Thomas Reske - Academia.edu (original) (raw)

Papers by Thomas Reske

Translational vision science & technology, 2015

A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and char... more A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and characterized for safety and effectiveness after implantation into the suprachoroidal space (SCS) of rabbit eyes. Thin films of two different polymers, Poly(3-hydroxybutyrate) (P(3HB)) and Poly(4-hydroxybutyrate) (P(4HB)), containing the drugs mitomycin C (MitC) or paclitaxel (PTX) were attached to silicone-tubes to create LDD devices. The release kinetics of these drugs were explored in vitro using high performance liquid chromatography (HPLC). Twenty-four New Zealand white rabbits, randomly divided into eight groups, were implanted with different kinds of microstents into SCS. The intraocular pressure (IOP) was monitored noninvasively. After 6 weeks, rabbits were sacrificed and enucleated eyes were used for anterior segment optical coherence tomography (OCT), micro magnetic resonance imaging (MRI), and histology. In vitro, faster drug release from both polymers was observed for MitC compa...

ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has ... more ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has contributed to the clinical success of this treatment option, the mechanism of drug release from steroid-eluting pacing leads is not completely understood. Besides, drug concentrations of steroids released into the heart-tissue remain unclear. Therefore, three different dissolution test methods were examined: a non-standardized (reagent tube), a compendial USP (paddle) and a hydrogel method. The experimental results indicate that dissolution from pacing leads is governed by a diffusion-controlled mechanism and occurs over a prolonged time. Furthermore, the integration of a hydrogel compartment seemed to have an impact on drug release leading to a decrease in release rate. Nevertheless, the experimental results emphasize different experimental parameters in dissolution testing may have a distinct influence on drug dissolution.

Journal of Materials Science: Materials in Medicine, 2013

Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an a... more Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an abluminally focussed release of the potent anti-proliferative drug sirolimus and a luminally focussed release of atorvastatin with stabilizing effect on atherosclerotic deposits and stimulating impact on endothelial function, both from biodegradable poly(L-lactide)-based stent coatings. With this concept we aim at simultaneous inhibition of in-stent restenosis as a result of disproportionally increased smooth muscle cell proliferation and migration as well as thrombosis due to failed or incomplete endothelialisation. The especially adapted spray-coating processes allowed the formation of smooth form-fit polymer coatings at the abluminal and luminal side with 70% respectively 90% of the drug/polymer solution being deposited at the intended stent surface. The impacts of tempering, sterilization, and layer composition on drug release are thoroughly discussed making use of a semi-empirical model. While tempering at 80 °C seems to be necessary for the achievement of adequate and sustained drug release, the coating sequence for DDES should be rather abluminal-luminal than luminal-abluminal, as reduction of the amount of sirolimus eluted luminally could then potentially minimize the provocation of endothelial dysfunction. In vitro proliferation and viability assays with smooth muscle and endothelial cells underline the high potential of the developed DDES.

Current Eye Research, 2013

For developing injectable lenses the retention properties of the capsular bag are important. Ther... more For developing injectable lenses the retention properties of the capsular bag are important. Therefore the apparent permeability coefficients of sodium fluorescein and fluorescent dextrans of different sizes were determined for the human anterior lens capsule to calculate a molecular weight cutoff from these data. In addition, permeability coefficients of drugs helpful for the suppression of secondary cataract were determined. Capsulorhexis specimens were fixed in a specially designed two compartment diffusion chamber to investigate the permeation of sodium fluorescein and fluorescent dextrans of different sizes (10, 40, 70 and 150 kDa) for 24 h (n ≥ 3) and of the antiproliferative drugs actinomycin D and methotrexate for 0.5, 24, 48 and 72 h (n ≥ 3). The molecular weight cutoff of the anterior lens capsule was found to be 166 ± 82 kDa. After 0.5 h, no passage of actinomycin D and methotrexate was detectable through the lens capsule. The apparent permeability coefficients for actinomycin D and methotrexate were calculated to 0.71 ± 0.02 µm/s and to 0.80 ± 0.13 µm/s, respectively. The capsular bag retains fluorescent dextrans with a molecular weight of >166 kDa. Hence, prepolymers are required to polymerize rapidly to be retained inside of the capsular bag. In addition, low-molecular substances intended as antiproliferative drugs for secondary cataract prevention should be applied within a time frame of five minutes in such a way that cells adjacent to the capsular bag will not be damaged.

Biomedizinische Technik/Biomedical Engineering, 2000

Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the i... more Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the interventional treatment of coronary artery disease. This new technology also holds potential for application in peripheral vascular settings. Our study reports on the development of a sirolimus-(SIR) eluting absorbable polymer stent made from a blend of poly(l-lactide) and poly(4-hydroxybutyrate) (PLLA/ P4HB) for peripheral vascular intervention. Stent prototypes were laser-cut from PLLA/P4HB tubes (I.D. = 2.2 mm, t = 250 µm), spray-coated with different PLLA/P4HB/SIR solutions, and bench-tested to determine expansion properties, fatigue, trackability and in vitro drug release kinetics. The stent prototypes were expanded with a 5.0 × 20 mm balloon catheter, and exhibited a recoil of 3.6% upon balloon deflation. Stent collapse pressure of 0.4 bar (300 mm Hg) was measured under external pressure load. Sustained scaffolding properties were observed in vitro over 14 weeks of radial fatigue loading (50 ± 25 mm Hg at 1.2 Hz). Trackability was demonstrated in bench tests with an 8 French contralateral introducer sheath. SIR release kinetics were adjusted over a broad range by varying the PLLA/P4HB ratio of the coating matrix. The newly developed absorbable SIR-eluting PLLA/P4HB stent successfully fulfilled the requirements for peripheral vascular intervention under in vitro conditions.

Talanta, 2008

This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) pro... more This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) products labeled with electrochemically active osmium tetroxide bipyridine can be detected voltammetrically by hybridization with probe strands immobilized on gold electrodes. These electroactive ssDNA targets have been obtained by means of Lambda Exonuclease treatment of the double-stranded PCR products followed by hybridization of the remaining single strands with short protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of these osmium labels have been obtained only upon hybridization with the immobilized probe strands. An optimal 50 • C hybridization temperature has been found with a saturation of the probe layer at 30 min hybridization time and 7.5 nmol/l target concentration. The blank capture probe layer alone did not yield any signal. Unprotected strands produced almost no interference. Such double-selective switch-on electrochemical hybridization assays hold great promise for the specific detection of PCR products.

Analytical Chemistry, Apr 1, 2007

Mikrochimica Acta, Aug 4, 2009

ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent ... more ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent label for biosensor applications regarding nucleic acids and protein detection. Labeling can easily be performed in the laboratory. Until now, almost only DNA species have been investigated using this label. Thymine (which occurs exclusively in DNA) is known to react much faster than cytosine and uracil. In order to explore the possibilities to modify and detect also RNA species in a timely fashion, we have investigated the kinetics of reactions of osmium tetroxide bipyridine with the pyrimidine bases in the micromolar concentration range at different temperatures by means of spectrophotometry. Results were confirmed using voltammetric detection for the determination of labeled oligonucleotides. The modification reaction can be easily completed at room temperature within 7h, even in case of cytosine and uracil. At 60°C, 3h are sufficient for complete modification of all pyrimidine bases that are found in natural nucleic acids. These findings will be important for future biosensor applications with RNA species as target molecules.

European Journal of Pharmaceutics and Biopharmaceutics, 2015

Lately, drug-coated balloons have been introduced in interventional cardiology as an approach to ... more Lately, drug-coated balloons have been introduced in interventional cardiology as an approach to treat occluded blood vessel. They were developed for the rapid transfer of antiproliferative drugs during the angioplasty procedure in stenosed vessels with the intent to reduce the risk of restenosis. In this study five different paclitaxel (PTX) balloon coatings were tested in vitro in order to examine how solvents and additives influence coating stability and drug transfer rates. PTX-coated balloons were advanced through a guiding catheter and a simulated coronary artery pathway under perfusion and were then inflated in a hydrogel acceptor compartment. The fractions transferred to the gel, remaining on the balloon and the PTX lost in the simulated coronary pathway were then analysed. The results obtained suggest that the solvent used for the coating process strongly influences the surface structure and the stability of the coating. Ethanol/water and acetone based PTX coatings showed the lowest drug transfer rates to the simulated vessel wall (both <1%) due to their high drug losses during the prior passage through the coronary artery model (more than 95%). Balloons coated with PTX from ethyl acetate-solutions showed smaller drug loss (83%±9%), but most of the remaining PTX was not transferred (mean balloon residue approximately 15%). Beside the solvent, especially the use of additives seemed to have a great impact on transfer properties. The balloon pre-treatment with a crosslinked polyvinylpyrrolidone (PVP) film was able to increase the PTX transfer rate from less than 1% (without PVP) to approximately 6%. The best results in this study were obtained for balloon coatings with commercially available SeQuent© Please balloons containing the contrast agent iopromide. For this formulation drug transfer rates of approximately 17% were determined. Fluorescence microscopic imaging could visualize the particulate transfer of labelled PTX from the balloon surface during dilatation. The findings of this study underline the importance of drug adhesion and coating stability for the efficiency of PTX transfer.

Translational vision science & technology, 2015

A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and char... more A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and characterized for safety and effectiveness after implantation into the suprachoroidal space (SCS) of rabbit eyes. Thin films of two different polymers, Poly(3-hydroxybutyrate) (P(3HB)) and Poly(4-hydroxybutyrate) (P(4HB)), containing the drugs mitomycin C (MitC) or paclitaxel (PTX) were attached to silicone-tubes to create LDD devices. The release kinetics of these drugs were explored in vitro using high performance liquid chromatography (HPLC). Twenty-four New Zealand white rabbits, randomly divided into eight groups, were implanted with different kinds of microstents into SCS. The intraocular pressure (IOP) was monitored noninvasively. After 6 weeks, rabbits were sacrificed and enucleated eyes were used for anterior segment optical coherence tomography (OCT), micro magnetic resonance imaging (MRI), and histology. In vitro, faster drug release from both polymers was observed for MitC compa...

European Journal of Pharmaceutics and Biopharmaceutics, 2015

In this study drug release from the CYPHER™ stent, the gold standard in drug-eluting stent therap... more In this study drug release from the CYPHER™ stent, the gold standard in drug-eluting stent therapy until the end of its marketing in 2011/2012, was systematically evaluated using different in vitro release tests. The test systems included incubations setups, the reciprocating holder apparatus (USP7), the flow-through cell apparatus (USP4) and the vessel-simulating flow-through cell (vFTC) specifically designed for stent testing. The results obtained show a large variability regarding the fractions released into the media after 7d ranging from 38.6%±4.5% to 74.6%±1.2%. The lowest fraction released was observed in the vFTC and the highest in an incubation setup with frequently changed media of a volume of 2mL. Differences were even observed when using fairly similar and simple incubations setups with mere changes of the media volume, under maintenance of sink conditions, and of the vessel geometry. From these data it can be concluded, that in vitro release even from a slow releasing drug-eluting stent is greatly influenced by the experimental conditions and care must be taken when choosing a suitable setup. Comparison of the obtained in vitro release profiles to published in vivo data did not result in a distinct superiority of any of the tested methods regarding the predictability for the situation in vivo due to large differences in the reported in vivo data. However, this comparison yielded that the release observed in vitro using the 2mL incubation setup and the reciprocating holder apparatus may be faster than the reported in vivo release. The results of this study also emphasize the necessity to use highly standardized release tests when comparisons between results from different experiments or even different labs are to be performed. In this context, the compendial methods are most likely offering the highest degree of standardization.

The invention relates to a method of labelling and analysing nucleic acids. More specifically, th... more The invention relates to a method of labelling and analysing nucleic acids. More specifically, the invention relates to a method of analysing nucleic acids, which comprises contacting the nucleic acids to be detected, which are in the form of single-stranded nucleic acid strands partially (i.e. over a part of the total length of the nucleic acid strands) hybridized with protective strands, with substances which specifically react with nucleobases of the single-stranded sections of the nucleic acid strands, and which are capable of subsequently participating in a reversible redox reaction in electroanalytical processes known to the skilled worker. 1. A method of detecting nucleic acid strands comprising labelling nucleic acid strands with redox markers and detecting the labeled strands via electrochemical detection of hybridization events, wherein a) single-stranded nucleic acid strands (target strands) are hybridized with one or more nucleic acid strands (protective strands A), wher...

ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has ... more ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has contributed to the clinical success of this treatment option, the mechanism of drug release from steroid-eluting pacing leads is not completely understood. Besides, drug concentrations of steroids released into the heart-tissue remain unclear. Therefore, three different dissolution test methods were examined: a non-standardized (reagent tube), a compendial USP (paddle) and a hydrogel method. The experimental results indicate that dissolution from pacing leads is governed by a diffusion-controlled mechanism and occurs over a prolonged time. Furthermore, the integration of a hydrogel compartment seemed to have an impact on drug release leading to a decrease in release rate. Nevertheless, the experimental results emphasize different experimental parameters in dissolution testing may have a distinct influence on drug dissolution.

Talanta, 2007

This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) pro... more This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) products labeled with electrochemically active osmium tetroxide bipyridine can be detected voltammetrically by hybridization with probe strands immobilized on gold electrodes. These electroactive ssDNA targets have been obtained by means of Lambda Exonuclease treatment of the double-stranded PCR products followed by hybridization of the remaining single strands with short protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of these osmium labels have been obtained only upon hybridization with the immobilized probe strands. An optimal 50 • C hybridization temperature has been found with a saturation of the probe layer at 30 min hybridization time and 7.5 nmol/l target concentration. The blank capture probe layer alone did not yield any signal. Unprotected strands produced almost no interference. Such double-selective switch-on electrochemical hybridization assays hold great promise for the specific detection of PCR products.

Microchimica Acta, 2009

ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent ... more ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent label for biosensor applications regarding nucleic acids and protein detection. Labeling can easily be performed in the laboratory. Until now, almost only DNA species have been investigated using this label. Thymine (which occurs exclusively in DNA) is known to react much faster than cytosine and uracil. In order to explore the possibilities to modify and detect also RNA species in a timely fashion, we have investigated the kinetics of reactions of osmium tetroxide bipyridine with the pyrimidine bases in the micromolar concentration range at different temperatures by means of spectrophotometry. Results were confirmed using voltammetric detection for the determination of labeled oligonucleotides. The modification reaction can be easily completed at room temperature within 7h, even in case of cytosine and uracil. At 60°C, 3h are sufficient for complete modification of all pyrimidine bases that are found in natural nucleic acids. These findings will be important for future biosensor applications with RNA species as target molecules.

Journal of Materials Science: Materials in Medicine, 2013

Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an a... more Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an abluminally focussed release of the potent anti-proliferative drug sirolimus and a luminally focussed release of atorvastatin with stabilizing effect on atherosclerotic deposits and stimulating impact on endothelial function, both from biodegradable poly(L-lactide)-based stent coatings. With this concept we aim at simultaneous inhibition of in-stent restenosis as a result of disproportionally increased smooth muscle cell proliferation and migration as well as thrombosis due to failed or incomplete endothelialisation. The especially adapted spray-coating processes allowed the formation of smooth form-fit polymer coatings at the abluminal and luminal side with 70% respectively 90% of the drug/polymer solution being deposited at the intended stent surface. The impacts of tempering, sterilization, and layer composition on drug release are thoroughly discussed making use of a semi-empirical model. While tempering at 80 °C seems to be necessary for the achievement of adequate and sustained drug release, the coating sequence for DDES should be rather abluminal-luminal than luminal-abluminal, as reduction of the amount of sirolimus eluted luminally could then potentially minimize the provocation of endothelial dysfunction. In vitro proliferation and viability assays with smooth muscle and endothelial cells underline the high potential of the developed DDES.

Electroanalysis, 2009

Single stranded DNA-targets from asymmetric polymerase chain reaction (PCR) of a sequence of the ... more Single stranded DNA-targets from asymmetric polymerase chain reaction (PCR) of a sequence of the gram positive, spore forming bacterium Clostridium acetobutylicum were detected by square-wave voltammetry after labeling with osmium tetroxide bipyridine and hybridization with DNA capture probes immobilized on gold electrodes. The asymmetric PCR, performed with a 10-fold excess of the forward-primer, was used without any further purification for hybridization with protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of 20 nmol/L targets were significantly higher at 50 8C compared with 23 8C hybridization temperature. A fully noncomplementary protective strand yielded thoroughly modified targets unable for further hybridization. Coupling this with thermal discrimination opens new opportunities for sequence specific DNA detection.

Electroanalysis, 2007

... The data points and their error bars represent average values of regarding measurements of 3 ... more ... The data points and their error bars represent average values of regarding measurements of 3 repetitive series (each series at a newly prepared SAM) and the regarding standard deviation, respectively. ... [36] T. Zerihun, P. Gründler, J. Electroanal. Chem. 1996, 415, 85. ...

Current Eye Research, 2013

For developing injectable lenses the retention properties of the capsular bag are important. Ther... more For developing injectable lenses the retention properties of the capsular bag are important. Therefore the apparent permeability coefficients of sodium fluorescein and fluorescent dextrans of different sizes were determined for the human anterior lens capsule to calculate a molecular weight cutoff from these data. In addition, permeability coefficients of drugs helpful for the suppression of secondary cataract were determined. Capsulorhexis specimens were fixed in a specially designed two compartment diffusion chamber to investigate the permeation of sodium fluorescein and fluorescent dextrans of different sizes (10, 40, 70 and 150 kDa) for 24 h (n ≥ 3) and of the antiproliferative drugs actinomycin D and methotrexate for 0.5, 24, 48 and 72 h (n ≥ 3). The molecular weight cutoff of the anterior lens capsule was found to be 166 ± 82 kDa. After 0.5 h, no passage of actinomycin D and methotrexate was detectable through the lens capsule. The apparent permeability coefficients for actinomycin D and methotrexate were calculated to 0.71 ± 0.02 µm/s and to 0.80 ± 0.13 µm/s, respectively. The capsular bag retains fluorescent dextrans with a molecular weight of >166 kDa. Hence, prepolymers are required to polymerize rapidly to be retained inside of the capsular bag. In addition, low-molecular substances intended as antiproliferative drugs for secondary cataract prevention should be applied within a time frame of five minutes in such a way that cells adjacent to the capsular bag will not be damaged.

Translational vision science & technology, 2015

A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and char... more A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and characterized for safety and effectiveness after implantation into the suprachoroidal space (SCS) of rabbit eyes. Thin films of two different polymers, Poly(3-hydroxybutyrate) (P(3HB)) and Poly(4-hydroxybutyrate) (P(4HB)), containing the drugs mitomycin C (MitC) or paclitaxel (PTX) were attached to silicone-tubes to create LDD devices. The release kinetics of these drugs were explored in vitro using high performance liquid chromatography (HPLC). Twenty-four New Zealand white rabbits, randomly divided into eight groups, were implanted with different kinds of microstents into SCS. The intraocular pressure (IOP) was monitored noninvasively. After 6 weeks, rabbits were sacrificed and enucleated eyes were used for anterior segment optical coherence tomography (OCT), micro magnetic resonance imaging (MRI), and histology. In vitro, faster drug release from both polymers was observed for MitC compa...

ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has ... more ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has contributed to the clinical success of this treatment option, the mechanism of drug release from steroid-eluting pacing leads is not completely understood. Besides, drug concentrations of steroids released into the heart-tissue remain unclear. Therefore, three different dissolution test methods were examined: a non-standardized (reagent tube), a compendial USP (paddle) and a hydrogel method. The experimental results indicate that dissolution from pacing leads is governed by a diffusion-controlled mechanism and occurs over a prolonged time. Furthermore, the integration of a hydrogel compartment seemed to have an impact on drug release leading to a decrease in release rate. Nevertheless, the experimental results emphasize different experimental parameters in dissolution testing may have a distinct influence on drug dissolution.

Journal of Materials Science: Materials in Medicine, 2013

Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an a... more Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an abluminally focussed release of the potent anti-proliferative drug sirolimus and a luminally focussed release of atorvastatin with stabilizing effect on atherosclerotic deposits and stimulating impact on endothelial function, both from biodegradable poly(L-lactide)-based stent coatings. With this concept we aim at simultaneous inhibition of in-stent restenosis as a result of disproportionally increased smooth muscle cell proliferation and migration as well as thrombosis due to failed or incomplete endothelialisation. The especially adapted spray-coating processes allowed the formation of smooth form-fit polymer coatings at the abluminal and luminal side with 70% respectively 90% of the drug/polymer solution being deposited at the intended stent surface. The impacts of tempering, sterilization, and layer composition on drug release are thoroughly discussed making use of a semi-empirical model. While tempering at 80 °C seems to be necessary for the achievement of adequate and sustained drug release, the coating sequence for DDES should be rather abluminal-luminal than luminal-abluminal, as reduction of the amount of sirolimus eluted luminally could then potentially minimize the provocation of endothelial dysfunction. In vitro proliferation and viability assays with smooth muscle and endothelial cells underline the high potential of the developed DDES.

Current Eye Research, 2013

For developing injectable lenses the retention properties of the capsular bag are important. Ther... more For developing injectable lenses the retention properties of the capsular bag are important. Therefore the apparent permeability coefficients of sodium fluorescein and fluorescent dextrans of different sizes were determined for the human anterior lens capsule to calculate a molecular weight cutoff from these data. In addition, permeability coefficients of drugs helpful for the suppression of secondary cataract were determined. Capsulorhexis specimens were fixed in a specially designed two compartment diffusion chamber to investigate the permeation of sodium fluorescein and fluorescent dextrans of different sizes (10, 40, 70 and 150 kDa) for 24 h (n ≥ 3) and of the antiproliferative drugs actinomycin D and methotrexate for 0.5, 24, 48 and 72 h (n ≥ 3). The molecular weight cutoff of the anterior lens capsule was found to be 166 ± 82 kDa. After 0.5 h, no passage of actinomycin D and methotrexate was detectable through the lens capsule. The apparent permeability coefficients for actinomycin D and methotrexate were calculated to 0.71 ± 0.02 µm/s and to 0.80 ± 0.13 µm/s, respectively. The capsular bag retains fluorescent dextrans with a molecular weight of >166 kDa. Hence, prepolymers are required to polymerize rapidly to be retained inside of the capsular bag. In addition, low-molecular substances intended as antiproliferative drugs for secondary cataract prevention should be applied within a time frame of five minutes in such a way that cells adjacent to the capsular bag will not be damaged.

Biomedizinische Technik/Biomedical Engineering, 2000

Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the i... more Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the interventional treatment of coronary artery disease. This new technology also holds potential for application in peripheral vascular settings. Our study reports on the development of a sirolimus-(SIR) eluting absorbable polymer stent made from a blend of poly(l-lactide) and poly(4-hydroxybutyrate) (PLLA/ P4HB) for peripheral vascular intervention. Stent prototypes were laser-cut from PLLA/P4HB tubes (I.D. = 2.2 mm, t = 250 µm), spray-coated with different PLLA/P4HB/SIR solutions, and bench-tested to determine expansion properties, fatigue, trackability and in vitro drug release kinetics. The stent prototypes were expanded with a 5.0 × 20 mm balloon catheter, and exhibited a recoil of 3.6% upon balloon deflation. Stent collapse pressure of 0.4 bar (300 mm Hg) was measured under external pressure load. Sustained scaffolding properties were observed in vitro over 14 weeks of radial fatigue loading (50 ± 25 mm Hg at 1.2 Hz). Trackability was demonstrated in bench tests with an 8 French contralateral introducer sheath. SIR release kinetics were adjusted over a broad range by varying the PLLA/P4HB ratio of the coating matrix. The newly developed absorbable SIR-eluting PLLA/P4HB stent successfully fulfilled the requirements for peripheral vascular intervention under in vitro conditions.

Talanta, 2008

This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) pro... more This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) products labeled with electrochemically active osmium tetroxide bipyridine can be detected voltammetrically by hybridization with probe strands immobilized on gold electrodes. These electroactive ssDNA targets have been obtained by means of Lambda Exonuclease treatment of the double-stranded PCR products followed by hybridization of the remaining single strands with short protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of these osmium labels have been obtained only upon hybridization with the immobilized probe strands. An optimal 50 • C hybridization temperature has been found with a saturation of the probe layer at 30 min hybridization time and 7.5 nmol/l target concentration. The blank capture probe layer alone did not yield any signal. Unprotected strands produced almost no interference. Such double-selective switch-on electrochemical hybridization assays hold great promise for the specific detection of PCR products.

Analytical Chemistry, Apr 1, 2007

Mikrochimica Acta, Aug 4, 2009

ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent ... more ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent label for biosensor applications regarding nucleic acids and protein detection. Labeling can easily be performed in the laboratory. Until now, almost only DNA species have been investigated using this label. Thymine (which occurs exclusively in DNA) is known to react much faster than cytosine and uracil. In order to explore the possibilities to modify and detect also RNA species in a timely fashion, we have investigated the kinetics of reactions of osmium tetroxide bipyridine with the pyrimidine bases in the micromolar concentration range at different temperatures by means of spectrophotometry. Results were confirmed using voltammetric detection for the determination of labeled oligonucleotides. The modification reaction can be easily completed at room temperature within 7h, even in case of cytosine and uracil. At 60°C, 3h are sufficient for complete modification of all pyrimidine bases that are found in natural nucleic acids. These findings will be important for future biosensor applications with RNA species as target molecules.

European Journal of Pharmaceutics and Biopharmaceutics, 2015

Lately, drug-coated balloons have been introduced in interventional cardiology as an approach to ... more Lately, drug-coated balloons have been introduced in interventional cardiology as an approach to treat occluded blood vessel. They were developed for the rapid transfer of antiproliferative drugs during the angioplasty procedure in stenosed vessels with the intent to reduce the risk of restenosis. In this study five different paclitaxel (PTX) balloon coatings were tested in vitro in order to examine how solvents and additives influence coating stability and drug transfer rates. PTX-coated balloons were advanced through a guiding catheter and a simulated coronary artery pathway under perfusion and were then inflated in a hydrogel acceptor compartment. The fractions transferred to the gel, remaining on the balloon and the PTX lost in the simulated coronary pathway were then analysed. The results obtained suggest that the solvent used for the coating process strongly influences the surface structure and the stability of the coating. Ethanol/water and acetone based PTX coatings showed the lowest drug transfer rates to the simulated vessel wall (both <1%) due to their high drug losses during the prior passage through the coronary artery model (more than 95%). Balloons coated with PTX from ethyl acetate-solutions showed smaller drug loss (83%±9%), but most of the remaining PTX was not transferred (mean balloon residue approximately 15%). Beside the solvent, especially the use of additives seemed to have a great impact on transfer properties. The balloon pre-treatment with a crosslinked polyvinylpyrrolidone (PVP) film was able to increase the PTX transfer rate from less than 1% (without PVP) to approximately 6%. The best results in this study were obtained for balloon coatings with commercially available SeQuent© Please balloons containing the contrast agent iopromide. For this formulation drug transfer rates of approximately 17% were determined. Fluorescence microscopic imaging could visualize the particulate transfer of labelled PTX from the balloon surface during dilatation. The findings of this study underline the importance of drug adhesion and coating stability for the efficiency of PTX transfer.

Translational vision science & technology, 2015

A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and char... more A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and characterized for safety and effectiveness after implantation into the suprachoroidal space (SCS) of rabbit eyes. Thin films of two different polymers, Poly(3-hydroxybutyrate) (P(3HB)) and Poly(4-hydroxybutyrate) (P(4HB)), containing the drugs mitomycin C (MitC) or paclitaxel (PTX) were attached to silicone-tubes to create LDD devices. The release kinetics of these drugs were explored in vitro using high performance liquid chromatography (HPLC). Twenty-four New Zealand white rabbits, randomly divided into eight groups, were implanted with different kinds of microstents into SCS. The intraocular pressure (IOP) was monitored noninvasively. After 6 weeks, rabbits were sacrificed and enucleated eyes were used for anterior segment optical coherence tomography (OCT), micro magnetic resonance imaging (MRI), and histology. In vitro, faster drug release from both polymers was observed for MitC compa...

European Journal of Pharmaceutics and Biopharmaceutics, 2015

In this study drug release from the CYPHER™ stent, the gold standard in drug-eluting stent therap... more In this study drug release from the CYPHER™ stent, the gold standard in drug-eluting stent therapy until the end of its marketing in 2011/2012, was systematically evaluated using different in vitro release tests. The test systems included incubations setups, the reciprocating holder apparatus (USP7), the flow-through cell apparatus (USP4) and the vessel-simulating flow-through cell (vFTC) specifically designed for stent testing. The results obtained show a large variability regarding the fractions released into the media after 7d ranging from 38.6%±4.5% to 74.6%±1.2%. The lowest fraction released was observed in the vFTC and the highest in an incubation setup with frequently changed media of a volume of 2mL. Differences were even observed when using fairly similar and simple incubations setups with mere changes of the media volume, under maintenance of sink conditions, and of the vessel geometry. From these data it can be concluded, that in vitro release even from a slow releasing drug-eluting stent is greatly influenced by the experimental conditions and care must be taken when choosing a suitable setup. Comparison of the obtained in vitro release profiles to published in vivo data did not result in a distinct superiority of any of the tested methods regarding the predictability for the situation in vivo due to large differences in the reported in vivo data. However, this comparison yielded that the release observed in vitro using the 2mL incubation setup and the reciprocating holder apparatus may be faster than the reported in vivo release. The results of this study also emphasize the necessity to use highly standardized release tests when comparisons between results from different experiments or even different labs are to be performed. In this context, the compendial methods are most likely offering the highest degree of standardization.

The invention relates to a method of labelling and analysing nucleic acids. More specifically, th... more The invention relates to a method of labelling and analysing nucleic acids. More specifically, the invention relates to a method of analysing nucleic acids, which comprises contacting the nucleic acids to be detected, which are in the form of single-stranded nucleic acid strands partially (i.e. over a part of the total length of the nucleic acid strands) hybridized with protective strands, with substances which specifically react with nucleobases of the single-stranded sections of the nucleic acid strands, and which are capable of subsequently participating in a reversible redox reaction in electroanalytical processes known to the skilled worker. 1. A method of detecting nucleic acid strands comprising labelling nucleic acid strands with redox markers and detecting the labeled strands via electrochemical detection of hybridization events, wherein a) single-stranded nucleic acid strands (target strands) are hybridized with one or more nucleic acid strands (protective strands A), wher...

ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has ... more ABSTRACT Although constant progress in pacing lead design and life time of pacemaker battery has contributed to the clinical success of this treatment option, the mechanism of drug release from steroid-eluting pacing leads is not completely understood. Besides, drug concentrations of steroids released into the heart-tissue remain unclear. Therefore, three different dissolution test methods were examined: a non-standardized (reagent tube), a compendial USP (paddle) and a hydrogel method. The experimental results indicate that dissolution from pacing leads is governed by a diffusion-controlled mechanism and occurs over a prolonged time. Furthermore, the integration of a hydrogel compartment seemed to have an impact on drug release leading to a decrease in release rate. Nevertheless, the experimental results emphasize different experimental parameters in dissolution testing may have a distinct influence on drug dissolution.

Talanta, 2007

This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) pro... more This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) products labeled with electrochemically active osmium tetroxide bipyridine can be detected voltammetrically by hybridization with probe strands immobilized on gold electrodes. These electroactive ssDNA targets have been obtained by means of Lambda Exonuclease treatment of the double-stranded PCR products followed by hybridization of the remaining single strands with short protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of these osmium labels have been obtained only upon hybridization with the immobilized probe strands. An optimal 50 • C hybridization temperature has been found with a saturation of the probe layer at 30 min hybridization time and 7.5 nmol/l target concentration. The blank capture probe layer alone did not yield any signal. Unprotected strands produced almost no interference. Such double-selective switch-on electrochemical hybridization assays hold great promise for the specific detection of PCR products.

Microchimica Acta, 2009

ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent ... more ABSTRACT The electroactive complex osmium tetroxide bipyridine holds great promise as a covalent label for biosensor applications regarding nucleic acids and protein detection. Labeling can easily be performed in the laboratory. Until now, almost only DNA species have been investigated using this label. Thymine (which occurs exclusively in DNA) is known to react much faster than cytosine and uracil. In order to explore the possibilities to modify and detect also RNA species in a timely fashion, we have investigated the kinetics of reactions of osmium tetroxide bipyridine with the pyrimidine bases in the micromolar concentration range at different temperatures by means of spectrophotometry. Results were confirmed using voltammetric detection for the determination of labeled oligonucleotides. The modification reaction can be easily completed at room temperature within 7h, even in case of cytosine and uracil. At 60°C, 3h are sufficient for complete modification of all pyrimidine bases that are found in natural nucleic acids. These findings will be important for future biosensor applications with RNA species as target molecules.

Journal of Materials Science: Materials in Medicine, 2013

Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an a... more Within the context of novel stent designs we developed a dual drug-eluting stent (DDES) with an abluminally focussed release of the potent anti-proliferative drug sirolimus and a luminally focussed release of atorvastatin with stabilizing effect on atherosclerotic deposits and stimulating impact on endothelial function, both from biodegradable poly(L-lactide)-based stent coatings. With this concept we aim at simultaneous inhibition of in-stent restenosis as a result of disproportionally increased smooth muscle cell proliferation and migration as well as thrombosis due to failed or incomplete endothelialisation. The especially adapted spray-coating processes allowed the formation of smooth form-fit polymer coatings at the abluminal and luminal side with 70% respectively 90% of the drug/polymer solution being deposited at the intended stent surface. The impacts of tempering, sterilization, and layer composition on drug release are thoroughly discussed making use of a semi-empirical model. While tempering at 80 °C seems to be necessary for the achievement of adequate and sustained drug release, the coating sequence for DDES should be rather abluminal-luminal than luminal-abluminal, as reduction of the amount of sirolimus eluted luminally could then potentially minimize the provocation of endothelial dysfunction. In vitro proliferation and viability assays with smooth muscle and endothelial cells underline the high potential of the developed DDES.

Electroanalysis, 2009

Single stranded DNA-targets from asymmetric polymerase chain reaction (PCR) of a sequence of the ... more Single stranded DNA-targets from asymmetric polymerase chain reaction (PCR) of a sequence of the gram positive, spore forming bacterium Clostridium acetobutylicum were detected by square-wave voltammetry after labeling with osmium tetroxide bipyridine and hybridization with DNA capture probes immobilized on gold electrodes. The asymmetric PCR, performed with a 10-fold excess of the forward-primer, was used without any further purification for hybridization with protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of 20 nmol/L targets were significantly higher at 50 8C compared with 23 8C hybridization temperature. A fully noncomplementary protective strand yielded thoroughly modified targets unable for further hybridization. Coupling this with thermal discrimination opens new opportunities for sequence specific DNA detection.

Electroanalysis, 2007

... The data points and their error bars represent average values of regarding measurements of 3 ... more ... The data points and their error bars represent average values of regarding measurements of 3 repetitive series (each series at a newly prepared SAM) and the regarding standard deviation, respectively. ... [36] T. Zerihun, P. Gründler, J. Electroanal. Chem. 1996, 415, 85. ...

Current Eye Research, 2013

For developing injectable lenses the retention properties of the capsular bag are important. Ther... more For developing injectable lenses the retention properties of the capsular bag are important. Therefore the apparent permeability coefficients of sodium fluorescein and fluorescent dextrans of different sizes were determined for the human anterior lens capsule to calculate a molecular weight cutoff from these data. In addition, permeability coefficients of drugs helpful for the suppression of secondary cataract were determined. Capsulorhexis specimens were fixed in a specially designed two compartment diffusion chamber to investigate the permeation of sodium fluorescein and fluorescent dextrans of different sizes (10, 40, 70 and 150 kDa) for 24 h (n ≥ 3) and of the antiproliferative drugs actinomycin D and methotrexate for 0.5, 24, 48 and 72 h (n ≥ 3). The molecular weight cutoff of the anterior lens capsule was found to be 166 ± 82 kDa. After 0.5 h, no passage of actinomycin D and methotrexate was detectable through the lens capsule. The apparent permeability coefficients for actinomycin D and methotrexate were calculated to 0.71 ± 0.02 µm/s and to 0.80 ± 0.13 µm/s, respectively. The capsular bag retains fluorescent dextrans with a molecular weight of >166 kDa. Hence, prepolymers are required to polymerize rapidly to be retained inside of the capsular bag. In addition, low-molecular substances intended as antiproliferative drugs for secondary cataract prevention should be applied within a time frame of five minutes in such a way that cells adjacent to the capsular bag will not be damaged.