highlights some clinical findings that use USMB as a therapeutic modality in cancer therapy.

Heterogeneous tissue construction by on-demand bubble-assisted acoustic patterning

Highly heterogeneous structures are closely related to the realization of the tissue functions of living organisms. However, precisely controlling the assembly of heterogeneous structures is still a crucial challenge. This work presents an on-demand bubble-assisted acoustic method for active cell patterning to achieve high-precision heterogeneous structures. Active cell patterning is achieved by the combined effect of acoustic radiation forces and microstreaming around oscillating bubble arrays. On-demand bubble arrays allow flexible construction of cell patterns with a precision of up to 45 μm. As a typical example, the in vitro model of hepatic lobules, composed of patterned endothelial cells and hepatic parenchymal cells, was constructed and cultured for 5 days. The good performance of urea and albumin secretion, enzymatic activity and good proliferation of both cells prove the feasibility of this technique. Overall, this bubble-assisted acoustic approach provides a simple and efficient strategy for on-demand large-area tissue construction, with considerable potential for different tissue model fabrication.

Intercellular Calcium Waves and Permeability Change Induced by Vertically Deployed Surface Acoustic Waves in a Human Cerebral Microvascular Endothelial Cell Line (hCMEC/D3) Monolayer

OBJECTIVE

The ultrasound-mediated blood-brain barrier (BBB) opening with microbubbles has been widely employed, while recent studies also indicate the possibility that ultrasound alone can open the BBB through a direct mechanical effect. However, the exact mechanisms through which ultrasound interacts with the BBB and whether it can directly trigger intracellular signaling and a permeability change in the BBB endothelium remain unclear.

METHODS

Vertically deployed surface acoustic waves (VD-SAWs) were applied on a human cerebral microvascular endothelial cell line (hCMEC/D3) monolayer using a 33-MHz interdigital transducer that exerts shear stress-predominant stimulation. The intracellular calcium response was measured by fluorescence imaging, and the permeability of the hCMEC/D3 monolayer was assessed by transendothelial electrical resistance (TEER).

DISCUSSION

At a certain intensity threshold, VD-SAWs induced an intracellular calcium surge that propagated to adjacent cells as intercellular calcium waves. VD-SAWs induced a TEER decrease in a pulse repetition frequency-dependent manner, thereby suggesting possible involvement of the mechanosensitive ion channels.

CONCLUSION

The unique VD-SAW system enables more physiological mechanical stimulation of the endothelium monolayer. Moreover, it can be easily combined with other measurement devices, providing a useful platform for further mechanistic studies on ultrasound-mediated BBB opening.

A review on photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a novel therapeutic technique based on the combination of ultrasound and laser. The underlying mechanism of PUT is the enhanced cavitation effect inside blood vessels. The enhanced cavitation activity can result in bio-effects such as reduced perfusion in microvessels. The reduced perfusion effect in microvessels in the eye has the potential to control the progression of eye diseases such as diabetic retinopathy and age-related macular degeneration. Several in vivo studies have demonstrated the feasibility of PUT in removing microvasculature in the eye using rabbit eye model and vasculature in the skin using rabbit ear model. Numerical studies using a bubble dynamics model found that cavitation is enhanced during PUT due to the dramatic increase in size of air/vapor nuclei in blood. In addition, the study conducted to model cavitation dynamics inside a blood vessel during PUT found stresses induced on the vessel wall during PUT are higher than that at normal physiological levels, which may be responsible for bio-effects. The concentration of vasodilators such as nitric oxide and prostacyclin were also found to be affected during PUT in an in vitro study, which may limit blood perfusion in vessels. The main advantage of PUT over conventional techniques is non-invasive, precise, and selective removal of microvessels with high efficiency at relatively low energy levels of ultrasound and laser, without affecting the nearby structures. However, the main limitation of vessel rupture/hemorrhage needs to be overcome through the development of real-time monitoring of treatment effects during PUT. In addition to the application in removing microvessels, PUT-based techniques were also explored in treating other diseases. Studies have found a combination of ultrasound and laser to be effective in removing blood clots inside veins, which has the potential to treat deep-vein thrombosis. The disruption of atherosclerotic plaque using combined ultrasound and laser was also tested, and the feasibility was demonstrated.

Immunomodulation and targeted drug delivery with high intensity focused ultrasound (HIFU): Principles and mechanisms

High intensity focused ultrasound (HIFU) is a non-invasive and non-ionizing sonic energy-based therapeutic technology for inducing thermal and non-thermal effects in tissues. Depending on the parameters, HIFU can ablate tissues by heating them to >55 °C to induce denaturation and coagulative necrosis, improve radio- and chemo-sensitizations and local drug delivery from nanoparticles at moderate hyperthermia (~41-43 °C), and mechanically fragment cells using acoustic cavitation (also known as histotripsy). HIFU has already emerged as an attractive modality for treating human prostate cancer, veterinary cancers, and neuromodulation. Herein, we comprehensively review the role of HIFU in enhancing drug delivery and immunotherapy in soft and calcified tissues. Specifically, the ability of HIFU to improve adjuvant treatments from various classes of drugs is described. These crucial insights highlight the opportunities and challenges of HIFU technology and its potential to support new clinical trials and translation to patients.

Mechanotherapy in oncology: Targeting nuclear mechanics and mechanotransduction

Mechanotherapy is proposed as a new option for cancer treatment. Increasing evidence suggests that characteristic differences are present in the nuclear mechanics and mechanotransduction of cancer cells compared with those of normal cells. Recent advances in understanding nuclear mechanics and mechanotransduction provide not only further insights into the process of malignant transformation but also useful references for developing new therapeutic approaches. Herein, we present an overview of the alterations of nuclear mechanics and mechanotransduction in cancer cells and highlight their implications in cancer mechanotherapy.

Recent trends in the applications of sonochemical reactors as an advanced oxidation process for the remediation of microbial hazards associated with water and wastewater: A critical review

Water is one of the major sources that spread human diseases through contamination with bacteria and other pathogenic microorganisms. This review focuses on microbial hazards as they are often present in water and wastewater and cause various human diseases. Among the currently used disinfection methods, sonochemical reactors (SCRs) that produce free radicals combined with advanced oxidation processes (AOPs) have received significant attention from the scientific community. Also, this review discussed various types of cavitation reactors, such as acoustic cavitation reactors (ACRs) utilizing ultrasonic energy (UE), which had been widely employed, involving AOPs for treating contaminated waters. Besides ACRs, hydrodynamic cavitation reactors (HCRs) also effectively destroy and deactivate microorganisms to varying degrees. Cavitation is the fundamental phenomenon responsible for initiating many sonochemical reactions in liquids. Bacterial degradation occurs mainly due to the thinning of microbial membranes, local warming, and the generation of free radicals due to cavitation. Over the years, although extensive investigations have focused on the antimicrobial effects of UE (ultrasonic energy), the primary mechanism underlying the cavitation effects in the disinfection process, inactivation of microbes, and chemical reactions involved are still poorly understood. Therefore, studies under different conditions often lead to inconsistent results. This review investigates and compares other mechanisms and performances from greener and environmentally friendly sonochemical techniques to the remediation of microbial hazards associated with water and wastewater. Finally, the energy aspects, challenges, and recommendations for future perspectives have been provided.

Effect of Recombinant Tissue Plasminogen Activator and 120-kHz Ultrasound on Porcine Intracranial Thrombus Density

Surgical intervention for the treatment of intracerebral hemorrhage (ICH) has been limited by inadequate lysis of the target thrombus. Adjuvant transcranial ultrasound exposure is hypothesized to improve thrombolysis, expedite hematoma evacuation and improve clinical outcomes. A juvenile porcine intracerebral hemorrhage model was established by direct infusion of autologous blood into the porcine white matter. Thrombi were either not treated (sham) or treated with recombinant tissue plasminogen activator alone (rt-PA only) or in combination with pulsed transcranial 120-kHz ultrasound (sonothrombolysis). After treatment, pigs were euthanized, the heads frozen and sectioned and the thrombi extracted. D-Dimer and thrombus density assays were used to assess degree of lysis. Both porcine and human D-dimer assays tested did not have sufficient sensitivity to detect porcine D-dimer. Thrombi treated with rt-PA with or without 120-kHz ultrasound had a significantly lower density compared with sham-treated thrombi. No enhancement of rt-PA-mediated thrombolysis was noted with the addition of 120-kHz ultrasound (sonothrombolysis). The thrombus density assay revealed thrombolytic efficacy caused by rt-PA in an in vivo juvenile porcine model of intracerebral hemorrhage. Transcranial sonothrombolysis did not enhance rt-PA-induced thrombolysis, likely because of the lack of exogenous cavitation nuclei.

C. elegans: Sensing the low-frequency profile of amplitude-modulated ultrasound

Several research groups have demonstrated that C. elegans can respond to pulsed ultrasound stimuli, and elucidating the underlying mechanisms is necessary to develop ultrasound neuromodulation. Here, amplitude-modulated (AM) ultrasound is applied to C. elegans, and its behavioral responses are investigated in detail. By loading surface acoustic waves (SAWs) onto free-moving worms on an agar surface, a carrier wave with a frequency of 8.80 MHz is selected. The signal is modulated by a rectangular or sinusoidal profile. It is demonstrated that sinusoidal modulation can produce similar responses in worms to rectangular modulation, with the strongest responses occurring at modulation frequencies of around 1.00 kHz. Meanwhile, the behavioral response is relatively weak when the ultrasonic signal is unmodulated, that is, when only the carrier wave is applied. At modulation frequencies other than 100.00 Hz to 10.00 kHz, the worms respond weakly, but when a second modulation frequency of 1.00 kHz is introduced, an improvement in response can be observed. These results suggest that C. elegans may sense the low-frequency envelope and respond to amplitude-modulated ultrasonic stimuli like an amplitude demodulator. MEC-4, an ion channel for touch sensing, is involved in the behavioral response of C. elegans to ultrasound in the present setup.

Focused Ultrasound and Ultrasound Stimulated Microbubbles in Radiotherapy Enhancement for Cancer Treatment

Radiation therapy (RT) has been the standard of care for treating a multitude of cancer types. However, ionizing radiation has adverse short and long-term side effects which have resulted in treatment complications for decades. Thus, advances in enhancing the effects of RT have been the primary focus of research in radiation oncology. To avoid the usage of high radiation doses, treatment modalities such as high-intensity focused ultrasound can be implemented to reduce the radiation doses required to destroy cancer cells. In the past few years, the use of focused ultrasound (FUS) has demonstrated immense success in a number of applications as it capitalizes on spatial specificity. It allows ultrasound energy to be delivered to a targeted focal area without harming the surrounding tissue. FUS combined with RT has specifically demonstrated experimental evidence in its application resulting in enhanced cell death and tumor cure. Ultrasound-stimulated microbubbles have recently proved to be a novel way of enhancing RT as a radioenhancing agent on its own, or as a delivery vector for radiosensitizing agents such as oxygen. In this mini-review article, we discuss the bio-effects of FUS and RT in various preclinical models and highlight the applicability of this combined therapy in clinical settings.

Comparison of Acoustofluidic and Static Systems for Ultrasound-Mediated Molecular Delivery to T Lymphocytes

Continuous-flow acoustofluidic technologies can potentially improve processing of T lymphocytes for cell therapies by addressing the limitations with viral and non-viral delivery methods. The objective of this study was to assess the intracellular delivery efficiency with acoustofluidic treatment compared with that of static ultrasound treatment. Optimization of parameters in acoustofluidic and static configurations was performed by assessing intracellular delivery of a fluorescent compound (calcein) in viable human Jurkat T lymphocytes. Ultrasound pressure and the concentration of cationic phospholipid-coated microbubbles influenced calcein delivery in both systems. In the static system, a treatment time of 45 s increased molecular delivery compared with 0-30 s (p < 0.01). Refined parameters were used to assess molecular delivery of small and large compounds (0.6-kDa calcein and 150-kDa fluorescein isothiocyanate-dextran, respectively) after ultrasound treatment with the acoustofluidic or static systems. Molecular delivery was similar with refined parameters for acoustofluidic treatment and static treatment (p > 0.05), even though acoustofluidic treatment had lower microbubble concentration (24 μg/mL vs. 94 μg/mL) and shorter treatment time (∼2-3 s vs. 45 s). This study indicates that the acoustofluidic system can significantly enhance intracellular molecular delivery, which could potentially enable acoustofluidic cell transfection during continuous flow processing for manufacture of cell therapies or other applications.

The Influence of Nanobubble Size and Stability on Ultrasound Enhanced Drug Delivery

Lipid-shelled nanobubbles (NBs) are emerging as potential dual diagnostic and therapeutic agents. Similar to their micron-scale counterparts, microbubbles (1-10 μm), they can act as ultrasound contrast agents as well as locally enhance therapeutic uptake. Recently, it has been shown that the reduced size of NBs (<1 μm) promotes increased uptake and accumulation in tumor interstitial space, which can enhance their diagnostic and therapeutic performance. However, accurate characterization of NB size and concentration is challenging and may limit their translation into clinical use. Their submicron nature limits accuracy of conventional microscopy techniques, while common light scattering techniques fail to distinguish between subpopulations present in NB samples (i.e., bubbles and liposomes). Due to the difficulty in the characterization of NBs, relatively little is known about the influence of size on their therapeutic performance. In this study, we describe a novel method of using a commercially available nanoparticle tracking analysis system, to distinguish between NBs and liposomes based on their differing optical properties. We used this technique to characterize three NB populations of varying size, isolated via centrifugation, and subsequently used this to assess their potential for enhancing localized delivery. Confocal fluorescence microscopy and image analysis were used to quantify the ultrasound enhanced uptake of fluorescent dextran into live colorectal cancer cells. Our results showed that the amount of localized uptake did not follow the expected trends, in which larger NB populations out-perform smaller NBs, at matched concentration. To understand this observed behavior, the stability of each NB population was assessed. It was found that dilution of the NB samples from their stock concentration influences their stability, and it is hypothesized that both the total free lipid and interbubble distance play a role in NB lifetime, in agreement with previously proposed theories and models.

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.

Assessment of bubble activity generated by histotripsy combined with echogenic liposomes

Objective.Histotripsy is a form of focused ultrasound therapy that uses the mechanical activity of bubbles to ablate tissue. While histotripsy alone degrades the cellular content of tissue, recent studies have demonstrated it effectively disrupts the extracellular structure of pathologic conditions such as venous thrombosis when combined with a thrombolytic drug. Rather than relying on standard administration methods, associating thrombolytic drugs with an ultrasound-triggered echogenic liposome vesicle will enable targeted, systemic drug delivery. To date, histotripsy has primarily relied on nano-nuclei inherent to the medium for bubble cloud generation, and microbubbles associated with echogenic liposomes may alter the histotripsy bubble dynamics. The objective of this work was to investigate the interaction of histotripsy pulse with echogenic liposomes.Approach.Bubble clouds were generated using a focused source in anin vitromodel of venous flow. Acoustic emissions generated during the insonation were passively acquired to assess the mechanical activity of the bubble cloud. High frame rate, pulse inversion imaging was used to track the change in echogenicity of the liposomes following histotripsy exposure.Main results.For peak negative pressures less than 20 MPa, acoustic emissions indicative of stable and inertial bubble activity were observed. As the peak negative pressure of the histotripsy excitation increased, harmonics of the excitation were observed in OFP t-ELIP solutions and plasma alone. Additional observations with high frame rate imaging indicated a transition of bubble behavior as the pulse pressure transitioned to shock wave formation.Significance.These observations suggest that a complex interaction between histotripsy pulses and echogenic liposomes that may be exploited for combination treatment approaches.

The impact of low intensity ultrasound on cells: Underlying mechanisms and current status

Low intensity ultrasound (LIUS) has been adopted for a variety of therapeutic purposes because of its bioeffects such as thermal, mechanical, and cavitation effects. The mechanism of impact and cellular responses of LIUS in cellular regulations have been revealed, which helps to understand the role of LIUS in tumor treatment, stem cell therapy, and nervous system regulation. The review summarizes the bioeffects of LIUS at the cellular level and its related mechanisms, detailing the corresponding theoretical basis and latest research in the study of LIUS in the regulation of cells. In the future, the design of specific LIUS-mediated treatment strategies may benefit from promising investigations which is hoped to provide encouraging therapeutic data.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

State-of-the-art of ultrasound-triggered drug delivery from ultrasound-responsive drug carriers

INTRODUCTION

The development of new tools to locally and non-invasively transferring therapeutic substances at the desired site in deep living tissue has been a long sought-after goal within the drug delivery field. Among the established methods, ultrasound (US) with US-responsive carriers holds great promise and demonstrates on-demand delivery of a variety of functional substances with spatial precision of several millimeters in deep-seated tissues in animal models and humans. These properties have motivated several explorations of US with US responsive carriers as a modality for neuromodulation and the treatment of various diseases, such as stroke and cancer.

AREAS COVERED

This article briefly discussed three specific mechanisms that enhance in vivo drug delivery via US with US-responsive carriers: 1) permeabilizing cellular membrane, 2) increasing the permeability of vessels, and 3) promoting cellular endocytotic uptake. Besides, a series of US-responsive drug carriers are discussed, with an emphasis on the relation between structural feature and therapeutic outcome.

EXPERT OPINION

This article summarized current development for each of US-responsive drug carrier, focusing on the routes of enhancing delivery and applications. The mechanisms of interaction between US-responsive carriers and US energy, such as cavitation, hyperthermia, and reactive oxygen species, as well as how these interactions can improve drug delivery into target cell/tissue. It can be expected that there are serval efforts to further identification of US-responsive particles, design of novel US waveform sequence, and survey of optimal combination between US parameters and US-responsive carriers for better controlling the spatiotemporal drug release profile, stability, and safety in vivo. The authors believe these will provide novel tools for precisely designing treatment strategies and significantly benefit the clinical management of several diseases.

Optimized acoustic streaming generated at oblique incident angles to improve ultrasound thrombolysis effect

BACKGROUND

Combined with thrombolytic drugs and/or microbubbles (MBs), ultrasound (US) has been regarded as a useful tool for thrombolysis treatment by taking its advantages of non-invasive, non-ionization, low cost and accurate targeting of tissues deep in body. Recently, low-intensity pulsed ultrasound (LIPUS), which can cause fewer complications by stable cavitation and acoustic streaming other than more violent effects, has attracted broad attention.

PURPOSE

However, the thrombolysis effect in practice might not achieve expectation because there is not an ideal parallel multilayer structure between the skin and the targeted vessel. Therefore, the current work aims to better elucidate the influence of US incident angle on the generation of acoustic streaming and thrombolysis effect.

METHODS

Systemic numerical and experimental studies, viz., finite element modeling (FEM), particle image velocimetry (PIV) and in vitro thrombolysis measurements, were performed to estimate the acoustical/streaming field pattern, maximum flow velocity and shear stress on the surface of thrombus, as well as the lysis rate generated at different conditions. These methods aim at verifying the hypothesis that streaming-induced vortices can further accelerate the dissolution of the thrombus and optimized thrombolysis effected can be achieved by adjusting US incident angles.

RESULTS

The pool data results showed that the variation trends of the flow velocity and shear stress obtained from FEM simulation and PIV experiments are qualitatively consistent with each other. There exists an optimal incident angle that can maximize the flow velocity and shear stress on the surface of thrombus, so that superior stirring and mixing effect can be generated. Furthermore, as the flow velocity and shear stress on thrombus surface are both highly correlated with the thrombolysis effect (the correlation coefficient R1 = 0.988, R2 = 0.958, respectively), the peak value of lysis rate (increase by at least 5.02%) also occurred at 10°.

CONCLUSIONS

The current results demonstrated that, with appropriately determined incident angle, higher thrombolysis rate could be achieved without increasing the driving pressure. It may shed the light on future US thrombolysis planning strategy that, if combined with other advanced technologies (e.g., machine-learning-based image analysis and image-guided adaptive US emission modulation), more efficient thrombolytic effect could be realized while minimizing undesired side-effects caused by excessively high pressure. This article is protected by copyright. All rights reserved.

Ultrasound-assisted ocular drug delivery: A review of current evidence

Efficient ocular drug delivery is a challenging clinical problem with various therapeutic options but no clearly preferred methodology. Given the ubiquity of ultrasound as a diagnostic technique, the safety profile of ultrasound in an ocular context, and the prospect of custom-made ultrasound-sensitive contrast agents, ultrasound presents an attractive ocular drug delivery modality. In this review, we evaluate our present understanding of ultrasound as it relates to ocular drug delivery and significant knowledge gaps in the field. In doing so, we hope to call attention to a potentially novel drug delivery pathway that could be manipulated to treat or cure ocular diseases.

Lysozyme microspheres incorporated with anisotropic gold nanorods for ultrasound activated drug delivery

We report on the fabrication of lysozyme microspheres (LyMs) incorporated with gold nanorods (NRs) as a distinctive approach for the encapsulation and release of an anticancer drug, 5-Fluorouracil (5-FU). LyMs with an average size of 4.0 ± 1.0 µm were prepared by a sonochemical method and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). The LyMs were examined using hydrophobic (nile red) as well as hydrophilic (trypan blue) dyes under confocal laser scanning microscopy (CLSM) to obtain information about the preferential distribution of fluorescent molecules. Notably, the fluorescent molecules were accumulated in the inner lining of LyMs as the core was occupied with air. The encapsulation efficiency of 5-FU for LyMs-NR was found to be ∼64%. The drug release from control LyMs as well as LyMs incorporated with NRs was investigated under the influence of ultrasound (US) at 200 kHz. The total release for control LyMs and LyMs incorporated with gold NRs was found to be ∼70 and 95% after 1 h, respectively. The density difference caused by NR incorporation on the shell played a key role in rupturing the LyMs-NR under US irradiation. Furthermore, 5-FU loaded LyMs-NR exhibited excellent anti-cancer activity against the THP-1 cell line (∼90% cell death) when irradiated with US of 200 kHz. The enhanced anti-cancer activity of LyMs-NR was caused by the transfer of released 5-FU molecules from bulk to the interior of the cell via temporary pores formed on the surface of cancer cells, i.e., sonoporation. Thus, LyMs-NR demonstrated here has a high potential for use as carriers in the field of drug delivery, bio-imaging and therapy.

Advances in Immunotherapy for the Treatment of Adult Glioblastoma: Overcoming Chemical and Physical Barriers

Glioblastoma, or glioblastoma multiforme (GBM, WHO Grade IV), is a highly aggressive adult glioma. Despite extensive efforts to improve treatment, the current standard-of-care (SOC) regimen, which consists of maximal resection, radiotherapy, and temozolomide (TMZ), achieves only a 12-15 month survival. The clinical improvements achieved through immunotherapy in several extracranial solid tumors, including non-small-cell lung cancer, melanoma, and non-Hodgkin lymphoma, inspired investigations to pursue various immunotherapeutic interventions in adult glioblastoma patients. Despite some encouraging reports from preclinical and early-stage clinical trials, none of the tested agents have been convincing in Phase III clinical trials. One, but not the only, factor that is accountable for the slow progress is the blood-brain barrier, which prevents most antitumor drugs from reaching the target in appreciable amounts. Herein, we review the current state of immunotherapy in glioblastoma and discuss the significant challenges that prevent advancement. We also provide thoughts on steps that may be taken to remediate these challenges, including the application of ultrasound technologies.

Contrast Ultrasound, Sonothrombolysis and Sonoperfusion in Cardiovascular Disease: Shifting to Theragnostic Clinical Trials

Contrast ultrasound has a variety of applications in cardiovascular medicine, both in diagnosing cardiovascular disease as well as providing prognostic information. Visualization of intravascular contrast microbubbles is based on acoustic cavitation, the characteristic oscillation that results in changes in the reflected ultrasound waves. At high power, this acoustic response generates sufficient shear that is capable of enhancing endothelium-dependent perfusion in atherothrombotic cardiovascular disease (sonoperfusion). The oscillation and collapse of microbubbles in response to ultrasound also induces microstreaming and jetting that can fragment thrombus (sonothrombolysis). Several preclinical studies have focused on identifying optimal diagnostic ultrasound settings and treatment regimens. Clinical trials have been performed in acute myocardial infarction, stroke, and peripheral arterial disease often with improved outcome. In the coming years, results of ongoing clinical trials along with innovation and improvements in sonothrombolysis and sonoperfusion will determine whether this theragnostic technique will become a valuable addition to reperfusion therapy.

Sonophoresis with ultrasound-responsive liquid-core nuclei for transdermal drug delivery

BACKGROUND

Sonophoresis can increase the delivery efficiency of various drugs into the skin. A recent advance in sonophoresis is the use of ultrasound-responsive liquid-core nuclei (URLN) to increase the probability of cavitation. In this study, we developed a URLN and ultrasound device, and demonstrated its effectiveness through in vitro and clinical tests.

MATERIALS AND METHODS

Three types of experiments were designed to evaluate the efficiency of sonophoresis with URLN. First, a Franz diffusion cell with cosmetic ingredients was used to analyze quantitatively the amount of drug delivered to the porcine skin. Second, after the application of sonophoresis with URLN, the porcine skin surface was examined using scanning electron microscopy (SEM) to see the changes in morphology. Finally, a clinical test was performed to verify the utility of sonophoresis with URLN.

RESULTS

The results indicate that sonophoresis with URLN can increase the amount of compound delivered by approximately 11.9-fold over 6 h for niacinamide and by 7.33-fold over 6 h for adenosine. In addition, we observed approximately 20-30 μm sized pores on porcine skin in SEM images. In clinical testing, the application of sonophoresis with cosmetics containing URLN for 3 min improved the efficiency of transdermal drug delivery by 1.9-fold, the depth of absorption by 2.0-fold, and the speed of absorption by 2.0-fold at 30 min after application.

CONCLUSION

We expect that sonophoresis with specialized URLN in transdermal drug delivery could be used widely for various skin-related applications.

Sonoporation: Past, Present, and Future

A surge of research in intracellular delivery technologies is underway with the increased innovations in cell-based therapies and cell reprogramming. Particularly, physical cell membrane permeabilization techniques are highlighted as the leading technologies because of their unique features, including versatility, independence of cargo properties, and high-throughput delivery that is critical for providing the desired cell quantity for cell-based therapies. Amongst the physical permeabilization methods, sonoporation holds great promise and has been demonstrated for delivering a variety of functional cargos, such as biomolecular drugs, proteins, and plasmids, to various cells including cancer, immune, and stem cells. However, traditional bubble-based sonoporation methods usually require special contrast agents. Bubble-based sonoporation methods also have high chances of inducing irreversible damage to critical cell components, lowering the cell viability, and reducing the effectiveness of delivered cargos. To overcome these limitations, several novel non-bubble-based sonoporation mechanisms are under development. This review will cover both the bubble-based and non-bubble-based sonoporation mechanisms being employed for intracellular delivery, the technologies being investigated to overcome the limitations of traditional platforms, as well as perspectives on the future sonoporation mechanisms, technologies, and applications.