Thermally-triggered 'off-on-off' response of gadolinium-hydrogel-lipid hybrid nanoparticles defines a customizable temperature window for non-invasive magnetic resonance imaging thermometry

A Nanoparticle Ink Allowing the High Precision Visualization of Tissue Engineered Scaffolds by MRI

Hydrogels are widely used as cell scaffolds in several biomedical applications. Once implanted in vivo, cell scaffolds must often be visualized, and monitored overtime. However, cell scaffolds appear poorly contrasted in most biomedical imaging modalities such as magnetic resonance imaging (MRI). MRI is the imaging technique of choice for high-resolution visualization of low-density, water-rich tissues. Attempts to enhance hydrogel contrast in MRI are performed with "negative" contrast agents that produce several image artifacts impeding the delineation of the implant's contours. In this study, a magnetic ink based on ultra-small iron oxide nanoparticles (USPIONs; <5 nm diameter cores) is developed and integrated into biocompatible alginate hydrogel used in cell scaffolding applications. Relaxometric properties of the magnetic hydrogel are measured, as well as biocompatibility and MR-visibility (T₁ -weighted mode; in vitro and in vivo). A 2-week MR follow-up study is performed in the mouse model, demonstrating no image artifacts, and the retention of "positive" contrast overtime, which allows very precise delineation of tissue grafts with MRI. Finally, a 3D-contouring procedure developed to facilitate graft delineation and geometrical conformity assessment is applied on an inverted template alginate pore network. This proof-of-concept establishes the possibility to reveal precisely engineered hydrogel structures using this USPIONs ink high-visibility approach.

Ca2+-Chelation-Induced Fabrication of Multistimuli-Responsive Charged Nanogels from Phospholipid-Polymer Conjugates and Use for Drug/Protein Loading

Thermoresponsive phospholipid-poly(N-isopropylacrylamide) (PL-PNIPAM) conjugates were synthesized via reversible addition fragmentation chain transfer polymerization mediated by a phospholipid-modified trithiocarbonate. Temperature triggered the micellization of the PL-PNIPAM conjugate to form phosphate group-decorated micelles in the aqueous solution. Driven by the chelation of phospholipids and Ca²⁺, the PL-PNIPAM conjugate and Ca²⁺ ions formed size-tunable nanoclusters at a temperature beyond the lower critical solution temperature. To fabricate cross-linked nanogels, NIPAM was copolymerized with N-succinimidyl acrylate (NSA) to obtain the PL-P(NIPAM-co-NSA) conjugate bearing pendent cross-linkable functionalities. Subsequently, the size-controllable nanogels containing disulfide linkages were generated at 37 °C by cross-linking the PL-P(NIPAM-co-NSA)/Ca²⁺ nanoclusters with cystamine through modulation of Ca²⁺ concentrations. These negatively charged nanogels demonstrate temperature/pH/reduction triple responsiveness. The nanogels can be efficiently loaded with doxorubicin (DOX) and proteins with various isoelectric points. The DOX-loaded nanogels exhibited a temperature/pH/reduction triple-responsive release profile. The immobilized RNase A, BSA, and GOx retained the protein bioactivity. The release of RNase A-loaded nanogels possesses a temperature-responsive profile. The immobilization of Lys and cytochrome C in nanogels inhibited protein bioactivity. However, the addition of NaCl triggered the recovery of bioactivity. These multistimuli-responsive nanogels can provide a versatile platform applicable in biotechnology and drug/protein delivery.

Advances in Nanomedicine Design: Multidisciplinary Strategies for Unmet Medical Needs

Globally, a rising burden of complex diseases takes a heavy toll on human lives and poses substantial clinical and economic challenges. This review covers nanomedicine and nanotechnology-enabled advanced drug delivery systems (DDS) designed to address various unmet medical needs. Key nanomedicine and DDSs, currently employed in the clinic to tackle some of these diseases, are discussed focusing on their versatility in diagnostics, anticancer therapy, and diabetes management. First-hand experiences from our own laboratory and the work of others are presented to provide insights into strategies to design and optimize nanomedicine- and nanotechnology-enabled DDS for enhancing therapeutic outcomes. Computational analysis is also briefly reviewed as a technology for rational design of controlled release DDS. Further explorations of DDS have illuminated the interplay of physiological barriers and their impact on DDS. It is demonstrated how such delivery systems can overcome these barriers for enhanced therapeutic efficacy and how new perspectives of next-generation DDS can be applied clinically.

Magnetic resonance thermometry using a GdIII-based contrast agent

The complexes described here serve as contrast agents for magnetic resonance imaging thermometry. The complexes differentially enhance contrast between 275 and 325 K. The basis of the temperature response of the fluorinated contrast complex is the modulation of water exchange caused by trifluoromethyl groups that can be chemically controlled.

Systematic overview of soft materials as a novel frontier for MRI contrast agents

Magnetic resonance imaging (MRI) is a well-known diagnostic technique used to obtain high quality images in a non-invasive manner. In order to increase the contrast between normal and pathological regions in the human body, positive (T1) or negative (T2) contrast agents (CAs) are commonly intravenously administered. The most efficient class of T1-CAs are based on kinetically stable and thermodynamically inert gadolinium complexes. In the last two decades many novel macro- and supramolecular CAs have been proposed. These approaches have been optimized to increase the performance of the CAs in terms of the relaxivity values and to reduce the administered dose, decreasing the toxicity and giving better safety and pharmacokinetic profiles. The improved performances may also allow further information to be gained on the pathological and physiological state of the human body. The goal of this review is to report a systematic overview of the nanostructurated CAs obtained and developed by manipulating soft materials at the nanometer scale. Specifically, our attention is centered on recent examples of fibers, hydrogels and nanogel formulations, that seem particularly promising for overcoming the problematic issues that have recently pushed the European Medicines Agency (EMA) to withdraw linear CAs from the market.

Gd(iii)-nanostructurated Constrast Agents (CAs) for Magnetic Resonance Imaging (MRI) can be designed and developed by manipulating soft material, including fibers, hydrogels and nanogels, in the nanometer scale.

Temperature-Responsive Magnetic Nanoparticles for Enabling Affinity Separation of Extracellular Vesicles

Small magnetic nanoparticles that have surfaces decorated with stimuli-responsive polymers can be reversibly aggregated via a stimulus, such as temperature, to enable efficient and rapid biomarker separation. To fully realize the potential of these particles, the synthesis needs to be highly reproducible and scalable to large quantity. We have developed a new synthesis for temperature-responsive magnetic nanoparticles via an in situ co-precipitation process of Fe2+/Fe3+ salts at room temperature with poly(acrylic acid)- block-poly( N-isopropylacrylamide) diblock co-polymer template, synthesized via the reversible addition-fragmentation chain-transfer polymerization method. These particles were 56% polymer by weight with a 6.5:1 Fe/COOH ratio and demonstrated remarkable stability over a 2 month period. The hydrodynamic diameter remained constant at ∼28 nm with a consistent transition temperature of 34 °C, and the magnetic particle separation efficiency at 40 °C was ≥95% over the 2 month span. These properties were maintained for all large-scale synthesis batches. To demonstrate the practical utility of the stimuli-responsive magnetic nanoparticles, the particles were incorporated into a temperature-responsive binary reagent system and efficiently separated a model protein biomarker (mouse IgG) as well as purified extracellular vesicles derived from a human biofluid, seminal plasma. The ease of using these particles will prove beneficial for various biomedical applications.

Recommendations for In Vitro and In Vivo Testing of Magnetic Nanoparticle Hyperthermia Combined with Radiation Therapy

Magnetic nanoparticle (MNP)-mediated hyperthermia (MH) coupled with radiation therapy (RT) is a novel approach that has the potential to overcome various practical difficulties encountered in cancer treatment. In this work, we present recommendations for the in vitro and in vivo testing and application of the two treatment techniques. These recommendations were developed by the members of Working Group 3 of COST Action TD 1402: Multifunctional Nanoparticles for Magnetic Hyperthermia and Indirect Radiation Therapy ("Radiomag"). The purpose of the recommendations is not to provide definitive answers and directions but, rather, to outline those tests and considerations that a researcher must address in order to perform in vitro and in vivo studies. The recommendations are divided into 5 parts: (a) in vitro evaluation of MNPs; (b) in vitro evaluation of MNP-cell interactions; (c) in vivo evaluation of the MNPs; (d) MH combined with RT; and (e) pharmacokinetic studies of MNPs. Synthesis and characterization of the MNPs, as well as RT protocols, are beyond the scope of this work.

Diruthenium(ii,iii) metallodrugs of ibuprofen and naproxen encapsulated in intravenously injectable polymer-lipid nanoparticles exhibit enhanced activity against breast and prostate cancer cells

A unique class of diruthenium(ii,iii) metallodrugs containing non-steroidal anti-inflammatory drug (NSAID), Ru₂(NSAID), have been reported to show anticancer activity in glioma models in vitro and in vivo. This work reports the encapsulation of the lead metallodrug of ibuprofen (HIbp), [Ru₂(Ibp)₄Cl] or RuIbp, and also of the new analogue of naproxen (HNpx), [Ru₂(Npx)₄Cl] or RuNpx, in novel intravenously (i.v.) injectable solid polymer-lipid nanoparticles (SPLNs). A rationally selected composition of lipids/polymers rendered nearly spherical Ru₂(NSAID)-SPLNs with a mean size of 120 nm and zeta potential of about -20 mV. The Ru₂(NSAID)-SPLNs are characterized by spectroscopic techniques and the composition in terms of ruthenium-drug species is analyzed by mass spectrometry. The metallodrug-loaded nanoparticles showed high drug loading (17-18%) with ∼100% drug loading efficiency, and good colloidal stability in serum at body temperature. Fluorescence-labeled SPLNs were taken up by the cancer cells in a time- and energy-dependent manner as analyzed by confocal microscopy and fluorescence spectrometry. The Ru₂(NSAID)-SPLNs showed enhanced cytotoxicity (IC₅₀ at 60-100 μmol L^-1 ) in relation to the corresponding Ru₂(NSAID) metallodrugs in breast (EMT6 and MDA-MB-231) and prostate (DU145) cancer cells in vitro. The cell viability of both metallodrug nanoformulations is also compared with those of the parent NSAIDs, HIbp and HNpx, and their corresponding NSAID-SPLNs. In vivo and ex vivo fluorescence imaging revealed good biodistribution and high tumor accumulation of fluorescence-labeled SPLNs following i.v. injection in an orthotopic breast tumor model. The enhanced anticancer activity of the metallodrug-loaded SPLNs in these cell lines can be associated with the advantages of the nanoformulations, assigned mainly to the stability of the colloidal nanoparticles suitable for i.v. injection and enhanced cellular uptake. The findings of this work encourage future in vivo efficacy studies to further exploit the potential of the novel Ru₂(NSAID)-SPLN nanoformulations for clinical application.

Gadolinium-based nanoscale MRI contrast agents for tumor imaging

Gadolinium-based nanoscale magnetic resonance imaging (MRI) contrast agents (CAs) have gained significant momentum as a promising nanoplatform for detecting tumor tissue in medical diagnosis, due to their favorable capability of enhancing the longitudinal relaxivity (r₁) of individual gadolinium ions, delivering to the region of interest a large number of gadolinium ions, and incorporating different functionalities. This mini-review highlights the latest developments and applications, and simultaneously gives some perspectives for their future development.

Design of nanocarriers for nanoscale drug delivery to enhance cancer treatment using hybrid polymer and lipid building blocks

Polymer-lipid hybrid nanoparticles (PLN) are an emerging nanocarrier platform made from building blocks of polymers and lipids. PLN integrate the advantages of biomimetic lipid-based nanoparticles (i.e. solid lipid nanoparticles and liposomes) and biocompatible polymeric nanoparticles. PLN are constructed from diverse polymers and lipids and their numerous combinations, which imparts PLN with great versatility for delivering drugs of various properties to their nanoscale targets. PLN can be classified into two types based on their hybrid nanoscopic structure and assembly methods: Type-I monolithic matrix and Type-II core-shell systems. This article reviews the history of PLN development, types of PLN, lipid and polymer candidates, fabrication methods, and unique properties of PLN. The applications of PLN in delivery of therapeutic or imaging agents alone or in combination for cancer treatment are summarized and illustrated with examples. Important considerations for the rational design of PLN for advanced nanoscale drug delivery are discussed, including selection of excipients, synthesis processes governing formulation parameters, optimization of nanoparticle properties, improvement of particle surface functionality to overcome macroscopic, microscopic and cellular biological barriers. Future directions and potential clinical translation of PLN are also suggested.

Biodegradable Smart Nanogels: A New Platform for Targeting Drug Delivery and Biomedical Diagnostics

Nanogels (or nanohydrogels) have been extensively investigated as one of the most promising nanoparticulate biomedical platforms owing to their advantageous properties that combine the characteristics of hydrogel systems with nanoparticles. Among them, smart nanogels that have the ability to respond to external stimuli, such as pH, redox, temperature, enzymes, light, magnetic field and so forth, are most attractive in the area of drug delivery. Besides, numerous multifunctionalized nanogels with high sensitivity and specificity were designed for diagnostic applications. In this feature article, we have reviewed and discussed the recent progress of biodegradable nanogels as smart nanocarriers of anticancer drugs and biomedical diagnostic agents for cancer.

Absolute MR thermometry using nanocarriers

Accurate time-resolved temperature mapping is crucial for the safe use of hyperthermia-mediated drug delivery. We here propose a magnetic resonance imaging temperature mapping method in which drug delivery systems serve not only to improve tumor targeting, but also as an accurate and absolute nano-thermometer. This method is based on the temperature-dependent chemical shift difference between water protons and the protons in different groups of drug delivery systems. We show that the chemical shift of the protons in the ethylene oxide group in polyethylene glycol (PEG) is temperature-independent, whereas the proton resonance of water decreases with increasing temperature. The frequency difference between both resonances is linear and does not depend on pH and physiological salt conditions. In addition, we show that the proton resonance of the methyl group in N-(2-hydroxypropyl)-methacrylamide (HPMA) is temperature-independent. Therefore, PEGylated liposomes, polymeric mPEG-b-pHPMAm-Lac2 micelles and HPMA copolymers can provide a temperature-independent reference frequency for absolute magnetic resonance (MR) thermometry. Subsequently, we show that multigradient echo MR imaging with PEGylated liposomes in situ allows accurate, time-resolved temperature mapping. In conclusion, nanocarrier materials may serve as highly versatile tools for tumor-targeted drug delivery, acting not only as hyperthermia-responsive drug delivery systems, but also as accurate and precise nano-thermometers.

Oxidation-responsive Eu(2+/3+)-liposomal contrast agent for dual-mode magnetic resonance imaging

An oxidation-responsive contrast agent for magnetic resonance imaging was synthesized using Eu(2+) and liposomes. Positive contrast enhancement was observed with Eu(2+), and chemical exchange saturation transfer was observed before and after oxidation of Eu(2+). Orthogonal detection modes render the concentration of Eu inconsequential to molecular information provided through imaging.

Environmentally responsive MRI contrast agents

Biomedical imaging techniques can provide a vast amount of anatomical information, enabling diagnosis and the monitoring of disease and treatment profile. MRI uniquely offers convenient, non-invasive, high resolution tomographic imaging. A considerable amount of effort has been invested, across several decades, in the design of non toxic paramagnetic contrast agents capable of enhancing positive MRI signal contrast. Recently, focus has shifted towards the development of agents capable of specifically reporting on their local biochemical environment, where a switch in image contrast is triggered by a specific stimulus/biochemical variable. Such an ability would not only strengthen diagnosis but also provide unique disease-specific biochemical insight. This feature article focuses on recent progress in the development of MRI contrast switching with molecular, macromolecular and nanoparticle-based agents.

Promising strategies for Gd-based responsive magnetic resonance imaging contrast agents

Magnetic resonance imaging is a powerful imaging modality that is often coupled with paramagnetic contrast agents based on gadolinium to enhance sensitivity and image quality. Responsive contrast agents are key to furthering the diagnostic potential of MRI, both to provide anatomical information and to discern biochemical activity. Recent design of responsive gadolinium-based T₁ agents has made interesting progress, with the development of novel complexes which sense their chemical environment through changes in the coordination of water molecules, the molecular tumbling time or the number of metal centres. Particular promising design strategies include the use of multimeric systems, and the development of dual imaging probes.