Functional applications of Al·Al2O3 nanowires : laser assisted α-Al2O3 synthesis and fabrication of micro-/nanostructured surfaces for cell compatibility studies

Recently, one-dimensional (1D) nanostructures have attracted considerable interest of nanoscience studies as well as nanotechnology applications. Especially 1D hetero-structural nanowires with a combination of two different materials, for instance metal/metal oxide composites, hold a great potential for various photonic and electronic applications. Thus, Al·Al2O3 core-shell nanowires, which were firstly reported by Veith et al., form an interesting class of such hetero-nanostructures. This thesis describes the preparation of functional surfaces composed of 1D nanostructures by CVD of a (tBuOAlH2)2 [bis(tert-butoxyaluminum dihydride)] precursor and laser treatment of such structures. Firstly, main attention is given to understand the underlying mechanisms controlling the 1D growth of Al·Al2O3 nanostructures. By applying systematically different deposition temperatures and flow rates, various nanostructures were synthesized. At high deposition temperatures chaotic Al·Al2O3 nanowires form, whereas at low deposition temperatures worm- and loop-like nanostructures are achieved. A new mask-less local deposition method, named selective CVD (SCVD), is introduced by selective heating of the substrate with electro magnetic induction. A controlled thermal gradient leads to the observation of stepwise 1D growth of nanostructures. As a continuation the of the local deposition approach,an LCVD system has been designed and fabricated to show the possibility to grow 1D complex structures. α-Al2O3 layers were synthesized by laser induced heating of deposited Al·Al2O3 nanowires. In particular, two laser processing approaches were investigated: continuous wave (CW) laser and pulsed laser treatments. CW laser treatment is useful to produce dense and fully crystalline α-Al2O3 layers which may be employed as hard and protective coatings. Pulsed laser treatment produces a large variety of nanostructures (nanopores, nanoprotrusions, nanospheres etc.) of Al2O3 which is interesting for studying cell-surface interactions. Micro /nanostructured surfaces prepared by direct deposition of (tBuOAlH2)2 and laser treatment were tested for biocompatibility. Jurkat cells seem to adhere selectively on Al·Al2O3 nanowires which may lead to applications in cancer diagnosis and therapy. Laser treated Al·Al2O3 layers exhibit a better biocompatibility for normal human dermal fibroblast (NHDF) cells. In addition, a preliminary study on neurons showed that Al·Al2O3 nanowires provide enhanced cellular adhesion and growth which can be interesting for various applications in medical fields as well as in biosciences.In jüngster Zeit konnten eindimensionale (1D) Nanostrukturen beträchtliches Interesse sowohl der Nanowissenschaften als auch der Anwender der Nanotechnologie auf sich ziehen. Insbesondere 1D heterostrukturelle Nanodrähte, kombiniert aus zwei unterschiedlichen Materialien, beispielsweise Metall-Metalloxid-Zusammensetzungen, verfügen über bedeutendes Potential für verschiedenste photonische und elektronische Anwendungen. So bilden die zuerst von Veith et al. beschriebenen Al·Al2O3-Kern-Hülle-Nanodrähte eine Klasse dieser Hetero-Nanostrukturen. Diese Dissertation behandelt die Herstellung funktionaler 1D-Oberflächen mittels Chemical Vapor Deposition (CVD) mit einem (tBuOAlH2)2-Präkursor und anschließender Laser-Prozessierung. Zunächst gilt das Hauptinteresse dem Verständnis des zugrundeliegenden Mechanismus, der das Wachstum der Al·Al2O3-Nanostrukturen beeinflusst. Durch systematische Verwendung unterschiedlicher Depositionstemperaturen und Präkursorflussraten werden verschiedene Nanostrukturen synthetisiert. Bei hohen Temperaturen bilden sich chaotische, unregelmäßige Al·Al2O3-Nanodrähte, während bei niedrigen Temperaturen wurm und schleifenartige Nanostrukturen erhalten werden. Als eine neue Depositionsmethode, ohne Verwendung einer Maske und durch selektives Erhitzen des Substrats mittels elektromagnetischer Induktion, wird das sogenannte selektive CVD-System (SCVD) eingeführt. Ein kontrollierter Temperaturgradient führt zu der Beobachtung des schrittweisen eindimensionalen Wachstums von Nanostrukturen. Desweiteren wird als Fortsetzung des lokalen Depositionsverfahrens ein Laser-CVD-Verfahren erarbeitet und entwickelt, um die Möglichkeit des Erzeugens komplexer 1D-Strukturen aufzuzeigen. α-Al2O3-Beschichtungen werden mittels laserinduzierter Erhitzung der Al·Al2O3-Nanodrähte synthetisiert. Im Einzelnen kommen zwei Laser Prozessierungsverfahren zur Anwendung: Continuous-wave(CW)-laser-Behandlung und die Prozessierung mittels gepulstem Laser. Die CW-Laser-Behandlung ist anwendbar für die Herstellung dichter und vollständig kristalliner α-Al2O3-Kompositschichten, die als harte, schützende Beschichtungen Verwendung finden können. Die Behandlung mit einem gepulsten Laser hingegen erzeugt eine große Bandbreite von Nanostrukturen (nanopores, nanoprotrusions, nanospheres etc.) aus Al2O3, die dem Studium von Zell-Oberflächen-Interaktionen dienen können. Durch direkte (tBuOAlH2)2-Deposition und anschließende Laserbehandlung erzeugte mikro- beziehungsweise nanostrukturierte Oberflächen werden auf ihre Biokompatibilität hin untersucht. Jurkat-Zellen adhärieren selektiv an Al·Al2O3-Nanodrähten, was zu der Verwendung dieser Strukturen in der Diagnose und Therapie von Karzinomerkrankungen führen kann. Laserbehandelte Al·Al2O3-Schichten zeigen eine gute Biokompatibilität für normale Fibroblasten der menschlichen Dermis (normal human dermal fibroblasts, NHDF). Desweiteren zeigen erste Untersuchungen an Neuronen (Nervenzellen), dass Al·Al2O3-Nanodrähte zu gesteigerter Adhäsion und vermehrtem Wachstum dieser Zellen führen, was für verschiedene Anwendungen sowohl im medizinischen Bereich als auch in den Biowissenschaften von Interesse ist

Nanoscale Synergetic Effects on Ag-TiO2 Hybrid Substrate for Photoinduced Enhanced Raman Spectroscopy (PIERS) with Ultra-Sensitivity and Reusability

Here, a 4N-in-1 hybrid substrate concept (nanocolumnar structures, nanocrack network, nanoscale mixed oxide phases, and nanometallic structures) for ultra-sensitive and reliable photo-induced-enhanced Raman spectroscopy (PIERS), is proposed. The use of the 4N-in-1 hybrid substrate leads to an ≈50-fold enhancement over the normal surface-enhanced Raman spectroscopy, which is recorded as the highest PIERS enhancement to date. In addition to an improved Raman signal, the 4N-in-1 hybrid substrate provides a high detection sensitivity which may be attributed to the activation possibility at extremely low UV irradiation dosage and prolonged relaxation time (long measurement time). Moreover, the 4N-in-1 hybrid substrate exhibits a superior photocatalytic degradation performance of analytes, allowing its reuse at least 18 times without any loss of PIERS activity. The use of the 4N-in-1 concept can be adapted to biomedicine, forensic, and security fields easily

Selective Laser Melting of 316L Austenitic Stainless Steel: Detailed Process Understanding Using Multiphysics Simulation and Experimentation

The parameter sets used during the selective laser melting (SLM) process directly affect the final product through the resulting melt-pool temperature. Achieving the optimum set of parameters is usually done experimentally, which is a costly and time-consuming process. Additionally, controlling the deviation of the melt-pool temperature from the specified value during the process ensures that the final product has a homogeneous microstructure. This study proposes a multiphysics numerical model that explores the factors affecting the production of parts in the SLM process and the mathematical relationships between them, using stainless steel 316L powder. The effect of laser power and laser spot diameter on the temperature of the melt-pool at different scanning velocities were studied. Thus, mathematical expressions were obtained to relate process parameters to melt-pool temperature. The resulting mathematical relationships are the basic elements to design a controller to instantly control the melt-pool temperature during the process. In the study, test samples were produced using simulated parameters to validate the simulation approach. Samples produced using simulated parameter sets resulting in temperatures of 2000 (K) and above had acceptable microstructures. Evaporation defects caused by extreme temperatures, unmelted powder defects due to insufficient temperature, and homogenous microstructures for suitable parameter sets predicted by the simulations were obtained in the experimental results, and the model was validated

PTFEP-Al2O3 hybrid nanowires reducing thrombosis and biofouling

Thrombosis and bacterial infection are major problems in cardiovascular implants. Here we demonstrated that a superhydrophobic surface composed of poly(bis(2,2,2-trifluoroethoxy)phosphazene) (PTFEP)-Al2O3 hybrid nanowires (NWs) is effective to reduce both platelet adhesion/activation and bacterial adherence/colonization. The proposed approach allows surface modification of cardiovascular implants which have 3D complex geometries. © 2019 The Royal Society of Chemistry

Initiated Chemical Vapor Deposition (iCVD) Functionalized Polylactic Acid-Marine Algae Composite Patch for Bone Tissue Engineering

The current study aimed to describe the fabrication of a composite patch by incorporating marine algae powders (MAPs) into poly-lactic acid (PLA) for bone tissue engineering. The prepared composite patch was functionalized with the co-polymer, poly (2-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate) (p(HEMA-co-EGDMA)) via initiated chemical vapor deposition (iCVD) to improve its wettability and overall biocompatibility. The iCVD functionalized MAP-PLA composite patch showed superior cell interaction of human osteoblasts. Following the surface functionalization by p(HEMA-co-EGDMA) via the iCVD technique, a highly hydrophilic patch was achieved without tailoring any morphological and structural properties. Moreover, the iCVD modified composite patch exhibited ideal cell adhesion for human osteoblasts, thus making the proposed patch suitable for potential biomedical applications including bone tissue engineering, especially in the fields of dentistry and orthopedy

Marine Algae Incorporated Polylactide Acid Patch: Novel Candidate for Targeting Osteosarcoma Cells without Impairing the Osteoblastic Proliferation

Biodegradable collagen-based materials have been preferred as scaffolds and grafts for diverse clinical applications in density and orthopedy. Besides the advantages of using such bio-originated materials, the use of collagen matrices increases the risk of infection transmission through the cells or the tissues of the graft/scaffold. In addition, such collagen-based solutions are not counted as economically feasible approaches due to their high production cost. In recent years, incorporation of marine algae in synthetic polymers has been considered as an alternative method for preparation grafts/scaffolds since they represent abundant and cheap source of potential biopolymers. Current work aims to propose a novel composite patch prepared by blending Sargassum vulgare powders (SVP) to polylactide (PLA) as an alternative to the porcine-derived membranes. SVP-PLA composite patches were produced by using a modified solvent casting method. Following detailed material characterization to assess the cytocompatibility, human osteoblasts (HOBs) and osteosarcoma cells (SaOS-2) were seeded on neat PLA and SVP-PLA patches. MTT and BrdU assays indicated a greater cytocompatibility and higher proliferation for HOBs cultured on SVP-PLA composite than for those cultured on neat PLA. SaOS-2 cells cultured on SVP-PLA exhibited a significant decrease in cell proliferation. The composite patch described herein exhibits an antiproliferative effect against SaOS-2 cells without impairing HOBs' adhesion and proliferation

Enhancing thermal conductivity of epoxy with a binary filler system of h-BN platelets and Al2O3 nanoparticles

Epoxy resin is a common adhesive bonding material used to join dissimilar materials, especially in the electronics and aerospace industries. However, its low thermal conductivity and high coefficient of thermal expansion limit the direct use of epoxy in practical applications. In order to improve thermo-mechanical properties, we have prepared a series of epoxy composites using a binary system of hexagonal-boron nitride (h-BN) and aluminum oxide (Al2O3) fillers and analyzed the effect of the ratio of these fillers on the thermal conductivity of composites. While h-BN platelets form the main thermal conductive network, Al2O3 nanoparticles bridge the separated h-BN platelets to build more thermal conductive pathways. We proposed the improving of thermal conductivity as well as the mechanical properties of the epoxy matrix by incorporating h-BN and Al2O3 fillers at an optimum ratio

Enhancing adhesion and alignment of human gingival fibroblasts on dental implants

Promoting the directional attachment of gingiva to the dental implant leads to the formation of tight connective tissue which acts as a seal against the penetration of oral bacteria. Such a directional growth is mostly governed by the surface texture. Material and methods: In this study, three different methods, mechanical structuring, chemical etching and laser treatment, have been explored for their applicability in promoting cellular attachment and alignment of human primary gingival fibroblasts (HGFIBs). Results: The effectiveness of mechanical structuring was shown as a simple and a cost-effective method to create patterns to align HGIFIBs. Conclusion: Combining mechanical structuring with chemical etching enhanced both cellular attachment and the cellular alignment474661667COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES88888.099049/2013-0