Aruta, Rosaria (2015) NANOSTRUCTURES FOR THERAPY AND DIAGNOSIS. [Tesi di dottorato]

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Abstract

The preparation of Nanostructures of desired shape, composition and with tailored properties is of wide scientific and technological interest. Indeed, a variety of nanoparticle architectures have been proposed as nanocarriers, these include liposomes, quantum dots (QD), gold-nanoshells, mesoporous materials, micelles, magnetic nanoparticles, dendrimers, and Carbon Nanotubes (CNTs) as so as several materials have been studied for use in active agents targeting. Among them, as asserted by different authors, hollow biopolymeric nanocapsules or (nanoencapsulated systems) as active substance carriers, compared to other particulated systems, show higher drug encapsulation efficiency due to optimized drug solubility in the core, low polymeric content compared such as to nanospheres, drug polymeric shell protection against degradation factor like pH and light and the reduction of tissue irritation due to the polymeric shell. Several research teams have extensively studied the nanoparticles formation mechanism, and generally there are several classical methods for the preparation of nanocapsular systems: nanoprecipitation, emulsion diffusion, emulsion evaporation, double emulsification, emulsion coacervation, polymer coating and layer by layer. Despite the fact the research proposed on these methods has shown important strategies, all these methods present critical challenges with a view of the industrial development. Indeed, it is important to take into account that the method chosen should also considerer other aspects such as active substance stability under operational conditions, particularly stirring, encapsulation efficiency, method feasibility, the generation of contaminants and the need for subsequent purification steps, solvent nature, the water volume required and time consumption. Likewise, the feasibility of scaling-up and cost should be considered. In these perspectives, to overcome some limitations of traditional processes in nanocapsular structure productions, such as sufficient scale-up to produce the cost reduction required to target volume markets and more complicated procedure not suitable to be industrialized, we focused our attention on the three main approaches: - the first one based on the Thermally Induced Phase Separation (TIPS) to produce nanocapsules for therapy - the second one related to the study of the micellization of block-copolymer to apply in the field of enhanced MRI - the last is the combining of the previous approaches by providing the deposition of the block-copolymer on the surface of the obtained nanocapsules. In the first part of the thesis, we developed a novel approach based on the thermodynamics of Thermally Induced Phase Separation (TIPS) to produce semicrystalline nanocapsules. Thermally Induced Phase Separation has extensively been used to fabricate various porous biodegradable scaffolds suitable for tissue engineering and drug delivery, even though it has never been studied neither to produce nanocapsules nor to produce semicrystalline nanocapsules. Because of the variety of parameters involved in TIPS process, such as types of polymers, polymer concentration, solvent/nonsolvent ratio, and quenching temperature, we individuate in this approach the possibility to create a value added process enables to overcome the issues related to the production of the nanocapsular systems even by preserving fundamental architectural properties. In this process, we started by a Poly-L-Lactic Acid (PLLA), a biopolymer largely studied by TIPS. PLLA is a Food&Drug Administration Approved polymer and it is biocompatible and biodegradable material which undergoes scission in the body to monomeric units of lactic acid as a natural intermediate in carbohydrate metabolism. The work also investigates thermodynamic parameters involved in the process able to induce for the first time simultaneously bending and crystallization of polymeric chain to form a nanocapsule. An explanation of this unusual crystallization phenomenon will be described in term of nanoscopic confinement of long flexible chain. Knowledge of the phase behavior of confined long flexible chain is a prerequisite to support the current interest in the construction of nanoscopic devices as so in confinement altering the statistical mechanical properties of DNA. In the second part of the thesis a Block copolymers of poly lactic acid (PLA) and polyethylene glycol (PEG) has been studied. Block copolymer are few of the commonly used polymers with hydrophilic and hydrophobic blocks which allows the formation of a stable nano-particulate suspension in an aqueous solvent, where PLA chains predominantly form the core and PEG chains are located outside. A systematic variation in their chemical structure, composition, size, and architecture; block copolymers offer advantages in tuning their shape and functionality in comparison to conventional amphiphiles such as low molecular weight surfactants and lipids. In particular, Diblock PLA-PEG copolymers and triblock PLA-PEG-PLA copolymers allow modulation of the biodegradation rate, the hydrophilicity, and the mechanical properties of the copolymers. Herein we present temperature/time-reliant self-assembly driven simple approach for the development of biocompatible nanostructures for MRI. Endeavor of the present research was to develop Gd loaded PLA-PEG-PLA NPs as the molecular MRI contrast agents to efficiently target tumor. A low molecular PLA-PEG-PLA have been designated to prepare well-demarcated NPs through optimization of kinetics of the self-assembly viz a viz temperature/time/concentration. The hydrophobic/hydrophilic moieties of block copolymer nanoparticles (BCN) were employed to adsorb GD+3 at the surface of BCNs to achieve multifunctional biodegradable NPs for MRI. The paramagnetic properties of the BCNs designed here compare sympathetically with Gd-based agents that have previously been reported. For example, while relaxivity of the commercial products, such Magnevist is of 4 mM-1 sec-1, our micelles can reach relaxivitry of around 30 mM-1 sec-1 , indicating a relaxivity significantly higher than the common paramagnetic contrast agents. Last part of the thesis has been devoted to the combination of the previous obtained structures in order to apply these new nanostructures in the theranostic field. For this reason only some Caolrimetric studies were performed. Nano-Isothermal Calorimetry (NanoITC) was used to evaluate the deposition of the block on the surface of the nanoparticles while Differential Scanning Calorimetry was used to show the melting properties of the combined system.

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