Ultrasound-sensitive nanodroplets achieve targeted neuromodulation

Dual-Functional Nanodroplet for Tumor Vasculature Ultrasound Imaging and Tumor Immunosuppressive Microenvironment Remodeling

Accurately evaluating tumor neoangiogenesis and conducting precise interventions toward an immune-favorable microenvironment are of significant clinical importance. In this study, a novel nanodroplet termed as the nanodroplet-based ultrasound contrast agent and therapeutic (NDsUCA/Tx) is designed for ultrasound imaging and precise interventions of tumor neoangiogenesis. Briefly, the NDsUCA/Tx shell is constructed from an engineered CMs containing the tumor antigen, vascular endothelial growth factor receptor 1 (VEGFR1) extracellular domain 2-3, and CD93 ligand multimerin 2. The core is composed of perfluorohexane and the immune adjuvant R848. After injection, NDsUCA/Tx is found to be enriched in the tumor vasculature with high expression of CD93. When triggered by ultrasound, the perfluorohexane in NDsUCA/Tx underwent acoustic droplet vaporization and generated an enhanced ultrasound signal. Some microbubbles exploded and the resultant debris (with tumor antigen and R848) together with the adsorbed VEGF are taken up by nearby cells. This cleared the local VEGF for vascular normalization, and also served as a vaccine to activate the immune response. Using a syngeneic mouse model, the satisfactory performance of NDsUCA/Tx in tumor vasculature imaging and immune activation is confirmed. Thus, a multifunctional NDsUCA/Tx is successfully developed for molecular imaging of tumor neoangiogenesis and precise remodeling of the tumor microenvironment.

Polydopamine Nanobowl-Armoured Perfluorocarbon Emulsions: Tracking Thermal- and Photothermal-Induced Phase Change through Neutron Scattering

Anisotropic polydopamine nanobowls (PDA NBs) show significant promise in biomedicine, distinguished by their unique optical properties and superior cellular uptake compared to spherical nanoparticles. This study presents a novel approach for creating multistimuli-activated PDA NB-armored emulsions, encapsulating perfluorohexane (NB-H) and perfluoropentane (NB-P) cores, with applications in controlled delivery and ultrasound imaging. Thermal and photothermal activation induced distinct responses in the emulsions, as evidenced by optical microscopy and thermogravimetric analysis. For the first time, neutron scattering techniques (SANS and USANS) under contrast matching conditions are applied to investigate these materials, revealing detailed droplet and microbubble structures and phase transition dynamics. These results show that NB-H droplets resist phase change under direct heating, whereas NB-P droplets respond more readily, exhibiting significant bubble formation. During photothermal activation with short near-infrared (NIR) exposure (15 min at 400 mW cm-2), SANS and USANS analyses reveal varying degrees of phase transition, proving this activation method to be more effective than direct heating. Importantly, NB-H and NB-P droplets have excellent ultrasound contrast enhancement and biocompatibility, indicating their potential for contrast-enhanced ultrasound imaging, theranostics, and photothermal applications. This comprehensive study advances the understanding of multifunctional colloidal materials in biomedicine, contributing essential knowledge to this rapidly evolving field.

The advance of ultrasound-enabled diagnostics and therapeutics

Point-of-care ultrasound demonstrates significant potential in biomedical research due to its noninvasive, real-time visualization, cost-effectiveness, and other biological benefits. Ultrasound irradiation can precisely control the mechanical and physicochemical effects on pathogenic lesions, enabling real-time visualization, tunable tissue penetration depth, and therapeutic applications. This review summarizes recent advancements in ultrasound-enabled diagnostics and therapeutics, focusing on mechanochemical effects that can be directly integrated into biomedical applications. Additionally, the structure-functionality relationships of sonotheranostic nanoplatforms are systematically discussed, providing insights into the underlying biological effects. Finally, the limitations of current ultrasonic medicine are discussed, along with potential expansions to facilitate patient-centered translations.

Investigating the hypotensive effect of focused ultrasound neuromodulation and barbiturate-loaded nanodroplets in healthy and hypertensive rats

BACKGROUND

Current strategies for reducing blood pressure (BP) are ineffective and unsafe for many patient populations, including drug-resistant hypertension and during pregnancy. Stimulating the periaqueductal grey (PAG) region has shown promise in treating drug-resistant hypertension in patients using deep brain stimulation.

OBJECTIVE

To develop a minimally invasive neuromodulation technique for the sustained treatment of hypertension.

METHODS

We have investigated BP reduction using focused ultrasound (FUS) (540 kHz) and anesthetic-loaded ultrasound-responsive nanodroplets to deliver pentobarbital to the PAG in normotensive (N = 27) and hypertensive (N = 20) male and female rats. BP, heart rate and plasma hormone content were collected before and after FUS exposure, and neuronal activity was mapped in the PAG using C-Fos and neuron subtype staining. Cavitation activity was monitored by detecting acoustic emissions from vaporizing nanodroplets, and neuromodulation was verified with immunohistochemistry.

RESULTS

Systolic and diastolic BP were reduced for 6 h following a single sonication of the PAG (-37/-28 mmHg systolic/diastolic), and the offline effect was extended to 4 days with consecutive sonications combined with systemically injected pentobarbital-loaded nanodroplets. In contrast, FUS applied to the frontal cortex had no effect on BP. Immunohistochemistry revealed stimulation of inhibitory neurons in the PAG region, indicating that the hypotensive effect was associated with a GABAergic pathway. The acoustic emissions from vaporizing droplets were found to correlate with neuron activity and change in BP, offering the potential for real-time treatment monitoring using ultrasound.

CONCLUSIONS

This work has implications for developing a new treatment for hypertension that has greater safety and broader applicability for vulnerable patient populations.

A review of temporal interference, nanoparticles, ultrasound, gene therapy, and designer receptors for Parkinson disease

In this review, we summarize preclinical and clinical trials investigating innovative neuromodulatory approaches for Parkinson disease (PD) motor symptom management. We highlight the following technologies: temporal interference, nanoparticles for drug delivery, blood-brain barrier opening, gene therapy, optogenetics, upconversion nanoparticles, magnetothermal nanoparticles, magnetoelectric nanoparticles, ultrasound-responsive nanoparticles, and designer receptors exclusively activated by designer drugs. These studies establish the basis for novel and promising neuromodulatory treatments for PD motor symptoms.

Transcranial focused ultrasound precise neuromodulation: a review of focal size regulation, treatment efficiency and mechanisms

Ultrasound is a mechanical wave that can non-invasively penetrate the skull to deep brain regions to activate neurons. Transcranial focused ultrasound neuromodulation is a promising approach, with the advantages of noninvasiveness, high-resolution, and deep penetration, which developed rapidly over the past years. However, conventional transcranial ultrasound's spatial resolution is low-precision which hinders its use in precision neuromodulation. Here we focus on methods that could increase the spatial resolution, gain modulation efficiency at the focal spot, and potential mechanisms of ultrasound neuromodulation. In this paper, we summarize strategies to enhance the precision of ultrasound stimulation, which could potentially improve the ultrasound neuromodulation technic.

A systematic review of preclinical and clinical transcranial ultrasound neuromodulation and opportunities for functional connectomics

BACKGROUND

Low-intensity transcranial ultrasound has surged forward as a non-invasive and disruptive tool for neuromodulation with applications in basic neuroscience research and the treatment of neurological and psychiatric conditions.

OBJECTIVE

To provide a comprehensive overview and update of preclinical and clinical transcranial low intensity ultrasound for neuromodulation and emphasize the emerging role of functional brain mapping to guide, better understand, and predict responses.

METHODS

A systematic review was conducted by searching the Web of Science and Scopus databases for studies on transcranial ultrasound neuromodulation, both in humans and animals.

RESULTS

187 relevant studies were identified and reviewed, including 116 preclinical and 71 clinical reports with subjects belonging to diverse cohorts. Milestones of ultrasound neuromodulation are described within an overview of the broader landscape. General neural readouts and outcome measures are discussed, potential confounds are noted, and the emerging use of functional magnetic resonance imaging is highlighted.

CONCLUSION

Ultrasound neuromodulation has emerged as a powerful tool to study and treat a range of conditions and its combination with various neural readouts has significantly advanced this platform. In particular, the use of functional magnetic resonance imaging has yielded exciting inferences into ultrasound neuromodulation and has the potential to advance our understanding of brain function, neuromodulatory mechanisms, and ultimately clinical outcomes. It is anticipated that these preclinical and clinical trials are the first of many; that transcranial low intensity focused ultrasound, particularly in combination with functional magnetic resonance imaging, has the potential to enhance treatment for a spectrum of neurological conditions.

Controlled ultrasonic interventions through the human skull

Transcranial focused ultrasound enables precise and non-invasive manipulations of deep brain circuits in humans, promising to provide safe and effective treatments of various neurological and mental health conditions. Ultrasound focused to deep brain targets can be used to modulate neural activity directly or localize the release of psychoactive drugs. However, these applications have been impeded by a key barrier-the human skull, which attenuates ultrasound strongly and unpredictably. To address this issue, we have developed an ultrasound-based approach that directly measures and compensates for the ultrasound attenuation by the skull. No additional skull imaging, simulations, assumptions, or free parameters are necessary; the method measures the attenuation directly by emitting a pulse of ultrasound from an array on one side of the head and measuring with an array on the opposite side. Here, we apply this emerging method to two primary future uses-neuromodulation and local drug release. Specifically, we show that the correction enables effective stimulation of peripheral nerves and effective release of propofol from nanoparticle carriers through an ex vivo human skull. Neither application was effective without the correction. Moreover, the effects show the expected dose-response relationship and targeting specificity. This article highlights the need for precise control of ultrasound intensity within the skull and provides a direct and practical approach for addressing this lingering barrier.

Targeted drug release from stable and safe ultrasound-sensitive nanocarriers

Targeted delivery of medication has the promise of increasing the effectiveness and safety of current systemic drug treatments. Focused ultrasound is emerging as noninvasive and practical energy for targeted drug release. However, it has yet to be determined which nanocarriers and ultrasound parameters can provide both effective and safe release. Perfluorocarbon nanodroplets have the potential to achieve these goals, but current approaches have either been effective or safe, but not both. We found that nanocarriers with highly stable perfluorocarbon cores mediate effective drug release so long as they are activated by ultrasound of sufficiently low frequency. We demonstrate a favorable safety profile of this formulation in a non-human primate. To facilitate translation of this approach into humans, we provide an optimized method for manufacturing the nanocarriers. This study provides a recipe and release parameters for effective and safe drug release from nanoparticle carriers in the body part specified by focused ultrasonic waves.

Recent advances in stimuli-responsive controlled release systems for neuromodulation

Neuromodulation aims to modulate the signaling activity of neurons or neural networks by the precise delivery of electrical stimuli or chemical agents and is crucial for understanding brain function and treating brain disorders. Conventional approaches, such as direct physical stimulation through electrical or acoustic methods, confront challenges stemming from their invasive nature, dependency on wired power sources, and unstable therapeutic outcomes. The emergence of stimulus-responsive delivery systems harbors the potential to revolutionize neuromodulation strategies through the precise and controlled release of neurochemicals in a specific brain region. This review comprehensively examines the biological barriers controlled release systems may encounter in vivo and the recent advances and applications of these systems in neuromodulation. We elucidate the intricate interplay between the molecular structure of delivery systems and response mechanisms to furnish insights for material selection and design. Additionally, the review contemplates the prospects and challenges associated with these systems in neuromodulation. The overarching objective is to propel the application of neuromodulation technology in analyzing brain functions, treating brain disorders, and providing insightful perspectives for exploiting new systems for biomedical applications.

Remotely controlled drug release in deep brain regions of non-human primates

Many areas of science and medicine would benefit from selective release of drugs in specific regions. Nanoparticle drug carriers activated by focused ultrasound-remotely applied, depth-penetrating energy-may provide such selective interventions. Here, we developed stable, ultrasound-responsive nanoparticles that can be used to release drugs effectively and safely in non-human primates. The nanoparticles were used to release propofol in deep brain visual regions. The release reversibly modulated the subjects' visual choice behavior and was specific to the targeted region and to the released drug. Gadolinium-enhanced MR imaging suggested an intact blood-brain barrier. Blood draws showed normal clinical chemistry and hematology. In summary, this study provides a safe and effective approach to release drugs on demand in selected deep brain regions at levels sufficient to modulate behavior.

Bridging Smart Nanosystems with Clinically Relevant Models and Advanced Imaging for Precision Drug Delivery

Intracellular delivery of nano-drug-carriers (NDC) to specific cells, diseased regions, or solid tumors has entered the era of precision medicine that requires systematic knowledge of nano-biological interactions from multidisciplinary perspectives. To this end, this review first provides an overview of membrane-disruption methods such as electroporation, sonoporation, photoporation, microfluidic delivery, and microinjection with the merits of high-throughput and enhanced efficiency for in vitro NDC delivery. The impact of NDC characteristics including particle size, shape, charge, hydrophobicity, and elasticity on cellular uptake are elaborated and several types of NDC systems aiming for hierarchical targeting and delivery in vivo are reviewed. Emerging in vitro or ex vivo human/animal-derived pathophysiological models are further explored and highly recommended for use in NDC studies since they might mimic in vivo delivery features and fill the translational gaps from animals to humans. The exploration of modern microscopy techniques for precise nanoparticle (NP) tracking at the cellular, organ, and organismal levels informs the tailored development of NDCs for in vivo application and clinical translation. Overall, the review integrates the latest insights into smart nanosystem engineering, physiological models, imaging-based validation tools, all directed towards enhancing the precise and efficient intracellular delivery of NDCs.

Remotely controlled drug release in deep brain regions of non-human primates

Many areas of science and medicine would benefit from selective release of drugs in specific regions of interest. Nanoparticle drug carriers activated by focused ultrasound-remotely applied, depth-penetrating energy-may provide such selective interventions. Here, we developed stable, ultrasound-responsive nanoparticles that can be used to release drugs effectively and safely in non-human primates. The nanoparticles were used to release propofol in deep brain visual regions. The release reversibly modulated the subjects' visual choice behavior and was specific to the targeted region and to the released drug. Gadolinium-enhanced MRI imaging suggested an intact blood-brain barrier. Blood draws showed normal clinical chemistry and hematology. In summary, this study provides a safe and effective approach to release drugs on demand in selected deep brain regions at levels sufficient to modulate behavior.

Ultrasound-responsive microbubbles and nanodroplets: A pathway to targeted drug delivery

Ultrasound-responsive agents have shown great potential as targeted drug delivery agents, effectively augmenting cell permeability and facilitating drug absorption. This review focuses on two specific agents, microbubbles and nanodroplets, and provides a sequential overview of their drug delivery process. Particular emphasis is given to the mechanical response of the agents under ultrasound, and the subsequent physical and biological effects on the cells. Finally, the state-of-the-art in their pre-clinical and clinical implementation are discussed. Throughout the review, major challenges that need to be overcome in order to accelerate their clinical translation are highlighted.

Direct Emulsification of Stable Superheated Perfluorobutane Nanodroplets by Sonication: Addressing the Limitations of the Microbubble Condensation Technique

OBJECTIVE

We have previously determined that direct formulation of a phospholipid-based perfluorobutane (PFB) emulsion using high-pressure homogenization produces monodispersed PFB nanodroplets (NDs) with relatively few non-PFB-filled NDs. In this article, we describe a simpler strategy to reproducibly formulate highly concentrated superheated PFB NDs using a probe sonicator, a more widely available tool.

METHODS

Similar to the homogenization technique, sonicating at low power a solution of phospholipids with condensed PFB at -10°C consistently yields NDs with an encapsulation efficiency close to 100% and very few non-PFB-filled particles.

RESULTS

The PFB emulsion is stable with absence of spontaneous vaporization at 37°C and for more than 14 d when frozen or refrigerated and for 3 d at 25°C. Acoustic droplet vaporization (ADV) occurred at a mechanical index >0.5 and continued to increase thereafter. The ADV threshold was similar for freshly made or frozen emulsion after thawing. In contrast to the microbubble (MB) condensation method, in which the ratio of non-PFB-filled to PFB-filled is 2000:1, particularly if MBs are not washed after formulation, nearly 94% of particles produced by direct sonication are PFB filled.

CONCLUSION

PFB NDs can be manufactured with high yield, stability and reproducibility using a probe sonicator that is available in many laboratories. Their ease of manufacture could spark discoveries into highly impactful ND-based diagnostic and therapeutic applications.

Ultrasound technology assisted colloidal nanocrystal synthesis and biomedical applications

Non-invasive and high spatiotemporal resolution mythologies for the diagnosis and treatment of disease in clinical medicine promote the development of modern medicine. Ultrasound (US) technology provides a non-invasive, real-time, and cost-effective clinical imaging modality, which plays a significant role in chemical synthesis and clinical translation, especially in in vivo imaging and cancer therapy. On the one hand, the US treatment is usually accompanied by cavitation, leading to high temperature and pressure, so-called "hot spot", playing a significant role in sonochemical-based colloidal synthesis. Compared with the classical nucleation synthetic method, the sonochemical synthesis strategy presents high efficiency for the fabrication of colloidal nanocrystals due to its fast nucleation and growth procedure. On the other hand, the US is attractive for in vivo and medical treatment, with applications increasing with the development of novel contrast agents, such as the micro and nano bubbles, which are widely used in neuromodulation, with which the US can breach the blood-brain barrier temporarily and safely, opening a new door to neuromodulation and therapy. In terms of cancer treatment, sonodynamic therapy and US-assisted synergetic therapy show great effects against cancer and sonodynamic immunotherapy present unparalleled potentiality compared with other synergetic therapies. Further development of ultrasound technology can revolutionize both chemical synthesis and clinical translation by improving efficiency, precision, and accessibility while reducing environmental impact and enhancing patient care. In this paper, we review the US-assisted sonochemical synthesis and biological applications, to promote the next generation US technology-assisted applications.

Controlled noninvasive modulation of deep brain regions in humans

Transcranial focused ultrasound provides noninvasive and reversible approaches for precise and personalized manipulations of brain circuits, with the potential to transform our understanding of brain function and treatments of brain dysfunction. However, effective applications in humans have been limited by the human head, which attenuates and distorts ultrasound severely and unpredictably. This has led to uncertain ultrasound intensities delivered into the brain. Here, we address this lingering barrier using a direct measurement approach that can be repeatedly applied to the human brain. The approach uses an ultrasonic scan of the head to measure and compensate for the attenuation of the ultrasound by all obstacles within the ultrasound path. No other imaging modality is required and the method is parameter-free and personalized to each subject. The approach accurately restores operators’ intended intensities inside ex-vivo human skulls. Moreover, the approach is critical for effective modulation of deep brain regions in humans. When applied, the approach modulates fMRI Blood Oxygen Level Dependent (BOLD) activity in disease-relevant deep brain regions. This tool unlocks the potential of emerging approaches based on low-intensity ultrasound for controlled manipulations of neural circuits in humans.

Transcranial focused ultrasound has had limited applications in humans due to the unpredictable distortions of ultrasound by the human head. Thomas Riis and colleagues report an approach which enables direct correction for the attenuation of ultrasound by the skull and hair, thus enabling controlled ultrasound therapies in humans.

Synchronous Intravital Imaging and Cavitation Monitoring of Antivascular Focused Ultrasound in Tumor Microvasculature Using Monodisperse Low Boiling Point Nanodroplets

Focused ultrasound-stimulated microbubbles can induce blood flow shutdown and ischemic necrosis at higher pressures in an approach termed antivascular ultrasound. Combined with conventional therapies of chemotherapy, immunotherapy, and radiation therapy, this approach has demonstrated tumor growth inhibition and profound synergistic antitumor effects. However, the lower cavitation threshold of microbubbles can potentially yield off-target damage that the polydispersity of clinical agent may further exacerbate. Here we investigate the use of a monodisperse nanodroplet formulation for achieving antivascular effects in tumors. We first develop stable low boiling point monodisperse lipid nanodroplets and examine them as an alternative agent to mediate antivascular ultrasound. With synchronous intravital imaging and ultrasound monitoring of focused ultrasound-stimulated nanodroplets in tumor microvasculature, we show that nanodroplets can trigger blood flow shutdown and do so with a sharper pressure threshold and with fewer additional events than conventionally used microbubbles. We further leverage the smaller size and prolonged pharmacokinetic profile of nanodroplets to allow for potential passive accumulation in tumor tissue prior to antivascular ultrasound, which may be a means by which to promote selective tumor targeting. We find that vascular shutdown is accompanied by inertial cavitation and complex-order sub- and ultraharmonic acoustic signatures, presenting an opportunity for effective feedback control of antivascular ultrasound.

Enhanced and spatially controllable neuronal activity induced by transcranial focused ultrasound stimulation combined with phase-change nanodroplets

Non-invasive ultrasound neuromodulation (USNM) is a powerful tool to explore neural circuits and treat neurological disorders. Due to the heterogeneity of the skull and regional variations in modulation and treatment objectives, it is necessary to develop an efficient and spatially controllable neuromodulation approach. Recently, transcranial focused ultrasound (tFUS) combined with external biomicro/nanomaterials for brain stimulation has garnered significant attention. This study focused on tFUS combined with perfluoropentane (PFP) nanodroplets (NDs) to improve the efficacy and spatial controllability of USNM. The developed two-stage variable pulse tFUS sequence that include the acoustic droplet vaporization (ADV) pulse for vaporizing PFP NDs into microbubbles (MBs) and the USNM sequence for inducing mechanical oscillations of the formed MBs to enhance neuronal activity. Further, adjusting the acoustic pressure of the ADV pulse generated the controllable vaporization regions, thereby achieving spatially controllable neuromodulation. The results showed that the mean densities of c-fos+ cells expression in the group of PFP NDs with ADV (109 ± 19 cells/mm2) were significantly higher compared to the group without ADV (37.34 ± 8.24 cells/mm2). The acoustic pressure of the ADV pulse with 1.98 MPa and 2.81 MPa in vitro generated the vaporization regions of 0.146 ± 0.032 cm2 and 0.349 ± 0.056 cm2, respectively. Under the same stimulation conditions, a larger vaporization region was also obtained with higher acoustic pressure in vivo, inducing a broader region of neuronal activation. Therefore, this study will serve as a valuable reference for developing the efficient and spatially controllable tFUS neuromodulation strategy.

Acoustomechanically activatable liposomes for ultrasonic drug uncaging

Ultrasound-activatable drug-loaded nanocarriers enable noninvasive and spatiotemporally-precise on-demand drug delivery throughout the body. However, most systems for ultrasonic drug uncaging utilize cavitation or heating as the drug release mechanism and often incorporate relatively exotic excipients into the formulation that together limit the drug-loading potential, stability, and clinical translatability and applicability of these systems. Here we describe an alternate strategy for the design of such systems in which the acoustic impedance and osmolarity of the internal liquid phase of a drug-loaded particle is tuned to maximize ultrasound-induced drug release. No gas phase, cavitation, or medium heating is necessary for the drug release mechanism. Instead, a non-cavitation-based mechanical response to ultrasound mediates the drug release. Importantly, this strategy can be implemented with relatively common pharmaceutical excipients, as we demonstrate here by implementing this mechanism with the inclusion of a few percent sucrose into the internal buffer of a liposome. Further, the ultrasound protocols sufficient for in vivo drug uncaging with this system are achievable with current clinical therapeutic ultrasound systems and with intensities that are within FDA and society guidelines for safe transcranial ultrasound application. Finally, this current implementation of this mechanism should be versatile and effective for the loading and uncaging of any therapeutic that may be loaded into a liposome, as we demonstrate for four different drugs in vitro, and two in vivo. These acoustomechanically activatable liposomes formulated with common pharmaceutical excipients promise a system with high clinical translational potential for ultrasonic drug uncaging of myriad drugs of clinical interest.

Nanodroplet-Based Super-Resolution Ultrasound Localization Microscopy

Over the past decade, super-resolution ultrasound localization microscopy (SR-ULM) has revolutionized ultrasound imaging with its capability to resolve the microvascular structures below the ultrasound diffraction limit. The introduction of this imaging technique enables the visualization, quantification, and characterization of tissue microvasculature. The early implementations of SR-ULM utilize microbubbles (MBs) that require a long image acquisition time due to the requirement of capturing sparsely isolated microbubble signals. The next-generation SR-ULM employs nanodroplets that have the potential to significantly reduce the image acquisition time without sacrificing the resolution. This review discusses various nanodroplet-based ultrasound localization microscopy techniques and their corresponding imaging mechanisms. A summary is given on the preclinical applications of SR-ULM with nanodroplets, and the challenges in the clinical translation of nanodroplet-based SR-ULM are presented while discussing the future perspectives. In conclusion, ultrasound localization microscopy is a promising microvasculature imaging technology that can provide new diagnostic and prognostic information for a wide range of pathologies, such as cancer, heart conditions, and autoimmune diseases, and enable personalized treatment monitoring at a microlevel.

Ultrasound meets the cell membrane: for enhanced endocytosis and drug delivery

Endocytosis plays a crucial role in drug delivery for precision therapy. As a non-invasive and spatiotemporal-controllable stimulus, ultrasound (US) has been utilized for improving drug delivery efficiency due to its ability to enhance cell membrane permeability. When US meets the cell membrane, the well-known cavitation effect generated by US can cause various biophysical effects, facilitating the delivery of various cargoes, especially nanocarriers. The comprehension of recent progress in the biophysical mechanism governing the interaction between ultrasound and cell membranes holds significant implications for the broader scientific community, particularly in drug delivery and nanomedicine. This review will summarize the latest research results on the biological effects and mechanisms of US-enhanced cellular endocytosis. Moreover, the latest achievements in US-related biomedical applications will be discussed. Finally, challenges and opportunities of US-enhanced endocytosis for biomedical applications will be provided.

Physical Characterization to Improve Scalability and Potential of Anesthetic-Loaded Nanodroplets

Drug-loaded perfluorocarbon nanodroplets (NDs) can be activated non-invasively by focused ultrasound (FUS) and allow for precise drug-delivery. Anesthetic-loaded NDs and transcranial FUS have previously achieved targeted neuromodulation. To assess the clinical potential of anesthetic-loaded NDs, in depth physical characterization and investigation of storage strategies and triggered-activation is necessary. Pentobarbital-loaded decafluorobutane nanodroplets (PBNDs) with a Definity-derived lipid shell (237 nm; 4.08 × 109 particles/mL) were fabricated and assessed. Change in droplet stability, concentration, and drug-release efficacy were tested for PBNDs frozen at -80 °C over 4 weeks. PBND diameter and the polydispersity index of thawed droplets remained consistent up to 14 days frozen. Cryo-TEM images revealed NDs begin to lose circularity at 7 days, and by 14 days, perfluorocarbon dissolution and lipid fragmentation occurred. The level of acoustic response and drug release decreases through prolonged storage. PBNDs showed no hemolytic activity at clinically relevant concentrations and conditions. At increasing sonication pressures, liquid PBNDs vaporized into gas microbubbles, and acoustic activity at the second harmonic frequency (2 f0) peaked at lower pressures than the subharmonic frequency (1/2 f0). Definity-based PBNDs have been thoroughly characterized, cryo-TEM has been shown to be suitable to image the internal structure of volatile NDs, and PBNDs can be reliably stored at -80 °C for future use up to 7 days without significant degradation, loss of acoustic response, or reduction in ultrasound-triggered drug release.

Anesthetic-loaded nanodroplets with focused ultrasound reduces agitation in Alzheimer's mice

OBJECTIVE

Alzheimer's disease (AD) is often associated with neuropsychiatric symptoms, including agitation and aggressive behavior. These symptoms increase with disease severity, ranging from 10% in mild cognitive impairment to 50% in patients with moderate-to-severe AD, pose a great risk for self-injury and injury to caregivers, result in high rates of institutionalization and great suffering for patients and families. Current pharmacological therapies have limited efficacy and a high potential for severe side effects. Thus, there is a growing need to develop novel therapeutics tailored to safely and effectively reduce agitation and aggressive behavior in AD. Here, we investigate for the first time the use of focused ultrasound combined with anesthetic-loaded nanodroplets (nanoFUS) targeting the amygdala (key structure in the neurocircuitry of agitation) as a novel minimally invasive tool to modulate local neural activity and reduce agitation and aggressive behavior in the TgCRND8 AD transgenic mice.

METHODS

Male and female animals were tested in the resident-intruder (i.e., aggressive behavior) and open-field tests (i.e., motor agitation) for baseline measures, followed by treatment with active- or sham-nanoFUS. Behavioral testing was then repeated after treatment.

RESULTS

Active-nanoFUS neuromodulation reduced aggressive behavior and agitation in male mice, as compared to sham-treated controls. Treatment with active-nanoFUS increased the time male mice spent in social-non-aggressive behaviors.

INTERPRETATION

Our results show that neuromodulation with active-nanoFUS may be a potential therapeutic tool for the treatment of neuropsychiatric symptoms, with special focus on agitation and aggressive behaviors. Further studies are necessary to establish cellular, molecular and long-term behavioral changes following treatment with nanoFUS.

Ultrasound-guided chemoradiotherapy of breast cancer using smart methotrexate-loaded perfluorohexane nanodroplets

Chemoradiotherapy with controlled-release nanocarriers such as sono-sensitive nanodroplets (NDs) can enhance the anticancer activity of chemotherapy medicines and reduces normal tissue side effects. In this study, folic acid-functionalized methotrexate-loaded perfluorohexane NDs with alginate shell (FA-MTX/PFH@alginate NDs) were synthesized, characterized, and their potential for ultrasound-guided chemoradiotherapy of breast cancer was investigated in vitro and in vivo. The cancer cell (4T1) viabilities and surviving fractions after NDs and ultrasound treatments were significantly decreased. However, this reduction was much more significant for ultrasound in combination with X-ray irradiation. The in vitro and in vivo results confirmed that MTX-loaded NDs are highly biocompatible and they have no significant hemolytic activity and organ toxicity. Furthermore, the in vivo results indicated that the FA-MTX/PFH@alginate NDs were accumulated selectively in the tumor region. In conclusion, FA-functionalized MTX/PFH@alginate NDs have a great theranostic performance for ultrasound-controlled drug delivery in combination with radiotherapy of breast cancer.

Multifunctional theragnostic ultrasmall gold nanodot-encapsuled perfluorocarbon nanodroplets for laser-focused ultrasound sequence irradiation (LFSI)-based enhanced tumor ablation

Despite the substantial potential of focused ultrasound therapy, its efficacy in cancer therapy has been limited due to the high cavitation threshold and safety concerns regarding the use of high-intensity energy pulses. Here, ultrasmall Au nanodot-loaded PEG-modified perfluorocarbon nanodroplets (Au-PFCnDs) were prepared and used as a therapeutic enhancer. A LFSI method was designed to achieve enhanced tumor ablation at a mild focused ultrasound (FUS) energy pulse with the assistance of the instinct photothermal effect of intratumor-permeable ultrasmall Au nanodots under 808 nm NIR laser irradiation. In addition to their therapeutic function, Au-PFCnDs can also generate multimodal images to provide information for tumor surveillance and treatment guidance. The experimental results also showed that the cRGD-targeted Au-PFCnDs could be more efficiently delivered into the tumor and selectively destroy tumors with no observable side effects on normal tissue under LFSI treatment.

Ultrasound-triggered oxygen-loaded nanodroplets enhance and monitor cerebral damage from sonodynamic therapy

In sonodynamic therapy, cellular toxicity from sonosensitizer drugs, such as 5-aminolevulinic acid hydrochloride (5-ALA), may be triggered with focused ultrasound through the production of reactive oxygen species (ROS). Here we show that by increasing local oxygen during treatment, using oxygen-loaded perfluorocarbon nanodroplets (250 +/- 8 nm), we can increase the damage induced by 5-ALA, and monitor the severity by recording acoustic emissions in the brain. To achieve this, we sonicated the right striatum of 16 healthy rats after an intravenous dose of 5-ALA (200 mg/kg), followed by saline, nanodroplets, or oxygen-loaded nanodroplets. We assessed haemorrhage, edema and cell apoptosis immediately following, 24 hr, and 48 hr after focused ultrasound treatment. The localized volume of damaged tissue was significantly enhanced by the presence of oxygen-loaded nanodroplets, compared to ultrasound with unloaded nanodroplets (3-fold increase), and ultrasound alone (40-fold increase). Sonicating 1 hr following 5-ALA injection was found to be more potent than 2 hr following 5-ALA injection (2-fold increase), and the severity of tissue damage corresponded to the acoustic emissions from droplet vaporization. Enhancing the local damage from 5-ALA with monitored cavitation activity and additional oxygen could have significant implications in the treatment of atherosclerosis and non-invasive ablative surgeries.

Ultrasound-assisted brain delivery of nanomedicines for brain tumor therapy: advance and prospect

Nowadays, brain tumors are challenging problems, and the key of therapy is ensuring therapeutic drugs cross the blood-brain barrier (BBB) effectively. Although the efficiency of drug transport across the BBB can be increased by innovating and modifying nanomedicines, they exert insufficient therapeutic effects on brain tumors due to the complex environment of the brain. It is worth noting that ultrasound combined with the cavitation effect of microbubbles can assist BBB opening and enhance brain delivery of nanomedicines. This ultrasound-assisted brain delivery (UABD) technology with related nanomedicines (UABD nanomedicines) can safely open the BBB, facilitate the entry of drugs into the brain, and enhance the therapeutic effect on brain tumors. UABD nanomedicines, as the main component of UABD technology, have great potential in clinical application and have been an important area of interest in the field of brain tumor therapy. However, research on UABD nanomedicines is still in its early stages despite the fact that they have been associated with many disciplines, including material science, brain science, ultrasound, biology, and medicine. Some aspects of UABD theory and technology remain unclear, especially the mechanisms of BBB opening, relationship between materials of nanomedicines and UABD technology, cavitation and UABD nanomedicines design theories. This review introduces the research status of UABD nanomedicines, investigates their properties and applications of brain tumor therapy, discusses the advantages and drawbacks of UABD nanomedicines for the treatment of brain tumors, and offers their prospects. We hope to encourage researchers from various fields to participate in this area and collaborate on developing UABD nanomedicines into powerful tools for brain tumor therapy.

Recent Studies on Hydrogels Based on H2O2-Responsive Moieties: Mechanism, Preparation and Application

H₂O₂ is essential for cellular processes and plays a vital role in the regulation of cell signaling pathways, which can be viewed as a warning signal for many kinds of disease including cancer, cardiovascular disease, reproductive abnormalities, diabetes, and renal failure. A H₂O₂-responsive hydrogel (H₂O₂-Gel) is a promising candidate for biomedical applications because of its good biocompatibility, similarity to soft biological tissues, ease of preparation, and its ability to respond to H₂O₂. In this study, the H₂O₂-responsive moieties used to fabricate H₂O₂-Gels were reviewed, including thioethers, disulfide bonds, selenides, diselenium bonds, diketones, boronic, and others. Next, the preparation method of H₂O₂-Gel was divided into two major categories according to their reaction mechanisms: either self-crosslinking or mechanisms entailing the addition of difunctional crosslinkers. Last, the applications of H₂O₂-Gels were emphasized, which have been viewed as desirable candidates in the fields of drug delivery, the detection of H₂O₂, glucose-responsive systems, ROS scavengers, tissue engineering, and cell-encapsulation.

Ultrasound-Activated Nanodroplet Disruption of the Enterococcus faecalis Biofilm in Dental Root Canal

Conventional methods used to control bacterial biofilm infection in root canals have poor efficacy, causing repeated and chronic infections, which pose a great challenge to clinical treatment. Microbubbles, due to their small size and ultrasound (US)-enhanced cavitation effects, have attracted considerable clinical attention. They possess the potential for therapeutic application in restricted spaces. We address the above problem with a strategy for the restricted space of root canals. Herein, phase-change nanodroplets (P-NDs) exposed to US are combined with common antibacterial drugs to disrupt a 7 day Enterococcus faecalis biofilm in an in vitro human tooth model. Specifically, the preparation of P-NDs is based on secondary cavitation. Their average particle size is ∼144 nm, and the stability is favorable. The clearance effect for the biofilm is notable (the disruption rate of P-NDs + US is 63.1%, P < 0.01), while the effect of an antibacterial in conjunction with 2% chlorhexidine (Chx) is significant (the antibiofilm rate of P-NDs@2% Chx + US is 96.2%, P < 0.001). Furthermore, biocompatibility testing on human periodontal ligament fibroblasts demonstrated that P-NDs are safe. In summary, the strategy that we have proposed is suitable for the removal of biofilms in root canals. Notably, it also has great potential for application in the treatment of bacterial infections in restricted spaces.

Acoustic properties across the human skull

Transcranial ultrasound is emerging as a noninvasive tool for targeted treatments of brain disorders. Transcranial ultrasound has been used for remotely mediated surgeries, transient opening of the blood-brain barrier, local drug delivery, and neuromodulation. However, all applications have been limited by the severe attenuation and phase distortion of ultrasound by the skull. Here, we characterized the dependence of the aberrations on specific anatomical segments of the skull. In particular, we measured ultrasound propagation properties throughout the perimeter of intact human skulls at 500 kHz. We found that the parietal bone provides substantially higher transmission (average pressure transmission 31 ± 7%) and smaller phase distortion (242 ± 44 degrees) than frontal (13 ± 2%, 425 ± 47 degrees) and occipital bone regions (16 ± 4%, 416 ± 35 degrees). In addition, we found that across skull regions, transmission strongly anti-correlated (R=-0.79) and phase distortion correlated (R=0.85) with skull thickness. This information guides the design, positioning, and skull correction functionality of next-generation devices for effective, safe, and reproducible transcranial focused ultrasound therapies.

Habenula as a Neural Substrate for Aggressive Behavior

Over the past decades, an ever growing body of literature has explored the anatomy, connections, and functions of the habenula (Hb). It has been postulated that the Hb plays a central role in the control of the monoaminergic system, thus influencing a wide range of behavioral responses, and participating in the pathophysiology of a number of psychiatric disorders and neuropsychiatric symptoms, such as aggressive behaviors. Aggressive behaviors are frequently accompanied by restlessness and agitation, and are commonly observed in patients with psychiatric disorders, intellectual disabilities, and neurodegenerative diseases of aging. Recently, the Hb has been explored as a new target for neuromodulation therapies, such as deep brain stimulation, with promising results. Here we review the anatomical organization of the habenula and discuss several distinct mechanisms by which the Hb is involved in the modulation of aggressive behaviors, and propose new investigations for the development of novel treatments targeting the habenula to reduce aggressive behaviors.

Precise Ultrasound Neuromodulation in a Deep Brain Region Using Nano Gas Vesicles as Actuators

Ultrasound is a promising new modality for non-invasive neuromodulation. Applied transcranially, it can be focused down to the millimeter or centimeter range. The ability to improve the treatment's spatial resolution to a targeted brain region could help to improve its effectiveness, depending upon the application. The present paper details a neurostimulation scheme using gas-filled nanostructures, gas vesicles (GVs), as actuators for improving the efficacy and precision of ultrasound stimuli. Sonicated primary neurons display dose-dependent, repeatable Ca²⁺ responses, closely synced to stimuli, and increased nuclear expression of the activation marker c-Fos in the presence of GVs. GV-mediated ultrasound triggered rapid and reversible Ca²⁺ responses in vivo and could selectively evoke neuronal activation in a deep-seated brain region. Further investigation indicate that mechanosensitive ion channels are important mediators of this effect. GVs themselves and the treatment scheme are also found not to induce significant cytotoxicity, apoptosis, or membrane poration in treated cells. Altogether, this study demonstrates a simple and effective method to achieve enhanced and better-targeted neurostimulation with non-invasive low-intensity ultrasound.

Sub-millimetre precision of drug delivery in the brain from ultrasound-triggered nanodroplets

Drug-loaded nanoscale cavitation agents, called nanodroplets, are an attractive solution to enhance and localize drug delivery, offering increased stability and prolonged half-life in circulation compared to microbubbles. However, the spatial precision with which drug can be released and delivered into brain tissue from such agents has not been directly mapped. Decafluorobutane lipid-shell droplets (206 +/- 6 nm) were loaded with a fluorescent blood-brain barrier (BBB)-penetrating dye (Nile Blue) and vaporized with ultrasound (1.66 MHz, 10 ms pulse length, 1 Hz pulse repetition frequency), generating transient echogenic microbubbles and delivering the encapsulated dye. The distribution and intensity of released fluorophore was mapped in a tissue-mimicking phantom, and in the brain of rats (Sprague Dawley, N = 4, n = 16). The release and distribution of dye was found to be pressure-dependent (0.2-3.5 MPa) and to occur only above the vaporization threshold of the nanodroplets (1.5 +/- 0.25 MPa in vitro, 2.4 +/- 0.05 MPa in vivo). Dye delivery was achieved with sub-millimetre spatial precision, covering an area of 0.4 to 1.5 mm in diameter, determined by the sonication pressure. The distribution and intensity of dye released at depth in the brain followed the axial pressure profile of the ultrasound beam. Nile Blue (354 Da, LogP 2.7) was compared to Nile Red (318 Da, LogP 3.8) and Quantum Dots (CdSe/ZnS, 5 nm diameter) to visualize the role of molecule size and lipophilicity in crossing the intact BBB following triggered release. Acoustic emissions were shown to predict the successful delivery of the BBB-penetrating dye and the extent of the distribution, demonstrating the theranostic capabilities of nanoscale droplets to precisely localize drug delivery in the brain.

Ultrasonic technologies in imaging and drug delivery

Ultrasonic technologies show great promise for diagnostic imaging and drug delivery in theranostic applications. The development of functional and molecular ultrasound imaging is based on the technical breakthrough of high frame-rate ultrasound. The evolution of shear wave elastography, high-frequency ultrasound imaging, ultrasound contrast imaging, and super-resolution blood flow imaging are described in this review. Recently, the therapeutic potential of the interaction of ultrasound with microbubble cavitation or droplet vaporization has become recognized. Microbubbles and phase-change droplets not only provide effective contrast media, but also show great therapeutic potential. Interaction with ultrasound induces unique and distinguishable biophysical features in microbubbles and droplets that promote drug loading and delivery. In particular, this approach demonstrates potential for central nervous system applications. Here, we systemically review the technological developments of theranostic ultrasound including novel ultrasound imaging techniques, the synergetic use of ultrasound with microbubbles and droplets, and microbubble/droplet drug-loading strategies for anticancer applications and disease modulation. These advancements have transformed ultrasound from a purely diagnostic utility into a promising theranostic tool.

Predicting initial nucleation events occurred in a metastable nanodroplet during acoustic droplet vaporization

Acoustic droplet vaporization (ADV) capable of converting liquid perfluorocarbon (PFC) micro/nanodroplets into gaseous microbubbles has gained much attention due to its medical potentials. However, its physical mechanisms for nanodroplets have not been well understood due to the disappeared superharmonic focusing effect and the prominent Laplace pressure compared to microdroplets, especially for the initial ADV nucleation occurring in a metastable PFC nanodroplet. The classical nucleation theory (CNT) was modified to describe the ADV nucleation via combining the phase-change thermodynamics of perfluoropentane (PFP) and the Laplace pressure effect on PFP nanodroplets. The thermodynamics was exactly predicted by the Redlich-Kwong equation of state (EoS) rather than the van der Waals EoS, based on which the surface tension of the vapor nucleus as a crucial parameter in the CNT was successfully obtained to modify the CNT. Compared to the CNT, the modified CNT eliminated the intrinsic limitations of the CNT, and it predicted a larger nucleation rate and a lower ADV nucleation threshold, which agree much better with experimental results. Furthermore, it indicated that the nanodroplet properties exert very strong influences on the nucleation threshold instead of the acoustic parameters, providing a potential strategy with an appropriate droplet design to reduce the ADV nucleation threshold. This study may contribute to further understanding the ADV mechanism for PFC nanodroplets and promoting its potential theranostic applications in clinical practice.