Thomas Posnicek

Fluidized Bed Adsorbent Systems for Extracorporeal Liver Support

Abstract:  Acute liver failure based on acute‐on‐chronic liver failure (AoCLF) or on acute severe damage of the liver caused by different etiologies includes complex mechanisms resulting in severe disturbances of principle liver functions. In order to compensate the liver’s function of detoxification as efficiently as possible, fluidized bed absorbent systems have been designed. In these systems, small particles with specific adsorption properties for toxins related to acute liver failure are applied. A special technology based on adsorbents in suspension has been developed under the guidance of our group and is prepared for clinical application during the coming year. This technology is called microspheres‐based detoxification system (MDS) and is based on microadsorbents with a diameter of 1–10 µm which are recirculated in suspension. The safety of the MDS is guaranteed by the use of fluorescently labeled magnetic microparticles, which in case of a membrane‐leakage are detected in the blood circuit by an optical system equipped with a magnetic trap. In vitro tests with two kinds of microadsorbents (a combination of a hydrophobic neutral resin and an anion exchange resin) showed excellent efficiency of the system with respect to adsorption capacity as well as to the kinetics of elimination of albumin‐bound substances (e.g. unconjugated bilirubin or cholic acid) and of non‐protein‐bound substances (e.g. phenol). Moreover, using a plasma filter or the Albuflow filter as membrane filters in the blood circuit, the MDS technology offers the possibility to remove inflammatory mediators such as tumor necrosis factor‐α (TNF) by additional use of specific adsorbents.

Detection of Fluorescently Labeled Microparticles in Blood

Background: A microsphere-based detoxification system is an adsorption system, whereby microadsorbent particles having diameters of 1–20 µm circulate in an extracorporeal filtrate circle. A thin-wall hollow-fiber membrane filter separates the microparticle-plasma suspension from the bloodstream. For patient safety, it is necessary to have a means to detect membrane ruptures that could lead to a release of microparticles into the patient’s bloodstream. Methods: An optical detection system was developed to monitor the venous bloodstream for the presence of microparticles from the filtrate circuit. For detection purposes, cellulose microspheres, both ferromagnetic and fluorescence labeled, were included with the microsphere adsorbant particles. In the case of a membrane rupture, the labeled particles would also be released into the bloodstream. By illuminating a small volume of blood with an excitation wavelength (590 nm) of the fluorescence marker, the particles can be detected by their emission light at 620 nm. The detector sensitivity is increased by collecting the ferromagnetic and fluorescently labeled microparticles using a magnetic trap. The efficiency of magnetic trap arrangements was tested by adjusting the magnet placements. Results: In vitro experiments were performed by pumping whole blood and labeled microparticles through the fluorescence detector. The efficiency of a magnetic trap arrangement was determined. With an optimal trap setup, 5–10 µl of labeled microparticles can be clearly detected in streaming whole blood. Conclusion: An easy to handle microparticle detector was developed, ready for use in particle based blood detoxification systems. The microparticle detection system fulfills the medical and technical requirements to bring the MDS into clinical tests.

A Target-Orientated Algorithm for Regional Citrate-Calcium Anticoagulation in Extracorporeal Therapies

Background: Citrate anticoagulation offers several advantages in comparison to conventional anticoagulation. Most algorithms for regional citrate-calcium anticoagulation are based on citrate and calcium chloride infusion coupled in a fixed proportion to the blood flow without considering the hematocrit (Hct)/plasma flow or the filter clearance of citrate and calcium. Methods: The aim of this study was to develop an algorithm for optimized citrate anticoagulation in extracorporeal therapies such as dialysis. A mathematical model was developed to calculate the volume of citrate infusion required to achieve a desired ionized calcium (iCa) target level in the extracorporeal circuit and to restore the total calcium level to a physiological value. Results: The model was validated by correlation analyses for different blood Hct values and shows an excellent fit to the laboratory measurements. Conclusion: The results for both iCa target concentrations, namely those after citrate and calcium infusion, proved that the software algorithm adapts well to variable treatment parameters.

Particle Transfer and Detection in a Microspheres Based Detoxification System

Extracorporeal blood purification by means of the adsorption system MDS is based on high specific microparticle adsorbent for toxin removal. A thin-wall hollow-fiber membrane filter separates the microparticle-plasma suspension from the bloodstream. For patient safety, it is necessary to have a means to detect membrane ruptures that could lead to a release of microparticles into the patients bloodstream. A non invasive optical detection system was developed to monitor the extracorporeal venous bloodstream for the presence of released microparticles. For detection, labeled microspheres are suspended with the adsorbent particles. In the case of a membrane rupture, the labeled particles would be released together with the microadsorbent. A detailed description for the system setup is introduced.

A Simple Pheromone Based On-Demand Routing Protocol for Wireless Sensor Networks

A simplified design for an on demand routing protocol using pheromone (attractiveness) gradients for data forwarding decisions is proposed. The developed Pheromone-based Routing Strategy (PRS) provides an easy concept for a data-centric routing protocol in wireless sensor networks. The protocol has a flat hierarchy, works on-demand, is source-initiated and has its origin in the idea of ant-based routing. During development of PRS, the important variable pheromone was turned into a special factor for link costs and is the sole determinant for data load propagation where the pheromone level of the sensor node defines its attractiveness for forwarding data. The link costs called pheromone are calculated from the sensor nodes’ energy status, as well as the received signal strength and the current buffer (sensor on board memory) fill level. PRS only supports node-to-sink data traffic and therefore is a lightweight approach to generalized multihop routing algorithms in WSNs. The PRS routing protocol is implemented on a MSP430F149 low power microcontroller using a CC2420 wireless interface which are acting together as a sensor node. For performance evaluation of PRS a multi-agent based simulation environment called NetLogo is used.

A Source Based On-Demand Data Forwarding Scheme for Wireless Sensor Networks

Wireless Sensor Networks WSNs are becoming more important in the medical and environmental field. The authors propose an on-demand routing protocol using sensor attractiveness-metric Pa gradients for data forwarding decisions within the network. Attractiveness-based routing provides an efficient concept for data-centric routing in wireless sensor networks. The protocol works on-demand, is source-initiated, has a flat hierarchy and has its origin in the idea of pheromone-based routing. The algorithm supports node-to-sink data traffic and is therefore a lightweight approach to generalized multihop routing algorithms in WSNs. The performance evaluation of the proposed protocol is done by extensive simulation using a multi-agent based simulation environment called NetLogo. The efficiency of the attractiveness-based routing algorithm is compared in simulations with the well known Dynamic Source Routing algorithm DSR. The authors conclude that the Pabased routing algorithm is well suited for easy to set up WSNs because of its simplicity of implementation and its adaptability to different scenarios by adjustable weighting factors for the nodes attractiveness metric.

Highly increased detection of silver stained protein bands in polyacrylamide gels with thermo-optical methods

Sodium dodecyl sulfate polyacrylamide gel electrophoresis is a well-known technique to separate proteins by their molecular weight. After electrophoresis, the gels are commonly stained for protein band analysis with silver stain; this allows the detection of protein loads to about 1 ng. To increase the detection sensitivity of the protein bands down in the subnanogram level, a sensor has been developed based on the thermal lens effect to scan and quantify protein loads which would remain undetected using the standard imaging systems. The thermal lens sensor is equipped with a 450 nm diode pump laser modulated at 1 Hz and a HeNe probe laser mounted in collinear geometry. The sensor could detect protein bands of 0.05 ng when the gel was soaked in methanol/water and 0.1 ng in water. The limit of detection ranged from 8 to 20 pg, depending on the soaking medium and the staining efficiency. Thus, the detection of silver stain by thermal lens effect results 10 to 20 times more sensitive than the standard colorimetric method.

Highly sensitive detection of labeled microparticles in blood

The Microspheres Based Detoxification system is an adsorption system, whereby microadsorbent particles with diameters of 1 to 20 mum circulate in an extracorporeal filtrate circuit. A thin-wall hollow-fiber membrane filter separates the microparticle-plasma suspension from the bloodstream. For patient safety, it is necessary to have a means to detect membrane ruptures that could lead to a release of microparticles into the patients bloodstream. An optical detection system was developed to monitor the venous bloodstream for the presence of microparticles from the filtrate circuit. For detection purposes, we use superparamagnetic monodisperse polystyrene microparticles (diameter 2.8mum) with a covalently bound fluorescence dye. The labeled marker beads are included with the microsphere-adsorbent particles in the MDS circuit. In the case of a membrane rupture, the labeled particles would also be released into the bloodstream. By illuminating a small volume of blood at the excitation wavelength (590 nm) of the fluorescence marker, the particles can be detected by their emission light at 620 nm. The detector sensitivity is increased by collecting the ferromagnetic and fluorescently labeled microparticles using a magnetic trap. In vitro experiments were performed by pumping whole blood and labeled microparticles through the fluorescence detector. With an optimal trap setup, less than 2mg of labeled microparticles can be clearly detected in streaming whole blood.

Development of a calcium sensitive fluorescence sensor as medical device

This calcium sensitive fluorescence sensor is based on a fluorescence dye immobilized in a hydrogel, which is placed onto the inner wall of a transparent measuring cell. The ionized calcium (iCa) sensitive fluorophore oregon green dextran (OG-dextran) reacts with the calcium ion resulting in an increase of fluorescence intensity proportional to the concentration of iCa. To measure the optical signal of the calcium sensitive fluorescence sensor an appropriate and very sensitive optical measurement device was developed. The aim of this sensor is to measure the ionic calcium concentration during extracorporeal citrate-calcium anticoagulation. Thus the newly developed calcium sensor can bring an enhancement for accurate online measurement of iCa during treatment and adjustment of iCa afterwards.