Toward a continuous intravascular glucose monitoring system

Brooke Leigh Beier, Purdue University

Abstract

Continuous, direct monitoring of blood glucose levels from a minimally invasive device can serve as a valuable management tool for diabetics and also individuals at risk of developing the disease. The most significant challenges for the development of such a device include the ability of a sensor to be exposed to the blood continuously without needing to be replaced, the transfer of data from within a blood vessel, and the optimization of the device's sensing capabilities. We present proof-of-concept studies that display the potential for using a glucose-sensitive hydrogel as a continuous glucose sensor. Studies to characterize the change in volume, impedance, porosity, and permeability of the glucose-sensitive hydrogel as a function of glucose concentration were performed, and the diffusivity of a small molecule through the hydrogel exposed to various glucose concentrations has been investigated. The swelling ratio, diffusivity, and porosity of the hydrogel all exhibited increasing behavior with increasing glucose concentration of exposure. Specifically, in glucose solutions of 50 mg/dL, 100 mg/dL, 200 mg/dL, and 300 mg/dL, the swelling ratios of the hydrogels were 4.9, 12.3, 15.9, and 21.7, respectively. The swelling was also determined to be reversible upon the transfer of the hydrogel to a solution having a lower glucose concentration than that of the solution of previous exposure. The impedance of the hydrogel was determined to depend solely on the thickness of the hydrogel and it had an average increase of 47 Ω/mm. Upon examining the surface microstructure of the hydrogel, it was concluded that the hydrogels exposed to 300 mg/dL glucose solution had a higher porosity ratio than the hydrogels exposed to the 100 mg/dL glucose solution. The diffusivity of 300 Da MW fluorescein isothiocyanate (FITC) was examined in hydrogels exposed to 100 mg/dL and 300 mg/dL glucose solutions and was found to be 9.31 x 10-14 m2/s and 41.4 x 10-14 m2/s, respectively, which was 3 to 4 orders of magnitude smaller than that of the FITC in glucose solution. Also, it was determined that there was an insignificant difference in the permeability of the hydrogels exposed to 100 mg/dL and 300 mg/dL glucose solutions with averages being 5.26 x 10-17 m2 and 5.80 x 10 -17 m2, respectively. These results demonstrate the feasibility of incorporating this hydrogel into a MEMS sensor to continuously monitor glucose levels. Such a sensor could be developed that can measure glucose concentration from changes in hydrogel thickness due to the swelling and shrinking of the hydrogel, which can be quantified by measuring the impedance across the polymer. Furthermore, such a sensor could be attached to the outer surface of a regular or drug-eluting FDA-approved stent to develop a continuous intravascular glucose monitoring system. This system would perform dual functions of monitoring glucose levels in the bloodstream while maintaining a patent vessel lumen.

Degree

M.S.B.M.E.

Advisors

Irazoqui, Purdue University.

Subject Area

Biomedical engineering

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