Biomedical subjects

Bert Müller

Publications and source records attributed to Bert Müller.

3 recordsLinked to original sources

PubMed2006

Optimization of the artificial urinary sphincter: modelling and experimental validation.

The artificial urinary sphincter should be long enough to prevent strangulation effects of the urethral tissue and short enough to avoid the improper dissection of the surrounding tissue. To optimize the sphincter length, the empirical three-parameter urethra compression model is proposed based on the mechanical properties of the urethra: wall pressure, tissue response rim force and sphincter periphery length. In vitro studies using explanted animal or human urethras and different artificial sphincters demonstrate its applicability. The pressure of the sphincter to close the urethra is shown to be a linear function of the bladder pressure. The force to close the urethra depends on the sphincter length linearly. Human urethras display the same dependences as the urethras of pig, dog, sheep and calf. Quantitatively, however, sow urethras resemble best the human ones. For the human urethras, the mean wall pressure corresponds to (-12.6 +/- 0.9) cmH2O and (-8.7 +/- 1.1) cmH2O, the rim length to (3.0 +/- 0.3) mm and (5.1 +/- 0.3) mm and the rim force to (60 +/- 20) mN and (100 +/- 20) mN for urethra opening and closing, respectively. Assuming an intravesical pressure of 40 cmH2O, and an external pressure on the urethra of 60 cmH2O, the model leads to the optimized sphincter length of (17.3 +/- 3.8) mm.

Adult↗

PubMed2004

Effect of excimer laser beam delivery and beam shaping on corneal sphericity in photorefractive keratectomy.

PURPOSE: To evaluate the impact of beam delivery and beam shaping on corneal profiles after myopic excimer laser photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, Charité-Campus Virchow Hospital, Humboldt University of Berlin, Berlin, Germany. METHODS: Standard myopic 193 nm excimer laser PRK of -3.0 diopters (D) and -6.0 D was performed in porcine eyes using 2 commercially available broad-beam lasers with band-mask and fractal-mask beam shaping, 2 flying-spot lasers, and a scanning-slit laser. A silicone replica was obtained to preserve the corneal profile and was measured with a dynamic focusing topometry system. RESULTS: The scanning-slit and flying-spot lasers created uniform profiles comparable to those in an untreated control group. Both broad-beam lasers with band-mask and fractal-mask beam shaping created central islands and paracentral profile valleys of 15.10 microm and 17.00 microm maximum height after -3.0 D PRK and 26.45 microm and 24.31 microm after -6.0 D PRK. An anti-central-island program, which applied a series of laser pulses centrally to compensate for the central profile elevations, did not eliminate the islands. Stromal surface roughness increased with ablation depth and was significantly worse after scanning-slit ablation than after broad-beam ablation. CONCLUSIONS: Laser-induced deviations from the intended uniform corneal profiles were associated with broad-beam ablation and increased ablation depth and therefore lessened the predictability of the refractive outcomes. Scanning-slit and flying-spot systems produced predictably uniform corneal profiles.

Animals↗

PubMed2002

Non-destructive three-dimensional evaluation of a polymer sponge by micro-tomography using synchrotron radiation.

X-ray micro-tomography, a non-destructive technique is used to uncover the complex 3-D micro-architecture of a degradable polymer sponge designed for bone augmentation. The measurements performed at HASYLAB at DESY are based on a synchrotron radiation source resulting in a spatial resolution of about 5.4 microm. In the present communication we report the quantitative analysis of the porosity and of the pore architecture. First, we elucidate that synchrotron radiation at the photon energy of 9 keV has an appropriate cross section for this low-weight material. Modifications in sponge micro-architecture during measurement are not detected. Second, the treatment of the data, an amount of 2.5 Gbyte to generate binary data is described. We compare the 3-D with the 2-D analysis in a quantitative manner. The obtained values for the mean distance to material within the sponge calculated from 2-D and 3-D data of the whole tomogram differ significantly: 12.5 microm for 3-D and 17.6 microm for 2-D analysis. If the pores exhibit a spherical shape as frequently found, the derived mean pore diameter, however, is overestimated only by 6% in the 2-D image analysis with respect to the 3-D evaluation. This approach can be applied to different porous biomaterials and composites even in a hydrated state close to physiological conditions, where any surface preparation artifact is avoided.

Absorbable Implants↗