Acidic pH-Activated Gas-Generating Nanoparticles with Pullulan Decorating for Hepatoma-Targeted Ultrasound Imaging

Recent Advancements in Ultrasound Contrast Agents Based on Nanomaterials for Imaging

Ultrasound (US) is a type of mechanical wave that is capable of transmitting energy through biological tissues. By utilization of various frequencies and intensities, it can elicit specific biological effects. US imaging (USI) technology has been continuously developed with the advantages of safety and the absence of radiation. The advancement of nanotechnology has led to the utilization of various nanomaterials composed of both organic and inorganic compounds as ultrasound contrast agents (UCAs). These UCAs enhance USI, enabling real-time monitoring, diagnosis, and treatment of diseases, thereby facilitating the widespread adoption of UCAs in precision medicine. In this review, we introduce various UCAs based on nanomaterials for USI. Their principles can be roughly divided into the following categories: carrying and transporting gases, endogenous gas production, and the structural characteristics of the nanomaterial itself. Furthermore, the synergistic benefits of US in conjunction with various imaging modalities and their combined application in disease monitoring and diagnosis are introduced. In addition, the challenges and prospects for the development of UCAs are also discussed.

Size and phase preservation of amorphous calcium carbonate nanoparticles in aqueous media using different types of lignin for contrast-enhanced ultrasound imaging

HYPOTHESIS

Calcium carbonate (CaCO3) nanoparticles could have great potential for contrast-enhanced ultrasound imaging (CEUS) due to their gas-generating properties and sensitivity to physiological conditions. However, the use of nano CaCO3 for biomedical applications requires the assistance of stabilizers to control the size and avoid the fast dissolution/recrystallization of the particles when exposed to aqueous conditions.

EXPERIMENTS

Herein, we report the stabilization of nano CaCO3 using lignin, and synthesized core-shell amorphous CaCO3-lignin nanoparticles (LigCC NPs) with a diameter below 100 nm. We have then investigated the echogenicity of the LigCC NPs by monitoring the consequent generation of contrast in vitro for 90 min in linear and non-linear B-mode imaging.

FINDINGS

This research explores how lignin type and structure affect stabilization efficiency, lignin structuration around CaCO3 cores, and particle echogenicity. Interestingly, by employing lignin as the stabilizer, it becomes possible to maintain the echogenic properties of CaCO3, whereas the use of lipid coatings prevents the production of signal generation in ultrasound imaging. This work opens new avenue for CEUS imaging of the vascular and extravascular space using CaCO3, as it highlights the potential to generate contrast for extended durations at physiological pH by utilizing the amorphous phase of CaCO3.

Recent Developments in CaCO3 Nano-Drug Delivery Systems: Advancing Biomedicine in Tumor Diagnosis and Treatment

Calcium carbonate (CaCO3), a natural common inorganic material with good biocompatibility, low toxicity, pH sensitivity, and low cost, has a widespread use in the pharmaceutical and chemical industries. In recent years, an increasing number of CaCO3-based nano-drug delivery systems have been developed. CaCO3 as a drug carrier and the utilization of CaCO3 as an efficient Ca2+ and CO2 donor have played a critical role in tumor diagnosis and treatment and have been explored in increasing depth and breadth. Starting from the CaCO3-based nano-drug delivery system, this paper systematically reviews the preparation of CaCO3 nanoparticles and the mechanisms of CaCO3-based therapeutic effects in the internal and external tumor environments and summarizes the latest advances in the application of CaCO3-based nano-drug delivery systems in tumor therapy. In view of the good biocompatibility and in vivo therapeutic mechanisms, they are expected to become an advancing biomedicine in the field of tumor diagnosis and treatment.

Nanotheranostics: Molecular Diagnostics and Nanotherapeutic Evaluation by Photoacoustic/Ultrasound Imaging in Small Animals

Nanotheranostics is a rapidly developing field that integrates nanotechnology, diagnostics, and therapy to provide novel methods for imaging and treating wide categories of diseases. Targeted nanotheranostics offers a platform for the precise delivery of theranostic agents, and their therapeutic outcomes are monitored in real-time. Presently, in vivo magnetic resonance imaging, fluorescence imaging, ultrasound imaging, and photoacoustic imaging (PAI), etc. are noninvasive imaging techniques that are preclinically available for the imaging and tracking of therapeutic outcomes in small animals. Additionally, preclinical imaging is essential for drug development, phenotyping, and understanding disease stage progression and its associated mechanisms. Small animal ultrasound imaging is a rapidly developing imaging technique for theranostics applications due to its merits of being nonionizing, real-time, portable, and able to penetrate deep tissues. Recently, different types of ultrasound contrast agents have been explored, such as microbubbles, echogenic exosomes, gas-vesicles, and nanoparticles-based contrast agents. Moreover, an optical image obtained through photoacoustic imaging is a noninvasive imaging technique that creates ultrasonic waves when pulsed laser light is used to expose an object and creates a picture of the tissue's distribution of light energy absorption on the object. Contrast agents for photoacoustic imaging may be endogenous (hemoglobin, melanin, and DNA/RNA) or exogenous (dyes and nanomaterials-based contrast agents). The integration of nanotheranostics with photoacoustic and ultrasound imaging allows simultaneous imaging and treatment of diseases in small animals, which provides essential information about the drug response and the disease progression. In this review, we have covered various endogenous and exogenous contrast agents for ultrasound and photoacoustic imaging. Additionally, we have discussed various drug delivery systems integrated with contrast agents for theranostic application. Further, we have briefly discussed the current challenges associated with ultrasound and photoacoustic imaging.

Application of Nanoparticles in the Diagnosis of Gastrointestinal Diseases: A Complete Future Perspective

The diagnosis of gastrointestinal (GI) diseases currently relies primarily on invasive procedures like digestive endoscopy. However, these procedures can cause discomfort, respiratory issues, and bacterial infections in patients, both during and after the examination. In recent years, nanomedicine has emerged as a promising field, providing significant advancements in diagnostic techniques. Nanoprobes, in particular, offer distinct advantages, such as high specificity and sensitivity in detecting GI diseases. Integration of nanoprobes with advanced imaging techniques, such as nuclear magnetic resonance, optical fluorescence imaging, tomography, and optical correlation tomography, has significantly enhanced the detection capabilities for GI tumors and inflammatory bowel disease (IBD). This synergy enables early diagnosis and precise staging of GI disorders. Among the nanoparticles investigated for clinical applications, superparamagnetic iron oxide, quantum dots, single carbon nanotubes, and nanocages have emerged as extensively studied and utilized agents. This review aimed to provide insights into the potential applications of nanoparticles in modern imaging techniques, with a specific focus on their role in facilitating early and specific diagnosis of a range of GI disorders, including IBD and colorectal cancer (CRC). Additionally, we discussed the challenges associated with the implementation of nanotechnology-based GI diagnostics and explored future prospects for translation in this promising field.

Perspectives on Usage of Functional Nanomaterials in Antimicrobial Therapy for Antibiotic-Resistant Bacterial Infections

The clinical applications of nanotechnology are emerging as widely popular, particularly as a potential treatment approach for infectious diseases. Diseases associated with multiple drug-resistant organisms (MDROs) are a global concern of morbidity and mortality. The prevalence of infections caused by antibiotic-resistant bacterial strains has increased the urgency associated with researching and developing novel bactericidal medicines or unorthodox methods capable of combating antimicrobial resistance. Nanomaterial-based treatments are promising for treating severe bacterial infections because they bypass antibiotic resistance mechanisms. Nanomaterial-based approaches, especially those that do not rely on small-molecule antimicrobials, display potential since they can bypass drug-resistant bacteria systems. Nanoparticles (NPs) are small enough to pass through the cell membranes of pathogenic bacteria and interfere with essential molecular pathways. They can also target biofilms and eliminate infections that have proven difficult to treat. In this review, we described the antibacterial mechanisms of NPs against bacteria and the parameters involved in targeting established antibiotic resistance and biofilms. Finally, yet importantly, we talked about NPs and the various ways they can be utilized, including as delivery methods, intrinsic antimicrobials, or a mixture.

Pullulan in pharmaceutical and cosmeceutical formulations: A review

Pullulan, an α-glucan polysaccharide, is colorless, odorless, non-toxic, non-carcinogenic, highly biocompatible, edible and biodegradable in nature. The long chains of glucopyranose rings in pullulan structure are linked together by α-(1 → 4) and α-(1 → 6) glycosidic linkages. The occurrence of both glycosidic linkages in the pullulan structure contributes to its distinctive properties. The unique structure of pullulan makes it a potent candidate for both pharmaceutical and cosmeceutical applications. In pharmaceuticals, it can be used as a drug carrier and in various dosage formulations. It has been widely used in drug targeting, implants, ocular dosage forms, topical formulations, oral dosage forms, and oral liquid formulations, etc. Pullulan can be used as a potential carrier of active ingredients and their site-specific delivery to skin layers for cosmeceutical applications. It has been extensively used in cosmeceutical formulations like creams, shampoo, lotions, sunscreen, facial packs, etc. The current review highlights applications of pullulan in pharmaceutical and cosmeceutical applications.

Ultrasound contrast agents from microbubbles to biogenic gas vesicles

Microbubbles have been the earliest and most widely used ultrasound contrast agents by virtue of their unique features: such as non-toxicity, intravenous injectability, ability to cross the pulmonary capillary bed, and significant enhancement of echo signals for the duration of the examination, resulting in essential preclinical and clinical applications. The use of microbubbles functionalized with targeting ligands to bind to specific targets in the bloodstream has further enabled ultrasound molecular imaging. Nevertheless, it is very challenging to utilize targeted microbubbles for molecular imaging of extravascular targets due to their size. A series of acoustic nanomaterials have been developed for breaking free from this constraint. Especially, biogenic gas vesicles, gas-filled protein nanostructures from microorganisms, were engineered as the first biomolecular ultrasound contrast agents, opening the door for more direct visualization of cellular and molecular function by ultrasound imaging. The ordered protein shell structure and unique gas filling mechanism of biogenic gas vesicles endow them with excellent stability and attractive acoustic responses. What's more, their genetic encodability enables them to act as acoustic reporter genes. This article reviews the upgrading progresses of ultrasound contrast agents from microbubbles to biogenic gas vesicles, and the opportunities and challenges for the commercial and clinical translation of the nascent field of biomolecular ultrasound.

Superiorly Stable Three-Layer Air Microbubbles Generated by Versatile Ethanol-Water Exchange for Contrast-Enhanced Ultrasound Theranostics

Microbubbles have been widely used as ultrasound contrast agents in clinical diagnosis. Moreover, most current preparation methods for microbubbles are uncontrollable, and the as-obtained microbubbles are unstable in aqueous solution or under ultrasound. Here, we report a strategy to prepare superiorly stable microbubbles with three-layer structures by the ethanol-water exchange. This versatile method can also be applied to prepare different kinds of protein microbubbles with various sizes for advanced biomedical applications. To demonstrate this, the protein air microbubbles are created, which is stable in water for several days with intact structures and exhibits excellent contrast-enhanced ultrasound imaging. Moreover, the protein air microbubbles can also deliver a mass of drugs while maintaining their stable structures, making them a platform for ultrasound imaging-guided drug delivery. The versatile protein air microbubbles have great potential for the design and application of theranostic platforms.

Acoustic-Based Theranostic Probes Activated by Tumor Microenvironment for Accurate Tumor Diagnosis and Assisted Tumor Therapy

Acoustic-based imaging techniques, including ultrasonography and photoacoustic imaging, are powerful noninvasive approaches for tumor imaging owing to sound transmission facilitation, deep tissue penetration, and high spatiotemporal resolution. Usually, imaging modes were classified into "always-on" mode and "activatable" mode. Conventional "always-on" acoustic-based probes often have difficulty distinguishing lesion regions of interest from surrounding healthy tissues due to poor target-to-background signal ratios. As compared, activatable probes have attracted attention with improved sensitivity, which can boost or amplify imaging signals only in response to specific biomolecular recognition or interactions. The tumor microenvironment (TME) exhibits abnormal physiological conditions that can be used to identify tumor sections from normal tissues. Various types of organic dyes and biomaterials can react with TME, leading to obvious changes in their optical properties. The TME also affects the self-assembly or aggregation state of nanoparticles, which can be used to design activatable imaging probes. Moreover, acoustic-based imaging probes and therapeutic agents can be coencapsulated into one nanocarrier to develop nanotheranostic probes, achieving tumor imaging and cooperative therapy. Satisfactorily, ultrasound waves not only accelerate the release of encapsulated therapeutic agents but also activate therapeutic agents to exert or enhance their therapeutic performance. Meanwhile, various photoacoustic probes can convert photon energy into heat under irradiation, achieving photoacoustic imaging and cooperative photothermal therapy. In this review, we focus on the recently developed TME-triggered ultrasound and photoacoustic theranostic probes for precise tumor imaging and targeted tumor therapy.

Tumor microenvironment enhanced NIR II fluorescence imaging for tumor precise surgery navigation via tetrasulfide mesoporous silica-coated Nd-based rare-earth nanocrystals

In vivo fluorescent imaging by using the new contrast agents emitted at short-wavelength infrared region (NIR II, 1000–1700 ​nm) presents an unprecedent advantages in imaging sensitivity and spatial resolution over traditional near-infrared (NIR) light. Recently, Nd-based rare-earth nanocrystals have attracted considerable attention due to the high quantum yield (∼40%) of their emission at NIR II. However, undesirable capture by reticuloendothelial system to bring strong background signal is unsatisfying for tumor discrimination. Here, GSH-sensitive tetrasulfide bond incorporated mesoporous silica shell has entrusted onto Nd-based down-conversion nanocrystals (DCNPs) surface to totally quench the fluorescence of DCNPs. After RGD conjugation on the silica surface, the NIR II contrast agents could actively target to liver tumors. Then tetrasulfide bonds can be broken during the silica framework decomposing in cytoplasm under high GSH concentration to result in NIR II fluorescence explosive recover. Benefiting from this specific response under tumor microenvironment, the NIR II signal in other organs was markedly reduced, while the signal-to-background ratio is prominently enhanced in tumors. Then, solid liver tumors were successfully resected under the guidance of our GSH responsive NIR II fluorescent imaging with no recurrence after 20-day of surgery. Meanwhile, by combining with the ignorable side effects, the Nd-based nanoprobes vastly improved the imaging resolution of tumor margin, opening a paradigm of NIR II fluorescent imaging-guided surgery.

Impact of Surface Area on Sensitivity in Autonomously Reporting Sensing Hydrogel Nanomaterials for the Detection of Bacterial Enzymes

The rapid and selective detection of bacterial contaminations and bacterial infections in a non-laboratory setting using advanced sensing materials holds the promise to enable robust point-of-care tests and rapid diagnostics for applications in the medical field as well as food safety. Among the various possible analytes, bacterial enzymes have been targeted successfully in various sensing formats. In this current work, we focus on the systematic investigation of the role of surface area on the sensitivity in micro- and nanostructured autonomously reporting sensing hydrogel materials for the detection of bacterial enzymes. The colorimetric sensing materials for the detection of β-glucuronidase (ß-GUS) from Escherichia coli (E. coli) were fabricated by template replication of crosslinked pullulan acetoacetate (PUAA) and by electrospinning chitosan/polyethylene oxide nanofibers (CS/PEO NFs), both equipped with the chromogenic substrate 5-bromo-4-chloro-3-indolyl-β-D-glucuronide. The investigation of the dependence of the initial reaction rates on surface area unveiled a linear relationship of rate and thereby time to observe a signal for a given concentration of bacterial enzyme. This knowledge was exploited in nanoscale sensing materials made of CS/PEO NFs with diameters of 295 ± 100 nm. Compared to bulk hydrogel slabs, the rate of hydrolysis was significantly enhanced in NFs when exposed to bacteria suspension cultures and thus ensuring a rapid detection of living E. coli that produces the enzyme β-GUS. The findings afford generalized design principles for the improvement of known and novel sensing materials towards rapid detection of bacteria by nanostructuring in medical and food related settings.

Synergic fabrication of pembrolizumab loaded doxorubicin incorporating microbubbles delivery for ultrasound contrast agents mediated anti-proliferation and apoptosis

This study evaluated pembrolizumab-conjugated, doxorubicin (DOX)-loaded microbubbles (PDMs) in combination with ultrasound (US) as molecular imaging agents for early diagnosis of B cell lymphomas, and as a targeted drug delivery system. Pembrolizumab, a monoclonal CD20 antibody, was attached to the surfaces of DOX-loaded microbubbles. PDM binding to B cell lymphoma cells was assessed using immunofluorescence. The cytotoxic effects of PDMs in combination with ultrasound (PDMs + US) were evaluated in vitro in CD20+ and CD20- cell lines, and its antitumor activities were assessed in Raji (CD20+) and Jurkat (CD20-) lymphoma cell-grafted mice. PDMs specifically bound to CD20+ cells in vitro and in vivo. Contrast enhancement was monitored in vivo via US. PDM peak intensities and contrast enhancement durations were higher in Raji than in Jurkat cell-grafted mice (p < 0.05). PDMs + US treatment resulted in improved antitumor effects and reduced systemic toxicity in Raji cell-grafted mice compared with other treatments (p < .05). Our results showed that PDMs + US enhanced tumor targeting, reduced systemic toxicity, and inhibited CD20+ B cell lymphoma growth in vivo. Targeted PDMs could be employed as US molecular imaging agents for early diagnosis, and are an effective targeted drug delivery system in combination with US for CD20+ B cell malignancy treatment.

Molecular Imaging-Guided Sonodynamic Therapy

Low-intensity ultrasound-triggered sonodynamic therapy (SDT) is a promising noninvasive therapeutic modality due to its strong tissue penetration ability. In recent years, with the development of nanotechnology, nanoparticle-based sonosensitizer-mediated SDT has been widely investigated. With the increasing demand for precise and personalized treatment, abundant novel sonosensitizers with imaging capabilities have been developed for determining the optimal therapeutic window, thus significantly enhancing treatment efficacy. In this review, we focus on the molecular imaging-guided SDT. The prevalent mechanisms of SDT are discussed, including ultrasonic cavitation, sonoluminescence, reactive oxygen species, and mechanical damage. In addition, we introduce the major molecular imaging techniques and the design principles based on nanoparticles to achieve efficient imaging. Furthermore, the imaging-guided SDT for the treatment of cancer, bacterial infections, and vascular diseases is summarized. The ultimate goal is to design more effective imaging-guided SDT modalities and provide novel ideas for clinical translation of SDT.

Biomineralization of Aggregation-Induced Emission-Active Photosensitizers for pH-Mediated Tumor Imaging and Photodynamic Therapy

As an efficient, noninvasive, and high spatiotemporal resolved approach, photodynamic therapy (PDT) has high therapeutic potential for cancer treatment, whereas its development still faces a number of challenges, such as the lack of efficient and stable photosensitizers (PSs) and the inadequate ability of PSs to accumulate at tumor sites and target responses. Herein, a pH-responsive calcium carbonate (CaCO₃)-mineralized AIEgen nanoprobe was prepared by using bovine serum albumin as the skeleton and loaded with a mitochondria-specific aggregation-induced emission (AIE)-active PS of 1-methyl-4-(4-(1,2,2-triphenylvinyl)styryl)quinolinium iodide (TPE-Qu⁺), which exhibits superior singlet oxygen (¹O₂)-generation ability and meanwhile possesses a bright near-infrared fluorescence emission. The biomineralized nanoparticles have small sizes (100 ± 10 nm) with good water dispersion and stability. With an increase in acidity (pH = 7.4-5.0), the internal TPE-Qu⁺ molecules are released gradually and accumulated in the mitochondria due to their hydrophobicity and electropositivity and then generate fluorescence emission and PDT under an external light source. Tumor inhibition and low acute toxicity were further successfully confirmed by the intracellular uptake test and 4T1-tumor-bearing mouse model.

Enzyme-Responsive Biopolymeric Nanogel Fibers by Extrusion: Engineering of High-Surface-Area Hydrogels and Application in Bacterial Enzyme Detection

The fabrication of covalently cross-linked high-surface-area biopolymeric nanogel fibers by nanopore extrusion is reported for the first time. The biopolymer pullulan was functionalized with tert-butyl acetoacetate via a transesterification reaction to synthesize the water-soluble ketone-rich precursor pullulan acetoacetate (PUAA). PUAA and carbonic dihydrazide (CDH) as cross-linker were extruded through anodic aluminum oxide (AAO) nanoporous membranes, which possessed an average pore diameter of 61 ± 2 nm. By changing the concentration of PUAA, the flow rate, and extrusion time, the step polymerization cross-linking reaction was controlled so that the polymer can be extruded gradually during cross-linking through the membrane, avoiding the formation of macroscopic bulk hydrogels and rupture of the AAO membrane. Fibers with diameters on the order of 250 nm were obtained. This approach was also expanded to functionalized PUAA derivatives together with the fluorogenic substrate 4-methylumbelliferyl-β-d-glucuronide MUGlcU in (PUAA-MUGlcU), which exhibited a mean equilibrium swelling ratio of 5.7 and 9.0 in Milli-Q water and in phosphate-buffered saline, respectively. β-Glucuronidase was sensitively detected via fluorescence of 4-methylumbelliferone, which was liberated in the enzymatic hydrolysis reaction of PUAA-MUGlcU. Compared to hydrogel slabs, the rate of the hydrolysis was >20% higher in the nanogel fibers, facilitating the rapid detection of β-glucuronidase-producing Escherichia coli (E. coli Mach1-T1). Nanopore extruded nanogel fibers are therefore considered a viable approach to enhance the functionality of hydrogels in surface-dominated processes.

Dual pH- and Glutathione-Responsive CO2-Generating Nanodrug Delivery System for Contrast-Enhanced Ultrasonography and Therapy of Prostate Cancer

Ultrasonography (US) contrast imaging using US contrast agents has been widely applied for the diagnosis and differential diagnosis of tumors. Commercial US contrast agents have limited applications because of their large size and shorter imaging time. At the same time, the desired therapeutic purpose cannot be achieved by applying only conventional US contrast agents. The development of nanoscale US agents with US imaging and therapeutic functions has attracted increasing attention. In this study, we successfully developed DOX-loaded poly-1,6-hexanedithiol-sodium bicarbonate nanoparticles (DOX@HADT-SS-NaHCO3 NPs) with pH-responsive NaHCO3 and GSH-responsive disulfide linkages. DOX@HADT-SS-NaHCO3 NPs underwent acid-triggered decomposition of NaHCO3 to generate CO2 bubbles and a reduction of disulfide linkages to further promote the release of CO2 and DOX. The potential of DOX@HADT-SS-NaHCO3 NPs for contrast-enhanced US imaging and therapy of prostate cancer was thoroughly evaluated using in vitro agarose gel phantoms and a C4-2 tumor-bearing nude mice model. These polymeric NPs displayed significantly enhanced US contrast at acidic pH and antitumor efficacy. Therefore, the NaHCO3 and DOX-encapsulated polymeric NPs hold tremendous potential for effective US imaging and therapy of prostate cancer.

Pullulan based stimuli responsive and sub cellular targeted nanoplatforms for biomedical application: Synthesis, nanoformulations and toxicological perspective

With growing interest in polymers of natural origin, innumerable polysaccharides have gained attention for their biomedical application. Pullulan, one of the FDA approved nutraceuticals, possesses multiple unique properties which make them highly advantageous for biomedical applications. This present review encompasses the sources, production, properties and applications of pullulan. It highlights various pullulan based stimuli-responsive systems (temperature, pH, ultrasound, magnetic), subcellular targeted systems (mitochondria, Golgi apparatus/endoplasmic reticulum, lysosome, endosome), lipid-vesicular systems (solid-lipid nanoparticles, liposomes), polymeric nanofibres, micelles, inorganic (SPIONs, gold and silver nanoparticles), carbon-based nanoplatforms (carbon nanotubes, fullerenes, nanodiamonds) and quantum dots. This article also gives insight into different biomedical, therapeutic and diagnostic applications of pullulan viz., imaging, tumor targeting, stem cell therapy, gene therapy, vaccine delivery, cosmetic applications, protein delivery, tissue engineering, photodynamic therapy and chaperone-like activities. The review also includes the toxicological profile of pullulan which is helpful for the development of suitable delivery systems for clinical applications.