Multimodal nanoparticulate bioimaging contrast agents

Stimulus-Responsive Ultrathin Films for Bioapplications: A Concise Review

The term "nanosheets" has been coined recently to describe supported and free-standing "ultrathin film" materials, with thicknesses ranging from a single atomic layer to a few tens of nanometers. Owing to their physicochemical properties and their large surface area with abundant accessible active sites, nanosheets (NSHs) of inorganic materials such as Au, amorphous carbon, graphene, and boron nitride (BN) are considered ideal building blocks or scaffolds for a wide range of applications encompassing electronic and optical devices, membranes, drug delivery systems, and multimodal contrast agents, among others. A wide variety of synthetic methods are employed for the manufacturing of these NSHs, and they can be categorized into (1) top-down approaches involving exfoliation of layered materials, or (2) bottom-up approaches where crystal growth of nanocomposites takes place in a liquid or gas phase. Of note, polymer template liquid exfoliation (PTLE) methods are the most suitable as they lead to the fabrication of high-performance and stable hybrid NSHs and NSH composites with the appropriate quality, solubility, and properties. Moreover, PTLE methods allow for the production of stimulus-responsive NSHs, whose response is commonly driven by a favorable growth in the appropriate polymer chains onto one side of the NSHs, resulting in the ability of the NSHs to roll up to form nanoscrolls (NSCs), i.e., open tubular structures with tunable interlayer gaps between their walls. On the other hand, this review gives insight into the potential of the stimulus-responsive nanostructures for biosensing and controlled drug release systems, illustrating the last advances in the PTLE methods of synthesis of these nanostructures and their applications.

The 3M Concept: Biomedical Translational Imaging from Molecules to Mouse to Man

Imaging keeps pervading biomedical sciences from the nanoscale to the bedside. Connecting the hierarchical levels of biomedicine with relevant imaging approaches, however, remains a challenge.

Here we present a concept, called “3M”, which can deliver a question, formulated at the bedside, across the wide-ranging hierarchical organization of the living organism, from the molecular level, through the small-animal scale, to whole-body human functional imaging. We present an example of nanoparticle development pipeline extending from atomic force microscopy to pre-clinical whole body imaging methods to highlight the essential features of the 3M concept, which integrates multi-scale resolution and quantification into a single logical process.

Using the nanoscale to human clinical whole body approach, we present the successful development, characterisation and application of Prussian Blue nanoparticles for a variety of imaging modalities, extending it to isotope payload quantification and shape-biodistribution relationships.

The translation of an idea from the bedside to the molecular level and back requires a set of novel combinatorial imaging methodologies interconnected into a logical pipeline. The proposed integrative molecules-to-mouse-to-man (3M) approach offers a promising, clinically oriented toolkit that lends the prospect of obtaining an ever-increasing amount of correlated information from as small a voxel of the human body as possible.

Superparamagnetic cobalt ferrite nanoparticles as T2 contrast agent in MRI: in vitro study

Superparamagnetic cobalt ferrite nanoparticles (CoFe₂O₄) possess favourite advantages for theranostic applications. Most of previous studies reported that CoFe₂O₄ magnetic nanoparticles (MNPs) are suitable candidates for induction of hyperthermia and transfection agents for drug delivery. The present study synthesized and investigated the potential use of CoFe₂O₄ as a contrast agent in magnetic resonance imaging (MRI) by using a conventional MRI system. The CoFe₂O₄ were synthesized using co-precipitation method and characterized by TEM, XRD, FTIR, EDX and VSM techniques. Relaxivities r₁ and r₂ of CoFe₂O₄ were then calculated using a 1.5 Tesla clinical magnetic field. The cytotoxicity of CoFe₂O₄ was evaluated by the MTT assay. Finally, the optimal concentrations of MNPs for MRI uses were calculated through the analysis of T₂ weighted imaging cell phantoms. The superparamagnetic CoFe2O4 NPs with an average stable size of 10.45 nm were synthesized. Relaxivity r₁,₂ calculations resulted in suitable r₂ and r₂/ r₁ with values of 58.6 and 51 that confirmed the size dependency on relaxivity values. The optimal concentration of MNPs for MR image acquisition was calculated as 0.154 mM. Conclusion: CoFe₂O₄ synthesized in this study could be considered as a suitable T₂ weighted contrast agent because of its high r₂/r₁ value.

Simultaneous optical and magnetophoretic monitoring of DNA hybridization using superparamagnetic and plasmonic colloids

The detection and separation of small biomolecules from complex mixtures and the possibility of their recovering for further analyses have great benefits for the early diagnosis and prognosis of diseases. Developing simple, sensitive, and cost-effective tools that allow the rapid and accurate assembly and isolation of molecular biomarkers has the potential to improve both patient care and hospital logistic efficiency towards personalized and affordable treatments of diseases.In this work, we presenta method consisting ofUV-vis-spectroscopy assisted-magnetophoresis for the monitoring of DNA hybridization. For this purpose, a magnetic device generating 7.5 T/m uniform magnetic field gradient was designed and incorporated to a commercial spectrophotometer. Different batches of colloidal superparamagnetic particles (SMPs), with different elemental compositions, were functionalized with twenty-mer complementary oligonucleotides, TB1 and TB2. When the functionalized SMPs-TB1 and SMPs-TB2 are mixed and incubated, the hybridization process of TB1 and TB2 occurs resulting in the formation of colloidal aggregates. When brought under the magnetic field, depending on the magnetic strength (Γ) of the formed aggregates, they separate either faster or slower than the non-functionalized SMPs. The difference in magnetic separation time (Δt) is optically monitored by measuring the real time transparency of the suspension at specific wavelengths. The detection of aggregates at concentrations of 0.001% w/v was achieved, showing Δt ranging from 113-228 s. Based on the changes of Δt, the study addresses how electrosteric, magnetic, and hydrogen bonding interactions affect the hybridization process and suggests optimum experimental conditions for accurate monitoring of TB1-TB2 hybridization.

Finely crafted quasi-core–shell gadolinium/layered double hydroxide hybrids for switching on/off bimodal CT/MRI contrasting nanodiagnostic platforms

Quasi core–shell structure of LDH platetes and Gd(OH)₃ nanorods were synthesized to control water approach to Gd(OH)₃ depending on pH.

Clinically-Applicable Perfluorocarbon-Loaded Nanoparticles For In vivo Photoacoustic, 19F Magnetic Resonance And Fluorescent Imaging

Photoacoustic imaging (PAI) is an emerging biomedical imaging technique that is now coming to the clinic. It has a penetration depth of a few centimeters and generates useful endogenous contrast, particularly from melanin and oxy-/deoxyhemoglobin. Indocyanine green (ICG) is a Food and Drug Administration-approved contrast agents for human applications, which can be also used in PAI. It is a small molecule dye with limited applications due to its fast clearance, rapid protein binding, and bleaching effect. Methods: Here, we entrap ICG in a poly(lactic-co-glycolic acid) nanoparticles together with a perfluorocarbon (PFC) using single emulsion method. These nanoparticles and nanoparticle-loaded dendritic cells were imaged with PA, 19F MR, and fluorescence imaging in vitro and in vivo. Results: We formulated particles with an average diameter of 200 nm. The encapsulation of ICG within nanoparticles decreased its photobleaching and increased the retention of the signal within cells, making it available for applications such as cell imaging. As little as 0.1x106 cells could be detected in vivo with PAI using automated spectral unmixing. Furthermore, we observed the accumulation of ICG signal in the lymph node after subcutaneous injection of nanoparticles. Conclusion: We show that we can label primary human dendritic cells with the nanoparticles and image them in vitro and in vivo, in a multimodal manner. This work demonstrates the potential of combining PAI and 19F MRI for cell imaging and lymph node detection using nanoparticles that are currently produced at GMP-grade for clinical use.

Thallium Labeled Citrate-Coated Prussian Blue Nanoparticles as Potential Imaging Agent

Background

The aim of this study was to develop and characterize a nanoparticle-based image-contrast platform which is biocompatible, chemically stable, and accessible for radiolabeling with ²⁰¹Tl. We explored whether this nanoparticle enhanced the T1 signal which might make it an MRI contrast agent as well.

Methods

The physical properties of citrate-coated Prussian blue nanoparticles (PBNPs) (iron(II);iron(III);octadecacyanide) doped with ²⁰¹Tl isotope were characterized with atomic force microscopy, dynamic light scattering, and zeta potential measurement. PBNP biodistribution was determined by using SPECT and MRI following intravenous administration into C57BL6 mice. Activity concentrations (MBq/cm³) were calculated from the SPECT scans for each dedicated volume of interest (VOI) of liver, kidneys, salivary glands, heart, lungs, and brain.

Results

PBNP accumulation peaked at 2 hours after injection predominantly in the kidneys and the liver followed by a gradual decrease in activity in later time points.

Conclusion

We synthetized, characterized, and radiolabeled a Prussian blue-based nanoparticle platform for contrast material applications. Its in vivo radiochemical stability and biodistribution open up the way for further diagnostic applications.

Magnetic nanobubbles with potential for targeted drug delivery and trimodal imaging in breast cancer: an in vitro study

Aim: The aim of this study was to improve tumor-targeted therapy for breast cancer by designing magnetic nanobubbles with the potential for targeted drug delivery and multimodal imaging. Materials & methods: Herceptin-decorated and ultrasmall superparamagnetic iron oxide (USPIO)/paclitaxel (PTX)-embedded nanobubbles (PTX-USPIO-HER-NBs) were manufactured by combining a modified double-emulsion evaporation process with carbodiimide technique. PTX-USPIO-HER-NBs were examined for characterization, specific cell-targeting ability and multimodal imaging. Results: PTX-USPIO-HER-NBs exhibited excellent entrapment efficiency of Herceptin/PTX/USPIO and showed greater cytotoxic effects than other delivery platforms. Low-frequency ultrasound triggered accelerated PTX release. Moreover, the magnetic nanobubbles were able to enhance ultrasound, magnetic resonance and photoacoustics trimodal imaging. Conclusion: These results suggest that PTX-USPIO-HER-NBs have potential as a multimodal contrast agent and as a system for ultrasound-triggered drug release in breast cancer.

Magnetic nanoparticles coated with polyarabic acid demonstrate enhanced drug delivery and imaging properties for cancer theranostic applications

Therapeutic targeting of tumor cells with drug nanocarriers relies upon successful interaction with membranes and efficient cell internalization. A further consideration is that engineered nanomaterials should not damage healthy tissues upon contact. A critical factor in this process is the external coating of drug delivery nanodevices. Using in silico, in vitro and in vivo studies, we show for the first time that magnetic nanoparticles coated with polyarabic acid have superior imaging, therapeutic, and biocompatibility properties. We demonstrate that polyarabic acid coating allows for efficient penetration of cell membranes and internalization into breast cancer cells. Polyarabic acid also allows reversible loading of the chemotherapeutic drug Doxorubicin, which upon release suppresses tumor growth in vivo in a mouse model of breast cancer. Furthermore, these nanomaterials provide in vivo contrasting properties, which directly compare with commercial gadolinium-based contrasting agents. Finally, we report excellent biocompatibility, as these nanomaterial cause minimal, if any cytotoxicity in vitro and in vivo. We thus propose that magnetic nanodevices coated with polyarabic acid offer a new avenue for theranostics efforts as efficient drug carriers, while providing excellent contrasting properties due to their ferrous magnetic core, which can help the future design of nanomaterials for cancer imaging and therapy.

Fabrication of letrozole formulation using chitosan nanoparticles through ionic gelation method

In this study, the anticancer drug letrozole (LTZ) was formulated using chitosan nanoparticles (CS-NPs) with the crosslinking agent sodium tripolyphosphate (TPP). The nano-formulation was optimized by varying the concentration of drug. The prepared particles were characterized using FTIR, TGA, XRD, SEM, TEM and DLS. From the FTIR results, the appearance of a new peak for CH, CC and CN confirms the formation of LTZ loaded chitosan nanoparticles. TEM images shows that the average particle size was in the range of 60-80nm and 20-40mm air dried and freeze dried samples respectively. Also the prepared formulation had been evaluated in vitro for determining its hemocompatability, biodegradability and serum stability. The preliminary studies supported that the chitosan nanoparticles formulation has biocompatibility and hemocompatible properties and it can act as an effective pharmaceutical excipient for letrozole.

Ultrafine graphene oxide–CoFe2O4 nanoparticle composite as T1 and T2 contrast agent for magnetic resonance imaging

Graphene oxide–CoFe₂O₄ nanoparticle composites were synthesized using a two step synthesis method in which graphene oxide was initially synthesized followed by precipitation of CoFe₂O₄ nanoparticles in a reaction mixture containing graphene oxide.

ZnO coated CoFe2O4 nanoparticles for multimodal bio-imaging

The potential of CoFe₂O₄–ZnO core–shell nanoparticles for fluorescence optical imaging and as a contrast agent for magnetic resonance imaging (MRI) is demonstrated.

A facile synthesis of versatile Cu2-xS nanoprobe for enhanced MRI and infrared thermal/photoacoustic multimodal imaging

A novel type of intelligent nanoprobe by using single component of Cu2-xS for multimodal imaging has been facilely and rapidly synthesized in scale via thermal decomposition followed by biomimetic phospholipid modification, which endows them with uniform and small nanoparticle size (ca.15 nm), well phosphate buffer saline (PBS) dispersity, high stability, and excellent biocompatibility. The as-synthesized Cu2-xS nanoprobes (Cu2-xS NPs) are capable of providing contrast enhancement for T1-weighted magnetic resonance imaging (MRI), as demonstrated by the both in vitro and in vivo imaging investigations for the first time. In addition, due to their strong near infrared (NIR) optical absorption, they can also serve as a candidate contrast agent for enhanced infrared thermal/photoacoustic imaging, to meet the shortfalls of MRI. Hence, complementary and potentially more comprehensive information can be acquired for the early detection and accurate diagnosis of cancer. Furthermore, negligible systematic side effects to the blood and tissue were observed in a relatively long period of 3 months. The distinctive multimodal imaging capability with excellent hemo/histocompatibility of the Cu2-xS NPs could open up a new molecular imaging possibility for detecting and diagnosing cancer or other diseases in the future.

The scope of nanoparticle therapies for future metastatic melanoma treatment

Metastatic melanoma is a highly aggressive malignancy that has traditionally been very difficult to treat. However, after decades of basic research into the signal transduction pathways that promote cancer cell survival, chemoresistance, growth, and crosstalk with the immune system, targeted therapies have now been developed that offer improved survival for patients with metastatic melanoma. Some of the most promising therapies that have been developed include ipilimumab, an anti-cytotoxic T lymphocyte antigen 4 antibody that enhances T-cell activity in the tumour, and selective BRAF inhibitors, such as vemurafenib that blocks tumour cell proliferation in patients with activating BRAF mutations. Although these treatments offer substantial hope for patients, they are not without their drawbacks, which include adverse side-effects, drug resistance, and eventual relapse. Nanotherapeutics holds significant promise to circumvent these shortcomings and has the additional advantage of potentially functioning as a diagnostic device. We will discuss the scope of the use of such multimodal nanoparticles for melanoma treatment and ask whether such particles can offer patients with metastatic melanoma improved prognoses for the future.

Synthesis, Characterization, In Vitro Phantom Imaging, and Cytotoxicity of A Novel Graphene-Based Multimodal Magnetic Resonance Imaging - X-Ray Computed Tomography Contrast Agent

Graphene nanoplatelets (GNPs), synthesized using potassium permanganate-based oxidation and exfoliation followed by reduction with hydroiodic acid (rGNP-HI), have intercalated manganese ions within the graphene sheets, and upon functionalization with iodine, show excellent potential as biomodal contrast agents for magnetic resonance imaging (MRI) and computed tomography (CT). Structural characterization of rGNP-HI nanoparticles with low- and high-resolution transmission electron microscope (TEM) showed disc-shaped nanoparticles (average diameter, 200 nm, average thickness, 3 nm). Energy dispersive X-ray spectroscopy (EDX) analysis confirmed the presence of intercalated manganese. Raman spectroscopy and X-ray diffraction (XRD) analysis of rGNP-HI confirmed the reduction of oxidized GNPs (O-GNPs), absence of molecular and physically adsorbed iodine, and the functionalization of graphene with iodine as polyiodide complexes (I₃^- and I₅^-). Manganese and iodine content were quantified as 5.1 ± 0.5 and 10.54 ± 0.87 wt% by inductively-coupled plasma optical emission spectroscopy and ion-selective electrode measurements, respectively. In vitro cytotoxicity analysis, using absorbance (LDH assay) and fluorescence (calcein AM) based assays, performed on NIH3T3 mouse fibroblasts and A498 human kidney epithelial cells, showed CD₅₀ values of rGNP-HI between 179-301 µg/ml, depending on the cell line and the cytotoxicity assay. CT and MRI phantom imaging of rGNP-HI showed high CT (approximately 3200% greater than HI at equimolar iodine concentration) and MRI (approximately 59% greater than equimolar Mn²⁺ solution) contrast. These results open avenues for further in vivo safety and efficacy studies towards the development of carbon nanostructure-based multimodal MRI-CT contrast agents.

Optically and magnetically doped ormosil nanoparticles for bioimaging: synthesis, characterization, and in vitro studies

(Left) Scheme depicting formation of ormosil nanoparticles, co-encapsulated with iron oxide nanoparticles and fluorophore. (Right) TEM image of the synthesized nanoparticles.

Fe Doped CdTeS Magnetic Quantum Dots for Bioimaging

A facile synthesis of 3-6 nm, water dispersible, near-infrared (NIR) emitting, quantum dots (QDs) magnetically doped with Fe is presented. Doping of alloyed CdTeS nanocrystals with Fe was achieved in situ using a simple hydrothermal method. The magnetic quantum dots (MQDs) were capped with NAcetyl-Cysteine (NAC) ligands, containing thiol and carboxylic acid functional groups to provide stable aqueous dispersion. The optical and magnetic properties of the Fe doped MQDs were characterized using several techniques. The synthesized MQDs are tuned to emit in the Vis-NIR (530-738 nm) wavelength regime and have high quantum yields (67.5-10%). NIR emitting (738 nm) MQDs having 5.6 atomic% Fe content exhibited saturation magnetization of 85 emu/gm[Fe] at room temperature. Proton transverse relaxivity of the Fe doped MQDs (738 nm) at 4.7 T was determined to be 3.6 mM^-1s^-1. The functional evaluation of NIR MQDs has been demonstrated using phantom and in vitro studies. These water dispersible, NIR emitting and MR contrast producing Fe doped CdTeS MQDs, in unagglomerated form, have the potential to act as multimodal contrast agents for tracking live cells.

Size-controlled and biocompatible Gd2 O3 nanoparticles for dual photoacoustic and MR imaging

The synthesis, characterization, and functional evaluation of new size-controlled and biocompatible Gd(2) O(3) nanoparticles as a bimodal contrast agent for use in photoacoustic (PA) and magnetic resonance (MR) imaging are reported. These nanoparticles show a clear PA image by themselves, without conjugation with gold, rare earth metals, or dyes. Relaxivity measurement by MR imaging clearly shows that their relaxivity, r(1) , is twice that of clinically available Gd-DTPA.

X-ray imaging of tumor growth in live mice by detecting gold-nanoparticle-loaded cells

We show that sufficient concentrations of gold nanoparticles produced by an original synthesis method in EMT-6 and CT-26 cancer cells make it possible to detect the presence, necrosis and proliferation of such cells after inoculation in live mice. We first demonstrated that the nanoparticles do not interfere with the proliferation process. Then, we observed significant differences in the tumor evolution and the angiogenesis process after shallow and deep inoculation. A direct comparison with pathology optical images illustrates the effectiveness of this approach.

X-ray microscopy and tomography detect the accumulation of bare and PEG-coated gold nanoparticles in normal and tumor mouse tissues

We demonstrate that, with appropriate staining, high-resolution X-ray microscopy can image complicated tissue structures--cerebellum and liver--and resolve large or small amounts of Au nanoparticles in these tissues. Specifically, images of tumor tissue reveal high concentrations of accumulated Au nanoparticles. PEG (poly(ethylene glycol)) coating is quite effective in enhancing this accumulation and significantly modifies the mechanism of uptake by reticuloendothelial system (RES) organs.

Nanoparticle delivery for metastatic breast cancer

Breast cancer represents a major ongoing public health problem as the most common non-cutaneous malignancy among U.S. women. While significant progress has been made in improving loco-regional treatments for breast cancer, relatively little progress has been made in diagnosing and treating patients with metastatic breast cancer. At present there are limited curative options for patients with breast cancer metastatic beyond regional nodes. Emerging nanotechnologies promise new approaches to early detection and treatment of metastatic breast cancer. Fulfilling the promise of nanotechnologies for patients with metastatic breast cancer will require delivery of nanomaterials to sites of metastatic disease. Future translational approaches will rely on an ever increasing understanding of the biology of breast cancer subtypes and their metastases. These important concepts will be highlighted and elucidated in this manuscript.

Nanoparticle delivery for metastatic breast cancer

Breast cancer represents a major ongoing public health problem as the most common non-cutaneous malignancy among U.S. women. While significant progress has been made in improving loco-regional treatments for breast cancer, relatively little progress has been made in diagnosing and treating patients with metastatic breast cancer. At present there are limited curative options for patients with breast cancer metastatic beyond regional nodes. Emerging nanotechnologies promise new approaches to early detection and treatment of metastatic breast cancer. Fulfilling the promise of nanotechnologies for patients with metastatic breast cancer will require delivery of nanomaterials to sites of metastatic disease. Future translational approaches will rely on an ever increasing understanding of the biology of breast cancer subtypes and their metastases. These important concepts will be highlighted and elucidated in this manuscript.

Toxicity of nanomaterials

Nanoscience has matured significantly during the last decade as it has transitioned from bench top science to applied technology. Presently, nanomaterials are used in a wide variety of commercial products such as electronic components, sports equipment, sun creams and biomedical applications. There are few studies of the long-term consequences of nanoparticles on human health, but governmental agencies, including the United States National Institute for Occupational Safety and Health and Japan's Ministry of Health, have recently raised the question of whether seemingly innocuous materials such as carbon-based nanotubes should be treated with the same caution afforded known carcinogens such as asbestos. Since nanomaterials are increasing a part of everyday consumer products, manufacturing processes, and medical products, it is imperative that both workers and end-users be protected from inhalation of potentially toxic NPs. It also suggests that NPs may need to be sequestered into products so that the NPs are not released into the atmosphere during the product's life or during recycling. Further, non-inhalation routes of NP absorption, including dermal and medical injectables, must be studied in order to understand possible toxic effects. Fewer studies to date have addressed whether the body can eventually eliminate nanomaterials to prevent particle build-up in tissues or organs. This critical review discusses the biophysicochemical properties of various nanomaterials with emphasis on currently available toxicology data and methodologies for evaluating nanoparticle toxicity (286 references).

Rational chemical design of the next generation of molecular imaging probes based on physics and biology: mixing modalities, colors and signals

In recent years, numerous in vivo molecular imaging probes have been developed. As a consequence, much has been published on the design and synthesis of molecular imaging probes focusing on each modality, each type of material, or each target disease. More recently, second generation molecular imaging probes with unique, multi-functional, or multiplexed characteristics have been designed. This critical review focuses on (i) molecular imaging using combinations of modalities and signals that employ the full range of the electromagnetic spectra, (ii) optimized chemical design of molecular imaging probes for in vivo kinetics based on biology and physiology across a range of physical sizes, (iii) practical examples of second generation molecular imaging probes designed to extract complementary data from targets using multiple modalities, color, and comprehensive signals (277 references).

Nanoparticles as contrast agents for in-vivo bioimaging: current status and future perspectives

Nanoparticle-based contrast agents are quickly becoming valuable and potentially transformative tools for enhancing medical diagnostics for a wide range of in-vivo imaging modalities. Compared with conventional molecular-scale contrast agents, nanoparticles (NPs) promise improved abilities for in-vivo detection and potentially enhanced targeting efficiencies through longer engineered circulation times, designed clearance pathways, and multimeric binding capacities. However, NP contrast agents are not without issues. Difficulties in minimizing batch-to-batch variations and problems with identifying and characterizing key physicochemical properties that define the in-vivo fate and transport of NPs are significant barriers to the introduction of new NP materials as clinical contrast agents. This manuscript reviews the development and application of nanoparticles and their future potential to advance current and emerging clinical bioimaging techniques. A focus is placed on the application of solid, phase-separated materials, for example metals and metal oxides, and their specific application as contrast agents for in-vivo near-infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI), positron emission tomography (PET), computed tomography (CT), ultrasound (US), and photoacoustic imaging (PAI). Clinical and preclinical applications of NPs are identified for a broad spectrum of imaging applications, with commentaries on the future promise of these materials. Emerging technologies, for example multifunctional and theranostic NPs, and their potential for clinical advances are also discussed.