Procedia Chemistry Procedia Chemistry 1 (2009) 1255–1258
www.elsevier.com/locate/procedia
Proceedings of the Eurosensors XXIII conference
Wireless implantable electronic platform for blood glucose level monitoring P. Valdastria,*, E. Susiloa, T. Försterb, C. Strohhöferb, A. Menciassia, P. Darioa a
CRIM-Lab, Scuola Superiore Sant’Anna, Pisa, Italy Fraunhofer IZM, Hansastr. 27d, Munich, Germany
b
Abstract A wireless programmable electronic platform for implantable monitoring of blood glucose level (BGL) was developed and preliminary tested on bench. This system allows extremely low power bidirectional telemetry, based on the IEEE802.15.4-2003 protocol, thus enabling typical battery lifetime up to six months and wireless networking of multiple sensors. During a single BGL measurement, the circuit drives a laser diode, for sensor excitation, and acquires the amplified signals coming from four different photodetectors. The electronics is designed to be integrated in a complete system for BGL monitoring to be implanted for at least six months under the skin of diabetic patients. Keywords: implantable telemetry, glucose monitoring, blood glucose level, diabetes, chronic monitoring
1. Introduction The application of implantable wireless devices for chronic monitoring of life threatening parameters is nowadays expanding thanks to novel low power technologies for biotelemetry [1]. Devices based on the IEEE 802.15.4-2003 protocol are able to last up to several years without a battery replacement [2]. Thanks to the availability of miniaturized components combined with advanced packaging techniques, dimensions of wireless electronics can be scaled down to implantable size [3]. The present work reports about a miniaturized implantable BGL monitoring device [4], focusing on the wireless electronic platform. Main requirements for this sub-unit are low power consumption, reduced dimensions, an adequate number of analog input, a safe level of radio frequency energy across the human body and a low cost. In order to meet all these requirements at once, the CC2430 from Texas Instruments Inc. was selected as core component of the telemetry platform. This device embeds an 8051 programmable microcontroller together with an IEEE 802.15.4-2003 compatible transceiver in a 7 x 7 mm2 package. 2. System Overview The detection principle is based on change of fluorescence resonant energy transfer (FRET) efficiency of a synthesized protein as a function of analyte concentration. The proteins are immobilized inside a hydrogel
* Corresponding author. Tel.: +39-050-883-489; fax: +39-050-883-497. E-mail address:
[email protected].
1876-6196/09 © 2009 Published by Elsevier B.V. Open access under CC BY-NC-ND license. doi:10.1016/j.proche.2009.07.313
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waveguide [5] and are excited with a laser diode coupled to the waveguide. Along the waveguide four photodiodes with optical filters are placed to detect the fluorescent signals. The current signals of the detectors are amplified and converted into voltage signals in the range between 0.9V and 3.8V. The microcontroller is programmed to switch on the laser diode through a proper driving circuit and to sample the four amplified signals coming from the photodiodes. Signals are acquired at 10 kHz and then averaged on board over 256 samples in order to get stable values. The sensing part can be disabled by the microcontroller through a switch in order to save power during idle mode. System architecture and typical measurement timing are reported in Fig. 1 and Fig. 2 respectively.
Fig. 1: System architecture of the implant.
Fig. 2: Detailed view of the measurement timing.
On the user side, a purposely developed transceiver interfaces the implant with the Universal Serial Bus (USB) port of a standard Personal Computer (PC). This transceiver embeds a CC2430 and a serial to USB converter (UM232, FTDI, UK). Each device is identified by a unique address, so that several implantable sensors can be monitored at once by the same external unit. Being this architecture based on a ZigBee [6] compliant hardware, a wireless sensor network scenario can be easily implemented. This would allow the on line monitoring of a huge number of patients (up to 65536) thanks to the 16-bit addressing of the ZigBee stack. In the present work, a Human Machine Interface (HMI) was developed in Labview 8.2 (National Instruments Inc., USA). This HMI enables the user to set the measurement parameters and to communicate with the implant. Acquired BGL samples are visualized on screen and stored in a spreadsheet file for future use.
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3. Results and discussion Preliminary tests showed a battery lifetime up to six months by sampling BGL every 15 minutes and by using a specially designed miniature cell from Tadiran Batteries with 350mAh. Thanks to a proper selection of the single components, the electronics can be scaled down in dimensions to be located within two miniaturized boards, being 17 mm and 13 mm in diameter each. The implant concept design, being 50 mm in length and 20 mm in diameter, is represented in Fig. 3. The system was preliminarily characterized by cycling between maximum and minimum signal levels achieved by addition and removal of Ca2+. Typical acquired plots are reported in Fig. 4.
Fig. 3: Implant concept design, final devised dimensions: length 50 mm, diameter 20 mm.
Fig. 4: Signals from the photodiodes in response to FRET changes in the measurement chamber. The changes were induced by flushing the measurement chamber and alternating solutions of CaCl2 and EDTA. Signal from YFP decreases with EDTA-caused loss of FRET, while signal from CFP increases. CaCl2 has the opposite effect.
Acknowledgements The work described in this paper has been supported by the European Commission in the framework of the FP6 European Project P. Cezanne (EU/IST-2006-031867).
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References 1. 2. 3. 4. 5. 6.
Panescu D. Emerging Technologies [wireless communication systems for implantable medical devices]. IEEE Engineering in Medicine and Biology Magazine 2008; 27:96-101. Valdastri P, Rossi S, Menciassi A, Lionetti V, Bernini F, Recchia FA, Dario P. An Implantable ZigBee Ready Telemetric Platform For In Vivo Monitoring Of Physiological Parameters. Sensors and Actuators A: Physical 2008; 142:369-378. Susilo E, Valdastri P, Menciassi A, Dario P. A Miniaturized Wireless Control Platform for Robotic Capsular Endoscopy using Pseudokernel Approach. Proc. of 22nd Eurosensors, 2008, winner of best paper award. The 6th Framework Programme European Project P.CEZANNE (EU/IST-2006-031867), 2006-2010, website: www.pcezanneportal.co.uk. The sensing proteins immobilized inside the hydrogel waveguide were prepared at the Polymer Institute of the Slovak Academy of Sciences, Bratislava. The ZigBee Alliance, [online]: www.zigbee.org.
