Browsing by Subject "AFM"

Sort by: Order: Results:

Now showing items 1-5 of 5
  • Winzely, Maximilian; Jouppila, Annukka; Ramer, Georg; Lux, Laurin; Lendl, Bernhard; Barreiro, Karina; Lassila, Riitta; Friedbacher, Gernot (2022)
    Antiplatelet and anticoagulant drugs are classified antithrombotic agents with the purpose to reduce blood clot formation. For a successful treatment of many known complex cardiovascular diseases driven by platelet and/or coagulation activity, the need of more than one antithrombotic agent is inevitable. However, combining drugs with different mechanisms of action enhances risk of bleeding. Dual anticoagulant and antiplatelet (APAC), a novel semisynthetic antithrombotic molecule, provides both anticoagulant and antiplatelet properties in preclinical studies. APAC is entering clinical studies with this new exciting approach to manage cardiovascular diseases. For a better understanding of the biological function of APAC, comprehensive knowledge of its structure is essential. In this study, atomic force microscopy (AFM) was used to characterize APAC according to its structure and to investigate the molecular interaction of APAC with von Willebrand factor (VWF), since specific binding of APAC to VWF could reduce platelet accumulation at vascular injury sites. By the optimization of drop-casting experiments, we were able to determine the volume of an individual APAC molecule at around 600 nm(3), and confirm that APAC forms multimers, especially dimers and trimers under the experimental conditions. By studying the drop-casting behavior of APAC and VWF individually, we depictured their interaction by using an indirect approach. Moreover, in vitro and in vivo conducted experiments in pigs supported the AFM results further. Finally, the successful adsorption of APAC to a flat gold surface was confirmed by using photothermal-induced resonance, whereby attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) served as a reference method.
  • Seppa, Jeremias; Reischl, Bernhard; Sairanen, Hannu; Korpelainen, Virpi; Husu, Hannu; Heinonen, Martti; Raiteri, Paolo; Rohl, Andrew L.; Nordlund, Kai; Lassila, Antti (2017)
    Due to their operation principle atomic force microscopes (AFMs) are sensitive to all factors affecting the detected force between the probe and the sample. Relative humidity is an important and often neglected-both in experiments and simulations-factor in the interaction force between AFM probe and sample in air. This paper describes the humidity control system designed and built for the interferometrically traceable metrology AFM (IT-MAFM) at VTT MIKES. The humidity control is based on circulating the air of the AFM enclosure via dryer and humidifier paths with adjustable flow and mixing ratio of dry and humid air. The design humidity range of the system is 20-60 % rh. Force-distance adhesion studies at humidity levels between 25 % rh and 53 % rh are presented and compared to an atomistic molecular dynamics (MD) simulation. The uncertainty level of the thermal noise method implementation used for force constant calibration of the AFM cantilevers is 10 %, being the dominant component of the interaction force measurement uncertainty. Comparing the simulation and the experiment, the primary uncertainties are related to the nominally 7 nm radius and shape of measurement probe apex, possible wear and contamination, and the atomistic simulation technique details. The interaction forces are of the same order of magnitude in simulation and measurement (5 nN). An elongation of a few nanometres of the water meniscus between probe tip and sample, before its rupture, is seen in simulation upon retraction of the tip in higher humidity. This behaviour is also supported by the presented experimental measurement data but the data is insufficient to conclusively verify the quantitative meniscus elongation.
  • Iivonen, Tomi; Kaipio, Mikko; Hatanpää, Timo; Mizohata, Kenichiro; Meinander, Kristoffer; Räisänen, Jyrki; Kim, Jiyeon; Ritala, Mikko; Leskelä, Markku (2019)
    In this work, we have studied the applicability of Co(BTSA)(2)(THF) [BTSA = bis(trimethylsilyl)amido] (THF = tetrahydrofuran) in atomic layer deposition (ALD) of cobalt oxide thin films. When adducted with THF, the resulting Co(BTSA)(2)(THF) showed good volatility and could be evaporated at 55 degrees C, which enabled film deposition in the temperature range of 75-250 degrees C. Water was used as the coreactant, which led to the formation of Co(II) oxide films. The saturative growth mode characteristic to ALD was confirmed with respect to both precursors at deposition temperatures of 100 and 200 degrees C. According to grazing incidence x-ray diffraction measurements, the films contain both cubic rock salt and hexagonal wurtzite phases of CoO. X-ray photoelectron spectroscopy measurements confirmed that the primary oxidation state of cobalt in the films is +2. The film composition was analyzed using time-of-flight elastic recoil detection analysis, which revealed the main impurities in the films to be H and Si. The Si impurities originate from the BTSA ligand and increased with increasing deposition temperature, which indicates that Co(BTSA)(2)(THF) is best suited for low-temperature deposition. To gain insight into the surface chemistry of the deposition process, an in situ reaction mechanism study was conducted using quadrupole mass spectroscopy and quartz crystal microbalance techniques. Based on the in situ experiments, it can be concluded that film growth occurs via a ligand exchange mechanism. Published by the AVS.
  • Rantataro, Samuel; Parkkinen, Ilmari; Pande, Ishan; Domanskyi, Andrii; Airavaara, Mikko; Peltola, Emilia; Laurila, Tomi (2022)
    Vertically aligned carbon nanofibers (VACNFs) are promising material candidates for neural biosensors due to their ability to detect neurotransmitters in physiological concentrations. However, the expected high rigidity of CNFs could induce mechanical mismatch with the brain tissue, eliciting formation of a glial scar around the electrode and thus loss of functionality. We have evaluated mechanical biocompatibility of VACNFs by growing nickel-catalyzed carbon nanofibers of different lengths and inter-fiber distances. Long nanofibers with large inter-fiber distance prevented maturation of focal adhesions, thus constraining cells from obtaining a highly spread morphology that is observed when astrocytes are being contacted with stiff materials commonly used in neural implants. A silicon nanopillar array with 500 nm inter-pillar distance was used to reveal that this inhibition of focal adhesion maturation occurs due to the surface nanoscale geometry, more precisely the inter-fiber distance. Live cell atomic force microscopy was used to confirm astrocytes being significantly softer on the long Ni-CNFs compared to other surfaces, including a soft gelatin hydrogel. We also observed hippocampal neurons to mature and form synaptic contacts when being cultured on both long and short carbon nanofibers, without having to use any adhesive proteins or a glial monoculture, indicating high cytocompatibility of the material also with neuronal population. In contrast, neurons cultured on a planar tetrahedral amorphous carbon sample showed immature neurites and indications of early-stage apoptosis. Our results demonstrate that mechanical biocompatibility of biomaterials is greatly affected by their nanoscale surface geometry, which provides means for controlling how the materials and their mechanical properties are perceived by the cells.
  • Heikkinen, Terho; Kassamakov, I.; Viitala, T.; Järvinen, M.; Vainikka, T.; Nolvi, A.; Bermudez, C.; Artigas, R.; Martinez, P.; Korpelainen, Raija; Lassila, A.; Haeggström, E. (2020)
    Modern microscopes and profilometers such as the coherence scanning interferometer (CSI) approach sub-nm precision in height measurements. Transfer standards at all measured size scales are needed to guarantee traceability at any scale and utilize the full potential of these instruments, but transfer standards with similar characteristics upon reflection to those of the measured samples are preferred. This is currently not the case for samples featuring dimensions of less than 10 nm and for biosamples with different optical charasteristics to silicon, silica or metals. To address the need for 3D images of biosamples with traceable dimensions, we introduce a transfer standard with dimensions guaranteed by natural self-assembly and a material that is optically similar to that in typical biosamples. We test the functionality of these transfer standards by first calibrating them using an atomic force microscope (AFM) and then using them to calibrate a CSI. We investigate whether a good enough calibration accuracy can be reached to enable a useful calibration of the CSI system. The result is that the calibration uncertainty is only marginally increased due to the sample.