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- ItemFabrication of metal nanoparticle arrays by controlled decomposition of polymer particles(Bristol : IOP Publishing, 2013) Brodoceanu, Daniel; Fang, Cheng; Voelcker, Nicolas Hans; Bauer, Christina T.; Wonn, Anne; Kroner, Elmar; Arzt, Eduard; Kraus, TobiasWe report a novel fabrication method for ordered arrays of metal nanoparticles that exploits the uniform arrangement of polymer beads deposited as close-packed monolayers. In contrast to colloidal lithography that applies particles as masks, we used thermal decomposition of the metal-covered particles to precisely define metal structures. Large arrays of noble metal (Au, Ag, Pt) nanoparticles were produced in a three-step process on silicon, fused silica and sapphire substrates, demonstrating the generality of this approach. Polystyrene spheres with diameters ranging between 110 nm and 1 µm were convectively assembled into crystalline monolayers, coated with metal and annealed in a resistive furnace or using an ethanol flame. The thermal decomposition of the polymer microspheres converted the metal layer into particles arranged in hexagonal arrays that preserved the order of the original monolayer. Both the particle size and the interparticle distance were adjusted via the thickness of the metal coating and the sphere diameter, respectively.
- ItemBioinspired pressure actuated adhesive system(Saarbrücken : Leibniz-Institut für Neue Materialien, 2011) Paretkar, Dadhichi R.; Kamperman, Marleen; Schneider, Andreas S.; Arzt, EduardWe developed a dry snythetic adhesive system inspired by gecko feet that can switch reversibly from adhesion to non-adhesion with applied pressure as external stimulus. Micropatterned polydimethylsiloxane (PDMS) surfaces with pillars of 30 µm length and 10 µm diameter were fabricated using photolithography and moulding. Adhesion properties were determined with a flat probe as a function of preload. For low and moderate applied compressive preloads, measured adhesion was 7.5 times higher on the patterned surfaces than on flat controls whereas for high preloads adhesion dropped to very low values. In situ imaging showed that the increased preload caused the pillars to deform by bending and/or buckling and to lose their adhesive contact. The elasticity of PDMS aids the pillar recovery to the upright position upon removal of preload enabling repeatability of the switch. Such systems have promising properties e.g. for industrial pick-and-carry operations.
- ItemCohesive detachment of an elastic pillar from a dissimilar substrate(Amsterdam : Elsevier, 2017) Fleck, Norman A.; Khaderi, Syed Nizamuddin; McMeeking, Robert M.; Arzt, EduardThe adhesion of micron-scale surfaces due to intermolecular interactions is a subject of in- tense interest spanning electronics, biomechanics and the application of soft materials to engineering devices. The degree of adhesion is sensitive to the diameter of micro-pillars in addition to the degree of elastic mismatch between pillar and substrate. Adhesion- strength-controlled detachment of an elastic circular cylinder from a dissimilar substrate is predicted using a Dugdale-type of analysis, with a cohesive zone of uniform tensile strength emanating from the interface corner. Detachment initiates when the opening of the cohesive zone attains a critical value, giving way to crack formation. When the cohe- sive zone size at crack initiation is small compared to the pillar diameter, the initiation of detachment can be expressed in terms of a critical value H c of the corner stress inten- sity. The estimated pull-offforce is somewhat sensitive to the choice of stick/slip boundary condition used on the cohesive zone, especially when the substrate material is much stiffer than the pillar material. The analysis can be used to predict the sensitivity of detachment force to the size of pillar and to the degree of elastic mismatch between pillar and sub- strate.
- Item"Gecko-Workshop 2010" - INM initiates new worldwide conference series(Saarbrücken : Leibniz-Institut für Neue Materialien, 2011) Kamperman, Marleen; Arzt, EduardIn July 2010, scientists from all over the world gathered at INM to discuss gecko inspired adhesion at a workshop entitled "Bioinspired adhesion: from geckos to new products". The talks covered a range of current issues, including natural attachment systems, developments in artificial gecko-mimics, advances in mechanical models and possible products. This was the first dedicated workshop on this topic. The attendees unanimously agreed to create an international workshop series based on the INM example.
- ItemAdhesion and relaxation of a soft elastomer on surfaces with skin like roughness(Amsterdam : Elsevier, 2018) Fischer, Sarah; Boyadzhieva, Silviya; Hensel, René; Kruttwig, Klaus; Arzt, EduardFor designing new skin adhesives, the complex mechanical interaction of soft elastomers with surfaces of various roughnesses needs to be better understood. We systematically studied the effects of a wide set of roughnesscharacteristics, film thickness, hold time and material relaxation on the adhesive behaviour of the silicone elastomer SSA 7–9800 (Dow Corning). As model surfaces, we used epoxy replicas obtained from substrates with roughness ranging from very smooth to skin-like. Our results demonstrate that films of thin and intermediate thickness (60 and 160 μm) adhered best to a sub-micron rough surface, with a pull-off stress of about 50 kPa. Significant variations in pull-off stress and detachment mechanism with roughness and hold time were found. In contrast, 320 μm thick films adhered with lower pull-off stress of about 17 kPa, but were less sensitive to roughness and hold time. It is demonstrated that the adhesion performance of the siliconefilms to rough surfaces can be tuned by tailoring the film thickness and contact time.
- ItemSurface structure influences contact killing of bacteria by copper(Hoboken, NJ : Wiley, 2014) Zeiger, Marco; Solioz, Marc; Edongué, Hervais; Arzt, Eduard; Schneider, Andreas S.Copper kills bacteria rapidly by a mechanism that is not yet fully resolved. The antibacterial property of copper has raised interest in its use in hospitals, in place of plastic or stainless steel. On the latter surfaces, bacteria can survive for days or even weeks. Copper surfaces could thus provide a powerful accessory measure to curb nosocomial infections. We here investigated the effect of the copper surface structure on the efficiency of contact killing of Escherichia coli, an aspect which so far has received very little attention. It was shown that electroplated copper surfaces killed bacteria more rapidly than either polished copper or native rolled copper. The release of ionic copper was also more rapid from electroplated copper compared to the other materials. Scanning electron microscopy revealed that the bacteria nudged into the grooves between the copper grains of deposited copper. The findings suggest that, in terms of contact killing, more efficient copper surfaces can be engineered.
- ItemSize dependent strength of bcc metal micropillars: towards high strength surfaces by micropatterning(Saarbrücken : Leibniz-Institut für Neue Materialien, 2010) Schneider, Andreas; Arzt, EduardThe size effect in body-centered cubic (bcc) metals was comprehensively investigated through microcompression tests performed on focused ion beam machined tungsten (W), molybdenum (Mo) and niobium (Nb) pillars, with single slip [235] and multiple slip [001] orientations. The relationship between yield strength and pillar diameter as well as the deformation morphologies were found to correlate with a parameter specific for bcc metals, i.e. the critical temperature Tc. This finding sheds new light on the phenomenon of small-scale plasticity in largely unexplored non-fcc metals. This effect may be used in the patterning of surfaces to achieve higher strengths.
- ItemElevated temperature adhesion of bioinspired polymeric micropatterns to glass(Amsterdam : Elsevier, 2017) Barreau, Viktoriia; Yu, Dan; Hensel, René; Arzt, EduardMicropatterned polymer surfaces that operate at various temperatures are required for emerging technical applications such as handling of objects or space debris. As the mechanical properties of polymers can vary significantly with temperature, adhesion performance can exhibit large variability. In the present paper, we experimentally study temperature effects on the adhesion of micropatterned adhesives (pillar length 20 μm, aspect ratios 0.4 and 2) made from three different polymers, i.e., polydimethylsiloxane (PDMS), perfluoropolyether dimethacrylate (PFPEdma), and polyurethane (PU-ht). PU specimens showed the highest pull-off stresses of about 57 kPa at 60 °C, i.e., more than twice the value of unpatterned control samples. The work of separation similarly showed a maximum at that temperature, which was identified as the glass transition temperature, Tg. PDMS and PFPEdma specimens were tested above their Tg. As a result, the adhesion properties decreased monotonically (about 50% for both materials) for temperature elevation from 20 to 120 °C. Overall, the results obtained in our study indicate that the operating temperature related to the glass transition temperature should be considered as a significant parameter for assessing the adhesion performance of micropatterned adhesives and in the technical design of adhesion devices.
- ItemEstimating the modulatory effects of nanoparticles on neuronal circuits using computational upscaling(Milton Park : Taylor & Francis, 2013) Busse, Michael; Stevens, David; Kraegeloh, Annette; Cavelius, Christian; Vukelic, Mathias; Arzt, Eduard; Strauss, Daniel J.Background: Beside the promising application potential of nanotechnologies in engineering, the use of nanomaterials in medicine is growing. New therapies employing innovative nanocarrier systems to increase specificity and efficacy of drug delivery schemes are already in clinical trials. However the influence of the nanoparticles themselves is still unknown in medical applications, especially for complex interactions in neural systems. The aim of this study was to investigate in vitro effects of coated silver nanoparticles (cAgNP) on the excitability of single neuronal cells and to integrate those findings into an in silico model to predict possible effects on neuronal circuits. Methods: We first performed patch clamp measurements to investigate the effects of nanosized silver particles, surrounded by an organic coating, on excitability of single cells. We then determined which parameters were altered by exposure to those nanoparticles using the Hodgkin–Huxley model of the sodium current. As a third step, we integrated those findings into a well-defined neuronal circuit of thalamocortical interactions to predict possible changes in network signaling due to the applied cAgNP, in silico. Results: We observed rapid suppression of sodium currents after exposure to cAgNP in our in vitro recordings. In numerical simulations of sodium currents we identified the parameters likely affected by cAgNP. We then examined the effects of such changes on the activity of networks. In silico network modeling indicated effects of local cAgNP application on firing patterns in all neurons in the circuit. Conclusion: Our sodium current simulation shows that suppression of sodium currents by cAgNP results primarily by a reduction in the amplitude of the current. The network simulation shows that locally cAgNP-induced changes result in changes in network activity in the entire network, indicating that local application of cAgNP may influence the activity throughout the network.
- ItemIndentation-induced two-way shape-memory effect in aged Ti-50.9 at.% Ni(Cambridge : Cambridge University Press, 2015) Frensemeier, Mareike; Arzt, Eduard; Qin, Enwei; Frick, Carl P.; Schneider, Andreas S.In this study, Vickers indentation was used to investigate the two-way shape-memory effect (TWSME) in an austenitic Ti-50.9 at.% Ni alloy, exposed to different heat treatments. Three aging treatments were used to manipulate the size of Ti3Ni4 precipitates. All samples were Vickers indented, and the indent depth was investigated as function of thermal cycling. The TWSME was found only in the material aged at 400 °C, which contained coherent precipitates. Thermal cycling shows stable TWSME, however, heating well above the austenite finish temperature lead to permanent austenitic protrusions. The results indicate that stabilized martensite plays a critical role in creating TWSME surfaces.