Spatiotemporal drug delivery using laser-generated-focused ultrasound system

An ultra-thin MXene film with high conversion efficiency for broadband ultrasonic photoacoustic transducer

High-pressure, broadband, and miniatured ultrasound emitters are urgently needed in biomedical imaging and treatment as well as non-destructive detection. In this work, we report a laser generated ultrasonic photoacoustic transducer (LGUPT) based on an ultra-thin layer of MXene (Ti3C2Tx) nanosheets. Under the excitation of 532nm nanosecond laser pulses, the amplitude of the generated sound pressure can reach 8.7MPa, with a bandwidth of 17.4MHz at the irradiation intensity of 17.72mJ/cm2. The photoacoustic conversion efficiency of the 1.2μm-thick MXene film/PDMS transducer was found to be 1.21×10-2, which is among the highest values reported to date. The MXene thin film can also be drop-casted on the curved surface of a focusing lens. The amplitude of the sound pressure signal can reach 25.3 MPa and the bandwidth 19.7MHz at a pulse laser energy of 28.12mJ/cm2. The width of the focal spot at -3 dB of maximum amplitude was found in the range of 0.14mm for the optical lens based LGUPT under the condition of a laser spot diameter of 15mm by theoretical simulation. The water processable focusing LGUPT demonstrated excellent ultrasonic cavitation effect on the tissue mimicking agar plate. Our experimental and theoretical work highlights the potential of ultra-thin MXene film based LGUPTs for high precision photoacoustic therapy, integrated imaging and sensing instruments.

Flexible Ultrasonic Transducers for Wearable Biomedical Applications: A Review on Advanced Materials, Structural Designs, and Future Prospects

Due to the rapid developments in materials science and fabrication techniques, wearable devices have recently received increased attention for biomedical applications, particularly in medical ultrasound (US) imaging, sensing, and therapy. US is ubiquitous in biomedical applications because of its noninvasive nature, nonionic radiating, high precision, and real-time capabilities. While conventional US transducers are rigid and bulky, flexible transducers can be conformed to curved body areas for continuous sensing without restricting tissue movement or transducer shifting. This article comprehensively reviews the application of flexible US transducers in the field of biomedical imaging, sensing, and therapy. First, we review the background of flexible US transducers. Following that, we discuss advanced materials and fabrication techniques for flexible US transducers and their enabling technology status. Finally, we highlight and summarize some promising preliminary data with recent applications of flexible US transducers in biomedical imaging, sensing, and therapy. We also provide technical barriers, challenges, and future perspectives for further research and development.

A Self-Healing Optoacoustic Patch with High Damage Threshold and Conversion Efficiency for Biomedical Applications

Compared with traditional piezoelectric ultrasonic devices, optoacoustic devices have unique advantages such as a simple preparation process, anti-electromagnetic interference, and wireless long-distance power supply. However, current optoacoustic devices remain limited due to a low damage threshold and energy conversion efficiency, which seriously hinder their widespread applications. In this study, using a self-healing polydimethylsiloxane (PDMS, Fe-Hpdca-PDMS) and carbon nanotube composite, a flexible optoacoustic patch is developed, which possesses the self-healing capability at room temperature, and can even recover from damage induced by cutting or laser irradiation. Moreover, this patch can generate high-intensity ultrasound (> 25 MPa) without the focusing structure. The laser damage threshold is greater than 183.44 mJ cm-2, and the optoacoustic energy conversion efficiency reaches a major achievement at 10.66 × 10-3, compared with other carbon-based nanomaterials and PDMS composites. This patch is also been successfully examined in the application of acoustic flow, thrombolysis, and wireless energy harvesting. All findings in this study provides new insight into designing and fabricating of novel ultrasound devices for biomedical applications.

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

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

Tumor Spheroids as Model to Design Acoustically Mediated Drug Therapies: A Review

Tumor spheroids as well as multicellular tumor spheroids (MCTSs) are promising 3D in vitro tumor models for drug screening, drug design, drug targeting, drug toxicity, and validation of drug delivery methods. These models partly reflect the tridimensional architecture of tumors, their heterogeneity and their microenvironment, which can alter the intratumoral biodistribution, pharmacokinetics, and pharmacodynamics of drugs. The present review first focuses on current spheroid formation methods and then on in vitro investigations exploiting spheroids and MCTS for designing and validating acoustically mediated drug therapies. We discuss the limitations of the current studies and future perspectives. Various spheroid formation methods enable the easy and reproducible generation of spheroids and MCTSs. The development and assessment of acoustically mediated drug therapies have been mainly demonstrated in spheroids made up of tumor cells only. Despite the promising results obtained with these spheroids, the successful evaluation of these therapies will need to be addressed in more relevant 3D vascular MCTS models using MCTS-on-chip platforms. These MTCSs will be generated from patient-derived cancer cells and nontumor cells, such as fibroblasts, adipocytes, and immune cells.

Exploring Possible Ways to Enhance the Potential and Use of Natural Products through Nanotechnology in the Battle against Biofilms of Foodborne Bacterial Pathogens

Biofilms enable pathogenic bacteria to survive in unfavorable environments. As biofilm-forming pathogens can cause rapid food spoilage and recurrent infections in humans, especially their presence in the food industry is problematic. Using chemical disinfectants in the food industry to prevent biofilm formation raises serious health concerns. Further, the ability of biofilm-forming bacterial pathogens to tolerate disinfection procedures questions the traditional treatment methods. Thus, there is a dire need for alternative treatment options targeting bacterial pathogens, especially biofilms. As clean-label products without carcinogenic and hazardous potential, natural compounds with growth and biofilm-inhibiting and biofilm-eradicating potentials have gained popularity as natural preservatives in the food industry. However, the use of these natural preservatives in the food industry is restricted by their poor availability, stability during food processing and storage. Also there is a lack of standardization, and unattractive organoleptic qualities. Nanotechnology is one way to get around these limitations and as well as the use of underutilized bioactives. The use of nanotechnology has several advantages including traversing the biofilm matrix, targeted drug delivery, controlled release, and enhanced bioavailability, bioactivity, and stability. The nanoparticles used in fabricating or encapsulating natural products are considered as an appealing antibiofilm strategy since the nanoparticles enhance the activity of the natural products against biofilms of foodborne bacterial pathogens. Hence, this literature review is intended to provide a comprehensive analysis of the current methods in nanotechnology used for natural products delivery (biofabrication, encapsulation, and nanoemulsion) and also discuss the different promising strategies employed in the recent and past to enhance the inhibition and eradication of foodborne bacterial biofilms.

Polymer/magnetite carriers functionalized by HER2-DARPin: Avoiding lysosomes during internalization and controlled toxicity of doxorubicin by focused ultrasound induced release

Nanomedicine has revolutionized the available treatment options during the last decade, but poor selectivity of targeted drug delivery and release is still poses a challenge. In this study, doxorubicin (DOX) and magnetite nanoparticles were encapsulated by freezing-induced loading, coated with polymeric shell bearing two bi-layers of polyarginine/dextran sulphate and finally modified with HER2-specific DARPin proteins. We demonstrated that the enhanced cellular uptake of these nanocarriers predominantly occurs by SKOV-3 (HER2+) cells, in comparison to CHO (HER2-) cells, together with the controlled DOX release using low intensity focused ultrasound (LIFU). In addition, a good ability of DARPin+ capsules to accumulate in the tumor and the possibility of combination therapy with LIFU were demonstrated. A relatively high sensitivity of the obtained nanocarriers to LIFU and their preferential interactions with mitochondria in cancer cells make these carriers promising candidates for cancer treatment, including novel approaches to overcome drug resistance.

Ultrasonic photoacoustic emitter of graphene-nanocomposites film on a flexible substrate

Photoacoustic devices generating high-amplitude and high-frequency ultrasounds are attractive candidates for medical therapies and on-chip bio-applications. Here, we report the photoacoustic response of graphene nanoflakes - Polydimethylsiloxane composite. A protocol was developed to obtain well-dispersed graphene into the polymer, without the need for surface functionalization, at different weight percentages successively spin-coated onto a Polydimethylsiloxane substrate. We found that the photoacoustic amplitude scales up with optical absorption reaching 11 MPa at ∼ 228 mJ/cm² laser fluence. We observed a deviation of the pressure amplitude from the linearity increasing the laser fluence, which indicates a decrease of the Grüneisen parameter. Spatial confinement of high amplitude (> 40 MPa, laser fluence > 55 mJ/cm²) and high frequency (Bw-6db ∼ 21.5 MHz) ultrasound was achieved by embedding the freestanding film in an optical lens. The acoustic gain promotes the formation of cavitation microbubbles for moderate fluence in water and in tissue-mimicking material. Our results pave the way for novel photoacoustic medical devices and integrated components.

Aspects of Antiviral Strategies Based on Different Phototherapy Approaches: Hit by the Light

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which caused the COVID-19 pandemic spreading around the world from late 2019, served as a ruthless reminder of the threat viruses pose to global public health. The synthesis of new antiviral drugs, as well as repurposing existing products, is a long-term ongoing process which has challenged the scientific community. One solution could be an effective, accessible, and rapidly available antiviral treatment based on phototherapy (PT). PT has been used to treat several diseases, and relies on the absorption of light by endogenous molecules or exogenous photosensitizers (PS). PT has often been used in cancer treatment and prophylaxis, and as a complement to established chemotherapy and immunotherapy in combined therapeutic strategy. Besides significant applications in anticancer treatment, studies have demonstrated the beneficial impact of PT on respiratory, systemic, emerging, and oncogenic viral infections. The aim of this review was to highlight the potential of PT to combat viral infections by summarizing current progress in photodynamic, photothermal, and photoacoustic approaches. Attention is drawn to the virucidal effect of PT on systemic viruses such as the human immunodeficiency virus and human herpes viruses, including the causative agent of Kaposi sarcoma, human herpes virus (HHV8). PT has good potential for disinfection in anti-norovirus research and against pandemic viruses like SARS-CoV-2.

Recent Advancements in Ultrasound Transducer: From Material Strategies to Biomedical Applications

Ultrasound is extensively studied for biomedical engineering applications. As the core part of the ultrasonic system, the ultrasound transducer plays a significant role. For the purpose of meeting the requirement of precision medicine, the main challenge for the development of ultrasound transducer is to further enhance its performance. In this article, an overview of recent developments in ultrasound transducer technologies that use a variety of material strategies and device designs based on both the piezoelectric and photoacoustic mechanisms is provided. Practical applications are also presented, including ultrasound imaging, ultrasound therapy, particle/cell manipulation, drug delivery, and nerve stimulation. Finally, perspectives and opportunities are also highlighted.

Acoustics at the nanoscale (nanoacoustics): A comprehensive literature review.: Part II: Nanoacoustics for biomedical imaging and therapy

In the past decade, acoustics at the nanoscale (i.e., nanoacoustics) has evolved rapidly with continuous and substantial expansion of capabilities and refinement of techniques. Motivated by research innovations in the last decade, for the first time, recent advancements of acoustics-associated nanomaterials/nanostructures and nanodevices for different applications are outlined in this comprehensive review, which is written in two parts. As part II of this two-part review, this paper concentrates on nanoacoustics in biomedical imaging and therapy applications, including molecular ultrasound imaging, photoacoustic imaging, ultrasound-mediated drug delivery and therapy, and photoacoustic drug delivery and therapy. Firstly, the recent developments of nanosized ultrasound and photoacoustic contrast agents as well as their various imaging applications are examined. Secondly, different types of nanomaterials/nanostructures as nanocarriers for ultrasound and photoacoustic therapies are discussed. Finally, a discussion of challenges and future research directions are provided for nanoacoustics in medical imaging and therapy.

Acoustics at the nanoscale (nanoacoustics): A comprehensive literature review.: Part I: Materials, devices and selected applications

In the past decade, acoustics at the nanoscale (i.e., nanoacoustics) has evolved rapidly with continuous and substantial expansion of capabilities and refinement of techniques. Motivated by research innovations in the last decade, for the first time, recent advancements of acoustics-associated nanomaterials/nanostructures and nanodevices for different applications are outlined in this comprehensive review, which is written in two parts. As part I of this two part review, firstly, active and passive nanomaterials and nanostructures for acoustics are presented. Following that, representative applications of nanoacoustics including material property characterization, nanomaterial/nanostructure manipulation, and sensing, are discussed in detail. Finally, a summary is presented with point of views on the current challenges and potential solutions in this burgeoning field.

Variable-focus optoacoustic lens with wide dynamic range and long focal length by using a flexible polymer nano-composite membrane

We demonstrate a variable-focus optoacoustic lens (VFOL) by pneumatically controlling a flexible polymer nano-composite membrane, which can produce laser-generated focused ultrasound (LGFU) with a high peak amplitude (>30 MPa) and a tight focal dimension (several hundred μm) over a wide dynamic range of focus variation (>20 mm) together with a long focal length up to 60 mm, each of which is widest and longest among optoacoustic lenses developed so far. Two different designs in lens dimension have been fabricated and characterized: VFOL-L with a 40-mm diameter and VFOL-S with 10 mm. VFOL-L exhibits a wide dynamic range of focal length variation from 38.52 to 60.39 mm with a center frequency near ~ 10 MHz, which is proper for practical long-range applications with several-cm depth. In comparison, VFOL-S covers a focal variation range from 6.75 to 11.1 mm with ~ 14 MHz, producing a relatively higher-pressure amplitude, which allows the inception of acoustic cavitation at an impedance-mismatched boundary. The nano-composite membrane of VFOL is actuated from a planar to deeply curved shape by externally injecting liquid into the VFOL, resulting in a focal gain up to 255 and a positive peak pressure of > 30 MPa in the VFOL-L case. The minimum-geometrical f-number as low as 0.963 is achieved at the shortest focal length (38.52 mm) with 6-dB lateral and axial spot dimensions of 304 μm and 2.86 mm, respectively. We expect that the proposed VFOL-based LGFU with a high peak pressure, a wide dynamic axial range, and a tight focal dimension are suitably applied for depth-dependent characterization of tissues and shockwave treatment, taking advantages of optoacoustic pulses as input with inherent broadband high-frequency characteristics.

Experimental Demonstration of a Stacked Hybrid Optoacoustic-Piezoelectric Transducer for Localized Heating and Enhanced Cavitation

Laser-generated focused ultrasound (LGFU) is an emerging modality for cavitation-based therapy. However, focal pressure amplitudes by LGFU alone to achieve pulsed cavitation are often lacking as a treatment depth increases. This requires a higher pressure from a transmitter surface and more laser energies that even approach to a damage threshold of transmitter. To mitigate the requirement for LGFU-induced cavitation, we propose LGFU configurations with a locally heated focal zone using an additional high-intensity focused ultrasound (HIFU) transmitter. After confirming heat-induced cavitation enhancement using two separate transmitters, we then developed a stacked hybrid optoacoustic-piezoelectric transmitter, which is a unique configuration made by coating an optoacoustic layer directly onto a piezoelectric substrate. This shared curvature design has great practical advantage without requiring the complex alignment of two focal zones. Moreover, this enabled the amplification of cavitation bubble density by 18.5-fold compared to the LGFU operation alone. Finally, the feasibility of tissue fragmentation was confirmed through a tissue-mimicking gel, using the combination of LGFU and HIFU (not via a stacked structure). We expect that the stacked transmitter can be effectively used for stronger and faster tissue fragmentation than the LGFU transmitter alone.

Current progress and prospects of organic nanoparticles against bacterial biofilm

Biofilm plays a vital role in the pathogenicity and resistance of bacteria, and is an important problem to be settled urgently in the treatment of bacterial diseases. Exploring effective strategies to control bacterial biofilm has become a hot research topic. Compared to other measures, organic nanomaterials have shown greater prospects in overcoming the problems of bacterial biofilms due to their unique properties. In order to explore more effective organic nanomaterials against biofilms, we used relevant keywords to search for related published publications on the Web of Science . On the basis of these searched publications, this review firstly summarized the properties, formulation, harmness, and treatment challenges of biofilm. Secondly, the current progress of organic nanomaterials against bacterial biofilm and its possible anti-biofilm mechanisms (e.g., reducing the adhesion of biofilms, enhancing the permeability of antimicrobial agents, maintaining drug stability, fighting against biofilm using specific actions) was analyzed. Thirdly, the influences on the anti-biofilm efficacy of organic nanomaterials were discussed from nanoparticles and biofilm characteristics. Finally, the challenges and prospects of organic nanoparticles against biofilm were concluded. This review may help researchers to realize the progress and challenges of nanoparticles against biofilm and thus help to design more efficient organic nanomaterial to fight against biofilms.

Modelling and measurement of laser-generated focused ultrasound: Can interventional transducers achieve therapeutic effects?

Laser-generated focused ultrasound (LGFU) transducers used for ultrasound therapy commonly have large diameters (6-15 mm), but smaller lateral dimensions (<4 mm) are required for interventional applications. To address the question of whether miniaturized LGFU transducers could generate sufficient pressure at the focus to enable therapeutic effects, a modelling and measurement study is performed. Measurements are carried out for both linear and nonlinear propagation for various illumination schemes and compared with the model. The model comprises several innovations. First, the model allows for radially varying acoustic input distributions on the surface of the LGFU transducer, which arise from the excitation light impinging on the curved transducer surfaces. This realistic representation of the source prevents the overestimation of the achievable pressures (shown here to be as high as 1.8 times). Second, an alternative inverse Gaussian illumination paradigm is proposed to achieve higher pressures; a 35% increase is observed in the measurements. Simulations show that LGFU transducers as small as 3.5 mm could generate sufficient peak negative pressures at the focus to exceed the cavitation threshold in water and blood. Transducers of this scale could be integrated with interventional devices, thereby opening new opportunities for therapeutic applications from inside the body.

Air-backed photoacoustic transmitter for significantly improving negative acoustic pressure output

Aiming to pursue an ultrasound signal with a significantly improved negative acoustic pressure level, which is one of the critical characteristics for exciting the ultrasound cavitation effect, a real applicable air-backed photoacoustic transmitter is presented. Different from the conventional solution of relying on a complicated focusing structure design, it works based on an acoustic signal phase reversal and amplitude superposition strategy. By using an innovative sandwich-like suspending photoacoustic layer with optimized structure design, the initial backward-propagating positive sound pressure can be converted into the forward-propagating negative one efficiently. For proof-of-concept demonstration, photoacoustic transmitter prototypes adopting a polydimethylsiloxane (PDMS)/candle soot nanoparticle/PDMS-PDMS composite as a photoacoustic conversion layer were fabricated and characterized. From experiment results, an acoustic signal with a remarkable ratio of negative pressure level to a positive one of 1.3 was successfully realized, which is the largest value ever reported, to the best of our knowledge. Moreover, when compared to the commonly used glass and PDMS-backing conditions in the photoacoustic area, nearly 200% and 400% enhancements in negative pressure output were achieved, respectively.

Dynamic acoustic focusing in photoacoustic transmitter

Photoacoustic transmitter represents a promising substitute for conventional piezoelectric counterparts. However, lack of easy and effective method for dynamically manipulating the focused acoustic field is a common and tricky problem faced by current photoacoustic technology. In this paper, a new strategy for constructing focus tunable photoacoustic transmitter is proposed. Different from existed prevailing device architecture, a sandwich like photoacoustic conversion layer is innovatively designed into a suspending elastic membrane with clamped boundary and it can be deformed using integrated pneumatic actuator. Owing to the membrane deflection property, concave spherical contours with variable radius of curvature can be obtained. Considering the shape determined sound emission characteristic, continuous tuning on the axial focusing length of the acoustic field has been successfully demonstrated in the photoacoustic transmitter for the first time. Besides, acoustic signal with significantly improved negative pressure has also been achieved especially at the focus, bringing additional advantage for applications.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

Attenuation of the human skull at broadband frequencies by using a carbon nanotube composite photoacoustic transducer

The shockwave generated from a focused carbon nanotube (CNT) composite photoacoustic transducer has a wide frequency band that reaches several MHz in a single pulse. The objective of this study was to measure the transmission characteristics of a shockwave generated by a CNT composite photoacoustic transducer through Asian skulls and compare the results with numerical simulation ones. Three Korean cadaver skulls were used, and five sites were measured for each skull. The average densities and sound speeds of the three skulls were calculated from computed tomography images. The sound pressure after skull penetration was about 11% of the one before skull penetration. High-frequency energy was mostly attenuated. The average attenuation coefficients measured at the five sites of the three skulls were 3.59 ± 0.29, 5.99 ± 1.07, and 3.90 ± 0.86 np/cm/MHz. These values were higher than those previously measured at 270, 836, and 1402 kHz from other groups. The attenuation coefficients simulated by Sim4life were slightly smaller than the experimental values, with similar trends at most sites. The attenuation coefficients varied with measurement sites, skull shape, and thickness. These results may provide important data for future applications of shockwaves in noninvasive neurological treatments.

Photoacoustic image-guided interventions

Photoacoustic imaging has demonstrated its potential for diagnosis over the last few decades. In recent years, its unique imaging capabilities, such as detecting structural, functional and molecular information in deep regions with optical contrast and ultrasound resolution, have opened up many opportunities for photoacoustic imaging to be used during image-guided interventions. Numerous studies have investigated the capability of photoacoustic imaging to guide various interventions such as drug delivery, therapies, surgeries, and biopsies. These studies have demonstrated that photoacoustic imaging can guide these interventions effectively and non-invasively in real-time. In this minireview, we will elucidate the potential of photoacoustic imaging in guiding active and passive drug deliveries, photothermal therapy, and other surgeries and therapies using endogenous and exogenous contrast agents including organic, inorganic, and hybrid nanoparticles, as well as needle-based biopsy procedures. The advantages of photoacoustic imaging in guided interventions will be discussed. It will, therefore, show that photoacoustic imaging has great potential in real-time interventions due to its advantages over current imaging modalities like computed tomography, magnetic resonance imaging, and ultrasound imaging.

Versatile and scalable fabrication method for laser-generated focused ultrasound transducers

A versatile and scalable fabrication method for laser-generated focused ultrasound transducers is proposed. The method is based on stamping a coated negative mold onto polydimethylsiloxane, and it can be adapted to include different optical absorbers that are directly transferred or synthesized in situ. Transducers with a range of sizes down to 3 mm in diameter are presented, incorporating two carbonaceous (multiwalled carbon nanoparticles and candle soot nanoparticles) and one plasmonic (gold nanoparticles) optically absorbing component. The fabricated transducers operate at central frequencies in the vicinity of 10 MHz with bandwidths in the range of 15-20 MHz. A transducer with a diameter of 5 mm was found to generate a positive peak pressure greater than 35 MPa in the focal zone with a tight focal spot of 150 μm in lateral width. Ultrasound cavitation on the tip of an optical fiber was demonstrated in water for a transducer with a diameter as small as 3 mm.

Ultrasound-Responsive Conversion of Microbubbles to Nanoparticles to Enable Background-Free in Vivo Photoacoustic Imaging

Photoacoustic (PA) imaging based on the photon-to-ultrasound conversion allows the imaging of optical absorbers in deep tissues with high spatial resolution. However, the inherent optical absorbance of biomolecules (e.g., hemoglobin, melanin, etc.) would show up as tissue background signals to interfere with signals from the contrast agent during in vivo PA imaging, limiting the imaging sensitivity. Herein, an ultrasound (US)-responsive PA imaging probe based on microbubbles (MBs) containing gold nanoparticles (Au NPs) is designed for in vivo "background-free" PA imaging. The obtained Au@lip MBs with separated Au NPs decorated within the lipid shell of MBs show low PA signals under near-infrared (NIR) excitation. Interestingly, under exposure to US pulses, those Au@lip MBs would burst to form nanoscale aggregates of Au@lip NPs, which exhibit significantly enhanced NIR PA signals due to their red-shifted surface plasmon resonance. Therefore, by subtracting the PA image captured pre-US burst from that captured post-US burst, the tissue background PA signals could be deducted to enable background-free PA imaging with high sensitivities as demonstrated by multiple ex vivo and in vivo experiments. This work presents a simple yet effective strategy to deduct background signals during PA imaging, which is promising for accurate PA detection of targets in tissues with a strong background.

Candle Soot Carbon Nanoparticles in Photoacoustics: Advantages and Challenges for Laser Ultrasound Transmitters

This manuscript provides a review of candle-soot nanoparticle (CSNP) composite laser ultrasound transmitters (LUT), and compares and contrasts this technology to other carboncomposite designs. Among many carbon-based composite LUTs, a CSNP composite has shown its advantages of maximum energy conversion and fabrication simplicity for developing highly efficient ultrasound transmitters. This review focuses on the advantages and challenges of the CSNP-composite transmitter in the aspects of nanostructure design, fabrication procedure, and promising applications. Included are a brief description of the basic principles of the laser ultrasound transmitter, a review of general properties of CSNPs, as well as details on the fabrication method, photoacoustic performance, and design factors. A comparison of the CSNP-nanocomposite to other carbon-nanocomposites is provided. Lastly, representative applications of carbon-nanocomposite transmitters and future perspectives on CSNP-composite transmitters are presented.

Simple yet universal fabrication strategy for a focused photoacoustic transmitter

Aiming to address existing technical challenges and explore a simple yet effective and universal solution for making a polydimethylsiloxane (PDMS)-based focused photoacoustic transmitter, a novel fabrication strategy is proposed. Different from the traditional technical route based on direct photoacoustic layer coating on a rigid concave substrate, it works by utilizing an elastomeric molding process, through which the originally flat photoacoustic conversion layer, consisting of PDMS-candle soot nanoparticles/PDMS-PDMS composite, is transformed into a concave contour with controllable radius of curvature and finally merged into a soft PDMS substrate. For proof-of-concept demonstration, two types of focused photoacoustic transmitters (6.3 mm and 8 mm focal lengths) operating at 5.3 MHz with -6  dB bandwidth of 134% are successfully fabricated, showing both distinct acoustic focusing capability and high energy conversion efficiency. Moreover, different from conventional focused counterparts, acoustic signals with nearly symmetric bi-polar waveform can be obtained at the focuses, facilitating ultrasound cavitation-based applications.

A Fiber Optic Ultrasonic Sensing System for High Temperature Monitoring Using Optically Generated Ultrasonic Waves

This paper presents the design, fabrication, and characterization of a novel fiber optic ultrasonic sensing system based on the photoacoustic (PA) ultrasound generation principle and Fabry-Perot interferometer principle for high temperature monitoring applications. The velocity of a sound wave traveling in a medium is proportional to the medium's temperature. The fiber optic ultrasonic sensing system was applied to measure the change of the velocity of sound. A fiber optic ultrasonic generator and a Fabry-Perot fiber sensor were used as the signal generator and receiver, respectively. A carbon black-polydimethylsiloxane (PDMS) material was utilized as the photoacoustic material for the fiber optic ultrasonic generator. Two tests were performed. The system verification test proves the ultrasound sensing capability. The high temperature test validates the high temperature measurement capability. The sensing system survived 700 °C. It successfully detects the ultrasonic signal and got the temperature measurements. The test results agreed with the reference sensor data. Two potential industry applications of fiber optic ultrasonic sensing system are, it could serve as an acoustic pyrometer for temperature field monitoring in an industrial combustion facility, and it could be used for exhaust gas temperature monitoring for a turbine engine.

Organic Semiconducting Agents for Deep-Tissue Molecular Imaging: Second Near-Infrared Fluorescence, Self-Luminescence, and Photoacoustics

Optical imaging has played a pivotal role in biology and medicine, but it faces challenges of relatively low tissue penetration and poor signal-to-background ratio due to light scattering and tissue autofluorescence. To overcome these issues, second near-infrared fluorescence, self-luminescence, and photoacoustic imaging have recently emerged, which utilize an optical region with reduced light-tissue interactions, eliminate real-time light excitation, and detect acoustic signals with negligible attenuation, respectively. Because there are only a few endogenous molecules absorbing or emitting above the visible region, development of contrast agents is essential for those deep-tissue optical imaging modalities. Organic semiconducting agents with π-conjugated frameworks can be synthesized to meet different optical imaging requirements due to their easy chemical modification and legible structure-property relation. Herein, the deep-tissue optical imaging applications of organic semiconducting agents including small-molecule agents and nanoparticle derivatives are summarized. In particular, the molecular engineering and nanoformulation approaches to further improve the tissue penetration and detection sensitivity of these optical imaging modalities are highlighted. Finally, current challenges and potential opportunities in this emerging subfield of biomedical imaging are discussed.

Experimental investigation on multiple breakdown in water induced by focused nanosecond laser

Multiple breakdowns in liquids still remains obscure for its complex, non-equilibrium and transient dynamic process. We introduced three methods, namely, plasma imaging, light-scattering technique, and acoustic detection, to measure the multiple breakdown in water induced by focused nanosecond laser pulses simultaneously. Our results showed that linear dependence existed among the cavitation-bubble lifetime, the far-field peak pressure of the initial shock wave, and the corresponding plasma volume. Such a relationship can be used to evaluate the ideal size and energy of each bubble during multiple breakdown. The major bubble lifetime was hardly affected by the inevitable coalescence of cavitation bubbles, thereby confirming the availability of light-scattering technique on the estimation of bubble size during multiple breakdown. Whereas, the strength of collapse-shock-wave and the subsequent rebound of bubbles was strongly influenced, i.e., the occurrence of multiple breakdown suppressed the cavitation-bubble energy being converted into collapse-shock-wave energy but enhanced conversion into rebound-bubble energy. This study is a valuable contribution to research on the rapid mixing of microfluidics, damage control of microsurgery, and photoacoustic applications.

Folate-receptor-targeted laser-activable poly(lactide-co-glycolic acid) nanoparticles loaded with paclitaxel/indocyanine green for photoacoustic/ultrasound imaging and chemo/photothermal therapy

BACKGROUND

Cancer is one of the most serious threats to human health. Precision medicine is an innovative approach to treatment, as part of which theranostic nanomedicine has been studied extensively. However, the required biocompatibility and substantial cost for the approval of nanomedicines hinder their clinical translation.

PURPOSE

We designed a novel type of theranostic nanoparticle (NP) folate-receptor-targeted laser-activatable poly(lactide-co-glycolic acid) (PLGA) NPs loaded with paclitaxel (Ptx)/indo-cyanine green (ICG)-folic acid-polyethylene glycol (PEG)-PLGA-Ptx@ICG-perfluorohexane (Pfh)- using safe and approved materials and drugs, which would facilitate clinical translation. With laser irradiation, highly efficient photothermal therapy can be achieved. Additionally, targeted NPs can be activated by near-infrared laser irradiation at a specific region, which leads to the sharp release of Ptx at areas of high folate-receptor expression and ensures a higher Ptx concentration within the tumor region, thereby leading to chemo/photothermal synergistic antitumor efficacy. Meanwhile, the NPs can be used as a dual-modality contrast agent for photoacoustic and ultrasound imaging.

MATERIALS AND METHODS

FA-PEG-PLGA-Ptx@ICG-Pfh NPs were prepared by sonification method and characterized for physicochemical properties. Cytotoxicity and in vivo biocompatibility were evaluated respectively by CCK8 assay and blood analysis. NPs as dual-modality contrast agents were evaluated by photoacoustic/ultrasound imaging system in vitro and in vivo. In vitro anticancer effect and in vivo anticancer therapy was evaluated by CCK8 assay and MDA-MB231 tumor-bearing mice model.

RESULTS

FA-PEG-PLGA-Ptx@ICG-Pfh NPs were in the size of 308±5.82 nm with negative zeta potential and showed excellent photothermal effect. The NPs could be triggered sharp release of Ptx by laser irradiation, and showed the good biocompatibility in vitro and in vivo. Through photoacoustic/ultrasound imaging, the NPs showed an excellent ability as dual-modality contrast agents in vitro and in vivo. FA-PEG-PLGA-Ptx@ICG-Pfh NPs with laser irradiation showed the best anticancer efficacy in vitro and in vivo.

CONCLUSION

Such a biocompatible and novel theranostic NP is expected to integrate dual-modality imaging with improved therapeutic efficacy and provide a promising paradigm for cancer therapy.

Organic Dye Based Nanoparticles for Cancer Phototheranostics

Phototheranostics, which simultaneously combines photodynamic and/or photothermal therapy with deep-tissue diagnostic imaging, is a promising strategy for the diagnosis and treatment of cancers. Organic dyes with the merits of strong near-infrared absorbance, high photo-to-radical and/or photothermal conversion efficiency, great biocompatibility, ready chemical structure fine-tuning capability, and easy metabolism, have been demonstrated as attractive candidates for clinical phototheranostics. These organic dyes can be further designed and fabricated into nanoparticles (NPs) using various strategies. Compared to free molecules, these NPs can be equipped with multiple synergistic functions and show longer lifetime in blood circulation and passive tumor-targeting property via the enhanced permeability and retention effect. In this article, the recent progress of organic dye-based NPs for cancer phototheranostic applications is summarized, which extends the anticancer arsenal and holds promise for clinical uses in the near future.

Study of Poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM) Microgel Particle Induced Deformations of Tissue-Mimicking Phantom by Ultrasound Stimulation

Poly(N-isopropylacrylamide) (pNIPAm) microgels (microgels) are colloidal particles that have been used extensively for biomedical applications. Typically, these particles are synthesized in the presence of an exogenous cross-linker, such as N,N'-methylenebis(acrylamide) (BIS); however, recent studies have demonstrated that pNIPAm microgels can be synthesized in the absence of an exogenous cross-linker, resulting in the formation of ultralow cross-linked (ULC) particles, which are highly deformable. Microgel deformability has been linked in certain cases to enhanced bioactivity when ULC microgels are used for the creation of biomimetic particles. We hypothesized that ultrasound stimulation of microgels would enhance particle deformation and that the degree of enhancement would negatively correlate with the degree of particle cross-linking. Here, we demonstrate in tissue-mimicking phantoms that using ultrasound insonification causes deformations of ULC microgel particles. Furthermore, the amount of deformation depends on the ultrasound excitation frequency and amplitude and on the concentration of ULC microgel particles. We observed that the amplitude of deformation increases with increasing ULC microgel particle concentration up to 2.5 mg/100 mL, but concentrations higher than 2.5 mg/100 mL result in reduced amount of deformation. In addition, we observed that the amplitude of deformation was significantly higher at 1 MHz insonification frequency. We also report that increasing the degree of microgel cross-linking reduces the magnitude of the deformation and increases the optimal concentration required to achieve the largest amount of deformation. Stimulated ULC microgel particle deformation has numerous potential biomedical applications, including enhancement of localized drug delivery and biomimetic activity. These results demonstrate the potential of ultrasound stimulation for such applications.

From Nano to Micro: using nanotechnology to combat microorganisms and their multidrug resistance

The spread of antibiotic resistance and increasing prevalence of biofilm-associated infections is driving demand for new means to treat bacterial infection. Nanotechnology provides an innovative platform for addressing this challenge, with potential to manage even infections involving multidrug-resistant (MDR) bacteria. The current review summarizes recent progress over the last 2 years in the field of antibacterial nanodrugs, and describes their unique properties, mode of action and activity against MDR bacteria and biofilms. Biocompatibility and commercialization are also discussed. As opposed to the more common division of nanoparticles (NPs) into organic- and inorganic-based materials, this review classifies NPs into two functional categories. The first includes NPs exhibiting intrinsic antibacterial properties and the second is devoted to NPs serving as a cargo for delivering antibacterial agents. Antibacterial nanomaterials used to decorate medical devices and implants are reviewed here as well.

Laser-Induced Focused Ultrasound for Cavitation Treatment: Toward High-Precision Invisible Sonic Scalpel

Beyond the implementation of the photoacoustic effect to photoacoustic imaging and laser ultrasonics, this study demonstrates a novel application of the photoacoustic effect for high-precision cavitation treatment of tissue using laser-induced focused ultrasound. The focused ultrasound is generated by pulsed optical excitation of an efficient photoacoustic film coated on a concave surface, and its amplitude is high enough to produce controllable microcavitation within the focal region (lateral focus <100 µm). Such microcavitation is used to cut or ablate soft tissue in a highly precise manner. This work demonstrates precise cutting of tissue-mimicking gels as well as accurate ablation of gels and animal eye tissues.

Photoacoustic Drug Delivery

Photoacoustic (PA) technology holds great potential in clinical translation as a new non-invasive bioimaging modality. In contrast to conventional optical imaging, PA imaging (PAI) enables higher resolution imaging with deeper imaging depth. Besides applications for diagnosis, PA has also been extended to theranostic applications. The guidance of PAI facilitates remotely controlled drug delivery. This review focuses on the recent development of PAI-mediated drug delivery systems. We provide an overview of the design of different PAI agents for drug delivery. The challenges and further opportunities regarding PA therapy are also discussed.

Diketopyrrolopyrrole-Triphenylamine Organic Nanoparticles as Multifunctional Reagents for Photoacoustic Imaging-Guided Photodynamic/Photothermal Synergistic Tumor Therapy

Herein, a donor-acceptor-donor (D-A-D) structured small molecule (DPP-TPA) is designed and synthesized for photoacoustic imaging (PAI) guided photodynamic/photothermal synergistic therapy. In the diketopyrrolopyrrole (DPP) molecule, a thiophene group is contained to increase the intersystem crossing (ISC) ability through the heavy atom effect. Simultaneously, triphenylamine (TPA) is introduced for bathochromic shift absorption as well as charge transport capacity enhancement. After formation of nanoparticles (NPs, ∼76 nm) by reprecipitation, the absorption of DPP-TPA NPs further displays obvious bathochromic-shift with the maximum absorption peak at 660 nm. What's more, the NPs architecture enhances the D-A-D structure, which greatly increases the charge transport capacity and impels the charge to generate heat by light. DPP-TPA NPs present high photothermal conversion efficiency (η = 34.5%) and excellent singlet oxygen (¹O₂) generation (Φ_Δ = 33.6%) under 660 nm laser irradiation. PAI, with high spatial resolution and deep biotissue penetration, indicates DPP-TPA NPs can rapidly target the tumor sites within 2 h by the enhanced permeability and retention (EPR) effect. Importantly, DPP-TPA NPs could effectively hinder the tumor growth by photodynamic/photothermal synergistic therapy in vivo even at a low dosage (0.2 mg/kg) upon laser irradiation (660 nm 1.0 W/cm²). This study illuminates the photothermal conversion mechanism of small organic NPs and demonstrates the promising application of DPP-TPA NPs in PAI guided phototherapy.

Overcoming T. gondii infection and intracellular protein nanocapsules as biomaterials for ultrasonically controlled drug release

One of the pivotal matters of concern in intracellular drug delivery is the preparation of biomaterials containing drugs that are compatible with the host target.

Using High-Intensity Focused Ultrasound as a Means to Provide Targeted Drug Delivery

High-intensity focused ultrasound (HIFU)–mediated drug delivery is a relatively novel technique used to deliver drugs to a targeted location in the body. High-intensity focused ultrasound–mediated drug delivery has a broad range of applications, such as tumor therapy, treating central nervous diseases, transsclera drug delivery, and cardiovascular treatments. Targeted treatments prove to be advantageous to systemic treatments due to the reduction in the associated side effects. Thus, this literature review focuses on the various applications of HIFU-mediated drug delivery as well as the mechanism involved. This article is intended to supply the reader with a detailed description of how this technique can be used as well as describe its potential to surpass other treatment methods. Further discussion on the efficiency, limitations, and future of HIFU-mediated drug delivery is addressed. Furthermore, the gaps in the published literature, relative to this topic, are discussed. Ultimately, HIFU-mediated drug delivery is a developing technique that could provide patients with exciting treatment options.

ATP-Responsive and Near-Infrared-Emissive Nanocarriers for Anticancer Drug Delivery and Real-Time Imaging

Stimuli-responsive and imaging-guided drug delivery systems hold vast promise for enhancement of therapeutic efficacy. Here we report an adenosine-5'-triphosphate (ATP)-responsive and near-infrared (NIR)-emissive conjugated polymer-based nanocarrier for the controlled release of anticancer drugs and real-time imaging. We demonstrate that the conjugated polymeric nanocarriers functionalized with phenylboronic acid tags on surface as binding sites for ATP could be converted to the water-soluble conjugated polyelectrolytes in an ATP-rich environment, which promotes the disassembly of the drug carrier and subsequent release of the cargo. In vivo studies validate that this formulation exhibits promising capability for inhibition of tumor growth. We also evaluate the metabolism process by monitoring the fluorescence signal of the conjugated polymer through the in vivo NIR imaging.