Biomedical subjects

Bazhang Yu

Publications and source records attributed to Bazhang Yu.

4 recordsLinked to original sources

PubMed2005

A long-term flexible minimally-invasive implantable glucose biosensor based on an epoxy-enhanced polyurethane membrane.

This paper describes the preparation method as well as the in vitro and in vivo evaluation of a novel flexible glucose biosensor designed for long-term subcutaneous implantation. An epoxy-enhanced polyurethane membrane, which includes ca. 30-40% epoxy resin adhesive and 50-70% polyurethane, has been developed and used for the first time as the outer protective membrane of the sensor. This new membrane was developed to increase the in vivo durability and lifetime of implantable biosensors. This epoxy-polyurethane membrane was shown to be porous and is of excellent durability. A sensor with such a membrane shows excellent long-term stability and can last for 4-8 months in solutions at room temperature. To verify the in vivo performance of the sensor, nine sensors were implanted in three rats and tested regularly. Eight sensors kept functioning well in the rats for 10-56 days. The ninth sensor was damaged during implantation. All original sensitivity data as well as four response curves obtained at days 7, 17, 52 and 56, respectively are presented.

Animals↗

PubMed2005

Coil-type implantable glucose biosensor with excess enzyme loading.

As part of our overall long-term objective of designing a glucose sensor for long-term subcutaneous implantation, a coil-type implantable glucose sensor loaded with excess glucose oxidase (GOD) inside the coils of a 0.125mm diameter coiled platinum-iridium wire has been developed. The excess GOD was immobilized in a glutaraldehyde/bovine serum albumin (BSA) gel reinforced with cotton and located inside the coils chamber of the sensor. The excess GOD increased the lifetime of the sensor. Based on this coil-type design, various coil-type glucose sensors with cellulose acetate (CA), poly(vinyl chloride)(PVC), polyurethane (PU), poly(bisphenol A carbonate) (PC) and Nafion outer membranes were investigated and compared. Comparatively, Nafion based biosensors provided the best long-term response stability. However, Nafion can still not meet the lifetime requirement of the coil-type sensor with high enzyme loading because the observed function failure of these sensors was indeed caused by outer membrane damage rather than loss of enzyme activity. Additional experiments also revealed that hydrogen peroxide accumulation occurred in the GOD impregnated cotton when the sensors were not polarized which could cause a small false positive measurement. However, this artifact can be easily avoided by using an appropriate measurement technique.

Animals↗

PubMed2005

Strategies for testing long-term transcutaneous amperometric glucose sensors.

OBJECTIVES: Transcutaneous and embedded devices were developed for use in characterizing the in vivo performance of subcutaneously implanted glucose sensors. The devices were used as a portal for accessing electrochemical glucose sensors from the exterior. They were designed to prevent the sensors from being pulled out of the animals and the sensor leads from breaking. Development of the devices took into consideration rodent mobility, infection control, and animal welfare balanced with sensor durability, accessibility, and functionality. METHODS: Our approach was developed over five animal protocols spanning a period of 6 months. A total of 68 sensors were implanted with 60 associated devices in 22 Sprague-Dawley outbred rats. RESULTS: The average sensor lifetime was 11.2 +/- 3.1 days with a maximum of 56 days. All-cause sensor failure averaged one sensor per day. As implantation devices were modified, failure attributable to the device was decreased by 40%. The resulting devices showed good durability and allowed for easy sensor access and testing. CONCLUSIONS: These data represent baseline sensor function against which future sensor improvements may be measured. The new devices and techniques described should be a valuable tool in the development of continuous glucose sensors.

Animals↗

PubMed2004

Electrochemistry of metal phthalocyanines in organic solvents at variable pressure.

High-pressure electrochemical investigations of representative metallophthalocyanines in solution are reported. The selected systems were ZnPc, CoPc, FePc, and CoTNPc (Pc = phthalocyanine, TNPc = tetraneopentoxyphthalocyanine) in several donor solvents and (for CoTNPc) dichlorobenzene, with [Bu(4)N][ClO(4)] as supporting electrolyte and a conventional Pt electrode referred to Ag(+)(CH(3)CN)/Ag. Electrode reaction volumes deltaV(cell) for CoTNPc and ZnPc show that consecutive ring reductions result in progressive increases in electrostriction of solvent in accordance with Drude-Nernst theory. Reductions of the metal center in CoTNPc and CoPc, however, result in much less negative values of deltaV(cell) than would be expected by analogy with ring reductions of the same charge type. This is attributable to loss of axial ligands following the insertion of antibonding 3d(z)2 electrons on going from Co(III) to low-spin Co(II) and then Co(I). In the same vein, rate constants for reduction of Co(III) centers to Co(II) were an order of magnitude slower than those for other metal center or phthalocyanine ring reductions because of Franck-Condon restrictions. The volumes of activation deltaV(el) were invariably positive for all the electrode reactions and in most cases were roughly equal to the volumes of activation for reactant diffusion deltaV(diff)(), indicating predominant rate control by solvent dynamics rather than by activation in the manner of transition-state theory for which negative deltaV(el) values are expected. For CoTNPc and CoPc in donor solvents, the deltaV(cell) and deltaV(el) data are consistent with the assignments of the successive reduction steps made for CoTNPc in DMF by Nevin et al. (Inorg. Chem. 1987, 26, 570).

Journal Article↗