Search PubMed⌕ Search

Biomedical subjects

E Wilkins

Publications and source records attributed to E Wilkins.

64 records · Page 4Linked to original sources
PubMed1977

A trial of clenbuterol in bronchial asthma.

Clenbuterol is a beta 2-sympathomimetic bronchodilator. In a double-blind cross-over trial in 19 asthmatic patients with reversible airways obstruction, oral administration of both clenbuterol (40 microgram) and salbutamol (4 mg) caused significantly greater increased in peak expiratory flow rate (PEFR) than placebo, that of clenbuterol lasting longer. The patients' subjective assessment also suggested the relief of their symptoms by the active drugs. Side-effects were minimal.

Adolescent↗
PubMedDate not supplied

Glucose biosensors based on oxygen electrode with sandwich-type membranes.

A glucose biosensor based on an amperometric oxygen electrode has been developed. Polycarbonate and Silastic membranes were assembled (glued together) to form a multilayer sandwich glucose diffusion barrier. The effects of the glue layer composition and thickness of the Silastic membrane on sensor response parameters have been investigated in order to optimize the sensor. The parameters measured were the sensitivity, the concentration range of the linear dependence of the sensor response to glucose, and the long-term operation time. The sensors with the sandwich-type glucose diffusion membrane (Silastic membrane prepared from 20% Silastic suspension, glue layer prepared from polyurethane, 0.5 w/v % in ThF solution and standard polycarbonate membrane) demonstrated linearity of response up to 520 mg/dl glucose at 25 degrees C and up to 400 mg/dl at 37 degrees C. These sensor showed good reproducibility of response without significant interference effects (from 1 to 5% of the background current value). The long-term continuous operational time of the sensors was over 40 days at 37 degrees C, and over 60 days at 25 degrees C.

Animals↗
PubMedDate not supplied

Performances of potentially implantable rechargeable glucose sensors in vitro at body temperature.

The authors developed a glucose sensor that operates in vitro at 37 degrees C for at least three months without recharging. The use of fine carbon particles upon which to immobilize the glucose oxidase makes it possible to recharge the sensor when enzymatic activity diminishes. This may enable the sensor to perform for at least a year when implanted, and thus reduce the frequency of surgical replacement. Recharging is accomplished by inserting a hypodermic needle into the septum of an implanted reservoir. Three types of carbon were investigated: graphite powder, carbon lamp black, and low-temperature isotropic carbon powder (ULTI). Two cross-linking procedures were tested. The sensor that remained operational for the longest time used the ULTI and the cross-linking procedure that mixed the enzyme, immobilized on carbon powder, with albumin and glutaraldehyde. This sensor operated continuously at 37 degrees C for at least three months. Further, it was put through four recharge cycles with ten days of successful operation after each without change. The sensor is very stable and the results obtained with it are reproducible.

Biosensing Techniques↗
PubMedDate not supplied

Glucose biosensors with enzyme entrapped in polymer coating.

The pursuit of reliable biosensors for measuring glucose levels has been ongoing for decades. Their importance lies partly in the development of the implantable artificial pancrease, which can be used to deliver insulin to diabetics without the need to test glucose levels externally, with automatic delivery based on physiologic demand. Glucose sensors can also be used in short-term monitoring of glucose levels in hospitals and clinical laboratories. Three types of glucose biosensors were studied. All were based on a two-electrode system: an insulated platinum wire as a hydrogen peroxide electrode, and a silver wire twisted around the platinum wire as both a reference and a counter electrode. Each was coated with the enzyme glucose oxidase entrapped in a polymer matrix of cellulose acetate (CA) or poly 2-hydroxyethyl methacrylate (HEMA), then dip-coated by an additional polymer coating of polyvinylchloride (PVC), polyurethane (PU), or HEMA. The experiments were designed mainly to study the effectiveness of polymer coatings as diffusion-limiting membranes. The effect of each coating on the linear response to glucose concentration was examined. It was shown that additional (multiple) coatings can increase the linearity of the sensor response. The best results were obtained when the sensor was PVC-dip-coated three times. This preparation had a linear response up to 600 mg/DL glucose concentration. The sensors coated with PU and HEMA have linearity up to 280 and 240 mg/DL glucose concentrations, respectively. It was also shown that the coatings reduce interference from certain body chemicals.

Biocompatible Materials↗
PubMedDate not supplied

Application of polytetrafluoroethylene (PTFE) membranes to control interference effects in a glucose biosensor.

The implantable feedback-controlled insulin delivery system provides the greatest potential for the control of certain types of diabetes mellitus. The development of an implantable glucose sensor is thus a prerequisite. A glucose biosensor using the enzyme glucose oxidase immobilized on fine carbon powder has been developed. Its in-vitro behavior is investigated in the presence of interfering substances commonly encountered in human blood and other body fluids. Here, in-vitro interference tests carried out on this sensor with polytetrafluoroethylene (PTFE) membranes are described. The authors used PTFE membranes (pore size 0.02 micron), some of which were coated with positively and negatively charged hydrogel layers. The sensors showed a stable and linear response to glucose concentrations > 300 mg/dL, in the presence of glucose alone in the phosphate buffer medium and in the presence of interferences. The interference effects of ascorbic acid, bilirubin, creatinine, L-cystine, glycine, uric acid, and urea on the amperometric signal of the sensor were studied. The PTFE membrane coated with the negatively charged hydrogel layer provided good protection for the enzyme electrode, especially in the presence of ionic interferants such as ascorbic acid and uric acid.

Biosensing Techniques↗
PubMedDate not supplied

Long-term performance of a rechargeable glucose electrode in vitro.

A rechargeable glucose sensor now under development performed satisfactorily for over eight months at 25 degrees C and over 90 days at 37 degrees C without recharging. A prototype sensor was operated through three recharge cycles, which increased the life of the sensor more than two months. This demonstrates the potential for reducing the frequency of surgical replacements. Earlier work utilized three forms of carbon upon which glucose oxidase was immobilized. Recent work reported herein demonstrates that the longer-performing sensor is realized with ultra-low-temperature isotropic (ULTI) carbon powder. Due to its fine particle size, the ULTI carbon with immobilized enzyme acts as a liquid suspension. The sensor is stable and there is no detectable degradation of the sensor components from one recharge cycle to the next.

Carbon↗
PubMedDate not supplied

A glucose biosensor based on an oxygen electrode: in-vitro performances in model buffer solution and in blood plasma.

An implantable biosensor for continuous monitoring of glucose levels in diabetic patients was developed. The biosensor is based on an amperometric oxygen electrode and glucose oxidase immobilized on carbon powder held in the form of a liquid suspension. The enzyme material can be replaced (the sensor recharged) without sensor disassembly. Sensors with polycarbonate glucose-diffusion membranes coated with silastic were studied. Calibration curves of the sensors in phosphate buffer solution and in undiluted blood plasma at body temperature were obtained and compared. Sensors were tested for long-term performance in vitro in model phosphate buffer solution and in blood plasma at room and at body temperature. Reproducibility of the sensor responses in plasma at body temperature was demonstrated. During continuous operation at body temperature, the sensors have a lifetime of at least six weeks.

Biomedical Engineering↗
PubMedDate not supplied

A needle-type sensor for monitoring glucose in whole blood.

A new surface-process technology employing electrochemical fixation of a bioactive substance (enzyme and heparin) to a sensor electrode was developed to provide biocompatability and functionality. The fabrication process includes electroentrapment of glucose oxidase and heparin on a platinum electrode by using 1,3-phenylenediamine codeposition. Electrochemically grown 1,3-phenylenediamine was also used as the outer coating of the sensor's enzyme electrode in order to extend the linear range. The sensor shows a sensitivity of 3 nA/mM and a linear range from 40 to 400 mg/dL at 37 degrees C when tested in whole blood. This sensor is characterized by a fast response. The sensor shows a minimum change in its performance when stored inactive in buffer for 12 weeks. When tested at physiologic glucose levels, the sensor demonstrates satisfactory low interference from common interfering substances. This technology seems promising for the preparation of implantable intravascular biosensors.

Anticoagulants↗