Single-Step Assembly of Multimodal Imaging Nanocarriers: MRI and Long-Wavelength Fluorescence Imaging

Co-encapsulation of organic polymers and inorganic superparamagnetic iron oxide colloidal crystals requires matched diffusion time scales

Nanoparticles (NPs) that contain both organic molecules and inorganic metal or metal oxide colloids in the same NP core are "composite nanoparticles" which are of interest in many applications, particularly in biomedicine as "theranostics" for the combined delivery of colloidal diagnostic imaging agents with therapeutic drugs. The rapid precipitation technique Flash NanoPrecipitation (FNP) enables continuous and scalable production of composite nanoparticles with hydrodynamic diameters between 40-200 nanometers (nm) that contain hydrophobic superparamagnetic iron oxide primary colloids. Composite NPs co-encapsulate these primary colloids (diameters of 6 nm, 15 nm, or 29 nm), a fluorescent dye (600 Daltons), and poly(styrene) homopolymer (1800, 50 000, or 200 000 Daltons) with NPs stabilized by a poly(styrene)-block-poly(ethylene glycol) (1600 Da-b-5000 Da) block copolymer. Nanoparticle assembly in FNP occurs by diffusion limited aggregation of the hydrophobic core components followed by adsorption of the hydrophobic block of the stabilizing polymer. The hydrodynamic diameter mismatch between the collapsed organic species and the primary colloids (0.5-5 nm versus 6-29 nm) creates a diffusion-aggregation time scale mismatch between components that can lead to nonstoichiometric co-encapsulation in the final nanoparticles; some nanoparticles are composites with primary colloids co-encapsulated alongside organics while others are devoid of the primary colloids and contain only organic species. We use a magnetic capture process to separate magnetic composite nanoparticles from organic-only nanoparticles and quantify the amount of iron oxide colloids and hydrophobic fluorescent dye (as a proxy for total hydrophobic polymer content) in the magnetic and nonmagnetic fractions of each formulation. Analysis of the microstructure in over 1100 individual nanoparticles by TEM imaging and composition measurements identifies the conditions that produce nonstoichiometric composite NP populations without co-encapsulated magnetic iron oxide colloids. Stoichiometric magnetically responsive composite NPs are produced when the ratio of characteristic diffusion-aggregation time scales between the inorganic primary colloid and the organic core component is less than 30 and all NPs in a dispersion contain organic and inorganic species in approximately the same ratio. These rules for assembly of colloids and organic components into homogeneous composite nanoparticles are broadly applicable.

Intestinal distribution of anionic, cationic, and neutral polymer-stabilized nanocarriers measured with a lanthanide (europium) tracer assay

Nanocarriers, more commonly called nanoparticles (NPs), have found increasing use as delivery vehicles which increase the oral bioavailability of poorly water-soluble and peptide therapeutics. Therapeutic bioavailability is commonly assessed by measuring plasma concentrations that reflect the absorption kinetics. This bioavailability is a convolution of the gastrointestinal distribution of the NP vehicle, the release rate of the encapsulated therapeutic cargo, and the absorption-metabolism-distribution kinetics of the released therapeutic. The spatiotemporal distribution of the NP vehicle in the gastrointestinal tract is not well studied and is a buried parameter in PK studies used to measure the effectiveness of an NP formulation. This work is a study of the intestinal distribution and fate of orally dosed NPs in male CD-1 mice over 24 h. NPs have identical hydrophobic cores - composed of poly(styrene) homopolymer, a naphthalocyanine dye, and oleate-coated europium oxide colloids - with one of four different surface stabilizers: neutral poly(styrene)-block-poly(ethylene glycol) (PS-b-PEG), moderately negative hydroxypropyl methylcellulose acetate succinate (HPMCAS), highly negative poly(styrene)-block-poly(acrylic acid) (PS-b-PAA), and highly cationic adsorbed chitosan HCl on PS-b-PAA stabilized NPs. NP hydrodynamic diameters are all below 200 nm, with some variation attributable to the molecular properties of the stabilizing polymer. The encapsulated hydrophobic europium oxide colloids do not release soluble europium ions, enabling the use of highly sensitive inductively coupled plasma mass spectrometry (ICP-MS) to detect NP concentrations in digested biological tissues. Highly anionically-charged PAA and cationically-charged chitosan stabilized NPs showed statistically significant increased retention compared to the neutral PEG-stabilized NPs at p < 0.05 significance and (1-β) > 0.95 power. HPMCAS-stabilized NPs showed statistically insignificant greater retention than PEG-stabilized NPs, and all NP formulations showed clearance from the intestines within 24 h. Different surface charges preferentially reside in different segments of the intestines, where cationic chitosan-stabilized NPs showed increased retention in the small intestines (ileum) and anionic PAA-stabilized NPs in the large intestines (caecum and colon). Modifying the surface charge of a NP can be used to modulate mucoadhesion, total retention, and intestinal segment specific retention, which enables the rational design of delivery vehicles that maximize residence times in appropriate locations.

Nanoparticle Assembly: From Self-Organization to Controlled Micropatterning for Enhanced Functionalities

Nanoparticles form long-range micropatterns via self-assembly or directed self-assembly with superior mechanical, electrical, optical, magnetic, chemical, and other functional properties for broad applications, such as structural supports, thermal exchangers, optoelectronics, microelectronics, and robotics. The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. This article provides a comprehensive review of nanoparticle assembly formed primarily via the balance of forces at the nanoscale (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer). The review commences with a general overview of nanoparticle self-assembly, with the state-of-the-art literature review and motivation. It subsequently reviews the recent progress in nanoparticle assembly without the presence of surface templates. Manufacturing techniques for surface template fabrication and their influence on nanoparticle assembly efficiency and effectiveness are then explored. The primary focus is the spatial organization and orientational preference of nanoparticles on non-templated and pre-templated surfaces in a controlled manner. Moreover, the article discusses broad applications of micropatterned surfaces, encompassing various fields. Finally, the review concludes with a summary of manufacturing methods, their limitations, and future trends in nanoparticle assembly.

Flash NanoPrecipitation as an Agrochemical Nanocarrier Formulation Platform: Phloem Uptake and Translocation after Foliar Administration

The increasing severity of pathogenic and environmental stressors that negatively affect plant health has led to interest in developing next-generation agrochemical delivery systems capable of precisely transporting active agents to specific sites within plants. In this work, we adapt Flash NanoPrecipitation (FNP), a scalable nanocarrier (NC) formulation technology used in the pharmaceutical industry, to prepare organic core-shell NCs and study their efficacy as foliar or root delivery vehicles. NCs ranging in diameter from 55 to 200 nm, with surface zeta potentials from -40 to +40 mV, and with seven different shell material properties were prepared and studied. Shell materials included synthetic polymers poly(acrylic acid), poly(ethylene glycol), and poly(2-(dimethylamino)ethyl methacrylate), naturally occurring compounds fish gelatin and soybean lecithin, and semisynthetic hydroxypropyl methylcellulose acetate succinate (HPMCAS). NC cores contained a gadolinium tracer for tracking by mass spectrometry, a fluorescent dye for tracking by confocal microscopy, and model hydrophobic compounds (alpha tocopherol acetate and polystyrene) that could be replaced by agrochemical payloads in subsequent applications. After foliar application onto tomato plants with Silwet L-77 surfactant, internalization efficiencies of up to 85% and NC translocation efficiencies of up to 32% were observed. Significant NC trafficking to the stem and roots suggests a high degree of phloem loading for some of these formulations. Results were corroborated by confocal microscopy and synchrotron X-ray fluorescence mapping. NCs stabilized by cellulosic HPMCAS exhibited the highest degree of translocation, followed by formulations with a significant surface charge. The results from this work indicate that biocompatible materials like HPMCAS are promising agrochemical delivery vehicles in an industrially viable pharmaceutical nanoformulation process (FNP) and shed light on the optimal properties of organic NCs for efficient foliar uptake, translocation, and delivery.

Sequential Flash NanoPrecipitation for the scalable formulation of stable core-shell nanoparticles with core loadings up to 90

Flash NanoPrecipitation (FNP) is a scalable, single-step process that uses rapid mixing to prepare nanoparticles with a hydrophobic core and amphiphilic stabilizing shell. Because the two steps of particle self-assembly - (1) core nucleation and growth and (2) adsorption of a stabilizing polymer onto the growing core surface - occur simultaneously during FNP, nanoparticles formulated at core loadings above approximately 70% typically exhibit poor stability or do not form at all. Additionally, a fundamental limit on the concentration of total solids that can be introduced into the FNP process has been reported previously. These limits are believed to share a common mechanism: entrainment of the stabilizing polymer into the growing particle core, leading to destabilization and aggregation. Here, we demonstrate a variation of FNP which separates the nucleation and stabilization steps of particle formation into separate sequential mixers. This scheme allows the hydrophobic core to nucleate and grow in the first mixing chamber unimpeded by adsorption of the stabilizing polymer, which is later introduced to the growing nuclei in the second mixer. Using this Sequential Flash NanoPrecipitation (SNaP) technique, we formulate stable nanoparticles with up to 90% core loading by mass and at 6-fold higher total input solids concentrations than typically reported.

Dual imaging agent for magnetic particle imaging and computed tomography

Magnetic particle imaging (MPI) is a novel biomedical imaging modality that allows non-invasive, tomographic, and quantitative tracking of the distribution of superparamagnetic iron oxide nanoparticle (SPION) tracers. While MPI possesses high sensitivity, detecting nanograms of iron, it does not provide anatomical information. Computed tomography (CT) is a widely used biomedical imaging modality that yields anatomical information at high resolution. A multimodal imaging agent combining the benefits of MPI and CT imaging would be of interest. Here we combine MPI-tailored SPIONs with CT-contrast hafnium oxide (hafnia) nanoparticles using flash nanoprecipitation to obtain dual-imaging MPI/CT agents. Co-encapsulation of iron oxide and hafnia in the composite nanoparticles was confirmed via transmission electron microscopy and elemental mapping. Equilibrium and dynamic magnetic characterization show a reduction in effective magnetic diameter and changes in dynamic magnetic susceptibility spectra at high oscillating field frequencies, suggesting magnetic interactions within the composite dual imaging tracers. The MPI performance of the dual imaging agent was evaluated and compared to the commercial tracer ferucarbotran. The dual-imaging agent has MPI sensitivity that is ∼3× better than this commercial tracer. However, worsening of MPI resolution was observed in the composite tracer when compared to individually coated SPIONs. This worsening resolution could result from magnetic dipolar interactions within the composite dual imaging tracer. The CT performance of the dual imaging agent was evaluated in a pre-clinical animal scanner and a clinical scanner, revealing better contrast compared to a commercial iodine-based contrast agent. We demonstrate that the dual imaging agent can be differentiated from the commercial iodine contrast agent using dual energy CT (DECT) imaging. Furthermore, the dual imaging agent displayed energy-dependent CT contrast arising from the combination of SPION and hafnia, making it potentially suitable for virtual monochromatic imaging of the contrast agent distribution using DECT.

Recent advances in mixing-induced nanoprecipitation: from creating complex nanostructures to emerging applications beyond biomedicine

Mixing-induced nanoprecipitation (MINP) is an efficient, controllable, scalable, versatile, and cost-effective technique for the preparation of nanoparticles. In addition to the formulation of drugs, MINP has attracted tremendous interest in other fields. In this review, we highlight recent advances in the preparation of nanoparticles with complex nanostructures via MINP and their emerging applications beyond biomedicine. First, the mechanisms of nanoprecipitation and four mixing approaches for MINP are briefly discussed. Next, three strategies for the preparation of nanoparticles with complex nanostructures including sequential nanoprecipitation, controlling phase separation, and incorporating inorganic nanoparticles, are summarized. Then, emerging applications including the engineering of catalytic nanomaterials, environmentally friendly photovoltaic inks, colloidal surfactants for the preparation of Pickering emulsions, and green templates for the synthesis of nanomaterials, are reviewed. Furthermore, we discuss the structure-function relationships to gain more insight into design principles for the development of functional nanoparticles via MINP. Finally, the remaining issues and future applications are discussed. This review will stimulate the development of nanoparticles with complex nanostructures and their broader applications beyond biomedicine.

Impact of RAFT chain transfer agents on the polymeric shell density of magneto-fluorescent nanoparticles and their cellular uptake

The impact of nanoparticle surface chemistry on cell interactions and especially cell uptake has become evident over the last few years in nanomedicine. Since PEG polymers have proved to be ideal tools for attaining stealthiness and favor escape from the in vivo mononuclear phagocytotic system, the accurate control of their geometry is of primary importance and can be achieved through reversible addition-fragmentation transfer (RAFT) polymerization. In this study, we demonstrate that the residual groups of the chain transfer agents (CTAs) introduced in the main chain exert a significant impact on the cellular internalization of functionalized nanoparticles. High-resolution magic angle spinning ¹H NMR spectroscopy and fluorescence spectroscopy permitted by the magneto-fluorescence properties of nanoassemblies (NAs) revealed the compaction of the PEG comb-like shell incorporating CTAs with a long alkyl chain, without changing the overall surface potential. As a consequence of the capability of alkyl units to self-assemble at the NA surface while hardly contributing more than 0.5% to the total polyelectrolyte weight, denser PEGylated NAs showed notably less internalization in all cells of the tumor microenvironment (tumor cells, macrophages and healthy cells). Interestingly, such differentiated uptake is also observed between pro-inflammatory M1-like and immunosuppressive M2-like macrophages, with the latter more efficiently phagocytizing NAs coated with a less compact PEGylated shell. In contrast, the NA diffusion inside multicellular spheroids, used to mimic solid tumors, appeared to be independent of the NA coating. These results provide a novel effort-saving approach where the sole variation of the chemical nature of CTAs in RAFT PEGylated polymers strikingly modulate the cell uptake of nanoparticles upon the organization of their surface coating and open the pathway toward selectively addressing macrophage populations for cancer immunotherapy.

An Overview of Micronanoswarms for Biomedical Applications

Micronanoswarms have attracted extensive attention worldwide due to their great promise in biomedical applications. The collective behaviors among thousands, or even millions, of tiny active agents indicate immense potential for benefiting the progress of clinical therapeutic and diagnostic methods. In recent years, with the development of smart materials, remote actuation modalities, and automatic control strategies, the motion dexterity, environmental adaptability, and functionality versatility of micronanoswarms are improved. Swarms can thus be designed as dexterous platforms inside living bodies to perform a multitude of tasks related to healthcare. Existing surveys summarize the design, functionalization, and biomedical applications of micronanorobots and the actuation and motion control strategies of micronanoswarms. This review presents the recent progress of micronanoswarms, aiming for biomedical applications. The recent advances on structural design of artificial, living, and hybrid micronanoswarms are summarized, and the biomedical applications that could be tackled using micronanoswarms are introduced, such as targeted drug delivery, hyperthermia, imaging and sensing, and thrombolysis. Moreover, potential challenges and promising trends of future developments are discussed. It is envisioned that the future success of these promising tools will have a significant impact on clinical treatment.

Recent Advances in Multimodal Molecular Imaging of Cancer Mediated by Hybrid Magnetic Nanoparticles

Cancer is the second leading cause of death in the world, which is why it is so important to make an early and very precise diagnosis to obtain a good prognosis. Thanks to the combination of several imaging modalities in the form of the multimodal molecular imaging (MI) strategy, a great advance has been made in early diagnosis, in more targeted and personalized therapy, and in the prediction of the results that will be obtained once the anticancer treatment is applied. In this context, magnetic nanoparticles have been positioned as strong candidates for diagnostic agents as they provide very good imaging performance. Furthermore, thanks to their high versatility, when combined with other molecular agents (for example, fluorescent molecules or radioisotopes), they highlight the advantages of several imaging techniques at the same time. These hybrid nanosystems can be also used as multifunctional and/or theranostic systems as they can provide images of the tumor area while they administer drugs and act as therapeutic agents. Therefore, in this review, we selected and identified more than 160 recent articles and reviews and offer a broad overview of the most important concepts that support the synthesis and application of multifunctional magnetic nanoparticles as molecular agents in advanced cancer detection based on the multimodal molecular imaging approach.

Fast nanoparticle rotational and translational diffusion in synovial fluid and hyaluronic acid solutions

Nanoparticles are under investigation as diagnostic and therapeutic agents for joint diseases, such as osteoarthritis. However, there is incomplete understanding of nanoparticle diffusion in synovial fluid, the fluid inside the joint, which consists of a mixture of the polyelectrolyte hyaluronic acid, proteins, and other components. Here, we show that rotational and translational diffusion of polymer-coated nanoparticles in quiescent synovial fluid and in hyaluronic acid solutions is well described by the Stokes-Einstein relationship, albeit with an effective medium viscosity that is much smaller than the macroscopic low shear viscosity of the fluid. This effective medium viscosity is well described by an equation for the viscosity of dilute polymer chains, where the additional viscous dissipation arises because of the presence of the polymer segments. These results shed light on the diffusive behavior of polymer-coated inorganic nanoparticles in complex and crowded biological environments, such as in the joint.

Nanoparticle size distribution quantification from transmission electron microscopy (TEM) of ruthenium tetroxide stained polymeric nanoparticles

HYPOTHESIS

Dynamic Light Scattering (DLS) generated particle size distributions (PSD) of polymer-stabilized nanoparticles are dependent on the optimization parameters used to generate an inversion solution fit to the measured autocorrelation function. The accuracy of the DLS PSD average and polydispersity can be determined by comparing analyzed Transmission Electron Microscopy (TEM) images with the DLS results if the TEM measured sizes can be corrected for the thickness of the hydrated polymer corona that impacts particle hydrodynamics but is a collapsed, desiccated shell in the TEM images.

EXPERIMENTS

Nanoparticles were prepared by Flash NanoPrecipitation with either poly(ethylene glycol) (PEG) or hydroxypropyl methylcellulose acetate succinate (HPMCAS) stabilizing polymers. Solvated nanoparticle size distributions were measured by DLS in aqueous media. The same nanoparticle dispersions were lyophilized onto TEM grids and stained by ruthenium tetroxide (RuO₄) vapor to improve electron contrast. Desiccated particle size distributions were generated by measuring a minimum of 300 particle diameters in the stained TEM images.

FINDINGS

Using our protocol for staining soft matter nanoparticles in TEM measurements, we have quantitatively analyzed the correlation between DLS and TEM generated PSDs. Average diameters disagree by the hydrated polymer corona thickness for each stabilizer due to the high-vacuum TEM environment, with 21.4 nm for PEG and 51.2 nm for HPMCAS. While corrected average diameter agrees within 10% for each technique, DLS consistently over-estimates the standard deviation of the PSD by 100% compared to the TEM measurement.

Flash Technology-Based Self-Assembly in Nanoformulation: From Fabrication to Biomedical Applications

Advances in nanoformulation have driven progress in biomedicine by producing nanoscale tools for biosensing, imaging, and drug delivery. Flash-based technology, the combination of rapid mixing technique with the self-assembly of macromolecules, is a new engine for the translational nanomedicine. Here, we review the state-of-the-art in flash-based self-assembly including theoretical and experimental principles, mixing device design, and applications. We highlight the fields of flash nanocomplexation (FNC) and flash nanoprecipitation (FNP), with an emphasis on biomedical applications of FNC, and discuss challenges and future directions for flash-based nanoformulation in biomedicine.

Microfluidic Assisted Flash Precipitation of Photocrosslinkable Fluorescent Organic Nanoparticles for Fine Size Tuning and Enhanced Photoinduced Processes

Highly concentrated dispersions of fluorescent organic nanoparticles (FONs), broadly used for optical tracking, bioimaging and drug delivery monitoring, are obtained using a newly designed micromixer chamber involving high impacting flows. Fine size tuning and narrow size distributions are easily obtained by varying independently the flow rates of the injected fluids and the concentration of the dye stock solution. The flash nanoprecipitation process employed herein is successfully applied to the fabrication of bicomposite FONs designed to allow energy transfer. Considerable enhancement of the emission signal of the energy acceptors is promoted and its origin is found to result from polarity rather than steric effects. Finally, we exploit the high spatial confinement encountered in FONs and their ability to encapsulate hydrophobic photosensitizers to induce photocrosslinking. An increase in the photocrosslinked FON stiffness is evidenced by measuring the elastic modulus at the nanoscale using atomic force microscopy. These results pave the way toward the straightforward fabrication of multifunctional and mechanically photoswitchable FONs, opening novel opportunities in sensing, multimodal imaging, and theranostics.

Accelerated Reaction Rates within Self-Assembled Polymer Nanoreactors with Tunable Hydrophobic Microenvironments

Performing reactions in the presence of self-assembled hierarchical structures of amphiphilic macromolecules can accelerate reactions while using water as the bulk solvent due to the hydrophobic effect. We leveraged non-covalent interactions to self-assemble filled-polymer micelle nanoreactors (NR) incorporating gold nanoparticle catalysts into various amphiphilic polymer nanostructures with comparable hydrodynamic nanoreactor size and gold concentration in the nanoreactor dispersion. We systematically studied the effect of the hydrophobic co-precipitant on self-assembly and catalytic performance. We observed that co-precipitants that interact with gold are beneficial for improving incorporation efficiency of the gold nanoparticles into the nanocomposite nanoreactor during self-assembly but decrease catalytic performance. Hierarchical assemblies with co-precipitants that leverage noncovalent interactions could enhance catalytic performance. For the co-precipitants that do not interact strongly with gold, the catalytic performance was strongly affected by the hydrophobic microenvironment of the co-precipitant. Specifically, the apparent reaction rate per surface area using castor oil (CO) was over 8-fold greater than polystyrene (750 g/mol, PS 750); the turnover frequency was higher than previously reported self-assembled polymer systems. The increase in apparent catalytic performance could be attributed to differences in reactant solubility rather than differences in mass transfer or intrinsic kinetics; higher reactant solubility enhances apparent reaction rates. Full conversion of 4-nitrophenol was achieved within three minutes for at least 10 sequential reactions demonstrating that the nanoreactors could be used for multiple reactions.

The clearance and biodistribution of magnetic composite nanoparticles in healthy and osteoarthritic rat knees

Intra-articular injections are the most direct route for administering osteoarthritis (OA) therapies, yet how drug carriers distribute within the joint remains understudied. To this end, we developed a magnetic composite nanoparticle that can be tracked with fluorescence in vivo via an in vivo imaging system (IVIS), and quantified ex vivo via electron paramagnetic resonance (EPR) spectroscopy. Using this particle, the effects of age and OA pathogenesis on particle clearance and distribution were evaluated in the medial meniscus transection model of OA (5-, 10-, and 15-month old male Lewis rats). At 9 weeks after meniscus transection, composite nanoparticles were injected and joint clearance was assessed via IVIS. At 2 weeks after injection, animals were euthanized and particle distribution was quantified ex vivo via EPR spectroscopy. IVIS and EPR spectroscopy data indicate a predominant amount of particles remained in the joint after 14 days. EPR spectroscopy data suggests particles cleared more slowly from OA knees than from the contralateral control, with particles clearing more slowly from 15-month old rats than from 5- and 10-month old rats. This study demonstrates the importance of including both age and OA as factors when evaluating nanoparticles for intra-articular drug delivery.

Microfluidics for Production of Particles: Mechanism, Methodology, and Applications

In the past two decades, microfluidics-based particle production is widely applied for multiple biological usages. Compared to conventional bulk methods, microfluidic-assisted particle production shows significant advantages, such as narrower particle size distribution, higher reproducibility, improved encapsulation efficiency, and enhanced scaling-up potency. Herein, an overview of the recent progress of the microfluidics technology for nano-, microparticles or droplet fabrication, and their biological applications is provided. For both nano-, microparticles/droplets, the previously established mechanisms behind particle production via microfluidics and some typical examples during the past five years are discussed. The emerging interdisciplinary technologies based on microfluidics that have produced microparticles or droplets for cellular analysis and artificial cells fabrication are summarized. The potential drawbacks and future perspectives are also briefly discussed.

Luminophore and Magnetic Multicore Nanoassemblies for Dual-Mode MRI and Fluorescence Imaging

Nanoassemblies encompass a large variety of systems (organic, crystalline, amorphous and porous). The nanometric size enables these systems to interact with biological entities and cellular organelles of similar dimensions (proteins, cells, …). Over the past 20 years, the exploitation of their singular properties as contrast agents has led to the improvement of medical imaging. The use of nanoprobes also allows the combination of several active units within the same nanostructure, paving the way to multi-imaging. Thus, the nano-object provides various additional information which helps simplify the number of clinical procedures required. In this review, we are interested in the combination between fluorescent units and magnetic nanoparticles to perform dual-mode magnetic resonance imaging (MRI) and fluorescent imaging. The effect of magnetic interaction in multicore iron oxide nanoparticles on the MRI contrast agent properties is highlighted.

Theranostic nanocarriers combining high drug loading and magnetic particle imaging

We report preparation of theranostic nanocarriers loaded with up to 50 wt% of the anticancer drug doxorubicin that contain magnetic nanoparticles which enable Magnetic Particle Imaging (MPI), an emerging technology for quantitative and unambiguous imaging of the nanocarriers. The nanocarriers, coated with poly(ethylene glycol)-block-poly(lactic acid) (PEG_4.9kD-b-PLA_6kD) block copolymer for colloidal stability, are composed of a hydrophobic core of precipitated hydrolysable doxorubicin prodrug (proDox) and magnetic nanoparticles. Transmission electron microscopy (TEM) shows evidence of precipitated proDox for nanocarriers with high drug loading of up to 50 wt%. MPI measurements show that the nanocarriers can be quantitatively imaged. The nanocarriers are internalized by MDA-MB-231 cells and their IC₅₀ value via metabolic assay is 1.1 µM, compared to 0.21 µM for free doxorubicin. The release rate from the nanocarriers was dependent on environmental pH. These nanocarriers with high drug loading and quantitative imaging are promising candidates for future applications.

Translational formulation of nanoparticle therapeutics from laboratory discovery to clinical scale

BACKGROUND

"Nanomedicine" is the application of purposely designed nano-scale materials for improved therapeutic and diagnostic outcomes, which cannot be otherwise achieved using conventional delivery approaches. While "translation" in drug development commonly encompasses the steps from discovery to human clinical trials, a different set of translational steps is required in nanomedicine. Although significant development effort has been focused on nanomedicine, the translation from laboratory formulations up to large scale production has been one of the major challenges to the success of such nano-therapeutics. In particular, scale-up significantly alters momentum and mass transfer rates, which leads to different regimes for the formation of nanomedicines. Therefore, unlike the conventional definition of translational medicine, a key component of "bench-to-bedside" translational research in nanomedicine is the scale-up of the synthesis and processing of the nano-formulation to achieve precise control of the nanoscale properties. This consistency requires reproducibility of size, polydispersity and drug efficacy.

METHODS

Here we demonstrate that Flash NanoPrecipitation (FNP) offers a scalable and continuous technique to scale up the production rate of nanoparticles from a laboratory scale to a pilot scale. FNP is a continuous, stabilizer-directed rapid precipitation process. Lumefantrine, an anti-malaria drug, was chosen as a representative drug that was processed into 200 nm nanoparticles with enhanced bioavailability and dissolution kinetics. Three scales of mixers, including a small-scale confined impinging jet mixer, a mid-scale multi-inlet vortex mixer (MIVM) and a large-scale multi-inlet vortex mixer, were utilized in the formulation. The production rate of nanoparticles was varied from a few milligrams in a laboratory batch mode to around 1 kg/day in a continuous large-scale mode, with the size and polydispersity similar at all scales.

RESULTS

Nanoparticles of 200 nm were made at all three scales of mixers by operating at equivalent Reynolds numbers (dynamic similarity) in each mixer. Powder X-ray diffraction and differential scanning calorimetry demonstrated that the drugs were encapsulated in an amorphous form across all production rates. Next, scalable and continuous spray drying was applied to obtain dried powders for long-term storage stability. For dissolution kinetics, spray dried samples produced by the large-scale MIVM showed 100% release in less than 2 h in both fasted and fed state intestinal fluids, similar to small-batch low-temperature lyophilization.

CONCLUSIONS

These results validate the successful translation of a nanoparticle formulation from the discovery scale to the clinical scale. Coupling nanoparticle production using FNP processing with spray drying offers a continuous nanofabrication platform to scale up nanoparticle synthesis and processing into solid dosage forms.

Rapid Self-Assembly of Metal/Polymer Nanocomposite Particles as Nanoreactors and Their Kinetic Characterization

Self-assembled metal nanoparticle-polymer nanocomposite particles as nanoreactors are a promising approach for performing liquid phase reactions using water as a bulk solvent. In this work, we demonstrate rapid, scalable self-assembly of metal nanoparticle catalyst-polymer nanocomposite particles via Flash NanoPrecipitation. The catalyst loading and size of the nanocomposite particles can be tuned independently. Using nanocomposite particles as nanoreactors and the reduction of 4-nitrophenol as a model reaction, we study the fundamental interplay of reaction and diffusion. The induction time is affected by the sequence of reagent addition, time between additions, and reagent concentration. Combined, our experiments indicate the induction time is most influenced by diffusion of sodium borohydride. Following the induction time, scaling analysis and effective diffusivity measured using NMR indicate that the observed reaction rate are reaction- rather than diffusion-limited. Furthermore, the intrinsic kinetics are comparable to ligand-free gold nanoparticles. This result indicates that the polymer microenvironment does not de-activate or block the catalyst active sites.

Scalable Solvothermal Synthesis of Superparamagnetic Fe3O4 Nanoclusters for Bioseparation and Theragnostic Probes

Magnetic nanoparticles have had a significant impact on a wide range of advanced applications in the academic and industrial fields. In particular, in nanomedicine, the nanoparticles require specific properties, including hydrophilic behavior, uniform and tunable dimensions, and good magnetic properties, which are still challenging to achieve by industrial-scale synthesis. Here, we report a gram-scale synthesis of hydrophilic magnetic nanoclusters based on a one-pot solvothermal system. Using this approach, we achieved the nanoclusters with controlled size composed of magnetite nanocrystals in close-packed superstructures that exhibited hydrophilicity, superparamagnetism, high magnetization, and colloidal stability. The proposed solvothermal method is found to be highly suitable for synthesizing industrial quantities (gram-per-batch level) of magnetic spheres with unchanged structural and magnetic properties. Furthermore, coating the magnetic spheres with an additional silica layer provided further stability and specific functionalities favorable for biological applications. Using in vitro and in vivo studies, we successfully demonstrated both positive and negative separation and the use of the magnetic nanoclusters as a theragnostic nanoprobe. This scalable synthetic procedure is expected to be highly suitable for widespread use in biomedical, energy storage, photonics, and catalysis fields, among others.

Quench ionic flash nano precipitation as a simple and tunable approach to decouple growth and functionalization for the one-step synthesis of functional LnPO4-based nanoparticles in water

A novel, one-step method for the synthesis of functional, organic-inorganic hybrid nanoparticles is reported. The quench ionic Flash NanoPrecipitation (qiFNP) method enables the straightforward synthesis of nanoparticles by decoupling the formation of the inorganic core and surface functionalization. As a proof-of-concept, the qiFNP method was successfully applied for the tunable and highly controlled synthesis of various LnPO4-based nanomaterials for bioimaging applications.

Controlling and Predicting Nanoparticle Formation by Block Copolymer Directed Rapid Precipitations

Nanoparticles have shown promise in several biomedical applications, including drug delivery and medical imaging; however, quantitative prediction of nanoparticle formation processes that scale from laboratory to commercial production has been lacking. Flash NanoPrecipitation (FNP) is a scalable technique to form highly loaded, block copolymer protected nanoparticles. Here, the FNP process is shown to strictly obey diffusion-limited aggregation assembly kinetics, and the parameters that control the nanoparticle size and the polymer brush density on the nanoparticle surface are shown. The particle size, ranging from 40 to 200 nm, is insensitive to the molecular weight and chemical composition of the hydrophobic encapsulated material, which is shown to be a consequence of the diffusion-limited growth kinetics. In a simple model derived from these kinetics, a single constant describes the 46 unique nanoparticle formulations produced here. The polymer brush densities on the nanoparticle surface are weakly dependent on the process parameters and are among the densest reported in the literature. Though modest differences in brush densities are observed, there is no measurable difference in the amount of protein adsorbed within this range. This work highlights the material-independent and universal nature of the Flash NanoPrecipitation process, allowing for the rapid translation of formulations to different stabilizing polymers and therapeutic loads.

Engineering and delivery of nanocolloids of hydrophobic drugs

A lot of efforts have been devoted to engineering the delivery of hydrophobic drugs due to the high demand of chemotherapy against cancer. While early developed liposomes and polymeric nanoparticles did not meet the requirements of high drug loading efficiency, pure drug nanoparticles appeared to meet these together with high stability. Current drug delivery systems demand an improved performance over the whole aspects of stability, loading capacity, and therapeutic effects. As a result, both new techniques based on traditional methods and totally new procedures are under investigation. In this review, we focus on the evaluation of pure drug nanolloids fabricated by different engineering protocols with emphasis on the size and morphology, delivery and controlled release, and therapeutic effects of these drug nanocolloids.

Using Flash Nanoprecipitation To Produce Highly Potent and Stable Cellax Nanoparticles from Amphiphilic Polymers Derived from Carboxymethyl Cellulose, Polyethylene Glycol, and Cabazitaxel

We report the use of flash nanoprecipitation (FNP) as an efficient and scalable means of producing Cellax nanoparticles. Cellax polymeric conjugates consisting of carboxymethyl cellulose functionalized with PEG and hydrophobic anticancer drugs, such as cabazitaxel (coined Cellax-CBZ), have been shown to have high potency against several oncology targets, including prostate cancer. FNP, a robust method used to create nanoparticles through rapid mixing, has been used to encapsulate several hydrophobic drugs with block copolymer stabilizers, but has never been used to form nanoparticles from random copolymers, such as Cellax-CBZ. To assess the potential of using FNP to produce Cellax nanoparticles, parameters such as concentration, mixing rate, solvent ratios, and subsequent dilution were tested with a target nanoparticle size range of 60 nm. Under optimized solvent conditions, particles were formed that underwent a subsequent rearrangement to form nanoparticles of 60 nm diameter, independent of Cellax-CBZ polymer concentration. This intraparticle relaxation, without interparticle association, points to a delicate balance of hydrophobic/hydrophilic domains on the polymer backbone. These particles were stable over time, and the random amphiphilicity did not lead to interparticle attractions, which would compromise the stability and corresponding narrow size distribution required for parenteral injection. The amphiphilic nature of these conjugates allows them to be processed into nanoparticles for sustained drug release and improved tumor selectivity. Preferred candidates were evaluated for plasma stability and cytotoxicity against the PC3 prostate cancer cell line in vitro. These parameters are important when assessing nanoparticle safety and for estimating potential efficacy, respectively. The optimal formulations showed plasma stability profiles consistent with long circulating nanoparticles, and cytotoxicity comparable to that of free CBZ. This study demonstrates that FNP is a promising technology for development of Cellax nanoparticles.

Assembly of Macrocycle Dye Derivatives into Particles for Fluorescence and Photoacoustic Applications

Optical imaging is a rapidly progressing medical technique that can benefit from the development of new and improved optical imaging agents suitable for use in vivo. However, the molecular rules detailing what optical agents can be processed and encapsulated into in vivo presentable forms are not known. We here present the screening of series of highly hydrophobic porphyrin, phthalocyanine, and naphthalocyanine dye macrocycles through a self-assembling Flash NanoPrecipitation process to form a series of water dispersible dye nanoparticles (NPs). Ten out of 19 tested dyes could be formed into poly(ethylene glycol) coated nanoparticles 60-150 nm in size, and these results shed insight on dye structural criteria that are required to permit dye assembly into NPs. Dye NPs display a diverse range of absorbance profiles with absorbance maxima within the NIR region, and have absorbance that can be tuned by varying dye choice or by doping bulking materials in the NP core. Particle properties such as dye core load and the compositions of co-core dopants were varied, and subsequent effects on photoacoustic and fluorescence signal intensities were measured. These results provide guidelines for designing NPs optimized for photoacoustic imaging and NPs optimized for fluorescence imaging. This work provides important details for dye NP engineering, and expands the optical imaging tools available for use.

Ionic Flash NanoPrecipitation (iFNP) for the facile, one-step synthesis of inorganic-organic hybrid nanoparticles in water

Ionic Flash NanoPrecipitation (iFNP) was evaluated as a novel method for the synthesis of inorganic-organic hybrid nanomaterials and proved to be remarkably effective, fast and practical. To prove the potential of iFNP, various nanostructured GdPO₄-based materials of biomedical imaging relevance were easily prepared in a one-step, tunable and highly controlled manner using only water as solvent.

Nanocarriers from GRAS Zein Proteins to Encapsulate Hydrophobic Actives

One factor limiting the expansion of nanomedicines has been the high cost of the materials and processes required for their production. We present a continuous, scalable, low cost nanoencapsulation process, Flash Nanoprecipitation (FNP) that enables the production of nanocarriers (NCs) with a narrow size distribution using zein corn proteins. Zein is a low cost, GRAS protein (having the FDA status of "Generally Regarded as Safe") currently used in food applications, which acts as an effective encapsulant for hydrophobic compounds using FNP. The four-stream FNP configuration allows the encapsulation of very hydrophobic compounds in a way that is not possible with previous precipitation processes. We present the encapsulation of several model active compounds with as high as 45 wt % drug loading with respect to zein concentration into ∼100 nm nanocarriers. Three examples are presented: (1) the pro-drug antioxidant, vitamin E-acetate, (2) an anticholera quorum-sensing modulator CAI-1 ((S)-3-hydroxytridecan-4-one; CAI-1 that reduces Vibrio cholerae virulence by modulating cellular communication), and (3) hydrophobic fluorescent dyes with a range of hydrophobicities. The specific interaction between zein and the milk protein, sodium caseinate, provides stabilization of the NCs in PBS, LB medium, and in pH 2 solutions. The stability and size changes in the three media provide information on the mechanism of assembly of the zein/active/casein NC.

Tuning the architectural integrity of high-performance magneto-fluorescent core-shell nanoassemblies in cancer cells

High-density nanoarchitectures, endowed with simultaneous fluorescence and contrast properties for MRI and TEM imaging, have been obtained using a simple self-assembling strategy based on supramolecular interactions between non-doped fluorescent organic nanoparticles (FON) and superparamagnetic nanoparticles. In this way, a high-payload core-shell structure FON@mag has been obtained, protecting the hydrophobic fluorophores from the surroundings as well as from emission quenching by the shell of magnetic nanoparticles. Compared to isolated nanoparticles, maghemite nanoparticles self-assembled as an external shell create large inhomogeneous magnetic field, which causes enhanced transverse relaxivity and exacerbated MRI contrast. The magnetic load of the resulting nanoassemblies is evaluated using magnetic sedimentation and more originally electrospray mass spectrometry. The role of the stabilizing agents (citrate versus polyacrylate anions) revealed to be crucial regarding the cohesion of the resulting high-performance magneto-fluorescent nanoassemblies, which questions their use after cell internalization as nanocarriers or imaging agents for reliable correlative light and electron microcopy.

Narrow Absorption NIR Wavelength Organic Nanoparticles Enable Multiplexed Photoacoustic Imaging

Photoacoustic (PA) imaging is an emerging hybrid optical-ultrasound based imaging technique that can be used to visualize optical absorbers in deep tissue. Free organic dyes can be used as PA contrast agents to concurrently provide additional physiological and molecular information during imaging, but their use in vivo is generally limited by rapid renal clearance for soluble dyes and by the difficulty of delivery for hydrophobic dyes. We here report the use of the block copolymer directed self-assembly process, Flash NanoPrecipitation (FNP), to form series of highly hydrophobic optical dyes into stable, biocompatible, and water-dispersible nanoparticles (NPs) with sizes from 38 to 88 nm and with polyethylene glycol (PEG) surface coatings suitable for in vivo use. The incorporation of dyes with absorption profiles within the infrared range, that is optimal for PA imaging, produces the PA activity of the particles. The hydrophobicity of the dyes allows their sequestration in the NP cores, so that they do not interfere with targeting, and high loadings of >75 wt % dye are achieved. The optical extinction coefficients (ε (mL mg(-1) cm(-1))) were essentially invariant to the loading of the dye in NP core. Co-encapsulation of dye with vitamin E or polystyrene demonstrates the ability to simultaneously image and deliver a second agent. The PEG chains on the NP surface were functionalized with folate to demonstrate folate-dependent targeting. The spectral separation of different dyes among different sets of particles enables multiplexed imaging, such as the simultaneous imaging of two sets of particles within the same animal. We provide the first demonstration of this capability with PA imaging, by simultaneously imaging nontargeted and folate-targeted nanoparticles within the same animal. These results highlight Flash NanoPrecipitation as a platform to develop photoacoustic tools with new diagnostic capabilities.

Biopharmaceutical Evaluation of Novel Cyclosporine A Nano-matrix Particles for Inhalation

PURPOSE

This study was undertaken to evaluate the biopharmaceutical properties of cyclosporine A (CsA)-loaded nano-matrix particles for inhalation.

METHODS

Nano-matrix particles of CsA with mannitol (nCsAm) were prepared by a flash nano-precipitation technique employing a multi-inlet vortex mixer and evaluated in terms of physicochemical properties, anti-inflammatory effect in the rat model of airway inflammation, pharmacokinetic behavior, and distributions of CsA to side-effect-related organs after intratracheal administration.

RESULTS

In nCsAm, spherical nano-particles of CsA were covered with mannitol and the mean particle size was 1.3 μm. The in vitro Next Generation Impactor analysis demonstrated fine inhalation performance with a fine particle fraction value of 65.8%. Intratracheal nCsAm (100 μg-CsA/rat) significantly attenuated the recruitment of inflammatory cells into the airway in the rat model of airway inflammation, followed by suppression of the inflammatory biomarkers. After intratracheal nCsAm at a pharmacologically effective dose (100 μg-CsA/rat), there was a 42-47-fold decrease in the distribution of CsA to side-effect-related organs such as the kidney and liver compared with oral CsA at a toxic dose (10 mg-CsA/kg), potentially leading to avoidance of systemic side-effects of CsA.

CONCLUSION

Upon these findings, nCsAm prepared with the flash nano-precipitation technique could be a novel dosage form of CsA for inhalation therapy of airway inflammation with a better safety margin.

Biodistribution and fate of core-labeled 125I polymeric nanocarriers prepared by Flash NanoPrecipitation (FNP)

Non-invasive medical imaging techniques such as positron emission tomography (PET) imaging are powerful platforms to track the fate of radiolabeled materials for diagnostic or drug delivery applications. Polymer-based nanocarriers tagged with non-standard PET radionuclides with relatively long half-lives (e.g. 64Cu: t1/2 = 12.7 h, 76Br: t1/2 = 16.2h, 89Zr: t1/2 = 3.3 d, 124I: t1/2 = 4.2 d) may greatly expand applications of nanomedicines in molecular imaging and therapy. However, radiolabeling strategies that ensure stable in vivo association of the radiolabel with the nanocarrier remain a significant challenge. In this study, we covalently attach radioiodine to the core of pre-fabricated nanocarriers. First, we encapsulated polyvinyl phenol within a poly(ethylene glycol) coating using Flash NanoPrecipitation (FNP) to produce stable 75 nm and 120 nm nanocarriers. Following FNP, we radiolabeled the encapsulated polyvinyl phenol with 125I via electrophilic aromatic substitution in high radiochemical yields (> 90%). Biodistribution studies reveal low radioactivity in the thyroid, indicating minimal leaching of the radiolabel in vivo. Further, PEGylated [125I]PVPh nanocarriers exhibited relatively long circulation half-lives (t1/2 α = 2.9 h, t1/2 β = 34.9 h) and gradual reticuloendothelial clearance, with 31% of injected dose in blood retained at 24 h post-injection.

pH-Activatable MnO-Based Fluorescence and Magnetic Resonance Bimodal Nanoprobe for Cancer Imaging

Stimuli-responsive nanoprobes that combine both fluorescence and magnetic resonance imaging (MRI) are anticipated to be highly beneficial for tumor visualization with high imaging sensitivity. By employing an interfacial templating scheme, a pH-activatable fluorescence/MRI dual-modality imaging nanoprobe is successfully developed based on the coencapsulation of MnO nanoparticles and coumarin-545T inside a hybrid silica nanoshell. To promote cancer cell targeting with high-specificity, the nanoprobes are also conjugated with folic acid to establish a greater affinity for cancer cells that over-express folate receptors on their cell membrane. In the new nanosystem, MnO nanoparticles are shown to function as an efficient fluorescence quencher of coumarin-545T prior to cellular uptake. However, fluorescence recovery is achieved upon acidic dissolution of the MnO nanoparticles following receptor-mediated endocytosis into the low pH compartments of the cancer cells. Meanwhile, the Mn(2+) ions thus released are also shown to exert a strong T1 contrast enhancement in the cancer cells. Therefore, by demonstrating the dual-activatable MRI and fluorescence imaging in response to the low pH conditions, it is envisioned that these nanoprobes would have tremendous potential for emerging cancer-imaging modalities such as image-guided cancer therapy.

Red-emitting, EtTP-5-based organic nanoprobes for two-photon imaging in 3D multicellular biological models

Biocompatible and biostable EtTP-5-loaded organic core–shell nanoparticles have been successfully evaluated for their potential as red-emitting fluorescent nanoprobes for two-photon imaging.

Preclinical imaging and translational animal models of cancer for accelerated clinical implementation of nanotechnologies and macromolecular agents

The majority of animal models of cancer have performed poorly in terms of predicting clinical performance of new therapeutics, which are most often first evaluated in patients with advanced, metastatic disease. The development and use of metastatic models of cancer may enhance clinical translatability of preclinical studies focused on the development of nanotechnology-based drug delivery systems and macromolecular therapeutics, potentially accelerating their clinical implementation. It is recognized that the development and use of such models are not without challenge. Preclinical imaging tools offer a solution by allowing temporal and spatial characterization of metastatic lesions. This paper provides a review of imaging methods applicable for evaluation of novel therapeutics in clinically relevant models of advanced cancer. An overview of currently utilized models of oncology in small animals is followed by image-based development and characterization of visceral metastatic cancer models. Examples of imaging tools employed for metastatic lesion detection, evaluation of anti-tumor and anti-metastatic potential and biodistribution of novel therapies, as well as the co-development and/or use of imageable surrogates of response, are also discussed. While the focus is on development of macromolecular and nanotechnology-based therapeutics, examples with small molecules are included in some cases to illustrate concepts and approaches that can be applied in the assessment of nanotechnologies or macromolecules.