Biomedical subjects

R Blindt

Publications and source records attributed to R Blindt.

5 recordsLinked to original sources

PubMed2005

A study on the primary and secondary nucleation of ice by power ultrasound.

Several different investigations have been carried out to study the primary and secondary nucleation of ice by sonocrystallisation. Firstly, the primary nucleation of discrete ice crystals in a supercooled sucrose solution has been observed. For increasing concentrations of sucrose solutions from 0 to 45 wt%, the nucleation temperature consistently occurs at a higher nucleation temperature in the presence of ultrasound. The nucleation temperature also increases as the power output and duty cycle of a commercial ultrasonic horn are increased. Snap shot images of the bubble clouds obtained from the ultrasonic horn also show that the number of bubbles appears to increase as the ultrasonic output is increased. This suggests that the nucleation of ice is related to the power output and number of cavitation bubbles. The effect of a single bubble on the sonocrystallisation of ice is discussed. High-speed movies (1120 fps) have shown that the crystallisation appears to occur in the immediate vicinity of the single bubble. In most cases, many crystals are observed and it is not known whether a single ice crystal is being fragmented by the bubble or whether many crystals are being initiated. The bubble appears to undergo a dancing regime, frequently splitting and rejoining and also emitting some small microbubbles. A study on the secondary nucleation of ice in sucrose solutions has been carried out using a unique ultrasonic cold stage device. Images taken using a microscope system show that the pre-existing ice dendrite crystals can be broken up into smaller fragments by an ultrasonic field. Cavitation bubbles appear to be important during the fragmentation process, possibly melting any ice crystals in their path. Flow patterns around cavitation bubbles have also been observed, and these may be responsible for the fragmentation of ice crystals.

Crystallization↗

PubMed2004

A high power ultrasonic array based test cell.

This paper describes the use of finite element (FE) analysis as a tool in the design process for laboratory based ultrasonic test cells. The system was designed to incorporate an array of ultrasonic transducers to provide a pressure focus in the centre of the cell and importantly, operate both above and below the cavitation threshold of the load medium. Furthermore, the cell incorporates a coolant jacket to accommodate temperature control of the load material associated with the process. A 2D FE model corresponding to a slice through the operational plane of the cell was developed and used to investigate the influence of cell wall material and thickness, transducer configuration, rotation of a metallic stirrer blade and heat transfer fluid on the cell acoustic response. Importantly, experimentally measured pressure field maps demonstrate good correlation with the FE predicted fields. A final manufactured test cell is shown to produce a highly focussed region of cavitation. Finally, the importance in accurately representing the acoustic properties of the constituent materials used in such FE models is demonstrated through an illustrated example.

Journal Article↗

PubMed2002

Rotational atherectomy for the treatment of in-stent restenosis.

Restenosis after coronary stent implantation remains the major limitation of this treatment modality. At present, re-dilatation is considered the therapeutic option of choice for focal lesions, however, long restenotic lesions (>10 mm) do not respond favourably. Despite the emerging concept of intracoronary radiation, encouraging acute procedural results are also reported for different debulking techniques (Excimer laser angioplasty, directional coronary atherectomy, and rotational atherectomy, or rotablation). Rotablation has been studied most extensively with acute and long- term results published in a total of more than 850 patients. Experimental and first clinical data indicate favourable results for the rotablator as compared to balloon angioplasty alone for the treatment of in-stent restenosis. Data from the first 2 randomized clinical trials (ROSTER-, and ARTIST-trial) have now been published with conflicting results: The european multicenter ARTIST-trial including 300 patients could not prove a benefit for the rotablator as compared to re-dilatation in patients with diffuse stent restenosis. On the contrary, the monocenter ROSTER-trial, which has been presented as an abstract until today, suggests a clinical benefit of patients treated by the rotablator if they were studied with intracoronary ultrasound prior to randomization. Currently, rotablation for the treatment of restenosis cannot be considered as the first line treatment modality in patients with in-stent restenosis. As a result of unsatisfying angiographic and clinical long-term results by the use of a variety of treatment modalities in diffuse stent restenosis, prevention of this iatrogenic entity has become mandatory.

Aged↗

PubMed2000

Abciximab inhibits the migration and invasion potential of human coronary artery smooth muscle cells.

In the EPIC trial, high-risk patients received the integrin receptor antagonist abciximab v placebo during and for 12 h following percutaneous coronary intervention with a significant 23% decrease of repeat revascularisation at 6 months. However, EPILOG and CAPTURE trials could not confirm these promising long-term results. Recently presented data from the EPISTENT trial suggested a beneficial effect of abciximab on restenosis in patients with diabetes. Based on these divergent results the aim of this study was to test whether alpha v beta 3 receptor blockade by abciximab could cause inhibition of human coronary smooth muscle cell (hcSMC) proliferation, migration, and invasion which represent crucial steps during restenosis development. In contrast to quiescent hcSMCs, proliferating cells were capable to migrate towards chemoattractive stimuli and even capable to invade through a basement membrane equivalent. Abciximab and LM609, an alpha v beta 3 specific inhibiting antibody, caused only a modest dose-dependent inhibition of hcSMC proliferation. On the contrary, the chemotactic and invasive potential of hcSMCs was significantly inhibited by abciximab administration 24 h prior to and during migration. (IC(50)=33.0 microg/ml for chemotaxis and IC(50)=0.5 microg/ml for invasion). For LM609 similar results were obtained. Administration of the drugs just during migration without pretreatment inhibited migration equally but invasion to a lower extent (abciximab: IC(50)=32.6 microg/ml for chemotaxis and IC(50)=44.9 microg/ml for invasion; LM609 IC(50)=3.1 microg/ml for chemotaxis and IC(50)=2.0 microg/ml for invasion). The attachment to the extracellular matrix proteins collagen I, collagen IV, laminin and vitronectin was not influenced. Pretreatment for 24 h with abciximab or LM609 did not cause a downregulation of the alpha v beta 3-integrin receptor. The results of this study indicate that the alpha v beta 3 antagonist abciximab is a potent inhibitor of hcSMC migration and invasion which could explain the observed lower reintervention rate after PTCA and stent implantation.

Abciximab↗

PubMed1999

Development of a new biodegradable intravascular polymer stent with simultaneous incorporation of bioactive substances.

OBJECTIVE: Due to the thrombogenicity and permanent implant nature of metallic stents, bioresorable synthetic polymers have been proposed for stents and local drug delivery systems. Bioresorbable polyesters like poly(D,L-lactide) demonstrated excellent biocompatibility in various tissues. This paper describes a novel method for the molding of these polymers. The specific CESP-process (Controlled Expansion of Saturated Polymers) is characterised by the use of the plasticizer carbon dioxide and allows the incorporation of bioactive substances at physiologic temperatures into the polymer bulk and the production of complex designed implants. METHODS: The CESP-process is characterised by the exposure of an amorphous polymer to an inert gas at high pressure with a significant lower glass transition point. The plasticizing effect makes it possible to process polylactides at a temperature close to room temperature. The low process temperature constitutes a key advantage for thermally sensitive polymers and allows the incorporation of thermally sensitive pharmaceutical additives. To obtain some preliminary information on the biocompatibility, in vitro cell toxicity testing as well as drug release assessment was performed. RESULTS: Different polymer sheets were produced using the CESP-process. Cytotoxicity was not observed in any molded polymer material. According to the mechanical and biocompatibility results Poly(D,L-lactide) (P-DL-LA) was investigated in the CESP-process. Finite element analysis was used to test the possible geometry of an adequate stent. A helical design was chosen and a stent-prototype was produced using the CESP-process. Peroxidase activity as an incorporated marker enzyme could be measured over 6 weeks. Different drug release profiles were obtained due to various pore sizes of the polymer. CONCLUSIONS: The new CESP-process can be used to process biodegradable polymers and to mold different stent geometries without inducing cytotoxic effects to the material. Furthermore, this procedure permits the simultaneous incorporation of bioactive substances during the molding process. Drug release kinetics can be regulated by different pore sizes of the material.

Absorbable Implants↗