The effect of particle size and shape on margination and adhesion propensity

textThis thesis presents an experimental study of the effect that particle size and shape have on nanoparticle magination and adhesion propensity in micro-capillaries. With the use of half elliptical cross-section microfluidic channels that were fabricated using photolithography as well as wet and dry etching techniques and geometrically mimetic of human microcirculation, particles ranging from 93 to 970 nm were flown and imaged individually adhering to the channel walls. The results show a significant increase in particle adhesion below 200 nm as well as the emergence of a critical particle diameter above which no particle adherence was observed. The volume delivery efficiency was also shown to increase below 200 nm, providing insight for the rational design of nanocarriers for targeted cancer therapeutics.Mechanical Engineerin

Nanoparticle margination, adhesion, and uptake in microflow

Various nanoparticles have been investigated as drug carriers for delivery to diseased cells in the body. Targeted delivery of nanocarriers specifically to diseased cells can help to shield collateral cells from harmful cytotoxic drugs and reduce the many harmful side effects associated with chemotherapy. Recent advancements in our understanding of the complex behavior of intravenously injected nanoparticles has informed the rational design of the next generation of tailored nanocarriers. However fundamental questions about the mechanisms driving the behavior of nanoparticles in vasculature remain. Phenomena important for particle margination, adhesion, and uptake as well as the dependence of each on nanoparticle characteristics such as size and shape still remain elusive. This dissertation reports an experimental study of the effects of size and shape on polymeric nanoparticle margination and uptake in bare and cell-containing microfluidic environments, respectively. It is found that the competition of Brownian force and electrostatic repulsive forces between particles near the wall and adhered particles on a bare glass substrate lead to insensitive size dependence of spherical particles on margination and adhesion propensity. With the presence of cells on channel walls and a reduced zeta potential, however, the repulsive force is reduced such that a dominant Brownian force leads to more uptake of smaller spherical particles in shear-adapted endothelial cells. In comparison, increased flow-driven rotation of non-spherical nanoparticles with increased size and aspect ratio enhances particle/cell interaction frequency which dominates the effect of Brownian motion and the energy for membrane deformation, leading to more uptake of larger and larger-aspect ratio non-spherical nanoparticles in shear adapted endothelial cells.Mechanical Engineerin

Reactive Ion Plasma Modification of Poly(Vinyl‐Alcohol) Increases Primary Endothelial Cell Affinity and Reduces Thrombogenicity

Bulk material properties and luminal surface interaction with blood determine the clinical viability of vascular grafts, and reducing intimal hyperplasia is necessary to improve their long‐term patency. Here, the authors report that the surface of a biocompatible hydrogel material, poly(vinyl alcohol) (PVA) can be altered by exposing it to reactive ion plasma (RIP) in order to increase primary endothelial cell attachment. The power and the carrier gas of the RIP treatment are varied and the resultant surface nitrogen, water contact angle, as well as the ability of the RIP‐treated surfaces to support primary endothelial colony forming cells is characterized. Additionally, in a clinically relevant shunt model, the amounts of platelet and fibrin attachment to the surface were quantified during exposure to non‐anticoagulated blood. Treatments with all carrier gases resulted in an increase in the surface nitrogen. Treating PVA with O2, N2, and Ar RIP increased affinity to primary endothelial colony forming cells. The RIP treatments did not increase the thrombogenicity compared to untreated PVA and had significantly less platelet and fibrin attachment compared to the current clinical standard of expanded polytetrafluoroethylene (ePTFE). These findings indicate that RIP‐treatment of PVA could lead to increased patency in synthetic vascular grafts

Size-Dependent Nanoparticle Uptake by Endothelial Cells in a Capillary Flow System

An in vitro cell culture system is developed for studying the uptake characteristics of nanoparticles (NPs) by endothelial cells under shear stress. Results show that the smaller polystyrene nanospheres are uptaken more than larger nanospheres for sizes ranging from 100 nm to 500 nm for 12, 24, and 48 hrs delivery times. While the result is similar to that found in static cultures, the observed trend is different from NP delivery behaviors to a simple glass surface in a flow, where no clear size dependence was observed because of repulsive electrostatic force on marginating NPs. The trend is also opposite to the behavior found in another study of the adhesion of labeled particles onto endothelial cells in whole blood flow. The comparison shows that the reduced zeta potential of NPs in a serum-containing cell medium and particle removal by cells results in reduced repulsive electrostatic force on marginating NPs. Consequently, the uptake behaviors are dominated by Brownian diffusion and cell membrane deformation process, which favor the uptake of NPs with reduced sizes

Mammalian cells preferentially internalize hydrogel nanodiscs over nanorods and use shape-specific uptake mechanisms

Size, surface charge, and material compositions are known to influence cell uptake of nanoparticles. However, the effect of particle geometry, i.e., the interplay between nanoscale shape and size, is less understood. Here we show that when shape is decoupled from volume, charge, and material composition, under typical in vitro conditions, mammalian epithelial and immune cells preferentially internalize disc-shaped, negatively charged hydrophilic nanoparticles of high aspect ratios compared with nanorods and lower aspect-ratio nanodiscs. Endothelial cells also prefer nanodiscs, however those of intermediate aspect ratio. Interestingly, unlike nanospheres, larger-sized hydrogel nanodiscs and nanorods are internalized more efficiently than their smallest counterparts. Kinetics, efficiency, and mechanisms of uptake are all shape-dependent and cell type-specific. Although macropinocytosis is used by both epithelial and endothelial cells, epithelial cells uniquely internalize these nanoparticles using the caveolae-mediated pathway. Human umbilical vein endothelial cells, on the other hand, use clathrin-mediated uptake for all shapes and show significantly higher uptake efficiency compared with epithelial cells. Using results from both upright and inverted cultures, we propose that nanoparticle internalization is a complex manifestation of three shape- and size-dependent parameters: particle surface-to-cell membrane contact area, i.e., particle–cell adhesion, strain energy for membrane deformation, and sedimentation or local particle concentration at the cell membrane. These studies provide a fundamental understanding on how nanoparticle uptake in different mammalian cells is influenced by the nanoscale geometry and is critical for designing improved nanocarriers and predicting nanomaterial toxicity

Scalable Imprinting of Shape-Specific Polymeric Nanocarriers Using a Release Layer of Switchable Water Solubility

There is increasing interest in fabricating shape-specific polymeric nano- and microparticles for efficient delivery of drugs and imaging agents. The size and shape of these particles could significantly influence their transport properties and play an important role in <i>in vivo</i> biodistribution, targeting, and cellular uptake. Nanoimprint lithography methods, such as jet-and-flash imprint lithography (J-FIL), provide versatile top-down processes to fabricate shape-specific, biocompatible nanoscale hydrogels that can deliver therapeutic and diagnostic molecules in response to disease-specific cues. However, the key challenges in top-down fabrication of such nanocarriers are scalable imprinting with biological and biocompatible materials, ease of particle-surface modification using both aqueous and organic chemistry as well as simple yet biocompatible harvesting. Here we report that a biopolymer-based sacrificial release layer in combination with improved nanocarrier-material formulation can address these challenges. The sacrificial layer improves scalability and ease of imprint-surface modification due to its switchable solubility through simple ion exchange between monovalent and divalent cations. This process enables large-scale bionanoimprinting and efficient, one-step harvesting of hydrogel nanoparticles in both water- and organic-based imprint solutions