Biological effects of ultrasound: development of safety guidelines. Part II: general review

Revealing physical interactions of ultrasound waves with the body through photoelasticity imaging

Ultrasound is a ubiquitous technology in medicine for screening, diagnosis, and treatment of disease. The functionality and efficacy of different ultrasound modes relies strongly on our understanding of the physical interactions between ultrasound waves and biological tissue structures. This article reviews the use of photoelasticity imaging for investigating ultrasound fields and interactions. Physical interactions are described for different ultrasound technologies, including those using linear and nonlinear ultrasound waves, as well as shock waves. The use of optical modulation of light by ultrasound is presented for shadowgraphic and photoelastic techniques. Investigations into shock wave and burst wave lithotripsy using photoelastic methods are summarized, along with other endoscopic forms of lithotripsy. Photoelasticity in soft tissue surrogate materials is reviewed, and its deployment in investigating tissue-bubble interactions, generated ultrasound waves, and traumatic brain injury, are discussed. With the continued growth of medical ultrasound, photoelasticity imaging can play a role in elucidating the physical mechanisms leading to useful bioeffects of ultrasound for imaging and therapy.

In Vivo Polymer Mechanochemistry with Polynucleotides

Polymer mechanochemistry utilizes mechanical force to activate latent functionalities in macromolecules and widely relies on ultrasonication techniques. Fundamental constraints of frequency and power intensity have prohibited the application of the polymer mechanochemistry principles in a biomedical context up to now, although medical ultrasound is a clinically established modality. Here, a universal polynucleotide framework is presented that allows the binding and release of therapeutic oligonucleotides, both DNA- and RNA-based, as cargo by biocompatible medical imaging ultrasound. It is shown that the high molar mass, colloidal assembly, and a distinct mechanochemical mechanism enable the force-induced release of cargo and subsequent activation of biological function in vitro and in vivo. Thereby, this work introduces a platform for the exploration of biological questions and therapeutics development steered by mechanical force.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

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

Transcranial Magneto-Acoustic Stimulation Protects Synaptic Rehabilitation from Amyloid-Beta Plaques via Regulation of Microglial Functions

Transcranial magneto-acoustic stimulation (TMAS), which is characterized by high spatiotemporal resolution and high penetrability, is a non-invasive neuromodulation technology based on the magnetic-acoustic coupling effect. To reveal the effects of TMAS treatment on amyloid-beta (Aβ) plaque and synaptic plasticity in Alzheimer's disease, we conducted a comparative analysis of TMAS and transcranial ultrasound stimulation (TUS) based on acoustic effects in 5xFAD mice and BV2 microglia cells. We found that the TMAS-TUS treatment effectively reduced amyloid plaque loads and plaque-associated neurotoxicity. Additionally, TMAS-TUS treatment ameliorated impairments in long-term memory formation and long-term potentiation. Moreover, TMAS-TUS treatment stimulated microglial proliferation and migration while enhancing the phagocytosis and clearance of Aβ. In 5xFAD mice with induced microglial exhaustion, TMAS-TUS treatment-mediated Aβ plaque reduction, synaptic rehabilitation improvement, and the increase in phospho-AKT levels were diminished. Overall, our study highlights that stimulation of hippocampal microglia by TMAS treatment can induce anti-cognitive impairment effects via PI3K-AKT signaling, providing hope for the development of new strategies for an adjuvant therapy for Alzheimer's disease.

Ultrasound robotics for precision therapy

In recent years, the application of microrobots in precision therapy has gained significant attention. The small size and maneuverability of these micromachines enable them to potentially access regions that are difficult to reach using traditional methods; thus, reducing off-target toxicities and maximizing treatment effectiveness. Specifically, acoustic actuation has emerged as a promising method to exert control. By harnessing the power of acoustic energy, these small machines potentially navigate the body, assemble at the desired sites, and deliver therapies with enhanced precision and effectiveness. Amidst the enthusiasm surrounding these miniature agents, their translation to clinical environments has proven difficult. The primary objectives of this review are threefold: firstly, to offer an overview of the fundamental acoustic principles employed in the field of microrobots; secondly, to assess their current applications in medical therapies, encompassing tissue targeting, drug delivery or even cell infiltration; and lastly, to delve into the continuous efforts aimed at integrating acoustic microrobots into in vivo applications.

Mechanochemical Activation of DNAzyme by Ultrasound

Controlling the activity of DNAzymes by external triggers is an important task. Here a temporal control over DNAzyme activity through a mechanochemical pathway with the help of ultrasound (US) is demonstrated. The deactivation of the DNAzyme is achieved by hybridization to a complementary strand generated through rolling circle amplification (RCA), an enzymatic polymerization process. Due to the high molar mass of the resulting polynucleic acids, shear force can be applied on the RCA strand through inertial cavitation induced by US. This exerts mechanical force and leads to the cleavage of the base pairing between RCA strand and DNAzyme, resulting in the recovery of DNAzyme activity. This is the first time that this release mechanism is applied for the activation of catalytic nucleic acids, and it has multiple advantages over other stimuli. US has higher penetration depth into tissues compared to light, and it offers a more specific stimulus than heat, which has also limited use in biological systems due to cell damage caused by hyperthermia. This approach is envisioned to improve the control over DNAzyme activity for the development of reliable and specific sensing applications.

Enhancing the growth of thermophilic Bacillus licheniformis YYC4 by low-intensity fixed-frequency continuous ultrasound

The effect of low-intensity fixed-frequency continuous ultrasound (LIFFCU) on the growth of Bacillus licheniformis YYC4 was investigated. The changes in morphology and activity of the organism, contributing to the growth were also explored. Compared with the control, a significant increase (48.95%) in the biomass of B. licheniformis YYC4 (at the logarithmic metaphase) was observed following the LIFFCU (28 kHz, 1.5 h and 120 W (equivalent to power density of 40 W/L)) treatment. SEM images showed that ultrasonication caused sonoporation, resulting in increased membrane permeability, evidenced by increase in cellular membrane potential, electrical conductivity of the culture, extracellular protein and nucleic acid, and intracellular Ca2+ content. Furthermore, LIFFCU action remarkably increased the extracellular protease activity, volatile components of the culture medium, microbial metabolic activity, and spore germination of the strain. Therefore, LIFFCU could be used to efficiently promote the growth of targeted microorganisms.

Virtual touch IQ elastography in the evaluation of fetal liver and placenta in pregnancies with gestational diabetes mellitus

OBJECTIVES

Elastography is considered a novel technique in the assessment of placenta parenchymal elasticity and very few data present the feasibility of elastography on human fetal tissue. This study aims to investigate the feasibility of fetal liver and placenta elastography and differences in pregnancies with GDM.

METHODS

Fifty-five women with GDM and 40 women with uncomplicated pregnancy as the control group was enrolled prospectively in this case-control study. Fetal liver VTIQ and placenta VTIQ elastography were performed between 25 and 39 weeks of pregnancy.

RESULTS

Mean placenta thickness at the level of umbilical cord insertion was significantly higher in the GDM group than in the control group (p=0.034). VTIQ elastography elasticity velocity (kPa) examinations revealed similar mean placenta and mean fetal liver stiffness in both groups. A weak to moderate correlation was observed between the mean elasticity of the placenta and the mean elasticity of the fetal liver (r=0.310; p=0.004).

CONCLUSIONS

Elastography may provide valuable information of especially on fetal tissue development and pathology. While placenta and fetal liver VTIQ elastography are feasible in pregnancy, the diagnostic value of these examinations in GDM is not certain and it seems to be that significant differences in SWE examinations that reflect structural changes in fetal tissue or placenta are more prominent in more chronic conditions such as type 1 and type 2 diabetes mellitus.

Drug delivery by sonosensitive liposome and microbubble with acoustic-lens attached ultrasound: an in vivo feasibility study in a murine melanoma model

Conventional chemotherapy methods have adverse off-target effects and low therapeutic efficiencies of drug release in target tumors. In this study, we proposed a combination therapy of doxorubicin (DOX)-loaded ultrasound (US)-sensitive liposomal nanocarriers (IMP301), microbubbles (MBs) under focused US exposure using convex acoustic lens-attached US (LENS) to tumor treatment. The therapeutic effects of each treatment in a murine melanoma model were evaluated using contrast-enhanced US (CEUS) and micro-computed tomography (micro-CT) imaging, bioluminescence and confocal microscopy imaging, and liquid chromatography-mass spectroscopy (LC/MS) analysis. Tumor-bearing mice were randomly assigned to one of the following groups: (1) G1: IMP301 only (n = 9); (2) G2: IMP301 + LENS (n = 9); (3) G3: IMP301 + MB + LENS (n = 9); (4) G4: DOXIL only (n = 9); and (5) G5: IMP301 without DOXIL group as a control group (n = 4). Ten days after tumor injection, tumor-bearing mice were treated according to each treatment strategy on 10th, 12th, and 14th days from the day of tumor injection. The CEUS images of the tumors in the murine melanoma model clearly showed increased echo signal intensity from MBs as resonant US scattering. The relative tumor volume of the G2 and G3 groups on the micro-CT imaging showed inhibited tumor growth than the reference baseline of the G5 group. DOX signals on bioluminescence and confocal microscopy imaging were mainly located at the tumor sites. LC/MS showed prominently higher intratumoral DOX concentration in the G3 group than in other treated groups. Therefore, this study effectively demonstrates the feasibility of the synergistic combination of IMP301, MBs, and LENS-application for tumor-targeted treatment. Thus, this study can enable efficient tumor-targeted treatment by combining therapy such as IMP301 + MBs + LENS-application.

A novel convex acoustic lens-attached ultrasound drug delivery system and its testing in a murine melanoma subcutaneous modelo

Target-specific drug release is indispensable to improve chemotherapeutic efficacy as it enhances drug uptake and penetration into tumors. Sono-responsive drug-loaded nano-/micro-particles are a promising solution for achieving target specificity by exposing them to ultrasound near tumors. However, the complicated synthetic processes and limited ultrasound (US) exposure conditions, such as limited control of ultrasound focal depth and acoustic power, prevent the practical application of this approach in clinical practice. Here, we propose a convex acoustic lens-attached US (CALUS) as a simple, economic, and efficient alternative of focused US for drug delivery system (DDS) application. The CALUS was characterized both numerically and experimentally using a hydrophone. In vitro, microbubbles (MBs) inside microfluidic channels were destroyed using the CALUS with various acoustic parameters (acoustic pressure [P], pulse repetition frequency [PRF], and duty cycle) and flow velocity. In vivo, tumor inhibition was evaluated using melanoma-bearing mice by characterizing tumor growth rate, animal weight, and intratumoral drug concentration with/without CALUS DDS. US beams were measured to be efficiently converged by CALUS, which was consistent with our simulation results. The acoustic parameters were optimized through the CALUS-induced MB destruction test (P = 2.34 MPa, PRF = 100 kHz, and duty cycle = 9%); this optimal parameter combination successfully induced MB destruction inside the microfluidic channel with an average flow velocity of up to 9.6 cm/s. The CALUS also enhanced the therapeutic effects of an antitumor drug (doxorubicin) in vivo in a murine melanoma model. The combination of the doxorubicin and the CALUS inhibited tumor growth by ∼55% more than doxorubicin alone, clearly indicating synergistic antitumor efficacy. Our tumor growth inhibition performance was better than other methods based on drug carriers, even without a time-consuming and complicated chemical synthesis process. This result suggests that our novel, simple, economic, and efficient target-specific DDS may offer a transition from preclinical research to clinical trials and a potential treatment approach for patient-centered healthcare.

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.

Cavitation with low-energy sonication during focused ultrasound thalamotomy for a patient with tremor-dominant Parkinson's disease: a potential risk

We report a patient with tremor-dominant Parkinson's disease who had a mild cavitation bioeffect during magnetic resonance-guided focused ultrasound thalamotomy. During the aligning phase with low-energy sonication, cavitation caused mild dysarthria and paresthesia, prompting treatment cessation. At the same time, tremor and rigidity improved. MRI revealed extensive high-intensity lesions in the thalamus 1 day after the procedure followed by steroid infusion, which resulted in resolution of adverse events. Tremor and rigidity improved 1.5 years after the procedure. Although cavitation can relieve tremors and rigidity, it should be carefully monitored due to potential permanent adverse events by unpredictable and unknown behaviors.

Sonopharmacology: controlling pharmacotherapy and diagnosis by ultrasound-induced polymer mechanochemistry

Active pharmaceutical ingredients are the most consequential and widely employed treatment in medicine although they suffer from many systematic limitations, particularly off-target activity and toxicity. To mitigate these effects, stimuli-responsive controlled delivery and release strategies for drugs are being developed. Fueled by the field of polymer mechanochemistry, recently new molecular technologies enabled the emergence of force as an unprecedented stimulus for this purpose by using ultrasound. In this research area, termed sonopharmacology, mechanophores bearing drug molecules are incorporated within biocompatible macromolecular scaffolds as preprogrammed, latent moieties. This review presents the novelties in controlling drug activation, monitoring, and release by ultrasound, while discussing the limitations and challenges for future developments.

3D-printed microrobots from design to translation

Microrobots have attracted the attention of scientists owing to their unique features to accomplish tasks in hard-to-reach sites in the human body. Microrobots can be precisely actuated and maneuvered individually or in a swarm for cargo delivery, sampling, surgery, and imaging applications. In addition, microrobots have found applications in the environmental sector (e.g., water treatment). Besides, recent advancements of three-dimensional (3D) printers have enabled the high-resolution fabrication of microrobots with a faster design-production turnaround time for users with limited micromanufacturing skills. Here, the latest end applications of 3D printed microrobots are reviewed (ranging from environmental to biomedical applications) along with a brief discussion over the feasible actuation methods (e.g., on- and off-board), and practical 3D printing technologies for microrobot fabrication. In addition, as a future perspective, we discussed the potential advantages of integration of microrobots with smart materials, and conceivable benefits of implementation of artificial intelligence (AI), as well as physical intelligence (PI). Moreover, in order to facilitate bench-to-bedside translation of microrobots, current challenges impeding clinical translation of microrobots are elaborated, including entry obstacles (e.g., immune system attacks) and cumbersome standard test procedures to ensure biocompatibility.

Microbots have attracted attention due to an ability to reach places and perform tasks which are not possible with conventional techniques in a wide range of applications. Here, the authors review the recent work in the field on the fabrication, application and actuation of 3D printed microbots offering a view of the direction of future microbot research.

Design, Implementation, and Medical Applications of 2-D Ultrasound Sparse Arrays

An ultrasound sparse array consists of a sparse distribution of elements over a 2-D aperture. Such an array is typically characterized by a limited number of elements, which in most cases is compatible with the channel number of the available scanners. Sparse arrays represent an attractive alternative to full 2-D arrays that may require the control of thousands of elements through expensive application-specific integrated circuits (ASICs). However, their massive use is hindered by two main drawbacks: the possible beam profile deterioration, which may worsen the image contrast, and the limited signal-to-noise ratio (SNR), which may result too low for some applications. This article reviews the work done for three decades on 2-D ultrasound sparse arrays for medical applications. First, random, optimized, and deterministic design methods are reviewed together with their main influencing factors. Then, experimental 2-D sparse array implementations based on piezoelectric and capacitive micromachined ultrasonic transducer (CMUT) technologies are presented. Sample applications to 3-D (Doppler) imaging, super-resolution imaging, photo-acoustic imaging, and therapy are reported. The final sections discuss the main shortcomings associated with the use of sparse arrays, the related countermeasures, and the next steps envisaged in the development of innovative arrays.

Enhancing cavitation dynamics and its mechanical effects with dual-frequency ultrasound

Objective. Acoustic cavitation and its mechanical effects (e.g. stress and strain) play a primary role in ultrasound applications. Introducing encapsulated microbubbles as cavitation nuclei and utilizing dual-frequency ultrasound excitation are highly effective approaches to reduce cavitation thresholds and enhance cavitation effects. However, the cavitation dynamics of encapsulated microbubbles and the resultant stress/strain in viscoelastic tissues under dual-frequency excitation are poorly understood, especially for the enhancement effects caused by a dual-frequency approach. The goal of this study was to numerically investigate the dynamics of a lipid-coated microbubble and the spatiotemporal distributions of the stress and strain under dual-frequency excitation. Approach. The Gilmore–Zener bubble model was coupled with a shell model for the nonlinear changes of both shell elasticity and viscosity to accurately simulate the cavitation dynamics of lipid-coated microbubbles in viscoelastic tissues. Then, the spatiotemporal evolutions of the cavitation-induced stress and strain in the surrounding tissues were characterized quantitatively. Finally, the influences of some paramount parameters were examined to optimize the outcomes. Main results. We demonstrated that the cavitation dynamics and associated stress/strain were prominently enhanced by a dual-frequency excitation, highlighting positive correlations between the maximum bubble expansion and the maximum stress/strain. Moreover, the results showed that the dual-frequency ultrasound with smaller differences in its frequencies and pressure amplitudes could enhance the bubble oscillations and stress/strain more efficiently, whereas the phase difference manifested small influences under these conditions. Additionally, the dual-frequency approach seemed to show a stronger enhancement effect with the shell/tissue viscoelasticity increasing to a certain extent. Significance. This study might contribute to optimizing the dual-frequency operation in terms of cavitation dynamics and its mechanical effects for high-efficient ultrasound applications.

Microgels react to force: mechanical properties, syntheses, and force-activated functions

Microgels are colloidal polymer networks with high molar mass and properties between rigid particles, flexible macromolecules, and micellar aggregates. Their unique stimuli-responsiveness in conjunction with their colloidal phase behavior render them useful for many applications ranging from engineering to biomedicine. In many scenarios either the microgel's mechanical properties or its interactions with mechanical force play an important role. Here, we firstly explain microgel mechanical properties and how these are measured by atomic force microscopy (AFM), then we equip the reader with the synthetic background to understand how specific architectures and chemical functionalities enable these mechanical properties, and eventually we elucidate how the interaction of force with microgels can lead to the activation of latent functionality. Since the interaction of microgels with force is a multiscale and multidisciplinary subject, we introduce and interconnect the different research areas that contribute to the understanding of this emerging field in this Tutorial Review.

Ex Vivo Evaluation of Mechanical Anisotropic Tissues with High-Frequency Ultrasound Shear Wave Elastography

The use of imaging devices to assess directional mechanics of tissues is highly desirable. This is because the directional mechanics depend on fiber orientation, and altered directional mechanics are closely related to the pathological status of tissues. However, measuring directional mechanics in tissues with high-stiffness is challenging due to the difficulty of generating localized displacement in these tissues using acoustic radiation force, a general method for generating displacement in ultrasound-based elastography. In addition, common ultrasound probes do not provide rotational function, which makes the measurement of directional mechanics inaccurate and unreliable. Therefore, we developed a high-frequency ultrasound mechanical wave elastography system that can accommodate a wide range of tissue stiffness and is also equipped with a motorized rotation stage for precise imaging of directional mechanics. A mechanical shaker was applied to the elastography system to measure tissues with high-stiffness. Phantom and ex vivo experiments were performed. In the phantom experiments, the lateral and axial resolution of the system were determined to be 144 μm and 168 μm, respectively. In the ex vivo experiments, we used swine heart and cartilage, both of which are considered stiff. The elastography system allows us to acquire the directional mechanics with high angular resolution in the heart and cartilage. The results demonstrate that the developed elastography system is capable of imaging a wide range of tissues and has high angular resolution. Therefore, this system might be useful for the diagnostics of mechanically anisotropic tissues via ex vivo tests.

Activation of Antibiotic-Grafted Polymer Brushes by Ultrasound

The ultrasound-mediated activation of drugs from macromolecular architectures using the principles of polymer mechanochemistry (sonopharmacology) is a promising strategy to gain spatiotemporal control over drug activity. Yet, conceptual challenges limit the applicability of this method. Especially low drug-loading content and low mechanochemical efficiency require the use of high carrier mass concentrations and prolonged exposure to ultrasound. Moreover, the activated drug is generally shielded by the hydrodynamic coil of the attached polymer fragment leading to a decreased drug potency. Here we present a carrier design for the ultrasound-induced activation of vancomycin, which is deactivated with its H-bond-complementary peptide target sequence. We show that the progression from mechanophore-centered linear chains to mechanophore-decorated polymer brushes increases drug-loading content, mechanochemical efficiency, and drug potency. These results may serve as a design guideline for future endeavors in the field of sonopharmacology.

Sanitary sewage disinfection with ultraviolet radiation and ultrasound

Currently, the world is facing a horrible situation due to SARS-CoV-2. Though its RNA was found in wastewater, there are still no studies on RNA contamination detected in sewage. Hence, a possible treatment of sewage is suggested in this work. The disinfection stage is extremely important in the treatment of effluents, minimizing the impacts on the receiving body of water and promoting public health. In this context, the sequential use of ultrasound and ultraviolet radiation, on a bench scale, was investigated as a way to improve the disinfection of anaerobically treated effluents. Two types of treated effluents were tested, by septic tank and anaerobic filter, for which, two ultrasound frequencies, 25 and 40 kHz, and four doses of UV, 3.6; 9.0; 18 and 36 mJ cm^-2 were applied. Physicochemical and microbiological parameters were observed for individual and sequential assays. The better quality of the anaerobic filter effluent influenced the performance of both processes, decreasing the concentration of organic load and turbidity, even though a concentration of total coliforms and Escherichia coli occurred in the lowest quality effluent (septic tank). The application of ultrasound has a positive effect on the inactivation of total coliforms and E. coli up to 1.0 log and provides better conditions for ultraviolet radiation to be sequentially applied. The UV radiation applied for the septic tank and the anaerobic filter inactivates 2.5 log for total coliforms and 3.5 log for E. coli, respectively. It is suggested that the disinfection methods applied in this work to inactivate gram-negative bacteria (E. coli) can also be applied to secondary treatment effluents, as well as being better tested for viruses, protozoa, and helminths.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13762-021-03764-7.

Synergies between therapeutic ultrasound, gene therapy and immunotherapy in cancer treatment

Due to the ease of use and excellent safety profile, ultrasound is a promising technique for both diagnosis and site-specific therapy. Ultrasound-based techniques have been developed to enhance the pharmacokinetics and efficacy of therapeutic agents in cancer treatment. In particular, transfection with exogenous nucleic acids has the potential to stimulate an immune response in the tumor microenvironment. Ultrasound-mediated gene transfection is a growing field, and recent work has incorporated this technique into cancer immunotherapy. Compared with other gene transfection methods, ultrasound-mediated gene transfection has a unique opportunity to augment the intracellular uptake of nucleic acids while safely and stably modulating the expression of immunostimulatory cytokines. The development and commercialization of therapeutic ultrasound systems further enhance the potential translation. In this Review, we introduce the underlying mechanisms and ongoing preclinical studies of ultrasound-based techniques in gene transfection for cancer immunotherapy. Furthermore, we expand on aspects of therapeutic ultrasound that impact gene therapy and immunotherapy, including tumor debulking, enhancing cytokines and chemokines and altering nanoparticle pharmacokinetics as these effects of ultrasound cannot be fully dissected from targeted gene therapy. We finally explore the outlook for this rapidly developing field.

Recent Advances of Energy Solutions for Implantable Bioelectronics

The emerging field of implantable bioelectronics has attracted widespread attention in modern society because it can improve treatment outcomes, reduce healthcare costs, and lead to an improvement in the quality of life. However, their continuous operation is often limited by conventional bulky and rigid batteries with a limited lifespan, which must be surgically removed after completing their missions and/or replaced after being exhausted. Herein, this paper gives a comprehensive review of recent advances in nonconventional energy solutions for implantable bioelectronics, emphasizing the miniaturized, flexible, biocompatible, and biodegradable power devices. According to their source of energy, the promising alternative energy solutions are sorted into three main categories, including energy storage devices (batteries and supercapacitors), internal energy-harvesting devices (including biofuel cells, piezoelectric/triboelectric energy harvesters, thermoelectric and biopotential power generators), and external wireless power transmission technologies (including inductive coupling/radiofrequency, ultrasound-induced, and photovoltaic devices). Their fundamentals, materials strategies, structural design, output performances, animal experiments, and typical biomedical applications are also discussed. It is expected to offer complementary power sources to extend the battery lifetime of bioelectronics while acting as an independent power supply. Thereafter, the existing challenges and perspectives associated with these powering devices are also outlined, with a focus on implantable bioelectronics.

Mechanochemical bond scission for the activation of drugs

Pharmaceutical drug therapy is often hindered by issues caused by poor drug selectivity, including unwanted side effects and drug resistance. Spatial and temporal control over drug activation in response to stimuli is a promising strategy to attenuate and circumvent these problems. Here we use ultrasound to activate drugs from inactive macromolecules or nano-assemblies through the controlled scission of mechanochemically labile covalent bonds and weak non-covalent bonds. We show that a polymer with a disulfide motif at the centre of the main chain releases an alkaloid-based anticancer drug from its β-carbonate linker by a force-induced intramolecular 5-exo-trig cyclization. Second, aminoglycoside antibiotics complexed by a multi-aptamer RNA structure are activated by the mechanochemical opening and scission of the nucleic acid backbone. Lastly, nanoparticle-polymer and nanoparticle-nanoparticle assemblies held together by hydrogen bonds between the peptide antibiotic vancomycin and its complementary peptide target are activated by force-induced scission of hydrogen bonds. This work demonstrates the potential of ultrasound to activate mechanoresponsive prodrug systems.

Acoustically Mediated Controlled Drug Release and Targeted Therapy with Degradable 3D Porous Magnetic Microrobots

Microrobots for targeted drug delivery are of great interest due to their minimal invasiveness and wireless controllability. Here, a magnetically driven porous degradable microrobot (PDM) is reported that consists of a 3D printed helical soft polymeric chassis made of a poly(ethylene glycol) diacrylate and pentaerythritol triacrylate matrix containing magnetite nanoparticles and the anticancer drug 5-fluorouracil (5-FU). The encapsulated Fe₃ O₄ nanoparticles render the PDM a precise wireless magnetic actuation by means of rotating magnetic fields (RMFs). The increased surface area of the porous PDM facilitates the acoustically induced drug release due to a higher response to the acoustic energy. The drug release profile from the PDM can be selected on command from three different modes, referred to herein as natural, burst, and constant, by differentiating the ultrasound exposure condition. Finally, in vitro test results reveal different therapeutic results for each release mode. The observed great reduction of cancer cell viability in the burst- and constant-release modes confirms that ultrasound with the proposed PDM can enhance the therapeutic effect by increasing drug concentration and sonoporation.

Current advances in ultrasound-combined nanobubbles for cancer-targeted therapy: a review of the current status and future perspectives

The non-specific distribution, non-selectivity towards cancerous cells, and adverse off-target side effects of anticancer drugs and other therapeutic molecules lead to their inferior clinical efficacy. Accordingly, ultrasound-based targeted delivery of therapeutic molecules loaded in smart nanocarriers is currently gaining wider acceptance for the treatment and management of cancer. Nanobubbles (NBs) are nanosize carriers, which are currently used as effective drug/gene delivery systems because they can deliver drugs/genes selectively to target sites. Thus, combining the applications of ultrasound with NBs has recently demonstrated increased localization of anticancer molecules in tumor tissues with triggered release behavior. Consequently, an effective therapeutic concentration of drugs/genes is achieved in target tumor tissues with ultimately increased therapeutic efficacy and minimal side-effects on other non-cancerous tissues. This review illustrates present developments in the field of ultrasound-nanobubble combined strategies for targeted cancer treatment. The first part of this review discusses the composition and the formulation parameters of NBs. Next, we illustrate the interactions and biological effects of combining NBs and ultrasound. Subsequently, we explain the potential of NBs combined with US for targeted cancer therapeutics. Finally, the present and future directions for the improvement of current methods are proposed.

NBs combined with ultrasound demonstrated the ability to enhance the targeting of anticancer agents and improve the efficacy.

Mechanochemical activation of disulfide-based multifunctional polymers for theranostic drug release

Drug delivery systems responsive to physicochemical stimuli allow spatiotemporal control over drug activity to overcome limitations of systemic drug administration. Alongside, the non-invasive real-time tracking of drug release and uptake remains challenging as pharmacophore and reporter function are rarely unified within one molecule. Here, we present an ultrasound-responsive release system based on the mechanochemically induced 5-exo-trig cyclization upon scission of disulfides bearing cargo molecules attached via β-carbonate linker within the center of a water soluble polymer. In this bifunctional theranostic approach, we release one reporter molecule per drug molecule to quantitatively track drug release and distribution within the cell in real-time. We use N-butyl-4-hydroxy-1,8-naphthalimide and umbelliferone as fluorescent reporter molecules to accompany the release of camptothecin and gemcitabine as clinically employed anticancer agents. The generality of this approach paves the way for the theranostic release of a variety of probes and drugs by ultrasound.

A theranostic approach for the mechanochemically induced release of drugs is presented to track drug release and uptake in real-time.

A Preliminary Study on the Safety of Elastography during Pregnancy: Hypoacusia, Anthropometry, and Apgar Score in Newborns

Transient or acoustic radiation force elastography (ARFE) is becoming the most extended technology to assess cervical effacement, additionally to the Bishop test and conventional ultrasound. However, a debate on the fetal safety has been opened due to the high intensity focused beam emitted to produce shear waves. This work is aimed at providing preliminary data to assess clinical effects of fetal exposure. A follow-up study in newborns of 42 women exposed to ARFE during pregnancy was carried out to explore neonatal hypoacusia, Apgar test, and anthropometry. No hypoacusia cases attributable to ARFE were observed. The Apgar test at five minutes scored normally in all the newborns. Comparisons between anthropometric measurements showed no significant statistically differences. The results preclude to state the harmfulness nor the safety of ARFE. However, given the concern on the high level of energy and the potential risk of harmful bioeffects, larger studies are recommended.

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

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

Ultrasound Image Optimization ("Knobology"): B-Mode

Ultrasound is a ubiquitous and indispensable diagnostic and therapeutic tool in medicine. Due to modern equipment and automatic image optimization, the introduction of ultrasound imaging currently requires only little technical and physical knowledge. However, in-depth knowledge of the device functions and underlying mechanisms is essential for optimal image adjustment and documentation. From a medical as well as an aesthetic point of view, the goal should always be to achieve the best possible image quality. The first part of this article provides an overview of the handling of ultrasound systems, fundamental adjustments, and their optimization in B-mode ultrasound.

Toward Drug Release Using Polymer Mechanochemical Disulfide Scission

Traditional pharmacotherapy suffers from multiple drawbacks that hamper patient treatment, such as the buildup of antibiotic resistances or low drug selectivity and toxicity during systemic application. To overcome these challenges, drug activity can be controlled by employing delivery, targeting, or release solutions that mostly rely on the response to external physicochemical stimuli. Due to various technical limitations, mechanical force as a stimulus in the context of polymer mechanochemistry has so far not been used for this purpose, yet it has been proven to be a convenient and robust method to site-selectively rearrange or cleave bonds with submolecular precision in the realm of materials chemistry. Here, we present an unprecedented mechanochemically responsive system capable of successively releasing small furan-containing molecules, including the furylated fluorophore dansyl and the drugs furosemide as well as furylated doxorubicin, by ultrasound-induced selective scission of disulfide-centered polymers in solution. We show that mechanochemically generated thiol-terminated polymers undergo a Michael-type addition to Diels-Alder (DA) adducts of furylated drugs and acetylenedicarboxylate derivatives, initiating the downstream release of the small molecule drug by a retro DA reaction. We believe that this method can serve as a blueprint for the activation of many other small molecules.

Effects of Therapeutic Ultrasound Applied to the Lumbar Region on Renal Function: A Randomized Controlled Prospective Trial

OBJECTIVES

Therapeutic ultrasound (TUS) is one of the most commonly used modalities in low back pain treatment. The objective of this study was to determine whether TUS applied to the low back region in patients with chronic low back pain had any effect on renal function.

METHODS

Forty patients with chronic low back pain were randomized to 2 groups by a block randomization method. Thirty-seven patients completed the final evaluation. All patients were treated for 5 sessions per week for 3 weeks with the same physiotherapy modalities (superficial heating and transcutaneous electrical nerve stimulation) and exercise therapy; in addition to these treatments, the second group was treated with TUS for 10 minutes (frequency, 1 MHz; intensity, 1.5 W/cm² ; and effective irradiation area of the transducer head, 5 cm² ). The serum creatinine, serum cystatin C, 24-hour urine creatinine, creatinine clearance, 24-hour urine microalbumin and microprotein, urine volume, and glomerular filtration rate were measured. The patients were evaluated at baseline (day 0) and the end of the treatment (day 21).

RESULTS

The serum cystatin C levels were increased in both groups, but this increase was not significant (P > .05). There was no difference between the groups in the percent change in all outcome measures (P > .05).

CONCLUSIONS

This showed that TUS applied to the low back region does not affect renal function.

Experimental Measurements of Ultrasound Attenuation in Human Chest Wall and Assessment of the Mechanical Index for Lung Ultrasound

Knowledge of the acoustic attenuation characteristics of the chest wall is necessary to estimate the acoustic exposure at the pleural surface during lung ultrasound and is useful in the prediction of bio-effects (e.g., pulmonary capillary hemorrhage) and the development of safe, effective lung imaging. Currently, this property is not well characterized in humans. The aim of this work was to characterize ultrasonic attenuation in human chest wall such that the ultrasound exposures of the lung can be estimated for clinically relevant conditions. In this study, we experimentally measured ultrasound transmitted through the intercostal tissue of 15 human cadaver chest wall samples relative to ultrasound transmitted through saline to determine attenuation coefficients for each sample. A GE Vivid 7 diagnostic ultrasound machine (GE Vingmed, Horten, Norway) and 3 S and 5 S phased array probes were used at center frequencies from 1.6 to 5 MHz. The chest wall samples varied in thickness from 2.3-5.5 cm with a median thickness of 3.8 cm. The frequency-normalized attenuation coefficient was approximately 1.44 dB/cm/MHz based on a linear best fit through all attenuation measurements. Attenuation characteristics varied appreciably between samples, and the sample-averaged linear attenuation coefficient was 1.43 ± 0.32 (mean ± standard deviation) dB/cm/MHz. This attenuation is higher than that previously measured in mammalian chest wall samples (1.1-1.3 dB/cm/MHz for mice and rats) and is much greater than that used by the mechanical index (0.3 dB/cm/MHz). Mechanical index values calculated using saline values de-rated by 0.3 dB/cm/MHz were up to 1.2 MPa/MHz^1/2 greater than those calculated using the measured through-tissue ultrasound waves. We conclude that the mechanical index overestimates exposures for lung ultrasound and thus may not be an appropriate dosimetry metric for pulmonary ultrasound.

Analysis in protein profile, antioxidant activity and structure-activity relationship based on ultrasound-assisted liquid-state fermentation of soybean meal with Bacillus subtilis

This study investigated effects of ultrasound on the contents of peptide and soluble protein, antioxidant activity, functionalities and structural characteristics of fermented soybean meal (FSBM) with Bacillus subtilis systematically. The results showed that there were significant effects of ultrasound treatments (frequency, treatment time and power density) on the contents of peptide and soluble protein (p < 0.05). Under the optimum ultrasound conditions (power density of 0.08 W/mL, frequency of 33 kHz and treatment time of 1 h) by single factor experiment, the contents of peptide and soluble protein increased by 31.27% and 18.79% compared to those of the control, respectively. Additionally, the in vitro antioxidant activity (•OH scavenging rate, Fe2+ chelating capacity and DPPH radical scavenging rate) and functional properties (emulsifying activity and emulsifying stability) of FSBM were found to be noticeably improved by ultrasound (p < 0.05). The fourier transform infrared (FTIR) spectroscopy revealed that ultrasound caused protein molecules to unfold with a decrease content of α-helix and β-turn and an increase in the proportion of β-sheet and random coil. Besides, atomic force microscope (AFM) results indicated that ultrasonication generally increased the surface roughness of protein and the protein sonicated with higher frequency (≥33 kHz) exhibited a greater height compared to lower frequency ultrasonication. Structure-activity relationship analysis illustrated that there was a good linear relationship between •OH scavenging rate and β-sheet/β-turn with Pearson's correlation coefficient r of -0.86/0.90. Collectively, the selection of ultrasonic parameters is essential for the preparation of functional protein and bioactive peptide by enhancing fermentation of agroindustrial by-products.

Ultrasound-degradable serum albumin nanoplatform forin situcontrolled drug release

An ultrasound-modulated drug release nanoplatform was fabricated using a degradable azo derivative (ACVA) as a crosslinker for excellent tissue penetration, and could realize controllable drug release according to the treatment needs.

Focused ultrasound-mediated noninvasive blood-brain barrier modulation: preclinical examination of efficacy and safety in various sonication parameters

OBJECTIVE The application of pharmacological therapeutics in neurological disorders is limited by the ability of these agents to penetrate the blood-brain barrier (BBB). Focused ultrasound (FUS) has recently gained attention for its potential application as a method for locally opening the BBB and thereby facilitating drug delivery into the brain parenchyma. However, this method still requires optimization to maximize its safety and efficacy for clinical use. In the present study, the authors examined several sonication parameters of FUS influencing BBB opening in small animals. METHODS Changes in BBB permeability were observed during transcranial sonication using low-intensity FUS in 20 adult male Sprague-Dawley rats. The authors examined the effects of FUS sonication with different sonication parameters, varying acoustic pressure, center frequency, burst duration, microbubble (MB) type, MB dose, pulse repetition frequency (PRF), and total exposure time. The focal region of BBB opening was identified by Evans blue dye. Additionally, H & E staining was used to identify blood vessel damage. RESULTS Acoustic pressure amplitude and burst duration were closely associated with enhancement of BBB opening efficiency, but these parameters were also highly correlated with tissue damage in the sonicated region. In contrast, MB types, MB dose, total exposure time, and PRF had an influence on BBB opening without conspicuous tissue damage after FUS sonication. CONCLUSIONS The study aimed to identify these influential conditions and provide safety and efficacy values for further studies. Future work based on the current results is anticipated to facilitate the implementation of FUS sonication for drug delivery in various CNS disease states in the near future.

Fermentation of Saccharomyces cerevisiae in a one liter flask coupled with an external circulation ultrasonic irradiation slot: Influence of ultrasonic mode and frequency on the bacterial growth and metabolism yield

In this study, the influences of ultrasonic treatments with different working modes (fixed frequency and sweeping frequency) and various frequencies on the bacterial growth and metabolism yield of Saccharomyces cerevisiae (S. cerevisiae) were investigated by employing an in situ ultrasonic irradiation slot coupled with a flask fermentation equipment. The results revealed that the in situ ultrasonic treatment could promote the bacterial growth and metabolism yield, and the effect of fixed frequency ultrasound (FF) was higher than sweeping frequency ultrasound (SF). The content of metabolite in the fermentation broth increased with FF and decreased after SF treatments. On the other hand, when the frequency of FF was more than 33 kHz, the growth of S. cerevisiae became weaken, and the mortality rate of S. cerevisiae increased in fermentation broth. At FF of 23 kHz and 48 h fermentation-time, ethanol content increased by 19.33%, and the content of β-phenylethanol and other volatile metabolites such as esters also increased. In conclusion, FF could significantly improve the growth of S. cerevisiae, and the FF of 23 kHz showed the optimum impact on fermentation process of S. cerevisiae.

Applications of Focused Ultrasound in Cerebrovascular Diseases and Brain Tumors

Oncology and cerebrovascular disease constitute two of the most common diseases afflicting the central nervous system. Standard of treatment of these pathologies is based on multidisciplinary approaches encompassing combination of interventional procedures such as open and endovascular surgeries, drugs (chemotherapies, anti-coagulants, anti-platelet therapies, thrombolytics), and radiation therapies. In this context, therapeutic ultrasound could represent a novel diagnostic/therapeutic in the armamentarium of the surgeon to treat these diseases. Ultrasound relies on mechanical energy to induce numerous physical and biological effects. The application of this technology in neurology has been limited due to the challenges with penetrating the skull, thus limiting a prompt translation as has been seen in treating pathologies in other organs, such as breast and abdomen. Thanks to pivotal adjuncts such as multiconvergent transducers, magnetic resonance imaging (MRI) guidance, MRI thermometry, implantable transducers, and acoustic windows, focused ultrasound (FUS) is ready for prime-time applications in oncology and cerebrovascular neurology. In this review, we analyze the evolution of FUS from the beginning in 1950s to current state-of-the-art. We provide an overall picture of actual and future applications of FUS in oncology and cerebrovascular neurology reporting for each application the principal existing evidences.

Nakagami-m parametric imaging for characterization of thermal coagulation and cavitation erosion induced by HIFU

Nowadays, both thermal and mechanical ablation techniques of HIFU associated with cavitation have been developed for noninvasive treatment. A specific challenge for the successful clinical implementation of HIFU is to achieve real-time imaging for the evaluation and determination of therapy outcomes such as necrosis or homogenization. Ultrasound Nakagami-m parametric imaging highlights the degrading shadowing effects of bubbles and can be used for tissue characterization. The aim of this study is to investigate the performance of Nakagami-m parametric imaging for evaluating and differentiating thermal coagulation and cavitation erosion induced by HIFU. Lesions were induced in basic bovine serum albumin (BSA) phantoms and ex vivo porcine livers using a 1.6 MHz single-element transducer. Thermal and mechanical lesions induced by two types of HIFU sequences respectively were evaluated using Nakagami-m parametric imaging and ultrasound B-mode imaging. The lesion sizes estimated using Nakagami-m parametric imaging technique were all closer to the actual sizes than those of B-mode imaging. The p-value obtained from the t-test between the mean m values of thermal coagulation and cavitation erosion was smaller than 0.05, demonstrating that the m values of thermal lesions were significantly different from that of mechanical lesions, which was confirmed by ex vivo experiments and histologic examination showed that different changes result from HIFU exposure, one of tissue dehydration resulting from the thermal effect, and the other of tissue homogenate resulting from mechanical effect. This study demonstrated that Nakagami-m parametric imaging is a potential real-time imaging technique for evaluating and differentiating thermal coagulation and cavitation erosion.

Shear wave elastography safety in fetus: A quantitative health risk assessment

PURPOSE

To identify the effects of shear wave elastography in the fetus for evaluation in widespread use.

MATERIALS AND METHODS

The Health Risk Assessment method proposed by the National Research Council was used with literature to evaluate the safety of shear wave elastography for the fetus regarding its potential effects in human tissues.

RESULTS

The experimental and epidemiologic data from 25 articles showed that shear wave elastography maintained the same thermal effect as pulsed Doppler ultrasound already authorized in obstetrics, and that cavitation effect on fetal tissue is improbable. Nonetheless, the vibratory character of shear waves could induce displacement of fetal tissue while potential effects of very short duration energy peaks of the radiation force focused wave front remain unknown.

CONCLUSION

The actual knowledge does not provide enough information to assess the effects of shear wave elastography on fetal tissues, thus these points have to be explored by further experimental studies.

Insight into ultrasound-mediated reactive oxygen species generation by various metal-porphyrin complexes

Ultrasound is used to trigger the cytotoxicity of chemical compounds, known as sonosensitisers, in an approach called sonodynamic therapy (SDT), which is under investigation herein. The generation of reactive oxygen species (ROS) has been proposed as the main biological occurrence that leads to the cytotoxic effects, which are achieved via the synergistic action of two components: the energy-absorbing sonosensitiser and ultrasound (US), which are both harmless per se. Despite some promising results, a lack of investigation into the mechanisms behind US sonosensitiser-mediated ROS generation has prevented SDT from reaching its full potential. The aim of this work is to investigate the US-responsiveness of a variety of metal-porphyrin complexes, free-base porphyrin and Fe(III), Zn(II) and Pd(II) porphyrin, by analyzing their ROS generation under US exposure and related bio-effects. All experiments were also carried out under light exposure and the results were used as references. Our results show that porphyrin ultrasound-responsiveness depends on the metal ion present, with Zn(II) and Pd(II) porphyrin being the most efficient in generating singlet oxygen and hydroxyl radicals. ROS production efficiency is lower after ultrasound exposure than after light exposure, because of the various physico-chemical mechanisms involved in sensitiser activation. US and porphyrin-mediated ROS generation is oxygen-dependent and the activation of porphyrin by US appears to be more compatible with sonoluminescence-based photo-activation rather than a radical path process that occurs via the homolytic bond rupture of water. Notably, the cytotoxicity results reported herein, which are mirrored by ex-cellulo data, confirm that the type of ROS generation achieved by the US activation of intracellular porphyrins is pivotal to the effectiveness of cancer cell killing.

High-intensity focused ultrasound ablation around the tubing

High-intensity focused ultrasound (HIFU) has been emerging as an effective and noninvasive modality in cancer treatment with very promising clinical results. However, a small vessel in the focal region could be ruptured, which is an important concern for the safety of HIFU ablation. In this study, lesion formation in the polyacrylamide gel phantom embedded with different tubing (inner diameters of 0.76 mm and 3 mm) at varied flow speeds (17–339 cm/s) by HIFU ablation was photographically recorded. Produced lesions have decreased length (~30%) but slightly increased width (~6%) in comparison to that without the embedded tubing. Meanwhile, bubble activities during the exposures were measured by passive cavitation detection (PCD) at the varied pulse repetition frequency (PRF, 10–30 Hz) and duty cycle (DC, 10%-20%) of the HIFU bursts. High DC and low flow speed were found to produce stronger bubble cavitation whereas no significant influence of the PRF. In addition, high-speed photography illustrated that the rupture of tubing was produced consistently after the first HIFU burst within 20 ms and then multiple bubbles would penetrate into the intraluminal space of tubing through the rupture site by the acoustic radiation force. Alignment of HIFU focus to the anterior surface, middle, and posterior surface of tubing led to different characteristics of vessel rupture and bubble introduction. In summary, HIFU-induced vessel rupture is possible as shown in this phantom study; produced lesion sizes and shapes are dependent on the focus alignment to the tubing, flow speed, and tubing properties; and bubble cavitation and the formation liquid jet may be one of the major mechanisms of tubing rupture as shown in the high-speed photography.