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  • Articles  (5)
  • Articles: DFG German National Licenses  (5)
  • Electrophysiology  (4)
  • porous silicon
  • Springer  (5)
  • 2000-2004  (5)
  • Technology  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Porosified Silicon Wafer Structures Impregnated With Platinum Anti-Tumor Compounds: Fabrication, Characterization, and Diffusion Studies (2000)
    Springer
    Biomedical microdevices 2 (2000), S. 265-272 
    Details
    ISSN: 1572-8781
    Keywords: porous silicon ; cis-platin ; drug delivery ; calcium phosphate ; carbo-platin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In this work, the incorporation and characterization of cis-platin (cis-diammine dichloroplatinum(II)), carbo-platin [cis-diammine(cyclobutane-1,1-dicarboxylato] platinum(II)), and Pt(en)Cl2 (ethylenediamminedichloro platinum(II)) within layers of calcium phosphate on porous Si/Si substrates are described. These materials have been characterized by scanning electron microscopy, secondary ion mass spectrometry, and X-ray energy dispersive spectroscopy. The diffusion of platinum species from the doped calcium phosphate layers has also been investigated by UV-visible absorption spectrometry and inductively-coupled plasma spectroscopy. The influence of initial platinum concentration, the impact of thermal annealing of the calcium phosphate/porous Si/Si matrix, as well as the effect of varying the ligand coordination sphere of the Pt complex on its ability to be delivered to the surroundings have also been analyzed. For the case of cis-platin, it is found that increasing the concentration of platinum complex in the electrolyte during cathodic growth of calcium phosphate results in a relatively greater concentration of Pt incorporated into the calcium phosphate layers and a larger amount of Pt which subsequently can be delivered to the surrounding medium upon exposure to solvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009951121205
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  • 2
    Electronic Resource
    Electronic Resource
    A Chamber to Permit Invasive Manipulation of Adherent Cells in Laminar Flow with Minimal Disturbance of the Flow Field (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 1184-1193 
    Details
    ISSN: 1573-9686
    Keywords: Hemodynamics ; Endothelial cells ; Electrophysiology ; Shear stress ; Biomechanics ; Biosensors ; Surface tension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract An obstacle to real-time in vitro measurements of endothelial cell responses to hemodynamic forces is the inaccessibility of the cells to instruments of measurement and manipulation. We have designed a parallel plate laminar flow chamber that permits access to adherent cells during exposure to flow. The “minimally invasive flow device” (MIF device) has longitudinal slits (1 mm wide) cut in the top plate of the chamber to allow insertion of a recording, measurement, or stimulating instrument (e.g., micropipette) into the flow field. Surface tension forces at the slit openings are sufficient to counteract the hydrostatic pressure generated in the chamber and thus prevent overflow. The invasive probe is brought near to the cell surface, makes direct contact with the cell membrane, or enters the cell. The slits provide access to a large number (and choice) of cells. The MIF device can maintain physiological levels of shear stress (〈1–15 dyn/cm2) without overflow in the absence and presence of fine instruments such as micropipettes used in electrophysiology, membrane aspiration, and microinjection. Microbead trajectory profiles demonstrated negligible deviations in laminar flow near the surface of target cells in the presence of microscale instruments. Patch-clamp electrophysiological recordings of flow-induced changes in membrane potential were demonstrated. The MIF device offers numerous possibilities to investigate real-time endothelial responses to well-defined flow conditions in vitro including electrophysiology, cell surface mechanical probing, local controlled chemical release, biosensing, microinjection, and amperometric techniques. © 2000 Biomedical Engineering Society. PAC00: 8780Fe, 8717Jj, 8719Uv, 8716Uv, 8719Nn
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.1317529
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  • 3
    Electronic Resource
    Electronic Resource
    Delayed Activation and Retrograde Propagation in Cardiac Muscle: Implication of Virtual Electrode Effects (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 1318-1325 
    Details
    ISSN: 1573-9686
    Keywords: Heart ; Electrophysiology ; Bidomain ; Reentry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Point cathodal stimulation of cardiac tissue was shown previously to produce both a dog-bone shaped virtual cathode transverse to the muscle fibers and two longitudinal virtual anodes. We hypothesize that virtual anodes can cause a region of delayed activation, separating two regions of early activation caused by the virtual cathode. Using a high-density electrode array in 42 superfused epicardial slices from 14 canine left ventricles, we observed regions of early and delayed activation and different pathways of retrograde propagation corresponding to the earlier patterns. Retrograde propagation was seen from the transversely located early activation area through areas of delayed activation toward the cathode, and from the early activation area toward the cathode directly. These pathways caused a wide dispersion in the direction of retrograde propagation (2° ± 31°, n = 179, relative to the fast axis of threshold activation; radial velocity: 0.5 ± 0.2m/s, n = 95, in 12 slices from 8 hearts with stimuli of 330 μs, 0.8–30 mA). Delayed activations were observed 0° ± 6° (n = 32) from the axis in 23 maps (at differing stimulation strengths) recorded in 13 slices from 10 hearts. We conclude that point cathodal stimulation induce delayed activation along the fiber axis and retrograde propagation both along and transverse to the axis. © 2000 Biomedical Engineering Society. PAC00: 8719Ff, 8719Hh, 8716Uv, 8754Dt, 8719Nn
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.1326029
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  • 4
    Electronic Resource
    Electronic Resource
    Origins of Spiral Wave Meander and Breakup in a Two-Dimensional Cardiac Tissue Model (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 755-771 
    Details
    ISSN: 1573-9686
    Keywords: Reentry ; Arrhythmias ; Restitution ; Stability ; Electrophysiology ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract We studied the stability of spiral waves in homogeneous two-dimensional cardiac tissue using phase I of the Luo–Rudy ventricular action potential model. By changing the conductance and the relaxation time constants of the ion channels, various spiral wave phenotypes, including stable, quasiperiodically meandering, chaotically meandering, and breakup were observed. Stable and quasiperiodically meandering spiral waves occurred when the slope of action potential duration (APD) restitution was 〈1 over all diastolic intervals visited during reentry; chaotic meander and spiral wave breakup occurred when the slope of APD restitution exceeded 1. Curvature of the wave changes both conduction velocity and APD, and their restitution properties, thereby modulating local stability in a spiral wave, resulting in distinct spiral wave phenotypes. In the LR1 model, quasiperiodic meander is most sensitive to the Na+ current, whereas chaotic meander and breakup are more dependent on the Ca2+ and K+ currents. © 2000 Biomedical Engineering Society. PAC00: 8719Hh, 8717Nn, 8717Aa, 8716Uv
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.1289474
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  • 5
    Electronic Resource
    Electronic Resource
    Model-Based Analysis of Optically Mapped Epicardial Activation Patterns and Conduction Velocity (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 1085-1092 
    Details
    ISSN: 1573-9686
    Keywords: Isolated heart ; Electrophysiology ; Rabbit ; Left ventricle ; Action potential ; Voltage-sensitive dye
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A novel parametric model-based method was developed to quantify epicardial conduction patterns and velocity in an isolated Langendorff-perfused rabbit heart. The method incorporated geometric and anatomical features of the left and right ventricles into the analysis. Optical images of propagation were obtained using the voltage-sensitive dye DI-4-ANEPPS, and a high-speed digital camera. Activation maps were extracted from these images and interpolated onto a three-dimensional finite-element model of epicardial geometry and fiber structure. Activation time was expressed as a function of local parametric coordinates, and a conduction velocity vector field was computed from the gradient of the scalar field. Activation times measured using bipolar electrodes did not differ significantly from times measured using the optical mapping technique. The method was able to detect a 34% decrease in average fiber velocity and a 28% decrease in average cross-fiber velocity following the addition of 0.5 mM heptanol into the perfusate. The combination of optical mapping with a three-dimensional geometric model of the ventricles provides a new tool to quantify wave-front propagation relative to anatomy at a relatively high spatial resolution. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8719Hh, 8719Ff, 8762+n, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.1314891
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