Layer-by-layer assembled micro and nano carriers for drug delivery applications

In nano- or microparticulate drug delivery, both control of the drug release and interaction of the particles with the cellular environment are critical attributes. Polyelectrolyte layering of the particle surface offers an interesting and facile way to modulate both attributes. Layer-by-Layer (LbL) technology involves the consecutive assembly of oppositely charged polyelectrolytes based on electrostatic interactions onto charged template surfaces. The relative ease of preparation through the LbL self- assembly, accurate control over the wall thickness as well as the flexibility in the choice of constituents qualifies these carriers to constitute an influential domain in the field of particulate technology. The bioactive agents may either be encapsulated in the core/template or inside the multilayers, with the option to tailor the properties of the carrier to the specific needs of the active material and therapeutic application. Despite having great potential in the design of versatile LbL carriers, there are very few studies that report the design of carriers suitable for drug delivery applications. In particular, the characterization and applications of biodegradable, biocompatible carriers, coated with polyelectrolyte multilayers, have not been extensively studied to date The objective is to fabricate, characterize and evaluate specific applications of polyelectrolyte multilayered carriers for drug delivery applications. Towards this objective, biodegradable and biocompatible micro and nano- LbL carriers were fabricated to study the drug release profiles, cellular interaction, intracellular transport and processing of polyelectrolyte multilayered carriers as delivery agents. Chapter 3 explains the general methods for fabrication of protein loaded LbL coated CaCO3 particles and their application to treat breast tumors. Up regulation of cysteine proteases in tumor cells constitute a major role in extra cellular matrix (ECM) degradation and metastatic invasion. Consequently inhibition of cysteine proteases (cathepsins) is envisaged as a promising strategy to restrict tumor growth. Towards this goal, this study reports the design of a biocompatible and biodegradable carrier for intracellular delivery of cathepsin B inhibitor (cystatin C) in breast tumor cells. In an approach to expand the application of vascular drug carriers, LbL self- assembly was exploited to impart added functionalities in order to overcome the disadvantages associated with the conventional erythrocyte delivery system, as detailed in chapter 4. The concept of introducing LbL multilayer shells as a surface modification ii strategy lead to unique means of controlling the release of bioactive molecules from erythrocyte carriers. Chapter 5 describes the application of LbL technology to hydroxyapatite (HA) nanoparticles for gene delivery applications. This work investigates the integration of proteins as well as nucleic acids (pDNA) in the multilayer shells and the intracellular gene delivery. Following the carrier design, studies were performed to delineate the intracellular trafficking of system that encompasses the molecular pathways associated with the uptake and intracellular processing. In this work, we show that nanoparticles with PEM coats offer a promising strategy for the development of safe and efficient vectors for the delivery of genes/siRNA into cells. Chapter 6 reports the design of LbL carriers endowed with biomimetic properties for passive targeting. In brief, membrane vesicles derived from human red blood cells were explored for surface modification of multilayer shells. Further, the influence of the membrane orientation on the phagocytic uptake by mononuclear phagocyte system (MPS) system was studied using monocytes as a model platform. To summarize, this thesis illustrates the modifications of the LbL concept in different applications such as protein delivery, gene delivery, controlled release, and passive targeting. The high level of control over the architecture of LbL carriers, such as size, shape, multilayer shells material and their surface functionality makes them a versatile carrier for drug delivery applications.DOCTOR OF PHILOSOPHY (MSE