Understanding the effect of physico-chemical properties of particles on cellular interactions

Polymeric micro and nanoparticles are useful carriers for drugs and vaccines. During these applications, particles come into contact with macrophages of the reticuloendothelial system leading to their internalization. On one hand, uptake of particles by macrophages affects their ability to deliver therapeutics to the target cells. On the other hand, intracellular delivery of therapeutics is dependent on macrophage uptake in diseases or vaccines involving these cells. Previous research efforts have focused on identifying crucial particle physico-chemical properties like size, shape, surface chemistry and stiffness that are capable of enhancing drug delivery. However, as particle fabrication techniques advance to meet the growing need to develop complex particles for enhancing therapeutic delivery, identification of the inter-dependence between multiple physical properties on cellular interactions is critical. A major challenge with current particle fabrication techniques is the inability to tune each of their physical properties separately and thereby limiting investigation of influence of inter-dependent properties on cellular interactions. Additionally, it is crucial to identify how individual properties alter cellular functions like cytokine production. To address these challenges, in this dissertation, we proposed a novel method that leverages the principles of self-assembly on soft templates to enable the tuning of multiple physical properties of particles while holding the surface chemistry constant. We investigated the combined effect of physical properties size, shape and stiffness on macrophage interactions in Fc receptor-mediated phagocytosis. These particles highlight the interplay between size, shape and stiffness during phagocytosis by macrophages and these studies can be leveraged to identify combinations of parameters that improve particle-based delivery to cells. In addition, this novel technique also enabled self-assembly of a commonly used stealth phosphorylcholine co-polymer on microparticles in a single step, which makes it widely applicable and less time consuming compared to currently published covalent methods. We next evaluated the effect of a particular physical property- shape to affect macrophage function- cytokine production when combined with active ligand chemistries. We identified that geometric presentation through an altered shape can elicit differential macrophage cytokine responses and similar responses can be noticed across varying ligands. We demonstrated the ability of geometric manipulation of ligands to alter macrophage cytokine response irrespective of the nature of the ligand, thereby suggesting a new avenue through which cell responses can be manipulated. Overall, these studies enable identification of design rules for engineering cell interactions and responses. These findings are significant to both the biomaterials and the larger immune-engineering communities that actively employ various strategies involving particle properties, and active ligands to elicit immunological responses. These methods, techniques and results can be used to further fundamental research involving tunable particle-cell interactions and to inform particle design for specific therapeutic applications based on the disease.Ph.D

Shape of ligand immobilized particles dominates and amplifies the macrophage cytokine response to ligands.

Macrophages aid in clearing synthetic particulates introduced into the body and bridge innate and adaptive immunity through orchestrated secretion of cytokines and chemokines. While the field has made tremendous progress in understanding the effect of particle physicochemical properties on particle-macrophage interactions, it is not known how macrophage functions like cytokine production are affected while presenting active ligands on particles with altered physical properties. Moreover, it is unknown if ligand presentation through an altered particle shape can elicit differential macrophage cytokine responses and if responses are ligand dependent. Therefore, we investigated the influence of geometric particle presentation of diverse ligands, bovine serum albumin, immunoglobulin-G and ovalbumin, on macrophage inflammatory cytokine response. Our results indicate that for similar ligand densities, ligand presentation on rods enhanced production of inflammatory cytokine tumor necrosis factor-alpha (TNF-α) compared to spheres regardless of the nature of the ligand and its cellular receptor. Surprisingly, TNF-α responses were affected by ligand density in a shape-dependent manner and did not correlate to total particle-macrophage association. This study demonstrates the ability of geometric manipulation of particle ligands to alter macrophage cytokine response irrespective of the nature of the ligand

Engineering Polyelectrolyte Capsules with Independently Controlled Size and Shape

Polyelectrolyte capsules (PECs) are a promising delivery system that has the ability to carry a large payload of a variety of cargoes. Controlling PEC properties is critical to understanding and tuning their cellular uptake efficiency, kinetics, and mechanism as well as their biodistribution in the body. The lack of a method to independently engineer PEC size, shape, and chemistry impedes both basic understanding of how physicochemical parameters affect PEC behavior in drug delivery and other applications, and the ability to optimize parameters for best function. Here, we report the successful fabrication of PECs having constant surface chemistry with independently controlled size and shape by combining soft organic templates created by the particle stretching method and a modified layer-by-layer (LBL) deposition process. Changing the template dispersion solution during LBL deposition from water to ethanol allowed us to overcome previous issues with organic templates, such as aggregation and template removal. These results will contribute not only to the basic study of the role of capsule shape and size on its function but also to the optimization of capsule properties for drug or imaging carriers, sensors, reactors, and other applications