Role of Carrier Size, Hemodynamics and Hemorheology in the Efficacy of Vascular-Targeted Spherical Drug Carriers.

Spherical polymeric particles in the submicron down to tens nanometers size range are extensively proposed for use as vascular-targeted drug carriers (VTDCs); however, very limited studies have explored their capacity to efficiently localize and adhere to the vascular wall. The studies presented in this dissertation are focused on characterizing the role of particle size, blood flow dynamics (hemodynamics) and blood cells (hemorheology) on dictating the targeting (localization and binding) efficiency of VTDCs at the vascular wall in physiological human bulk blood flow via in vitro parallel plate flow assays. The presented results show that the binding efficiency of VTDCs is a function of particle size in all flow types (i.e. laminar, pulsatile and recirculating flow) and is strongly modulated by the presence of red blood cells (RBCs). Specifically, the migration of RBCs away from the wall under shear flow creating the RBC-free layer (CFL) at the wall vicinity where leukocytes and microspheres are disproportionally concentrated whereas nanospheres tend to get trapped within the RBC core. The binding of localized particle is either enhanced or hindered depending on the ratio of particle size to the CFL width that can vary with the volume fraction of RBCs (% Hct), blood vessel size and wall shear rate. White blood cells (WBCs) tend to hinder microsphere binding due to their collision with bound particles associated with their tethering on the vascular wall, which increases the drag force on particles leading to particle removal. Overall, the presented results suggest that intermediate-size microspheres, 2–5 micrometers, not nanospheres or large microspheres, are the optimal particle sizes for targeting the wall from human blood flow in medium to large-sized blood vessels relevant in several cardiovascular diseases. The relevance of the presented in vitro results were valid with ex vivo model of mouse blood where it is found that the subtle differences in RBC sizes and hemorheology among various animal models utilized in drug delivery research can differently manipulate the particle dynamics and their eventual adhesion in blood flow; thus, raising the awareness of possible result deviation from animal models to human.Ph.D.Chemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91589/1/phapanin_1.pd

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 VTC’s 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

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

Sample images of activated HUVEC monolayers exposed to PLGA in different flow mediums.

<p>Phase image of 1.4 µm sLe^a-coated PLGA spheres bound to IL1-β-activated HUVEC monolayer after 5 min of flow of particles in (A) RBC-in-Buffer, (B) whole blood, and (C) plasma at 200 s⁻¹. Image taken at 20× magnification. sLe^a density  = 1500+/−100 sites/µm² (SEM). Particle concentration  = 5e5 particles/mL. Scale bar  = 20 µm</p

Summary of the adhesion of PLGA spheres from flow of buffer, plasma and blood to an activated endothelial cell monolayer.

<p>(A) A depiction of particle margination in buffer, plasma and blood flow. Binding density after 5 min of flow for (B) 5 µm, (C) 1.4 µm and (D) 300 nm sLe^a-coated pLGA particles to activated HUVEC monolayer from laminar buffer, plasma, or whole blood at 200 s⁻¹. Particle concentration  = 5e5 particles/mL for 5 and 1.4 µm data and 1e6 particles/mL for the 330 nm particles. sLe^a density  = 1,700+/−100 sites/µm² (SEM) surface for 5 µm, 1500+/−100 sites/µm² (SEM) for 1.4 µm and 9,000+/−400 sites/µm² (SEM) for 330 nm particles. N = 3 distinct donors (donors A, B and C).</p

Adhesion of sLe^a–coated PS spheres or anti-ICAM-coated PLGA spheres to activated HUVEC under various flow conditions.

<p>(A) Adhesion of 5 µm sLe^a–coated PS spheres in laminar whole blood and buffer flows to activated HUVEC at 200 s⁻¹ for 7 human subjects. N = 2 (distinct trials) for each blood bar. (B) Average adhesion of 5 µm anti-ICAM-coated PLGA spheres to activated HUVEC from laminar buffer, plasma, or whole blood flow of three low PLGA binding donors at 200 s⁻¹. Laminar flow was run for 5 min. Particle concentration in flow  = 5e5 spheres/mL. sLe^a density  = 1,800+/−200 sites/µm² (SEM) and anti-ICAM-1 density  = 3500+/−500 sites/µm² (SEM). #  =  Not significant with respect to the whole blood trial. N = 3 distinct trials (donors) for the plasma and blood flow assays.</p

The average mean particle diameter (Z-average) and polydispersity indexes (PDI) for PLGA spheres in filtered phosphate buffer saline with calcium and magnesium ions (PBS+/+) are measured via dynamic light scattering (DLS) technique using a Malvern Zetasizer Nano ZSP equipped with a back scattering detector (173 degrees).

<p>The average mean particle diameter (Z-average) and polydispersity indexes (PDI) for PLGA spheres in filtered phosphate buffer saline with calcium and magnesium ions (PBS+/+) are measured via dynamic light scattering (DLS) technique using a Malvern Zetasizer Nano ZSP equipped with a back scattering detector (173 degrees).</p

Phase and fluorescence images of small PLGA spheres.

<p>Phase image of 1.4 µm PLGA particles in PBS+/+ (A) and plasma (B), and fluorescence image of 330 nm PLGA in PBS+/+ (C) and plasma (D). Particles were added to the desired medium for 5 min in static after which a small amount of the particle solution is placed on a coverslip for imaging. All images shown were taken at a 40× magnification. Scale bar  = 10 µm.</p

Adhesion of PEGylated and non-PEGylated 1.4 µm sLe^a-targeted spheres to HUVEC in laminar buffer or whole blood flow at 200 s⁻¹ (5 min).

<p>A PEG density of 16,000 site/µm² estimated to be the brush conformation is used. sLe^a density  = 1,800+/−200 sites/µm² for both PEGylated and un-PEGylated particles. Particle concentration in flow  = 5e5 spheres/mL.</p