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End date: 2024 × Start date: 2020 × End date: 2024 × DDC: 600 × Publisher: Amsterdam [u.a.] : Elsevier Science × WGL Institute: IOM ×

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    Design of biomimetic collagen matrices by reagent-free electron beam induced crosslinking: Structure-property relationships and cellular response
    (Amsterdam [u.a.] : Elsevier Science, 2019) Riedel, Stefanie; Hietschold, Philine; Krömmelbein, Catharina; Kunschmann, Tom; Konieczny, Robert; Knolle, Wolfgang; Mierke, Claudia T.; Zink, Mareike; Mayr, Stefan G.
    Novel strategies to mimic mammalian extracellular matrix (ECM) in vitro are desirable to study cell behavior, diseases and new agents in drug delivery. Even though collagen represents the major constituent of mammalian ECM, artificial collagen hydrogels with characteristic tissue properties such as network size and stiffness are difficult to design without application of chemicals which might be even cytotoxic. In our study we investigate how high energy electron induced crosslinking can be utilized to precisely tune collagen properties for ECM model systems. Constituting a minimally invasive approach, collagen residues remain intact in the course of high energy electron treatment. Quantification of the 3D pore size of the collagen network as a function of irradiation dose shows an increase in density leading to decreased pore size. Rheological measurements indicate elevated storage and loss moduli correlating with an increase in crosslinking density. In addition, cell tests show well maintained viability of NIH 3T3 cells for irradiated collagen gels indicating excellent cellular acceptance. With this, our investigations demonstrate that electron beam crosslinked collagen matrices have a high potential as precisely tunable ECM-mimetic systems with excellent cytocompatibility.
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    Influence of substrate dimensionality on the growth mode of epitaxial 3D-bonded GeTe thin films: From 3D to 2D growth
    (Amsterdam [u.a.] : Elsevier Science, 2019) Hilmi, Isom; Lotnyk, Andriy; Gerlach, Jürgen W.; Schumacher, Philipp; Rauschenbach, Bernd
    The pseudo-binary line of Sb2Te3-GeTe contains alloys featuring different crystalline characteristics from two-dimensionally (2D-) bonded Sb2Te3 to three-dimensionally (3D-) bonded GeTe. Here, the growth scenario of 3D-bonded GeTe is investigated by depositing epitaxial GeTe thin films on Si(111) and Sb2Te3-buffered Si(111) substrates using pulsed laser deposition (PLD). GeTe thin films were grown in trigonal structure within a temperature window for epitaxial growth of 210–270 °C on unbuffered Si(111) substrates. An unconventional growth onset was characterized by the formation of a thin amorphous GeTe layer. Nonetheless, the as-grown film is found to be crystalline. Furthermore, by employing a 2D-bonded Sb2Te3 thin film as a seeding layer on Si(111), a 2D growth of GeTe is harnessed. The epitaxial window can substantially be extended especially towards lower temperatures down to 145 °C. Additionally, the surface quality is significantly improved. The inspection of the local structure of the epitaxial films reveals the presence of a superposition of twinned domains, which is assumed to be an intrinsic feature of such thin films. This work might open a way for an improvement of an epitaxy of a 3D-bonded material on a highly-mismatched substrate (e.g. Si (111)) by employing a 2D-bonded seeding layer (e.g. Sb2Te3).
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    Ion beam figuring machine for ultra-precision silicon spheres correction
    (Amsterdam [u.a.] : Elsevier Science, 2015) Arnold, Thomas; Pietag, Fred
    In the framework of the Avogadro project, isotopically enriched 28Si spheres had been manufactured as artifacts for the assessment of various physical quantities including the sphere volume which finally leads to a very accurate determination of the Avogadro constant NA. The Avogadro constant is an important input datum for the redefinition of the unit of mass, the kilogram, on the basis of fundamental physical constants. During the recent measurement campaign, it has turned out that one of the main contributions to the overall uncertainty of NA is the sphericity error and consequently the interferometric volume measurement. Since chemical–mechanical polishing has reached its limits with respect to form accuracy due to the sensitivity of material removal rate to crystal orientation, it has been proposed to use ion beam figuring for further reduction of sphericity error from currently 50 nm PV to values <10 nm PV. In this paper, a new concept and realization of a multi-axis ion beam figuring machine dedicated for deterministic correction of silicon spheres is presented. Aspects of long term tool stability and alignment procedures in order to relate the ion beam footprint to the sphere surface are covered. Furthermore, a process dwell time calculation and tool path generation method dedicated for spheres manufacturing will be presented and discussed.