Alex J. Thompson

Margination propensity of vascular-targeted spheres from blood flow in a microfluidic model of human microvessels.

Many variants of vascular-targeted carriers (VTCs) have been investigated for therapeutic intervention in several human diseases. However, in order to optimize the functionality of VTC in vivo, carriers physical properties, such as size and shape, are important considerations for a VTC design that evades the reticuloendothelial system (RES) and successfully interacts with the targeted vessel wall. Nonetheless, little evidence has been presented on the role of size in VTCs interactions with the vascular wall, particularly in the microcirculation. Thus, in this work, we explore how particle size, along with hemodynamics (blood shear rate and vessel size) and hemorheology (blood hematocrit) affect the capacity for spheres to marginate (localize and adhere) to inflamed endothelium in a microfluidic model of human microvessels. Microspheres, particularly the 2 μm spheres, were found to show disproportionately higher margination than nanospheres in all hemodynamic conditions evaluated due to the poor ability of the latter to localize to the wall region from midstream. This work represents the first evidence that nanospheres may not exhibit near wall excess in microvessels, e.g., arterioles and venules, and therefore may not be suitable for imaging and drug delivery applications in cancer and other diseases affecting microvessels.

The margination propensity of ellipsoidal micro/nanoparticles to the endothelium in human blood flow

Particle shape is becoming increasingly recognized as an important parameter for the development of vascular-targeted carriers (VTCs) for disease treatment and diagnosis. However, limited research exists that investigates how particle shape coupled with hemodynamics affects VTC margination (localization and adhesion). In this study, we investigate the effects of particle shape parameters (volume, aspect ratio, axis length) on the margination efficacy of targeted spheres and prolate ellipsoids (rods) to an inflamed endothelial wall from human blood flow in an inxa0vitro model of human vasculature. Overall, particles with 2xa0μm equivalent spherical diameters (ESD) display higher margination than particles with either 1xa0μm or 500xa0nm ESDs. Interestingly, rod-shaped microparticles (1xa0μm or 2xa0μm ESD) with high aspect ratios display significantly improved margination compared to spheres of equal volume, particularly under high shear rates and disturbed flow profiles. Nanorods (500xa0nm ESD), even with high aspect ratio, do not display enhanced margination compared to that of equivalent spheres, which suggests that nanorods, like nanospheres, display minimal margination due to their inability to effectively localize to the vessel wall in the presence of RBCs.

In vivo evaluation of vascular-targeted spheroidal microparticles for imaging and drug delivery application in atherosclerosis

OBJECTIVEnVascular-targeting remains a promising strategy for improving the diagnosis and treatment of coronary artery disease (CAD) by providing localized delivery of imaging and therapeutic agents to atherosclerotic lesions. In this work we evaluate how size and shape affects the capacity for a vascular-targeted carrier system to bind inflamed endothelial cells over plaque using ApoExa0-/- mice with developed atherosclerosis.nnnMETHODnWe investigated the adhesion levels along mouse aortae of ellipsoidal and spherical particles targeted to the inflammatory molecules E-selectin and VCAM-1, as well as the biodistribution of targeted and untargeted particles in major organs following injection via tail-vein and a 30-min circulation time.nnnRESULTSnWe found that targeted ellipsoidal microparticles adhered to mouse aortae at higher levels than microspheres of similar volume, particularly at segments that contained atherosclerotic plaques. Moreover, both ellipsoidal and spherical nanoparticles displayed the same minimal adhesion levels compared to both types of microparticles evaluated, likely due to poor localization of nanoparticles to the vessel wall in blood flow. We found that microparticles targeted to plaque-associated inflammation were retained at higher levels in the lungs than untargeted particles, largely due to molecular interaction with the pulmonary endothelium. The level of the mechanical entrapment of ellipsoidal microparticles in the lungs was also not significantly different from that of microspheres of the same volume despite a ∼3-fold higher major axis length for the ellipsoids.nnnCONCLUSIONSnParticle shape and size should be considered in the design of carrier systems to target atherosclerosis, as these parameters can be tuned to improve carrier performance.

Plasma Protein Corona Modulates the Vascular Wall Interaction of Drug Carriers in a Material and Donor Specific Manner

The nanoscale plasma protein interaction with intravenously injected particulate carrier systems is known to modulate their organ distribution and clearance from the bloodstream. However, the role of this plasma protein interaction in prescribing the adhesion of carriers to the vascular wall remains relatively unknown. Here, we show that the adhesion of vascular-targeted poly(lactide-co-glycolic-acid) (PLGA) spheres to endothelial cells is significantly inhibited in human blood flow, with up to 90% reduction in adhesion observed relative to adhesion in simple buffer flow, depending on the particle size and the magnitude and pattern of blood flow. This reduced PLGA adhesion in blood flow is linked to the adsorption of certain high molecular weight plasma proteins on PLGA and is donor specific, where large reductions in particle adhesion in blood flow (>80% relative to buffer) is seen with ∼60% of unique donor bloods while others exhibit moderate to no reductions. The depletion of high molecular weight immunoglobulins from plasma is shown to successfully restore PLGA vascular wall adhesion. The observed plasma protein effect on PLGA is likely due to material characteristics since the effect is not replicated with polystyrene or silica spheres. These particles effectively adhere to the endothelium at a higher level in blood over buffer flow. Overall, understanding how distinct plasma proteins modulate the vascular wall interaction of vascular-targeted carriers of different material characteristics would allow for the design of highly functional delivery vehicles for the treatment of many serious human diseases.

Characterization of an S-nitroso-N-acetylpenicillamine–based nitric oxide releasing polymer from a translational perspective

ABSTRACT Due to the role of nitric oxide (NO) in regulating a variety of biological functions in humans, numerous studies on different NO releasing/generating materials have been published over the past two decades. Although NO has been demonstrated to be a strong antimicrobial and potent antithrombotic agent, NO-releasing (NOrel) polymers have not reached the clinical setting. While increasing the concentration of the NO donor in the polymer is a common method to prolong the NO release, this should not be at the cost of mechanical strength or biocompatibility of the original material. In this work, it was shown that the incorporation of S-nitroso-penicillamine (SNAP), an NO donor molecule, into Elast-eon E2As (a copolymer of mixed soft segments of polydimethylsiloxane and poly(hexamethylene oxide)), does not adversely impact the physical and biological attributes of the base polymer. Incorporating 10 wt% of SNAP into E2As reduces the ultimate tensile strength by only 20%. The inclusion of SNAP did not significantly affect the surface chemistry or roughness of E2As polymer. Ultraviolet radiation, ethylene oxide, and hydrogen peroxide vapor sterilization techniques retained approximately 90% of the active SNAP content and did not affect the NO-release profile over an 18-day period. Furthermore, these NOrel materials were shown to be biocompatible with the host tissues as observed through hemocompatibility and cytotoxicity analysis. In addition, the stability of SNAP in E2As was studied under a variety of storage conditions, as they pertain to translational potential of these materials. SNAP-incorporated E2As stored at room temperature for over six months retained 87% of its initial SNAP content. Stored and fresh films exhibited similar NO release kinetics over an 18-day period. Combined, the results from this study suggest that SNAP-doped E2As polymer is suitable for commercial biomedical applications due to the reported physical and biological characteristics that are important for commercial and clinical success. GRAPHICAL ABSTRACT

Dense nanoparticles exhibit enhanced vascular wall targeting over neutrally buoyant nanoparticles in human blood flow.

For vascular-targeting carrier (VTC) systems to be effective, carriers must be able to localize and adhere to the vascular wall at the target site. Research suggests that neutrally buoyant nanoparticles are limited by their inability to localize to the endothelium, making them sub-optimal as carriers. This study examines whether particle density can be exploited to improve the targeting (localization and adhesion) efficiency of nanospheres to the vasculature. Silica spheres with 500 nm diameter, which have a density roughly twice that of blood, exhibit improved adhesion to inflamed endothelium in an in vitro model of human vasculature compared to neutrally buoyant polystyrene spheres of the same size. Silica spheres also display better near-wall localization in the presence of red blood cells than they do in pure buffer, likely resulting in the observed improvement in adhesion. Titania spheres (4 times more dense than blood) adhere at levels higher than polystyrene, but only in conditions when gravity or centrifugal force acts in the direction of adhesion. In light of the wide array of materials proposed for use as carrier systems for drug delivery and diagnostics, particle density may be a useful tool for improving the targeting of diseased tissues.

One-step fabrication of agent-loaded biodegradable microspheroids for drug delivery and imaging applications

Non-spherical particles may offer advantages over conventional spherical systems for drug delivery applications. This work describes the fabrication of agent-loaded poly(lactic-co-glycolic acid) (PLGA) spheroids via the emulsion solvent evaporation (ESE) method. The versatility of this technique for loading a variety of therapeutics is demonstrated via loading of paclitaxel, bovine serum albumin, and cadmium sulfide nanoparticles into PLGA spheroids. The encapsulation efficiency for spheroids fabricated via oil-in-water (O/W) emulsions is highest at low aqueous phase surfactant concentrations while the encapsulation efficiency for spheroids made via water-in-oil-in-water (W/O/W) is highest at high aqueous phase surfactant concentrations and basic aqueous phase pH values. Particle aspect ratio polydispersity can be minimized via the use of high aqueous phase PVA concentration and pH. The ESE technique is an attractive alternative to recently described methods for fabrication of non-spherical particles due to its simplicity in setup, high particle yield and adaptability to a variety of biodegradable polymers and therapeutics.

A small-scale, rolled-membrane microfluidic artificial lung designed towards future large area manufacturing

Artificial lungs have been used in the clinic for multiple decades to supplement patient pulmonary function. Recently, small-scale microfluidic artificial lungs (μAL) have been demonstrated with large surface area to blood volume ratios, biomimetic blood flow paths, and pressure drops compatible with pumpless operation. Initial small-scale microfluidic devices with blood flow rates in the μl/min to ml/min range have exhibited excellent gas transfer efficiencies; however, current manufacturing techniques may not be suitable for scaling up to human applications. Here, we present a new manufacturing technology for a microfluidic artificial lung in which the structure is assembled via a continuous rolling and bonding procedure from a single, patterned layer of polydimethyl siloxane (PDMS). This method is demonstrated in a small-scale four-layer device, but is expected to easily scale to larger area devices. The presented devices have a biomimetic branching blood flow network, 10u2009μm tall artificial capillaries, and a 66u2009μm thick gas transfer membrane. Gas transfer efficiency in blood was evaluated over a range of blood flow rates (0.1-1.25u2009ml/min) for two different sweep gases (pure O2, atmospheric air). The achieved gas transfer data closely follow predicted theoretical values for oxygenation and CO2 removal, while pressure drop is marginally higher than predicted. This work is the first step in developing a scalable method for creating large area microfluidic artificial lungs. Although designed for microfluidic artificial lungs, the presented technique is expected to result in the first manufacturing method capable of simply and easily creating large area microfluidic devices from PDMS.

Stability of Polyethylene Glycol and Zwitterionic Surface Modifications in PDMS Microfluidic Flow Chambers

Blood-material interactions are crucial to the lifetime, safety, and overall success of blood contacting devices. Hydrophilic polymer coatings have been employed to improve device lifetime by shielding blood contacting materials from the natural foreign body response, primarily the intrinsic pathway of the coagulation cascade. These coatings have the ability to repel proteins, cells, bacteria, and other micro-organisms. Coatings are desired to have long-term stability, so that the nonthrombogenic and nonfouling effects gained are long lasting. Unfortunately, there exist limited studies which investigate their stability under dynamic flow conditions as encountered in a physiological setting. In addition, direct comparisons between multiple coatings are lacking in the literature. In this study, we investigate the stability of polyethylene glycol (PEG), zwitterionic sulfobetaine silane (SBSi), and zwitterionic polyethylene glycol sulfobetaine silane (PEG-SBSi) grafted by a room temperature, sequential flow chemistry process on polydimethylsiloxane (PDMS) over time under ambient, static fluid (no flow), and physiologically relevant flow conditions and compare the results to uncoated PDMS controls. PEG, SBSi, and PEG-SBSi coatings maintained contact angles below 20° for up to 35 days under ambient conditions. SBSi and PEG-SBSi showed increased stability and hydrophilicity after 7 days under static conditions. They also retained contact angles ≤40° for all shear rates after 7 days under flow, demonstrating their potential for long-term stability. The effectiveness of the coatings to resist platelet adhesion was also studied under physiological flow conditions. PEG showed a 69% reduction in adhered platelets, PEG-SBSi a significant 80% reduction, and SBSi a significant 96% reduction compared to uncoated control samples, demonstrating their potential applicability for blood contacting applications. In addition, the presented coatings and their stability under shear may be of interest in other applications including marine coatings, lab on a chip devices, and contact lenses, where it is desirable to reduce surface fouling due to proteins, cells, and other organisms.

A Membrane Lung Design Based on Circular Blood Flow Paths

Current hollow fiber membrane lungs feature a predominantly straight blood path length across the fiber bundle, resulting in limited O2 transfer efficiency because of the diffusion boundary layer effect. Using computational fluid dynamics and optical flow visualization methods, a hollow fiber membrane lung was designed comprising unique concentric circular blood flow paths connected by gates. The prototype lung, comprising a fiber surface area of 0.28 m2, has a rated flow of 2u2009L/min, and the oxygenation efficiency is 357u2009ml/min/m2. The CO2 clearance of the lung is 200u2009ml/min at the rated blood flow. Given its high gas transfer efficiency, as well as its compact size, low priming volume, and propensity for minimal thrombogenicity, this lung design has the potential to be used in a range of acute and chronic respiratory support applications, including providing total respiratory support for infants and small children and CO2 clearance in adults.