PEGylated PRINT nanoparticles: the impact of PEG density on protein binding, macrophage association, biodistribution, and pharmacokinetics

PEGylation of therapeutic oligonucletides: From linear to highly branched PEG architectures

PEGylation, the attachment of poly(ethylene glycol) (PEG), has been adopted to improve the pharmacokinetic properties of oligonucleotide therapeutics for nearly 30 years. Prior efforts mainly focused on the investigation of linear or slightly branched PEG having different molecular weights, terminal functional groups, and possible oligonucleotide sites for functionalization. Recent studies on highly branched PEG (including brush, star, and micellar structures) indicate superior properties in several areas including cellular uptake, gene regulation efficacy, reduction of side effects, and biodistribution. This review focuses on comparing the effects of PEG architecture on the physiochemical and biological properties of the PEGylated oligonucleotide.

Golden-star nanoparticles as adjuvant effectively promotes immune response to foot-and-mouth disease virus-like particles vaccine

Virus-like particles (VLPs) have become a hot topic in modern vaccine research because of its safety, facile production, and immune properties. To further enhance the immune effect of VLPs, we synthesized and used gold-star nanoparticles (AuSNs) as adjuvant for vaccine. Foot-and-mouth disease (FMD) VLPs as target antigen were combined with AuSNs. The FMD VLPs-AuSNs complex was characterized through sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blot, ultraviolet light absorption, and morphological measurement analyses. Result indicated that the FMD VLPs-AuSNs complex is non-toxic in different cell lines. AuSNs can effectively promote the entry of FMD VLPs into cells and improve macrophages activation when combined with FMD VLPs compared with FMD VLPs alone. Further animal vaccination and challenge tests revealed that the specific immune response and protection rate of AuSNs adjuvant group is higher than that of conventional mineral oil (ISA206) adjuvant group. AuSNs can effectively improve the immune protection effects of FMD VLPs vaccines, and exhibit potential as a new adjuvant for other vaccines.

Effects of core size and PEG coating layer of iron oxide nanoparticles on the distribution and metabolism in mice

Introduction

In vivo distribution of polyethylene glycol (PEG)ylated functional nanoparticles is vital for determining their imaging function and therapeutic efficacy in nanomedicine. However, contradictory results have been reported regarding the effect of core size and PEG surface of the nanoparticles on biodistribution.

Methods

To clarify this ambiguous understanding, using iron oxide nanoparticles (IONPs) as a model system, we investigated the effect of core size and PEG molecule weights on in vivo distribution in mice. Three PEGylated IONPs, including 14 nm IONP@PEG2,000, 14 nm IONP@PEG5,000, and 22 nm IONP@PEG5,000, were prepared with a hydrodynamic size of 26, 34, and 81 nm, respectively. The blood pharmacokinetics and tissue distribution were investigated in detail.

Results

The results indicated that the PEG layer, rather than core size, played a dominant role in determining the half-life time of IONPs. Specifically, increased molecular weight of the PEG layer led to a longer half-life time. These PEGylated IONPs were mainly excreted by liver clearance. While the PEG molecular layer constituted the key factor to determine the clearance ratio, core size affected the clearance rate.

Conclusion

Complete blood count analysis and histopathology suggested excellent biocompatibility of PEGylated IONPs for future clinical trials.

Sequentially self-assembled polysaccharide-based nanocomplexes for combined chemotherapy and photodynamic therapy of breast cancer

Combination of chemotherapy and photodynamic therapy has emerged as a promising anticancer strategy. Polysaccharide-based nanoparticles are being intensively explored as drug carriers for different forms of combination therapy. In this study, novel multifunctional polysaccharide-based nanocomplexes were prepared from aldehyde-functionalized hyaluronic acid and hydroxyethyl chitosan via sequential self-assembly method. Stable nanocomplexes were obtained through both Schiff's base bond and electrostatic interactions. Chemotherapeutics doxorubicin and pro-photosensitizer 5-aminolevulinic acid were chemically conjugated onto the nanocomplexes via Schiff base linkage. Anti-HER2 antibody as targeting moiety was decorated onto the surface of nanocomplexes. The obtained near-spherical shaped nanocomplexes had an average size of 140 nm and a zeta potential of -24.6 mV, and displayed pH-responsive surface charge reversal and drug release. Active targeting strategy significantly enhanced the cellular uptake of nanocomplexes and combined anticancer efficiency of chemo-photodynamic dual therapy in breast cancer MCF-7 cells. These results suggested that the nanocomplexes had great potential for targeted combination therapy of breast cancer.

Nanoengineering of Poly(ethylene glycol) Particles for Stealth and Targeting

The assembly of particles composed solely or mainly of poly(ethylene glycol) (PEG) is an emerging area that is gaining increasing interest within bio-nano science. PEG, widely considered to be the "gold standard" among polymers for drug delivery, is providing a platform for exploring fundamental questions and phenomena at the interface between particle engineering and biomedicine. These include the targeting and stealth behaviors of synthetic nanomaterials in biological environments. In this feature article, we discuss recent work in the nanoengineering of PEG particles and explore how they are enabling improved targeting and stealth performance. Specific examples include PEG particles prepared through surface-initiated polymerization, mesoporous silica replication via postinfiltration, and particle assembly through metal-phenolic coordination. This particle class exhibits unique in vivo behavior (e.g., biodistribution and immune cell interactions) and has recently been explored for drug delivery applications.

The effect of surface poly(ethylene glycol) length on in vivo drug delivery behaviors of polymeric nanoparticles

Engineering nanoparticles of reasonable surface poly(ethylene glycol) (PEG) length is important for designing efficient drug delivery systems. Eliminating the disturbance by other nanoproperties, such as size, PEG density, etc., is crucial for systemically investigating the impact of surface PEG length on the biological behavior of nanoparticles. In the present study, nanoparticles with different surface PEG length but similar other nanoproperties were prepared by using poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL) copolymers of different molecular weights and incorporating different contents of PCL₃₅₀₀ homopolymer. The molecular weight of PEG block in PEG-PCL was between 3400 and 8000 Da, the sizes of nanoparticles were around 100 nm, the terminal PEG density was controlled at 0.4 PEG/nm² (or the frontal PEG density was controlled at 0.16 PEG/nm²). Using these nanoproperties well-designed nanoparticles, we demonstrated PEG length-dependent changes in the biological behaviors of nanoparticles and exhibited nonmonotonic improvements as the PEG molecular weight increased from 3400 to 8000 Da. Moreover, under the experimental conditions, we found nanoparticles with a surface PEG length of 13.8 nm (MW = 5000 Da) significantly decreased the absorption with serum protein and interaction with macrophages, which led to prolonged blood circulation time, enhanced tumor accumulation and improved antitumor efficacy. The present study will help to establish a relatively precise relationship between surface PEG length and the in vivo behavior of nanoparticles.

Bioinspired Shielding Strategies for Nanoparticle Drug Delivery Applications

Nanoparticle delivery systems offer advantages over free drugs, in that they increase solubility and biocompatibility. Nanoparticles can deliver a high payload of therapeutic molecules while limiting off-target side effects. Therefore, delivery of an existing drug with a nanoparticle frequently results in an increased therapeutic index. Whether of synthetic or biologic origin, nanoparticle surface coatings are often required to reduce immune clearance and thereby increase circulation times allowing the carriers to reach their target site. To this end, polyethylene glycol (PEG) has long been used, with several PEGylated products reaching clinical use. Unfortunately, the growing use of PEG in consumer products has led to an increasing prevalence of PEG-specific antibodies in the human population, which in turn has fueled the search for alternative coating strategies. This review highlights alternative bioinspired nanoparticle shielding strategies, which may be more beneficial moving forward than PEG and other synthetic polymer coatings.

Ultrasmall Noble Metal Nanoparticles: Breakthroughs and Biomedical Implications

As a bridge between individual atoms and large plasmonic nanoparticles, ultrasmall (core size <3 nm) noble metal nanoparticles (UNMNPs) have been serving as model for us to fundamentally understand many unique properties of noble metals that can only be observed at an extremely small size scale. With decades'efforts, many significant breakthroughs in the synthesis, characterization and functionalization of UNMNPs have laid down a solid foundation for their future applications in the healthcare. In this review, we aim to tightly correlate these breakthroughs with their biomedical applications and illustrate how to utilize these breakthroughs to address long-standing challenges in the clinical translation of nanomedicines. In the end, we offer our perspective on the remaining challenges and opportunities at the frontier of biomedical-related UNMNPs research.

Block copolymer crystalsomes with an ultrathin shell to extend blood circulation time

In water, amphiphilic block copolymers (BCPs) can self-assemble into various micelle structures depicting curved liquid/liquid interface. Crystallization, which is incommensurate with this curved space, often leads to defect accumulation and renders the structures leaky, undermining their potential biomedical applications. Herein we report using an emulsion-solution crystallization method to control the crystallization of an amphiphilic BCP, poly (l-lactide acid)-b-poly (ethylene glycol) (PLLA-b-PEG), at curved liquid/liquid interface. The resultant BCP crystalsomes (BCCs) structurally mimic the classical polymersomes and liposomes yet mechanically are more robust thanks to the single crystal-like crystalline PLLA shell. In blood circulation and biodistribution experiments, fluorophore-loaded BCCs show a 24 h circulation half-life and a 8% particle retention in the blood even at 96 h post injection. We further demonstrate that this good performance can be attributed to controlled polymer crystallization and the unique BCC nanostructure.

In block copolymer vesicles, crystallization often leads to defects and renders the structures leaky that undermines their potential biomedical application. Here the authors use an emulsion solution method to control the crystallization of an amphiphilic block copolymer at the curved liquid/liquid interface to improve the blood circulation time.

Reassessment of long circulation via monitoring of integral polymeric nanoparticles justifies a more accurate understanding

Monitoring of payloads results in a biased perception of long circulation of nanoparticles. Instead, herein, the long-circulation effect was re-confirmed by monitoring integral nanoparticles, but circulation was not found to be as long as generally perceived. In contrast, disparate pharmacokinetics were obtained by monitoring a model drug, paclitaxel, highlighting the bias of the conventional protocol.

How Low Can You Go? Low Densities of Poly(ethylene glycol) Surfactants Attract Stealth Proteins

It is now well-established that the surface chemistry and "stealth" surface functionalities such as poly(ethylene glycol) (PEG) chains of nanocarriers play an important role to decrease unspecific protein adsorption of opsonizing proteins, to increase the enrichment of specific stealth proteins, and to prolong the circulation times of the nanocarriers. At the same time, PEG chains are used to provide colloidal stability for the nanoparticles. However, it is not clear how the chain length and density influence the unspecific and specific protein adsorption keeping at the same time the stability of the nanoparticles in a biological environment. Therefore, this study aims at characterizing the protein adsorption patterns depending on PEG chain length and density to define limits for the amount of PEG needed for a stealth effect by selective protein adsorption as well as colloidal stability during cell experiments. PEG chains are introduced using the PEGylated Lutensol AT surfactants, which allow easy modification of the nanoparticle surface. These findings indicate that a specific enrichment of stealth proteins already occurs at low PEG concentrations; for the decrease of unspecific protein adsorption and finally the colloidal stability a full surface coverage is advised.

Compartmentalized Microhelices Prepared via Electrohydrodynamic Cojetting

Anisotropically compartmentalized microparticles have attracted increasing interest in areas ranging from sensing, drug delivery, and catalysis to microactuators. Herein, a facile method is reported for the preparation of helically decorated microbuilding blocks, using a modified electrohydrodynamic cojetting method. Bicompartmental microfibers are twisted in situ, during electrojetting, resulting in helical microfibers. Subsequent cryosectioning of aligned fiber bundles provides access to helically decorated microcylinders. The unique helical structure endows the microfibers/microcylinders with several novel functions such as translational motion in response to rotating magnetic fields. Finally, microspheres with helically patterned compartments are obtained after interfacially driven shape shifting of helically decorated microcylinders.

Dendritic PEG outer shells enhance serum stability of polymeric micelles

A higher surface density of poly(ethylene glycol) (PEG) on polymeric micelles enhances their stability in serum, leading to improved plasma circulation. To obtain fundamental, mechanistic understanding of the PEG effect associated with polymeric architecture/configuration, we have synthesized PEGylated dendron-based copolymers (PDCs) and linear block copolymers (LBCs) with similar molecular weights. These copolymers formed dendron (hyperbranched) and linear micelles, respectively, which were compared in terms of their stabilities in serum, micelle-serum protein interactions, and in vivo biodistributions. Overall, the dendron micelles exhibited a better serum stability (longer half-life) and thus a slower release profile than the linear micelles. Fluorescence quenching assays and molecular dynamics (MD) simulations revealed that the high serum stability of the dendron micelles can be attributed to reduced micelle-serum protein interactions, owing to their dendritic, dense PEG outer shell. These results provide an important design cue for various polymeric micelles and nanoparticles.

The in vivo fates of plant viral nanoparticles camouflaged using self-proteins: overcoming immune recognition

Nanoparticles offer a promising avenue for targeted delivery of therapies. To slow clearance, nanoparticles are frequently stealth-coated to prevent opsonization and immune recognition. Serum albumin (SA) has been used as a bio-inspired stealth coating. To develop this shielding strategy for clinical applications, it is critical to understand the interactions between the immune system and SA-camouflaged nanoparticles. This work investigates the in vivo processing of SA-coated nanoparticles using tobacco mosaic virus (TMV) as a model system. In comparing four different SA-formulations, the particles with high SA coverage conjugated to TMV via a short linker performed the best at preventing antibody recognition. Irrelevant of the coating chemistry, all formulations led to similar levels of TMV-specific antibodies after repeat administration in mice; importantly though, SA-specific antibodies were not detected and the TMV-specific antibodies were unable to recognize shielded SA-coated TMV. Upon uptake in macrophages, the shielding agent and nanoparticle separate, where TMV trafficked to the lysosome and SA appears to recycle. The distinct intracellular fates of the TMV carrier and SA shielding agent explain why anti-TMV but not SA-specific antibodies are generated. This work characterizes the outcomes of SA-camouflaged TMV after immune recognition, and highlights the effectiveness of SA as a nanoparticle shielding agent.

Hydrophilicity Regulates the Stealth Properties of Polyphosphoester-Coated Nanocarriers

Increasing the plasma half-life is an important goal in the development of drug carriers, and can be effectively achieved through the attachment of polymers, in particular poly(ethylene glycol) (PEG). While the increased plasma half-life has been suggested to be a result of decreased overall protein adsorption on the hydrophilic surface in combination with the adsorption of specific proteins, the molecular reasons for the success of PEG and other hydrophilic polymers are still widely unknown. We prepared polyphosphoester-coated nanocarriers with defined hydrophilicity to control the stealth properties of the polymer shell. We found that the log P value of the copolymer controls the composition of the protein corona and the cell interaction. Upon a significant change in hydrophilicity, the overall amount of blood proteins adsorbed on the nanocarrier remained unchanged, while the protein composition varied. This result underlines the importance of the protein type for the protein corona and cellular uptake.

Noninvasive monitoring of nanoparticle clearance and aggregation in blood circulation by in vivo flow cytometry

Nanoparticles have been widely used in biomedical research as drug carriers or imaging agents for living animals. Blood circulation is crucial for the delivery of nanoparticles, which enter the bloodstream through injection, inhalation, or dermal exposure. However, the clearance kinetics of nanoparticles in blood circulation has been poorly studied, mainly because of the limitations of conventional detection methods, such as insufficient blood sample volumes or low spatial-temporal resolution. In addition, formation of nanoparticle aggregates is a key determinant for biocompatibility and drug delivery efficiency. Aggregation behavior of nanoparticles in blood is studied using dynamic light scattering in serum or serum protein solutions, which is still very different from in vivo condition. In this work, we monitored the dynamics of nanoparticle concentration and formation of nanoparticle aggregates in the bloodstream in live animals using in vivo flow cytometry (IVFC). The results indicated that nanoparticles in smaller size could stay longer in the bloodstream. Polyethylene glycol (PEG)-modification could prolong circulating time and reduce the formation of aggregates in the blood circulation. Our work shows that IVFC can be a powerful tool for pharmacokinetic studies of nanoparticles and other drug carriers, assessing cell-targeting efficiency, as well as potentially measuring cardiac output and hepatic function in vivo.

Insights into maleimide-thiol conjugation chemistry: Conditions for efficient surface functionalization of nanoparticles for receptor targeting

Maleimide-thiol chemistry is widely used for the design and preparation of ligand-decorated drug delivery systems such as poly(lactide-co-glycolide) (PLGA) based nanoparticles (NPs). While many publications on nanocarriers functionalized exploiting this strategy are available in the literature, the conditions at which this reaction takes place vary among publications. This paper presents a comprehensive study on the conjugation of the peptide cRGDfK and the nanobody 11A4 (both containing a free thiol group) to maleimide functionalized PLGA NPs by means of the maleimide-thiol click reaction. The influence of different parameters, such as the nanoparticles preparation method and storage conditions as well as the molar ratio of maleimide to ligand used for conjugation, on the reaction efficiency has been evaluated. The NPs were prepared by a single or double emulsion method using different types and concentrations of surfactants and stored at 4 or 20 °C before reaction with the targeting moieties. Several maleimide to ligand molar ratios and different reaction times were studied and the conjugation efficiency was determined by quantification of the not-bound ligand by liquid chromatography. The kind of emulsion used to prepare the NPs as well as the type and concentration of surfactant used had no effect on the conjugation efficiency. Reaction between the maleimide groups present in the NPs and cRGDfK was optimal at a maleimide to thiol molar ratio of 2:1, reaching a conjugation efficiency of 84 ± 4% after 30 min at room temperature in 10 mM HEPES pH 7.0. For 11A4 nanobody the optimal reaction efficiency, 58 ± 12%, was achieved after 2 h of incubation at room temperature in PBS pH 7.4 using a 5:1 maleimide to protein molar ratio. Storage of the NPs at 4 °C for 7 days prior to their exposure to the ligands resulted in approximately 10% decrease in the reactivity of maleimide in contrast to storage at 20 °C which led to almost 40% of the maleimide being unreactive after the same storage time. Our findings demonstrate that optimization of this reaction, particularly in terms of reactant ratios, can represent a significant increase in the conjugation efficiency and prevent considerable waste of resources.

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.

Biodistribution Analysis of NIR-Labeled Nanogels Using in Vivo FMT Imaging in Triple Negative Human Mammary Carcinoma Models

The purpose of this study is to evaluate the biodistribution properties of random-copolymer-based core-cross-linked nanogels of various sizes and surface poly(ethylene glycol) composition. Systematic variations of near-IR labeled nanogels, comprising varying particle sizes (28-135 nm), PEG corona quantity (0-50 mol %), and PEG length (PEG M_n 1000, 2000, and 5000), were prepared and injected in mice that had been subcutaneously implanted with MDA-MB-231-luc-D3H2LN human mammary carcinoma. In vivo biodistribution was obtained using fluorescence molecular tomography imaging at 0, 6, 24, 48, and 72 h postinjection. Retention of total body probe and percentages of total injected dose in the tumor, liver, spleen, lungs, heart, intestines, and kidneys were obtained. Smaller nanogels (∼30-40 nm) with a high PEG conjugation (∼43-46 mol %) of M_n 2000 on their coronas achieved the highest tumor specificity with peak maximum 27% ID/g, a statistically significant propensity toward accumulation with 16.5% ID/g increase from 0 to 72 h of imaging, which constitutes a 1.5-fold increase. Nanogels with greater tumor localization also had greater retention of total body probe over 72 h. Nanogels without extensive PEGylation were rapidly excreted, even at similar sizes to PEGylated nanogels exhibiting whole body retention. Of all tissues, the liver had the highest % ID, however, like other tissues, it displayed a monotonic decrease over time, suggesting nanogel clearance by hepatic metabolism. Ex vivo quantification of individual tissues from gross necropsy at 72 h postinjection generally correlated with the FMT analysis, providing confidence in tissue signal segmentation in vivo. The parameters determined to most significantly direct a nanogel to the desired tumor target can lead to improve effectiveness for nanogels as therapeutic delivery vehicles.

Preventing Obstructions of Nanosized Drug Delivery Systems by the Extracellular Matrix

Although nanosized drug delivery systems are promising tools for the treatment of severe diseases, the extracellular matrix (ECM) constitutes a major obstacle that endangers therapeutic success. Mobility of diffusing species is restricted not only by small pore size (down to as low as 3 nm) but also by electrostatic interactions with the network. This article evaluates commonly used in vitro models of ECM, analytical methods, and particle types with respect to their similarity to native conditions in the target tissue. In this cross-study evaluation, results from a wide variety of mobility studies are analyzed to discern general principles of particle-ECM interactions. For instance, cross-linked networks and a negative network charge are essential to reliably recapitulate key features of the native ECM. Commonly used ECM mimics comprised of one or two components can lead to mobility calculations which have low fidelity to in vivo results. In addition, analytical methods must be tailored to the properties of both the matrix and the diffusing species to deliver accurate results. Finally, nanoparticles must be sufficiently small to penetrate the matrix pores (ideally R_d/p < 0.5; d = particle diameter, p = pore size) and carry a neutral surface charge to avoid obstructions. Larger (R_d/p >> 1) or positively charged particles are trapped.

Nanoparticle Properties Modulate Their Attachment and Effect on Carrier Red Blood Cells

Attachment of nanoparticles (NPs) to the surface of carrier red blood cells (RBCs) profoundly alters their interactions with the host organism, decelerating NP clearance from the bloodstream while enabling NP transfer from the RBC surface to the vascular cells. These changes in pharmacokinetics of NPs imposed by carrier RBCs are favorable for many drug delivery purposes. On the other hand, understanding effects of NPs on the carrier RBCs is vital for successful translation of this novel drug delivery paradigm. Here, using two types of distinct nanoparticles (polystyrene (PSNP) and lysozyme-dextran nanogels (LDNG)) we assessed potential adverse and sensitizing effects of surface adsorption of NPs on mouse and human RBCs. At similar NP loadings (approx. 50 particles per RBC), adsorption of PSNPs, but not LDNGs, induces RBCs agglutination and sensitizes RBCs to damage by osmotic, mechanical and oxidative stress. PSNPs, but not LDNGs, increase RBC stiffening and surface exposure of phosphatidylserine, both known to accelerate RBC clearance in vivo. Therefore, NP properties and loading amounts have a profound impact on RBCs. Furthermore, LDNGs appear conducive to nanoparticle drug delivery using carrier RBCs.

Coating Metal Nanoparticle Surfaces with Small Organic Molecules Can Reduce Nonspecific Cell Uptake

Elucidation of mechanisms of uptake of nanoparticles by cells and methods to prevent this uptake is essential for many applications of nanoparticles. Most recent studies have focused on the role of proteins that coat nanoparticles and have employed PEGylation, particularly dense coatings of PEG, to reduce protein opsonization and cell uptake. Here we show that small molecule coatings on metallic nanoparticles can markedly reduce cell uptake for very sparsely PEGylated nanoparticles. Similar results were obtained in media with and without proteins, suggesting that protein opsonization is not the primary driver of this phenomenon. The reduction in cell uptake is proportional to the degree of surface coverage by the small molecules. Probing cell uptake pathways using inhibitors suggested that the primary role of increased surface coverage is to reduce nanoparticles' interactions with the scavenger receptors. This work highlights an under-investigated mechanism of cell uptake that may have played a role in many other studies and also suggests that a wide variety of molecules can be used alongside PEGylation to stably passivate nanoparticle surfaces for low cell uptake.

PEGylation for enhancing nanoparticle diffusion in mucus

The viscoelastic mucus secretions coating exposed organs such as the lung airways and the female reproductive tract can trap and quickly eliminate not only foreign pathogens and ultrafine particles but also particle-based drug delivery systems, thus limiting sustained and targeted drug delivery at mucosal surfaces. To improve particle distribution across the mucosa and enhance delivery to the underlying epithelium, many investigators have sought to develop nanoparticles capable of readily traversing mucus. The first synthetic nanoparticles shown capable of rapidly penetrating physiological mucus secretions utilized a dense coating of polyethylene glycol (PEG) covalently grafted onto the surface of preformed polymeric nanoparticles. In the decade since, PEG has become the gold standard in engineering mucus-penetrating drug carriers for sustained and targeted drug delivery to the lungs, gastrointestinal tract, eyes, and female reproductive tract. This review summarizes the history of the development of various PEG-based mucus-penetrating particles, and highlights the key physicochemical properties of PEG coatings and PEGylation strategies to achieve muco-inert PEG coatings on nanoparticle drug carriers for improved drug and gene delivery at mucosal surfaces.

Computational studies of micellar and nanoparticle nanomedicines

The review highlights recent computational modeling of micellar and nanoparticle nanomedicines, which elucidates their functional roles in atomistic details.

Surface-grafted polyethylene glycol conformation impacts the transport of PEG-functionalized liposomes through a tumour extracellular matrix model

The effect of surface PEGylation on nanoparticle transport through an extracellular matrix (ECM) is an important determinant for tumor targeting success. Fluorescent stealth liposomes (base lipid DOPC) were prepared incorporating different proportions of PEG-grafted lipids (2.5, 5 and 10% of the total lipid content) for a series of PEG molecular weights (1000, 2000 and 5000 Da). The ECM was modelled using a collagen matrix. The kinetics of PEGylated liposome adhesion to and transport in collagen matrices were tracked using fluorescence correlation spectroscopy (FCS) and confocal microscopy, respectively. Generalized least square regressions were used to determine the temporal correlations between PEG molecular weight, surface density and conformation, and the liposome transport in a collagen hydrogel over 15 hours. PEG conformation determined the interaction of liposomes with the collagen hydrogel and their transport behaviour. Interestingly, liposomes with mushroom PEG conformation accumulated on the interface of the collagen hydrogel, creating a dense liposomal front with short diffusion distances into the hydrogels. On the other hand, liposomes with dense brush PEG conformation interacted to a lesser extent with the collagen hydrogel and diffused to longer distances. In conclusion, a better understanding of PEG surface coating as a modifier of transport in a model ECM matrix has resulted. This knowledge will improve design of future liposomal drug carrier systems.

The effect of surface PEGylation on nanoparticle transport through an extracellular matrix (ECM) is an important determinant for tumor targeting success.

Particle Targeting in Complex Biological Media

Over the past few decades, nanoengineered particles have gained increasing interest for applications in the biomedical realm, including diagnosis, imaging, and therapy. When functionalized with targeting ligands, these particles have the potential to interact with specific cells and tissues, and accumulate at desired target sites, reducing side effects and improve overall efficacy in applications such as vaccination and drug delivery. However, when targeted particles enter a complex biological environment, the adsorption of biomolecules and the formation of a surface coating (e.g., a protein corona) changes the properties of the carriers and can render their behavior unpredictable. For this reason, it is of importance to consider the potential challenges imposed by the biological environment at the early stages of particle design. This review describes parameters that affect the targeting ability of particulate drug carriers, with an emphasis on the effect of the protein corona. We highlight strategies for exploiting the protein corona to improve the targeting ability of particles. Finally, we provide suggestions for complementing current in vitro assays used for the evaluation of targeting and carrier efficacy with new and emerging techniques (e.g., 3D models and flow-based technologies) to advance fundamental understanding in bio-nano science and to accelerate the development of targeted particles for biomedical applications.

Magnetic Particle Imaging for Highly Sensitive, Quantitative, and Safe in Vivo Gut Bleed Detection in a Murine Model

Gastrointestinal (GI) bleeding causes more than 300 000 hospitalizations per year in the United States. Imaging plays a crucial role in accurately locating the source of the bleed for timely intervention. Magnetic particle imaging (MPI) is an emerging clinically translatable imaging modality that images superparamagnetic iron-oxide (SPIO) tracers with extraordinary contrast and sensitivity. This linearly quantitative modality has zero background tissue signal and zero signal depth attenuation. MPI is also safe: there is zero ionizing radiation exposure to the patient and clinically approved tracers can be used with MPI. In this study, we demonstrate the use of MPI along with long-circulating, PEG-stabilized SPIOs for rapid in vivo detection and quantification of GI bleed. A mouse model genetically predisposed to GI polyp development (ApcMin/+) was used for this study, and heparin was used as an anticoagulant to induce acute GI bleeding. We then injected MPI-tailored, long-circulating SPIOs through the tail vein, and tracked the tracer biodistribution over time using our custom-built high resolution field-free line (FFL) MPI scanner. Dynamic MPI projection images captured tracer accumulation in the lower GI tract with excellent contrast. Quantitative analysis of the MPI images show that the mice experienced GI bleed rates between 1 and 5 μL/min. Although there are currently no human scale MPI systems, and MPI-tailored SPIOs need to undergo further development and evaluation, clinical translation of the technique is achievable. The robust contrast, sensitivity, safety, ability to image anywhere in the body, along with long-circulating SPIOs lends MPI outstanding promise as a clinical diagnostic tool for GI bleeding.

Impact of Cross-Linker Valency on Gold Nanoparticle Aggregate Formation and Cellular Uptake

Synthesis of spherical, biocompatible nanoparticle aggregates using a small molecular cross-linker is a simple and flexible approach for the controlled assembly of gold nanoparticles. This strategy can be extended to a variety of cross-linkers, making it possible to the test the effect of cross-linker properties on aggregate formation and physicochemical properties. Here, we synthesized aggregates using a series of structurally homologous cross-linkers with differing valencies. These aggregates have the same size, morphology, surface charge, surface coating, and stability in salt, media, and low pH conditions, but they differ in their stability to cyanide etching and uptake by cells. This highlights the fine-tuning of nanoparticle aggregate properties that can be achieved by using small-molecule cross-linkers.

Neutrophil-Particle Interactions in Blood Circulation Drive Particle Clearance and Alter Neutrophil Responses in Acute Inflammation

Although nano- and microparticle therapeutics have been studied for a range of drug delivery applications, the presence of these particles in blood flow may have considerable and understudied consequences to circulating leukocytes, especially neutrophils, which are the largest human leukocyte population. The objective of this work was to establish if particulate drug carriers in circulation interfere with normal neutrophil adhesion and migration. Circulating blood neutrophils in vivo were found to be capable of rapidly binding and sequestering injected carboxylate-modified particles of both 2 and 0.5 μm diameter within the bloodstream. These neutrophil-particle associations within the vasculature were found to suppress neutrophil interactions with an inflamed mesentery vascular wall and hindered neutrophil adhesion. Furthermore, in a model of acute lung injury, intravenously administered drug-free particles reduced normal neutrophil accumulation in the airways of C57BL/6 mice between 52% and 60% versus particle-free mice and between 93% and 98% in BALB/c mice. This suppressed neutrophil migration resulted from particle-induced neutrophil diversion to the liver. These data indicate a considerable acute interaction between injected particles and circulating neutrophils that can drive variations in neutrophil function during inflammation and implicate neutrophil involvement in the clearance process of intravenously injected particle therapeutics. Such an understanding will be critical toward both enhancing designs of drug delivery carriers and developing effective therapeutic interventions in diseases where neutrophils have been implicated.

Rod-Shaped Active Drug Particles Enable Efficient and Safe Gene Delivery

Efficient microRNAs (miRNA) delivery into cells is a promising strategy for disease therapy, but is a major challenge because the available conventional nonviral vectors have significant drawbacks. In particular, after these vectors are entrapped in lysosomes, the escape efficiency of genes from lysosomes into the cytosol is less than 2%. Here, a novel approach for lethal-7a (let-7a) replacement therapy using rod-shaped active pure drug nanoparticles (≈130 nm in length, PNPs) with a dramatically high drug-loading of ≈300% as vectors is reported. Importantly, unlike other vectors, the developed PNPs/let-7a complexes (≈178 nm, CNPs) can enter cells and bypass the lysosomal route to localize to the cytosol, achieving efficient intracellular delivery of let-7a and a 50% reduction in expression of the target protein (KRAS). Also, CNPs prolong the t1/2 of blood circulation by ≈threefold and increase tumor accumulation by ≈1.5-2-fold, resulting in significantly improved antitumor efficacies. Additionally, no damage to normal organs is observed following systemic injection of CNPs. In conclusion, rod-shaped active PNPs enable efficient and safe delivery of miRNA with synergistic treatment for disease. This nanoplatform would also offer a viable strategy for the potent delivery of proteins and peptides in vitro and in vivo.

Tuning the Multifunctionality of Iron Oxide Nanoparticles Using Self-Assembled Mixed Lipid Layers

We present an approach to tuning the multifunctionality of iron oxide nanoparticles (IONs) using mixed self-assembled monolayers of cationic lipid and anionic polyethylene glycol (PEG) lipid. By forming stable, monodispersed lipid-coated IONs (L-IONs) through a solvent-exchange technique, we were able to demonstrate the relationship between surface charge, the magnetic transverse relaxivity (r₂ from T₂-weighted images), and the binding capacity of small interfering ribonucleic acids (siRNAs) as a function of the cationic-to-anionic (PEG) lipid ratio. These properties were controlled by the cationic charge and the PEG conformation; relaxivity and siRNA binding could be varied in the mushroom and brush regimes but not at high brush densities. In vitro results combining cell viability, uptake, and transfection efficiency using HeLa cells suggest that the functional physicochemical and biological properties of L-IONs may be best achieved using catanionic lipid coatings near equimolar ratios of cationic to anionic PEG-lipids.

Templated Polymer Replica Nanoparticles to Facilitate Assessment of Material-Dependent Pharmacokinetics and Biodistribution

Surface modification is frequently used to tailor the interactions of nanoparticles with biological systems. In many cases, the chemical nature of the treatments employed to modify the biological interface (for example attachment of hydrophilic polymers or targeting groups) is the focus of attention. However, isolation of the fundamental effects of the materials employed to modify the interface are often confounded by secondary effects imparted by the underlying substrate. Herein, we demonstrate that polymer replica particles templated from degradable mesoporous silica provide a facile means to evaluate the impact of surface modification on the biological interactions of nanomaterials, independent of the substrate. Poly(ethylene glycol) (PEG), poly(N-(2 hydroxypropyl)methacrylamide) (PHPMA), and poly(methacrylic acid) (PMA) were templated onto mesoporous silica and cross-linked and the residual particles were removed. The resulting nanoparticles, comprising interfacial polymer alone, were then investigated using a range of in vitro and in vivo tests. As expected, the PEG particles showed the best stealth properties, and these trends were consistent in both in vitro and in vivo studies. PMA particles showed the highest cell association in cell lines in vitro and were rapidly taken up by monocytes in ex vivo whole blood, properties consistent with the very high in vivo clearance subsequently seen in rats. In contrast, PHPMA particles showed rapid association with both granulocytes and monocytes in ex vivo whole blood, even though in vivo clearance was less rapid than the PMA particles. Rat studies confirmed better systemic exposure for PEG and PHPMA particles when compared to PMA particles. This study provides a new avenue for investigating material-dependent biological behaviors of polymer particles, irrespective of the properties of the underlying core, and provides insights for the selection of polymer particles for future biological applications.

Mechanistic understanding of in vivo protein corona formation on polymeric nanoparticles and impact on pharmacokinetics

In vitro incubation of nanomaterials with plasma offer insights on biological interactions, but cannot fully explain the in vivo fate of nanomaterials. Here, we use a library of polymer nanoparticles to show how physicochemical characteristics influence blood circulation and early distribution. For particles with different diameters, surface hydrophilicity appears to mediate early clearance. Densities above a critical value of approximately 20 poly(ethylene glycol) chains (MW 5 kDa) per 100 nm² prolong circulation times, irrespective of size. In knockout mice, clearance mechanisms are identified for nanoparticles with low and high steric protection. Studies in animals deficient in the C3 protein showed that complement activation could not explain differences in the clearance of nanoparticles. In nanoparticles with low poly(ethylene glycol) coverage, adsorption of apolipoproteins can prolong circulation times. In parallel, the low-density-lipoprotein receptor plays a predominant role in the clearance of nanoparticles, irrespective of poly(ethylene glycol) density. These results further our understanding of nanopharmacology.

Understanding the interaction between nanoparticles and biomolecules is crucial for improving current drug-delivery systems. Here, the authors shed light on the essential role of the surface and other physicochemical properties of a library of nanoparticles on their in vivo pharmacokinetics.

Stealth Biocompatible Si-Based Nanoparticles for Biomedical Applications

A challenge regarding the design of nanocarriers for drug delivery is to prevent their recognition by the immune system. To improve the blood residence time and prevent their capture by organs, nanoparticles can be designed with stealth properties using polymeric coating. In this study, we focused on the influence of surface modification with polyethylene glycol and/or mannose on the stealth behavior of porous silicon nanoparticles (pSiNP, ~200 nm). In vivo biodistribution of pSiNPs formulations were evaluated in mice 5 h after intravenous injection. Results indicated that the distribution in the organs was surface functionalization-dependent. Pristine pSiNPs and PEGylated pSiNPs were distributed mainly in the liver and spleen, while mannose-functionalized pSiNPs escaped capture by the spleen, and had higher blood retention. The most efficient stealth behavior was observed with PEGylated pSiNPs anchored with mannose that were the most excreted in urine at 5 h. The biodegradation kinetics evaluated in vitro were in agreement with these in vivo observations. The biocompatibility of the pristine and functionalized pSiNPs was confirmed in vitro on human cell lines and in vivo by cytotoxic and systemic inflammation investigations, respectively. With their biocompatibility, biodegradability, and stealth properties, the pSiNPs functionalized with mannose and PEG show promising potential for biomedical applications.

Biocompatibility assessment of functionalized magnetic mesoporous silica nanoparticles in human HepaRG cells

Magnetic mesoporous silica nanoparticles (M-MSNs) are a promising class of nanoparticles for drug delivery. However, a deep understanding of the toxicological mechanisms of action of these nanocarriers is essential, especially in the liver. The potential toxicity on HepaRG cells of pristine, pegylated (PEG), and lipid (DMPC) M-MSNs were compared. Based on MTT assay and real-time cell impedance, none of these NPs presented an extensive toxicity on hepatic cells. However, we observed by transmission electron microscopy (TEM) that the DMPC and pristine M-MSNs were greatly internalized. In comparison, PEG M-MSNs showed a slower cellular uptake. Whole gene expression profiling revealed the M-MSNs molecular modes of action in a time- and dose-dependent manner. The lowest dose tested (1.6 µg/cm²) induced no molecular effect and was defined as 'No Observed Transcriptional Effect level.' The dose 16 µg/cm² revealed nascent but transient effects. At the highest dose (80 µg/cm²), adverse effects have clearly arisen and increased over time. The limit of biocompatibility for HepaRG cells could be set at 16 µg/cm² for these NPs. Thanks to a comparative pathway-driven analysis, we highlighted the sequence of events that leads to the disruption of hepatobiliary system, elicited by the three types of M-MSNs, at the highest dose. The Adverse Outcome Pathway of hepatic cholestasis was implicated. Toxicogenomics applied to cell cultures is an effective tool to characterize and compare the modes of action of many substances. We propose this strategy as an asset for upstream selection of the safest nanocarriers in the framework of regulation for nanobiosafety.

Targeting tumor associated macrophages: The new challenge for nanomedicine

The engineering of new nanomedicines with ability to target and kill or re-educate Tumor Associated Macrophages (TAMs) stands up as a promising strategy to induce the effective switching of the tumor-promoting immune suppressive microenvironment, characteristic of tumors rich in macrophages, to one that kills tumor cells, is anti-angiogenic and promotes adaptive immune responses. Alternatively, the loading of monocytes/macrophages in blood circulation with nanomedicines, may be used to profit from the high infiltration ability of myeloid cells and to allow the drug release in the bulk of the tumor. In addition, the development of TAM-targeted imaging nanostructures, can be used to study the macrophage content in solid tumors and, hence, for a better diagnosis and prognosis of cancer disease. The major challenges for the effective targeting of TAM with nanomedicines and their application in the clinic have already been identified. These challenges are associated to the undesirable clearance of nanomedicines by, the mononuclear phagocyte system (macrophages) in competing organs (liver, lung or spleen), upon their intravenous injection; and also to the difficult penetration of nanomedicines across solid tumors due to the abnormal vasculature and the excessive extracellular matrix present in stromal tumors. In this review we describe the recent nanotechnology-base strategies that have been developed to target macrophages in tumors.