Perfluorohexane Nanodroplets Research Articles

Gold nanoparticle-coating reduces the acoustic pressure threshold for nanodroplet vaporization

Nanodroplets with a low-boiling-point perfluorocarbon (PFC) may vaporize spontaneously at physiological temperatures. Using a high-boiling-point PFC, e.g., perfluorohexane (PFH), can enable ultrasound-triggered vaporization for applications in imaging and drug delivery. However, PFH requires relatively high ultrasound (US) pressures for vaporization compared to low-boiling-point PFCs, making its use challenging. We investigated the feasibility of reducing the vaporization threshold by gold-coating lipid-encapsulated PFH nanodroplets (Au-PFH-NDs). We synthesized Au-PFH-NDs with 200 nm mean particle size and 5.12 × 10−4 pg mass of gold-coating per nanodroplet. B-mode images of the emulsion perfused in a flow phantom were used to determine the pressure threshold for ND vaporization upon exposure to 2 MHz focused US (f-number of 1.27, 0.5% duty cycle). The pressure threshold for Au-PFH-NDs (3.97 ± 0.63 MPa) was significantly lower (p < 0.05) than that of NDs without gold-coating (7.07 ± 0.02 MPa), indicating that gold-coating reduced the vaporization pressure threshold. In addition, the pressure threshold of the Au-PFH-NDs was not significantly different (p > 0.05) from that of perfluoropentane (PFP) NDs (4.16 ± 0.01 MPa). These results suggest that the Au-PFH-NDs can be vaporized at similar pressures as PFP NDs, but are more stable at physiological temperatures. These findings are the first step towards employing gold-coated PFC nanodroplets with a lower vaporization pressure threshold for multimodal imaging and drug delivery.

Ultrasound-Responsive Nanodroplet-Based Targeted Therapy via Conversion to Microbubbles.

Ultrasound-based therapy is appealing as it can be used via a wireless approach at remote parts of the body including the brain. Microbubbles are commonly used in such therapy due to their highly sound-responsive property. However, the larger size of microbubbles limits selective targeting in vitro/in vivo. Here, we report the design of nanodroplets of 70-130 nm in size that can be easily converted to microbubbles via ultrasound exposure. The advantage of this approach is that smaller nanodroplets can be used for cell/subcellular targeting, and next, they can be used for therapy by converting to microbubbles. More specifically, folate/dopamine-terminated perfluorohexane nanodroplets are designed that are loaded with a molecular drug. These nanodroplets are used for selective cell targeting, followed by ultrasound-induced microbubble conversion that is associated with drug release and intracellular reactive oxygen species generation. This approach has been used for selective cell therapy applications. The designed nanodroplet and approach can be used for the enhanced therapeutic performance of existing drugs.

Sonodynamic therapy of the breast cancer cells (4T1) using gold nanoclusters-loaded ultrasound-activated nanodroplets

Sonodynamic therapy (SDT) has been developed as a new approach to non-invasive cancer treatment. Nanoparticles (NPs) as sonosensitizers can enhance the efficiency of this method. In this study, bovine serum albumin-functionalized gold nanoclusters (BSA-AuNCs) were loaded in synthesized perfluorohexane nanodroplets (PFH NDs) stabilized by an alginate shell. The characterization results showed that AuNCs/PFH NDs had an appropriate size, good ζ-potential, and excellent stability for biological applications. Loading AuNCs as a sonosensitizer in ultrasound-activated NDs can enhance ultrasound therapy efficiency. The rough surface of AuNCs enhances the probability of cavitation by ultrasound waves which induces biological effects. Ultrasound (US) imaging confirmed this strategy. According to US images, the AuNCs-loaded and unloaded NDs showed good echogenicity. However, the presence of gold nanoclusters in NDs structure significantly increased their echogenicity. The in vitro studies were performed on 4T1 breast cancer and L929 normal cells. The MTT assay indicated that the high biocompatibility of NDs. The results of cellular internalization of NDs by 4T1 cells showed that ultrasound can facilitate cellular uptake of AuNCs/PFH NDs approximately 2.6-fold more than non-sonicated samples. The results of SDT investigation using MTT, colony, and apoptosis assays showed that the therapeutic effect of ultrasound on cancer cells was enhanced in the presence of AuNCs-loaded NDs. In conclusion, AuNCs/PFH NDs with excellent properties can be used as a theranostic agent for ultrasound-guided and -activated sonodynamic therapy.

Characterising the chemical and physical properties of phase-change nanodroplets

Phase-change nanodroplets have attracted increasing interest in recent years as ultrasound theranostic nanoparticles. They are smaller compared to microbubbles and they may distribute better in tissues (e.g. in tumours). They are composed of a stabilising shell and a perfluorocarbon core. Nanodroplets can vaporise into echogenic microbubbles forming cavitation nuclei when exposed to ultrasound. Their perfluorocarbon core phase-change is responsible for the acoustic droplet vaporisation. However, methods to quantify the perfluorocarbon core in nanodroplets are lacking. This is an important feature that can help explain nanodroplet phase change characteristics. In this study, we fabricated nanodroplets using lipids shell and perfluorocarbons. To assess the amount of perfluorocarbon in the core we used two methods, 19F NMR and FTIR. To assess the cavitation after vaporisation we used an ultrasound transducer (1.1 MHz) and a high-speed camera. The 19F NMR based method showed that the fluorine signal correlated accurately with the perfluorocarbon concentration. Using this correlation, we were able to quantify the perfluorocarbon core of nanodroplets. This method was used to assess the content of the perfluorocarbon of the nanodroplets in solutions over time. It was found that perfluoropentane nanodroplets lost their content faster and at higher ratio compared to perfluorohexane nanodroplets. The high-speed imaging indicates that the nanodroplets generate cavitation comparable to that from commercial contrast agent microbubbles. Nanodroplet characterisation should include perfluorocarbon concentration assessment as critical information for their development.

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

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

EGFR-Targeted Perfluorohexane Nanodroplets for Molecular Ultrasound Imaging.

Perfluorocarbon nanodroplets offer an alternative to gaseous microbubbles as contrast agents for ultrasound imaging. They can be acoustically activated to induce a liquid-to-gas phase transition and provide contrast in ultrasound images. In this study, we demonstrate a new strategy to synthesize antibody-conjugated perfluorohexane nanodroplet (PFHnD-Ab) ultrasound contrast agents that target cells overexpressing the epidermal growth factor receptor (EGFR). The perfluorohexane nanodroplets (PFHnD) containing a lipophilic DiD fluorescent dye were synthesized using a phospholipid shell. Antibodies were conjugated to the surface through a hydrazide-aldehyde reaction. Cellular binding was confirmed using fluorescence microscopy; the DiD fluorescence signal of the PFHnD-Ab was 5.63× and 6× greater than the fluorescence signal in the case of non-targeted PFHnDs and the EGFR blocking control, respectively. Cells were imaged in tissue-mimicking phantoms using a custom ultrasound imaging setup consisting of a high-intensity focused ultrasound transducer and linear array imaging transducer. Cells with conjugated PFHnD-Abs exhibited a significantly higher (p < 0.001) increase in ultrasound amplitude compared to cells with non-targeted PFHnDs and cells exposed to free antibody before the addition of PFHnD-Abs. The developed nanodroplets show potential to augment the use of ultrasound in molecular imaging cancer diagnostics.

Ultrasound responsive Gd-DOTA/doxorubicin-loaded nanodroplet as a theranostic agent for magnetic resonance image-guided controlled release drug delivery of melanoma cancer

Theranostic agents use simultaneous for diagnostic and therapeutic procedures. In the present study, the effect of Gd-DOTA/doxorubicin-loaded perfluorohexane nanodroplets as a theranostic nanoparticle for control released drug delivery and ultrasound/MR imaging was investigated on B16F10 melanoma cancer cells. The intracellular uptake was performed by inductively coupled plasma optical emission spectrometry (ICP-OES) that indicated sonicated Gd-DOTA/DOX@PFH NDs uptake by cancer cells was approximately 1.5 times more than the non-sonicated nanodroplets after 12 h. In vitro and in vivo toxicity assays revealed that synthesized NDs are biocompatible and do not have organ toxicity. Ultrasound exposure significantly enhanced the release of doxorubicin from NDs (P-value< 0.05). Ultrasound echogenicity and T1-MRI relaxometry indicated that synthesized NDs have strong ultrasound signal intensity and high r1 relaxivity (6.34 mM−1 S−1). The concentration of DOX in mice vital organs for Gd-DOTA/DOX NDs was significantly lower than that of free DOX. Doxorubicin concentration after 150 min in the tumor region for the DOX-loaded Gd-NDs+US group reached 14.8 μg/g followed by sonication, which was 2.3 fold higher than that of the non-sonicated group. According to the obtained results, the synthesized nanodroplets, with excellent diagnostic (ultrasound/MRI) and therapeutic properties, could be promising theranostic agents in cancer imaging and drug delivery for chemotherapeutic application.

Synthesis and characterization of phase shift dextran stabilized nanodroplets for ultrasound-induced cancer therapy: A novel nanobiotechnology approach

The nanobiotechnology, one heck of a biotechnology approach, is considered as a focal point in drug delivery systems. Although, plenty of novel approaches are reported in this area, it tackles with strict challenged which confine its broad application. Therefore, there is a need to dig deep into it along with all details. Here, a novel nanobiotechnology approach is described in detail for synthesis and characterization of phase shift dextran stabilized nanodroplets for ultrasound-induced cancer therapy. The aim of this work was to study the effect of parameters including homogenization speed and formulation of dextran and surfactant concentrations on particle size, entrapment efficiency and drug release kinetics of dextran stabilized perfluorohexane nanodroplets containing doxorubicin (Dox) drug. The obtained results showed that the particle size and encapsulation efficiency significantly increased by increasing polymer concentration. In addition, by increasing the homogenization speed, the particle size was increased while entrapment efficiency was decreased. On the other hand, by increasing the surfactant concentration, the particle size and entrapment efficiency reached to optimum values of 47.2 nm and 80.2%, respectively. In vitro release profile of doxorubicin was an apparently biphasic release process and 7–13% of drug was released after 24 h incubation in PBS with pH of 5.5, depending on the nanodroplets (ND) composition. Ultrasound exposure for 10 min resulted in triggered release of 82.95% of Dox from optimal formulation of sample C3 (0.1%w/v dextran, homogenization speed of 24000 rpm and Dox content of 500 µg).

Controllable formation of bulk perfluorohexane nanodroplets by solvent exchange.

Perfluorocarbon (PFC) nanodroplets have rapidly developed into useful ultrasound imaging agents in modern medicine due to their non-toxic and stable chemical properties that facilitate disease diagnosis and targeted therapy. In addition, with the good capacity for carrying breathing gases and the anti-infection ability, they are employed as blood substitutes and are the most ideal liquid respirators. However, it is still a challenge to prepare stable PFC nanodroplets of uniform size and high concentration for their efficient use. Herein, we developed a simple and highly reproducible method, i.e., propanol-water exchange, to prepare highly homogeneous and stable perfluorohexane (PFH) bulk nanodroplets. Interestingly, the size distribution and concentration of formed nanodroplets could be regulated by controlling the volume fraction of PFH and percentage of propanol in the propanol-water mixture. We demonstrated good reproducibility in the formation of bulk nanodroplets with PFH volume fractions of 1/2000-1/200 and propanol percentage of 5-40%, with uniform particle size distribution and high droplet concentration. Also, the prepared nanodroplets were very stable and could survive for several hours. We constructed a ternary phase diagram to describe the relationship between the PFH volume ratio, propanol concentration, and the size distribution and concentration of the formed PFH nanodroplets. This study provides a very useful method to prepare uniform size, high concentration and stable PFC nanodroplets for their medical applications.

Repeated Acoustic Vaporization of Perfluorohexane Nanodroplets for Contrast-Enhanced Ultrasound Imaging.

Superheated perfluorocarbon nanodroplets are emerging ultrasound imaging contrast agents that boast biocompatible components, unique phase-change dynamics, and therapeutic loading capabilities. Upon exposure to a sufficiently high-intensity pulse of acoustic energy, the nanodroplet's perfluorocarbon core undergoes a liquid-to-gas phase change and becomes an echogenic microbubble, providing ultrasound contrast. The controllable activation leads to high-contrast images, while the small size of the nanodroplets promotes longer circulation times and better in vivo stability. One drawback, however, is that the nanodroplets can only be vaporized a single time, limiting their versatility. Recently, we and others have addressed this issue by using a perfluorohexane core, which has a boiling point above body temperature. Thus after vaporization, the microbubbles recondense back into their stable nanodroplet form. Previous work with perfluorohexane nanodroplets relied on optical activation via pulsed laser absorption of an encapsulated dye. This strategy limits the imaging depth and temporal resolution of the method. In this study, we overcome these limitations by demonstrating acoustic droplet vaporization with 1.1-MHz high-intensity focused ultrasound (HIFU). A short-duration, high-amplitude pulse of focused ultrasound provides a sufficiently strong peak negative pressure to initiate vaporization. A custom imaging sequence was developed to enable the synchronization of a HIFU transducer and a linear array imaging transducer. We show a visualization of repeated acoustic activation of perfluorohexane nanodroplets in polyacrylamide tissue-mimicking phantoms. We further demonstrate the detection of hundreds of vaporization events from individual nanodroplets with activation thresholds well below the tissue cavitation limit. Overall, this approach has the potential to result in reliable and repeatable contrast-enhanced ultrasound imaging at clinically relevant depths.

Bifunctional alginate/chitosan stabilized perfluorohexane nanodroplets as smart vehicles for ultrasound and pH responsive delivery of anticancer agents

The combination of ultrasound and chemotherapy has been proposed as a promising strategy to achieve a better anticancer therapeutic efficacy. Here we present a facile strategy to construct novel bifunctional nanodroplets as smart vehicles for ultrasound and pH responsive delivery of anticancer agents. PFH is used as core and chitosan/alginate complexes are used as the stable shells of the nanodroplets. The effects of alginate/chitosan ratio, and the amount of surfactant as well as PFH on the size, size distribution, and encapsulation efficiency of nanodroplets are systematically investigated with the optimized formulation identified. The release of the encapsulated doxorubicin hydrochloride can be triggered by changing the pH value of the surrounding environment and the exposure to ultrasound. The nanodroplets also show strong ultrasound contrast via droplet-to-bubble transition as demonstrated by B-mode ultrasound imaging. The hemolytic activity and cytotoxicity are further studied, revealing the biocompatibility of the nanodroplets. The in vivo antitumor results demonstrate that the prepared droplets show excellent antitumor therapeutic efficacy and outstanding tumor-targeting ability. The proposed alginate/chitosan stabilized PFH nanodroplets represent an important advance in fabricating multifunctional therapeutic materials with great promises in the applications of combined antitumor therapies.

Ultrasmall MoS2 nanodots-wrapped perfluorohexane nanodroplets for dual-modal imaging and enhanced photothermal therapy

Development of a multifunctional nanotherapeutic agent with high contrast-enhanced dual-modal imaging and photothermal therapy (PTT) efficacy is of great interest. Combination of ultrasound (US) and computed tomography (CT) imaging offers high spatial resolution images, showing great potential in medical imaging. Herein, the semiconducting perfluorohexane (PFH) nanodroplets, MoS2-PFH-PLLAs, are developed by stabilizing PFH droplets with the coating shell of poly (lactic-co-glycolic acid) (PLLA) and encapsulating the droplets with photoabsorbers of ultrasmall molybdenum disulfide (MoS2) nanodots. Upon near-infrared (NIR) irradiation, the MoS2-PFH-PLLAs can absorb the NIR light and convert it into heat, which not only promotes liquid-to-gas phase transition of PFH but also triggers photothermal heating, resulting in contrast-enhanced US/CT imaging and photothermal killing effect in vitro. Furthermore, the production of microbubbles can serve as the blasting agents to collaboratively enhance PTT efficacy after NIR irradiation. When intravenously injected into tumor-bearing mice, the MoS2-PFH-PLLAs exhibit a dual-modal US/CT imaging-guided synergistically therapeutic efficacy under NIR irradiation, resulting in tumor ablation. These nanotherapeutic agents demonstrate good biocompatibility, highly contrast-enhanced US/CT imaging, and combinational enhanced PTT efficacy.

Cavitation characteristics of flowing low and high boiling-point perfluorocarbon phase-shift nanodroplets during focused ultrasound exposures.

This work investigated and compared the dynamic cavitation characteristics between low and high boiling-point phase-shift nanodroplets (NDs) under physiologically relevant flow conditions during focused ultrasound (FUS) exposures at different peak rarefactional pressures. A passive cavitation detection (PCD) system was used to monitor cavitation activity during FUS exposure at various acoustic pressure levels. Root mean square (RMS) amplitudes of broadband noise, spectrograms of the passive cavitation detection signals, and normalized inertial cavitation dose (ICD) values were calculated. Cavitation activity of low-boiling-point perfluoropentane (PFP) NDs and high boiling-point perfluorohexane (PFH) NDs flowing at in vitro mean velocities of 0-15cm/s were compared in a 4-mm diameter wall-less vessel in a transparent tissue-mimicking phantom. In the static state, both types of phase-shift NDs exhibit a sharp rise in cavitation intensity during initial FUS exposure. Under flow conditions, cavitation activity of the PFH NDs reached the steady state less rapidly compared to PFP NDs under the lower acoustic pressure (1.35MPa); at the higher acoustic pressure (1.65MPa), the RMS amplitude increased more sharply during the initial FUS exposure period. In particular, the RMS-time curves of the PFP NDs shifted upward as the mean flow velocity increased from 0 to 15cm/s; the RMS amplitude of the PFH ND solution increased from 0 to 10cm/s and decreased at 15cm/s. Moreover, amplitudes of the echo signal for the low boiling-point PFP NDs were higher compared to the high boiling-point PFH NDs in the lower frequency range, whereas the inverse occurred in the higher frequency range. Both PFP and PFH NDs showed increased cavitation activity in the higher frequency under the flow condition compared to the static state, especially PFH NDs. At 1.65MPa, normalized ICD values for PFH increased from 0.93±0.03 to 0.96±0.04 and from 0 to 10cm/s, then decreased to 0.86±0.05 at 15cm/s. This work contributes to our further understanding of cavitation characteristics of phase-shift NDs under physiologically relevant flow conditions during FUS exposure. In addition, the results provide a reference for selecting suitable phase-shift NDs to enhance the efficiency of cavitation-mediated ultrasonic applications.

Sensitive detection of dopamine with ultrasound cavitation-enhanced fluorescence method

Detection of dopamine (DA) is critical to medical diagnosis, and most of existing methods require sophisticated instruments and long processing time. Although fluorimetric methods show high sensitivity and selectivity, fluorescent probes are complicated. Ultrasound cavitation occurs when liquids are irradiated with ultrasound and comprises the formation, growth, and explosive collapse of microbubbles. In this study, we found that ultrasound cavitation accelerated the formation of polyethyleneimine-polydopamine fluorescent nanoparticles (PEI-PDA NPs), thereby enhancing the sensitivity and reducing the reaction time of DA detection. Perfluorohexane nanodroplets served as exogenous cavitation nuclei and were added into the reaction system to enhance the cavitation effect. During cavitation, water molecular was split into hydroxyl and hydrogen free radicals because of the high temperature. Hydroxyl free radicals accelerated the oxidation of DA, which polymerized into PDA. PDA then reacted with PEI and formed PEI-PDA NPs. The fluorescence intensity of PEI-PDA NPs made with ultrasound cavitation was higher than that of samples treated without ultrasound. The enhanced fluorescent intensity resulted in increased sensitivity of DA detection and less time due to accelerated reaction. Under the optimized conditions, the fluorescence intensity at 525 nm and DA concentrations exhibited good linear relationship within 0.1–100 μM. The detection limit was 25 nM. The method also showed excellent selectivity when 10 times interfering chemicals were mixed with DA. Further experiments carried out in cerebrospinal fluid indicated acceptable accuracy and reproducibility.

Oxygen Nanoshuttles for Tumor Oxygenation and Enhanced Cancer Treatment

Oxygen Nanoshuttles for Tumor Oxygenation and Enhanced Cancer Treatment

Toward optimization of blood brain barrier opening induced by laser-activated perfluorocarbon nanodroplets.

The blood brain barrier (BBB), a component of the brain's natural defense system, is often a roadblock for the monitoring and treatment of neurological disorders. Recently, we introduced a technique to open the blood brain barrier through the use of laser-activated perfluorohexane nanodroplets (PFHnDs), a phase-change nanoagent that undergoes repeated vaporization and recondensation when excited by a pulsed laser. Laser-activated PFHnDs were shown to enable noninvasive and localized opening of the BBB, allowing extravasation of various sized agents into the brain tissue. In this current work, the laser-activated PFHnD-induced BBB opening is further explored. In particular, laser fluence and the number of laser pulses used for the PFHnD-induced BBB opening are examined and evaluated both qualitatively and quantitatively to determine the effect of these parameters on BBB opening. The results of these studies show trends between increased laser fluence and an increased BBB opening as well as between an increased number of laser pulses and an increased BBB opening, however, with limitations on the extent of the BBB opening after a certain number of pulses. Overall, the results of these studies serve as a guideline to choosing suitable laser parameters for safe and effective BBB opening.

Fluorous-phase iron oxide nanoparticles as enhancers of acoustic droplet vaporization of perfluorocarbons with supra-physiologic boiling point

Perfluorocarbon emulsion nanodroplets containing iron oxide nanoparticles (IONPs) within their inner perfluorohexane (PFH) core were prepared to investigate potential use as an acoustically activatable ultrasound contrast agent, with the hypothesis that incorporation of IONPs into the fluorous phase of a liquid perfluorocarbon emulsion would potentiate acoustic vaporization. IONPs with an oleic acid (OA) hydrophobic coating were synthesized through chemical co-precipitation. To suspend IONP in PFH, OA was exchanged with perfluorononanoic acid (PFNA) via ligand exchange to yield fluorophilic PFNA-coated IONPs (PFNA-IONPs). Suspensions with various amounts of PFNA-IONPs (0–15% w/v) in PFH were emulsified in saline by sonication, using 5% (w/v) egg yolk phospholipid as an emulsifier. PFNA-IONPs were characterized with transmission electron microscopy (TEM), transmission electron cryomicroscopy (cryoTEM), and thermogravimetric analysis (TGA) with Fourier transform infrared spectroscopy (FTIR). IONP were between 5 and 10 nm in diameter as measured by electron microscopy, and hydrodynamic size of the PFH nanodroplets were 150 to 230 nm as measured by dynamic light scattering (DLS). Acoustic droplet vaporization of PFH nanodroplets (PFH-NDs) was induced using conversion pulses (100 cycle at 1.1 MHz and 50% duty cycle) provided by a focused ultrasound transducer, and formed microbubbles were imaged using a clinical ultrasound scanner. The acoustic pressure threshold needed for PFH-NDs vaporization decreased with increasing temperature and IONP content. PFH-NDs containing 5% w/v IONP converted to microbubbles at 42 °C at 2.18 MI, which is just above the exposure limits of 1.9 MI allowed by the FDA for clinical ultrasound scanners, whereas 10 and 15% emulsion vaporized at 1.87 and 1.24 MI, respectively. Furthermore, 5% IONP-loaded PFH-NDs injected intravenously into melanoma-bearing mice at a dose of 120 mg PFH/kg, converted into detectable microbubbles in vivo 5 h, but not shortly after injection, indicating that this technique detects NDs accumulated in tumors.

Leveraging the Imaging Transmit Pulse to Manipulate Phase-Change Nanodroplets for Contrast-Enhanced Ultrasound.

Phase-change perfluorohexane nanodroplets (PFHnDs) are a new class of recondensable submicrometer-sized contrast agents that have potential for contrast-enhanced and super-resolution ultrasound imaging with an ability to reach extravascular targets. The PFHnDs can be optically triggered to undergo vaporization, resulting in spatially stationary, temporally transient microbubbles. The vaporized PFHnDs are hyperechoic in ultrasound imaging for several to hundreds of milliseconds before recondensing to their native, hypoechoic, liquid nanodroplet state. The decay of echogenicity, i.e., the dynamic behavior of the ultrasound signal from optically triggered PFHnDs in ultrasound imaging, can be captured using high-frame-rate ultrasound imaging. We explore the possibility to manipulate the echogenicity dynamics of optically triggered PFHnDs in ultrasound imaging by changing the phase of the ultrasound imaging pulse. Specifically, the ultrasound imaging system was programmed to transmit two imaging pulses with inverse polarities. We show that the imaging pulse phase can affect the amplitude and the temporal behavior of PFHnD echogenicity in ultrasound imaging. The results of this study demonstrate that the ultrasound echogenicity is significantly increased (about 78% improvement) and the hyperechoic timespan of optically triggered PFHnDs is significantly longer (about four times) if the nanodroplets are imaged by an ultrasound pulse starting with rarefactional pressure versus a pulse starting with compressional pressure. Our finding has direct and significant implications for contrast-enhanced ultrasound imaging of droplets in applications such as super-resolution imaging and molecular imaging where detection of individual or low-concentration PFHnDs is required.

IR780 loaded perfluorohexane nanodroplets for efficient sonodynamic effect induced by short-pulsed focused ultrasound

Inertial cavitation is crucial for the therapeutic effects of sonodynamic. Therefore, approaches that can induce highly efficient inertial cavitation should be of benefit for sonodynamic effect. Our previous study demonstrated that highly efficient inertial cavitation activity can be achieved through the combinatorial use of a short-pulsed focused ultrasound (SPFU) sequence and perfluorohexane (PFH) nanodroplets. Herein, we applied the SPFU sequence and PFH nanodroplets in sonodynamic. A hydrophobic sonosensitizer, IR780 iodine, was loaded inside denatured bovine serum albumin-shelled PFH (PFH@BSA-IR780) nanodroplets. The sonodynamic efficacy was validated by treating HeLa cervical cancer cells. Under SPFU exposure, PFH@BSA-IR780 nanodroplets were highly effective in promoting reactive oxygen species generation and inducing cancer cell death. A significant decrease in cell viability was achieved within just 10 s. Besides the cytotoxicity of ROS, the mechanical bioeffects of inertial cavitation also led to severe cell death resulting from higher acoustic power or the longer treatment time. The application of the SPFU sequence coupled with PFH@BSA-IR780 nanodroplets is a promising strategy for efficient sonodynamic.

Speed-of-sound Estimation of Dual-acoustic Waves using Laser-activated Nanodroplets

A coherency of photoacoustic and ultrasound waves is dependent on the accuracy of the speedof- sound. This study evaluates the feasibility of a speed-of-sound estimation method for dual photoacoustic and ultrasound waves using laser-activated phase-change perfluorohexane nanodroplets (PFHnDs). The proposed method demonstrates that the estimated speed-of-sound (ESS) is close to the expected speed-of-sound for the medium (deviation = 0.3%), so it is useful for phase aberration correction in dual ultrasound and photoacoustic imaging.