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Ollmar S, Fernandez Schrunder A, Birgersson U, Kristoffersson T, Rusu A, Thorsson E, Hedenqvist P, Manell E, Rydén A, Jensen-Waern M, Rodriguez S. A battery-less implantable glucose sensor based on electrical impedance spectroscopy. Sci Rep 2023; 13:18122. [PMID: 37872272 PMCID: PMC10593792 DOI: 10.1038/s41598-023-45154-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 10/17/2023] [Indexed: 10/25/2023] Open
Abstract
The ability to perform accurate continuous glucose monitoring without blood sampling has revolutionised the management of diabetes. Newer methods that can allow measurements during longer periods are necessary to substantially improve patients' quality of life. This paper presents an alternative method for glucose monitoring which is based on electrical impedance spectroscopy. A battery-less implantable bioimpedance spectroscope was designed, built, and used in an in vivo study on pigs. After a recovery period of 14 days post surgery, a total of 236 subcutaneous bioimpedance measurements obtained from intravenous glucose tolerance tests, with glucose concentration ranges between 77.4 and 523.8 mg/dL, were analyzed. The results show that glucose concentrations estimated by subcutaneous bioimpedance measurements correlate very well to the blood glucose reference values. The pigs were clinically healthy throughout the study, and the postmortem examinations revealed no signs of adverse effects related to the sensor. The implantation of the sensor requires minor surgery. The implant, being externally powered, could in principle last indefinitely. These encouraging results demonstrate the potential of the bioimpedance method to be used in future continuous glucose monitoring systems.
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Affiliation(s)
- Stig Ollmar
- Department of Clinical Science, Intervention and Technology, Karolinska Institute, Stockholm, Sweden
| | | | - Ulrik Birgersson
- Department of Clinical Science, Intervention and Technology, Karolinska Institute, Stockholm, Sweden
| | | | - Ana Rusu
- School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, 16440, Kista, Sweden
| | - Elina Thorsson
- Pathology Unit, Department of Biomedical Science and Veterinary Public Health, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Patricia Hedenqvist
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Elin Manell
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Anneli Rydén
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Marianne Jensen-Waern
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden
| | - Saul Rodriguez
- School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, 16440, Kista, Sweden.
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Choi H, Barker E, Abduljabar AA, Anumba D, Porch A. Cervical Tissue Hydration Level Monitoring by a Resonant Microwave Coaxial Probe. SENSORS (BASEL, SWITZERLAND) 2022; 22:9527. [PMID: 36502229 PMCID: PMC9738423 DOI: 10.3390/s22239527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 11/24/2022] [Accepted: 11/29/2022] [Indexed: 06/17/2023]
Abstract
Cervical tissue hydration level is one of the most important parameters to monitor in the early diagnosis of preterm birth. Electrical-impedance-spectroscopy-based techniques are often used, but they suffer from limited accuracy. Open microwave coaxial probes have been widely used as a broadband dielectric characterization technique for human tissue samples due to their versatility, but with limited accuracy due to their nonresonant nature. In this work, a resonant microwave open coaxial probe with multiple harmonic resonances is proposed as a sensing platform for tissue-hydration-level monitoring. The mechanical design was analyzed and verified by finite-element full 3D electromagnetic simulation and experiments. Dominant sources of errors and the ways to mitigate them were discussed. In vitro experiments were carried out on human cervix samples to verify the precision and accuracy by comparing the results to a commercial skin-hydration sensor. The proposed sensor shows mean fractional frequency shift of (3.3 ± 0.3) × 10-4 per unit % over the entire data. This translates into an absolute frequency shift (ΔfN) of 252 ± 23 kHz/%, 455 ± 41 kHz/%, and 647 ± 57 kHz/% at second, fourth, and sixth harmonic resonance, respectively.
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Affiliation(s)
- Heungjae Choi
- School of Engineering, Cardiff University, 14-17 The Parade, Cardiff CF24 3AA, UK
| | - Emilia Barker
- School of Clinical Dentistry, University of Sheffield, 19 Claremont Crescent, Sheffield S10 2TA, UK
| | | | - Dilly Anumba
- Department of Oncology and Metabolism, JW4/40, Level 4, Jessop Wing, Tree Root Walk, Sheffield S10 2SF, UK
| | - Adrian Porch
- School of Engineering, Cardiff University, 14-17 The Parade, Cardiff CF24 3AA, UK
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