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

Gold Nanorod-Loaded Nano-Contrast Agent with Composite Shell-Core Structure for Ultrasonic/Photothermal Imaging-Guided Therapy in Ischemic Muscle Disorders

Purpose

This study aims to broaden the application of nano-contrast agents (NCAs) within the realm of the musculoskeletal system. It aims to introduce novel methods, strategies, and insights for the clinical management of ischemic muscle disorders, encompassing diagnosis, monitoring, evaluation, and therapeutic intervention.

Methods

We developed a composite encapsulation technique employing O-carboxymethyl chitosan (OCMC) and liposome to encapsulate NCA-containing gold nanorods (GNRs) and perfluoropentane (PFP). This nanoscale contrast agent was thoroughly characterized for its basic physicochemical properties and performance. Its capabilities for in vivo and in vitro ultrasound imaging and photothermal imaging were authenticated, alongside a comprehensive biocompatibility assessment to ascertain its effects on microcirculatory perfusion in skeletal muscle using a murine model of hindlimb ischemia, and its potential to augment blood flow and facilitate recovery.

Results

The engineered GNR@OCMC-liposome/PFP nanostructure exhibited an average size of 203.18±1.49 nm, characterized by size uniformity, regular morphology, and a good biocompatibility profile. In vitro assessments revealed NCA's potent photothermal response and its transformation into microbubbles (MBs) under near-infrared (NIR) irradiation, thereby enhancing ultrasonographic visibility. Animal studies demonstrated the nanostructure's efficacy in photothermal imaging at ischemic loci in mouse hindlimbs, where NIR irradiation induced rapid temperature increases and significantly increased blood circulation.

Conclusion

The dual-modal ultrasound/photothermal NCA, encapsulating GNR and PFP within a composite shell-core architecture, was synthesized successfully. It demonstrated exceptional stability, biocompatibility, and phase transition efficiency. Importantly, it facilitates the encapsulation of PFP, enabling both enhanced ultrasound imaging and photothermal imaging following NIR light exposure. This advancement provides a critical step towards the integrated diagnosis and treatment of ischemic muscle diseases, signifying a pivotal development in nanomedicine for musculoskeletal therapeutics.

Pyroptosis Induction with Nanosonosensitizer-Augmented Sonodynamic Therapy Combined with PD-L1 Blockade Boosts Efficacy against Liver Cancer

Induction of pyroptosis can promote anti-PD-L1 therapeutic efficacy due to the release of pro-inflammatory cytokines, but current approaches can cause off target toxicity. Herein, a phthalocyanine-conjugated mesoporous silicate nanoparticle (PMSN) is designed for amplifying sonodynamic therapy (SDT) to augment oxidative stress and induce robust pyroptosis in tumors. The sub-10 nm diameter structure and c(RGDyC)-PEGylated modification enhance tumor targeting and renal clearance. The unique porous architecture of PMSN doubles ROS yield and enhances pyroptotic cell populations in tumors (25.0%) via a cavitation effect. PMSN-mediated SDT treatment efficiently reduces tumor mass and suppressed residual tumors in treated and distant sites by synergizing with PD-L1 blockade (85.93% and 77.09%, respectively). Furthermore, loading the chemotherapeutic, doxorubicin, into PMSN intensifies SDT-pyroptotic effects and increased efficacy. This is the first report of the use of SDT regimens to induce pyroptosis in liver cancer. This noninvasive and effective strategy has potential for clinical translation.

Sono-activated materials for enhancing focused ultrasound ablation: Design and application in biomedicine

The ablation effect of focused ultrasound (FUS) has played an increasingly important role in the biomedical field over the past decades, and its non-invasive features have great advantages, especially for clinical diseases where surgical treatment is not available or appropriate. Recently, rapid advances in the adjustable morphology, enzyme-mimetic activity, and biostability of sono-activated materials have significantly promoted the medical application of FUS ablation. However, a systematic review of sono-activated materials based on FUS ablation is not yet available. This progress review focuses on the recent design, fundamental principles, and applications of sono-activated materials in the FUS ablation biomedical field. First, the different ablation mechanisms and the key factors affecting ablation are carefully determined. Then, the design of sono-activated materials with high FUS ablation efficiencies is comprehensively discussed. Subsequently, the representative biological applications are summarized in detail. Finally, the primary challenges and future perspectives are also outlined. We believe this timely review will provide key information and insights for further exploration of focused ultrasound ablation and new inspiration for designing future sono-activated materials. STATEMENT OF SIGNIFICANCE: The ablation effect of focused ultrasound (FUS) has played an increasingly important role in the biomedical field over the past decades. However, there are also some challenges of FUS ablation, such as skin burns, tumour recurrence after thermal ablation, and difficulty in controlling cavitation ablation. The rapid advance in adjustable morphology, enzyme-mimetic activity, and biostability of sono-activated materials has significantly promoted the medical application of FUS ablation. However, the systematic review of sono-activated materials based on FUS ablation is not yet available. This progress review focuses on the recent design, fundamental principles, and applications in the FUS ablation biomedical field of sono-activated materials. We believe this timely review will provide key information and insights for further exploration of FUS ablation.

Antibacterial Effect of Acoustic Cavitation Promoted by Mesoporous Silicon Nanoparticles

As-prepared mesoporous silicon nanoparticles, which were synthesized by electrochemical etching of crystalline silicon wafers followed by high-energy milling in water, were explored as a sonosensitizer in aqueous media under irradiation with low-intensity ultrasound at 0.88 MHz. Due to the mixed oxide-hydride coating of the nanoparticles' surfaces, they showed both acceptable colloidal stability and sonosensitization of the acoustic cavitation. The latter was directly measured and quantified as a cavitation energy index, i.e., time integral of the magnitude of ultrasound subharmonics. The index turned out to be several times greater for nanoparticle suspensions as compared to pure water, and it depended nonmonotonically on nanoparticle concentration. In vitro tests with Lactobacillus casei revealed a dramatic drop of the bacterial viability and damage of the cells after ultrasonic irradiation with intensity of about 1 W/cm² in the presence of nanoparticles, which themselves are almost non-toxic at the studied concentrations of about 1 mg/mL. The experimental results prove that nanoparticle-sensitized cavitation bubbles nearby bacteria can cause bacterial lysis and death. The sonosensitizing properties of freshly prepared mesoporous silicon nanoparticles are beneficial for their application in mild antibacterial therapy and treatment of liquid media.

Dual-Mode Fluorescence/Ultrasound Imaging with Biocompatible Metal-Doped Graphene Quantum Dots

Sonography offers many advantages over standard methods of diagnostic imaging due to its non-invasiveness, substantial tissue penetration depth, and low cost. The benefits of ultrasound imaging call for the development of ultrasound-trackable drug delivery vehicles that can address a variety of therapeutic targets. One disadvantage of the technique is the lack of high-precision imaging, which can be circumvented by complementing ultrasound contrast agents with visible and, especially, near-infrared (NIR) fluorophores. In this work, we, for the first time, develop a variety of lightly metal-doped (iron oxide, silver, thulium, neodymium, cerium oxide, cerium chloride, and molybdenum disulfide) nitrogen-containing graphene quantum dots (NGQDs) that demonstrate high-contrast properties in the ultrasound brightness mode and exhibit visible and/or near-infrared fluorescence imaging capabilities. NGQDs synthesized from glucosamine precursors with only a few percent metal doping do not introduce additional toxicity in vitro, yielding over 80% cell viability up to 2 mg/mL doses. Their small (<50 nm) sizes warrant effective cell internalization, while oxygen-containing surface functional groups decorating their surfaces render NGQDs water soluble and allow for the attachment of therapeutics and targeting agents. Utilizing visible and/or NIR fluorescence, we demonstrate that metal-doped NGQDs experience maximum accumulation within the HEK-293 cells 6-12 h after treatment. The successful 10-fold ultrasound signal enhancement is observed at 0.5-1.6 mg/mL for most metal-doped NGQDs in the vascular phantom, agarose gel, and animal tissue. A combination of non-invasive ultrasound imaging with capabilities of high-precision fluorescence tracking makes these metal-doped NGQDs a viable agent for a variety of theragnostic applications.

Recent progress on bioimaging strategies based on Janus nanoparticles

Janus nanoparticles refer to a kind of asymmetric-structured nanoparticles composed of two or more distinct sides with differences in chemical nature and/or polarity on each side and thus can integrate two or more properties in one single particle. Due to their unique structure and surface properties, Janus nanoparticles have shown broad application potentials in optics, nuclear magnetic resonance, multi-mode imaging, and other fields. Unlike traditional contrast agents used in biological imaging, Janus nanoparticles are asymmetrically and directionally oriented to ensure stable partitioning of individual nanoparticles while integrating more functions. Much advancement have been carried out in the past few years, with some studies partially covering bioimaging applications. However, to our best knowledge, there are still no review papers specifically dedicated to the bioimaging applications with Janus nanoparticles. Bearing this in mind and taking the current challenges in this field into consideration, herein, we discuss representative approaches orchestrated for bioimaging applications, with the focus on the improvement of imaging quality brought by Janus nanoparticles and the development of multifunctional nanoplatforms in biological imaging fields, such as theranostics and therapies. Finally, based on the research experience of our group in this field, prospects for future research trends are put forward to provide new ideas for designing new Janus nanoparticles for clinical bioimaging.

Next-Generation Colloidal Materials for Ultrasound Imaging Applications

Ultrasound has important applications, predominantly in the field of diagnostic imaging. Presently, colloidal systems such as microbubbles, phase-change emulsion droplets and particle systems with acoustic properties and multiresponsiveness are being developed to address typical issues faced when using commercial ultrasound contrast agents, and to extend the utility of such systems to targeted drug delivery and multimodal imaging. Current technologies and increasing research data on the chemistry, physics and materials science of new colloidal systems are also leading to the development of more complex, novel and application-specific colloidal assemblies with ultrasound contrast enhancement and other properties, which could be beneficial for multiple biomedical applications, especially imaging-guided treatments. In this article, we review recent developments in new colloids with applications that use ultrasound contrast enhancement. This work also highlights the emergence of colloidal materials fabricated from or modified with biologically derived and bio-inspired materials, particularly in the form of biopolymers and biomembranes. Challenges, limitations, potential developments and future directions of these next-generation colloidal systems are also presented and discussed.

Gas-stabilizing nanoparticles for ultrasound imaging and therapy of cancer

The use of ultrasound in the clinic has been long established for cancer detection and image-guided tissue biopsies. In addition, ultrasound-based methods have been widely explored to develop more effective cancer therapies such as localized drug delivery, sonodynamic therapy, and focused ultrasound surgery. Stabilized fluorocarbon microbubbles have been in use as contrast agents for ultrasound imaging in the clinic for several decades. It is also known that microbubble cavitation could generate thermal, mechanical, and chemical effects in the tissue to improve ultrasound-based therapies. However, the large size, poor stability, and short-term cavitation activity of microbubbles limit their applications in cancer imaging and therapy. This review will focus on an alternative type of ultrasound responsive material; gas-stabilizing nanoparticles, which can address the limitations of microbubbles with their nanoscale size, robustness, and high cavitation activity. This review will be of interest to researchers who wish to explore new agents to develop improved methods for molecular ultrasound imaging and therapy of cancer.

Enhancing Cancer Immunotherapeutic Efficacy with Sonotheranostic Strategies

Immunotherapy has revolutionized the modality for establishing a firm immune response and immunological memory. However, intrinsic limitations of conventional low responsive poor T cell infiltration and immune related adverse effects urge the coupling of cancer nanomedicines with immunotherapy for boosting antitumor response under ultrasound (US) sensitization to mimic dose-limiting toxicities for safe and effective therapy against advanced cancer. US is composed of high-frequency sound waves that mediate targeted spatiotemporal control over release and internalization of the drug. The unconventional US triggered immunogenic nanoengineered arena assists the limited immunogenic dose, limiting toxicities and efficacies. In this Review, we discuss current prospects of enhanced immunotherapy using nanomedicine under US. We highlight how nanotechnology designs and incorporates nanomedicines for the reprogramming of systematic immunity in the tumor microenvironment. We also emphasize the mechanical and biological potential of US, encompassing sonosensitizer activation for enhanced immunotherapeutic efficacies. Finally, the smartly converging combinational platform of US stimulated cancer nanomedicines for amending immunotherapy is summarized. This Review will widen scientists' ability to explore and understand the limiting factors for combating cancer in a precisely customized way.

Optical Monitoring of the Biodegradation of Porous and Solid Silicon Nanoparticles

Silicon nanoparticles (SiNP) are currently of great interest, especially in biomedicine, because of their unique physicochemical properties combined with biodegradability. SiNPs can be obtained in various ways and can have either a non-porous solid (sol-) or porous (por-) structure. In this work, we carry out detailed optical monitoring of sol- and por-SiNP biodegradation using Raman and photoluminescence (PL) micro-spectroscopy. SiNPs were obtained by ultrasound grinding of sol- or por-silicon nanowires, created by silver-assisted chemical etching of crystalline Si with different doping levels. In this case, sol-SiNPs consist of nanocrystals 30 nm in size, while por-SiNPs consist of small 3 nm nanocrystals and 16 nm pores. Both SiNPs show low in vitro cytotoxicity towards MCF-7 and HEK293T cells up to 800 μg/mL. The appearance of the F-band (blue–yellow) PL, as well as a decrease in the intensity of the Raman signal, indicate the gradual dissolution of the sol-SiNPs during 20 days of incubation. At the same time, the rapid dissolution of por-SiNP within 24 h is identified by the quenching of their S-band (red) PL and the disappearance of the Raman signal. The obtained results are important for development of intelligent biodegradable drug delivery systems based on SiNPs.

Stimuli-responsive nanobubbles for biomedical applications

Stimuli-responsive nanobubbles have received increased attention for their application in spatial and temporal resolution of diagnostic techniques and therapies, particularly in multiple imaging methods, and they thus have significant potential for applications in the field of biomedicine. This review presents an overview of the recent advances in the development of stimuli-responsive nanobubbles and their novel applications. Properties of both internal- and external-stimuli responsive nanobubbles are highlighted and discussed considering the potential features required for biomedical applications. Furthermore, the methods used for synthesis and characterization of nanobubbles are outlined. Finally, novel biomedical applications are proposed alongside the advantages and shortcomings inherent to stimuli-responsive nanobubbles.

Macrophage-Laden Gold Nanoflowers Embedded with Ultrasmall Iron Oxide Nanoparticles for Enhanced Dual-Mode CT/MR Imaging of Tumors

The design of multimodal imaging nanoplatforms with improved tumor accumulation represents a major trend in the current development of precision nanomedicine. To this end, we report herein the preparation of macrophage (MA)-laden gold nanoflowers (NFs) embedded with ultrasmall iron oxide nanoparticles (USIO NPs) for enhanced dual-mode computed tomography (CT) and magnetic resonance (MR) imaging of tumors. In this work, generation 5 poly(amidoamine) (G5 PAMAM) dendrimer-stabilized gold (Au) NPs were conjugated with sodium citrate-stabilized USIO NPs to form hybrid seed particles for the subsequent growth of Au nanoflowers (NFs). Afterwards, the remaining terminal amines of dendrimers were acetylated to form the dendrimer-stabilized Fe₃O₄/Au NFs (for short, Fe₃O₄/Au DSNFs). The acquired Fe₃O₄/Au DSNFs possess an average size around 90 nm, display a high r₁ relaxivity (1.22 mM^-1 s^-1), and exhibit good colloidal stability and cytocompatibility. The created hybrid DSNFs can be loaded within MAs without producing any toxicity to the cells. Through the mediation of MAs with a tumor homing and immune evasion property, the Fe₃O₄/Au DSNFs can be delivered to tumors more efficiently than those without MAs after intravenous injection, thus significantly improving the MR/CT imaging performance of tumors. The developed MA-mediated delivery system may hold great promise for enhanced tumor delivery of other contrast agents or nanomedicines for precision cancer nanomedicine applications.

Surface Wettability of Nanoparticle Modulated Sonothrombolysis

Sonodynamic therapy (SDT) is a non-invasive and highly penetrating treatment strategy under ultrasound irradiation. However, uncertainty in the mechanism of SDT has seriously hindered its future clinical application. Here, the mechanism of SDT enhanced by the wettability of nanoparticles is investigated. Nanoparticles can adsorb and stabilize nanobubbles in liquid, thus enhancing SDT efficiency. The stability of the nanobubbles is positively correlated with the desorption energy of the nanoparticles, which is determined by the wettability of the nanoparticles. This conclusion is verified for mesoporous silica and polystyrene nanoparticles and it is found that nanoparticles with a water contact angle of about 90° possess the largest desorption energy. To further apply this conclusion, thrombus models are constructed on rats and the experimental results demonstrate that nanoparticles with the largest desorption energy have the highest thrombolytic efficiency. It is believed that these findings will help to better understand the SDT mechanism and guide new strategies for rational design of nanoparticles adopted in SDT.

Bifunctional Therapeutic Application of Low-Frequency Ultrasound Associated with Zinc Phthalocyanine-Loaded Micelles

Purpose

Sonodynamic therapy (SDT) is a new therapeutic modality for the noninvasive cancer treatment based on the association of ultrasound and sonosensitizer drugs. Topical SDT requires the development of delivery systems to properly transport the sonosensitizer, such as zinc phthalocyanine (ZnPc), to the skin. In addition, the delivery system itself can participate in sonodynamic events and influence the therapeutic response. This study aimed to develop ZnPc-loaded micelle to evaluate its potential as a topical delivery system and as a cavitational agent for low-frequency ultrasound (LFU) application with the dual purpose of promoting ZnPc skin penetration and generating reactive oxygen species (ROS) for SDT.

Methods

ZnPc-loaded micelles were developed by the thin-film hydration method and optimized using the Quality by Design approach. Micelles’ influence on LFU-induced cavitation activity was measured by potassium iodide dosimeter and aluminum foil pits experiments. In vitro skin penetration of ZnPc was assessed after pretreatment of the skin with LFU and simultaneous LFU treatment using ZnPc-loaded micelles as coupling media followed by 6 h of passive permeation of ZnPc-loaded micelles. The singlet oxygen generation by LFU irradiation of the micelles was evaluated using two different hydrophilic probes. The lipid peroxidation of the skin was estimated using the malondialdehyde assay after skin treatment with simultaneous LFU using ZnPc-loaded micelles. The viability of the B16F10 melanoma cell line was evaluated using resazurin after treatment with different concentrations of ZnPc-loaded micelles irradiated or not with LFU.

Results

The micelles increased the solubility of ZnPc and augmented the LFU-induced cavitation activity in two times compared to water. After 6 h ZnPc-loaded micelles skin permeation, simultaneous LFU treatment increased the amount of ZnPc in the dermis by more than 40 times, when compared to non-LFU-mediated treatment, and by almost 5 times, when compared to LFU pretreatment protocol. The LFU irradiation of micelles induced the generation of singlet oxygen, and the lipoperoxidation of the skin treated with the simultaneous LFU was enhanced in three times in comparison to the non-LFU-treated skin. A significant reduction in cell viability following treatment with ZnPc-loaded micelles and LFU was observed compared to blank micelles and non-LFU-treated control groups.

Conclusion

LFU-irradiated mice can be a potential approach to skin cancer treatment by combining the functions of increasing drug penetration and ROS generation required for SDT.

Gas-Stabilizing Sub-100 nm Mesoporous Silica Nanoparticles for Ultrasound Theranostics

Recent studies have demonstrated that gas-stabilizing particles can generate cavitating micron-sized bubbles when exposed to ultrasound, offering excellent application potential, including ultrasound imaging, drug delivery, and tumor ablation. However, the majority of the reported gas-stabilizing particles are relatively large (>200 nm), and smaller particles require high acoustic pressures to promote cavitation. Here, this paper reports the preparation of sub-100 nm gas-stabilizing nanoparticles (GSNs) that can initiate cavitation at low acoustic intensities, which can be delivered using a conventional medical ultrasound imaging system. The highly echogenic GSNs (F127-hMSN) were prepared by carefully engineering the surfaces of ∼50 nm mesoporous silica nanoparticles. It was demonstrated that the F127-hMSNs could be continuously imaged with ultrasound in buffer or biological solutions or agarose phantoms for up to 20 min. Also, the F127-hMSN can be stored in phosphate-buffered saline for at least a month with no loss in ultrasound responsiveness. The particles significantly degraded when diluted in simulated body fluids, indicating possible biodegradation of the F127-hMSNs in vivo. Furthermore, at ultrasound imaging conditions, F127-hMSNs did not cause detectable cell death, supporting the potential safety of these particles. Finally, strong cavitation activity generation by the F127-hMSNs under high-intensity focused ultrasound insonation was demonstrated and applied to effectively ablate cancer cells.

Black Mesoporous Silicon as a Contrast Agent for LED-Based 3D Photoacoustic Tomography

Mesoporous silicon (PSi) nanoparticles have been widely studied in different biomedical imaging modalities due to their several beneficial material properties. However, they have not been found to be suitable for photoacoustic imaging due to their poor photothermal conversion performance. In the present study, biodegradable black mesoporous silicon (BPSi) nanoparticles with strong light absorbance were developed as superior image contrast agents for photoacoustic tomography (PAT), which was realized with a light-emitting diode (LED) instead of the commonly used laser. LED-based PAT offers the advantages of low cost, compactness, good mobility, and easy operation as compared to the traditional laser-based PAT modality. Nevertheless, the poor imaging sensitivity of the LED-PAT systems has been the main barrier to prevent their wide biomedical application because the LED light has low optical energy. The present study demonstrated that the imaging sensitivity of the LED-PAT system was significantly enhanced with the PEGylated BPSi (PEG-BPSi) nanoparticles. The PEG-BPSi nanoparticles were clearly detectable with a low concentration of 0.05 mg/mL in vitro and with an LED radiation energy of 5.2 μJ. The required concentration of the PEG-BPSi nanoparticles was 10 times lesser than that of the reference gold nanoparticles to reach the corresponding level of the imaging contrast. The ex vivo studies demonstrated that the submillimeter BPSi nanoparticle-based absorbers were distinguishable in chicken breast tissues. The strong contrast provided by the BPSi particles indicated that these particles can be utilized as novel contrast agents in PAT, especially in LED-based systems with low light intensity.

Biomedical Applications for Gas-Stabilizing Solid Cavitation Agents

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

Cavitation Induced by Janus-Like Mesoporous Silicon Nanoparticles Enhances Ultrasound Hyperthermia

The presence of nanoparticles lowers the levels of ultrasound (US) intensity needed to achieve the therapeutic effect and improves the contrast between healthy and pathological tissues. Here, we evaluate the role of two main mechanisms that contribute to the US-induced heating of aqueous suspensions of biodegradable nanoparticles (NPs) of mesoporous silicon prepared by electrochemical etching of heavily boron-doped crystalline silicon wafers in a hydrofluoric acid solution. The first mechanism is associated with an increase of the attenuation of US in the presence of NPs due to additional scattering and viscous dissipation, which was numerically simulated and compared to the experimental data. The second mechanism is caused by acoustic cavitation leading to intense bubble collapse and energy release in the vicinity of NPs. This effect is found to be pronounced for as-called Janus NPs produced via a nano-stopper technique, which allow us to prepare mesoporous NPs with hydrophobic inner pore walls and hydrophilic external surface. Such Janus-like NPs trap air inside the pores when dispersed in water. The precise measurement of the heating dynamics in situ enabled us to detect the excessive heat production by Janus-like NPs over their completely hydrophilic counterparts. The excessive heat is attributed to the high intensity cavitation in the suspension of Janus-like NPs. The present work elicits the potential of specifically designed Janus-like mesoporous silicon NPs in the field of nanotheranostics based on ultrasound radiation.

Efficient exosome delivery in refractory tissues assisted by ultrasound-targeted microbubble destruction

Recently, exosomes have been emerged as promising drug delivery carriers, while certain tissues are intrinsically resistant to exosomes. Therapeutically improving the drug delivery efficiency in these tissues/organs would certainly broaden the potential application of exosomes in future. Ultrasound-targeted microbubble destruction (UTMD) is a promising technique for non-invasive, targeted drug delivery. In this study, we explore the possibility that UTMD assists exosome delivery in these intrinsically resistant tissues. Mice were subjected to tail vein injection of DiR-labeled exosomes together with/without UTMD of SonoVue^TM, followed by in vivo and ex vivo tracking of the exosomes. As expected, heart, adipose tissue, and skeletal muscle were found reluctant to exosomes from different origins. Targeted destruction of the ultrasound microbubbles (SonoVue^TM) in the heart and adipose tissue region significantly increased the exosome infiltration and endocytosis there, as revealed by fluorescence imaging and confocal laser scanning microscope (CLSM). UTMD treatment 1 h prior to exosome injection failed to facilitate the exosome endocytosis in the targeted region, indicating that the transient promoting effects of UTMD. Moreover, increases of UTMD (numerous pulses) did not linearly enhance the exosome delivery. Together, our study here has established a novel strategy for targeted delivery of exosomes in the reluctant tissues, by combining the advantages of ultrasound microbubbles and exosomes in drug delivery.

One-Step Nanosurface Self-Assembly of d-Peptides Renders Bubble-Free Ultrasound Theranostics

The surface bioinspired modification of particles and films is a mainstream direction in biomaterial design and application. The interfacial coating of extracellular-matrix-like hydrogel can endow functional inorganic nanoparticles high circulation stability and biocompatibility but remains challenging due to large surface tension difference between organic gelators and solid nanosurfaces. Herein, the supramolecular hydrogel of NapG_dF_dF_dK around gold nanorods (Au NRs-Gel) has been constructed by the amidation-grafting modification and the protonation-induced interface-assistant assembly of peptide precursors. As a proof of concept study, the acoustic cavitation experiments and in vitro ultrasound imaging have proved that the abundant hydrophobic microdomains as well as the water-rich network in the supramolecular hydrogel can serve as valid sites to efficiently generate and stabilize nanobubbles as cavitation seeds to realize bubble-free ultrasound imaging. In vivo augmented ultrasound imaging and imaging-guided high intensity focused ultrasound (HIFU) therapy based on the Balb/c mice bearing HeLa tumor model have been conducted. As the first example of using nanosurface hydrogelation to endow nanoparticles with bubble-free ultrasound theranostic ability, this work offers a simple approach to design multifunctional nanovehicles for ultrasound-guided drug/protein/gene delivery.

Stem cell-mediated delivery of nanogels loaded with ultrasmall iron oxide nanoparticles for enhanced tumor MR imaging

The development of new nanoplatforms with enhanced tumor accumulation for accurate diagnosis still remains a great challenge in current precision nanomedicine. Herein, we report the design of stem cell-mediated delivery of nanogels (NGs) loaded with ultrasmall iron oxide (Fe3O4) nanoparticles (NPs) for enhanced magnetic resonance (MR) imaging of tumors. In this study, sodium citrate-stabilized ultrasmall Fe3O4 NPs with a size of 3.16 ± 1.30 nm were first synthesized using a solvothermal route, coated with polyethyleneimine (PEI), and used as crosslinkers to crosslink alginate (AG) NGs formed via a double emulsion approach, where the AG carboxyl groups were pre-activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The thus prepared Fe3O4 NP-loaded NGs (AG/PEI-Fe3O4 NGs) with a size of 47.68 ± 3.41 nm are water-dispersible, colloidally stable, cytocompatible in a given concentration range, display a relatively high r1 relaxivity (r1 = 1.5 mM-1 s-1), and are able to be taken up by bone mesenchymal stem cells without compromising cell viability and stem cell characteristics. Due to the tumor-chemotaxis or tumor tropism, the BMSCs are able to mediate the enhanced delivery of AG/PEI-Fe3O4 NGs to the tumor site after intravenous injection, thus enabling significantly strengthened MR imaging of tumors when compared to free NGs. These findings suggest that the developed AG/PEI-Fe3O4NGs, once mediated by stem cells may serve as a novel, safe, effective and targeted platform for enhanced MR imaging of tumors.