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Antonio BALLESTRAZZI

Personale tecnico amministrativo
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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Pubblicazioni

2023 - Friction and wear of DLC films deposited on additive manufactured AlSi10Mg: the role of surface finishing [Articolo su rivista]
Salerno, E.; Casotti, D.; Paolicelli, G.; Gualtieri, E.; Ballestrazzi, A.; Gazzadi, G. C.; Bolelli, G.; Lusvarghi, L.; Valeri, S.; Rota, A.
abstract

2020 - Tribological response of laser-textured steel pins with low-dimensional micrometric patterns [Articolo su rivista]
Fiaschi, G.; Di Lauro, M.; Ballestrazzi, A.; Rota, A.; Biscarini, F.; Valeri, S.
abstract

Our purpose was to study the tribological eects of surface texturing at the mesoscale, generally disregarded. We realized hemispherical dimples on 100Cr6 steel pins using a ns-pulsed Nd:YAG laser. Both radius and depth of the patterns fall in the very-low part of the micrometric scale, ranging respectively from 10 to 13 m and from 4 to 6.5 m. To map Stribeck curves, we used a pin-on-disk apparatus and a commercial motor oil as lubricant. The results conrm that the post-texturing lapping process is crucial to achieve a reduction in the coecient of friction. These patterns show a tribological eect mainly in mixed lubrication regime, and partially in hydrodynamic regime. Even very small dierences in radius and depth may induce very dierent response, evidencing the need of very ne tuning of the geometrical characteristics of the patterns. The lower friction was recorded for larger and deeper dimples. Friction reduction for increasing dimples density has been found as well. Endurance tests in boundary lubrication regime show a more stable coecient of friction and a larger mean lifetime of patterned surfaces with respect to polished one. Furthermore, water-contact-angle tests show a weak hydrophobic eect for high aspect ratio patterns. However, no correlation was observed between wettability and tribological response.

2019 - A chemical, mechanical, and tribological analysis of DLC coatings deposited by magnetron sputtering [Articolo su rivista]
Fiaschi, G.; Rota, A.; Ballestrazzi, A.; Marchetto, D.; Vezzalini, E.; Valeri, S.
abstract

Diamond-like carbon is one of the most studied and used solid lubricants on the market. Despite this large use and its outstanding mechanical and tribological properties, there are still some unclear aspects related to its self-lubricant properties, and some drawbacks in the deposition methods. We deposited soft DLC films on Si(100), iron, and stainless steel substrates by PVD magnetron sputtering technique with a Cr/CrN adhesive interlayer. The DLC films were characterized from a chemical, mechanical, and tribological point of view. Our aim was to connect the coating chemical and mechanical characteristics to the different conditions used for the deposition, such as discharge power and substrate-target distance. We found a stronger sp(3) dependence on the discharge power for DLC deposited closer to the target. The tribological results did not depend on the chosen substrate-target distance, but rather on the hardness of the substrate. This could be ascribed to the better mechanical coupling of soft DLC films on harder substrates.

2018 - Qualitative and semiquantitative analysis of the protein coronas associated to different functionalized nanoparticles [Articolo su rivista]
Pederzoli, Francesca; Tosi, Giovanni; Genovese, Filippo; Belletti, Daniela; Vandelli, Maria Angela; Ballestrazzi, Antonio; Forni, Flavio; Ruozi, Barbara
abstract

The investigation on protein coronas (PCs) adsorbed onto nanoparticle (NP) surface is representing an open issue due to difficulties in detection and clear isolation of the adsorbed proteins. In this study, we investigated protocols able to isolate the compositions of PCs of three polymeric NPs.

2017 - Novel Curcumin loaded nanoparticles engineered for Blood-Brain Barrier crossing and able to disrupt Abeta aggregates [Articolo su rivista]
Ruozi, Barbara; Belletti, Daniela; Pederzoli, Francesca; Masoni, Martina; Keller, JOHANNES ROBIN; Ballestrazzi, Antonio; Vandelli, Maria Angela; Tosi, Giovanni; Grabrucker, Andreas M.
abstract

The formation of extracellular aggregates built up by deposits of β-amyloid (Aβ) is a hallmark of Alzheimer's disease (AD). Curcumin has been reported to display anti-amyloidogenic activity, not only by inhibiting the formation of new Aβ aggregates, but also by disaggregating existing ones. However, the uptake of Curcumin into the brain is severely restricted by its low ability to cross the blood-brain barrier (BBB). Therefore, novel strategies for a targeted delivery of Curcumin into the brain are highly desired. Here, we encapsulated Curcumin as active ingredient in PLGA (polylactide-co-glycolic-acid) nanoparticles (NPs), modified with g7 ligand for BBB crossing. We performed in depth analyses of possible toxicity of these NPs, uptake, and, foremost, their ability to influence Aβ pathology in vitro using primary hippocampal cell cultures. Our results show no apparent toxicity of the formulated NPs, but a significant decrease of Aβ aggregates in response to Curcumin loaded NPs. We thus conclude that brain delivery of Curcumin using BBB crossing NPs is a promising future approach in the treatment of AD.

2017 - Surface passivation by graphene in the lubrication of iron: A comparison with bronze [Articolo su rivista]
Marchetto, Diego; Restuccia, Paolo; Ballestrazzi, Antonio; Righi, Maria Clelia; Rota, Alberto; Valeri, Sergio
abstract

It has been recently reported that graphene is able to significantly reduce the friction coefficient of steel-on-steel sliding contacts. The microscopic origin of this behavior has been attributed to the mechanical action of load carrying capacity. However, a recent work highlighted the importance of the chemical action of graphene. According to this work graphene reduces the adhesion of iron interfaces by reducing the surface energy thanks to a passivation effect. The aim of the present work is to clarify the still debated lubricating behavior of graphene flakes. We perform pin-on-disc experiments using liquid dispersed graphene solution as a lubricant. Two different materials, pure iron and bronze are tested against 100Cr6 steel. Raman spectroscopy is used to analyze the surfaces after the friction tests. The results of these tests prove that graphene flakes have a beneficial effect on the friction coefficient. At the same time they show a tendency of graphene to passivate the native iron surfaces that are exposed during sliding as a consequence of wear.

2017 - The role of humidity and oxygen on MoS2 thin films deposited by RF PVD magnetron sputtering [Articolo su rivista]
Serpini, Elisabetta; Rota, Alberto; Ballestrazzi, Antonio; Marchetto, Diego; Gualtieri, Enrico; Valeri, Sergio
abstract

MoS2 is usually applied as thick films (1 μm and above) on sliding counterparts to decrease friction and wear. Thick films of MoS2 generally grow columnar-like and the bending or fracture of these columns during sliding are supposed to be the origin of the good tribological performances. In the present work, we studied the tribological behavior of 200 nm MoS2 films prepared by RF magnetron sputtering, with emphasis on the friction mechanisms. We performed ball-on-disc tests at different values of residual humidity, in pure oxygen atmosphere and at different temperatures, in order to disentangle the role of water and molecular oxygen during sliding. We found that, despite the fact that the inner structure of these thin films is not lamellar, the tribological behavior is similar to thicker ones. The friction in absence of humidity is well below that in standard conditions and the lifetime of the film is strongly enhanced. We observed similar performances in humid air while keeping the sample at 75 °C. Our results clearly demonstrated that absorbed water causes the deterioration of the lubricating properties of the films, while film oxidation plays only a marginal role.

2015 - Electrospun Fibers Containing Bio-Based Ricinoleic Acid: Effect of Amount and Distribution of Ricinoleic Acid Unit on Antibacterial Properties [Articolo su rivista]
Totaro, G.; Paltrinieri, L.; Mazzola, G.; Vannini, M.; Sisti, L.; Gualandi, C.; Ballestrazzi, A.; Valeri, S.; Pollicino, A.; Celli, A.; Di Gioia, D.; Focarete, M. L.
abstract

Novel bio-based and biodegradable electrospun membranes, containing bactericidal ricinoleic acid (RA) units either by copolymerization with butylene succinate (BS) units or by blending PRA and PBS homopolymers, are characterized in their chemical, thermal, mechanical and surface properties. In the blends E. coli and S. aureus mortality rate increases with PRA amount, while the copolymer shows lower bactericidal activity compared to the blend with similar composition. XPS demonstrates that in the blends an enrichment of RA units at the fiber surface occurs during electrospinning due to phase separation, while in the copolymer RA units are homogeneously dispersed along fiber cross-section.

2014 - Friction on ice: Influence of surface topography [Relazione in Atti di Convegno]
Spagni, A.; Gualtieri, E.; Ballestrazzi, A.; Rota, A.; Valeri, S.
abstract

2011 - Ag Surface Diffusion and Out-of-Bulk Segregation in CrN-Ag Nano-Composite Coatings [Articolo su rivista]
Incerti, Luca; Rota, Alberto; Ballestrazzi, Antonio; Gualtieri, Enrico; Valeri, Sergio
abstract

CrN-Ag nanocomposite coatings are deposited on Si(100) wafers and 20MnCr5 steel disks in amixed Ar+N2 atmosphere by reactive magnetron sputtering. Structure, composition and morphologywere investigated by Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES),X-ray Photoemission Spectroscopy (XPS), X-ray Diffraction (XRD) and Focused Ion Beam (FIB)cross sectional analysis. The as deposited film matrix is mainly composed by CrN phase (78%), buta relevant part (28%) is composed by Cr2N. Ag agglomerates in the CrN matrix forming elongatedgrains 200–400 nm wide and 50–100 nm high, which extends on the top of CrN columns. At thesurface Ag aggregates into two different structures: large tetrahedral crystalline clusters, with typicaldimension ranging from 200 to 500 nm, and smaller Ag nanoparticles with diameter of 15–25 nm.The annealing in N2 atmosphere up to 500 C does not affect size and distribution of the Aggrains in the sub-surface region, while it induces a size increase of the bigger Ag clusters onthe surface, mainly related to Ag surface diffusion and clusters coalescence. Annealing at highertemperature leads to an evident Ag out-of-bulk segregation, generating Ag depleted voids in thenear-surface region, and further increasing of the Ag clusters size at the surface. Tribological testson as deposited CrN-Ag film reveal a coefficient of friction against a steel ball reduced with respectto CrN film, probably related to the presence of Ag which acts as solid lubricant, but the coatingis removed after a very short sliding distance. The poor mechanical properties of the realized Agbasedcoatings are confirmed by lower hardness and Young modulus values with respect to pureCrN.

2010 - PLGA nanoparticles surface decorated with the sialic acid, N-acetylneuraminic acid [Articolo su rivista]
Bondioli, Lucia; Costantino, Luca; Ballestrazzi, Antonio; Lucchesi, Davide; Boraschi, Diana; Pellati, Federica; Benvenuti, Stefania; Tosi, Giovanni; Vandelli, Maria Angela
abstract

There is a broad interest in the development of nanoparticles (NPs) carrying on their surface carbohydrates such as sialic acids. It is known that these carbohydrates influence the biological and physical properties of biopharmaceutical proteins and living cells. Macromolecular compounds containing these carbohydrates showed an anti-recognition effect, exert an antiviral effect and also are able to be recognized by the cell surface of some kind of cancer cells. Thus, in the present research we performed two different approaches in order to obtain polymeric (poly(d,l-lactide-co-glycolide), PLGA) NPs surface decorated with the sialic acid N-acetylneuraminic acid (Neu5Ac). The first strategy that has been followed is based on the derivatization of the polyester PLGA with the thioderivative of Neu5Ac, starting material for the preparation of the NPs; the second is based on the synthesis of compounds potentially able to insert their lipophilic moiety into the underivatized PLGA NPs during their preparation, and to display their hydrophilic moiety (Neu5Ac) on their surface. The first approach allowed the obtainment of NPs surface decorated with Neu5Ac, as evidenced by ESCA spectroscopy and interaction with the lectin Wheat Germ Agglutinin. Moreover, a formulation of these NPs suitable for in vitro assays showed that they are phagocytosed by human monocytes with an apparently different mechanism with respect of those made of underivatized PLGA. The second strategy led to NPs in which their surface appears to be very different with respect to the NPs obtained following the first strategy, with the carboxylic groups of Neu5Ac markedly shielded. Thus, the new Neu5Ac-modified PLGA polyester represent a useful starting material for the preparation of NPs surface decorated with this sialic acid.

2010 - Tribology and wettability of nano-machined silicon rough surfaces [Poster]
Incerti, Luca; Ballestrazzi, Antonio; Rota, Alberto; Gualtieri, Enrico; Valeri, Sergio
abstract

1 – Introduction The more and more pressing demand for eliminating liquid lubricants in mechanical devices, due to their environmental costs, represents an important challenge for the tribological community. Low-friction coatings, like layered materials (graphite, Mo2S), soft metals (Ag, Au), non-layered metal oxides (MoO3, V2O5), can substitute liquid lubricants, but presently they are characterized by poor mechanical properties. On the other hand, hard ceramic coatings, like CrN, TiN, TiCN, TiAlN, have been studied for the last three decades for their high hardness, chemical inertness, high oxidation resistance and low wear rate. The aim of our study is to couple the properties of hard ceramics with those of soft metals low friction coatings. The nanostructuring of CrN-Ag ternary coating represents an appealing solution. 2 – Main Body of Text We studied the tribo-mechanical properties of CrN-Ag ternary coatings, where Ag clusters are dispersed in a CrN thick film. Some preliminary tests were also performed on a similar system, composed by Ag/CrN multilayers. CrN-Ag composite coatings were deposited on Si(100) and on a steel (20MnCr5) using PVD Magnetron Sputtering in a mixed N2+Ar atmosphere (P=5mtorr), with temperature ranging from RT to 500°. Structure, composition and morphology of both systems were characterized by Auger Electron Spectroscopy, X-rays diffraction and cross sectional analysis (depth-profiling AES, FIB cross section). The co-deposition of CrN and Ag in N2 atmosphere leads to the formation of a composite nanostructured coating, where Ag clusters behave as solid lubricant in the hard CrN bulk. Tribo-mechanical properties were measured with a ball-on-disc tribometer and a Berckovich nanoindenter. 3 – Conclusion By tuning the preparation conditions we were able to control the size, the distribution and the self organization of Ag nanoclusters in the CrN matrix, thus controlling frictional behavior.