Experimental and numerical investigations of mechanical displacements in surface acoustic wave bounded beams.

The present paper studies experimentally and numerically the surface acoustic wave (SAW) field on a piezoelectric substrate generated by interdigital transducers (IDT). On the one hand, mechanical displacements produced by the SAW are measured with the help of a laser Doppler vibrometer. On the other hand, mechanical displacements are computed by the two-dimensional finite element method in frequency domain followed by the spatial Fourier transform. Combining these two steps of computations results in the intended two-dimensional distribution of mechanical displacements on the substrate surface. The comparison of experimental and numerical data obtained for a series of different IDTs reveals that it is possible to estimate the shape of the SAW beam and the absolute value of mechanical displacement amplitude using only the basic parameters of the IDT and its electrical admittance measured by a network analyzer.

The complexity of surface acoustic wave fields used for microfluidic applications.

Using surface acoustic waves (SAW) for the agitation and manipulation of fluids and immersed particles or cells in lab-on-a-chip systems has been state of the art for several years. Basic tasks comprise fluid mixing, atomization of liquids as well as sorting and separation (or trapping) of particles and cells, e.g. in so-called acoustic tweezers. Even though the fundamental principles governing SAW excitation and propagation on anisotropic, piezoelectric substrates are well-investigated, the complexity of wave field effects including SAW diffraction, refraction and interference cannot be comprehensively simulated at this point of time with sufficient accuracy. However, the design of microfluidic actuators relies on a profound knowledge of SAW propagation, including superposition of multiple SAWs, to achieve the predestined functionality of the devices. Here, we present extensive experimental results of high-resolution analysis of the lateral distribution of the complex displacement amplitude, i.e. the wave field, alongside with the electrical S-parameters of the generating transducers. These measurements were carried out and are compared in setups utilizing travelling SAW (tSAW) excited by single interdigital transducer (IDT), standing SAW generated between two IDTs (1DsSAW, 1D acoustic tweezers) and between two pairs of IDTs (2DsSAW, 2D acoustic tweezers) with different angular alignment in respect to pure Rayleigh mode propagation directions and other practically relevant orientations. For these basic configurations, typically used to drive SAW-based microfluidics, the influence of common SAW phenomena including beam steering, coupling coefficient dispersion and diffraction on the resultant wave field is investigated. The results show how tailoring of the acoustic conditions, based on profound knowledge of the physical effects, can be achieved to finally realize a desired behavior of a SAW-based microacoustic-fluidic system.

Converse Magnetoelectric Composite Resonator for Sensing Small Magnetic Fields.

Magnetoelectric (ME) thin film composites consisting of sputtered piezoelectric (PE) and magnetostrictive (MS) layers enable for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities a magnetic bias field is necessary to operate at the maximum piezomagnetic coefficient of the MS phase, harnessing mechanical resonances further enhances this direct ME effect size. Despite being able to detect very small AC field amplitudes, exploiting mechanical resonances directly, implies a limitation to available signal bandwidth along with the inherent inability to detect DC or very low frequency magnetic fields. The presented work demonstrates converse ME modulation of thin film Si cantilever composites of mesoscopic dimensions (25 mm × 2.45 mm × 0.35 mm), employing piezoelectric AlN and magnetostrictive FeCoSiB films of 2 µm thickness each. A high frequency mechanical resonance at about 515 kHz leads to strong induced voltages in a surrounding pickup coil with matched self-resonance, leading to field sensitivities up to 64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as well as about 70 pT/Hz1/2 at 10 Hz, without the need for a magnetic bias field, pave the way towards biomagnetic applications.

Coronary-like revascularization for atherosclerotic renal artery stenosis--results in 181 consecutive patients.

AIMS: The aim of this study was to document the early outcome of coronary-like revascularization for atherosclerotic renal artery stenosis (ARAS). METHODS AND RESULTS: A total of 181 consecutive patient, 102 men, mean age 66.1 (+/- 9.2) years and 79 females, mean age 68.4 (+/- 9.2) years and 198 lesions were treated between February 1999 and May 2004 for ARAS and retrospectively analyzed. At least one major cardiovascular risk factor was present in 179 (98.9%) patients. Pre-dilatation ARAS was 81.3+/-9.6%, 27 ARAS were 50-70% and no ARAS was <50%. 135 (68.2%) of the ARAS lesions were ostial and 63 (31.8%) were non-ostial. In 17 (9.4%) patients bilateral ARAS were present. Technical success defined as residual stenosis < or =30% was achieved in 178 (98.3%) of patients and 195 (98.5%) of lesions. In one patient (0.5%) the target ARAS could not be crossed, in two (1.1%) patients residual stenosis was >30%. No major adverse cardiac or cerebral effects were observed. In 3.9% of patients minor local complications of the access site occurred; 4 (2.2%) inguinal hematoma, 3 (1.7%) pseudoaneurysm were documented. Serum creatinine concentrations and systolic and diastolic blood pressure before and after the intervention were not statistically different. CONCLUSIONS: Coronary-like approach to ARAS revascularization is technically feasible and associated with a very low complication rate.

Carotid-artery stenting in a high-risk patient population--single centre, single operator results.

AIMS: The aim of this study was to assess the outcome of carotid-artery stenting (CAS) in high-risk patients in routine clinical settings while excluding the impact of multiple operators and the learning curve of individual operators on the outcome, and to determine the impact of individual risk factors, including vascular multimorbidity, on the outcome. METHODS AND RESULTS: A total of 143 consecutive patients, 100 (69.9%) males and 43 (30.1%) females, mean age 68.7+/-8 years treated between February 1999 and May 2004 in the Heart Centre Coswig by a single operator for a symptomatic (n=37) and asymptomatic (n=106) on average greater than 70% (82.3+/-10.7%) or 80% (85.0+/-9.1%) NASCET carotid-artery stenosis, respectively, were studied. At least one NASCET exclusion criteria was present in 140 patients (97.9%), and vascular multimorbidity was present in 94 (65.7%) patients. In 28 (19.6%) patients there was a complete occlusion of the contralateral internal carotid artery and in 12 (8.4%) patients the procedure was performed prior to emergency coronary bypass surgery. In all, 47 (32.9%) procedures were performed without and 96 (67.1%) were performed with thromboembolic protection. Technical success was achieved in all patients. Combined neurological complications, TIA, PRIND and stroke, occurred in 5 (3.5%) patients, of which 3 (2.1%) were PRIND and 2 (1.4%) were strokes. The neurological complications were more frequent and more severe in symptomatic patients compared to asymptomatic patients (PRIND 2.7% vs 1.9%; stroke 0% vs 5.4%). In patients in whom thromboembolic protection was used, the rate of neurological complications was lower compared to those without protection (PRIND 1.0% vs 4.3%; stroke 1.0% vs. 2.1%). There was no death related to the procedure. Neurological complications were more frequent and more severe in patients with vascular multimorbidity compared to those with an isolated carotid-artery stenosis (4.2% vs 2.0%). The rate of neurological complications was similar in type II diabetics and nondiabetics (2.9% vs 4.1%). In 4.2%, minor complications related to the arterial puncture site were observed (3.5% hematoma not requiring blood transfusion, 0.7% pseudoaneurysm). At follow-up after a minimum of 6 months, 9 (6.3%) patients had died, the majority of whom had died of cardiovascular disease (3.5%). CONCLUSIONS: CAS can be performed with an acceptable risk in high-risk patients in routine clinical settings when it is performed by an experienced operator. The use of thromboembolic protection devices reduces the risk of neurological complications. Presence of vascular multimorbidity, but not diabetes, appears to increase the risk of all causes and of neurological complications.

Nonviral monocyte chemoattractant protein-1 gene transfer improves arteriogenesis after femoral artery occlusion.

Local infusion of recombinant monocyte chemoattractant protein-1 (MCP-1) has been shown to enhance collateral artery formation in rabbit and pig hindlimb models. Owing to clinical disadvantages of protein infusion, a nonviral, liposome-based MCP-1 gene transfer was developed. Collateralization in a porcine hindlimb model served to provide a proof-of-principle for the functional benefit of MCP-1 overexpression. Development of arterial conductance as a measure of functionally relevant collateralization was evaluated in occluded as well as untreated hindlimbs in each animal. At the time of occlusion, MCP-1 and control DNA/DC-30 lipoplexes were transferred to femoral arteries of Goettingen minipigs (two therapeutic MCP-1 groups: 2 and 4 microg and one control group), using the Infiltrator local drug-delivery device. At 2 weeks following occlusion, collateralization was determined as changes in peripheral haemodynamic conductance, peripheral over aortic blood pressure ratio and angiographically visible morphology of the peripheral vessel tree. Nonviral MCP-1 gene transfer significantly improved peripheral conductance (control 11.69+/-2.78%, 2 microg 23.81+/-2.81%, P<0.05 and 4 microg 23.36+/-3.1%, P<0.05; n=12 per group) as well as the ratio of peripheral over aortic blood pressure (control 0.64+/-0.03%, 2 microg 0.75+/-0.02%, P<0.05 and 4 mug 0.75+/-0.02%, P<0.05; n=12 per group) when compared to the untreated controls 2 weeks after occlusion. Thus, it could be demonstrated for the first time that in situ overexpression of MCP-1 following local nonviral gene transfer is a potential approach to improve peripheral collateralization.

[Follow-up during the 1st postoperative year after endovascular exclusion of abdominal aortic aneurysms]. / Verlaufsbeobachtung im ersten postoperativen Jahr nach endovaskulärer Ausschaltung von Bauchaortenaneurysmata (BAA).

Between January 1995 and December 1996 15 patients, 13 male and 2 female, underwent a transfemoral repair of an infrarenal aortic aneurysm with endovascular stent grafts. In one case the indication was an anastomotic aneurysm after bypass grafting. Stent-systems (MIALHE) were used in 9 cases as a bifurcation graft and in 6 cases as a tube graft. The patients' mean age was 70.2 years. The follow up period ranged from 3 months to one year. The implantation of the stent grafts was primarily successful in all cases. In 6 patients procedure related complications occurred. One postoperative death occurred due to multiple organ failure. In one case a persisting leakage at the proximal end of the stent graft led to a rupture of the aneurysm. Another patient developed gangrene of the colon. Both had to be corrected surgically. There were 3 persisting leakages at the distal end of the stent graft. They were treated with the implantation of covered stents, percutaneously and transfemorally twice and conservatively once. In the follow up, all stent grafts were patent. There were 4 complications in the 6 months follow up: one covered rupture of the common iliac artery at the distal end of the stent graft and one distal leakage at the common iliac artery as well as 2 leakages at the stent graft junction, caused by commencing desintegration were repaired by interventional procedures.