Potential role of size and hemodynamics in the efficacy of vascular-targeted spherical drug carriers

The interaction between particles and vascular endothelium in blood flow

Particle-based drug delivery systems have shown promising application potential to treat human diseases; however, an incomplete understanding of their interactions with vascular endothelium in blood flow prevents their inclusion into mainstream clinical applications. The flow performance of nano/micro-sized particles in the blood are disturbed by many external/internal factors, including blood constituents, particle properties, and endothelium bioactivities, affecting the fate of particles in vivo and therapeutic effects for diseases. This review highlights how the blood constituents, hemodynamic environment and particle properties influence the interactions and particle activities in vivo. Moreover, we briefly summarized the structure and functions of endothelium and simulated devices for studying particle performance under blood flow conditions. Finally, based on particle-endothelium interactions, we propose future opportunities for novel therapeutic strategies and provide solutions to challenges in particle delivery systems for accelerating their clinical translation. This review helps provoke an increasing in-depth understanding of particle-endothelium interactions and inspires more strategies that may benefit the development of particle medicine.

Dual-targeting fucoidan-based microvesicle for arterial thrombolysis and re-occlusion inhibition

Arterial thrombosis is a critical thrombotic disease that poses a significant threat to human health. However, the existing clinical treatment of arterial thrombosis lacks effective targeting and precise drug release capability. In this study, we developed a system for targeted delivery and on-demand release in arterial thrombosis treatment. The carrier was constructed using chitosan (CS) and fucoidan (Fu) through layer-by-layer assembly, with subsequent surface modification using cRGD peptide. Upon encapsulation of urokinase-type plasminogen activator (uPA), the resulting therapeutic drug delivery system, uPA-CS/Fu@cRGD, demonstrated dual-targeting abilities towards P-selectin and αIIbβ3, as well as pH and platelet-responsive release properties. Importantly, we have demonstrated that the dual targeting effect exhibits higher targeting efficiency at shear rates simulating thrombosed arterial conditions (1800 s-1) compared to single targeting for the first time. In the mouse common iliac artery model, uPA-CS/Fu@cRGD exhibited great thrombolytic capability while promoting the down-regulation of coagulation factors (FXa and PAI-1) and inflammatory factors (TNF-α and IL-6), thus improving the thrombus microenvironment and exerting potential in preventing re-occlusion. Our dual-target and dual-responsive, fucoidan-based macrovesicle represent a promising platform for advanced drug target delivery applications, with potential to prevent coagulation tendencies as well as improving thrombolytic and reducing the risk of re-occlusion.

Polystyrene microplastics induce size-dependent multi-organ damage in mice: Insights into gut microbiota and fecal metabolites

Particle size is one of the most important factors in determining the biological toxicity of microplastics (MPs). In this study, we attempted to examine the systemic toxicity of polystyrene MPs of different sizes (0.5 µm MP1 and 5 µm MP2) in C57BL/6 J mice. After the mice were given oral gavage of MPs for 8 consecutive weeks, histopathology and molecular biology assays, 16 S rRNA sequencing of the gut microbiota, and untargeted metabolomics were performed. The results showed that MPs were distributed in the organs in a size-dependent manner, with smaller particles demonstrating greater biodistribution. Further analysis indicated that exposure to MPs caused multi-organ damage through distinct toxicity pathways. Specifically, exposure to 0.5 µm MP1 led to excessive accumulation and induced more serious inflammation and mechanical damage in the spleen, kidney, heart, lung, and liver. However, 5 µm MP2 led to more severe intestinal barrier dysfunction, as well as gut dysbiosis and metabolic disorder in association with neuroinflammation. These results are helpful in expanding our knowledge of the toxicity of MPs of different sizes in mammalian models.

Using Gaussian process for velocity reconstruction after coronary stenosis applicable in positron emission particle tracking: An in-silico study

Accurate velocity reconstruction is essential for assessing coronary artery disease. We propose a Gaussian process method to reconstruct the velocity profile using the sparse data of the positron emission particle tracking (PEPT) in a biological environment, which allows the measurement of tracer particle velocity to infer fluid velocity fields. We investigated the influence of tracer particle quantity and detection time interval on flow reconstruction accuracy. Three models were used to represent different levels of stenosis and anatomical complexity: a narrowed straight tube, an idealized coronary bifurcation with stenosis, and patient-specific coronary arteries with a stenotic left circumflex artery. Computational fluid dynamics (CFD), particle tracking, and the Gaussian process of kriging were employed to simulate and reconstruct the pulsatile flow field. The study examined the error and uncertainty in velocity profile reconstruction after stenosis by comparing particle-derived flow velocity with the CFD solution. Using 600 particles (15 batches of 40 particles) released in the main coronary artery, the time-averaged error in velocity reconstruction ranged from 13.4% (no occlusion) to 161% (70% occlusion) in patient-specific anatomy. The error in maximum cross-sectional velocity at peak flow was consistently below 10% in all cases. PEPT and kriging tended to overestimate area-averaged velocity in higher occlusion cases but accurately predicted maximum cross-sectional velocity, particularly at peak flow. Kriging was shown to be useful to estimate the maximum velocity after the stenosis in the absence of negative near-wall velocity.

The flow of anisotropic nanoparticles in solution and in blood

The alignment of anisotropic nanoparticles in flow has been used for a range of applications such as the preparation of strong fibres and the assembly of in-plane aligned 1D-nanoobjects that are used for electronic devices, sensors, energy and biological application. Important is also the flow behaviour of nanoparticles that were designed for nanomedical applications such as drug delivery. It is widely observed that non-spherical nanoparticles have longer circulation times and a more favourable biodistribution. To be able to understand this behaviour, researchers have turned to analyzing the flow of non-spherical nanoparticles in the blood stream. In this review, an overview of microfluidic techniques that are used to monitor the alignment of anisotropic nanoparticles in solution will be provided, which includes analysis by small angle X-ray scattering (SAXS) and polarized light microscopy. The flow of these nanoparticles in blood is then discussed as the presence of red blood cells causes margination of some nanoparticles. Using fluorescence microscopy, the extent of margination can be identified, which coincides with the ability of nanoparticles to adhere to the cells grown along the wall. While these studies are mainly carried out in vitro using blood, initial investigations in vivo were able to confirm the unusual flow of anisotropic nanoparticles.

Current research trends of nanomedicines

Owing to the inherent shortcomings of traditional therapeutic drugs in terms of inadequate therapeutic efficacy and toxicity in clinical treatment, nanomedicine designs have received widespread attention with significantly improved efficacy and reduced non-target side effects. Nanomedicines hold tremendous theranostic potential for treating, monitoring, diagnosing, and controlling various diseases and are attracting an unfathomable amount of input of research resources. Against the backdrop of an exponentially growing number of publications, it is imperative to help the audience get a panorama image of the research activities in the field of nanomedicines. Herein, this review elaborates on the development trends of nanomedicines, emerging nanocarriers, in vivo fate and safety of nanomedicines, and their extensive applications. Moreover, the potential challenges and the obstacles hindering the clinical translation of nanomedicines are also discussed. The elaboration on various aspects of the research trends of nanomedicines may help enlighten the readers and set the route for future endeavors.

Effects of Microfluidic Shear on the Plasmid DNA Structure: Implications for Polymeric Gene Delivery Vectors

Microfluidic manufacturing of advanced gene delivery vectors necessitates consideration of the effects of microfluidic shear forces on the structural integrity of plasmid DNA (pDNA). In this paper, we expose pDNA to variable shear forces in a two-phase, gas-liquid microfluidic reactor and apply gel electrophoresis to analyze the products of on-chip shear-induced degradation. The effects of shear rate, solvent environment, pDNA size, and copolymer complexation on shear-induced degradation are investigated. We find that small naked pDNA (pUC18, 2.7 kb) exhibits shear rate-dependent shear degradation in the microfluidic channels in a mixed organic solvent (dioxane/water/acetic acid; 90/10/<0.1 w/w/w), with the extents of both supercoil isoform relaxation and complete fragmentation increasing as the maximum shear rates increase from 4 × 105 to 2 × 106 s-1. However, over the same range of shear rates, the same pDNA sample shows no evidence of microfluidic shear-induced degradation in a pure aqueous environment. Quiescent control experiments in the same mixed organic solvent prove that a combination of solvent and shear forces is involved in the observed shear-induced degradation. Furthermore, we show that shear degradation effects in mixed organic solvents can be significantly attenuated by complexation of pDNA with the block copolymer polycaprolactone-block-poly(2-vinylpyridine) prior to exposure to microfluidic shear. Finally, we demonstrate that medium (pDSK519, 8.1 kb) and large (pRK290, 20 kb) naked pDNA are more sensitive to shear-induced microfluidic degradation in the mixed organic solvent environment than small pDNA, with both plasmids showing complete fragmentation even at the lowest shear rate, although we found no evidence of shear-induced damage in water for the largest investigated naked pDNA even at the highest flow rate. The resulting understanding of the interplay of the solvent and shear effects during microfluidic processing should inform microfluidic manufacturing routes to new gene therapy formulations.

Shear stress regulation of nanoparticle uptake in vascular endothelial cells

Nanoparticles (NPs) hold tremendous targeting potential in cardiovascular disease and regenerative medicine, and exciting clinical applications are coming into light. Vascular endothelial cells (ECs) exposure to different magnitudes and patterns of shear stress (SS) generated by blood flow could engulf NPs in the blood. However, an unclear understanding of the role of SS on NP uptake is hindering the progress in improving the targeting of NP therapies. Here, the temporal and spatial distribution of SS in vascular ECs and the effect of different SS on NP uptake in ECs are highlighted. The mechanism of SS affecting NP uptake through regulating the cellular ROS level, endothelial glycocalyx and membrane fluidity is summarized, and the molecules containing clathrin and caveolin in the engulfment process are elucidated. SS targeting NPs are expected to overcome the current bottlenecks and change the field of targeting nanomedicine. This assessment on how SS affects the cell uptake of NPs and the marginalization of NPs in blood vessels could guide future research in cell biology and vascular targeting drugs.

Cargo-free particles divert neutrophil-platelet aggregates to reduce thromboinflammation

The combination of inflammation and thrombosis is a hallmark of many cardiovascular diseases. Under such conditions, platelets are recruited to an area of inflammation by forming platelet-leukocyte aggregates via interaction of PSGL-1 on leukocytes and P-selectin on activated platelets, which can bind to the endothelium. While particulate drug carriers have been utilized to passively redirect leukocytes from areas of inflammation, the downstream impact of these carriers on platelet accumulation in thromboinflammatory conditions has yet to be studied. Here, we explore the ability of polymeric particles to divert platelets away from inflamed blood vessels both in vitro and in vivo. We find that untargeted and targeted micron-sized polymeric particles can successfully reduce platelet adhesion to an inflamed endothelial monolayer in vitro in blood flow systems and in vivo in a lipopolysaccharide-induced, systemic inflammation murine model. Our data represent initial work in developing cargo-free, anti-platelet therapeutics specifically for conditions of thromboinflammation.

Margination of 2D Platelet Microparticles in Blood

Margination describes the movement of particles toward the endothelial wall within blood vessels. While there have been several studies tracking the margination of spherical particles in blood, the behavior of anisotropic particle shapes is not well described. In this study 2D platelet particles which possess many attractive qualities for use as a drug delivery system, with their high surface area allowing for increased surface binding activity, were directly monitored and margination quantified. The margination propensity of 1 and 2 μm 2D platelet particles was contrasted to that of 2 μm spherical particles at apparent wall shear rates (WSRs) of 50, 100, and 200 s^-1 by both directly tracking labeled particles using fluorescent microscopy as well as using small-angle X-ray scattering (SAXS). For fluorescence studies, margination was quantified using the margination parameter M, which describes the number of particles found closest to the walls of a microfluidic device, with an M-value of 0.2 indicating no margination. Increased margination was seen in 2D platelet particles when compared to spherical particles tested at all flow rates, with M-values of 0.39 and 0.31 seen for 1 and 2 μm 2D platelet particles, respectively, while 2 μm spherical particles had an M-value of 0.21. Similarly, margination was observed qualitatively using SAXS, with increased scattering seen for platelet particles near the microfluidic channel wall. For all particles, increased margination was seen at increasing shear rates.

Shear stress leads to the dysfunction of endothelial cells through the Cav-1-mediated KLF2/eNOS/ERK signaling pathway under physiological conditions

To investigate the mechanism of shear stress on endothelial cell dysfunction for providing a theoretical basis for the reduction of arteriovenous fistula dysfunction. The in vitro parallel plate flow chamber was used to form different forces and shear stress to mimic the hemodynamic changes in human umbilical vein endothelial cells, and the expression and distribution of krüppel-like factor 2 (KLF2), caveolin-1 (Cav-1), p-extracellular regulated protein kinase (p-ERK), and endothelial nitric oxide synthase (eNOS) were detected by immunofluorescence and real-time quantitative polymerase chain reaction. With the prolongation of the shear stress action time, the expression of KLF2 and eNOS increased gradually, while the expression of Cav-1 and p-ERK decreased gradually. In addition, after cells were exposed to oscillatory shear stress (OSS) and low shear stress, the expression of KLF2, Cav-1, and eNOS decreased and the expression of p-ERK increased. The expression of KLF2 increased gradually with the prolongation of action time, but it was still obviously lower than that of high shear stress. Following the block of Cav-1 expression by methyl β-cyclodextrin, eNOS expression decreased, and KLF2 and p-ERK expression increased. OSS may lead to endothelial cell dysfunction by Cav-1-mediated KLF2/eNOS/ERK signaling pathway.

Targeted thrombolysis by magnetoacoustic particles in photothrombotic stroke model

BACKGROUND

Recombinant tissue plasminogen activator (rtPA) has a short half-life, and additional hemorrhagic transformation (HT) can occur when treatment is delayed. Here, we report the design and thrombolytic performance of 3 [Formula: see text]m discoidal polymeric particles loaded with rtPA and superparamagnetic iron oxide nanoparticles (SPIONs), referred to as rmDPPs, to address the HT issues of rtPA.

METHODS

The rmDPPs consisted of a biodegradable polymeric matrix, rtPA, and SPIONs and were synthesized via a top-down fabrication.

RESULTS

The rmDPPs could be concentrated at the target site with magnetic attraction, and then the rtPA could be released under acoustic stimulus. Therefore, we named that the particles had magnetoacoustic properties. For the in vitro blood clot lysis, the rmDPPs with magnetoacoustic stimuli could not enhance the lytic potential compared to the rmDPPs without stimulation. Furthermore, although the reduction of the infarcts in vivo was observed along with the magnetoacoustic stimuli in the rmDPPs, more enhancement was not achieved in comparison with the rtPA. A notable advantage of rmDPPs was shown in delayed administration of rmDPPs at poststroke. The late treatment of rmDPPs with magnetoacoustic stimuli could reduce the infarcts and lead to no additional HT issues, while rtPA alone could not show any favorable prognosis.

CONCLUSION

The rmDPPs may be advantageous in delayed treatment of thrombotic patients.

Shape-specific microfabricated particles for biomedical applications: a review

The storied history of controlled the release systems has evolved over time; from degradable drug-loaded sutures to monolithic zero-ordered release devices and nano-sized drug delivery formulations. Scientists have tuned the physico-chemical properties of these drug carriers to optimize their performance in biomedical/pharmaceutical applications. In particular, particle drug delivery systems at the micron size regime have been used since the 1980s. Recent advances in micro and nanofabrication techniques have enabled precise control of particle size and geometry-here we review the utility of microplates and discoidal polymeric particles for a range of pharmaceutical applications. Microplates are defined as micrometer scale polymeric local depot devices in cuboid form, while discoidal polymeric nanoconstructs are disk-shaped polymeric particles having a cross-sectional diameter in the micrometer range and a thickness in the hundreds of nanometer range. These versatile particles can be used to treat several pathologies such as cancer, inflammatory diseases and vascular diseases, by leveraging their size, shape, physical properties (e.g., stiffness), and component materials, to tune their functionality. This review highlights design and fabrication strategies for these particles, discusses their applications, and elaborates on emerging trends for their use in formulations.

Dual Coating of Chitosan and Albumin Negates the Protein Corona-Induced Reduced Vascular Adhesion of Targeted PLGA Microparticles in Human Blood

Vascular-targeted carriers (VTCs) have the potential to localize therapeutics and imaging agents to inflamed, diseased sites. Poly (lactic-co-glycolic acid) (PLGA) is a negatively charged copolymer commonly used to construct VTCs due to its biodegradability and FDA approval. Unfortunately, PLGA VTCs experienced reduced adhesion to inflamed endothelium in the presence of human plasma proteins. In this study, PLGA microparticles were coated with chitosan (CS), human serum albumin (HSA), or both (HSA-CS) to improve adhesion. The binding of sialyl Lewis A (a ligand for E-selectin)-targeted PLGA, HSA-PLGA, CSPLGA, and HSA-CSPLGA to activated endothelial cells was evaluated in red blood cells in buffer or plasma flow conditions. PLGA VTCs with HSA-only coating showed improvement and experienced 35–52% adhesion in plasma compared to plasma-free buffer conditions across all shear rates. PLGA VTCs with dual coating—CS and HSA—maintained 80% of their adhesion after exposure to plasma at low and intermediate shears and ≈50% at high shear. Notably, the protein corona characterization showed increases at the 75 and 150 kDa band intensities for HSA-PLGA and HSA-CSPLGA, which could correlate to histidine-rich glycoprotein and immunoglobulin G. The changes in protein corona on HSA-coated particles seem to positively influence particle binding, emphasizing the importance of understanding plasma protein–particle interactions.

Micro-particle entrapment dynamics in microfluidic pulmonary capillary networks

The journey of vascular targeted carriers (VTC) in the circulatory system is highly intricate and includes navigation through different vessel structures, such as the vast pulmonary capillary network (PCN) in the lungs where particles can get entrapped and lead to blockage. Here, we leverage microfluidic PCN models to explore, for the first time, micro-particle capillary entrapment, in a well-controlled biophysical environment mimicking human physiological hemodynamics at true scale. This in vitro strategy mimics the challenges of vascular carrier transport during their journey in the smallest capillaries of the body (∼5 µm). Specifically, we explore in the PCN model entrapment dynamics of spherical micro-particles of different diameters (i.e. 3, 4 and 4.5 µm) at different concentrations, comparing their motion in cell-free buffer to that in the presence of red blood cells (RBCs). Notably, while 3 µm particles exhibit undisturbed transport in all of the examined concentrations, both in cell-free buffer and in the presence of RBCs, particles of 4 and 4.5 µm exhibit a concentration-dependent transport where the presence of RBCs leads in fact to reduced entrapment. Our experiments suggest that collisions of micro-particles with RBCs can facilitate their navigability, allowing for carrier transport that would lead otherwise to rapid entrapment in a cell-free environment. Altogether, the proposed preclinical in vitro assays offer rapid screening opportunities for design optimization of VTC transport in capillary networks.

Targeting vascular inflammation through emerging methods and drug carriers

Acute inflammation is a common dangerous component of pathogenesis of many prevalent conditions with high morbidity and mortality including sepsis, thrombosis, acute respiratory distress syndrome (ARDS), COVID-19, myocardial and cerebral ischemia-reperfusion, infection, and trauma. Inflammatory changes of the vasculature and blood mediate the course and outcome of the pathology in the tissue site of insult, remote organs and systemically. Endothelial cells lining the luminal surface of the vasculature play the key regulatory functions in the body, distinct under normal vs. pathological conditions. In theory, pharmacological interventions in the endothelial cells might enable therapeutic correction of the overzealous damaging pro-inflammatory and pro-thrombotic changes in the vasculature. However, current agents and drug delivery systems (DDS) have inadequate pharmacokinetics and lack the spatiotemporal precision of vascular delivery in the context of acute inflammation. To attain this level of precision, many groups design DDS targeted to specific endothelial surface determinants. These DDS are able to provide specificity for desired tissues, organs, cells, and sub-cellular compartments needed for a particular intervention. We provide a brief overview of endothelial determinants, design of DDS targeted to these molecules, their performance in experimental models with focus on animal studies and appraisal of emerging new approaches. Particular attention is paid to challenges and perspectives of targeted therapeutics and nanomedicine for advanced management of acute inflammation.

Theranostic Microbubbles with Homogeneous Ligand Distribution for Higher Binding Efficacy

Phospholipid-coated targeted microbubbles are used for ultrasound molecular imaging and locally enhanced drug delivery, with the binding efficacy being an important trait. The use of organic solvent in microbubble production makes the difference between a heterogeneous or homogeneous ligand distribution. This study demonstrates the effect of ligand distribution on the binding efficacy of phospholipid-coated ανβ3-targeted microbubbles in vitro using a monolayer of human umbilical-vein endothelial cells and in vivo using chicken embryos. Microbubbles with a homogeneous ligand distribution had a higher binding efficacy than those with a heterogeneous ligand distribution both in vitro and in vivo. In vitro, 1.55× more microbubbles with a homogeneous ligand distribution bound under static conditions, while this was 1.49× more under flow with 1.25 dyn/cm2, 1.56× more under flow with 2.22 dyn/cm2, and 1.25× more in vivo. The in vitro dissociation rate of bound microbubbles with homogeneous ligand distribution was lower at low shear stresses (1–5 dyn/cm2). The internalized depth of bound microbubbles was influenced by microbubble size, not by ligand distribution. In conclusion, for optimal binding the use of organic solvent in targeted microbubble production is preferable over directly dispersing phospholipids in aqueous medium.

Biophysical targeting of high-risk cerebral aneurysms

Localized delivery of diagnostic/therapeutic agents to cerebral aneurysms, lesions in brain arteries, may offer a new treatment paradigm. Since aneurysm rupture leading to subarachnoid hemorrhage is a devastating medical emergency with high mortality, the ability to noninvasively diagnose high-risk aneurysms is of paramount importance. Moreover, treatment of unruptured aneurysms with invasive surgery or minimally invasive neurointerventional surgery poses relatively high risk and there is presently no medical treatment of aneurysms. Here, leveraging the endogenous biophysical properties of brain aneurysms, we develop particulate carriers designed to localize in aneurysm low-shear flows as well as to adhere to a diseased vessel wall, a known characteristic of high-risk aneurysms. We first show, in an in vitro model, flow guided targeting to aneurysms using micron-sized (2 μm) particles, that exhibited enhanced targeting (>7 folds) to the aneurysm cavity while smaller nanoparticles (200 nm) showed no preferable accumulation. We then functionalize the microparticles with glycoprotein VI (GPVI), the main platelet receptor for collagen under low-medium shear, and study their targeting in an in vitro reconstructed patient-specific aneurysm that contained a disrupted endothelium at the cavity. Results in this model showed that GPVI microparticles localize at the injured aneurysm an order of magnitude (>9 folds) more than control particles. Finally, effective targeting to aneurysm sites was also demonstrated in an in vivo rabbit aneurysm model with a disrupted endothelium. Altogether, the presented biophysical strategy for targeted delivery may offer new treatment opportunities for cerebral aneurysms.

Polymeric particle-based therapies for acute inflammatory diseases

Acute inflammation is essential for initiating and coordinating the body's response to injuries and infections. However, in acute inflammatory diseases, inflammation is not resolved but propagates further, which can ultimately lead to tissue damage such as in sepsis, acute respiratory distress syndrome and deep vein thrombosis. Currently, clinical protocols are limited to systemic steroidal treatments, fluids and antibiotics that focus on eradicating inflammation rather than modulating it. Strategies based on stem cell therapeutics and selective blocking of inflammatory molecules, despite showing great promise, still lack the scalability and specificity required to treat acute inflammation. By contrast, polymeric particle systems benefit from uniform manufacturing at large scales while preserving biocompatibility and versatility, thus providing an ideal platform for immune modulation. Here, we outline design aspects of polymeric particles including material, size, shape, deformability and surface modifications, providing a strategy for optimizing the targeting of acute inflammation.

Deformable microparticles for shuttling nanoparticles to the vascular wall

Vascular-targeted drug carriers must localize to the wall (i.e., marginate) and adhere to a diseased endothelium to achieve clinical utility. The particle size has been reported as a critical physical property prescribing particle margination in vitro and in vivo blood flows. Different transport process steps yield conflicting requirements-microparticles are optimal for margination, but nanoparticles are better for intracellular or tissue delivery. Here, we evaluate deformable hydrogel microparticles as carriers for transporting nanoparticles to a diseased vascular wall. Depending on microparticle modulus, nanoparticle-loaded poly(ethylene glycol)-based hydrogel microparticles delivered significantly more 50-nm nanoparticles to the vessel wall than freely injected nanoparticles alone, resulting in >3000% delivery increase. This work demonstrates the benefit of optimizing microparticles' efficient margination to enhance nanocarriers' transport to the vascular wall.

Development and Characterization of PLGA-Based Multistage Delivery System for Enhanced Payload Delivery to Targeted Vascular Endothelium

Vascular-targeted drug delivery remains an attractive platform for therapeutic and diagnostic interventions in human diseases. This work focuses on the development of a poly-lactic-co-glycolic-acid (PLGA)-based multistage delivery system (MDS). MDS consists of two stages: a micron-sized PLGA outer shell and encapsulated drug-loaded PLGA nanoparticles. Nanoparticles with average diameters of 76, 119, and 193 nm are successfully encapsulated into 3-6 µm MDS. Sustained in vitro release of nanoparticles from MDS is observed for up to 7 days. Both MDS and nanoparticles arebiocompatible with human endothelial cells. Sialyl-Lewis-A (sLe^A ) is successfully immobilized on the MDS and nanoparticle surfaces to enable specific targeting of inflamed endothelium. Functionalized MDS demonstrates a 2.7-fold improvement in endothelial binding compared to PLGA nanoparticles from human blood laminar flow. Overall, the presented results demonstrate successful development and characterization of MDS and suggest that MDS can serve as an effective drug carrier, which can enhance the margination of nanoparticles to the targeted vascular wall.

Computational and experimental investigation of particulate matter deposition in cerebral side aneurysms

Intracranial aneurysms frequently develop blood clots, plaque and inflammations, which are linked to enhanced particulate mass deposition. In this work, we propose a computational model for particulate deposition, that accounts for the influence of field forces, such as gravity and electrostatics, which produce an additional flux of particles perpendicular to the fluid motion and towards the wall. This field-mediated flux can significantly enhance particle deposition in low-shear environments, such as in aneurysm cavities. Experimental investigation of particle deposition patterns in in vitro models of side aneurysms, demonstrated the ability of the model to predict enhanced particle adhesion at these sites. Our results showed a significant influence of gravity and electrostatic forces (greater than 10%), indicating that the additional terms presented in our models may be necessary for modelling a wide range of physiological flow conditions and not only for ultra-low shear regions. Spatial differences between the computational model and the experimental results suggested that additional transport and fluidic mechanisms affect the deposition pattern within aneurysms. Taken together, the presented findings may enhance our understanding of pathological deposition processes at cardiovascular disease sites, and facilitate rational design and optimization of cardiovascular particulate drug carriers.

Methylene blue-filled biodegradable polymer particles as a contrast agent for optical coherence tomography

Optical coherence tomography (OCT) images largely lack molecular information or molecular contrast. We address that issue here, reporting on the development of biodegradable micro and nano-spheres loaded with methylene blue (MB) as molecular contrast agents for OCT. MB is a constituent of FDA approved therapies and widely used as a dye in off-label clinical applications. The sequestration of MB within the polymer reduced toxicity and improved signal strength by drastically reducing the production of singlet oxygen and leuco-MB. The former leads to tissue damage and the latter to reduced image contrast. The spheres are also strongly scattering which improves molecular contrast signal localization and enhances signal strength. We demonstrate that these contrast agents may be imaged using both pump-probe OCT and photothermal OCT, using a 830 nm frequency domain OCT system and a 1.3 µm swept source OCT system. We also show that these contrast agents may be functionalized and targeted to specific receptors, e.g. the VCAM receptor known to be overexpressed in inflammation.

Endothelial Cell Targeting by cRGD-Functionalized Polymeric Nanoparticles under Static and Flow Conditions

Since α_vβ₃ integrin is a key component of angiogenesis in health and disease, Arg-Gly-Asp (RGD) peptide-functionalized nanocarriers have been investigated as vehicles for targeted delivery of drugs to the α_vβ₃ integrin-overexpressing neovasculature of tumors. In this work, PEGylated nanoparticles (NPs) based on poly(lactic-co-glycolic acid) (PLGA) functionalized with cyclic-RGD (cRGD), were evaluated as nanocarriers for the targeting of angiogenic endothelium. For this purpose, NPs (~300 nm) functionalized with cRGD with different surface densities were prepared by maleimide-thiol chemistry and their interactions with human umbilical vein endothelial cells (HUVECs) were evaluated under different conditions using flow cytometry and microscopy. The cell association of cRGD-NPs under static conditions was time-, concentration- and cRGD density-dependent. The interactions between HUVECs and cRGD-NPs dispersed in cell culture medium under flow conditions were also time- and cRGD density-dependent. When washed red blood cells (RBCs) were added to the medium, a 3 to 8-fold increase in NPs association to HUVECs was observed. Moreover, experiments conducted under flow in the presence of RBC at physiologic hematocrit and shear rate, are a step forward in the prediction of in vivo cell–particle association. This approach has the potential to assist development and high-throughput screening of new endothelium-targeted nanocarriers.

Targeting functionalized nanoparticles to activated endothelial cells under high wall shear stress

Local inflammation of the endothelium is associated with a plethora of cardiovascular diseases. Vascular-targeted carriers (VTCs) have been advocated to provide focal effective therapeutics to these disease sites. Here, we examine the design of functionalized nanoparticles (NPs) as VTCs that can specifically localize at an inflamed vessel wall under pathological levels of high shear stress, associated for example with clinical (or in vivo) conditions of vascular narrowing and arteriogenesis. To test this, carboxylated fluorescent 200 nm polystyrene particles were functionalized with ligands to activated endothelium, that is, an E-selectin binding peptide (Esbp), an anti ICAM-1 antibody, or using a combination of both. The functionalized NPs were investigated in vitro using microfluidic models lined with inflamed (TNF-α stimulated) and control endothelial cells (EC). Specifically, their adhesion was monitored under different relevant wall shear stresses (i.e., 40-300 dyne/cm2) via real-time confocal microscopy. Experiments reveal a significantly higher specific adhesion of the examined functionalized NPs to activated EC for the window of examined wall shear stresses. Moreover, particle adhesion correlated with the surface coating density whereby under high surface coating (i.e., ~10,000 molecule/particle), shear-dependent particle adhesion increased significantly. Altogether, our results show that functionalized NPs can be designed to target inflamed endothelial cells under high shear stress. Such VTCs underscore the potential for attractive avenues in targeting drugs to vasoconstriction and arteriogenesis sites.

Increased Adhesive Potential of Antiphospholipid Syndrome Neutrophils Mediated by β2 Integrin Mac-1

OBJECTIVE

While the role of antiphospholipid antibodies in activating endothelial cells has been extensively studied, the impact of these antibodies on the adhesive potential of leukocytes has received less attention. This study was undertaken to investigate the extent to which antiphospholipid syndrome (APS) neutrophils adhere to resting endothelial cells under physiologic flow conditions and the surface molecules required for that adhesion.

METHODS

Patients with primary APS (n = 43), patients with a history of venous thrombosis but negative test results for antiphospholipid antibodies (n = 11), and healthy controls (n = 38) were studied. Cells were introduced into a flow chamber and perfused across resting human umbilical vein endothelial cells (HUVECs). Surface adhesion molecules were quantified by flow cytometry. Neutrophil extracellular trap release (NETosis) was assessed in neutrophil-HUVEC cocultures.

RESULTS

Upon perfusion of anticoagulated blood through the flow chamber, APS neutrophils demonstrated increased adhesion as compared to control neutrophils under conditions representative of either venous (n = 8; P < 0.05) or arterial (n = 15; P < 0.0001) flow. At the same time, APS neutrophils were characterized by up-regulation of CD64, CEACAM1, β2 -glycoprotein I, and activated Mac-1 on their surface (n = 12-18; P < 0.05 for all markers). Exposing control neutrophils to APS plasma or APS IgG resulted in increased neutrophil adhesion (n = 10-11; P < 0.0001) and surface marker up-regulation as compared to controls. A monoclonal antibody specific for activated Mac-1 reduced the adhesion of APS neutrophils in the flow-chamber assay (P < 0.01). The same monoclonal antibody reduced NETosis in neutrophil-HUVEC cocultures (P < 0.01).

CONCLUSION

APS neutrophils demonstrate increased adhesive potential, which is dependent upon the activated form of Mac-1. In patients, this could lower the threshold for neutrophil-endothelium interactions, NETosis, and possibly thrombotic events.

Model Particulate Drug Carriers Modulate Leukocyte Adhesion in Human Blood Flows

Drug carriers have been widely explored as a method of improving the efficacy of therapeutic drugs for a variety of diseases, including those involving inflammation. However, few of these formulations have advanced past clinical trials. There are still major gaps in our understanding of how drug carriers impact leukocytes, particularly in inflammatory conditions. In this work, we investigated how targeted and nontargeted drug carriers affect the function of leukocytes in blood flow. We explored three primary mechanisms: (1) collisions in blood flow disrupt leukocyte adhesion, (2) specific binding to the endothelium competes with leukocytes for binding sites, and (3) particle phagocytosis alters leukocyte phenotype, resulting in reduced adhesion. We find that each of these mechanisms contributes to significantly reduced leukocyte adhesion to an inflamed endothelium, and that particle phagocytosis may be the most significant driver of this effect. These results are crucial for understanding the totality of the impact of drug carriers on leukocyte behavior and response to inflammation and should inform the future design of any such drug carriers.

From design to the clinic: practical guidelines for translating cardiovascular nanomedicine

Cardiovascular diseases (CVD) account for nearly half of all deaths in Europe and almost 30% of global deaths. Despite the improved clinical management, cardiovascular mortality is predicted to rise in the next decades due to the increasing impact of aging, obesity, and diabetes. The goal of emerging cardiovascular nanomedicine is to reduce the burden of CVD using nanoscale medical products and devices. However, the development of novel multicomponent nano-sized products poses multiple technical, ethical, and regulatory challenges, which often obstruct their road to successful approval and use in clinical practice. This review discusses the rational design of nanoparticles, including safety considerations and regulatory issues, and highlights the steps needed to achieve efficient clinical translation of promising nanomedicinal products for cardiovascular applications.

Antimargination of Microparticles and Platelets in the Vicinity of Branching Vessels

We investigate the margination of microparticles/platelets in blood flow through complex geometries typical for in vivo vessel networks: a vessel confluence and a bifurcation. Using three-dimensional lattice Boltzmann simulations, we confirm that behind the confluence of two vessels, a cell-free layer devoid of red blood cells develops in the channel center. Despite its small size of roughly 1 μm, this central cell-free layer persists for up to 100 μm after the confluence. Most importantly, we show from simulations that this layer also contains a significant amount of microparticles/platelets and validate this result by in vivo microscopy in mouse venules. At bifurcations, however, a similar effect does not appear, and margination is largely unaffected by the geometry. This antimargination toward the vessel center after a confluence may explain earlier in vivo observations, which found that platelet concentrations near the vessel wall are seen to be much higher on the arteriolar side (containing bifurcations) than on the venular side (containing confluences) of the vascular system.

Magnetic Accumulation of SPIONs under Arterial Flow Conditions: Effect of Serum and Red Blood Cells

Magnetic drug targeting utilizes an external magnetic field to target superparamagnetic iron oxide nanoparticles (SPIONs) and their cargo to the diseased vasculature regions. In the arteries, the flow conditions affect the behavior of magnetic particles and the efficacy of their accumulation. In order to estimate the magnetic capture of SPIONs in more physiological-like settings, we previously established an ex vivo model based on human umbilical cord arteries. The artery model was employed in our present studies in order to analyze the effects of the blood components on the efficacy of magnetic targeting, utilizing 2 types of SPIONs with different physicochemical characteristics. In the presence of freshly isolated human plasma or whole blood, a strong increase in iron content measured by AES was observed for both particle types along the artery wall, in parallel with clotting activation due to endogenous thrombin generation in plasma. Subsequent studies therefore utilized SPION suspensions in serum and washed red blood cells (RBCs) at hematocrit 50%. Interestingly, in contrast to cell culture medium suspensions, magnetic accumulation of circulating SPION-3 under the external magnet was achieved in the presence of RBCs. Taken together, our data shows that the presence of blood components affects, but does not prevent, the magnetic accumulation of circulating SPIONs.

The Margination of Particles in Areas of Constricted Blood Flow

Stroke is a leading cause of death globally and is caused by stenoses, abnormal narrowings of blood vessels. Recently, there has been an increased interest in shear-activated particle clusters for the treatment of stenosis, but there is a lack of literature investigating the impact of different stenosis geometries on particle margination. Margination refers to the movement of particles toward the blood vessel wall and is desirable for drug delivery. The current study investigated ten different geometries and their effects on margination. Microfluidic devices with a constricted area were fabricated to mimic a stenosed blood vessel with different extent of occlusion, constricted length, and eccentricity (gradualness of the constriction and expansion). Spherical fluorescent particles with a diameter of 2.11 μm were suspended in blood and tracked as they moved into, through, and out of the constricted area. A margination parameter, M, was used to quantify margination based on the particle distribution after velocity normalization. Experimental results suggested that a constriction leads to an enhanced margination, whereas an expansion is responsible for a decrease in margination. Further, margination was found to increase with increasing percent occlusion and constriction length, likely a result of higher shear rate and longer residence time, respectively. Margination decreases as the stenosis geometry becomes more gradual (eccentricity increases) with the exception of a sudden constriction/expansion geometry. The findings demonstrate the importance of geometric effects on margination and call for detailed numerical modeling and geometric characterization of the stenosed areas to fully understand the underlying physics.

Effect of physicochemical and surface properties on in vivo fate of drug nanocarriers

Over the years, a plethora of materials - natural and synthetic - have been engineered at a nanoscopic level and explored for drug delivery. Nanocarriers based on such materials could improve the payload's pharmacokinetics and achieve the desired pharmacological response at the target tissue. Despite the development of rationally designed drug nanocarriers, only a handful of such formulations have been successfully translated into the clinic. The physicochemical properties (size, shape, surface chemistry, porosity, elasticity, and many others) of these nanocarriers influence its biological identity, which in presence of biological barriers in vivo, could significantly modulate the therapeutic index of its cargo and alter the desired outcome. Further, complexities associated with developing effective drug nanocarriers have led to conflicting views of its safety, permeation of biological barriers and cellular uptake. Here, in this review, we emphasize the effect of physicochemical properties of nanocarriers on their interactions with the biological milieu. The review will discuss in depth, how modulating the physicochemical properties would influence a drug nanocarrier's behavior in vivo and the mechanisms underlying these effects. The goal of this review is to summarize the design considerations based on these properties and to provide a conceptual template for achieving improved therapeutic efficacy with enhanced patient compliance.

Calcium-binding nanoparticles for vascular disease

Cardiovascular disease (CVD) including atherosclerosis is the leading cause of death worldwide. As CVDs and atherosclerosis develop, plaques begin to form in the blood vessels and become calcified. Calcification within the vasculature and atherosclerotic plaques have been correlated with rupture and consequently, acute myocardial infarction. However, current imaging methods to identify vascular calcification have limitations in determining plaque composition and structure. Nanoparticles can overcome these limitations due to their versatility and ability to incorporate a wide range of targeting and contrast agents. In this review, we summarize the current understanding of calcification in atherosclerosis, their role in instigating plaque instability, and clinical methodologies to detect and analyze vascular calcification. In addition, we highlight the potential of calcium-targeting ligands and nanoparticles to create novel calcium-detecting tools.

Effect of flow on targeting and penetration of angiopep-decorated nanoparticles in a microfluidic model blood-brain barrier

The blood-brain barrier (BBB) limits transport of nanoparticles from the circulation to the brain parenchyma. Angiopep-2, a peptide which functions as a brain transport vector, can be coupled to nanoparticles in order to facilitate binding and internalization by brain endothelial cells (ECs), and subsequent BBB penetration. This multi-step process may be affected by blood flow over brain ECs, as flow influences endothelial cell phenotype as well as interactions of nanoparticles with ECs. In the present study a microfluidic BBB model was constructed to evaluate binding and internalization by brain ECs, as well as BBB penetration of Angiopep-2 coupled liposomes (Ang2-Liposomes) in static and flow conditions. Ang2 conjugation to liposomes markedly improved binding relative to unconjugated liposomes. Ang2-Liposomes bound and were internalized efficiently by brain endothelial cells after static incubation or with 1 dyne/cm² of fluid shear stress (FSS), while binding was reduced at a FSS of 6 dyne/cm². Penetration of the model microfluidic BBB by Ang2-Liposomes was higher at a FSS of 1 dyne/cm² and 6 dyne/cm² than with static incubation. Analysis of barrier function and control experiments for receptor-mediated penetration provided insight into the magnitude of transcellular versus paracellular transport at each tested FSS. Overall, the results demonstrate that flow impacted the binding and BBB penetration of Ang2-functionalized nanoparticles. This highlights the relevance of the local flow environment for in vitro modeling of the performance of nanoparticles functionalized with BBB penetrating ligands.

Quantifying Platelet Margination in Diabetic Blood Flow

Patients with type 2 diabetes mellitus (T2DM) develop thrombotic abnormalities strongly associated with cardiovascular diseases. In addition to the changes of numerous coagulation factors such as elevated levels of thrombin and fibrinogen, the abnormal rheological effects of red blood cells (RBCs) and platelets flowing in blood are crucial in platelet adhesion and thrombus formation in T2DM. An important process contributing to the latter is the platelet margination. We employ the dissipative particle dynamics method to seamlessly model cells, plasma, and vessel walls. We perform a systematic study on RBC and platelet transport in cylindrical vessels by considering different cell shapes, sizes, and RBC deformabilities in healthy and T2DM blood, as well as variable flowrates and hematocrit. In particular, we use cellular-level RBC and platelet models with parameters derived from patient-specific data and present a sensitivity study. We find T2DM RBCs, which are less deformable compared to normal RBCs, lower the transport of platelets toward the vessel walls, whereas platelets with higher mean volume (often observed in T2DM) lead to enhanced margination. Furthermore, increasing the flowrate or hematocrit enhances platelet margination. We also investigated the effect of platelet shape and observed a nonmonotonic variation with the highest near-wall concentration corresponding to platelets with a moderate aspect ratio of 0.38. We examine the role of white blood cells (WBCs), whose count is increased notably in T2DM patients. We find that WBC rolling or WBC adhesion tends to decrease platelet margination due to hydrodynamic effects. To the best of our knowledge, such simulations of blood including all blood cells have not been performed before, and our quantitative findings can help separate the effects of hydrodynamic interactions from adhesive interactions and potentially shed light on the associated pathological processes in T2DM such as increased inflammatory response, platelet activation and adhesion, and ultimately thrombus formation.

Recent and prominent examples of nano- and microarchitectures as hemoglobin-based oxygen carriers

Blood transfusions, which usually consist in the administration of isolated red blood cells (RBCs), are crucial in traumatic injuries, pre-surgical conditions and anemias. Although RBCs transfusion from donors is a safe procedure, donor RBCs can only be stored for a maximum of 42 days under refrigerated conditions and, therefore, stockpiles of RBCs for use in acute disasters do not exist. With a worldwide shortage of donor blood that is expected to increase over time, the creation of oxygen-carriers with long storage life and compatibility without typing and cross-matching, persists as one of the foremost important challenges in biomedicine. However, research has so far failed to produce FDA approved RBCs substitutes (RBCSs) for human usage. As such, due to unacceptable toxicities, the first generation of oxygen-carriers has been withdrawn from the market. Being hemoglobin (Hb) the main component of RBCs, a lot of effort is being devoted in assembling semi-synthetic RBCS utilizing Hb as the oxygen-carrier component, the so-called Hb-based oxygen carriers (HBOCs). However, a native RBC also contains a multi-enzyme system to prevent the conversion of Hb into non-functional methemoglobin (metHb). Thus, the challenge for the fabrication of next-generation HBOCs relies in creating a system that takes advantage of the excellent oxygen-carrying capabilities of Hb, while preserving the redox environment of native RBCs that prevents or reverts the conversion of Hb into metHb. In this review, we feature the most recent advances in the assembly of the new generation of HBOCs with emphasis in two main approaches: the chemical modification of Hb either by cross-linking strategies or by conjugation to other polymers, and the Hb encapsulation strategies, usually in the form of lipidic or polymeric capsules. The applications of the aforementioned HBOCs as blood substitutes or for oxygen-delivery in tissue engineering are highlighted, followed by a discussion of successes, challenges and future trends in this field.

PEGylation of model drug carriers enhances phagocytosis by primary human neutrophils

Targeted drug carriers are attractive for the delivery of therapeutics directly to the site of a disease, reducing systemic side effects and enhancing the efficacy of therapeutic molecules. However, the use of particulate carriers for drug delivery comes with its own set of challenges and barriers. Among these, a great deal of research effort has focused on protecting carriers from clearance by phagocytes via altering carrier surface chemistry, mostly with the use of polyethylene glycol (PEG) chain coatings. However, few papers have explored the effects of PEGylation on uptake by freshly-obtained primary human phagocytes in physiological conditions. In this work, we investigate the effect of PEGylation on particle uptake by primary human neutrophils in vitro and compare these effects to several cell lines and other model phagocytic cells systems. We find that human neutrophils in whole blood preferentially phagocytose PEGylated particles (e.g., ∼40% particle positive neutrophils for PEGylated versus ∼20% for carboxylated polystyrene microspheres) and that this effect is linked to factors present in human plasma. Model phagocytes internalized PEGylated particles less efficiently or equivalently to carboxylated particles in culture medium but preferentially phagocytosed PEGylated particles in the human plasma (e.g., ∼86% versus ∼63% PEGylated versus carboxylated particle positive cells, respectively). These findings have significant implications for the efficacy of PEGylation in designing long-circulating drug carriers, as well as the need for thorough characterization of drug carrier platforms in a wide array of in vitro and in vivo assays.

STATEMENT OF SIGNIFICANCE

The work in this manuscript is highly significant to the field of drug delivery, as it explores in-depth the effects of polyethylene glycol (PEG) coatings, which are frequently used to prevent phagocytic clearance of particulate drug carriers, on the phagocytosis of such carriers by neutrophils, the most abundant leukocyte in blood circulation. Surprisingly, we find that PEGylation enhances uptake by primary human neutrophils, specifically in the presence of human plasma. This result suggests that PEGylation may not confer the benefits in humans once thought, and may help to explain why PEG has not become the "magic bullet" it was once thought to be in the field of particulate drug delivery.

Influence of particle size and shape on their margination and wall-adhesion: implications in drug delivery vehicle design across nano-to-micro scale

Intravascular drug delivery technologies majorly utilize spherical nanoparticles as carrier vehicles. Their targets are often at the blood vessel wall or in the tissue beyond the wall, such that vehicle localization towards the wall (margination) becomes a pre-requisite for their function. To this end, some studies have indicated that under flow environment, micro-particles have a higher propensity than nano-particles to marginate to the wall. Also, non-spherical particles theoretically have a higher area of surface-adhesive interactions than spherical particles. However, detailed systematic studies that integrate various particle size and shape parameters across nano-to-micro scale to explore their wall-localization behavior in RBC-rich blood flow, have not been reported. We address this gap by carrying out computational and experimental studies utilizing particles of four distinct shapes (spherical, oblate, prolate, rod) spanning nano- to-micro scale sizes. Computational studies were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package, with Dissipative Particle Dynamics (DPD). For experimental studies, model particles were made from neutrally buoyant fluorescent polystyrene spheres, that were thermo-stretched into non-spherical shapes and all particles were surface-coated with biotin. Using microfluidic setup, the biotin-coated particles were flowed over avidin-coated surfaces in absence versus presence of RBCs, and particle adhesion and retention at the surface was assessed by inverted fluorescence microscopy. Our computational and experimental studies provide a simultaneous analysis of different particle sizes and shapes for their retention in blood flow and indicate that in presence of RBCs, micro-scale non-spherical particles undergo enhanced 'margination + adhesion' compared to nano-scale spherical particles, resulting in their higher binding. These results provide important insight regarding improved design of vascularly targeted drug delivery systems.

Nanoparticle localization in blood vessels: dependence on fluid shear stress, flow disturbances, and flow-induced changes in endothelial physiology

Nanoparticles in the bloodstream are subjected to complex fluid forces as they move through the curves and branches of healthy or tumor vasculature. While nanoparticles are known to preferentially accumulate in angiogenic vessels, little is known about the flow conditions in these vessels and how these conditions may influence localization. Here, we report a methodology which combines confocal imaging of nanoparticle-injected transgenic zebrafish embryos, 3D modeling of the vasculature, particle mapping, and computational fluid dynamics, to quantitatively assess the effects of fluid forces on nanoparticle distribution in vivo. Six-fold lower accumulation was found in zebrafish arteries compared to the lower velocity veins. Nanoparticle localization varied inversely with shear stress. Highest accumulation was present in regions of disturbed flow found at branch points and curvatures in the vasculature. To further investigate cell-particle association under flow, human endothelial cells were exposed to nanoparticles under hemodynamic conditions typically found in human vessels. Physiological adaptations of endothelial cells to 20 hours of flow enhanced nanoparticle accumulation in regions of disturbed flow. Overall our results suggest that fluid shear stress magnitude, flow disturbances, and flow-induced changes in endothelial physiology modulate nanoparticle localization in angiogenic vessels.

Influence of protein corona and caveolae-mediated endocytosis on nanoparticle uptake and transcytosis

Transcytosis of nanoparticles (NPs) is emerging as an attractive alternative to the paracellular route in cancer drug delivery with studies suggesting targeting caveolae-mediated endocytosis to maximize NP transcytosis. However, there are limited studies on transcytosis of NPs, especially for corona-coated NPs. Most studies focused on cellular uptake as an indirect measure of the NP's transcellular permeability (Pd). Here, we probed the effect of protein corona on the uptake and transcytosis of 20, 40, 100, and 200 nm polystyrene nanoparticles (pNP-PC) across HUVECs in a microfluidic channel that modelled the microvasculature. We observed increased cell uptake with size of pNP-PC although it was the smallest 20 nm pNP-PC that exhibited the highest transcellular Pd. In the absence of corona however, cell uptake decreased with size, and the largest 200 nm pNP-PEG exhibited the lowest transcellular Pd. By inhibiting caveolae-mediated endocytosis in HUVECs, smaller pNPs had a larger drop in cell uptake than larger pNPs, regardless of surface coating. However, only the smallest (20 nm) and largest (200 nm) pNP-PC had a decrease in Pd following inhibition with MβCD. Our findings showed that the protein corona affected the transcytosis of NPs, and their uptake by caveolae-mediated endocytosis did not necessarily lead to transcytosis.

Vascular-targeted particle binding efficacy in the presence of rigid red blood cells: Implications for performance in diseased blood

The field of drug delivery has taken an interest in combating numerous blood and heart diseases via the use of injectable vascular-targeted carriers (VTCs). However, VTC technology has encountered limited efficacy due to a variety of challenges associated with the immense complexity of the in vivo blood flow environment, including the hemodynamic interactions of blood cells, which impact their margination and adhesion to the vascular wall. Red blood cell (RBC) physiology, i.e., size, shape, and deformability, drive cellular distribution in blood flow and has been shown to impact VTC margination to the vessel wall significantly. The RBC shape and deformability are known to be altered in certain human diseases, yet little experimental work has been conducted towards understanding the effect of these alterations, specifically RBC rigidity, on VTC dynamics in physiological blood flow. In this work, we investigate the impact of RBCs of varying stiffnesses on the adhesion efficacy of particles of various sizes, moduli, and shapes onto an inflamed endothelial layer in a human vasculature-inspired, in vitro blood flow model. The blood rigid RBC compositions and degrees of RBC stiffness evaluated are analogous to conditions in diseases such as sickle cell disease. We find that particles of different sizes, moduli, and shapes yield drastically different adhesion patterns in blood flow in the presence of rigid RBCs when compared to 100% healthy RBCs. Specifically, up to 50% reduction in the localization and adhesion of non-deformable 2 μm particles to the vessel wall was observed in the presence of rigid RBCs. Interestingly, deformable 2 μm particles showed enhanced vessel wall localization and adhesion, by up to 85%, depending on the rigidity of RBCs evaluated. Ultimately, this work experimentally clarifies the importance of considering RBC rigidity in the intelligent design of particle therapeutics and highlights possible implications for a wide range of diseases relating to RBC deformability.

Top-down fabrication of shape-controlled, monodisperse nanoparticles for biomedical applications

Nanoparticles for biomedical applications are generally formed by bottom-up approaches such as self-assembly, emulsification and precipitation. But these methods usually have critical limitations in fabrication of nanoparticles with controllable morphologies and monodispersed size. Compared with bottom-up methods, top-down nanofabrication techniques offer advantages of high fidelity and high controllability. This review focuses on top-down nanofabrication techniques for engineering particles along with their biomedical applications. We present several commonly used top-down nanofabrication techniques that have the potential to fabricate nanoparticles, including photolithography, interference lithography, electron beam lithography, mold-based lithography (nanoimprint lithography and soft lithography), nanostencil lithography, and nanosphere lithography. Varieties of current and emerging applications are also covered: (i) targeting, (ii) drug and gene delivery, (iii) imaging, and (iv) therapy. Finally, a future perspective of the nanoparticles fabricated by the top-down techniques in biomedicine is also addressed.