AWIMS for continuous blood glucose monitoring
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Joined: Jun 2010
09-01-2011, 12:26 PM
CONTINUOUS blood glucose monitoring can help to significantly reduce (between 40% to 75%) the symptoms associated with diabetes . Currently, a few continuous blood glucose monitoring systems are commercially available which can continuously monitor the blood glucose level up to only a few days .A very promising approach to long-term continuous glucose monitoring is to implant a glucose sensor along with an electronic instrument, required for data measurement and communication, in the human body and measure the glucose level continuously. The sensor can be implanted just underneath the skin and be in contact with capillary blood or even interstitial fluid .
Most of the published works that have employed the aforementioned idea suffer from some problems. First, the previously presented implantable units have relatively large sizes primarily due to the construction of the implantable device using discrete electronic components assembled on medium-size circuit boards; and second, due to using a battery for powering the implant. The size of the implant plays a key role in the success of the monitoring system. A smaller implant can be more easily packaged and be simply implanted via outpatient surgery. It also provides more comfort for the patient and more options for the implantation site. However, the most important advantage of a smaller implant is that it promises a longer consistent in-vivo monitoring lifetime because a smaller implant is less sensitive to a patient’s movement; thus, the tissue surrounding the implant comes to stability more rapidly and stays stable for a longer period of time .
A second problem of the previously published implantable units is that they have used conventional electrochemical glucose sensors (either oxygen-based or hydrogen peroxide-based sensors) for glucose sensing. The conventional sensors have several limitations when they are implanted in the body, such as the requirement for oxygen, short lifetime (low chemical stability), and interference from other chemical species, such as urate, ascorbic acid, and acetaminophen.
A third problem is associated with the requirement for batteries that can power the implant for a long period of time; not only does this result in an enlarged size of the implant but also decreases the lifetime of the implant.
Our approach to the aforementioned problems is to miniaturize the implantable unit.
CONCEPTUAL DESIGN OF PROPOSED MICROSYSTEM
The system includes
1) microfabricating the glucose sensor 2) integrating all of the interfacing circuits into an integrated-circuit (IC) chip (transponder chip) and 3) attaching the microfabricated glucose sensor to the transponder chip using flip-chip bonding. Fig. 1 shows a conceptual design of our proposed microsystem.
Fig:1 : Conceptual design of the proposed microsystem for continuous blood glucose monitoring.
Our glucose sensor is a novel electrochemical glucose biosensor developed at the research group of Prof. V. Birss in the Department of Chemistry at the University of Calgary. The sensor can function without the need for oxygen, and demonstrates good chemical stability, reproducibility, and biocompatibility.These characteristics make the sensor an appropriate choice for our microsystem.
Due to the problems associated with using a battery or a wired link ,we have used a passive telemetry link for power and data transfer between the implantable microsystem and the external reader. The link operates at the industrial-scientific-medical(ISM) frequency band of 13.56 MHz.