This thesis reports the research activity carried out over the last 3 years in the Laboratory of Industrial Corrosion Control at the University of Trento. The subject is related to corrosion control through an organic coating paint system for steel substrates. In other words, it coveres the investigation of anticorrosive pigments as viable alternatives to replace the use of hazardous and toxic substances commonly present into an organic coating paint system and in addition to this, to reduce emissions of volatile organic compounds (VOC), the organic coating paint system itself has been designed to be solvent-free. Much of the work over the development of a water based full paint system containing the environmentally friendly nanoparticles was based on electrochemical techniques. Therefore, the contents within the next pages are divided into three main parts: i) a background about the use of electrochemical techniques for corrosion and corrosion control through organic coatings; ii) the electrochemical investigations of the environmentally friendly anticorrosive pigments; iii) the incorporation into one water based organic coating system. Also, great effort has been spent to understand the mechanisms of the coatings degradation as well as the mechanisms of anticorrosion protection given by the pigments. In this way, the results of interest have been delivered to scientific community via a number of publications in different journals as well as congresses participations. Lastly, the activities in this thesis were supported by the SteelCoat project. SteelCoat was a consortium cooperation project within the EU Seventh Frame Programme (FP7), involving several companies and universities.

A lot of money is spent every year on the restoration of the concrete on structures and manufactured elements deteriorated by different types of degradation. Degradation of concretes is attributable to inadequate mix-design; anyway some environments are so aggressive that requiring additional care in order to increase durability. One of the most aggressive environments for concrete is acidic one, such as in the inner walls of sewer pipes. Deterioration of sewer pipes, made in concrete, is a great problem when service life is lower than 30 or less years, and maintenance or even replacement of damaged concrete sewer pipes are requested. In the case of a sewer pipe, the exposure class is the XA3, which concerns concrete structures exposed to chemical attacks by sulphate ions and aggressive chemical agents. To achieve a 30+ design life, materials exhibiting long-term durability have to be selected. However an extensive characterization of the most common concrete used for this application lacks due to the complexity of the chemical attack during service life. The processes leading to corrosion of the concrete sewer pipes are really complex. As previously described by some authors, hydrogen sulphide produced by anaerobic wastewater is released into the pipe, where micro-organisms convert aerobically hydrogen sulphite to sulphuric acid, which reacts with the concrete. The acid attacks first the calcium hydroxide and even tobermorite gel. Accordingly, under attack, calcium hydroxide forms gypsum and the calcium silicate hydrate (C-S-H) forms both anhydrous gypsum and an incoherent mass. However, different types of sulphate ions can be found in the wastewater. In the presence of a sodium sulphate source, calcium hydroxide reacts to form secondary gypsum. It is important to find out how to control these processes in order to increase the life of the facilities. The literature results lacking in prediction of the concrete resistance, because the experiments neglected both the presence of aggregate and the real conditions in the sewage pipes. Actually, it has been observed that the rate of degradation is higher just above the waterline at the sides of the pipes, where the fluctuating water level continually wash away the sulphate deposits, reducing the degradation resistance. Given that formation of hydrogen sulphide and sulphuric acid is the controlling factor, it is likely that pH is not continuously below 4, value for a fast concrete degradation, but shows a not well predictable wavy trend. It is worth noting that alternate wetting and drying of the concrete is even more detrimental than a continuous exposure to chemical attack. Thus the knowledge of the degradation rate is preliminary to the choice of a protection method or to design a suitable formulation of the mixes. Aim of this thesis is to develop procedures for evaluating the resistance of concrete mixes for sewage pipes. At this regard it seems that the concrete should be formulated for resisting cyclically to acid and sulphate attack. Indeed, the previous theories, which were developed so far upon testing standard mortars in acidic or sulphate solution, have to be critically revised, taking into account that the real attack involves cyclically both acid and sulphates. In this thesis new data, which were recorded on various concretes with different composition through a new chemical test, alternating acid and sulphate attack are described and discussed. The aim is to discriminate the effect and the behaviour of concrete compositions in an aggressive environment, as close as possible to the real attack condition, and in the meantime sufficiently fast. The concretes under investigation contain portland-limestone cement, blast furnace slag cement, sulphates resistance pozzolanic cement with or without silica fume, respectively, at constant water/cement ratio (w/c 0.39), and two type of aggregates, limestone and silicates. This thesis is divided in two main parts: the first part regards the studies on concrete degradation in aggressive environment and the second one describes the development of protective system. After an introduction of the degradation problem in chapter one, chapter two describes the studies on degradation of different concretes prepared with various cements and limestone aggregate, using a cyclic acid/sulphate test with sulphuric acid and sodium sulphate. Chapter three shows the results regarding the degradation of different cements prepared with two type of aggregates, limestone and silicates, using a cyclic test with acid sulphuric and a complex (mixed) sulphate solution (containing sulphates). The second part of the thesis describes the development of a pozzolanic coating and the results of the cyclic acid/complex sulphate test on a concrete with this protective coating. The last chapter shows preliminary results regarding the development of a new hybrid coating, which contains also zirconium oxide and could have a protective effect without the drawbacks evidenced upon using pozzolanic addition or coating.

In material science, the possibility of creating chemical or physical patterns on various materials has opened a wide range of possibilities. Several techniques are available for patterning; among these, self assembled structures raised great interest. Changing the environmental humidity during solvent evaporation from a cast polymer solution, the condensation of water droplets is promoted, which self-assembled in a regular array; these drops form a template for the formation of an array of pores on the film, called Breath Figures. A similar mechanism seems to happen not only during film casting, but also during the formation of fibers in the electrospinning process. This work is focused on the understanding of the mechanisms involved in pores formation due to the interaction of polymeric solution surface with humidity. The process parameters were controlled to tune the pores arrays features, according to the purpose they are used for. Moreover, the interface between the polymeric surface and the water droplets was exploited to promote the migration of hydrophilic chemical groups, obtaining the chemical functionalization of the inner surfaces of pores. In this way, a topographical and chemical pattern was obtained on the film surface. The formation of pores was studied on the surfaces of flat films and on electrospun fibers; both structures were developed for two main applications: drug release and interactions with cells. Porous films were demonstrated to release proteins in a controlled manner, depending on pores features and on chemical patterning. In particular, the release of protein with high molecular weight was developed. Films were demonstrated to influence cells adhesion depending on pores dimension and distribution. Pores on the surface of fibers where demonstrated to influence the release of drugs from mats produced by coaxial electrospinning. Similarly to films, electrospun fibers were studied to understand their ability to influence cells behavior. The final aim is the production of patches for drug release and of scaffolds that combine the ability to support tissue growth and the release of therapeutic molecules.

In this project, the synergetic effect of a graphene interphase in epoxy/glass fibers composites was investigated by coating glass fibers (GF) with graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets by an electrophoretic deposition (EPD) technique. Graphite oxide was prepared using modified Hummers method in which raw graphite powder was oxidized using potassium permanganate (KMnO4) in acidic solution. Using ultrasonic technique, the graphite oxide was dispersed homogenously in water to create a stable GO suspension which was used as a bath in the EPD process. For the coating process, two copper plates were used as electrodes in the EPD process in which GF were placed in front of anode for GO deposition since GO tends to carry negative charges due to oxygen functional groups attached on the graphene structure as produced in the modified Hummers method. The deposition was carried out at different applied fields while maintaining the dispersion concentration and deposition time constant. This process produced GF coated with GO nanosheets, while to obtain GF coated with rGO, GO coated fibers were subjected to chemical reduction process where the fibers were placed in an environment of hydrazine hydrate which reduced the GO coating on GF. Through this step, rGO coated GF were obtained. The oxidation level of GO and rGO was evaluated using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron (XPS) spectroscopy techniques which confirmed the successful oxidation of graphite powder into graphite oxide due to liquid chemical oxidation process while the hydrazine reduction method reduced the oxygen amount from 34% to 10% in GO hence converting it into rGO. Scanning electron microscopy analysis of coated fibers revealed uniform coating of GF with GO and rGO where the amount of deposition increased with increased applied field. The effect of GO or rGO coating on GF obtained by EPD process was first evaluated by determining the adhesion between GF and epoxy matrix. Single fiber fragmentation test was utilized to determine the interfacial shear strength (ISS) between the uncoated or coated fibers and epoxy matrix. Single fiber epoxy composites were prepared by using GO and rGO coated fibers and were tested using a mini-tensile testing machine and monitoring the lengths of fragments of fibers obtained during the tensile test. It was observed that in case of GO coated fibers, the ISS increased by 218% in comparison to uncoated fiber based composite. The increase of interfacial adhesion in this case, it can be attributed to the fact that GO carries oxygen functional groups which creates physical and chemical bonding between both the GF surface and the epoxy matrix. For investigating the interactions between GF and GO, atomic force microscopy (AFM) was used to determine the interfacial adhesion between them by scratching GO on GF. It was proved that the delamination strength was higher than the ISS, hence proving the efficacy of the selected GO deposition method. On the other hand, single fiber fragmentation tests indicated a 70% increase in ISS for rGO coated GF when embedded in the epoxy matrix as compared to uncoated fibers. This increment is lower than that observed for GO coated fibers and it has been attributed to the fact that rGO does not possess enough oxygen based functional groups to efficiently interact with the polymer matrix. The observed increase in ISS with respect to uncoated GF is based on the frictional forces offered by the roughness of rGO nanosheets. This confirms that the presence of an interphase (either GO or rGO) creates favorable load transfer mechanism through either chemical or physical bonding or even both depending on the nature of the interphase. To test further the positive effect of GO based interphase in epoxy/glass composites in terms of mechanical reinforcement, multifiber (uncoated and GO or rGO coated) reinforced epoxy composites were created by hand lay-up method. Laminas of fibers were wetted by epoxy resin and stacked over one another in certain number depending on the thickness of the resultant composite. These composites were subjected to various mechanical tests, such as flexural tests, short-beam shear tests, mode I interlaminar fracture toughness and creep tests which also confirmed that GO and rGO based interphase in epoxy/glass composites increase the performances of the composite with respect to that of the uncoated GF based composites. GO proved to be the best interphase in terms of mechanical properties obtained, as proved before. The multifunctionality of such interphases based on graphene was analyzed and confirmed using multiple tests on epoxy/glass composites containing uncoated and coated (GO or rGO). In particular, the electrical and thermal conductivity of the composites were tested in which the composites based on rGO interphase showed the highest conductivity which not only confirms that rGO coated fibers in epoxy/glass composites render the composites conductive but also proves the successful chemical reduction process used in this work. These conductive composites were subjected to piezoresistivity tests in which the applied longitudinal strain in different modes resulted in change in resistance thus showing a possibility of using such composites as strain sensing devices or for structural health monitoring purposes in automotive or aerospace applications. These conductive composite specimens were also analyzed for their dielectric properties. The tests showed increased permittivity values as compared to both uncoated and GO coated composites thus revealing the possibility to use composites containing rGO coated fibers for electromagnetic interference shielding applications.

In this PhD project, novel polymer nanocomposites are developed with the aim to increase the performances of 3D-printed parts obtained by fused deposition modeling (FDM). The attention is focused on carbon-based nanomaterials incorporated into an acrylonitrile–butadiene–styrene (ABS) polymer by a solvent-free process. ABS-based nanocomposites were prepared by incorporating different kinds and amounts of graphene nanoplatelets (GNP), carbon nanotubes (CNT) and hybrid (GNP/CNT) systems. In order to understand the effect of the manufacturing process on the material’s properties, the samples were produced into two different processing routes: (i) melt compounding and compression molding, and (ii) melt compounding, following by filament extrusion, and fused deposition modelling (FDM). Several characterization techniques were employed in order to evaluate the flowablity, morphology, mechanical and functional properties of the materials. In the first part of work, ABS-graphene nanocomposites are described. Two ABS matrices having different viscosity were compared with the addition of various types of commercial graphene nanoplatelets (xGnP® M5, C300, C500, and C750 by XG Sciences) in the range 2-8 wt%. The better processability and higher stiffening effect on compression molded plates were achieved by utilizing the low viscosity ABS. The effects of GNPs on the thermal, electromagnetic shielding (EMI SE), electrical and mechanical behaviour of an ABS matrix were investigated. Melt flow index (MFI) values almost linearly decreased with all the type of GNP, especially with the highest surface area nanofiller (GNP-C750). Due to large size of graphene, nanocomposites filled with GNP-M5 showed the better properties of in electromagnetic interference shielding efficiency (EMI SE) and stiffness. Consequently, GNP-M5 were selected and incorporated at 4 wt% in ABS filaments used to feed a FDM machine to obtain specimens with various build orientations. The elastic modulus and dynamic storage moduli of 3D printed parts along three different build orientations were increased by the presence of GNP-M5 in the ABS matrix. At the same time, a decrease in both strength and strain at break was observed when GNP-M5 is added to ABS. Moreover, higher thermal stability was induced on 3D printed parts by GNP, as indicated by a reduction in both coefficient of linear thermal expansion and creep compliance. A comparison between 3D printed and compression molded parts highlighted the importance of the orientation effects induced by the FDM process. In the second part of work, the results of the investigation on ABS-carbon nanotubes nanocomposites are reported. ABS-CNT nanocomposites plate production by compression molding and their characterization was a preliminary step. Nanocomposite ABS/CNT filaments at 1-8 wt % were obtained by using direct melt compounding and extrusion. The optimal CNT content in the filaments for FDM was found to be 6 wt %; for this composite, a detailed investigation of the thermal, mechanical and electrical properties was performed. The presence of CNT in ABS filaments and 3D-printed parts resulted in a significant enhancement of the tensile modulus and strength, accompanied by a reduction of the elongation at break. As documented by dynamic mechanical thermal analysis, the stiffening effect of CNT in ABS is particularly pronounced at high temperatures. Besides, the presence of CNT in 3D-printed parts accounts for better creep and thermal dimensional stabilities of 3D-printed parts, accompanied by a reduction of the coefficient of thermal expansion. 3D-printed nanocomposite samples with 6 wt% of CNT exhibited a good electrical conductivity, even if lower than pristine composite filaments. In addition, the strain sensing capabilities of the conducting 3D-printed samples with 6 wt% of CNT with two different infill patterns (HC, and H45) were studied. Upon the strain applied, the resistance change and damage in the conductive FDM parts were detectable. Fatigue and creep loading on FDM products were also carried out. In last part of work, ABS-GNP-CNT hybrid nanocomposites are described. ABS nanocomposites plates with addition GNP-M5 and CNT at 2-8 wt% were compared. A significant higher reduction in MFI value by the addition of CNT compared to GNP was observed. The ABS/GNP nanocomposites showed the slightly higher stiffness and the creep stability compared to the ABS/CNT nanocomposites, but showed the lower tensile strength. Also, the ABS/CNT samples showed significant higher electrical properties in comparison to ABS/GNP. The total nanofiller content of CNT/GNP hybrid plates was fixed at 6 wt%. The hybrid nanocomposites showed a linear increase in modulus and strength as a function to CNT/M5 ratio. Moreover, conductive hybrid nanocomposite plates were obtained by the addition of CNT. The composition of 50:50 of CNT/GNP at 6 wt% was selected for FDM process due to the good compromise between processability and properties (e.g. mechanical and electrical). In agreement with electrical resistivity, EMI SE of 6 wt% ABS/CNT and 50:50 hybrid ABS nanocomposites resulted to be -46 dB and -31.7 dB for plate samples. EMI SE of FDM parts is about for -14 dB HC and H45 build orientation and –25 dB for PC build orientation printing from ABS/CNT nanocomposites, while parts had EMI SE about -12 dB for HC and H45 and -16 dB for PC from hybrid nanocomposites.

The comminution and tuning of several structural parameters of materials is often accomplished following a top-down route by high energy grinding. The reduced size of the particles constituting the end product and the incorporation of defects cause modified materials properties and increased solid-state chemical reactivity. Among grinding devices, the planetary ball mill features high efficiency and versatility, being suitable for almost any kind of material, from metals and ceramics to organic compounds and pharmaceuticals. While its design and the working principle are rather simple, since grinding occurs by impacts between milling media (balls and jar) and mill charge, the characteristics of the end product strongly depend on a multitude of variables, determining balls trajectories and velocities and, in turn, the nature of impulsive forces exchanged during collisions. Numerical models can enourmously contribute to shed light on the process by providing the time evolution of kinematic and dynamic properties of milling media as well as quantities involved in contact events, permitting to understand the role of each milling variable and to design the characteristics of the end product. This Thesis chiefly proposes the implementation of a multibody dynamics model of the planetary ball milling process, its direct and indirect validation – respectively against movie collected in-operando and properties of the end product revealed by the analysis of X-ray powder diffraction data –, the evaluation of the effect of selected milling variables and the investigation of innovative solutions defining specific collisions features, obtained by the re-design of the jar shape. Some relevant case studies are also presented, namely the exfoliation of a bulk for the production of 2D nanostructured materials and the milling of the pharmaceutical compound Efavirenz, aimed at inducing structural and microstructural transformations enhancing dissolution properties.

Tissue engineering is a discipline that aims at regenerating damaged biological tissues by using a cell-construct engineered in vitro made of cells grown into a porous 3D scaffold. The role of the scaffold is to guide cell growth and differentiation by acting as a bioresorbable temporary substrate that will be eventually replaced by new tissue produced by cells. As a matter or fact, the obtainment of a successful engineered tissue requires a multidisciplinary approach that must integrate the basic principles of biology, engineering and material science. The present Ph.D. thesis aimed at developing and characterizing innovative polymeric bioresorbable scaffolds made of hydrolysable polyesters. The potentialities of both commercial polyesters (i.e. poly-e-caprolactone, polylactide and some lactide copolymers) and of non-commercial polyesters (i.e. poly-w-pentadecalactone and some of its copolymers) were explored and discussed. Two techniques were employed to fabricate scaffolds: supercritical carbon dioxide (scCO2) foaming and electrospinning (ES). The former is a powerful technology that enables to produce 3D microporous foams by avoiding the use of solvents that can be toxic to mammalian cells. The scCO2 process, which is commonly applied to amorphous polymers, was successfully modified to foam a highly crystalline poly(w-pentadecalactone-co-e-caprolactone) copolymer and the effect of process parameters on scaffold morphology and thermo-mechanical properties was investigated. In the course of the present research activity, sub-micrometric fibrous non-woven meshes were produced using ES technology. Electrospun materials are considered highly promising scaffolds because they resemble the 3D organization of native extra cellular matrix. A careful control of process parameters allowed to fabricate defect-free fibres with diameters ranging from hundreds of nanometers to several microns, having either smooth or porous surface. Moreover, versatility of ES technology enabled to produce electrospun scaffolds from different polyesters as well as “composite” non-woven meshes by concomitantly electrospinning different fibres in terms of both fibre morphology and polymer material. The 3D-architecture of the electrospun scaffolds fabricated in this research was controlled in terms of mutual fibre orientation by properly modifying the instrumental apparatus. This aspect is particularly interesting since the micro/nano-architecture of the scaffold is known to affect cell behaviour. Since last generation scaffolds are expected to induce specific cell response, the present research activity also explored the possibility to produce electrospun scaffolds bioactive towards cells. Bio-functionalized substrates were obtained by loading polymer fibres with growth factors (i.e. biomolecules that elicit specific cell behaviour) and it was demonstrated that, despite the high voltages applied during electrospinning, the growth factor retains its biological activity once released from the fibres upon contact with cell culture medium. A second fuctionalization approach aiming, at a final stage, at controlling cell adhesion on electrospun scaffolds, consisted in covering fibre surface with highly hydrophilic polymer brushes of glycerol monomethacrylate synthesized by Atom Transfer Radical Polymerization. Future investigations are going to exploit the hydroxyl groups of the polymer brushes for functionalizing the fibre surface with desired biomolecules. Electrospun scaffolds were employed in cell culture experiments performed in collaboration with biochemical laboratories aimed at evaluating the biocompatibility of new electrospun polymers and at investigating the effect of fibre orientation on cell behaviour. Moreover, at a preliminary stage, electrospun scaffolds were also cultured with tumour mammalian cells for developing in vitro tumour models aimed at better understanding the role of natural ECM on tumour malignity in vivo.

Il rapido progresso della tecnologia, lo sviluppo di prodotti altamente sofisticati, la forte competizione globale e l’aumento delle aspettative dei clienti hanno messo nuove pressioni sui produttori per garantire la commercializzazione di beni caratterizzati da una qualità sempre crescente. Sono gli stessi clienti che da anni si aspettano di trovare sul mercato prodotti contraddistinti da un livello estremo di affidabilità e sicurezza. Tutti siamo consapevoli della necessità per un prodotto di essere quanto più sicuro ed affidabile possibile; ma, nonostante siano passati oramai 30 anni di studi e ricerche, quando cerchiamo di quantificare ingegneristicamente queste caratteristiche riconducibili genericamente al termine qualità, oppure quando vogliamo provare a calcolare i benefici concreti che l’attenzione a questi fattori quali affidabilità e sicurezza producono su un business, allora le discordanze restano forti. E le discordanze restano evidenti anche quando si tratta di definire quali siano gli “strumenti più idonei” da utilizzare per migliorare l’affidabilità e la sicurezza di un prodotto o processo. Sebbene lo stato dell’arte internazionale proponga un numero significativo di metodologie per il miglioramento della qualità, tutte in continuo perfezionamento, tuttavia molti di questi strumenti della “Total Quality” non sono concretamente applicabili nella maggior parte delle realtà industriale da noi incontrate. La non applicabilità di queste tecniche non riguarda solo la dimensione più limitata delle aziende italiane rispetto a quelle americane e giapponesi dove sono nati e stati sviluppati questi strumenti, oppure alla poca possibilità di effettuare investimenti massicci in R&D, ma è collegata anche alla difficoltà che una azienda italiana avrebbe di sfruttare opportunamente i risultati sui propri territori e propri mercati. Questo lavoro si propone di sviluppare una metodologia semplice e organica per stimare i livelli di affidabilità e di sicurezza raggiunti dai sistemi produttivi e dai prodotti industriali. Si pone inoltre di andare al di là del semplice sviluppo di una metodologia teorica, per quanto rigorosa e completa, ma di applicare in forma integrata alcuni dei suoi strumenti a casi concreti di elevata valenza industriale. Questa metodologia come anche, più in generale, tutti gli strumenti di miglioramento di affidabilità qui presentati, interessano potenzialmente una vasta gamma di campi produttivi, ma si prestano con particolare efficacia in quei settori dove coesistono elevate produzioni e fortissime esigenze qualitative dei prodotti. Di conseguenza, per la validazione ed applicazione ci si è rivolti al settore dell’automotive, che da sempre risulta particolarmente sensibile ai problemi di miglioramento di affidabilità e sicurezza. Questa scelta ha portato a conclusioni la cui validità va al di là di valori puramente tecnici, per toccare aspetti non secondari di “spendibilità” sul mercato dei risultati ed ha investito aziende di primissimo piano sul panorama industriale italiano.

Lo studio effettuato pone le sue basi sulla ricerca di materiali stradali che combinino ad elevati standard prestazionali, la riduzione dell’impatto ambientale in fase realizzativa e manutentiva. In particolare il seguente lavoro si occupa dello studio di 7 leganti modificati con polimeri ed additivati con cere. I primi infatti conferiscono alla miscela maggiore elastoplasticità, incrementandone la durabilità e la resistenza a fatica. Nei secondi la presenza del materiale paraffinico contribuisce a ridurre la viscosità del bitume, consentendo un notevole abbassamento della temperatura di produzione e stesa della miscela. Numerosi studi hanno dimostrato che le caratteristiche meccaniche della pavimentazione sono fortemente influenzate dal grado di ossidazione delle componenti organiche del bitume, ovvero dal fenomeno dell’invecchiamento o aging. Pertanto allo studio reologico del bitume, si sono affiancate prove di simulazione dell’ invecchiamento nel breve e lungo termine. In fase di ricerca sperimentale si sono analizzati i leganti modificati ed additivati secondo la teoria della viscoelasticità, simulando le reali condizioni di carico ed invecchiamento alle quali il bitume è sottoposto. Tutte le prove di caratterizzazione reologica avanzata sono state effettuate mediante l’utilizzo del DSR (Dynamic Shear Rheometer - UNI EN 14770 ) in varie configurazioni di prova e l’invecchiamento a breve termine è stato simulato mediante RTFOT (Rolling thin film oven test -UNI EN 12607-1). Si è proposto inoltre una nuova procedura di aging invecchiando il bitume alla temperatura di Twork, ovvero a quel valore della temperatura tale per cui, in fase di messa in opera, si avrà una distribuzione molecolare omogenea del modificante all’interno del bitume. / The use of modified asphalt binders in hot-mix asphalt has steadily increased over the past several decades. Modified asphalt binders currently make up over 20% of paving grade asphalt laid in all over the world, and the percentage continues to grow. In these recent years, the Warm Mix Asphalt (WMA) are spreading widely in the new road constructions and pavement rehabilitations. The main intent of WMA is to produce mixtures with similar strength, durability, and performance characteristics as traditional hot mixes using substantially reduced production temperatures. The pavement technology combine the use of polymer with the warm additive, that it will be the main core of this research. However, selecting appropriate temperatures for handling these binders has been an issue with the use of wax – polymer modified asphalt binders. The traditional method of determining appropriate mixing and compaction temperatures for an asphalt binder is based on relatively simple viscosity measurements of the asphalt. However, this method often yields excessively high temperatures for many modified binders that have caused concerns with degradation of the binder’s properties and emission problems in laboratories during preparation of samples and during production and placement of asphalt mixtures in the field.

Loss of vascular function associated with cardiovascular disease, such as arthrosclerosis, represents the leading medical epidemic in the United States and typically requires surgical intervention through synthetic or autologous vascular grafts. To overcome the limitations associated with adult cell sources, which are often restricted by supply or compromised by disease, mesenchymal stem cells (MSCs) have emerged as potential candidates for vascular tissue engineering. While evidence suggests the roles of several factors influencing MSC differentiation into vascular phenotypes, including matrix rigidity, geometry and chemistry, the phenomena associated with these events are still largely unknown. Further, the development of mature vascular phenotypes, such as vascular smooth muscle cells (vSMCs), with functional behavior remains elusive to the research community. This thesis proposed to engineer and direct specific and mature vascular differentiation from MSCs by way of highly tailored matrices mimicking the vascular niche environment. Taking inspiration from natural organization, we contend that a biomimetic design approach to tissue scaffolds that display features of the natural cellular microenvironment whilst mimicking the bulk tissue properties may elicit highly specific differentiation of MSCs to vascular phenotypes. To validate our hypothesis, we employed a systemic approach incorporating physical and chemical microenvironmental cues, i.e. stiffness, biological ligands and chemical factors, with the aim to augment vascular phenotype expression, functionality, and final incorporation into a tailored biomaterial scaffolds. First, we present a novel technique for the preparation of silk hydrogels directly from high pressure CO2 environments without the need for crosslinking agents or additional additives such as surfactants or co-solvents. Through this novel method, we demonstrate the utility of CO2 as a volatile electrolyte, capable of sufficiently influencing the sol-gel transition of silk proteins, resulting in the formation of stable hydrogels with properties suitable for biomedical applications. Second, we hypothesized that suitable soluble factor regimen and matrix rigidity can instruct MSC differentiation towards more mature, functional vSMCs. To address this, we investigated cellular differentiation on tunable SF hydrogels prepared using a solvent-free CO2 processing method. The focus of this portion of the thesis is on exploiting the combined use of substrate stiffness and growth factor (TGF- β1) on SF matrices, with the aim of correlating the effects on the vascular commitment of human mesenchymal stem cells (hMSCs). Our data reveal that hMSC differentiation into mature SMCs can be achieved within modest culture periods (72 h) by combining appropriate SF hydrogel stiffness (33 kPa) with growth factor (TGF-β1). These findings advance our understanding of how complex multicomponent biomaterials, whereby mimicking the intricacy of natural tissue environments, can play a significant role in developing optimal stem cell differentiation protocols. Third, we postulated that the presentation of ECM proteins on 3D matrices with tunable stiffness will augment the differentiation of MSCs to vascular lineages. To address this, we established a high-throughput ECM platform based on soft, fibrous PEG hydrogels meanwhile highly-tunable in stiffness and 3-dimensional geometry. Using this technique, we identified several microenvironments supporting MSC adhesion, spreading and differentiation toward early vascular lineages. This portion of the thesis supports the hypothesis that a complex milieu exists coupling protein functional behavior with substrate rigidity and that this phenomenon may potentially be exploited through proper application of high-throughput screening methodologies. In the final work of this thesis, we explored the integration of ECM-derived small engineered peptides with 3D soft matrices to refine the differentiation of MSCs to vascular phenotypes, and further successfully recapitulate the complex vascular niche necessary for specific and efficient MSC differentiation into vascular lineages. In line with this, we report the development of a microarray platform based on electrospun nanofibrous hydrogels of photoclickable thiol-ene poly(ethylene glycol) (PEG) hydrogels. Here, we demonstrate the ability to control primary cell adhesion to soft, fibrous hydrogels functionalized with RGD peptide. However, future work will be focused on designing combinatorial peptide studies, whereby, the integration of several biological ligands of interest with tunable physical properties can instruct stem cell differentiation in a highly specific manner. This thesis has provided fundamental insights into the effects of physiological stimuli on vascular differentiation of MSC in terms of the specificity and maturity of the final differentiated cells. Better understanding of such mechanisms will prove paramount in the sequential stages of MSC differentiation to mature vascular cells. Additionally, the findings of this thesis will help to better define the process of regenerating functional healthy vascular tissue from MSCs. Altogether, a combinatorial approach investigating the effects of matrix elasticity, biological ligands and growth factors on MSC differentiation in a 3D nanofiber culture will be critical towards understanding and recapitulating MSC differentiation in the in vivo vascular environment.