PubMed Health⌕ Search

Biomedical subjects

G J Richter

Publications and source records attributed to G J Richter.

9 recordsLinked to original sources
PubMed1993

[Development and evaluation of an electrocatalytic glucose sensor for diabetes therapy].

For the continuous measurement of glucose levels in vivo, an electrocatalytic glucose sensor has been developed. Electrochemical determination of the glucose concentration is effected by measurement of the impedance, which at given potentials is directly dependent on the glucose concentration in the solution. For evaluation and determination of long-term stability, the sensor was first implanted in the carotid artery in the form of a flow-through cell, and was later inserted into the vena cava of a sheep in the form of a catheter. Sensor response was checked periodically by performing glucose tolerance tests. During the implantation period, we also tested the sensitivity of the sensor towards various blood components and medicaments. By adapting sensor calibration, it proved possible to suppress these cross-sensitivity effects. The flow-through cell type of sensor remained functional for up to 71 days post-implantation. So far, data for the catheter-type sensor cover an indwelling time of up to 30 days.

Animals↗
PubMed1988

The electrocatalytic glucose sensor.

An electrocatalytic glucose sensor is a very useful component of an artificial beta cell in controlling the insulin dosage in the diabetes therapy. The advantage is its potential long-term stability and the disadvantage is its lack of selectivity. The principle and experimental results with different electrolytes will be described. In saline solution the mean deviation in glucose response is up to 15% if the amino acid and urea concentrations raise from minimum to their physiological maximum values.

Animals↗
PubMed1981

Chronic threshold of stimulating electrodes: comparison of activated vitreous carbon with conventional platinum-iridium electrodes in animal tests.

Electrodes made of vitreous carbon are inert, corrosion-resistant, inactive to electrocatalytic reactions and are especially biocompatible. Upon activation, they attain a capacitance of 20 to 40 mF and become "non-polarizable". Therefore, they should be particularly suitable as stimulating and sensing electrodes for cardiac pacemakers. The connective tissue layer that develops around the electrode because of the foreign-body reaction is less than 100 micron thick. The threshold rise, through lower than that of conventional Pt-Ir or ELGILOY electrodes, cannot be attributed exclusively to the connective tissue layer that is formed. Under favourable conditions, the threshold in animal experiments remains below 525 mV. Blood-spaces adjoining the electrodes are found at higher chronic threshold values.

Animals↗
PubMed1980

Threshold measurements using stimulating electrodes of different materials in the skeletal muscles of cats.

In the skeletal muscle of cats, semispherical stimulating electrodes having a radius of 1.2 mm deliver a mean threshold current of 0.15 mA, corresponding to 1.7 mA/cm2. These values are doubled within a period of four weeks after chronic implantation. In the case of non-polarizable electrodes the mean threshold voltage increases from 108 mV to 171 mV. The lowest individual values range between 50 mV and 60 mV at the time of implantation. The highest value is around 500 mV after four weeks. The high values have been observed with strongly polarizing ELGILOY electrodes. The chronic threshold energies vary between 3 x 10(-8) Ws for activated vitreous carbon electrodes and 17.5 x 10(-8) Ws for ELGILOY electrodes. There are two reasons for the low threshold energy of activated vitreous carbon electrodes. One reason is their low polarization, and the other is their better compatibility. Connective tissue layers with a thickness between 25 micron and 50 micron are found around well healed carbon electrodes.

Alloys↗
PubMed1979

Development of an electrocatalytic glucose sensor.

For the determination of glucose in body fluids, the electrocatalytic sensor, besides the enzyme sensor, is quite suitable, particularly for long-term intracorporeal operation. The measuring response is disturbed by the fluctuating concentrations of the interfering substances that are simultaneously present in body fluids. However, the disturbance can essentially be controlled, as is shown in the case of amino acids. Their marked influence on glucose oxidation is suppressed at a membrane-covered sensor electrode by the use of a potential step method.

Artificial Organs↗
PubMed1978

Electrochemical behavior of amino acids and their influence on the anodic oxidation of glucose in neutral media.

Body fluids contain a large number of amino acids along with glucose. Therefore, the electrochemical behavior of amino acids should be considered in studying the anodic oxidation reaction of glucose for biological applications. Potential-sweep and steady-state measurements with different platinum electrodes under neutral conditions have shown that the oxidation of amino acids is basically possible. However, their presence, especially as a mixture, has a remarkable influence on the glucose oxidation and the anodic reaction is strongly inhibited. With respect to the degree of inhibition, they can be classified into two groups. The inhibiting effect is particularly drastic in the case of basic and unsaturated amino acids as well as the ones containing sulphur because of their strong absorption at the electrode surface. The glucose currents are inhibited by about 90% under steady-state. In addition to the direct electrochemical inhibition, the following bacterial decomposition of amino acids is probably also responsible for the drastic effect. However, about 10% of the glucose currents still remain measurable indicating that glucose is detectable at physiological concentrations even under extremly unfavorable conditions. This result is of basic importance in operating a biofuel cell or in measuring glucose concentrations.

Amino Acids↗
PubMedDate not supplied

Development and present status of an electrocatalytic glucose sensor.

For the determination of glucose in body fluids the electrocatalytic sensor seems to be quite favorable, particularly for long-term intracorporeal operation. The measuring response is disturbed by the fluctuating concentrations of interfering substances that are present in body fluids. However, the disturbance can be for the most part controlled, as shown in the case of amino acids. Their marked influence on glucose oxidation is suppressed at a membrane-covered sensor electrode by using a potential step method.

Amino Acids↗