Galvanic Deposition of Hydroxyapatite/Chitosan/Collagen Coatings on 304 Stainless Steel

The galvanic deposition method was used to deposit Hydroxyapatite/Chitosan/Collagen coatings on 304 stainless steel. Galvanic deposition is an alternative and valid way to fabricate bio-coatings with high biocompatibility and good anticorrosion properties. Physical-chemical characterizations were carried out to investigate chemical composition and morphology of the samples. Coatings consist of a mixture of calcium phosphate (Brushite and Hydroxyapatite) with chitosan and collagen. Corrosion tests were performed in the simulated body fluid (SBF) after different aging times. Results show that, in comparison with bare 304 stainless steel, coating shifts corrosion potential to anodic values and reduces corrosion current density. Nevertheless, the aging in SBF led to a completely conversion of brushite into hydroxyapatite. The release of metal ions, measured after 21 days of aging in SBF solution, is very low due to the presence of coating that slow-down the corrosion rate of steel

Galvanic deposition of Chitosan-AgNPs as antibacterial coating

Thanks to mechanical properties similar human bones, metallic materials represent the best choice for fabrication of orthopedic implants. Although metals could be widely used in the field of biomedical implants, corrosion phenomena could occur, causing metal ions releasing around periprosthetic tissues leading, in the worst cases, to the development of infections. In these cases, patients need prolonged antibiotic therapies that may cause bacterial resistance. Preventing bacterial colonization of biomedical surfaces is the key to limiting the spread of infections. Antibacterial coatings have become a very active field of research, strongly stimulated by the increasing urgency of identifying alternatives to the traditional administration of antibiotics. Nowadays, the research was focused on coating science to deal with these issues. In particular, the development of the antibacterial composite coatings could be a viable way to provide not only a corrosion resistance but also an antibacterial action and biocompatibility. Chitosan is a great biomaterial used in medicine. It is a natural bioactive polymer and is the second most abundant in nature polysaccharide after cellulose. Chitosan comes from the deacetylation of chitin, a homopolymer of beta-(1-4)-N-acetyl-D-glucosamine, derived from exoskeleton of crustaceans. It is high biocompatible and it is also used in drug delivery. In addition, chitosan has chelating properties due to the amino groups of polysaccharide that are responsible of selective chelation with metal ions. In particular, the attention has been paid to silver nanoparticles for their high stability, low toxicity, biocompatibility and antibacterial properties. These ones are incorporated in polymeric matrix (e.g. chitosan) and they are capable to interact physically with cell walls of bacteria. In this study Chitosan-Silver nanoparticles composite coating on AISI 304L was investigated. These coatings were realized by an alternative method of deposition respect to traditional ones based on galvanic coupling. This process doesn’t request any external power supply and is very easy to carried out. The difference of the electrochemical redox potential between the substrate (cathode) and a sacrificial anode is the pivotal role of the process. Deposition rate is controlled by the ratio of cathodic and anodic area. In practice, electrons generated by anode corrosion flow towards to more noble metal thanks to a short-circuit. As soon electrons arrive to the cathode, the base electrogeneration reactions of nitrate ions and water molecules occur. Production of hydroxyl ions causes an increasing of pH at substrate/solution interface. Hence, deprotonation of amine group leads precipitation of chitosan (pKa=6.4) onto surface. At the same time, silver nanoparticles are incorporated in polymeric matrix of chitosan. Physical-chemical characterizations of the coatings were carried out in order to investigate morphology and chemical composition. In addition, corrosion tests (potentiodynamic polarization and electrochemical impedance spectroscopy) were executed in a simulated body fluid to scrutinize the corrosion resistance. Furthermore, the release of silver nanoparticles from coating in SBF were studied

The Morphology of Atmospheric Aerosol and Some Implications

The morphology of individual atmospheric particles, including their mixing state, shape and internal structure, can have important atmospheric implications. Understanding the mechanisms leading to specific morphologies, the role of morphology in different atmospheric processes, and accounting for these details in models present considerable challenges. Several approaches are currently underway to make progress toward the resolution of these difficulties; for example, development and deployment of improved single particle analytical and observational tools, use of accurate electromagnetic models to quantitatively predict the interactions of solar radiation with single complex particles, and particle resolved models. In this presentation we will present single particle analyses of samples collected during several field campaigns. Implications of these results on the effects upon aerosol optical properties will be discussed

Galvanic Deposition of Calcium Phosphate/Bioglass Composite Coating on AISI 316L

Calcium phosphate/Bioglass composite coatings on AISI 316L were investigated with regard to their potential role as a beneficial coating for orthopedic implants. These coatings were realized by the galvanic co-deposition of calcium phosphate compounds and Bioglass particles. A different amount of Bioglass 45S5 was used to study its effect on the performance of the composite coatings. The morphology and chemical composition of the coatings were investigated before and after their aging in simulated body fluid. The coatings uniformly covered the AISI 316L substrate and consisted of a brushite and hydroxyapatite mixture. Both phases were detected using X-ray diffraction and Raman spectroscopy. Additionally, both analyses revealed that brushite is the primary phase. The presence of Bioglass was verified through energy-dispersive X-ray spectroscopy, which showed the presence of a silicon peak. During aging in simulated body fluid, the coating was subject to a dynamic equilibrium of dissolution/reprecipitation with total conversion in only the hydroxyapatite phase. Corrosion tests performed in simulated body fluid at different aging times revealed that the coatings made with 1 g/L of Bioglass performed best. These samples have a corrosion potential of −0.068V vs. Ag/AgCl and a corrosion current density of 8.87 × 10−7 A/cm2. These values are better than those measured for bare AISI 316L (−0.187 V vs. Ag/AgCl and 2.52 × 10−6 A/cm2, respectively) and remained superior to pure steel for all 21 days of aging. This behavior indicated the good protection of the coating against corrosion phenomena, which was further confirmed by the very low concentration of Ni ions (0.076 ppm) released in the aging solution after 21 days of immersion. Furthermore, the absence of cytotoxicity, verified through cell viability assays with MC3T3-E1 osteoblastic cells, proves the biocompatibility of the coatings

Green and Integrated Wearable Electrochemical Sensor for Chloride Detection in Sweat

Wearable sensors for sweat biomarkers can provide facile analyte capability and monitoring for several diseases. In this work, a green wearable sensor for sweat absorption and chloride sensing is presented. In order to produce a sustainable device, polylactic acid (PLA) was used for both the substrate and the sweat absorption pad fabrication. The sensor material for chloride detection consisted of silver-based reference, working, and counter electrodes obtained from upcycled compact discs. The PLA substrates were prepared by thermal bonding of PLA sheets obtained via a flat die extruder, prototyped in single functional layers via CO2 laser cutting, and bonded via hot-press. The effect of cold plasma treatment on the transparency and bonding strength of PLA sheets was investigated. The PLA membrane, to act as a sweat absorption pad, was directly deposited onto the membrane holder layer by means of an electrolyte-assisted electrospinning technique. The membrane adhesion capacity was investigated by indentation tests in both dry and wet modes. The integrated device made of PLA and silver-based electrodes was used to quantify chloride ions. The calibration tests revealed that the proposed sensor platform could quantify chloride ions in a sensitive and reproducible way. The chloride ions were also quantified in a real sweat sample collected from a healthy volunteer. Therefore, we demonstrated the feasibility of a green and integrated sweat sensor that can be applied directly on human skin to quantify chloride ions

Inhibition of nuclear PTEN tyrosine phosphorylation enhances glioma radiation sensitivity through attenuated DNA repair

Ionizing radiation (IR) and chemotherapy are standard of care treatments for glioblastoma (GBM) patients and both result in DNA damage, however, the clinical efficacy is limited due to therapeutic resistance. We identified a mechanism of such resistance mediated by phosphorylation of PTEN on tyrosine 240 (pY240-PTEN) by FGFR2. pY240-PTEN is rapidly elevated and bound to chromatin through interaction with Ki-67 in response to IR treatment and facilitates the recruitment of RAD51 to promote DNA repair. Blocking Y240 phosphorylation confers radiation sensitivity to tumors and extends survival in GBM preclinical models. Y240FPten knock-in mice showed radiation sensitivity. These results suggest that FGFR-mediated pY240-PTEN is a key mechanism of radiation resistance and is an actionable target for improving radiotherapy efficacy

Extensive soot compaction by cloud processing from laboratory and field observations

Soot particles form during combustion of carbonaceous materials and impact climate and air quality. When freshly emitted, they are typically fractal-like aggregates. After atmospheric aging, they can act as cloud condensation nuclei, and water condensation or evaporation restructure them to more compact aggregates, affecting their optical, aerodynamic, and surface properties. Here we survey the morphology of ambient soot particles from various locations and different environmental and aging conditions. We used electron microscopy and show extensive soot compaction after cloud processing. We further performed laboratory experiments to simulate atmospheric cloud processing under controlled conditions. We find that soot particles sampled after evaporating the cloud droplets, are significantly more compact than freshly emitted and interstitial soot, confirming that cloud processing, not just exposure to high humidity, compacts soot. Our findings have implications for how the radiative, surface, and aerodynamic properties, and the fate of soot particles are represented in numerical models

Extensive Soot Compaction by Cloud Processing from Laboratory and Field Observations

Soot particles form during combustion of carbonaceous materials and impact climate and air quality. When freshly emitted, they are typically fractal-like aggregates. After atmospheric aging, they can act as cloud condensation nuclei, and water condensation or evaporation restructure them to more compact aggregates, affecting their optical, aerodynamic, and surface properties. Here we survey the morphology of ambient soot particles from various locations and different environmental and aging conditions. We used electron microscopy and show extensive soot compaction after cloud processing. We further performed laboratory experiments to simulate atmospheric cloud processing under controlled conditions. We find that soot particles sampled after evaporating the cloud droplets, are significantly more compact than freshly emitted and interstitial soot, confirming that cloud processing, not just exposure to high humidity, compacts soot. Our findings have implications for how the radiative, surface, and aerodynamic properties, and the fate of soot particles are represented in numerical models.Peer reviewe

The second ACTRIS inter-comparison (2016) for Aerosol Chemical Speciation Monitors (ACSM) : Calibration protocols and instrument performance evaluations

AbstractThis work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Center (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulfate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artifacts in individual instruments, such as the overestimation of m/z 44 from organic aerosol. This effect was quantified by the m/z (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artifact was applied to the measurements acquired during this study. For some instruments (those with high artifacts), this fragmentation table adjustment led to an ?overcorrection? of the f44 (m/z 44/Org) signal. This correction based on measurements made with pure NH4NO3, assumes that the magnitude of the artifact is independent of chemical composition. Using data acquired at different NH4NO3 mixing ratios (from solutions of NH4NO3 and (NH4)2SO4) we observe that the magnitude of the artifact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO3 mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artifact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry.Peer reviewe