Strategies for Image-Guided Therapy, Surgery, and Drug Delivery Using Photoacoustic Imaging

Recent Advance in Biological Responsive Nanomaterials for Biosensing and Molecular Imaging Application

In recent decades, as a subclass of biomaterials, biologically sensitive nanoparticles have attracted increased scientific interest. Many of the demands for physiologically responsive nanomaterials in applications involving the human body cannot be met by conventional technologies. Due to the field's importance, considerable effort has been expended, and biologically responsive nanomaterials have achieved remarkable success thus far. This review summarizes the recent advancements in biologically responsive nanomaterials and their applications in biosensing and molecular imaging. The nanomaterials change their structure or increase the chemical reaction ratio in response to specific bio-relevant stimuli (such as pH, redox potentials, enzyme kinds, and concentrations) in order to improve the signal for biologically responsive diagnosis. We use various case studies to illustrate the existing issues and provide a clear sense of direction in this area. Furthermore, the limitations and prospects of these nanomaterials for diagnosis are also discussed.

Design Principles Governing the Development of Theranostic Anticancer Agents and Their Nanoformulations with Photoacoustic Properties

The unmet need to develop novel approaches for cancer diagnosis and treatment has led to the evolution of theranostic agents, which usually include, in addition to the anticancer drug, an imaging agent based mostly on fluorescent agents. Over the past few years, a non-invasive photoacoustic imaging modality has been effectively integrated into theranostic agents. Herein, we shed light on the design principles governing the development of theranostic agents with photoacoustic properties, which can be formulated into nanocarriers to enhance their potency. Specifically, we provide an extensive analysis of their individual constituents including the imaging dyes, drugs, linkers, targeting moieties, and their formulation into nanocarriers. Along these lines, we present numerous relevant paradigms. Finally, we discuss the clinical relevance of the specific strategy, as also the limitations and future perspectives, and through this review, we envisage paving the way for the development of theranostic agents endowed with photoacoustic properties as effective anticancer medicines.

Impact of skin tone on photoacoustic oximetry and tools to minimize bias

The major optical absorbers in tissue are melanin and oxy/deoxy-hemoglobin, but the impact of skin tone and pigmentation on biomedical optics is still not completely understood or adequately addressed. Melanin largely governs skin tone with higher melanin concentration in subjects with darker skin tones. Recently, there has been extensive debate on the bias of pulse oximeters when used with darker subjects. Photoacoustic (PA) imaging can measure oxygen saturation similarly as pulse oximeters and could have value in studying this bias. More importantly, it can deconvolute the signal from the skin and underlying tissue. Here, we studied the impact of skin tone on PA signal generation, depth penetration, and oximetry. Our results show that subjects with darker skin tones exhibit significantly higher PA signal at the skin surface, reduced penetration depth, and lower oxygen saturation compared to subjects with lighter skin tones. We then suggest a simple way to compensate for these signal differences.

pH-Responsive Nanoparticles for Enhanced Antitumor Activity by High-Intensity Focused Ultrasound Therapy Combined with Sonodynamic Therapy

BACKGROUND

Therapeutic ultrasound (US) has been extensively explored for its inherent high tissue-penetrating capability and on-demand irradiation without radioactive damage. Although high-intensity focused ultrasound (HIFU) is evolved as such an outstanding US-based approach, its insufficient therapeutic effect and the high-intensity induced potential damage to surrounding normal tissues hindered its development towards practical application. As opposed to high intensity ultrasound, sonodynamic therapy (SDT) is a low intensity US-based method which exhibits certain therapeutic effects against cancer via sonosensitizers-generated reactive oxygen species (ROS) overproduction.

METHODS

Hematoporphyrin monomethyl ether (HMME) loaded CaCO3 nanoparticles (designated as Ca@H) were synthesized by a gas diffusion method. The pH-responsive performance, in vitro SDT, ex vivo HIFU therapy (HIFUT), photoacoustic (PA) imaging and in vivo HIFUT combined with SDT were investigated thoroughly.

RESULTS

Ca@H NPs gradually decomposed in acid tumor microenvironment, produced CO2 and released HMME. Both CO2 and HMME enhanced photoacoustic (PA) imaging. The generated CO2 bubbles also enhanced HIFUT by inducing an enlarged ablation area. The tumor ablation efficiency (61.04%) was significantly improved with a combination of HIFU therapy and SDT.

CONCLUSION

pH-responsive Ca@H NPs have been successfully constructed for PA imaging-guided/monitored HIFUT combined with SDT. With the assistance of pH-responsive Ca@H NPs, the combination of these two US-based therapies is expected to play a role in the treatment of non-invasive tumor in the future.

NIR-II Fluorescent Activatable Drug Delivery Nanoplatform for Cancer-Targeted Combined Photodynamic and Chemotherapy

Nanotheranostics with integrated imaging functions can help monitor nanoparticle accumulation in tumors, thus achieving synergism and higher therapeutic accuracy in cancer therapy. However, it remains challenging to monitor the release of therapeutic drugs in real time from a nanoparticulate drug delivery system (nano-DDS) in the body. Herein, we developed a nano-DDS for fluorescence imaging in the second near-infrared window (NIR-II) region, which can be used for monitoring the responsive release of drugs and cancer-targeted combined photodynamic and chemotherapy. There is a linear correlation between the cumulative release of the drug and the NIR-II fluorescence intensity. Moreover, hyaluronidase/glutathione dual-response RGD-SS-DOX/Ce6@HA-IR-1061 (RSSDCHI) exhibited a higher tumor-to-normal-tissue ratio in NIR-II fluorescence imaging and enhanced antitumor efficacy in vivo. This makes it possible to visualize drug release at the cellular level by the nanocomposites and to predict the treatment effect according to the NIR-II fluorescence intensity in the tumor site, serving as a promising nanoplatform for precision nanomedicine.

Mitochondria-targeted nanoplatforms for enhanced photodynamic therapy against hypoxia tumor

Background

Photodynamic therapy (PDT) is a promising therapeutic modality that can convert oxygen into cytotoxic reactive oxygen species (ROS) via photosensitizers to halt tumor growth. However, hypoxia and the unsatisfactory accumulation of photosensitizers in tumors severely diminish the therapeutic effect of PDT. In this study, a multistage nanoplatform is demonstrated to overcome these limitations by encapsulating photosensitizer IR780 and oxygen regulator 3-bromopyruvate (3BP) in poly (lactic-co-glycolic acid) (PLGA) nanocarriers.

Results

The as-synthesized nanoplatforms penetrated deeply into the interior region of tumors and preferentially remained in mitochondria due to the intrinsic characteristics of IR780. Meanwhile, 3BP could efficiently suppress oxygen consumption of tumor cells by inhibiting mitochondrial respiratory chain to further improve the generation of ROS. Furthermore, 3BP could abolish the excessive glycolytic capacity of tumor cells and lead to the collapse of ATP production, rendering tumor cells more susceptible to PDT. Successful tumor inhibition in animal models confirmed the therapeutic precision and efficiency. In addition, these nanoplatforms could act as fluorescence (FL) and photoacoustic (PA) imaging contrast agents, effectuating imaging-guided cancer treatment.

Conclusions

This study provides an ideal strategy for cancer therapy by concurrent oxygen consumption reduction, oxygen-augmented PDT, energy supply reduction, mitochondria-targeted/deep-penetrated nanoplatforms and PA/FL dual-modal imaging guidance/monitoring. It is expected that such strategy will provide a promising alternative to maximize the performance of PDT in preclinical/clinical cancer treatment.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01196-6.

Repurposing ICG enables MR/PA imaging signal amplification and iron depletion for iron-overload disorders

Precise and noninvasive theranostic methods to quantify and deplete focal iron are of crucial importance for iron-overload disorders. Here, we developed an indocyanine green (ICG)–based imaging platform to reveal Fe³⁺ in vitro and in vivo. The high sensitivity and specificity of ICG-Fe interaction facilitated MR images with a marked correlation between T₁ signal intensity ratio (T₁SIR) changes and Fe³⁺ concentration in rodent models and humans. On the basis of these findings, a rational design for coordination-driven self-assembly ICG-Lecithin (ICG/Leci) was proposed to determine Fe³⁺. The enhancement of photoacoustic signal at 890 nm with increasing Fe³⁺ concentration showed an over 600% higher linear slope than that of T₁SIR changes in animal models. ICG/Leci also promoted a 100% increase in iron depletion in the liver compared with deferoxamine. The high MR sensitivity and superior photoacoustic contrast, combined with enhanced iron depletion, demonstrate that ICG/Leci is a promising theranostic agent for simultaneous detection and treatment of iron-overload disorders.

Early Diagnosis and Real-Time Monitoring of Regional Lung Function Changes to Prevent Chronic Obstructive Pulmonary Disease Progression to Severe Emphysema

First- and second-hand exposure to smoke or air pollutants is the primary cause of chronic obstructive pulmonary disease (COPD) pathogenesis, where genetic and age-related factors predispose the subject to the initiation and progression of obstructive lung disease. Briefly, airway inflammation, specifically bronchitis, initiates the lung disease, leading to difficulty in breathing (dyspnea) and coughing as initial symptoms, followed by air trapping and inhibition of the flow of air into the lungs due to damage to the alveoli (emphysema). In addition, mucus obstruction and impaired lung clearance mechanisms lead to recurring acute exacerbations causing progressive decline in lung function, eventually requiring lung transplant and other lifesaving interventions to prevent mortality. It is noteworthy that COPD is much more common in the population than currently diagnosed, as only 16 million adult Americans were reported to be diagnosed with COPD as of 2018, although an additional 14 million American adults were estimated to be suffering from COPD but undiagnosed by the current standard of care (SOC) diagnostic, namely the spirometry-based pulmonary function test (PFT). Thus, the main issue driving the adverse disease outcome and significant mortality for COPD is lack of timely diagnosis in the early stages of the disease. The current treatment regime for COPD emphysema is most effective when implemented early, on COPD onset, where alleviating symptoms and exacerbations with timely intervention(s) can prevent steep lung function decline(s) and disease progression to severe emphysema. Therefore, the key to efficiently combatting COPD relies on early detection. Thus, it is important to detect early regional pulmonary function and structural changes to monitor modest disease progression for implementing timely interventions and effectively eliminating emphysema progression. Currently, COPD diagnosis involves using techniques such as COPD screening questionnaires, PFT, arterial blood gas analysis, and/or lung imaging, but these modalities are limited in their capability for early diagnosis and real-time disease monitoring of regional lung function changes. Hence, promising emerging techniques, such as X-ray phase contrast, photoacoustic tomography, ultrasound computed tomography, electrical impedance tomography, the forced oscillation technique, and the impulse oscillometry system powered by robust artificial intelligence and machine learning analysis capability are emerging as novel solutions for early detection and real time monitoring of COPD progression for timely intervention. We discuss here the scope, risks, and limitations of current SOC and emerging COPD diagnostics, with perspective on novel diagnostics providing real time regional lung function monitoring, and predicting exacerbation and/or disease onset for prognosis-based timely intervention(s) to limit COPD–emphysema progression.

Tumor microenvironment-responsive dynamic inorganic nanoassemblies for cancer imaging and treatment

Dynamic inorganic nanoassemblies (DINAs) have emerged as smart nanomedicine platforms with promising potential for bioimaging and targeted drug delivery. In this review, we keep abreast of the advances in development of tumor microenvironment (TME)-responsive DINAs to meet the challenges associated with precise cancer therapy. TME-responsive DINAs are designed to achieve precise switches of structures/functions in response to TME-specific stimuli including reactive oxygen species (ROS), reduced pH and hypoxia, so as to enhance the tumor accumulation of nanoassemblies, overcome the biological barriers during intratumoral penentration of therapeutics, and achieve tumor-specific imaging and therapy. This progress report will summarize various types of recently reported smart DINAs for TME-responsive tumor imaging and therapy. Their future development towards potential clinical translation will also be discussed.

Diagnostic Radionuclides Labeled on Biomimetic Nanoparticles for Enhanced Follow-Up Photothermal Therapy of Cancer

Imaging-guided local therapy is the most effective strategy to treat primary cancers in patients. However, the local therapeutic effect should be further improved under the premise of absence of induction of additional side effects. It would be meaningful to analyze the potential assistance of nuclear imaging to the follow-up treatments. In this study,cancer-targeted copper sulfide nanoparticles with ^99m Tc labeling (^99m Tc-M-CuS-PEG) are prepared using-cancer cell membranes as a synthesis reactor and applied for the potential single-photon emission computed tomography/photoacoustic imaging-guided and ^99m Tc-amplified photothermal therapy of cancer. Owing to the homologous targeting capability of the cancer cell membrane, M-CuS-PEG selectively accumulates in homologous tumor sites. After labeling with ^99m Tc, M-CuS-PEG with a high near-infrared light absorbance can realize bimodal imaging-guided photothermal therapy of cancer. Furthermore, the labeled ^99m Tc significantly enhances the cell uptake of M-CuS-PEG by inducing G2/M arrest of the cell cycle, further improving the photothermal antitumor effect, which is positively correlated with endocytosis of the photothermal conversion reagent. Therefore, a novel cancer-targeted theranostic nanoplatform is developed and it is revealed that the labeled ^99m Tc can not only guide but also amplify the subsequent therapy of cancer, providing a conceptual strategy for cancer theranostics with a high biosafety.

Hyaluronic acid-based nanogels derived from multicomponent self-assembly for imaging-guided chemo-photodynamic cancer therapy

Multifunctional theranostic nanoplatforms integrated of imaging function, multi-modality therapy, stimuli-responsiveness, and targeted delivery are of highly desirable attributes in achieving precise medicine. However, preparation of multifunctional nanoplatforms often involves laborious, multiple steps and inevitably utilizes low-biocompatible or non-functional components. Herein we report a facile, one-step self-assembly strategy to fabricate hyaluronic acid (HA)-based multifunctional tumor theranostic nanoplatform by employing magnetic resonance imaging (MRI) agent Mn2+ as a reversible crosslink agent for histidine-grafted HA, along with simultaneously loading chemotherapeutic agent doxorubicin hydrochloride (DOX) and photodynamic therapy agent chlorin e6, to realize MRI-guided targeted chemo-photodynamic cancer therapy. The targeted delivery and stimuli-responsive payload release were demonstrated in vitro and in vivo. Furthermore, the combined chemo-photodynamic therapy of the nanoassembly dramatically improved the cancer therapeutic outcome, in comparison with that of free DOX and nanoplatform solely loaded DOX in a melanoma bearing mice. Our one step assemble strategy is of great potential in clinic transformation.

Photostability enhancement of silica-coated gold nanostars for photoacoustic imaging guided photothermal therapy

Gold nanostars (GNSs) are promising contrast agents for simultaneous photothermal therapy and photoacoustic imaging (PAI) owing to their excellent photothermal conversion efficiency. However, GNSs are easily reshaped under transient high-intensity laser pulses, which can cause a rapid shift in the light absorption peak, resulting in a decrease in both therapeutic and monitoring effects. In this work, we synthesized GNSs without toxic surfactants and coated them with a silica shell to retain their shape, thus maintaining their photostability. The excellent performance of these silica-coated GNSs was verified through both in vitro and in vivo PAI experiments. The silica-coated GNSs exhibited a threefold improvement in photoacoustic stability, as compared with the non-coated GNSs. The proposed silica coating method for GNSs was found to improve the photostability of GNSs, making them efficient, safe, and reliable nanoparticles for PAI.

Optothermal properties of plasmonic inorganic nanoparticles for photoacoustic applications

Plasmonic systems are becoming a favourable alternative to dye molecules in the generation of photoacoustic signals for spectroscopy and imaging. In particular, inorganic nanoparticles are appealing because of their versatility. In fact, as the shape, size and chemical composition of nanoparticles are directly correlated with their plasmonic properties, the excitation wavelength can be tuned to their plasmon resonance by adjusting such traits. This feature enables an extensive spectral range to be covered. In addition, surface chemical modifications can be performed to provide the nanoparticles with designed functionalities, e.g., selective affinity for specific macromolecules. The efficiency of the conversion of absorbed photon energy into heat, which is the physical basis of the photoacoustic signal, can be accurately determined by photoacoustic methods. This review contrasts studies that evaluate photoconversion in various kinds of nanomaterials by different methods, with the objective of facilitating the researchers' choice of suitable plasmonic nanoparticles for photoacoustic applications.

A Photoacoustic Contrast Agent for miR-21 via NIR Fluorescent Hybridization Chain Reaction

Nucleic acids are well-established biomarkers of cancer with immense value in diagnostics and basic research. However, strategies to monitor these species in tissue can be challenging due to the need for amplification of imaging signal from low analyte concentrations with high specificity. Photoacoustic (PA) imaging is gaining traction for molecular imaging of proteins, small biomolecules, and nucleic acids by coupling pulsed near-infrared (NIR) excitation with broadband acoustic detection. This work introduces a PA nucleic acid contrast agent that harnesses NIR fluorophore and quencher-tagged hybridization chain reaction (HCR) for signal amplification. This HCR probe was designed to enable contact quenching between NIR dye-quencher pairs by coercing their direct alignment when miR-21, a microRNA cancer biomarker, is detected. The probe demonstrated a ratiometric PA limit of detection of 148 pM miR-21, sequence specificity against one- and two-base mutations, and selectivity over other microRNAs. It was further tested in live human ovarian cancer (SKOV3) and noncancerous (HEK 293T) cells to exemplify in situ PA activation based on differences in endogenous miR-21 regulation (p = 0.0002). The probe was lastly tested in tissue mimicking phantoms to exemplify sustained contrast in centimeter-range depths and 85.3% photostability after 15 min of laser irradiation. The probe's miR-21-specific activation and its ability to maintain contrast in biologically relevant absorbing and scattering media support its consideration for live-cell PA microscopy and potential cancer diagnostics. Results from this probe also underscore the combined detection power between ratiometric PA signaling and strand amplification for more sensitive DNA-based PA sensors.

Defect-engineered porphyrinic metal-organic framework nanoparticles for targeted multimodal cancer phototheranostics

Defect-engineered porphyrinic MOF nanoparticles were fabricated with an in situ one-pot protocol using cypate as the co-ligand and modulator. This multifunctional nanoplatform integrated the photothermal and multimodal imaging properties of cypate with the photodynamic effects of porphyrins, thus achieving targeted multimodal cancer phototheranostics after folic acid modification.

Activatable Carbocyanine Dimers for Photoacoustic and Fluorescent Detection of Protease Activity

Activatable contrast agents are of ongoing research interest because they offer low background and high specificity to the imaging target. Engineered sensitivity to protease activity is particularly desirable because proteases are critical biomarkers in cancer, infectious disease, inflammatory disorders, and so forth. Herein, we developed and characterized a set of peptide-linked cyanine conjugates for dual-modal detection of protease activity via photoacoustic (PA) and fluorescence imaging. The peptide-dye conjugates were designed to undergo contact quenching via intramolecular dimerization and contained n dyes (n = 2, 3, or 4) with n - 1 cleavable peptide substrates. The absorption peaks of the conjugates were blue-shifted 50 nm relative to the free dye and had quenched fluorescence. This effect was sensitive to solvent polarity and could be reversed by solvent switching from water to dimethyl sulfoxide. Employing trypsin as a model protease, we observed a 2.5-fold recovery of the peak absorbance, 330-4600-fold fluorescent enhancement, and picomolar detection limits following proteolysis. The dimer probe was further characterized for PA activation. Proteolysis released single dye-peptide fragments that produced a 5-fold PA enhancement through the increased absorption at 680 nm with nanomolar sensitivity to trypsin. The peptide substrate could also be tuned for protease selectivity; as a proof-of-concept, we detected the main protease (M^pro) associated with the viral replication in SARS-CoV-2 infection. Last, the activated probe was imaged subcutaneously in mice and signal was linearly correlated to the cleaved probe. Overall, these results demonstrate a tunable scaffold for the PA molecular imaging of protease activity with potential value in areas such as disease monitoring, tumor imaging, intraoperative imaging, in vitro diagnostics, and point-of-care sensing.

Emerging contrast agents for multispectral optoacoustic imaging and their biomedical applications

Optoacoustic imaging is a hybrid biomedical imaging modality which collects ultrasound waves generated via photoexciting contrast agents in tissues and produces images of high resolution and penetration depth. As a functional optoacoustic imaging technique, multispectral optoacoustic imaging, which can discriminate optoacoustic signals from different contrast agents by illuminating samples with multi-wavelength lasers and then processing the collected data with specific algorithms, assists in the identification of a specific contrast agent in target tissues and enables simultaneous molecular and physiological imaging. Moreover, multispectral optoacoustic imaging can also generate three-dimensional images for biological tissues/samples with high resolution and thus holds great potential in biomedical applications. Contrast agents play essential roles in optoacoustic imaging, and they have been widely explored and applied as probes and sensors in recent years, leading to the emergence of a variety of new contrast agents. In this review, we aim to summarize the latest advances in emerging contrast agents, especially the activatable ones which can respond to specific biological stimuli, as well as their preclinical and clinical applications. We highlight their design strategies, discuss the challenges and prospects in multispectral optoacoustic imaging, and outline the possibility of applying it in clinical translation and public health services using synthetic contrast agents.

In vivo noninvasive preclinical tumor hypoxia imaging methods: a review

Tumors exhibit areas of decreased oxygenation due to malformed blood vessels. This low oxygen concentration decreases the effectiveness of radiation therapy, and the resulting poor perfusion can prevent drugs from reaching areas of the tumor. Tumor hypoxia is associated with poorer prognosis and disease progression, and is therefore of interest to preclinical researchers. Although there are multiple different ways to measure tumor hypoxia and related factors, there is no standard for quantifying spatial and temporal tumor hypoxia distributions in preclinical research or in the clinic. This review compares imaging methods utilized for the purpose of assessing spatio-temporal patterns of hypoxia in the preclinical setting. Imaging methods provide varying levels of spatial and temporal resolution regarding different aspects of hypoxia, and with varying advantages and disadvantages. The choice of modality requires consideration of the specific experimental model, the nature of the required characterization and the availability of complementary modalities as well as immunohistochemistry.

A pH-sensitive nanoagent self-assembled from a highly negatively-charged phthalocyanine with excellent biosafety for photothermal therapy

Photothermal therapy (PTT) is a promising strategy for cancer treatment. However, the development of highly efficient photothermal agents with excellent biosafety, particularly with low liver retention, is very meaningful for clinical applications, but it is also challenging. We herein prepared a pH-sensitive nanoagent (NanoPc3) by the self-assembly of a zinc(ii) phthalocyanine substituted with hexadeca-sulphonates linked by hydrazone bonds for photoacoustic imaging and PTT. Due to the highly negative surface potential (-30.80 mV in water), NanoPc3 could effectively escape the phagocytosis of the reticuloendothelial system and be rapidly cleared from normal tissues, leading to little accumulation in the liver and excellent biosafety. The highly negatively-charged NanoPc3 changed into nearly neutral nanoparticles (NanoPc3H) under slightly acidic conditions, resulting in enhanced cellular uptake and retention time in tumor tissues. Moreover, the tumor of H22 tumor-bearing mice treated with NanoPc3 almost disappeared, suggesting an outstanding photothermal antitumor effect. NanoPc3 also hardly showed skin phototoxicity under irradiation. Its excellent antitumor effect and biosafety make NanoPc3 highly promising in clinical applications. This work will provide a new strategy for the design of tumor-targeted photothermal nanoagents with high biosafety.

Aggregation-Enhanced Photoluminescence and Photoacoustics of Atomically Precise Gold Nanoclusters in Lipid Nanodiscs (NANO2)

The authors designed a structurally stable nano-in-nano (NANO2) system highly capable of bioimaging via an aggregation-enhanced NIR excited emission and photoacoustic response achieved based on atomically precise gold nanoclusters protected by linear thiolated ligands [Au25(SC n H2n+1)18, n = 4-16] encapsulated in discoidal phospholipid bicelles through a one-pot synthesis. The detailed morphological characterization of NANO2 is conducted using cryogenic transmission electron microscopy, small/wide angle X-ray scattering with the support of molecular dynamics simulations, providing information on the location of Au nanoclusters in NANO2. The photoluminescence observed for NANO2 is 20-60 times more intense than that of the free Au nanoclusters, with both excitation and emission wavelengths in the near-infrared range, and the photoacoustic signal is more than tripled. The authors attribute this newly discovered aggregation-enhanced photoluminescence and photoacoustic signals to the restriction of intramolecular motion of the clusters' ligands. With the advantages of biocompatibility and high cellular uptake, NANO2 is potentially applicable for both in vitro and in vivo imaging, as the authors demonstrate with NIR excited emission from in vitro A549 human lung and the KB human cervical cancer cells.

Real-Time Quantification of Cartilage Degeneration by GAG-Targeted Cationic Nanoparticles for Efficient Therapeutic Monitoring in Living Mice

One of the characterizations of degenerative cartilage disease is the progressive loss of glycosaminoglycans (GAGs). The real-time imaging method to quantify GAGs is of great significance for the biochemical analysis of cartilage and diagnosis and therapeutic monitoring of cartilage degeneration in vivo. To this end, a cationic photoacoustic (PA) contrast agent, poly-l-lysine melanin nanoparticles (PLL-MNPs), specifically targeting anionic GAGs was developed in this study to investigate whether it can image cartilage degeneration. PLL-MNP assessed GAG depletion by Chondroitinase ABC in vitro rat cartilage and intact ex vivo mouse knee joint. A papain-induced cartilage degenerative mice model was used for in vivo photoacoustic imaging (PAI). Oral cartilage supplement glucosamine sulfate was intragastrically administered for mice cartilage repair and the therapeutic efficacy was monitored by PLL-MNP-enhanced PAI. Histologic findings were used to further confirm PAI results. In vitro results revealed that the PLL-MNPs not only had a high binding ability with GAGs but also sensitively monitored GAG content changes by PAI. The PA signal was gradually weakened along with the depletion of GAGs in cartilage. Particularly, PLL-MNPs depicted the cartilage structure and the distribution of GAGs was demonstrated in PA images in ex vivo joints. Compared with the normal joint, a lower signal intensity was detected from degenerative joint at 3 weeks after papain injection, suggesting an early diagnosis of cartilage lesion by PLL-MNPs. Importantly, this PA-enhanced nanoprobe was suitable for monitoring in vivo efficacy of glucosamine sulfate, which effectively blocked cartilage degradation in a high dose manner. In vivo imaging findings correlated well with histological examinations. PLL-MNPs provided sensitive visualization of cartilage degeneration and promising monitoring of therapeutic response in living subjects.

Photoacoustic Imaging and Photothermal Therapy of Semiconducting Polymer Nanoparticles: Signal Amplification and Second Near-Infrared Construction

Photoacoustic (PA) imaging and photothermal therapy (PTT) have attracted extensive attention in disease diagnosis and treatment. Although many exogenous contrast agents have been developed for PA imaging and PTT, the design guidelines to amplify their imaging and therapy performances remain challenging and are highly demanded. Semiconducting polymer nanoparticles (SPNs) composed of polymers with π-electron delocalized backbones can be designed to amplify their PA imaging and PTT performance, because of their clear structure-property relation and versatility in modifying their molecular structures to tune their photophysical properties. This review summarizes the recent advances in the photoacoustic imaging and photothermal therapy applications of semiconducting polymer nanoparticles with a focus on signal amplification and second near-infrared (NIR-II, 1000-1700 nm) construction. The strategies such as structure-property screening, fluorescence quenching, accelerated heat dissipation, and size-dependent heat dissipation are first discussed to amplify the PA brightness of SPNs for in vivo PA. The molecular approaches to shifting the absorption of SPNs for NIR-II PA imaging and PTT are then introduced so as to improve the tissue penetration depth for diagnosis and therapy. At last, current challenges and perspectives of SPNs in the field of imaging and therapy are discussed.

Acceptor Engineering for Optimized ROS Generation Facilitates Reprogramming Macrophages to M1 Phenotype in Photodynamic Immunotherapy

Reprogramming tumor-associated macrophages to an antitumor M1 phenotype by photodynamic therapy is a promising strategy to overcome the immunosuppression of tumor microenvironment for boosted immunotherapy. However, it remains unclear how the reactive oxygen species (ROS) generated from type I and II mechanisms, relate to the macrophage polarization efficacy. Herein, we design and synthesize three donor-acceptor structured photosensitizers with varied ROS-generating efficiencies. Surprisingly, we discovered that the extracellular ROS generated from type I mechanism are mainly responsible for reprogramming the macrophages from a pro-tumor type (M2) to an anti-tumor state (M1). In vivo experiments prove that the photosensitizer can trigger photodynamic immunotherapy for effective suppression of the tumor growth, while the therapeutic outcome is abolished with depleted macrophages. Overall, our strategy highlights the designing guideline of macrophage-activatable photosensitizers.

Applications of indocyanine green in brain tumor surgery: review of clinical evidence and emerging technologies

Indocyanine green (ICG) is a water-soluble dye that was approved by the FDA for biomedical purposes in 1956. Initially used to measure cardiocirculatory and hepatic functions, ICG's fluorescent properties in the near-infrared (NIR) spectrum soon led to its application in ophthalmic angiography. In the early 2000s, ICG was formally introduced in neurosurgery as an angiographic tool. In 2016, the authors' group pioneered a novel technique with ICG named second-window ICG (SWIG), which involves infusion of a high dose of ICG (5.0 mg/kg) in patients 24 hours prior to surgery. To date, applications of SWIG have been reported in patients with high-grade gliomas, meningiomas, brain metastases, pituitary adenomas, craniopharyngiomas, chordomas, and pinealomas.The applications of ICG have clearly expanded rapidly across different specialties since its initial development. As an NIR fluorophore, ICG has advantages over other FDA-approved fluorophores, all of which are currently in the visible-light spectrum, because of NIR fluorescence's increased tissue penetration and decreased autofluorescence. Recently, interest in the latest applications of ICG in brain tumor surgery has grown beyond its role as an NIR fluorophore, extending into shortwave infrared imaging and integration into nanotechnology. This review aims to summarize reported clinical studies on ICG fluorescence-guided surgery of intracranial tumors, as well as to provide an overview of the literature on emerging technologies related to the utility of ICG in neuro-oncological surgeries, including the following aspects: 1) ICG fluorescence in the NIR-II window; 2) ICG for photoacoustic imaging; and 3) ICG nanoparticles for combined diagnostic imaging and therapy (theranostic) applications.

Challenges and opportunities for small volumes delivery into the skin

Each individual's skin has its own features, such as strength, elasticity, or permeability to drugs, which limits the effectiveness of one-size-fits-all approaches typically found in medical treatments. Therefore, understanding the transport mechanisms of substances across the skin is instrumental for the development of novel minimal invasive transdermal therapies. However, the large difference between transport timescales and length scales of disparate molecules needed for medical therapies makes it difficult to address fundamental questions. Thus, this lack of fundamental knowledge has limited the efficacy of bioengineering equipment and medical treatments. In this article, we provide an overview of the most important microfluidics-related transport phenomena through the skin and versatile tools to study them. Moreover, we provide a summary of challenges and opportunities faced by advanced transdermal delivery methods, such as needle-free jet injectors, microneedles, and tattooing, which could pave the way to the implementation of better therapies and new methods.

Pd nanoparticles as a plasmonic material: synthesis, optical properties and applications

This review provides an overview of current progress in Pd nanoparticles supporting localized surface plasmon resonance and their applications. We begin by analyzing briefly the optical properties of Pd putting particular focus on outlining the origin of its size- and shape-dependent LSPR, high refractive index sensitivity, and high absorption contribution. The differences in the optical behavior with Au and Ag, the primary plasmonic materials, are highlighted. The main strategies to synthesize Pd nanoparticles, pure or hybrid, with well-defined optical properties are then reviewed. In this section, we include only those works that carry out the study of the optical properties of the nanoparticles. The applications of plasmonic Pd nanoparticles are also discussed in detail. This review is concluded with a section devoted to the future perspectives highlighting the most relevant challenges to be addressed to take Pd nanoparticles from the laboratory to real applications.

Ceria-based nanotheranostic agent for rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease that affects 1-2% of the human population worldwide, and effective therapies with targeted delivery for local immune suppression have not been described. We address this problem by developing a novel theranostic nanoparticle for RA and assessed its therapeutic and targeting effects under image-guidance. Methods: Albumin-cerium oxide nanoparticles were synthesized by the biomineralization process and further conjugated with near-infrared, indocyanine green (ICG) dye. Enzymatic-like properties and reactive oxygen species (ROS) scavenging activities, as well as the ability to reprogram macrophages, were determined on a monocyte cell line in culture. The therapeutic effect and systemic targeting potential were evaluated in collagen-induced arthritis (CIA) mouse model using optical/optoacoustic tomographic imaging. Results: Small nanotheranostics with narrow size distribution and high colloidal stability were fabricated and displayed high ROS scavenging and enzymatic-like activity, as well as advanced efficacy in a converting pro-inflammatory macrophage phenotype into anti-inflammatory phenotype. When administrated into affected animals, these nanoparticles accumulated in inflamed joints and revealed a therapeutic effect similar to the gold-standard therapy for RA, methotrexate. Conclusions: The inflammation-targeting, inherent contrast and therapeutic activity of this new albumin-cerium oxide nanoparticle may make it a relevant agent for assessing severity in RA, and other inflammatory diseases, and controlling inflammation with image-guidance. The design of these nanotheranostics will enable potential clinical translation as systemic therapy for RA.

Photoacoustic Imaging as a Tool for Assessing Hair Follicular Organization

Follicular unit extraction (FUE) and follicular unit transplantation (FUT) account for 99% of hair transplant procedures. In both cases, it is important for clinicians to characterize follicle density for treatment planning and evaluation. The existing gold-standard is photographic examination. However, this approach is insensitive to subdermal hair and cannot identify follicle orientation. Here, we introduce a fast and non-invasive imaging technique to measure follicle density and angles across regions of varying density. We first showed that hair is a significant source of photoacoustic signal. We then selected regions of low, medium, and high follicle density and showed that photoacoustic imaging can measure the density of follicles even when they are not visible by eye. We performed handheld imaging by sweeping the transducer across the imaging area to generate 3D images via maximum intensity projection. Background signal from the dermis was removed using a skin tracing method. Measurement of follicle density using photoacoustic imaging was highly correlated with photographic determination (R² = 0.96). Finally, we measured subdermal follicular angles-a key parameter influencing transection rates in FUE.

Feasibility Study of Precise Balloon Catheter Tracking and Visualization with Fast Photoacoustic Microscopy

Correct guiding of the catheter is a critical issue in almost all balloon catheter applications, including arterial stenosis expansion, coronary arterial diseases, and gastrointestinal tracking. To achieve safe and precise guiding of the balloon catheter, a novel imaging method with high-resolution, sufficient depth of penetration, and real-time display is required. Here, we present a new balloon catheter guiding method using fast photoacoustic microscopy (PAM) technique for precise balloon catheter tracking and visualization as a feasibility study. We implemented ex vivo and in vivo experiments with three different medium conditions of balloon catheter: no air, air, and water. Acquired cross-sectional, maximum amplitude projection (MAP), and volumetric 3D PAM images demonstrated its capability as a new imaging guiding tool for balloon catheter tracking and visualization.

Photoacoustic imaging for surgical guidance: Principles, applications, and outlook

Minimally invasive surgeries often require complicated maneuvers and delicate hand-eye coordination and ideally would incorporate "x-ray vision" to see beyond tool tips and underneath tissues prior to making incisions. Photoacoustic imaging has the potential to offer this feature but not with ionizing x-rays. Instead, optical fibers and acoustic receivers enable photoacoustic sensing of major structures-such as blood vessels and nerves-that are otherwise hidden from view. This imaging process is initiated by transmitting laser pulses that illuminate regions of interest, causing thermal expansion and the generation of sound waves that are detectable with conventional ultrasound transducers. The recorded signals are then converted to images through the beamforming process. Photoacoustic imaging may be implemented to both target and avoid blood-rich surgical contents (and in some cases simultaneously or independently visualize optical fiber tips or metallic surgical tool tips) in order to prevent accidental injury and assist device operators during minimally invasive surgeries and interventional procedures. Novel light delivery systems, counterintuitive findings, and robotic integration methods introduced by the Photoacoustic & Ultrasonic Systems Engineering Lab are summarized in this invited Perspective, setting the foundation and rationale for the subsequent discussion of the author's views on possible future directions for this exciting frontier known as photoacoustic-guided surgery.

[Surgery 4.0-are we ready?]

The increasing networking of data systems in medicine is not only leading to modern interdisciplinarity in the sense of cooperation between different medical departments, but also poses new challenges regarding the building and room infrastructure. The surgical operating room of the future expands or augments its reality, away from the pure building characteristics, towards an intelligent and communicative space platform. The building infrastructure (operating theatre) serves as sensor and actuator. Thus, it is possible to inform about missing diagnostics as well as to register them directly in the contextualization of the planned surgical intervention or to integrate them into the processes. Integrated operating theatres represent a comprehensive computer platform based on a corresponding system architecture with software-based protocols. An underlying modular system consisting of various modules for image acquisition and analysis, interaction and visualization supports the integration and merging of heterogeneous data that are generated in a hospital operation. Integral building data (e.g., air conditioning, lighting control, device registration) are merged with patient-related data (age, type of illness, concomitant diseases, existing diagnostic CT and MRI images). New systems coming onto the market, as well as already existing systems will have to be measured by the extent to which they will be able to guarantee this integration of information-similar to the development from mobile phone to smartphone. Cost reduction should not be the only legitimizing argument for the market launch, but the vision of a new quality of surgical perception and action.

Optimizing Irradiation Geometry in LED-Based Photoacoustic Imaging with 3D Printed Flexible and Modular Light Delivery System

Photoacoustic (PA) imaging–a technique combining the ability of optical imaging to probe functional properties of the tissue and deep structural imaging ability of ultrasound–has gained significant popularity in the past two decades for its utility in several biomedical applications. More recently, light-emitting diodes (LED) are being explored as an alternative to bulky and expensive laser systems used in PA imaging for their portability and low-cost. Due to the large beam divergence of LEDs compared to traditional laser beams, it is imperative to quantify the angular dependence of LED-based illumination and optimize its performance for imaging superficial or deep-seated lesions. A custom-built modular 3-D printed hinge system and tissue-mimicking phantoms with various absorption and scattering properties were used in this study to quantify the angular dependence of LED-based illumination. We also experimentally calculated the source divergence of the pulsed-LED arrays to be 58° ± 8°. Our results from point sources (pencil lead phantom) in non-scattering medium obey the cotangential relationship between the angle of irradiation and maximum PA intensity obtained at various imaging depths, as expected. Strong dependence on the angle of illumination at superficial depths (−5°/mm at 10 mm) was observed that becomes weaker at intermediate depths (−2.5°/mm at 20 mm) and negligible at deeper locations (−1.1°/mm at 30 mm). The results from the tissue-mimicking phantom in scattering media indicate that angles between 30–75° could be used for imaging lesions at various depths (12 mm–28 mm) where lower LED illumination angles (closer to being parallel to the imaging plane) are preferable for deep tissue imaging and superficial lesion imaging is possible with higher LED illumination angles (closer to being perpendicular to the imaging plane). Our results can serve as a priori knowledge for the future LED-based PA system designs employed for both preclinical and clinical applications.

Physical triggering strategies for drug delivery

Physically triggered systems hold promise for improving drug delivery by enhancing the controllability of drug accumulation and release, lowering non-specific toxicity, and facilitating clinical translation. Several external physical stimuli including ultrasound, light, electric fields and magnetic fields have been used to control drug delivery and they share some common features such as spatial targeting, spatiotemporal control, and minimal invasiveness. At the same time, they possess several distinctive features in terms of interactions with biological entities and/or the extent of stimulus response. Here, we review the key advances of such systems with a focus on discussing their physical mechanisms, the design rationales, and translational challenges.

Multiplexed whole-animal imaging with reversibly switchable optoacoustic proteins

We introduce two photochromic proteins for cell-specific in vivo optoacoustic (OA) imaging with signal unmixing in the temporal domain. We show highly sensitive, multiplexed visualization of T lymphocytes, bacteria, and tumors in the mouse body and brain. We developed machine learning-based software for commercial imaging systems for temporal unmixed OA imaging, enabling its routine use in life sciences.

Yolk-shell nanovesicles endow glutathione-responsive concurrent drug release and T1 MRI activation for cancer theranostics

The effort of incorporating therapeutic drugs with imaging agents has been one of the mainstreams of nanomedicine, which holds great promise in cancer treatment in terms of monitoring therapeutic drug activity and evaluating prognostic index. However, it is still technically challenging to develop nanomedicine endowing a spatiotemporally controllable mechanism of drug release and activatable imaging capability. Here, we developed a yolk-shell type of GSH-responsive nanovesicles (NVs) in which therapeutic drug (Doxorubicin, DOX) and magnetic resonance imaging (MRI) contrast agent (ultrasmall paramagnetic iron oxide nanoparticles, USPIO NPs) formed complexes (denoted as USD) and were encapsulated inside the NVs. The formation of USD complexes is mediated by both the electrostatic adsorption between DOX and poly(acrylic acid) (PAA) polymers and the DOX-iron coordination effect on USPIO NPs. The obtained USD NVs showed a unique yolk-shell structure with restrained drug activity and quenched T1 MRI contrast ability which, on the other hand, can respond to glutathione (GSH) and lead to drug release and T1 contrast activation in a spatiotemporally concurrent manner. Furthermore, the USD NVs exhibited great potential to kill HCT116 cancer cells in vitro and effectively inhibit the tumor growth in vivo. This study may shed light on the design of sophisticated nanotheranostics in precision nanomedicine.

TME-activatable theranostic nanoplatform with ATP burning capability for tumor sensitization and synergistic therapy

Adenosine triphosphate (ATP), as a key substance for regulating tumor progression in the tumor microenvironemnt (TME), is an emerging target for tumor theranostics. Herein, we report a minimalist but versatile nanoplatform with simultaneously TME-responsive drug release, TME-enhanced imaging, ATP-depletion sensitized chemotherapy and photothermal therapy for intelligent tumor theranostics.

Methods: The Fe³⁺ and tannic acid (TA) coordination were self-deposited on doxorubicin (Dox) in a facile method to prepare Dox-encapsulated nanoparticles (DFTNPs).

Results: When irradiated by a near infrared laser, the DFTNPs could elevate the temperature in the tumor region efficiently. Subsequently, the Dox could be released by the disassembly of Fe³⁺/TA in the TME to initiate chemotherapy. Particularly, the smart nanoagent not only enabled ATP-depletion and enhanced the therapeutic effect of chemotherapy, but also acted as photothermal transduction agent for photothermal therapy. Moreover, the nanoagent also acted as T₁-weighted MR imaging,photoacoustic imaging and photothermal imaging contrast agent. The mice treated by DFTNPs plus laser showed a complete tumor eradication in 14d observation.

Conclusion: This as-prepared versatile nanoplatform offers new insights toward the application of smart nanoagents for improved tumor theranostics.

Photoacoustic Imaging Probes Based on Tetrapyrroles and Related Compounds

Photoacoustic imaging (PAI) is a rapidly evolving field in molecular imaging that enables imaging in the depths of ultrasound and with the sensitivity of optical modalities. PAI bases on the photoexcitation of a chromophore, which converts the absorbed light into thermal energy, causing an acoustic pressure wave that can be captured with ultrasound transducers, in generating an image. For in vivo imaging, chromophores strongly absorbing in the near-infrared range (NIR; > 680 nm) are required. As tetrapyrroles have a long history in biomedical applications, novel tetrapyrroles and inspired mimics have been pursued as potentially suitable contrast agents for PAI. The goal of this review is to summarize the current state of the art in PAI applications using tetrapyrroles and related macrocycles inspired by it, highlighting those compounds exhibiting strong NIR-absorption. Furthermore, we discuss the current developments of other absorbers for in vivo photoacoustic (PA) applications.

CARS-imaging guidance for fs-laser ablation precision surgery

Due to ageing populations the number of tumors is increasing worldwide. Successful surgical treatment requires complete resection of tumors to reduce recurrence rates. To reach this goal, novel methods combining in vivo tumor and tumor margin detection with low invasive precision surgical tools are needed. Coherent anti-Stokes Raman scattering (CARS) imaging is a highly promising optical tool for visualizing tumors based on characteristic changes in tissue morphology and molecular composition, while fs-laser ablation is to date the most precise surgical tool established in ophthalmology. In this contribution, CARS imaging has been combined with fs-laser ablation as a new approach for image-guided precision surgery for the first time. CARS guided fs-ablation has been applied to ablate brain, liver, skin, muscular and vascular tissues with μm-precision using sub-100 fs pulses of μJ level. We demonstrate superior imaging performance and contrast as well as detection of tissue margins by coherent Raman microscopy in comparison to laser reflectance imaging. The combination of CARS-image-guided tissue ablation is a promising tool for minimally invasive surgeries particularly in the vicinity of functional structures in the future.

Efficient photoacoustic imaging using indocyanine green (ICG) loaded functionalized mesoporous silica nanoparticles

Photoacoustic (PA) imaging is gaining momentum due to its greater depth of field, low background, and 3D imaging capabilities. However, traditional PA imaging agents (e.g. dyes, quantum dots, etc.) are usually unstable in plasma and bind to serum proteins, and thus cleared rapidly. Because of this, the nanoparticle encapsulation of PA imaging agents is becoming increasingly popular. Therefore, the rational design of carrier nanoparticles for this purpose is necessary for strong imaging signal intensity, high biosafety, and precise targeting. Herein, we systematically evaluate the influence of the chemical and physical surface functionalization of mesoporous silica nanoparticles (MSNs) on the photo-stability, loading, release, and photoacoustic (PA) signal strength of the FDA approved small molecule contrast agent, indocyanine green (ICG). Chemical functionalization involved the modification of MSNs with silanes having amine (NH2) or phosphonate (PO3) terminal groups, whereas physical modifications were performed by capping the ICG loaded MSNs with lipid bilayer (LB) or layer-by-layer (LBL) polyelectrolyte coatings. The NH2-MSNs display the highest ICG mass loading capacity (16.5 wt%) with a limited release of ICG (5%) in PBS over 48 h, while PO3-MSNs only loaded ICG around 3.5 wt%. The physically modified MSNs (i.e. LBMSNs and LBLMSNs) were vacuum loaded resulting in approximately 9 wt% loading and less than 10% ICG release in 48 h. Pure ICG was highly photo-unstable and showed 20% reduction in photoluminescence (PL) within 3 h of exposure to 800 nm, while the ICG loaded onto functionalized MSNs did not photo-degrade. Among the tested formulations, NH2-MSNs and LBLMSNs presented 4-fold in vitro PA signal intensity enhancement at a 200 μg mL-1 equivalent ICG dose. Similar to the in vitro PA imaging, NH2-MSNs and LBLMSNs performed the best when subcutaneously injected into mouse cadavers with 1.29- and 1.43-fold PA signal enhancement in comparison to the pure ICG, respectively.

Real-time and multimodality image-guided intelligent HIFU therapy for uterine fibroid

Rationale: High-intensity focused ultrasound (HIFU) therapy represents a noninvasive surgical approach to treat uterine fibroids. The operation of HIFU therapy relies on the information provided by medical images. In current HIFU therapy, all operations such as positioning of the lesion in magnetic resonance (MR) and ultrasound (US) images are manually performed by specifically trained doctors. Manual processing is an important limitation of the efficiency of HIFU therapy. In this paper, we aim to provide an automatic and accurate image guidance system, intelligent diagnosis, and treatment strategy for HIFU therapy by combining multimodality information.

Methods: In intelligent HIFU therapy, medical information and treatment strategy are automatically processed and generated by a real-time image guidance system. The system comprises a novel multistage deep convolutional neural network for preoperative diagnosis and a nonrigid US lesion tracking procedure for HIFU intraoperative image-assisted treatment. In the process of intelligent therapy, the treatment area is determined from the autogenerated lesion area. Based on the autodetected treatment area, the HIFU foci are distributed automatically according to the treatment strategy. Moreover, an image-based unexpected movement warning and other physiological monitoring are used during the intelligent treatment procedure for safety assurance.

Results: In the experiment, we integrated the intelligent treatment system on a commercial HIFU treatment device, and eight clinical experiments were performed. In the clinical validation, eight randomly selected clinical cases were used to verify the feasibility of the system. The results of the quantitative experiment indicated that our intelligent system met the HIFU clinical tracking accuracy and speed requirements. Moreover, the results of simulated repeated experiments confirmed that the autodistributed HIFU focus reached the level of intermediate clinical doctors. Operations performed by junior- or middle-level operators with the assistance of the proposed system can reach the level of operation performed by senior doctors. Various experiments prove that our proposed intelligent HIFU therapy process is feasible for treating common uterine fibroid cases.

Conclusion: We propose an intelligent HIFU therapy for uterine fibroid which integrates multiple medical information processing procedures. The experiment results demonstrated that the proposed procedures and methods can achieve monitored and automatic HIFU diagnosis and treatment. This research provides a possibility for intelligent and automatic noninvasive therapy for uterine fibroid.

miR-216a-targeting theranostic nanoparticles promote proliferation of insulin-secreting cells in type 1 diabetes animal model

Aberrant expression of miRNAs in pancreatic islets is closely related to the development of type 1 diabetes (T1D). The aim of this study was to identify key miRNAs dysregulated in pancreatic islets during T1D progression and to develop a theranostic approach to modify their expression using an MRI-based nanodrug consisting of iron oxide nanoparticles conjugated to miRNA-targeting oligonucleotides in a mouse model of T1D. Isolated pancreatic islets were derived from NOD mice of three distinct age groups (3, 8 and 18-week-old). Total RNA collected from cultured islets was purified and global miRNA profiling was performed with 3D-Gene global miRNA microarray mouse chips encompassing all mouse miRNAs available on the Sanger miRBase V16. Of the miRNAs that were found to be differentially expressed across three age groups, we identified one candidate (miR-216a) implicated in beta cell proliferation for subsequent validation by RT-PCR. Alterations in miR-216a expression within pancreatic beta cells were also examined using in situ hybridization on the frozen pancreatic sections. For in vitro studies, miR-216a mimics/inhibitors were conjugated to iron oxide nanoparticles and incubated with beta cell line, βTC-6. Cell proliferation marker Ki67 was evaluated. Expression of the phosphatase and tensin homolog (PTEN), which is one of the direct targets of miR-216a, was analyzed using western blot. For in vivo study, the miR-216a mimics/inhibitors conjugated to the nanoparticles were injected into 12-week-old female diabetic Balb/c mice via pancreatic duct. The delivery of the nanodrug was monitored by in vivo MRI. Blood glucose of the treated mice was monitored post injection. Ex vivo histological analysis of the pancreatic sections included staining for insulin, PTEN and Ki67. miRNA microarray demonstrated that the expression of miR-216a in the islets from NOD mice significantly changed during T1D progression. In vitro studies showed that treatment with a miR-216a inhibitor nanodrug suppressed proliferation of beta cells and increased the expression of PTEN, a miR-216a target. In contrast, introduction of a mimic nanodrug decreased PTEN expression and increased beta cell proliferation. Animals treated in vivo with a mimic nanodrug had higher insulin-producing functionality compared to controls. These observations were in line with downregulation of PTEN and increase in beta cell proliferation in that group. Our studies demonstrated that miR-216a could serve as a potential therapeutic target for the treatment of diabetes. miR-216a-targeting theranostic nanodrugs served as exploratory tools to define functionality of this miRNA in conjunction with in vivo MR imaging.

Evaluation of visible NIR-I and NIR-II light penetration for photoacoustic imaging in rat organs

In this study, we evaluate the penetration capability of light in visible, near-infrared-I (NIR-I) and near-infrared-II (NIR-II) optical windows for photoacoustic macroscale imaging inside 9 biological tissues with three typical penetration depths. An acoustic resolution photoacoustic microscopy is designed to guarantee the consistent experiment conditions except excitation wavelength. Experimental results show that short NIR-II (1000-1150 nm) shows the best performance inside kidney, spleen and liver tissues at all depths, while NIR-I (700-1000 nm) works better for muscle, stomach, heart and brain tissues, especially in deep imaging. This study proposes the optimal selection of illumination wavelengths for photoacoustic macroscale imaging in rat organs, which enables the best signal-to-noise ratio (SNR) of the observed target.

Fluorinated Chitosan To Enhance Transmucosal Delivery of Sonosensitizer-Conjugated Catalase for Sonodynamic Bladder Cancer Treatment Post-intravesical Instillation

Sonodynamic therapy (SDT) is a noninvasive ultrasound-triggered therapeutic strategy for site-specific treatment of tumors with great depth penetration. The design of nano-sonosensitizers suitable for SDT treatment of bladder cancer (BCa) post-intravesical instillation has not yet been reported. Herein, a transmucosal oxygen-self-production SDT nanoplatform is developed to achieve highly efficient SDT against BCa. In this system, fluorinated chitosan (FCS) is synthesized as a highly effective nontoxic transmucosal delivery carrier to assemble with meso-tetra(4-carboxyphenyl)porphine-conjugated catalase (CAT-TCPP). The formed CAT-TCPP/FCS nanoparticles after intravesical instillation into the bladder cavity exhibit excellent transmucosal and intratumoral penetration capacities and could efficiently relieve hypoxia in tumor tissues by the catalase-catalyzed O₂ generation from tumor endogenous H₂O₂ to further improve the therapeutic efficacy of SDT to ablate orthotopic bladder tumors under ultrasound. Our work presents a nano-sonosensitizer formulation with FCS to enhance transmucosal delivery and intratumoral diffusion and CAT to improve tumor oxygenation, promising for instillation-based SDT to treat bladder tumors without the concern of systemic toxicity.

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.