Stress-induced stabilization of pyrolyzed polyacrylonitrile and carbon nanotubes electrospun fibers

The unique properties of graphitic carbons have gained widespread attention towards their development and application. Carbon materials can be synthesized by thermal decomposition and, more specifically, carbon pyrolysis from polymer precursors. The paper shows the pyrolysis process of polyacrylonitrile (PAN) in the presence of multi-walled carbon nanotubes (MWCNTs) according to different manufacturing process conditions. The electrospinning process of the PAN-MWCNTs solution on multi-plates collectors was firstly analyzed. The morphology and the particles arrangement of the electrospun fibers was studied under scanning and transmission electron microscopes. Moreover, the composite fibrous mats were characterized by RAMAN spectroscopy to identify the effects of a mechanical tension application during the thermal stabilization phase performed before the pyrolysis treatment to obtain carbon fibers from the precursor polymer. The results show that the graphitization of the pyrolyzed fibers is enhanced by the combination of MWCNTs and a mechanical stress applied during the thermal treatment

Hybrid multi-layered scaffolds produced via grain extrusion and electrospinning for 3D cell culture tests

Purpose: The purpose of this paper is to focus on the production of scaffolds with specific morphology and mechanical behavior to satisfy specific requirements regarding their stiffness, biological interactions and surface structure that can promote cell-cell and cell-matrix interactions though proper porosity, pore size and interconnectivity. Design/methodology/approach: This case study was focused on the production of multi-layered hybrid scaffolds made of polycaprolactone and consisting in supporting grids obtained by Material Extrusion (ME) alternated with electrospun layers. An open source 3D printer was utilized, with a grain extrusion head that allows the production and distribution of strands on the plate according to the designed geometry. Square grid samples were observed under optical microscope showing a good interconnectivity and spatial distribution of the pores, while scanning electron microscope analysis was used to study the electrospun mats morphology. Findings: A good adhesion between the ME and electrospinning layers was achieved by compression under specific thermomechanical conditions obtaining a hybrid three-dimensional scaffold. The mechanical performances of the scaffolds have been analyzed by compression tests, and the biological characterization was carried out by seeding two different cells phenotypes on each side of the substrates. Originality/value: The structure of the multi-layered scaffolds demonstrated to play an important role in promoting cell attachment and proliferation in a 3D culture formation. It is expected that this design will improve the performances of osteochondral scaffolds with a strong influence on the required formation of an interface tissue and structure that need to be rebuilt

micro structuring of titanium collectors by laser ablation technique a promising approach to produce micro patterned scaffolds for tissue engineering applications

Abstract Multi-scale micro-structured scaffolds can sustain attachment and orientation of different cells phenotypes. An innovative use of laser ablation technique to build micro-structured titanium surfaces to be used as collectors in both electrophoretic deposition and electrospinning processes was investigated. To produce micro-patterned scaffolds, a negative replica patterning was exploited by designing specific patterns to be laser ablated on titanium plates. This method allows the deposition of the scaffolds on the mold, thus reproducing the micro-features on the scaffold surface. The titanium surface morphology depending on ablation parameters was studied and the capability of the process in replicating the micro-pattern was characterized

SWARM Optimization of Force Model Parameters in Micromilling

Because of the improvement of machine-tool and tool performances in micro cutting field, the interest on these processes is increasing. Therefore, researchers involved in micro manufacturing processes focused their attention on these types of processes with the aim of improving the knowledge on the phenomena occurring during micro cutting operations. The objective of this work is to develop a modelling procedure for forecasting cutting forces in micromilling considering the tool run-out and the cutting tool geometry. The designed modelling procedure combines information coming from a force model, an optimization strategy and some experimental tests. The implemented force model is based on specific cutting pressure and actual instantaneous chip section. The tool run-out and the cutting tool geometry were considered in the analytical model. The adopted optimization strategy was based on the Particles Swarm strategy due to its suitability in solving analytical non-linear models. The experimental tests consisted in realizing micro slots on a sample made of Ti6Al4V. The comparison between experimental and analytical data demonstrates the good ability of the proposed procedure in correctly defining the model parameters

EFFETTI BIOLOGICI PRECOCI DELL'INQUINAMENTO ATMOSFERICO NEI BAMBINI: LO STUDIO RESPIRA E IL PROGETTO MAPEC_LIFE

EARLY BIOLOGICAL EFFECTS OF AIR POLLUTION ON CHILDREN: THE RESPIRA STUDY AND THE MAPEC_LIFE PROJECT Elisabetta Ceretti Abstract of the PhD Thesis Background Air pollution is a global problem: airborne or deposited pollutants can be found worldwide, from highly polluted to remote areas. Epidemiological studies attribute the most severe effects from air pollution to particulate matter, which has been associated with cardiovascular diseases, lung cancer and other chronic diseases. In 2013, the International Agency for Research on Cancer (IARC) classified air pollution and particulate matter as carcinogenic to human. Among the whole population, children are at higher risk of suffering the health consequences of airborne chemicals, for various reason. First, children have higher level of physical activity, spend more time outside and have a higher air intake than adults. Second, children are more vulnerable to the adverse effects of air pollution due to their small body size, fast growth rate and relatively immature organs (lungs, in particular), body function, immune system and cell repair mechanisms. Lastly, some data suggest that genetic damage, caused by environmental pollutants, viruses or lifestyle factors, occurring early in life can increase the risk of carcinogenesis in adulthood. Various studies have analyzed the genotoxic effects of urban air pollution exposure in the general population and in highly exposed subjects. In particular, a significant association was found between high levels of urban pollution (PM10 and ozone) and DNA damage detected by the comet assay in human blood lymphocytes and leukocytes and nasal mucosa cells. As regard children, very few data are available on biomarkers of early effect of air pollution. Methods In this research work, some results of two molecular epidemiology cross-sectional projects are presented. Both of them had the objective of evaluating the associations between air pollution and early biological effects in children. The first is the RESPIRA study (Italian acronym for \u201cRischio ESPosizione Inquinamento aRia Atmosferica\u201d), a small pilot study performed on pre-school children living and attending pre-school in Brescia, a highly polluted town in Northern Italy. The children were recruited in 6 pre-schools located in different areas of the town and their buccal cells were collected to evaluate two biomarkers of early effects: primary DNA damage, detected by comet assay in salivary leukocytes, and micronucleus frequency, investigated in epithelial buccal cells. Child exposure to air pollution was assessed analyzing PM0.5 samples collected near each school in the same days of biological sampling, and retrieving air quality data from the Regional Agency for Environmental Protection. Furthermore, information about some confounding factors was collected by means of a questionnaire filled in by children\u2019s parents. The second study is the MAPEC_LIFE project (Monitoring Air Pollution Effects on Children for supporting public health policy), funded by EU Life+ Programme (LIFE12 ENV/IT/000614) which, in addition to the evaluation of the associations between air pollution and early biological effects in children, aims to propose a model for estimating the global risk of early biological effects due to air pollutants and other factors in children. The MAPEC_LIFE project was carried out on 6-8-year-old children living in five Italian towns in two different seasons. Two biomarkers of early biological effects, primary DNA damage detected with the comet assay and frequency of micronuclei, were investigated in buccal cells of children. Details of children diseases, socio-economic status, exposures to other pollutants and life-style were collected using a questionnaire administered to children\u2019s parents. Child exposure to urban air pollution was assessed by analysing PM0.5 samples collected in the school areas for PAHs and nitro-PAHs concentration, lung toxicity and in vitro genotoxicity on bacterial and human cells. Data on the chemical features of the urban air during the study period were obtained from the Regional Agency for Environmental Protection. The project created also the opportunity to approach the issue of air pollution with the children, trying to raise their awareness on air quality, its health effects and some healthy behaviors by means of an educational intervention in the schools. Results The RESPIRA study involved six pre-schools in Brescia, in two consecutive winter seasons. During the sampling months, PM10, PM2.5 and NO2 were very often over the EU limit values for daily means. Organic extracts of PM0.5 collected near schools induced genotoxic effects in bacterial and human cells in in vitro tests. Regarding DNA damage in children cells, mean micronucleus frequency in epithelial buccal cells of children was 0.29 \ub1 0.13%, higher than usually found among children living in areas with low or medium-high levels of air pollution, and significantly associated with the concentration of PM10, PM2.5 and NO2. On the other hand, the preliminary results of the comet assay showed some differences between primary DNA damage detected in children attending schools in the different areas of the town. This difference was not detected with the micronucleus test. However, the level of damage resulted from the comet assay on salivary leukocytes of children was not comparable with other literature data, due to the lack of similar studies. The MAPEC_LIFE project involved 26 primary schools in the five Italian towns. Environmental and biological samplings were repeated in the same schools and on the same children for two different seasons, winter and late spring. A total of 1125 children were recruited and sampled for two times. The results of the various in vitro and in vivo tests are still ongoing. Some preliminary results about the samples of the first season in Brescia were presented here. PM10, PM2,5 and NO2 levels remained high for all the winter period, even if they were lower than those registered in the RESPIRA seasons. The organic extracts of PM0.5 collected near each school induced point mutation in Salmonella typhimurium, particularly in the YG1021 strain, but the number of net revertants per cubic meter seem to be slightly lower than other data found in literature. As regard genotoxicity tests on buccal cells of the 283 children recruited in Brescia, no data were available so far for the comet assay, which encountered some reading difficulties. On the other hand, micronucleus frequency detected in MAPEC_LIFE children (0.06 \ub1 0.08%) was very lower than micronucleus levels found in the RESPIRA study. Statistical analysis of the results is still ongoing, but at the end they will show if the differences in micronucleus frequency between the two studies are due to the level of exposure to air pollution experienced by the children or to other factors. Conclusions The associations between levels of air pollutants, air mutagenicity and biomarkers of early effects will be investigated. A tentative model to calculate the global absolute risk of having early biological effects for air pollution and other variables together will be proposed and may be useful to support policy-making and community interventions to protect children from possible health effects of air pollutants

Production of carbonized micro-patterns by photolithography and pyrolysis

The preparation of carbon micro-patterns is reported in this paper. Different carbon micro-patterns were created using photolithography of the epoxy-based negative photoresist SU-8. Photoresist patterns were optimized in terms of resolution and aspect ratio and subsequently subjected to pyrolysis to obtain carbonized and conductive 3D structures. The latter step requires the optimization of the resist cross-linking time as well as the temperature and time of the resist post-bake. This step is crucial in order to avoid any severe modification of the geometry of the patterns produced during the actual pyrolysis. By observing optical and scanning electron microscope images, the morphology of the structures before and after pyrolysis was studied and the same patterns were also characterized by a laser probe profilometer. Finally, the thus obtained carbon patterns on Si wafers were used to carry out cell culture tests with Neural Stem Cells (NSC). The adhesion and the arrangement of the stem cells were analyzed to verify the ability of the patterned substrates to guide the orientation and, therefore, the differentiation of the cells

Driver roll speed influence in Ring Rolling process

Ring Rolling is an advanced local incremental forming technology to fabricate directly precise seamless ring-shape parts with various dimensions and materials. To produce a high-quality ring different speed laws should be defined: the speed laws of the Idle and Axial rolls must be set to control the ring cross section and the Driver roll angular velocity must be chosen to avoid too high localized deformation on the ring cross section. Usually, in industrial environment, a constant rotation is set for the Driver roll, but this approach does not guarantee a constant ring angular velocity because of its diameter expansion. In particular, the higher is the ring diameter the lower is its angular velocity. The main risk due to this constrain is the generation of a non-uniform ring geometry. An innovative approach is to design a Driver Roll speed law to obtain a constant ring angular velocity. In this paper a FEM approach was followed to investigate the Driver roll speed influence on the Ring Rolling process. Different Driver roll speed laws were tested starting from a model defined in an industrial plant. Results will be analyzed by a geometrical and physical point of view

Finite element simulation of high speed micro milling in the presence of tool run-out with experimental validations

Micro milling process of CuZn37 brass is considered important due to applications in tool production for micro moulding and micro replication technology. The variations in material properties, work material adhesion to tool surfaces, burr formation, and tool wear result in loss of productivity. The deformed chip shapes together with localized temperature, plastic strain, and cutting forces during micro milling process can be predicted using finite element (FE) modeling and simulation. However, toolworkpiece engagement suffers from tool run-out affecting process performance in surface generation. This work provides experimental investigations on effects of tool run-out as well as process insight obtained from simulation of chip flow, with and without considering tool run-out. Scanning electron microscope (SEM) observation of the 3D chip shapes demonstrates ductile deformed surfaces together with localized serration behavior. FE simulations are utilized to investigate the effects of micro milling operation, cutting speed, and feed rate on forces, chip flow, and shapes. Predicted cutting forces and chip flow results from simulations are compared with force measurements, tool run-out, and chip morphology revealing reasonable agreements

Process parameters effect on mechanical properties and fatigue behaviour of friction stir weld AA6060 joints

Friction stir welding (FSW) is the most remarkable welding technology that has been invented and developed in the last decade. It is a solid-state welding process in which a rotating tool is driven into the material and translated along the interface of two or more plates. This technology has been successfully used to join materials that are considered difficult to be welded by fusion welding methods. FSW has potentially significant applications in many industrial fields such as aerospace, automotive, and naval industry. Anyway, FSW technology requires a meticulous understanding of the process and consequent mechanical properties of the welds in order to be used in the production of high performance components. The present work deals with an experimental campaign aimed at the evaluation of the mechanical properties of AA6060 T6 friction stir welded joints. The butt joints obtained using two different tool geometries (standard and threaded) were performed by varying the welding parameters, namely, tool rotating speed and feed rate. The standard tool was a very simple device fabricated using AISI 1040 steel, with a flat shoulder and a cylindrical pin. The threaded tool was a more complex device based on two main components: a tool holder, with a flat shoulder, and a threaded probe obtained using a commercial thread forming tap. The quality of the joints was evaluated in terms of both tensile strength (UTS) and fatigue behavior. The study of axial pulsing fatigue properties required the fabrication of a specific testing device able to avoid parasite bending moments. In order to estimate the more efficient and effective tool type, the welding forces (axial and longitudinal) were also measured

Multi-layered Scaffolds Production via Fused Deposition Modeling (FDM) Using an Open Source 3D Printer: Process Parameters Optimization for Dimensional Accuracy and Design Reproducibility

Abstract One of the most applied strategies in tissue engineering consists in the development of 3D porous scaffolds with similar composition to the specific tissue. In fact, the microstructure of the scaffolds influences the final structure of the in growing tissue. In this study, multi-layered PCL scaffolds were produced with modified Fab@home FDM printer in order to analyze the influence of the extrusion technology (filament or powder extrusion head) and of the process parameters on the deposited material. In particular, dimensions and uniformity of both deposited filament and grid of the scaffolds were analyzed to understand the influence of the process parameters so as to optimize the FDM production technology