PtSnIr/C anode electrocatalysts: promoting effect in direct ethanol fuel cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH2, PtO2, SnO2 and IrO2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded.

Characterization of vascular wall progenitor cells and their role in therapeutic angiogenesis and Monckeberg's sclerosis

Recently, the existence of a capillary-rich vasculogenic zone has been identified in adult human arteries between the tunica media and adventitia; in this area it has been postulated that Mesenchymal Stem Cells (MSCs) may be present amidst the endothelial progenitors and hematopoietic stem cells. This hypothesis is supported by several studies claiming to have found the in vivo reservoir of MSCs in post-natal vessels and by the presence of ectopic tissues in the pathological artery wall. We demonstrated that the existence of multipotent progenitors is not restricted to microvasculature; vascular wall resident MSCs (VW-MSCs) have been isolated from multidistrict human large and middle size vessels (aortic arch, thoracic aorta and femoral artery) harvested from healthy multiorgan donors. Each VW-MSC population shows characteristics of embryonic-like stem cells and exhibits angiogenic, adipogenic, chondrogenic and leiomyogenic potential but less propensity to osteogenic ifferentiation. Human vascular progenitor cells are also able to engraft, differentiate into mature endothelial cells and support muscle function when injected in a murine model of hind limb ischemia. Conversely, VW-MSCs isolated from calcified femoral arteries display a good response to osteogenic commitment letting us to suppose that VW-MSCs could have an important role in the onset of vascular pathologies such as Mönckeberg sclerosis. Taken together these results show two opposite roles of vascular progenitor cells and underline the importance of establishing their in vivo pathological and regenerative potential to better understand pathological events and promote different therapeutic strategies in cardiovascular research and clinical applications.

Synthesis and characterization of Poly(vinylphosphonic acid) for proton exchange membranes in fuel cells

Vinylphosphonic acid (VPA) was polymerized at 80 ºC by free radical polymerization to give polymers (PVPA) of different molecular weight depending on the initiator concentration. The highest molecular weight, Mw, achieved was 6.2 x 104 g/mol as determined by static light scattering. High resolution nuclear magnetic resonance (NMR) spectroscopy was used to gain microstructure information about the polymer chain. Information based on tetrad probabilities was utilized to deduce an almost atactic configuration. In addition, 13C-NMR gave evidence for the presence of head-head and tail-tail links. Refined analysis of the 1H NMR spectra allowed for the quantitative determination of the fraction of these links (23.5 percent of all links). Experimental evidence suggested that the polymerization proceeded via cyclopolymerization of the vinylphosphonic acid anhydride as an intermediate. Titration curves indicated that high molecular weight poly(vinylphosphonic acid) PVPA behaved as a monoprotic acid. Proton conductors with phosphonic acid moieties as protogenic groups are promising due to their high charge carrier concentration, thermal stability, and oxidation resistivity. Blends and copolymers of PVPA have already been reported, but PVPA has not been characterized sufficiently with respect to its polymer properties. Therefore, we also studied the proton conductivity behaviour of a well-characterized PVPA. PVPA is a conductor; however, the conductivity depends strongly on the water content of the material. The phosphonic acid functionality in the resulting polymer, PVPA, undergoes condensation leading to the formation of phosphonic anhydride groups at elevated temperature. Anhydride formation was found to be temperature dependent by solid state NMR. Anhydride formation affects the proton conductivity to a large extent because not only the number of charge carriers but also the mobility of the charge carriers seems to change.

Numerical simulation of interdigitated back contact hetero-junction solar cells

The goal of this thesis is the application of an opto-electronic numerical simulation to heterojunction silicon solar cells featuring an all back contact architecture (Interdigitated Back Contact Hetero-Junction IBC-HJ). The studied structure exhibits both metal contacts, emitter and base, at the back surface of the cell with the objective to reduce the optical losses due to the shadowing by front contact of conventional photovoltaic devices. Overall, IBC-HJ are promising low-cost alternatives to monocrystalline wafer-based solar cells featuring front and back contact schemes, in fact, for IBC-HJ the high concentration doping diffusions are replaced by low-temperature deposition processes of thin amorphous silicon layers. Furthermore, another advantage of IBC solar cells with reference to conventional architectures is the possibility to enable a low-cost assembling of photovoltaic modules, being all contacts on the same side. A preliminary extensive literature survey has been helpful to highlight the specific critical aspects of IBC-HJ solar cells as well as the state-of-the-art of their modeling, processing and performance of practical devices. In order to perform the analysis of IBC-HJ devices, a two-dimensional (2-D) numerical simulation flow has been set up. A commercial device simulator based on finite-difference method to solve numerically the whole set of equations governing the electrical transport in semiconductor materials (Sentuarus Device by Synopsys) has been adopted. The first activity carried out during this work has been the definition of a 2-D geometry corresponding to the simulation domain and the specification of the electrical and optical properties of materials. In order to calculate the main figures of merit of the investigated solar cells, the spatially resolved photon absorption rate map has been calculated by means of an optical simulator. Optical simulations have been performed by using two different methods depending upon the geometrical features of the front interface of the solar cell: the transfer matrix method (TMM) and the raytracing (RT). The first method allows to model light prop-agation by plane waves within one-dimensional spatial domains under the assumption of devices exhibiting stacks of parallel layers with planar interfaces. In addition, TMM is suitable for the simulation of thin multi-layer anti reflection coating layers for the reduction of the amount of reflected light at the front interface. Raytracing is required for three-dimensional optical simulations of upright pyramidal textured surfaces which are widely adopted to significantly reduce the reflection at the front surface. The optical generation profiles are interpolated onto the electrical grid adopted by the device simulator which solves the carriers transport equations coupled with Poisson and continuity equations in a self-consistent way. The main figures of merit are calculated by means of a postprocessing of the output data from device simulation. After the validation of the simulation methodology by means of comparison of the simulation result with literature data, the ultimate efficiency of the IBC-HJ architecture has been calculated. By accounting for all optical losses, IBC-HJ solar cells result in a theoretical maximum efficiency above 23.5% (without texturing at front interface) higher than that of both standard homojunction crystalline silicon (Homogeneous Emitter HE) and front contact heterojuction (Heterojunction with Intrinsic Thin layer HIT) solar cells. However it is clear that the criticalities of this structure are mainly due to the defects density and to the poor carriers transport mobility in the amorphous silicon layers. Lastly, the influence of the most critical geometrical and physical parameters on the main figures of merit have been investigated by applying the numerical simulation tool set-up during the first part of the present thesis. Simulations have highlighted that carrier mobility and defects level in amorphous silicon may lead to a potentially significant reduction of the conversion efficiency.

The search for Multiple Myeloma Stem cells: molecular characterization and self-renewal mechanisms involved in the disease persistence

The existence of Multiple Myeloma Stem cells (MMSCs)is supposed to be one of the major causes of MM drug-resistance. However, very little is known about the molecular characteristics of MMSCs, even if some studies suggested that these cells resembles the memory B cells. In order to molecularly characterize MMSCs, we isolated the 138+138- population. For each cell fraction we performed a VDJ rearrangement analysis. The complete set of aberrations were performed by SNP Array 6.0 and HG-U133 Plus 2.0 microarray analyses (Affymetrix). The VDJ rearrangement analyses confirmed the clonal relationship between the 138+ clone and the immature clone. Both BM and PBL 138+ clones showed exactly the same genomic macroalterations. In the BM and PBL 138-19+27+ cell fractions several micro-alterations (range: 1-350 Kb) unique of the memory B cells clone were highlighted. Any micro-alterations detected were located out of any genomic variants region and are presumably associated to the MM pathogenesis, as confirmed by the presence of KRAS, WWOX and XIAP genes among the amplified regions. To get insight into the biology of the clonotypic B cell population, we compared the gene expression profile of 8 MM B cells samples 5 donor B cells vs, thus showing a differential expression of 11480 probes (p-value: <0,05). Among the self-renewal mechanisms, we observed the down-regulation of Hedgehog pathway and the iperactivation of Notch and Wnt signaling. Moreover, these immature cells showed a particular phenotype correlated to resistance to proteasome inhibitors (IRE1α-XBP1: -18.0; -19.96. P<0,05). Data suggested that the MM 138+ clone might resume the end of the complex process of myelomagenesis, whereas the memory B cells have some intriguing micro-alterations and a specific transcriptional program, supporting the idea that these post germinal center cells might be involved in the transforming event that originate and sustain the neoplastic clone.

Musculoskeletal tissue regeneration by human non-embryonic stem cells

The aim of this thesis was to investigate the regenerative potential of alternative sources of stem cells, derived from human dental pulp (hDPSCs) and amniotic fluid (hAFSCs) and, specifically, to evaluate their capability to be committed towards osteogenic and myogenic lineages, for the eventual applicability of these stem cells to translational strategies in regenerative medicine of bone and skeletal muscle tissues. The in vitro bone production by stem cells may represent a radical breakthrough in the treatment of pathologies and traumas characterized by critical bone mass defects, with no medical or surgical solution. Human DPSCs and AFSCs were seeded and pre-differentiated on different scaffolds to test their capability to subsequently reach the osteogenic differentiation in vivo, in order to recover critical size bone defects. Fibroin scaffold resulted to be the best scaffold promoting mature bone formation and defect correction when combined to both hDPSCs and hAFSCs. This study also described a culture condition that might allow human DPSCs to be used for human cell therapy in compliance with good manufacturing practices (GMPs): the use of human serum (HS) promoted the expansion and the osteogenic differentiation of hDPSCs in vitro and, furthermore, allowed pre-differentiated hDPSCs to regenerate critical size bone defects in vivo. This thesis also showed that hDPSCs and hAFSCs can be differentiated towards the myogenic lineage in vitro, either when co-cultured with murine myoblasts and when differentiated alone after DNA demethylation treatment. Interestingly, when injected into dystrophic muscles of SCID/mdx mice - animal model of Duchenne Muscular Dystrophy (DMD) - hDPSCs and hAFSCs pre-differentiated after demethylating treatment were able to regenerate the skeletal muscle tissue and, particularly, to restore dystrophin expression. These observations suggest that human DPSCs and AFSCs might be eventually applied to translational strategies, in order to enhance the repair of injured skeletal muscles in DMD patients.

Toward a 3D in vitro model based on decellularized thymus to maintain adult thymic ephitelial cells functionality

During my PhD,I have been develop an innovative technique to reproduce in vitro the 3D thymic microenvironment, to be used for growth and differentiation of thymocytes, and possible transplantation replacement in conditions of depressed thymic immune regulation. The work has been developed in the laboratory of Tissue Engineering at the University Hospital in Basel, Switzerland, under the tutorship of Prof.Ivan Martin. Since a number of studies have suggested that the 3D structure of the thymic microenvironment might play a key role in regulating the survival and functional competence of thymocytes, I’ve focused my effort on the isolation and purification of the extracellular matrix of the mouse thymus. Specifically, based on the assumption that TEC can favour the differentiation of pre-T lymphocytes, I’ve developed a specific decellularization protocol to obtain the intact, DNA-free extracellular matrix of the adult mouse thymus. Two different protocols satisfied the main characteristics of a decellularized matrix, according to qualitative and quantitative assays. In particular, the quantity of DNA was less than 10% in absolute value, no positive staining for cells was found and the 3D structure and composition of the ECM were maintained. In addition, I was able to prove that the decellularized matrixes were not cytotoxic for the cells themselves, and were able to increase expression of MHC II antigens compared to control cells grown in standard conditions. I was able to prove that TECs grow and proliferate up to ten days on top the decellularized matrix. After a complete characterization of the culture system, these innovative natural scaffolds could be used to improve the standard culture conditions of TEC, to study in vitro the action of different factors on their differentiation genes, and to test the ability of TECs to induce in vitro maturation of seeded T lymphocytes.

Sirolimus and everolimus reduce albumin endocytosis in proximal tubule cells via an angiotensin II-dependent pathway

The proliferation signal inhibitors (PSIs) sirolimus (SRL) and everolimus (ERL) often induce proteinuria due to glomerular but also tubular dysfunction in transplant patients. The beneficial effect of angiotensin converting enzyme inhibitors (ACE-I) and angiotensin II (Ang II) type 1 receptor blockers (ARB) has been reported.

MMP19 is upregulated during melanoma progression and increases invasion of melanoma cells

During the progression of cutaneous melanomas, matrix metalloproteinases (MMPs) facilitate the tumour cells to traverse the basement membrane and invade the dermis. In this study, we analysed the expression of MMP19 in the course of melanoma progression. Although MMP19 was absent in melanocytes and melanoma cells of early stages of melanoma development, its expression was strongly upregulated in the neighbouring keratinocytes that may facilitate the vertical outgrowth of melanoma cells. In contrast to early stages, MMP19 was upregulated during the vertical growth phase of melanoma and in metastases. The upregulation of MMP19 in melanoma of Clark levels IV and V correlates with that of MMP2 and also simultaneously with ceased expression of E-cadherin. To reveal whether MMP19 facilitates the invasion of melanomas, we examined adhesion and migratory capacity of selected melanoma cell lines. Melanoma cell lines with low expression of MMP19 exhibited increased adhesion to various substrates and lower migration in comparison with the cell line with higher expression of MMP19. Moreover, ectopic expression of MMP19 could restore the migratory capacity of melanoma cells with low endogenous level of MMP19. These results suggest that the increase of MMP19 expression hallmarks the progression of cutaneous melanoma and might augment melanoma growth by promoting the invasion of tumour cells.

Agrin is required for survival and function of monocytic cells

Agrin, an extracellular matrix protein belonging to the heterogeneous family of heparan sulfate proteoglycans (HSPGs), is expressed by cells of the hematopoietic system but its role in leukocyte biology is not yet clear. Here we demonstrate that agrin has a crucial, nonredundant role in myeloid cell development and functions. We have identified lineage-specific alterations that affect maturation, survival and properties of agrin-deficient monocytic cells, and occur at stages later than stem cell precursors. Our data indicate that the cell-autonomous signals delivered by agrin are sensed by macrophages through the α-DC (DG) receptor and lead to the activation of signaling pathways resulting in rearrangements of the actin cytoskeleton during the phagocytic synapse formation and phosphorylation of extracellular signal-regulated kinases (Erk 1/2). Altogether, these data identify agrin as a novel player of innate immunity.