Local drug and gene delivery through microbubbles

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Optimal Treatment Parameters for Ultrasound-Stimulated Microbubbles in Upregulating Proliferation and Stemness of Bone Marrow Mesenchymal Stem Cells

OBJECTIVES

Ultrasound-targeted microbubble disruption (UTMD) is a widely used technique to improve the differentiation and proliferation capacity of mesenchymal stem cells (MSCs), but the optimal therapeutic parameters for UTMD are unclear. In this study, we aimed to find the appropriate peak negative pressure (PNP), which is a key parameter for enhancing the stemness properties and proliferation of MSCs.

METHODS

Experiments were performed in UTMD group, ultrasound (US) group under different PNP exposure conditions (0.5, 1.0, and 1.5 MPa), and control group. Apoptosis safety was analyzed by flow cytometry and MSC proliferation was measured at 12, 24, and 36 hours after irradiation by cell counting kit 8. The expression of the stemness genes NANOG, OCT-4, and SOX-2 were determined by enzyme-linked immunosorbent assay (ELISA) or reverse transcription polymerase chain reaction.

RESULTS

The results showed that the 1.5 MPa UTMD-treated group had the highest proliferation capacity of MSCs at 24 hours. ELISA or quantitative reverse transcription polymerase chain reaction results showed that UTMD treatment of the 1.5 MPa group significantly upregulated the expression of the stemness genes NANOG, SOX-2, and OCT-4.

CONCLUSIONS

In conclusion, the appropriate peak PNP value of UTMD was 1.5 MPa, and 1.5 MPa-mediated UTMD group obviously promoted MSCs proliferation and maintained stemness by upregulating the expression of stemness genes.

In Vivo Sonoporation Effect Under the Presence of a Large Amount of Micro-Nano Bubbles in Swine Liver

OBJECTIVES

Sonoporation as a method of intracellular drug and gene delivery has not yet progressed to being used in vivo. The aim of this study was to prove the feasibility of sonoporation at a level practical for use in vivo by using a large amount of carbon dioxide micro-nano bubbles.

METHODS

The carbon dioxide micro-nano bubbles and 100 mg of cisplatin were intra-arterially injected to the swine livers, and ultrasound irradiation was performed from the surface of the liver under laparotomy during the intra-arterial injection. After the intra-arterial injection, ultrasound-irradiated and nonirradiated liver tissues were immediately excised. Tissue platinum concentration was measured using inductively coupled plasma mass spectrometry. Liver tissue platinum concentrations were compared between the irradiated tissue and nonirradiated tissue using the Wilcoxon signed rank test.

RESULTS

The mean (SD) liver tissue platinum concentration was 6.260*103 (2.070) ng/g in the irradiated liver tissue and 3.280*103 (0.430) ng/g in the nonirradiated liver tissue, showing significantly higher concentrations in the irradiated tissue ( P = 0.004).

CONCLUSIONS

In conclusion, increasing the tissue concentration of administered cisplatin in the livers of living swine through the effect of sonoporation was possible in the presence of a large amount of micro-nano bubbles.

From concept to early clinical trials: 30 years of microbubble-based ultrasound-mediated drug delivery research

Ultrasound mediated drug delivery, a promising therapeutic modality, has evolved remarkably over the past three decades. Initially designed to enhance contrast in ultrasound imaging, microbubbles have emerged as a main vector for drug delivery, offering targeted therapy with minimized side effects. This review addresses the historical progression of this technology, emphasizing the pivotal role microbubbles play in augmenting drug extravasation and targeted delivery. We explore the complex mechanisms behind this technology, from stable and inertial cavitation to diverse acoustic phenomena, and their applications in medical fields. While the potential of ultrasound mediated drug delivery is undeniable, there are still challenges to overcome. Balancing therapeutic efficacy and safety and establishing standardized procedures are essential areas requiring attention. A multidisciplinary approach, gathering collaborations between researchers, engineers, and clinicians, is important for exploiting the full potential of this technology. In summary, this review highlights the potential of using ultrasound mediated drug delivery in improving patient care across various medical conditions.

An Acoustic Device for Ultra High-Speed Quantification of Cell Strain During Cell-Microbubble Interaction

Microbubbles utilize high-frequency oscillations under ultrasound stimulation to induce a range of therapeutic effects in cells, often through mechanical stimulation and permeabilization of cells. One of the largest challenges remaining in the field is the characterization of interactions between cells and microbubbles at therapeutically relevant frequencies. Technical limitations, such as employing sufficient frame rates and obtaining sufficient image resolution, restrict the quantification of the cell's mechanical response to oscillating microbubbles. Here, a novel methodology was developed to address many of these limitations and improve the image resolution of cell-microbubble interactions at high frame rates. A compact acoustic device was designed to house cells and microbubbles as well as a therapeutically relevant acoustic field while being compatible with a Shimadzu HPV-X camera. Cell viability tests confirmed the successful culture and proliferation of cells, and the attachment of DSPC- and cationic DSEPC-microbubbles to osteosarcoma cells was quantified. Microbubble oscillation was observed within the device at a frame rate of 5 million FPS, confirming suitable acoustic field generation and ultra high-speed image capture. High spatial resolution in these images revealed observable deformation in cells following microbubble oscillation and supported the first use of digital image correlation for strain quantification in a single cell. The novel acoustic device provided a simple, effective method for improving the spatial resolution of cell-microbubble interaction images, presenting the opportunity to develop an understanding of the mechanisms driving the therapeutic effects of oscillating microbubbles upon ultrasound exposure.

Evaluating the effects of radiation and acoustically-stimulated microbubble therapy in an in vivo breast cancer model

Ultrasound-stimulated microbubbles (USMB) cause localized vascular effects and sensitize tumors to radiation therapy (XRT). We investigated acoustic parameter optimization for combining USMB and XRT. We treated breast cancer xenograft tumors with 500 kHz pulsed ultrasound at varying pressures (570 or 740 kPa), durations (1 to 10 minutes), and microbubble concentrations (0.01 to 1% (v/v)). Radiation therapy (2 Gy) was administered immediately or after a 6-hour delay. Histological staining of tumors 24 hours after treatment detected changes in cell morphology, cell death, and microvascular density. Significant cell death resulted at 570 kPa after a 1-minute exposure with 1% (v/v) microbubbles with or without XRT. However, significant microvascular disruption required higher ultrasound pressure and exposure duration greater than 5 minutes. Introducing a 6-hour delay between treatments (USMB and XRT) showed a similar tumor effect with no further improvement in response as compared to when XRT was delivered immediately after USMB.

Efficacy optimization of low frequency microbubble-mediated sonoporation as a drug delivery platform to cancer cells

Ultrasound insonation of microbubbles can be used to form pores in cell membranes and facilitate the local trans-membrane transport of drugs and genes. An important factor in efficient delivery is the size of the delivered target compared to the generated membrane pores. Large molecule delivery remains a challenge, and can affect the resulting therapeutic outcomes. To facilitate large molecule delivery, large pores need to be formed. While ultrasound typically uses megahertz frequencies, it was recently shown that when microbubbles are excited at a frequency of 250 kHz (an order of magnitude below the resonance frequency of these agents), their oscillations are significantly enhanced as compared to the megahertz range. Here, to promote the delivery of large molecules, we suggest using this low frequency and inducing large pore formation through the high-amplitude oscillations of microbubbles. We assessed the impact of low frequency microbubble-mediated sonoporation on breast cancer cell uptake by optimizing the delivery of 4 fluorescent molecules ranging from 1.2 to 70 kDa in size. The optimal ultrasound peak negative pressure was found to be 500 kPa. Increasing the pressure did not enhance the fraction of fluorescent cells, and in fact reduced cell viability. For the smaller molecule sizes, 1.2 kDa and 4 kDa, the groups treated with an ultrasound pressure of 500 kPa and MB resulted in a fraction of 58% and 29% of fluorescent cells respectively, whereas delivery of 20 kDa and 70 kDa molecules yielded 10% and 5%, respectively. These findings suggest that low-frequency (e.g., 250 kHz) insonation of microbubbles results in high amplitude oscillation in vitro that increase the uptake of large molecules. Successful ultrasound-mediated molecule delivery requires the careful selection of insonation parameters to maximize the therapeutic effect by increasing cell uptake.

Appraisal for the Potential of Viral and Nonviral Vectors in Gene Therapy: A Review

Over the past few decades, gene therapy has gained immense importance in medical research as a promising treatment strategy for diseases such as cancer, AIDS, Alzheimer’s disease, and many genetic disorders. When a gene needs to be delivered to a target cell inside the human body, it has to pass a large number of barriers through the extracellular and intracellular environment. This is why the delivery of naked genes and nucleic acids is highly unfavorable, and gene delivery requires suitable vectors that can carry the gene cargo to the target site and protect it from biological degradation. To date, medical research has come up with two types of gene delivery vectors, which are viral and nonviral vectors. The ability of viruses to protect transgenes from biological degradation and their capability to efficiently cross cellular barriers have allowed gene therapy research to develop new approaches utilizing viruses and their different genomes as vectors for gene delivery. Although viral vectors are very efficient, science has also come up with numerous nonviral systems based on cationic lipids, cationic polymers, and inorganic particles that provide sustainable gene expression without triggering unwanted inflammatory and immune reactions, and that are considered nontoxic. In this review, we discuss in detail the latest data available on all viral and nonviral vectors used in gene delivery. The mechanisms of viral and nonviral vector-based gene delivery are presented, and the advantages and disadvantages of all types of vectors are also given.

A theranostic 3D ultrasound imaging system for high resolution image-guided therapy

Microbubble contrast agents are a diagnostic tool with broad clinical impact and an increasing number of indications. Many therapeutic applications have also been identified. Yet, technologies for ultrasound guidance of microbubble-mediated therapy are limited. In particular, arrays that are capable of implementing and imaging microbubble-based therapy in three dimensions in real-time are lacking. We propose a system to perform and monitor microbubble-based therapy, capable of volumetric imaging over a large field-of-view. To propel the promise of the theranostic treatment strategies forward, we have designed and tested a unique array and system for 3D ultrasound guidance of microbubble-based therapeutic protocols based on the frequency, temporal and spatial requirements. Methods: Four 256-channel plane wave scanners (Verasonics, Inc, WA, USA) were combined to control a 1024-element planar array with 1.3 and 2.5 MHz therapeutic and imaging transmissions, respectively. A transducer aperture of ~40×15 mm was selected and Field II was applied to evaluate the point spread function. In vitro experiments were performed on commercial and custom phantoms to assess the spatial resolution, image contrast and microbubble-enhanced imaging capabilities. Results: We found that a 2D array configuration with 64 elements separated by λ-pitch in azimuth and 16 elements separated by 1.5λ-pitch in elevation ensured the required flexibility. This design, of 41.6 mm × 16 mm, thus provided both an extended field-of-view, up to 11 cm x 6 cm at 10 cm depth and steering of ±18° in azimuth and ±12° in elevation. At a depth of 16 cm, we achieved a volume imaging rate of 60 Hz, with a contrast ratio and resolution, respectively, of 19 dB, 0.8 mm at 3 cm and 20 dB and 2.1 mm at 12.5 cm. Conclusion: A single 2D array for both imaging and therapeutics, integrated with a 1024 channel scanner can guide microbubble-based therapy in volumetric regions of interest.

Biological Effects and Applications of Bulk and Surface Acoustic Waves on In Vitro Cultured Mammal Cells: New Insights

Medical imaging has relied on ultrasound (US) as an exploratory method for decades. Nonetheless, in cell biology, the numerous US applications are mainly in the research and development phase. In this review, we report the main effects on human or mammal cells of US induced by bulk or surface acoustic waves (SAW). At low frequencies, bulk US can lead to cell death. Under specific intensities and exposure times, however, cell proliferation and migration can be enhanced through cytoskeleton fluidization (a reorganization of the actin filaments and microtubules). Cavitation phenomena, frequencies of resonance close to those of the biological compounds, and mechanical transfers of energy from the acoustic pressure could explain those biological outcomes. At higher frequencies, no cavitation is observed. However, USs of high frequency stimulate ionic channels and increase cell permeability and transfection potency. Surface acoustic waves are increasingly exploited in microfluidics, especially for precise cell manipulations and cell sorting. With applications in diagnosis, infection, cancer treatment, or wound healing, US has remarkable potential. More mechanotransduction studies would be beneficial to understand the distinct roles of temperature rise, acoustic streaming and mechanical and electrical stimuli in the field.

Metformin-Loaded Polymer-Based Microbubbles/Nanoparticles Generated for the Treatment of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease that is increasingly common all over the world with a high risk of progressive hyperglycemia and high microvascular and macrovascular complications. The currently used drugs in the treatment of T2DM have insufficient glucose control and can carry detrimental side effects. Several drug delivery systems have been investigated to decrease the side effects and frequency of dosage, and also to increase the effect of oral antidiabetic drugs. In recent years, the use of microbubbles in biomedical applications has greatly increased, and research into microactive carrier bubbles continues to generate more and more clinical interest. In this study, various monodisperse polymer nanoparticles at different concentrations were produced by bursting microbubbles generated using a T-junction microfluidic device. Morphological analysis by scanning electron microscopy, molecular interactions between the components by FTIR, drug release by UV spectroscopy, and physical analysis such as surface tension and viscosity measurement were carried out for the particles generated and solutions used. The microbubbles and nanoparticles had a smooth outer surface. When the microbubbles/nanoparticles were compared, it was observed that they were optimized with 0.3 wt % poly(vinyl alcohol) (PVA) solution, 40 kPa pressure, and a 110 μL/min flow rate, thus the diameters of the bubbles and particles were 100 ± 10 μm and 70 ± 5 nm, respectively. Metformin was successfully loaded into the nanoparticles in these optimized concentrations and characteristics, and no drug crystals and clusters were seen on the surface. Metformin was released in a controlled manner at pH 1.2 for 60 min and at pH 7.4 for 240 min. The process and structures generated offer great potential for the treatment of T2DM.

A novel ultrasound-mediated nanodroplet-based gene delivery system for osteoporosis treatment

This project aimed to develop, optimize, and test an ultrasound-responsive targeted nanodroplet system for the delivery of osteoporosis-related silencing gene Cathepsin K small interfering RNA (CTSK siRNA) for osteoporosis treatment. The nanodroplet (ND) is composed of a gas core made from perfluorocarbon, stabilized with albumin, encapsulated with CTSK siRNA, and embedded with alendronate (AL) for bone targeting (CTSK siRNA-ND-AL). Following the development, the responsiveness of CTSK siRNA-ND-AL to a therapeutic ultrasound probe was examined. The results of biocompatibility tests with human bone marrow-derived mesenchymal stem cells proved no significant cell death (P > 0.05). When the CTSK siRNA-ND-AL was supplemented with human osteoclast precursors, they suppressed osteoclastogenesis. Thus, this project establishes the potential of nanotechnology and ultrasound to deliver genes into the osteoclasts. This research also presents a novel ultrasound responsive and targeted nanodroplet platform that can be used as a gene and drug delivery system for various diseases including cancer.

Electrohydrodynamic atomisation driven design and engineering of opportunistic particulate systems for applications in drug delivery, therapeutics and pharmaceutics

Electrohydrodynamic atomisation (EHDA) technologies have evolved significantly over the past decade; branching into several established and emerging healthcare remits through timely advances in the engineering sciences and tailored conceptual process designs. More specifically for pharmaceutical and drug delivery spheres, electrospraying (ES) has presented itself as a high value technique enabling a plethora of different particulate structures. However, when coupled with novel formulations (e.g. co-flows) and innovative device aspects (e.g., materials and dimensions), core characteristics of particulates are manipulated and engineered specifically to deliver an application driven need, which is currently lacking, ranging from imaging and targeted delivery to controlled release and sensing. This demonstrates the holistic nature of these emerging technologies; which is often overlooked. Parametric driven control during particle engineering via the ES method yields opportunistic properties when compared to conventional methods, albeit at ambient conditions (e.g., temperature and pressure), making this extremely valuable for sensitive biologics and molecules of interest. Furthermore, several processing (e.g., flow rate, applied voltage and working distance) and solution (e.g., polymer concentration, electrical conductivity and surface tension) parameters impact ES modes and greatly influence the production of resulting particles. The formation of a steady cone-jet and subsequent atomisation during ES fabricates particles demonstrating monodispersity (or near monodispersed), narrow particle size distributions and smooth or textured morphologies; all of which are successfully incorporated in a one-step process. By following a controlled ES regime, tailored particles with various intricate structures (hollow microspheres, nanocups, Janus and cell-mimicking nanoparticles) can also be engineered through process head modifications central to the ES technique (single-needle spraying, coaxial, multi-needle and needleless approaches). Thus, intricate formulation design, set-up and combinatorial engineering of the EHDA process delivers particulate structures with a multitude of applications in tissue engineering, theranostics, bioresponsive systems as well as drug dosage forms for specific delivery to diseased or target tissues. This advanced technology has great potential to be implemented commercially, particularly on the industrial scale for several unmet pharmaceutical and medical challenges and needs. This review focuses on key seminal developments, ending with future perspectives addressing obstacles that need to be addressed for future advancement.

Co-delivery of CPP decorated doxorubicin and CPP decorated siRNA by NGR-modified nanobubbles for improving anticancer therapy

A combination of doxorubicin (DOX) and small interfering RNA (siRNA) is proven effective for the reverse of multidrug resistance. However, rapid degradation and poor cellular internalization of siRNA hinder their synergistic action. To improve the combination effect, asparagine-glycine-arginine peptide (NGR) -modified nanobubbles (NBs) containing cell-penetrating peptide (CPP) decorated DOX and CPP decorated c-myc siRNA were constructed. Diameters of these NBs were about 245 nm and zeta potentials were about -3 mV. Encapsulation efficiencies (EE) of DOX exceeded 80%. Release of DOX could be triggered by ultrasound (US) since above 80% DOX was released from NBs after sonication while less than 5% DOX was discharged without treatment of US. These NBs were considered stable during 24 h since the decrease of particle size was no more than 10 nm, variances of EE were less than 5%, and changes of transmission (ΔT) were less than 3%. More drugs in formulation decorated with CPP and NGR were accumulated in the tumor when combined with sonication. The evident synergistic action of DOX, siRNA, NBs, and US was verified in mice with strong antitumor efficacy. Taken together, NGR-modified NBs containing CPP-DOX and CPP-siRNA are able to realize time- and spatial-controlled drug delivery and show potential application prospects.

Bubbles in microfluidics: an all-purpose tool for micromanipulation

In recent decades, the integration of microfluidic devices and multiple actuation technologies at the microscale has greatly contributed to the progress of related fields. In particular, microbubbles are playing an increasingly important role in microfluidics because of their unique characteristics that lead to specific responses to different energy sources and gas-liquid interactions. Many effective and functional bubble-based micromanipulation strategies have been developed and improved, enabling various non-invasive, selective, and precise operations at the microscale. This review begins with a brief introduction of the morphological characteristics and formation of microbubbles. The theoretical foundations and working mechanisms of typical micromanipulations based on acoustic, thermodynamic, and chemical microbubbles in fluids are described. We critically review the extensive applications and the frontline advances of bubbles in microfluidics, including microflow patterns, position and orientation control, biomedical applications, and development of bubble-based microrobots. We lastly present an outlook to provide directions for the design and application of microbubble-based micromanipulation tools and attract the attention of relevant researchers to the enormous potential of microbubbles in microfluidics.

Smart responsive-calcium carbonate nanoparticles for dual-model cancer imaging and treatment

Contrast-enhanced ultrasound (CEUS) is widely applied in cancer diagnosis clinically. However, the gas-filled contrast agents are unstable in the blood and exhibit shorter imaging time, which limit their clinical use. In this study, a diagnostic nanoparticle system was developed for dual-mode imaging (ultrasound and fluorescence), which after encapsulation with doxorubicin (DOX) demonstrated simultaneous therapeutic function towards cancer treatment. Thus, calcium carbonate (CaCO₃) nanoparticles were encapsulated with doxorubicin (DOX) to obtain CaCO₃-DOX. Under acidic conditions, it produced carbon dioxide (CO₂) to enhance ultrasound imaging and increase the release of DOX. After intravenously injecting CaCO₃-DOX to tumor-bearing mice, in the presence of an ultrasound field, CO₂bubbles were sufficiently generated at the tumor tissues for echogenic reflectivity. Also, the indocyanine green (ICG) was encapsulated into CaCO₃ nanoparticles, to further detect the tumor with fluorescence. The resultant theranostic nanoparticle system exhibited therapeutic efficacy towards tumour-bearing mice. Overall, this investigation provides an attractive strategy for dual-mode cancer diagnostics.

Plasmid-loadable magnetic/ultrasound-responsive nanodroplets with a SPIO-NP dispersed perfluoropentane core and lipid shell for tumor-targeted intracellular plasmid delivery

Using ultrasound activating contrast agents to induce sonoporation is a potential strategy for effective lesion-targeted gene delivery. Previous reports have proven that submicron nanodroplets have a better advantage than microbubbles in that they can pass through tumor vasculature endothelial gaps by passive targeting; however, they cannot achieve an adequate dose in tumors to facilitate ultrasound-enhanced gene delivery. Additionally, a few studies focused on delivering macromolecular genetic materials (i.e. overexpression plasmid and CRISPR plasmid) have presented more unique advantages than small-molecular genetic materials (i.e. miRNA mimics, siRNA and shRNA etc.), such as enhancing the expression of target genes with long-term effectiveness. Thereby, we constructed novel plasmid-loadable magnetic/ultrasound-responsive nanodroplets, where superparamagnetic iron oxide nanoparticle dispersed perfluoropentane was encapsulated with lipids to which plasmids could be adhered, and branched polyethylenimine was used to protect the plasmids from enzymolysis. Furthermore, in vitro and in vivo studies were performed to verify the magnetic tumor-targeting ability of the plasmid-loadable magnetic/ultrasound-responsive nanodroplets and focused ultrasound enhanced intracellular plasmid delivery. The plasmid-loadable magnetic/ultrasound-responsive nanodroplets, carrying 16-19 plasmids per droplet, had desirable diameters less than 300 nm, and integrated the merits of excellent magnetic targeting capabilities and phase transition sensitivity to focused ultrasound. Under programmable focused ultrasound exposure, the plasmid-loadable magnetic/ultrasound-responsive nanodroplets underwent a phase-transition into echogenic microbubbles and the subsequent inertial cavitation of the microbubbles achieved an ∼40% in vitro plasmid delivery efficiency. Following intravenous administration, T2-weighted magnet resonance imaging, scanning electron microscopy and inductively coupled plasma optical emission spectrometry of the tumors showed significantly enhanced intratumoral accumulation of the plasmid-loadable magnetic/ultrasound-responsive nanodroplets under an external magnetic field. And a GFP ELISA assay and immunofluorescence staining indicated that focused ultrasound-induced inertial cavitation of the plasmid-loadable magnetic/ultrasound-responsive nanodroplets significantly enhanced the intracellular delivery of plasmids within the tumor after magnet-assisted accumulation, while only lower GFP levels were observed in the tumors on applying focused ultrasound or an external magnet alone. Taken together, utilizing the excellent plasmid-loadable magnetic/ultrasound-responsive nanodroplets combined with magnetism and ultrasound could efficiently deliver plasmids to cancer cells, which could be a potential strategy for macromolecular genetic material delivery in the clinic to treat cancer.

Sonodelivery in Skeletal Muscle: Current Approaches and Future Potential

There are currently multiple approaches to facilitate gene therapy via intramuscular gene delivery, such as electroporation, viral delivery, or direct DNA injection with or without polymeric carriers. Each of these methods has benefits, but each method also has shortcomings preventing it from being established as the ideal technique. A promising method, ultrasound-mediated gene delivery (or sonodelivery) is inexpensive, widely available, reusable, minimally invasive, and safe. Hurdles to utilizing sonodelivery include choosing from a large variety of conditions, which are often dependent on the equipment and/or research group, and moderate transfection efficiencies when compared to some other gene delivery methods. In this review, we provide a comprehensive look at the breadth of sonodelivery techniques for intramuscular gene delivery and suggest future directions for this continuously evolving field.

A review of ultrasound-mediated microbubbles technology for cancer therapy: a vehicle for chemotherapeutic drug delivery

Background:

The unique behaviour of microbubbles under ultrasound acoustic pressure makes them useful agents for drug and gene delivery. Several studies have demonstrated the potential application of microbubbles as a non-invasive, safe and effective technique for targeted delivery of drugs and genes. The drugs can be incorporated into the microbubbles in several different approaches and then carried to the site of interest where it can be released by destruction of the microbubbles using ultrasound to achieve the required therapeutic effect.

Methods:

The objective of this article is to report on a review of the recent advances of ultrasound-mediated microbubbles as a vehicle for delivering drugs and genes and its potential application for the treatment of cancer.

Conclusion:

Ultrasound-mediated microbubble technology has the potential to significantly improve chemotherapy drug delivery to treatment sites with minimal side effects. Moreover, the technology can induce temporary and reversible changes in the permeability of cells and vessels, thereby allowing for drug delivery in a spatially localised region which can improve the efficiency of drugs with poor bioavailability due to their poor absorption, rapid metabolism and rapid systemic elimination.

Drug Loading in Poly(butyl cyanoacrylate)-Based Polymeric Microbubbles

Microbubbles (MB) are routinely used ultrasound (US) contrast agents that have recently attracted increasing attention as stimuli-responsive drug delivery systems. To better understand MB-based drug delivery, we studied the role of drug hydrophobicity and molecular weight on MB loading, shelf-life stability, US properties, and drug release. Eight model drugs, varying in hydrophobicity and molecular weight, were loaded into the shell of poly(butyl cyanoacrylate) (PBCA) MB. In the case of drugs with progesterone as a common structural backbone (i.e., for corticosteroids), loading capacity and drug release correlated well with hydrophobicity and molecular weight. Conversely, when employing drugs with no structural similarity (i.e., four different fluorescent dyes), loading capacity and release did not correlate with hydrophobicity and molecular weight. All model drug-loaded MB formulations could be equally efficiently destroyed upon exposure to US. Together, these findings provide valuable insights on how the physicochemical properties of (model) drug molecules affect their loading and retention in and US-induced release from polymeric MB, thereby facilitating the development of drug-loaded MB formulations for US-triggered drug delivery.

Ultrasound-responsive lipid microbubbles for drug delivery: A review of preparation techniques to optimise formulation size, stability and drug loading

Lipid-shelled microbubbles have received extensive interest to enhance ultrasound-responsive drug delivery outcomes due to their high biocompatibility. While therapeutic effectiveness of microbubbles is well established, there remain limitations in sample homogeneity, stability profile and drug loading properties which restrict these formulations from seeing widespread use in the clinical setting. In this review, we evaluate and discuss the most encouraging leads in lipid microbubble design and optimisation. We examine current applications in drug delivery for the systems and subsequently detail shell compositions and preparation strategies that improve monodispersity while retaining ultrasound responsiveness. We review how excipients and storage techniques help maximise stability and introduce different characterisation and drug loading techniques and evaluate their impact on formulation performance. The review concludes with current quality control measures in place to ensure lipid microbubbles can be reproducibly used in drug delivery.

Numerical modeling of the dynamics of bubble oscillations subjected to fast variations in the ambient pressure with a coupled level set and volume of fluid method

A numerical method for modeling and understanding the dynamics of bubble oscillations subjected to fast variations in the ambient pressure is proposed under low Mach number conditions. In the present work, the method uses a single-fluid continuum formalism of weakly compressible axisymmetric Navier-Stokes equations for the numerical simulation of liquid-gas flows with surface tension and adopts the interface capturing approach based on a coupled level set and volume of fluid (CLSVOF) method for describing the moving and deformed interfaces. To demonstrate the efficacy of the proposed method, first, the numerical results of the radial oscillations of a spherical gas bubble are tested with the numerical solutions of Rayleigh-Plesset equation. Then, the numerical method is applied to reproduce the growth and subsequent collapse of a bubble in an infinite liquid medium observed in experiments. Finally, the numerical simulation of the interaction of two oscillating bubbles at small separation distance is evaluated in response to a moderate step change in the ambient pressure. It is shown that two deformable bubbles undergo coupled radial and oscillatory translational motions which eventually results in the bubbles' attraction and coalescence caused by the secondary Bjerknes forces. The numerical predictions show very good accuracy with the experimental and numerical results reported in the literature.

Ultrasound-responsive droplets for therapy: A review

The last two decades have seen the development of acoustically activated droplets, also known as phase-change emulsions, from a diagnostic tool to a therapeutic agent. Through bubble effects and triggered drug release, these superheated agents have found potential applications from oncology to neuromodulation. The aim of this review is to summarise the key developments in therapeutic droplet design and use, to discuss the current challenges slowing clinical translation, and to highlight the new frontiers progressing towards clinical implementation. The literature is summarised by addressing the droplet design criteria and by carrying out a multiparametric study of a range of droplet formulations and their associated vaporisation thresholds.

Microbubble-Mediated Enhanced Delivery of Curcumin to Cervical Cancer Cells

The major bottleneck in the current chemotherapy treatment of cancer is the low bioavailability and high cytotoxicity. Targeted delivery of drug to the cancer cells can reduce the cytotoxicity and increase the bioavailability. In this context, microbubbles are currently being explored as drug-delivery vehicles to effectively deliver drug to the tumors or cancerous cells. Microbubbles when used along with ultrasound can enhance drug uptake and inhibit the growth of tumor cells. Several potential anticancer molecules exhibit poor water solubility, which limits their use in therapeutic applications. Such poorly water soluble molecules can be coadministered with microbubbles or encapsulated within or loaded on the microbubbles surface, to enhance the effectiveness of these molecules against cancer cells. Curcumin is one of such potential anticancer molecules obtained from the rhizome of herbal spice, turmeric. In this work, curcumin-loaded protein microbubbles were synthesized and examined for effective in vitro delivery of curcumin to HeLa cells. Microbubbles in the size range of 1-10 μm were produced using perfluorobutane as core gas and bovine serum albumin (BSA) as shell material and were loaded with curcumin. The amount of curcumin loaded on the microbubble surface was estimated using UV-vis spectroscopy, and the average curcumin loading was found to be ∼54 μM/10⁸ microbubbles. Kinetics of in vitro curcumin release from microbubble surface was also estimated, where a 4-fold increase in the rate of curcumin release was obtained in the presence of ultrasound. Sonication and incubation of HeLa cells with curcumin-loaded BSA microbubbles enhanced the uptake of curcumin by ∼250 times. Further, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay confirmed ∼71% decrease in cell viability when HeLa cells were sonicated with curcumin-loaded microbubbles and incubated for 48 h.

The therapeutic effect in gliomas of nanobubbles carrying siRNA combined with ultrasound-targeted destruction

Background

Nanobubbles (NBs) combined with ultrasound-targeted destruction (UTD) have become promising potential carriers for drug or siRNA delivery. Due to their nano-size, NBs could penetrate tumor blood vessels and accumulate in intercellular spaces so that "sonoporation" induced by UTD would act directly on the tumor cells to increase cell membrane permeability.

Methods

Based on the successful the fabrication of NBs, we synthesized NBs carrying siRNA (NBs-siRNA) by using a biotin-streptavidin system. We then utilized ultrasound irradiation (UI)-targeted NBs-siRNA to improve siRNA transfection and achieve the inhibition of glioma growth.

Results

NBs as carriers combined with UI effectively enhanced siRNA transfection and the effect of silencing targeted genes in vitro. Additionally, a better therapeutic effect was shown in the NBs-siRNA with UI group in vivo compared with that of microbubbles (MBs) with UI or NBs-siRNA without UI.

Conclusion

These results indicated that NBs combined with UTD might be an ideal delivery vector for siRNA to achieve the noninvasive treatment of glioma.

Precise Placement of Microbubble Templates at Single Entity Resolution

Microbubbles have been used as a soft template to produce hollow structures for diverse applications in chemistry, materials science, and biomedicine. It is a challenge, however, to control their size and position at single-entity level. We report on an on-demand method to produce and place a single microbubble with programmed size and position. The method exploits scanning an electrolyte-filled micropipette to place a hydrogen (H₂) bubble, generated by water electrolysis, on the desired position. The bubble growth is self-limited after the bubble size fits to the pipet aperture, yielding well-controlled bubble size. The bubble growth dynamics within the pipet is successfully investigated by a methodology that combines phase-contrast X-ray imaging and electric-current measurement. We show that the microbubbles, accurately controlled in size and position, can be used for the fabrication of various polypyrrole microcontainer arrays. We expect the scanning-pipet strategy could be generalized for manipulating various soft materials at will.

Oxygen-Carrying Micro/Nanobubbles: Composition, Synthesis Techniques and Potential Prospects in Photo-Triggered Theranostics

Microbubbles and nanobubbles (MNBs) can be prepared using various shells, such as phospholipids, polymers, proteins, and surfactants. MNBs contain gas cores due to which they are echogenic and can be used as contrast agents for ultrasonic and photoacoustic imaging. These bubbles can be engineered in various sizes as vehicles for gas and drug delivery applications with novel properties and flexible structures. Hypoxic areas in tumors develop owing to an imbalance of oxygen supply and demand. In tumors, hypoxic regions have shown more resistance to chemotherapy, radiotherapy, and photodynamic therapies. The efficacy of photodynamic therapy depends on the effective accumulation of photosensitizer drug in tumors and the availability of oxygen in the tumor to generate reactive oxygen species. MNBs have been shown to reverse hypoxic conditions, degradation of hypoxia inducible factor 1α protein, and increase tissue oxygen levels. This review summarizes the synthesis methods and shell compositions of micro/nanobubbles and methods deployed for oxygen delivery. Methods of functionalization of MNBs, their ability to deliver oxygen and drugs, incorporation of photosensitizers and potential application of photo-triggered theranostics, have also been discussed.

Size-Modulable Nanoprobe for High-Performance Ultrasound Imaging and Drug Delivery against Cancer

Among medical imaging modalities available in the clinic, ultrasonography is the most convenient, inexpensive, ionizing-radiation-free, and most common. Micrometer-size perfluorocarbon bubbles have been used as efficient contrast for intravascular ultrasonography, but they are too big for tumor penetration. Nanodroplets (250-1000 nm) encapsulating both perfluorocarbon and drug have been used as an ultrasound-triggered release drug delivery platform against cancer, but they are generally not useful as a tumor imaging agent. The present study aims to develop a type of pH-sensitive, polymersome-based, perfluorocarbon encapsulated ultrasonographic nanoprobe, capable of maintaining at 178 nm during circulation and increasing to 437 nm at the acidic tumor microenvironment. Its small size allowed efficient tumor uptake. At the tumor site, the nanoparticle swells, resulting in lowering of the vaporization threshold for the perfluorocarbon, efficient conversion of nanoprobes to echogenic nano/microbubbles for ultrasonic imaging, and eventual release of doxorubicin from the theranostic nanoprobe for deep tissue chemotherapy, triggered by irradiation with low-frequency ultrasound.

An in vitro proof-of-principle study of sonobactericide

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

Nano Air Seeds Trapped in Mesoporous Janus Nanoparticles Facilitate Cavitation and Enhance Ultrasound Imaging

The current contrast agents utilized in ultrasound (US) imaging are based on microbubbles which suffer from a short lifetime in systemic circulation. The present study introduces a new type of contrast agent for US imaging based on bioresorbable Janus nanoparticles (NPs) that are able to generate microbubbles in situ under US radiation for extended time. The Janus NPs are based on porous silicon (PSi) that was modified via a nanostopper technique. The technique was exploited to prepare PSi NPs which had hydrophobic pore walls (inner face), while the external surfaces of the NPs (outer face) were hydrophilic. As a consequence, when dispersed in an aqueous solution, the Janus NPs contained a substantial amount of air trapped in their nanopores. The specific experimental setup was developed to prove that these nano air seeds were indeed acting as nuclei for microbubble growth during US radiation. Using the setup, the cavitation thresholds of the Janus NPs were compared to their completely hydrophilic counterparts by detecting the subharmonic signals from the microbubbles. These experiments and the numerical simulations of the bubble dynamics demonstrated that the Janus NPs generated microbubbles with a radii of 1.1 μm. Furthermore, the microbubbles generated by the NPs were detected with a conventional medical ultrasound imaging device. Long systemic circulation time was ensured by grafting the NPs with two different PEG polymers, which did not affect adversely the microbubble generation. The present findings represent an important landmark in the development of ultrasound contrast agents which possess the properties for both diagnostics and therapy.

Ultrasound-guided drug delivery in cancer

Recent advancements in ultrasound and microbubble (USMB) mediated drug delivery technology has shown that this approach can improve spatially confined delivery of drugs and genes to target tissues while reducing systemic dose and toxicity. The mechanism behind enhanced delivery of therapeutics is sonoporation, the formation of openings in the vasculature, induced by ultrasound-triggered oscillations and destruction of microbubbles. In this review, progress and challenges of USMB mediated drug delivery are summarized, with special focus on cancer therapy.

Microbubbles used for contrast enhanced ultrasound and theragnosis: a review of principles to applications

Ultrasound was developed several decades ago as a useful imaging modality, and it became the second most popular diagnostic tool due to its non-invasiveness, real-time capabilities, and safety. Additionally, ultrasound has been used as a therapeutic tool with several therapeutic agents and in nanomedicine. Ultrasound imaging is often used to diagnose many types of cancers, including breast, stomach, and thyroid cancers. In addition, ultrasound-mediated therapy is used in cases of joint inflammation, rheumatoid arthritis, and osteoarthritis. Microbubbles, when used as ultrasound contrast agents, can act as echo-enhancers and therapeutic agents, and they can play an essential role in ultrasound imaging and ultrasound-mediated therapy. Recently, various types of ultrasound contrast agents made of lipid, polymer, and protein shells have been used. Air, nitrogen, and perfluorocarbon are usually included in the core of the microbubbles to enhance ultrasound imaging, and therapeutic drugs are conjugated and loaded onto the surface or into the core of the microbubbles, depending on the purpose and properties of the substance. Many research groups have utilized ultrasound contrast agents to enhance the imaging signal in blood vessels or tissues and to overcome the blood-brain barrier or blood-retina barrier. These agents are also used to help treat diseases in various regions or systems of the body, such as the cardiovascular system, or as a cancer treatment. In addition, with the introduction of targeted moiety and multiple functional groups, ultrasound contrast agents are expected to have a potential future in ultrasound imaging and therapy. In this paper, we briefly review the principles of ultrasound and introduce the underlying theory, applications, limitations, and future perspectives of ultrasound contrast agents.

Fabrication of ultrasound-responsive microbubbles via coaxial electrohydrodynamic atomization for triggered release of tPA

A single-step fabrication method, coaxial electrohydrodynamic atomization (CEHDA), was developed to synthesize drug-loaded microbubbles (MBs) for combination treatment of ischemic stroke. The bioactivity of therapeutic agent (tPA, tissue plasminogen activator) after preparation was evaluated, showing that CEHDA could be very promising method for producing MBs with therapeutic functions. The bubble performance and tPA release profiles were also examined by exposing the bubbles to 2MHz ultrasound of various intensities. The results showed that the mean diameter of tPA-loaded MBs was found to fluctuate about its original diameter when exposed to ultrasound and higher intensity ultrasound was more effective in triggering the burst of CEHDA MBs. High ultrasound-triggered bubble disintegration effectiveness in a short period (first 5min) fits well with the requirement of short ultrasound exposure time for human brain. Moreover, a numerical model was also applied to investigate the stability of the fabricated MBs in the bloodstream. It was found that MB dissolution time increased with initial radius, decreased with initial surface tension and increased with initial shell resistance but it was barely affected by the average excessive bloodstream pressure.

Physicochemical Characterization of the Shell Composition of PBCA-Based Polymeric Microbubbles

Microbubbles (MB) are routinely used as contrast agents for ultrasound (US) imaging. In recent years, MB have also attracted interest as drug delivery systems. Soft-shelled lipidic MB tend to be more advantageous for US imaging, while hard-shelled polymeric MB appear to be more suitable for drug delivery purposes because of their thicker shell and the resulting higher drug loading capacity. The physicochemical composition of the shell of polymeric MB, however, remains largely unknown. This study sets out to evaluate the molecular weight and polydispersity of the building blocks constituting the shell of poly(butyl cyanoacrylate) (PBCA) MB. Several different PBCA MB were synthesized, varying preparation parameters such as pH, surfactant, stirring speed, and stirring time. Using gel permeation chromatography, it is found that the number average molecular weight (M _n ) of the polymer chains in the shell of PBCA MB is 4 kDa, and that >99% of the polymer chains are below 40 kDa. This demonstrates that virtually all polymeric building blocks in the shell of PBCA MB have a size which allows for renal excretion, thereby supporting their use for drug delivery applications.

PBCA-based polymeric microbubbles for molecular imaging and drug delivery

Microbubbles (MB) are routinely used as contrast agents for ultrasound (US) imaging. We describe different types of targeted and drug-loaded poly(n-butyl cyanoacrylate) (PBCA) MB, and demonstrate their suitability for multiple biomedical applications, including molecular US imaging and US-mediated drug delivery. Molecular imaging of angiogenic tumor blood vessels and inflamed atherosclerotic endothelium is performed by modifying the surface of PBCA MB with peptides and antibodies recognizing E-selectin and VCAM-1. Stable and inertial cavitation of PBCA MB enables sonoporation and permeabilization of blood vessels in tumors and in the brain, which can be employed for direct and indirect drug delivery. Direct drug delivery is based on US-induced release of (model) drug molecules from the MB shell. Indirect drug delivery refers to US- and MB-mediated enhancement of extravasation and penetration of co-administered drugs and drug delivery systems. These findings are in line with recently reported pioneering proof-of-principle studies showing the usefulness of (phospholipid) MB for molecular US imaging and sonoporation-enhanced drug delivery in patients. They aim to exemplify the potential and the broad applicability of combining MB with US to improve disease diagnosis and therapy.

Hypoxic Preconditioning Combined with Microbubble-Mediated Ultrasound Effect on MSCs Promote SDF-1/CXCR4 Expression and its Migration Ability: An In Vitro Study

Our objective is to investigate the promoting effect of hypoxic preconditioning combined with microbubble (MB)-mediated ultrasound (US) on the SDF-1/CXCR4 expression and the migration ability of mesenchymal stem cells (MSCs). Based on the uniform design, the parameters of MB-mediated US, such as the total treatment time (T), acoustic intensity (Q), and the dosage of MBs, were optimized firstly. The results were assessed by regression analysis. Using the optimum irradiation parameters, the concentration of SDF-1 in the supernatant, the expression levels of membrane CXCR4, and the cell viability of hypoxic MSCs or normoxic MSCs were compared. The in vitro transwell migration assay was performed as well. The best combination of parameters for more SDF-1 secretion and less MSCs death was T = 30 s, A = 0.6 W/cm(2), and MB = 10(6)/ml. After 24 h of hypoxic preconditioning, the expression of SDF-1 and surface CXCR4 was increased in the hypoxic MSC group as compared to the normoxic MSC group (P < 0.05). On the basis of that, MB-mediated US could further upregulate the expression of SDF-1/CXCR4 with the optimum parameters (P < 0.05), while the cell viability was only decreased by about 9-10 % compared to the untreated groups. The number of successfully migrated cells was also the largest in the hypoxic preconditioning combined with MB-mediated US group than all the other groups. The results obtained indicate the combination of hypoxic preconditioning, and MB-mediated US can upregulate the SDF-1/CXCR4 expression and improve the migration ability in MSCs.

Gene delivery systems by the combination of lipid bubbles and ultrasound

Gene therapy is promising for the treatment of many diseases including cancers and genetic diseases. From the viewpoint of safety, ultrasound (US)-mediated gene delivery with nano/ microbubbles was recently developed as a novel non-viral vector system. US-mediated gene delivery using nano/microbubbles are able to produce transient changes in the permeability of the cell membrane after US-induced cavitation while reducing cellular damage and enables the tissue-specific or the site-specific intracellular delivery of gene both in vitro and in vivo. We have recently developed novel lipid nanobubbles (Lipid Bubbles). These nanobubbles can also be used to enhance the efficacy of the US-mediated genes (plasmid DNA, siRNA, and miRNA etc.) delivery. In this review, we describe US-mediated delivery systems combined with nano/microbubbles and discuss their feasibility as non-viral vector systems.

Enhancement of Drug Delivery in Tumors by Using Interaction of Nanoparticles with Ultrasound Radiation

Efficacy and safety of cancer chemo- and biotherapy are limited by poor penetration of anti-cancer drugs from blood into tumor cells. Tumor blood vessel wall, slow diffusion in the interstitium, and cancer cell membrane create physiological barriers for anti-cancer drugs, in particular promising macromolecular agents. Recently, we proposed to use selective accumulation of exogenous nano- and microparticles in tumors followed by ultrasound-induced cavitation for safe and efficient drug and gene delivery. In this paper, we first investigated the influence of polystyrene nanoparticles (100 and 280 nm in diameter and concentration up to 0.2% w/w) on cavitation threshold in water at the frequency of 20 kHz. Then, using optimal irradiation parameters found in the first part of this work, we studied efficacy of cancer chemotherapy with this technique. The experiments were performed in athymic nude mice bearing human colon KM20 tumors, which are highly resistant to chemotherapy. Ultrasound with the frequency of 20 kHz in combination with i.v. injected polystyrene nanoparticles was applied to enhance delivery of chemotherapeutic agent 5-fluorouracil. Our studies demonstrated that ultrasound irradiation in combination with the nanoparticle and drug injections significantly decreased tumor volume and resulted in complete tumor regression at optimal irradiation conditions, while the volume of control (non-irradiated) tumors increased despite drug injections. These data suggest that ultrasound-induced drug delivery may improve efficacy of current cancer treatment regimens.

Micromanaging cardiac regeneration: Targeted delivery of microRNAs for cardiac repair and regeneration

The loss of cardiomyocytes during injury and disease can result in heart failure and sudden death, while the adult heart has a limited capacity for endogenous regeneration and repair. Current stem cell-based regenerative medicine approaches modestly improve cardiomyocyte survival, but offer neglectable cardiomyogenesis. This has prompted the need for methodological developments that crease de novo cardiomyocytes. Current insights in cardiac development on the processes and regulatory mechanisms in embryonic cardiomyocyte differentiation provide a basis to therapeutically induce these pathways to generate new cardiomyocytes. Here, we discuss the current knowledge on embryonic cardiomyocyte differentiation and the implementation of this knowledge in state-of-the-art protocols to the direct reprogramming of cardiac fibroblasts into de novo cardiomyocytes in vitro and in vivo with an emphasis on microRNA-mediated reprogramming. Additionally, we discuss current advances on state-of-the-art targeted drug delivery systems that can be employed to deliver these microRNAs to the damaged cardiac tissue. Together, the advances in our understanding of cardiac development, recent advances in microRNA-based therapeutics, and innovative drug delivery systems, highlight exciting opportunities for effective therapies for myocardial infarction and heart failure.

Microbubble-mediated ultrasound promotes accumulation of bone marrow mesenchymal stem cell to the prostate for treating chronic bacterial prostatitis in rats

Chronic bacterial prostatitis (CBP) is an intractable disease. Although bone marrow mesenchymal stem cells (BMMSCs) are able to regulate inflammation in CBP, the effect of microbubble-mediated ultrasound- induced accumulation of BMMSCs on CBP remains unclear. To address this gap, a model of CBP was established in SD rats, which were then treated with BMMSCs alone (BMMSC group), BMMSCs with ultrasound (ultrasound group), BMMSCs with microbubble-mediated ultrasound (MMUS group) and compared with a healthy control group. A therapeutic-ultrasound apparatus was used to treat the prostate in the presence of circulating microbubbles and BMMSCs. The BMMSC distribution was assessed with in vivo imaging, and the prostate structure with light microscopy. Real-time quantitative RT-PCR, ELISA, and immunohistochemistry were used to assess the expressions of TNF-α and IL-1β. More BMMSCs were found in the prostate in the MMUS group than in the CBP, ultrasound, and BMMSC groups. Inflammatory cell infiltration, fibrous tissue hyperplasia, and tumor-like epithelial proliferation were significantly reduced in the MMUS group, as were the mRNA and protein expressions of TNF-α and IL-1β. Microbubble-mediated ultrasound-induced accumulation of BMMSCs can inhibit inflammation and decrease TNF-α and IL-1β expressions in the prostate of CBP rats, suggesting that this method may be therapeutic for CPB.