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  • Artikel: DFG Deutsche Nationallizenzen  (31)
  • Polymer and Materials Science  (29)
  • Conductivity  (2)
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  • Artikel: DFG Deutsche Nationallizenzen  (31)
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  • 1
    ISSN: 1432-2013
    Schlagwort(e): Key words Arteries ; Conductivity ; Conductance method ; Double indicator dilution method ; Shear rate ; Intravascular ultrasound
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract A double indicator dilution technique for determining the mean cross-sectional area (CSA) of a blood vessel in vivo is presented. Analogous to the thermodilution method, dilution of hypertonic saline was measured by an electrical conductance technique. Because the change in conductance rather than absolute conductance was used to calculate CSA, pulsatile changes in shear rate of blood and conductance of surrounding tissues had no effect on the data. To calculate CSA from an ion mass balance, cardiac output was needed and estimated from the thermodilution curve using the same “cold” (hypertonic) saline injection. The mean CSA, obtained from this double indicator dilution method (CSAGD), was compared with the CSA obtained from the intravascular ultrasound method (IVUS) in 44 paired observations in six piglets. The regression line is close to the line of identity (CSAGD = −1.83 + 1.06⋅CSAIVUS, r = 0.96). The difference between both CSAs was independent of the diameter of the vessel, on average −0.99 mm2± 2.64 mm2 (mean CSAGD = 46.84 ± 8.21 mm2, mean CSAIVUS = 47.82 ± 9.08 mm2) and not significant. The results show that the double indicator dilution method is a reliable technique for estimating the CSA of blood vessels in vivo.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1573-9686
    Schlagwort(e): Conductivity ; Erythrocytes ; Ultrasound ; Shear stress
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract A modified conductance method to determine the cross-sectional areas (CSAs) of arteries in piglets was evaluated in vivo. The method utilized a conductance catheter having four electrodes. Between the outer electrodes an alternating current was applied and between the inner electrodes the induced voltage difference was measured and converted into a conductance. CSA was determined from measured conductance minus parallel conductance, which is the conductance of the tissues surrounding the vessel times the length between the measuring electrodes of the conductance catheter divided by the conductivity of blood. The parallel conductance was determined by injecting hypertonic saline to change blood conductivity. The conductivity of blood was calculated from temperature and hematocrit and corrected for maximal deformation and changes in orientation of the erythrocytes under shear stress conditions. The equations to calculate the conductivity of blood were obtained from in vitro experiments. In vivo average aortic CSAs, determined with the conductance method CSA (G) in five piglets, were compared to those determined with the intravascular ultrasound method CSA(IVUS). The regression equation between both values was CSA (G) =−0.09+1.00·CSA(IVUS) r=0.97, n=53. The mean difference between the values was −0.29% · 5.57% (2 standard deviations). We conclude that the modified conductance method is a reliable technique to estimate the average cross-sectional areas of the aorta in piglets. © 1999 Biomedical Engineering Society. PAC99: 8780-y, 8437+q, 8719Nn
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 4 (1993), S. 213-219 
    ISSN: 1045-4861
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The aim of this study was to investigate the bone response to three different types of titanium (Ti) alloys and hydroxyapatite (HA) coated titanium alloy by histological and histomorphometrical analysis. Therefore, implants made of these materials were inserted into the tibia of rabbits. Implantation times were 6 and 16 weeks. The histological evaluation included measurement of the amount of bone apposition and analysis of the bone reaction and interface characteristics around the implants. The results demonstrated no marked differences in bony reaction to the different implant materials. In addition, the HA coatings showed loss of thickness. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 24 (1990), S. 295-307 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: This study reports on certain aspects of wound-healing around percutaneous implants. Plasma-sprayed and dense hydroxylapatite, titanium, and carbon test implants were inserted into the tibia and the cranium of 12 rabbits. Four and 8 months after insertion, the animals were sacrificed and the implants with their surrounding tissues were processed histologically. Light- and transmission electron microscopic investigations were performed. It is found that direct and indirect boneanchoring favors the longevity of percutaneous implants. No differences in tissue reaction between the various implant materials were observed.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 511-518 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: To evaluate the effect of surface treatment and surface microtexture on cellular behavior, smooth and microtextured silicone substrata were produced. The microtextured substrata possessed parallel surface grooves with a width and spacing of 2.0 (SilD02), 5.0 (SilD05), and 10 μm (SilD10). The groove depth was approximately 0.5 μm. Subsequently, these substrata were either left untreated (NT) or treated by ultraviolet irradiation (UV), radiofrequency glow discharge treatment (RFGD), or both (UVRFGD). After characterization of the substrata, rat dermal fibroblasts (RDF) were cultured on the UV, RFGD, and UVRFGD treated surfaces for 1, 3, 5, and 7 days. Comparison between the NT and UV substrata revealed that UV treatment did not influence the contact angles and surface energies of surfaces with a similar surface topography. However, the contact angles of the RFGD and UVRFGD substrata were significantly smaller than those of the UV and NT substrata. The dimension of the surface microevents did not influence the wettability characteristics. Cell culture experiments revealed that RDF cell growth on UV-treated surfaces was lower than on the RFGD and UVRFGD substrata. SEM examination demonstrated that the parallel surface grooves on the SilD02 and SilD05 substrata were able to induce stronger cell orientation and alignment than the events on SilD10 surfaces. By combining all of our findings, the most important conclusion was that physicochemical parameters such as wettability and surface free energy influence cell growth but play no measurable role in the shape and orientation of cells on microtextured surfaces. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 1047-1054 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: This study reports on the soft-tissue response to titanium fiber mesh percutaneous implants. The implants were inserted in the backs of 15 rabbits. The surgical procedure was performed in two steps: implantation of the subcutaneous part of the implants and, after 3 months, fixation of the percutaneous part into the subcutaneous part. Two and 6 months after insertion the animals were sacrificed and the implants, with their surrounding tissues, were processed histologically. Light microscopic analysis demonstrated that only one implant showed considerable skin retraction in the percutaneous area. Around the rest of the implants no downgrowth or only a very limited epidermal downgrowth was observed. Furthermore, the fiber mesh material showed good biocompatible behavior. These results confirm the previous finding that sintered titanium fiberweb structures are effective for the stabilization of percutaneous devices located in soft tissues and can improve their performance. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 7
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The effects of discharge radiofrequency (RF) power and film thickness were studied on the characteristics of Ca5(PO4)3OH (hydroxyapatite) thin films fabricated by RF magnetron sputtering. The structure and chemical composition were investigated with α-step (thickness), scanning electron microscopy (SEM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), and infrared absorption spectrometry (FTIR). The films were analyzed assputtered and after annealing at 550°C under argon flow. SEM showed that the film surfaces had no cracks or other defects. X-ray diffraction showed that the deposited films were amorphous with low-discharge RF power, and crystalline with high-discharge RF power. After annealing, all the films had the same crystalline structure as apatite. However, the RBS measurements revealed that all films had a higher calcium-phosphate ratio than standard synthetic hydroxyapatite. Furthermore, statistical testing of the RBS data revealed the existence of only a weak correlation between the Ca/P ratio and the discharge power level. Although all sputtered films showed phosphate bonds in the infrared spectrum, only after annealing did the OH bonds of hydroxyapatite become visible. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 8
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The aim of this study was to investigate the bone response to calcium phosphate (Ca-P) plasma-spray and radiofrequency magnetron sputter-coated implants with comparable roughness. Therefore, tapered conical screw designed implants were installed in the trabecular bone of the femurs of nine goats. They were provided with two types of coatings, a plasma-spray dual coating of fluorapatite and hydroxyapatite (FA/HA-PS) and a titanium plasma-spray coating, covered with an amorphous Ca-P magnetron sputtercoating (TPS/Ca-P-a). These implants were evaluated histologically and mechanically after 3 months of implantation. A well-controlled method to apply and measure a torsional force to load the screw-type implants to the point of failure was introduced. All implants healed uneventful and were well fixed. No significant difference (Student t test, p 〉 0.05) for the torsional failure force was measured for both type of coatings. Nevertheless, SEM revealed differently situated fracture planes. Light microscopy showed intimate bone-implant contact for both types of coatings; original drill margins were still visible. A lamellar type of bone with some remodeling lacunae was shown. Histomorphometry revealed a higher percentage of bone contact for the FA/HA-PS-coated implants (student t test, p 〈 0.05). Measurement of the amount of bone revealed more bone mass around TPS/Ca-P-a-coated implants (analysis of variance and Tukey multiple comparison, p 〈 0.05). © 1997 John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 464-474 
    ISSN: 0021-9304
    Schlagwort(e): calcium phosphate coatings ; magnetron sputtering ; osteoblast ; in vitro ; bone ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: In previous studies we developed a RF magnetron sputter technique for the production of thin Ca-P coatings. With this technique coatings can be produced that vary in Ca/P ratio as well as in structural appearance. The aim of this investigation was to obtain more understanding of the biological behavior of these coatings by way of in vitro experiments. The effect of noncoated titanium (Ti) and three different Ca-P-sputtered surfaces on the proliferation and differentiation (morphology and matrix production) of osteoblast-like cells was studied. Proliferation was determined using counting procedures; morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescent markers and energy-dispersive X-ray microanalysis (EDX) were used to obtain quantitative and compositional information about the resultant calcified extracellular matrix (ECM). Results demonstrated that proliferation of the osteoblast-like cells was significantly (p 〈 0.05) higher on noncoated than on Ca-P-coated samples. On the other hand, more mineralized ECM was formed on the coated surfaces. In addition, TEM confirmed that the cells on the coated substrates were surrounded by ECM with collagen fibers embedded in crystallized, needle-shaped structures. On the basis of these findings, we concluded that: (1) the investigated Ca-P sputter coatings possess the capacity to activate the differentiation and expression of osteogenic cells, and (2) bone formation proceeds faster on Ca-P surfaces than on Ti substrates. Further, this bone-inductive effect appeared to be dependent on the Ca-P ratio of the deposited coatings. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 464-474, 1998.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 624-632 
    ISSN: 0021-9304
    Schlagwort(e): calcium phosphate coatings ; interface strength ; RF magnetron sputter deposition ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: In previous studies, an RF magnetron sputter technique was developed for the production of thin calcium phosphate coatings. Several deposition parameters were found to influence the growth rate and the stoichiometry of the coatings. For instance, deposition with additional oxygen pressure decreased the Ca to P ratio of the coatings to 1.67. For application of these coatings on actual Ti implants, it is important to know their adhesive tensile strength with the implant surface and how it varies with the deposition parameters. Motivated by these goals, the aim of this study was to measure the adhesive tensile strength of these coatings with Ti substrates and to study its variation with the deposition parameters. Since most mechanical characterization methods are incapable of providing a direct measure of the interface's fundamental strength, a novel laser spallation experiment was used to accomplish this task. In this experiment, a compressive stress pulse is generated on the back side of a substrate by impinging a 3-ns long Nd:YAG laser pulse. The stress pulse propagates through the substrate and is reflected into a tensile stress wave from the free surface of the coating deposited on its front surface. The returning tensile pulse pries off the coating if its amplitude is high enough. The peak interface tensile stress is computed by using the optically recorded free surface displacement of the coating. Because interface decohesion is accomplished at a strain rate of almost 107 s-1, all inelastic processes essentially are suppressed and the measured value essentially is the intrinsic tensile strength of the interface. Tensile strength values in the range of 500-900 MPa were recorded for the interfaces between sputter-deposited calcium-phosphate coatings and Ti substrates. To confirm the locus of failure, the spalled spots were examined using SEM and EDS. The variation in the measured values was related to the changes in the deposition conditions. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 624-632, 1998.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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