Effect of a Radiotherapeutic Megavoltage Beam on Ultrasound Contrast Agents.

Collateral damage to healthy surrounding tissue during conventional radiotherapy increases when deviations from the treatment plan occur. Ultrasound contrast agents (UCAs) are a possible candidate for radiation dose monitoring. This study investigated the size distribution and acoustic response of two commercial formulations, SonoVue/Lumason and Definity/Luminity, as a function of dose on clinical megavoltage photon beam exposure (24 Gy). SonoVue samples exhibited a decrease in concentration of bubbles smaller than 7 µm, together with an increase in acoustic attenuation and a decrease in acoustic scattering. Definity samples did not exhibit a significant response to radiation, suggesting that the effect of megavoltage photons depends on the UCA formulation. For SonoVue, the influence of the megavoltage photon beam was especially apparent at the second harmonic frequency, and can be captured using pulse inversion and amplitude modulation (3.5-dB decrease for the maximum dose), which could eventually be used for dosimetry in a well-controlled environment.

Delicately Designed Cancer Cell Membrane-Camouflaged Nanoparticles for Targeted 19F MR/PA/FL Imaging-Guided Photothermal Therapy.

Our exploration of multimodal nanoprobes aims to combine photoacoustic (PA) imaging, 19F magnetic resonance (MR), and fluorescence (FL) imaging, which offers complementary advantages such as high spatial resolution, unlimited penetration, and high sensitivity to enable more refined images for accurate tumor diagnoses. In this research, perfluorocarbons (PFCs) and indocyanine green (ICG) are encapsulated by poly(lactic-co-glycolic acid) (PLGA) for intravital 19F MR/FL/PA tri-modal imaging-guided photothermal therapy. Then, it is coated with an A549 cancer cell membrane (AM) to fabricate versatile theranostic nanoprobes (AM-PP@ICGNPs). After systemic administration, FLI reveals time-dependent tumor homing of NPs with high sensitivity, 19F MRI provides tumor localization of NPs without background signal interference, and PAI illustrates the detailed distribution of NPs inside the tumor with high spatial resolution. What is more, AM-PP@ICGNPs accumulated in the tumor area exhibit a prominent photothermal effect (48.4 °C) under near infrared (NIR) laser irradiation and realize an enhanced antitumor response in vivo. These benefits, in combination with the excellent biocompatibility, make AM-PP@ICGNPs a potential theranostic nanoagent for accurate tumor localization and ultimately achieve superior cancer therapy.

Microwave-assisted cleavage of cysteine perfluoroaryl thioethers.

The cysteine- perfluoroarene SNAr reaction allows for the sequence-specific attachment of dyes and affinity tags to peptides and proteins. However, while many methods exist for the desulfuration of native and functionalized cysteine residues, there are no reports of their application to perfluoroarylated cysteines. Herein we report both the hydrogenolysis of a perfluoroarylated cysteine to alanine and elimination to dehydroalanine, reactions that are both accelerated by microwave irradiation.

Evaluation of the Theranostic Potential of Perfluorohexane-Based Acoustic Nanodroplets.

In this study, we have prepared perfluorohexane (PFH)-based acoustic nanodroplets (PFH-NDs) and evaluated their theranostic characteristics. Nile Red (NR) was incorporated into PFH-NDs as a model of hydrophobic drugs (NR-PFH-NDs). The mean particle diameters of PFH-NDs and NR-PFH-NDs were 205 ± 1.8 nm and 346.3 ± 6 nm, respectively. There was no significant PFH leakage from PFH-NDs during 90 min incubation at 37°C in the presence of 10% rat serum. The in vitro ultrasonography showed that the phase transition of PFH-NDs from liquid droplets to gassed bubbles could be induced by therapeutic low-intensity ultrasound with a frequency of 1 MHz and an intensity of 5 W/cm2. Irradiation of ultrasound in combination with NR-PFH-NDs enhanced uptake of NR in murine adenocarcinoma cells (C26). After intravenous injection of PFH-NDs to mice, PFH gradually disappeared from blood circulation with an elimination half-life of 43.3 min. Intravenous injection of PFH-NDs also resulted in significant contrast enhancement in the mouse carotid artery upon therapeutic low-intensity ultrasound irradiation. These results suggest the potential of PFH-NDs as a novel contrast agent for further theranostic applications.

Bio-inspired photonic crystals for naked eye quantification of nucleic acids.

Herein, a chip imitating the desert beetle shell was presented for naked eye nucleic acid quantification. The hydrophobic photonic crystal substrate treated by ultraviolet local irradiation could effectively disperse the sample into hundreds of droplets for digital loop-mediated isothermal amplification (dLAMP). Pyrophosphate (PPI), a by-product of the LAMP reaction, combined with magnesium ions to form a poorly soluble precipitate. It could be fixed on a silica substrate due to complexation, resulting in the disappearance of the structural color of the photonic crystals. The number of points without structural color contains the information of the copy number of nucleic acids in the sample. This chip could achieve the naked eye quantitative detection of Salmonella DNA without fluorescence or other chromogenic reagents. Thus, the chip designed in this study can help the development of digital nucleic acid detection under limited resource settings (LRS) and can be suitable for POCT (point of care test) standards.

Selective intracellular delivery of perfluorocarbon nanodroplets for cytotoxicity threshold reduction on ultrasound-induced vaporization.

BACKGROUND: Phase-change nanodroplets (PCNDs), which are liquid perfluorocarbon nanoparticles, have garnered much attention as ultrasound-responsive nanomedicines. The vaporization phenomenon has been employed to treat tumors mechanically. However, the ultrasound pressure applied to induce vaporization must be low to avoid damage to nontarget tissues. AIMS: Here, we report that the pressure threshold for vaporization to induce cytotoxicity can be significantly reduced by selective intracellular delivery of PCNDs into targeted tumors. METHODS AND RESULTS: In vitro experiments revealed that selective intracellular delivery of PCNDs induced PCND aggregation specifically inside the targeted cells. This close-packed configuration decreased the pressure threshold for vaporization to induce cytotoxicity. Moreover, following ultrasound exposure, significant decrease was observed in the viability of cells that incorporated PCNDs (35%) but not in the viability of cells that did not incorporate PCNDs (88%). CONCLUSIONS: Intracellular delivery of PCNDs reduced ultrasound pressure applied for vaporization to induce cytotoxicity. Confocal laser scanning microscopy and flow cytometry revealed that prolonged PCND-cell incubation increased PCND uptake and aggregation. This aggregation effect might have contributed to the cytotoxicity threshold reduction effect.

Study of hybrid membrane filtration and photocatalysis for removal of perfluorooctanoic acid (PFOA) in groundwater.

Groundwater contamination in Thailand from leaking of leachate due to improper solid waste disposal can cause contamination by PFOA (one of the perfluorinated compounds). This study proposed a new idea for the removal of PFOA from groundwater using a combination of membrane filtration and photocatalysis. Spiked groundwater samples were treated by nanofiltration and the rejected part was sent to a UV contact tank for photocatalysis. All samples were analyzed by high-performance liquid chromatography-tandem mass spectrometer (HPLC-MS/MS). The results showed that the removal efficiency of nanofiltration was 99.62%, and the rejected part was degraded by photocatalysis at an efficiency of 59.64%. Thus, the contaminants released to the environment were only 34.23%, which is around three times lower than nanofiltration alone. The results of this technical feasibility study proved that hybrid membrane filtration and photocatalysis are able to remove and degrade the contaminants in the rejected part significantly before being released to the environment, which has been the biggest gap in the processing of membrane filtration, and should be studied further in other aspects, such as fouling effects, energy consumption, and operating costs in a long-term pilot run.

Effects of pH and coexisting chemicals on photolysis of perfluorooctane sulfonate using an excited xenon dimer lamp.

Vacuum ultraviolet (VUV) photolysis at the wavelength of 172 nm in a sulfate solution was introduced as a more efficient process for perfluorooctane sulfonate (PFOS) degradation than ultraviolet (UV) photolysis at 254 nm. The effects of pH and coexisting chemicals on VUV photolysis under the coexistence of 100 mM sulfate were investigated. VUV irradiation successfully degraded PFOS, and the degradation rate was 5.5 times higher than by UV photolysis. Direct VUV photolysis was inferred to mainly contribute to PFOS degradation. PFOS degradation by VUV irradiation was enhanced at pH less than 2 due to sulfate radicals generated via VUV photolysis of sulfate ions. Consequently, VUV photolysis was superior to UV photolysis for PFOS removal on both the removal rate and energy efficiency. However, the inorganic chemicals phosphoric acid and nitric acid strongly inhibited PFOS degradation, probably by masking PFOS from VUV rays by their VUV absorption. Accordingly, PFOS separation from inorganic materials such as phosphate and nitrate will be recommended for the application of VUV techniques for PFOS removal. In this research, organic solvent abstraction was inferred to be one of candidates for PFOS separation.

Noninvasive, targeted gene therapy for acute spinal cord injury using LIFU-mediated BDNF-loaded cationic nanobubble destruction.

Various gene delivery systems have been widely studied for the acute spinal cord injury (SCI) treatment. In the present study, a novel type of brain-derived neurotrophic factor (BDNF)-loaded cationic nanobubbles (CNBs) conjugated with MAP-2 antibody (mAbMAP-2/BDNF/CNBs) was prepared to provide low-intensity focused ultrasound (LIFU)-targeted gene therapy. In vitro experiments, the ultrasound-targeted tranfection to BDNF overexpressioin in neurons and efficiently inhibition neuronal apoptosis have been demonstrated, and the elaborately designed mAbMAP-2/BDNF/CNBs can specifically target to the neurons. Furthermore, in a acute SCI rat model, LIFU-mediated mAbMAP-2/BDNF/CNBs transfection significantly increased BDNF expression, attenuated histological injury, decreased neurons loss, inhibited neuronal apoptosis in injured spinal cords, and increased BBB scores in SCI rats. LIFU-mediated mAbMAP-2/BDNF/CNBs destruction significantly increase transfection efficiency of BDNF gene both in vitro and in vivo, and has a significant neuroprotective effect on the injured spinal cord. Therefore, the combination of LIFU irradiation and gene therapy through mAbMAP-2/BDNF/CNBs can be considered as a novel non-invasive and targeted treatment for gene therapy of SCI.

Impact of humic acid on the photoreductive degradation of perfluorooctane sulfonate (PFOS) by UV/Iodide process.

Iodide photolysis under UV illumination affords an effective method to produce hydrated electrons (eaq-) in aqueous solution. Therefore, UV/Iodide photolysis can be utilized for the reductive degradation of many recalcitrant pollutants. However, the effect of naturally occurring organic matter (NOM) such as humic and fulvic acids (HA/FA), which may impact the efficiency of UV/Iodide photoreduction, is poorly understood. In this study, the UV photoreductive degradation of perfluorooctane sulfonate (PFOS) in the presence of I- and HA is studied. PFOS undergoes a relatively slow direct photoreduction in pure water, a moderate level of degradation via UV/Iodide, but a rapid degradation via UV/Iodide/HA photolysis. After 1.5 h of photolysis, 86.0% of the initial [PFOS] was degraded in the presence of both I- and HA with a corresponding defluorination ratio of 55.6%, whereas only 51.7% of PFOS was degraded with a defluorination ratio of 4.4% via UV/Iodide illumination in the absence of HA. The relative enhancement in the presence of HA in the photodegradation of PFOS can be attributed to several factors: a) HA enhances the effective generation of eaq- due to the reduction of I2, HOI, IO3- and I3- back to I-; b) certain functional groups of HA (i.e., quinones) enhance the electron transfer efficiency as electron shuttles; c) a weakly-bonded association of I- and PFOS with HA increases the reaction probability; and d) absorption of UV photons by HA itself produces eaq-. The degradation and defluorination efficiency of PFOS by UV/Iodide/HA process is dependent on pH and HA concentration. As pH increases from 7.0 to 10.0, the enhancement effect of HA improves significantly. The optimal HA concentration for the degradation of 0.03 mM PFOS is 1.0 mg L-1.

Nitrogen dioxide radicals mediated mineralization of perfluorooctanoic acid in aqueous nitrate solution with UV irradiation.

Effective decomposition of perfluorooctanoic acid (PFOA) has received increasing attention in recent years because of its global occurrence and resistance to most conventional treatment processes. In this study, the complete mineralization of PFOA was achieved by the UV-photolysis of nitrate aqueous solution (UV/Nitrate), where the in-situ generated nitrogen dioxide radicals (NO2) efficiently mediated the degradation of PFOA. In particular, when the twinborn hydroxyl radicals were scavenged, the production of more NO2 radicals realized the complete mineralization of PFOA. DFT calculations further confirm the feasibility of PFOA removal with NO2. Near-stoichiometric equivalents of fluoride released rather than the related intermediates were detected in solution after decomposition of PEOA, further demonstrating the complete degradation of PFOA. Possible PFOA degradation pathways were proposed on the basis of experimental results. This work offers an efficient strategy for the complete mineralization of perfluorinated chemicals, and also sheds light on the indispensable roles of nitrogen dioxide radicals for environmental pollutants removal.

Removal of PFOA in groundwater by Fe0 and MnO2 nanoparticles under visible light.

The main objective of this study was to find a cost-effective, efficient and environmentally-friendly solution to remove perfluorooctanic acid (PFOA) from groundwater by using Fe0 and MnO2 nanoparticles. The selected method was expected to be applicable to the remediation of PFOA-contaminated groundwater. Phytotoxicity of the nanoparticle treatment was studied to demonstrate the safe application of the nanomaterials. Zero-valent Fe (100 mg L-1) and MnO2 (100 mg L-1) nanoparticles, produced in our lab, were used to remove PFOA up to 10 mg L-1. The test was conducted under visible light with or without addition of 0.88 mol L-1 H2O2 in a pH range of 0.5-11.0 for a duration of 18 h. Using Fe nanoparticles, a higher percentage of PFOA was removed under extreme acidic environment of pH 0.5 than under the basic environment of pH 11.0, and a minimum removal rate was reached under the neutral environment. The Fe nanoparticles were more efficient than the MnO2 nanoparticles at pH 0.5 with a removal rate of 69.7% and 89.7% without and with H2O2 addition, respectively. Phytotoxicity study showed that the treatment by Fe nanoparticles under mild pH reduced the phytotoxicity of groundwater-associated PFOA to Arabidopsis thaliana. The Fe nanoparticles did not show negative effect to A. thaliana under the experimental conditions used in this study.

Acoustic Behavior of a Reactivated, Commercially Available Ultrasound Contrast Agent.

BACKGROUND: Commercially available microbubbles such as Definity contain octafluoropropane encapsulated in a lipid shell. This perfluorocarbon can be compressed into liquid nanodroplets at room temperatures and activated with transthoracic diagnostic ultrasound. The aim of this study was to determine the size range and acoustic characteristics of Definity nanodroplets (DNDs) compared with Definity microbubbles (DMBs). METHODS: An in vitro flow system was used with a diagnostic ultrasound transducer (S5-1, iE33). DMBs were prepared using package insert instructions. DNDs were prepared by cooling DMBs in a -10°C to -15°C isopropyl alcohol bath before hand-pressurizing the solution. The formed DNDs were sized, diluted to 1% solutions, and infused continuously into a phosphate-buffered saline solution running within Silastic tubing. Acoustic intensity (AI) was compared with equivalent dilutions of DMBs at different mechanical indices (MIs) ranging from 0.2 to 1.4 (n = 6 comparisons at each MI) using real-time 56-Hz and triggered 2-Hz frame rates (FRs). A 3-cm-thick tissue-mimicking phantom was used to simulate transthoracic attenuation. In vivo transthoracic studies were performed in four normal pigs infused with 10% intravenous infusions of DMBs or DNDs at real-time and triggered end-systolic FRs to compare differences in myocardial and left ventricular cavity AI. RESULTS: DNDs were smaller than DMBs and ranged in size from 50 to 1,000 nm. In vitro studies revealed that at an MI of 0.2 and an FR of 56 Hz, DMBs had high AI (37 ± 2 dB), but AI dropped to 25 ± 2 dB at an MI of 1.0 (P < .001, analysis of variance). In comparison, DNDs had virtually no AI at MIs of 0.2 to 0.6 at both triggered and 56-Hz FRs (1 ± 0 dB), but AI increased to 34 ± 2 dB at an MI of 1.4 using an FR of 56 Hz (P < .001 vs MI of 0.2). AI also persisted longer at 56 Hz with DNDs when using higher MIs. In vivo studies demonstrated higher myocardial AI for DNDs at higher MIs when using real-time FR, most likely from microvascular nanodroplet activation. CONCLUSION: These data indicate significant differences in acoustic responses of the commercially available DMBs when administered as an equivalent number of DNDs. The DND formulation may render them more useful for high-MI real-time imaging and other targeted transthoracic diagnostic applications.

Noninvasive Ablation of Prostate Cancer Spheroids Using Acoustically-Activated Nanodroplets.

We have developed acoustically activated nanodroplets (NDs) using an amphiphilic triblock copolymer, which self-assembles and encapsulates different perfluorocarbons including perfluoropentane (PFP) and perfluorohexane (PFH). Applying histotripsy pulses (i.e., short, high pressure, ultrasound pulses) to solutions of PFP- and PFH-NDs generated bubble clouds at a significantly reduced acoustic pressure compared to the cavitation pressure observed for histotripsy treatment alone. In this report, we summarize the results of combining histotripsy at low frequency (345 and 500 kHz) with PFP-NDs and PFH-NDs on the ablation of PC-3 and C4-2B prostate cancer cells. Using custom built histotripsy transducers coupled to a microscope and a high speed recording camera, we imaged the generation of a cavitation bubble cloud in response to different ultrasound regimes in solution and in tissue-mimicking gel phantoms. We quantified the associated ablation of individual cancer cells and 3D spheroids suspended in solution and embedded in tissue phantoms to compare the ablative capacity of PFP-NDs and PFH-NDs. Results show that histotripsy pulses at high acoustic pressure (26.2 MPa) ablated 80% of prostate cancer spheroids embedded in tissue-mimicking gel phantoms. In comparison, combining histotripsy pulses at a dramatically lower acoustic pressure (12.8 MPa) with PFP-NDs and PFH-NDs caused an ablation of 40% and 80% of the tumor spheroid volumes, respectively. These results show the potential of acoustically activated NDs as an image-guided ablative therapy for solid tumors and highlight the higher ablative capacity of PFH-NDs, which correlates with the boiling point of the encapsulated PFH and the stability of the formed bubble cloud.

Microwave-activated nanodroplet vaporization for highly efficient tumor ablation with real-time monitoring performance.

The fast development of nanotechnology has provided a new efficient strategy for enhancing the therapeutic efficiency of various treatment modalities against cancer. However, the improvement of minimally invasive microwave therapy based on nanomaterials has not been realized. In this work, we successfully designed and synthesized a novel folate-targeted nanodroplet (TPN) with a composite mixture of perfluorocarbons as the core and lipid as the shell, which exerts the distinctive dual functions as the adjuvant for highly efficient percutaneous ultrasound imaging-guided microwave ablation (MWA) of tumors. Based on the unique phase-changeable performance of TPN nanosystem, a novel microwave-droplet vaporization (MWDV) strategy was proposed, for the first time, to overcome the critical issues of traditional acoustic-droplet vaporization (ADV) and optical-droplet vaporization (ODV) for cancer theranostics. Especially, the elaborately designed TPN can overcome the challenges of indistinct imaging of ablation margin and the limited ablation zone of MWA modality against cancer. The high efficiency of this new MWDV strategy has been systematically elucidated in vitro, ex vivo and in vivo. Therefore, such a successful demonstration of the role of nanomaterials (TPN in this case) in ultrasound imaging-guided MWA therapy against cancer provides a highly feasible strategy to effectively enhance the MWA outcome with the specific features of high efficiency and biosafety.

Acoustic Cavitation Enhances Focused Ultrasound Ablation with Phase-Shift Inorganic Perfluorohexane Nanoemulsions: An In Vitro Study Using a Clinical Device.

Purpose. To investigate whether acoustic cavitation could increase the evaporation of a phase-shift inorganic perfluorohexane (PFH) nanoemulsion and enhance high intensity focused ultrasound (HIFU) ablation. Materials and Methods. PFH was encapsulated by mesoporous silica nanocapsule (MSNC) to form a nanometer-sized droplet (MSNC-PFH). It was added to a tissue-mimicking phantom, whereas phosphate buffered saline (PBS) was added as a control (PBS-control). HIFU (P ac = 150 W, t = 5/10 s) exposures were performed in both phantoms with various duty cycles (DC). US images, temperature, and cavitation emissions were recorded during HIFU exposure. HIFU-induced lesions were measured and calculated. Results. Compared to PBS-control, MSNC-PFH nanoemulsion could significantly increase the volume of HIFU-induced lesion (P < 0.01). Peak temperatures were 78.16 ± 5.64°C at a DC of 100%, 70.17 ± 6.43°C at 10%, 53.17 ± 4.54°C at 5%, and 42.00 ± 5.55°C at 2%, respectively. Inertial cavitation was much stronger in the pulsed-HIFU than that in the continuous-wave HIFU exposure. Compared to 100%-DC exposure, the mean volume of lesion induced by 5 s exposure at 10%-DC was significantly larger, but smaller at 2%-DC. Conclusions. MSNC-PFH nanoemulsion can significantly enhance HIFU ablation. Appropriate pulsed-HIFU exposure could significantly increase the volume of lesion and reduce total US energy required for HIFU ablation.

Photochemical defluorination of aqueous perfluorooctanoic acid (PFOA) by Fe(0)/GAC micro-electrolysis and VUV-Fenton photolysis.

Perfluorooctanoic acid (PFOA) is extremely persistent and bioaccumulative in the environment; thus, it is very urgent to investigate an effective and moderate technology to treat the pollution of PFOA. In this study, a process combined iron and granular activated carbon (Fe(0)/GAC) micro-electrolysis with VUV-Fenton system is employed for the remediation of PFOA. Approximately 50 % PFOA (10 mg L(-1)) could be efficiently defluorinated under the following conditions: pH 3.0, dosage of Fe 7.5 g L(-1), dosage of GAC 12.5 g L(-1), and concentration of H2O2 22.8 mmol L(-1). Meanwhile, during the process, evident defluorination was observed and the concentration of fluoride ion was eventually 3.23 mg L(-1). The intermediates including five shorter-chain perfluorinated carboxylic acids (PFCAs), i.e., C7, C6, C5, C4, and C3, were also analyzed by high-performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS) and defluorination mechanisms of PFOA was proposed, which involved photochemical of OH·, direct photolysis (185-nm VUV), and photocatalytic degradation of PFOA in the presence of Fe(3+) (254-nm UV).

USMB-induced synergistic enhancement of aminoglycoside antibiotics in biofilms.

This study evaluated the effect of combining antibiotics with ultrasound and microbubbles (USMB) toward the eradication of biofilms. Pseudomonas aeruginosa PAO1 biofilms were treated with the antibiotics gentamicin sulfate or streptomycin sulfate, or a combination of USMB with the respective antibiotics. Biofilm structure was quantified using confocal laser scanning microscopy with COMSTAT analysis, while activity was measured as whole-biofilm CO2 production in a continuous-flow biofilm model. The combined antibiotic-USMB treatment significantly impacted biofilm biomass, thickness and surface roughness compared to antibiotics alone (p<0.05). USMB exposure caused the formation of craters (5-20µm in diameter) in the biofilms, and when combined with gentamicin, activity was significantly lower, compared to gentamicin, USMB or untreated controls, respectively. Interestingly, the CO2 production rate following combined streptomycin-USMB treatment was higher than after streptomycin alone, but significantly lower than USMB alone and untreated control. These results show strong evidence of a synergistic effect between antibiotics and USMB, although the varied response to different antibiotics emphasize the need to optimize the USMB exposure conditions to maximize this synergism and ultimately transfer this technology into clinical or industrial practice.

Interfacial Rheological Properties of Contrast Microbubble Targestar P as a Function of Ambient Pressure.

In this Technical Note, we determine the interfacial rheological parameters of the encapsulation of the contrast agent Targestar P using ultrasound attenuation. The characteristic parameters are obtained according to two interfacial rheological models. The properties-surface dilatational elasticity (0.09 ± 0.01 N/m) and surface dilatational viscosity (8 ± 0.1E-9 N·s/m)-are found to be of similar magnitude for both models. Contrast microbubbles experience different ambient pressure in different organs. We also measure these parameters as functions of ambient pressure using attenuation measured at different overpressures (0, 100 and 200 mm Hg). For each value of ambient hydrostatic pressure, we determine the rheological properties, accounting for changes in the size distribution caused by the pressure change. We discuss different models of size distribution change under overpressure: pure adiabatic compression or gas exchange with surrounding medium. The dilatational surface elasticity and viscosity are found to increase with increasing ambient pressure.

Effects of Droplet Composition on Nanodroplet-Mediated Histotripsy.

Nanodroplet-mediated histotripsy (NMH) is a targeted ablation technique combining histotripsy with nanodroplets that can be selectively delivered to tumor cells. In two previous studies, polymer-encapsulated perfluoropentane nanodroplets were used to generate well-defined ablation similar to that obtained with histotripsy, but at significantly lower pressure, when NMH therapy was applied at a pulse repetition frequency (PRF) of 10 Hz. However, cavitation was not maintained over multiple pulses when ultrasound was applied at a lower PRF (i.e., 1-5 Hz). We hypothesized that nanodroplets with a higher-boiling-point perfluorocarbon core would provide sustainable cavitation nuclei, allowing cavitation to be maintained over multiple pulses, even at low PRF, which is needed for efficient and complete tissue fractionation via histotripsy. To test this hypothesis, we investigated the effects of droplet composition on NMH therapy by applying histotripsy at various frequencies (345 kHz, 500 kHz, 1.5 MHz, 3 MHz) to tissue phantoms containing perfluoropentane (PFP, boiling point ∼29°C, surface tension ∼9.5 mN/m) and perfluorohexane (PFH, boiling point ∼56°C, surface tension ∼11.9 mN/m) nanodroplets. First, the effects of droplet composition on the NMH cavitation threshold were investigated, with results revealing a significant decrease (>10 MPa) in the peak negative pressure (p-) cavitation threshold for both types of nanodroplets compared with controls. A slight decrease (∼1-3 MPa) in threshold was observed for PFP phantoms compared with PFH phantoms. Next, the ability of nanodroplets to function as sustainable cavitation nuclei over multiple pulses was investigated, with results revealing that PFH nanodroplets were sustainable cavitation nuclei over 1,000 pulses, whereas PFP nanodroplets were destroyed during the first few pulses (<50 pulses), likely because of the lower boiling point. Finally, tissue phantoms containing a layer of embedded red blood cells were used to compare the damage generated for NMH treatments using PFP and PFH droplets, with results indicating that PFH nanodroplets significantly improved NMH ablation, allowing for well-defined lesions to be generated at all frequencies and PRFs tested. Overall, the results of this study provide significant insight into the role of droplet composition in NMH therapy and provide a rational basis to tailor droplet parameters to improve NMH tissue fractionation.