HYBRID MULTI-LASER POWDER BED FUSION

In Laser Powder Bed Fusion (LPBF) systems, both single fibre systems and multi-laser systems are currently at the forefront of industry and academic research. Among the multi-laser approaches, Diode Area Melting (DAM) stands out as a novel alternative to conventional single-fibre LPBF systems. DAM offers the advantage of processing metal powder feedstock with a low cooling rate, courtesy of its short-wavelength, low-power diode lasers. However, the system is challenged by its lack of precision processing capabilities. In contrast, single fibre LPBF is renowned for its ability to process metals with high precision, owing to its high-power laser and high velocity scanning capabilities. Yet, these systems suffer from a deficiency in high cooling rates and microstructure control. This thesis introduces a groundbreaking Hybrid Laser Powder Bed Fusion (HLPBF) system, which combines two distinct laser processing methods to explore their effects on microstructure control. Firstly, a HLPBF system was developed, comprising a traversing DAM laser head equipped with an array of nine 450 nm (4W each) diode lasers alongside a conventional 200W single fibre LPBF and galvo-scanning head operating at a wavelength of 1064 nm. Subsequently, single fibre LPBF and DAM systems were individually tested to establish a literature background for hybrid processing, including parameter maps (based on normalised energy density), side and top surface roughness, heat-affected zones, cross-sectional densities, and microstructure investigations. During the investigations with the 450 nm DAM, a new phenomenon termed the 'crescent effect' was identified and added to the literature. This effect explains the wide, slow-moving melt pool's impact on the solidified sample. The hybrid processing phase commenced with the processing of Ti6Al4V feedstock utilizing both laser types within a single sample for the first time. A specific scanning strategy delineated separate laser processing regions within the same sample, including an overlap where both lasers interacted to fuse the feedstock and bridge the two regions. The regions melted by the fibre laser experienced significantly higher cooling rates (~107 ℃/s) compared to DAM regions (~600 ℃/s), resulting in finer microstructures characterized by acicular α´/α phases. In contrast, DAM regions exhibited larger α+β grains with parent β grain sizes approximately 13 times larger than those in the fibre laser-melted zone. In addition to its microstructural spatial tailoring capabilities, this investigation of the hybrid laser system also illuminates variations in the laser-induced heat-affected zone, surface roughness, and mechanical properties across DAM, single fibre LPBF, and overlap regions within fabricated Ti6Al4V samples

Development of the additively manufactured stainless steel 316L and AlSi10Mg alloys by in situ alloying and post-process treatment

L'abstract è presente nell'allegato / the abstract is in the attachmen

Transmedia Strategies for Participatory Politics in Russia: Alexey Navalny’s Grassroots Campaign

Transmedia storytelling scholarship has been progressing rapidly over recent decades. Yet, a question that remains open is the lack of analysis of political transmedia campaigns. This political communication thesis contributes to filling that gap. Its goal is to develop a flexible and locally-specific approach to analysing transmedia political campaigning. To understand the context that affects the destinies of transmedia grassroots campaigns, the study turns to social movement and grassroots activism scholarships. In particular, it employs the idea of political opportunity structures to conceptualise those external opportunities and threats that affects transmedia campaigns in politics. To mitigate the negative aspects of a political climate, reduce the costs of political participation for active citizens and make their political change efforts more efficient, political organisers can mobilise valuable resources through transmedia campaigning, the thesis argues. Thus, the thesis incorporates the analysis of opportunity structures and mobilising resources to propose a new analytical approach to the study of political transmedia campaigns. Because this analytical approach reinterprets transmedia strategies through the lens of opportunity structures and resource mobilisation, I will refer to it in the thesis as the opportunity structures and mobilising resources (OSMR) analytical approach. The thesis tests it with the case study of Alexey Navalny\u27s 2013 mayoral campaign for Moscow. The case study outlines the opportunity structures of modern Russia and discusses the transmedia strategies Navalny’s campaign used to overcome some of their negative aspects. In doing so, the thesis enriches transmedia storytelling scholarship with insights from other disciplines and offers a flexible and locally specific approach to analysing political transmedia campaigns

Biocomposites

Biocomposites are composite materials consisting of either a polymer matrix or a filler based on biological resources. They have been widely used in numerous applications such as storage devices, photocatalysts, packaging, furniture, biosensors, energy, construction, the automotive industry, and so on due to their great versatility and satisfactory performance. This book focuses on composites made from natural materials (natural fibers and biopolymers) and relates their physical, mechanical, electrical, structural, and biological characteristics as well as their potential applications in biomedicine, pharmaceuticals, and engineering

The Sustainability of Agro-Food and Natural Resource Systems in the Mediterranean Basin

Agriculture; Food Science; Environmental Science and Engineerin

Influences of skin barrier, a nanoparticle-based vehicle and solvents on cutaneous drug delivery

It is challenging to overcome the stratum corneum (SC) barrier to deliver drugs into the skin. Nanoparticle (NP)-based drug delivery systems show the advantages of cutaneous penetration improvement and controllable and targeted drug release. Besides, solvents, as a big group of penetration enhancers, provide another strategy, which is easily accessible, low-cost, and flexibly changeable in components. Apart from the skin penetration enhancement based on formulations, the disrupted barrier of diseased skin could change the skin penetration of drugs too. Thus, the present thesis investigated the influences of the SC barrier function, a pH-sensitive Eudragit® L00 nanoparticle, and the solvents of water and ethanol on cutaneous drug delivery. To determine the influence of the SC barrier on drug delivery, the SC thickness remaining on the skin after different numbers of tape stripping (TS) or cyanoacrylate stripping (CS) were quantified using two-photon microscopy, and the correlation of the SC reduction with the skin permeability changes was studied. The amount of SC removed by each tape decreased along with the skin depth, while a nearly constant SC thickness was removed by each CS. CS can remove the SC, viable skin layers and the hair follicle (HF), while TS can only remove the SC. Nevertheless, the removal of the entire human SC can be attained by both TS and CS, which were 4 times CS or 50 tape strips. The skin permeability to the model drug PCA linearly increased with the reduction of the SC thickness on the skin. These findings provide useful references to separating different skin layers for the quantification of drugs in the skin and establishing ex vivo barrier-disrupted skin models with different extents of barrier disruption. Especially, the barrier-disrupted skin, obtained by performing 30 tape strips on the intact porcine ear skin, could simulate atopic dermatitis (AD) skin to some extent. This ex vivo skin model could be used for evaluating dermal formulations in the initial development stage and reduce the number of animal and human studies. Next, the influences of the SC barrier on the skin penetration behavior of DxPCA-loaded pH-sensitive Eudragit® L100 NPs were investigated by EPR and CLSM using intact and barrier disrupted porcine skin. The pH-sensitive NP exhibited a triggered drug release in vitro at a pH above 5.9. When applied to the skin, the drug DxPCA was slowly released from the NPs in the case of the barrier-disrupted skin, whereas this was under the EPR detect limited for the intact skin. The disrupted SC barrier increased the exchange of the endogenous fluid of the skin with the external medium of the NP dispersion. Due to the exchange, the pH of the external medium of the NPs was increased, leading to the change in the NP structure and thus to the drug release. The improved drug release of the NPs is part of the reason for the higher drug penetration into the viable skin layers of the barrier-disrupted skin compared to the intact skin. These results indicate the feasibility of using this pH-sensitive NP to realize the targeted drug release and enhanced drug delivery into the viable skin layers of the AD skin lesions so that the side effects of the drug Dx could be reduced. Concerning the spatial localization of the NP, the EPR results indicate that the pH-sensitive NPs cannot pass through the disrupted SC of the skin, let alone the intact SC barrier. Besides, the accumulation of Nile red-loaded NPs in HFs and the transfolliclular penetration of Nile red was observed, which indicates that HFs can serve as a reservoir where drugs are sustained released from the NPs and provide a shortcut for drugs to penetrate across the HF into the deep viable skin layers. The drug release of the pH-sensitive NPs inside HFs may be due to the high sebum content and the high HF pH. Lastly, water and ethanol are omnipresent in topical formulations, serving as dispersion media for NPs, low-toxic dissolution media, and penetration enhancers. The solvent effects of ethanol, PBS and the cosolvent ethanol-PBS (1:1, V/V) on the penetration of the hydrophilic model drug PCA into the excised human skin and porcine ear skin were investigated by EPR. Absolute ethanol showed poor ability to deliver PCA into the skin due to the crystallization of PCA caused by ethanol evaporation. PBS and the cosolvent are superior to ethanol, delivering a similar high amount of PCA into the skin. Despite a similar total amount of PCA in the skin, the cosolvent delivered more drugs into the viable skin compared to PBS. This shows the solvents effects on the macroscopic localization of drugs in the skin. Nevertheless, more than 95% of the penetrated drugs accumulated in the SC regardless of the solvents, showing that the SC is a predominant barrier and the main reservoir for the skin penetration of hydrophilic PCA. Furthermore, the solvents influenced the microscopic localization of PCA in the SC. PCA distributed in both the intercellular skin lipids and corneocytes when using the three solvents. From PBS to ethanol, with more ethanol in the solvent, the fraction of PCA distributed in the intercellular lipids decreased from 74% to 37%. The reason may be that ethanol enhances the diffusion of PCA from the intercellular lipids into the corneocytes, implying the coexistence of intercellular and transcellular skin pathways for PCA. In conclusion, the studies conducted in this thesis i) provide correlation of the extent of the SC barrier disruption with the number of applied TS or CS and show the feasibility of using TS to establish an ex vivo barrier-disrupted skin model that mimics AD skin to some degree; ii) give insights of the influence of the SC barrier on the drug release of NPs on the skin and the following skin penetration of drugs, and show the promising application of the pH-sensitive NP in reducing the side effects of Dx for the treatment of AD; iii) expand the knowledge of solvent effects on the spatial localization of drugs in the SC and give a hint for the skin pathway of hydrophilic drugs