Sensors implantable

Most of the sensors implanted in the subcutaneous tissue are 200-250 jam (33-31 ga) in diameter. They are usually implanted using a guide cannula whose outside diameter is 21-23 ga (813-635 jam). This insertion process will cause some tissue injury including breaking of capillaries. Experience in our laboratories has shown, however, that the damage is very slight and an edema around the implant, typically the size of a mosquito bite, disappears after about 24 h. 

Thome-Duret V, Gangnerau MN, Zhang Y, Wilson GS, Reach G. Modification of the sensitivity of glucose sensor implanted into subcutaneous tissue. Diabete et Metabolisme 1996, 22, 174-178. 

CholeauC, Klein JC, Reach G, AussedatB, Demaria-Pesce V, Wilson GS, Gifford R, Ward WK. Calibration of a subcutaneous amperometric glucose sensor implanted for 7 days in diabetic patients. Part 2. Superiority of the one-point calibration method. Biosensors Bioelectronics 2002, 17, 647-654. 

Sensors implanted in experimental subjects need to be carefully calibrated prior to testing in vivo. Immediately following testing, calibration validation needs to be performed to demonstrate that the calibration was not lost during the testing procedure. It is important to maintain proper calibration to eliminate any variability produced by the sensors themselves. If sensors are not appropriately calibrated prior to experimentation, it will not be possible to get an accurate measure of the variability due to tissue effects. 

Johnson K, Mastrototaro J, Howey D, Brunelle R, Burden-Brady P, Bryan N, Andrew C, Rowe H, Allen D, Noffke B, McMahan WC, Morff RJ, Lipson D, Nevin RS. In vivo evaluation of an electroenzymatic glucose sensor implanted in subcutaneous tissue. Biosensors Bioelectronics 1992, 7, 709-714. 

Moatti-Sirat D, Capron F, Poitout V, Reach G, Bindra D, Zhang Y, Wilson G, Thevenot D. Towards continuous glucose monitoring in vivo evaluation of a miniaturized glucose sensor implanted for several days in rat subcutaneous tissue. Diabetologia 1992, 35, 225. 

Figure 9.8 Tissue cross-section of (A) control and (B) NO-releasing sensor implant site. Reprinted from Ref. 48 with permission of John Wiley Sons, Inc. Copyright 2005 John Wiley Sons, Inc. (See the color version of this figure in Color Plates section.)...

The efficacy of exciting and collecting emission data from PEG hydrogel sensors implanted in an in vivo rat model was also assessed experimentally.115... 

Transdermal emission spectra were successfully collected from sensors implanted approximately 500 pm below the skin surface. In addition, a bolus injection of glucose into the tail vein resulted in measurable spectral changes from the implants. This important developmental step proved some feasibility of the smart tattoo concept as a means of monitoring glucose in a minimally invasive manner. 

Healthcare personalized access for individuals, relatives, care givers, and other specialists to real-time or historical information generated by wearable sensors, implantable devices, or home-based diagnostics units will facilitate the movement towards home- or community-based healthcare rather than the current, unsustainable, hospital-centric model in the developed world. In addition, access to low cost communications and diagnostics will also provide a means to rapidly improve the delivery of healthcare in less well-developed regions. 

An example of the response of the glucose sensor implanted subcutaneously in a rat is shown in Figure 1. The glycaemia modification was performed by an intramuscular administration of glucagon at time zero followed by insulin at time 30. The so called "apparent subcutaneous glycaemia" (6,7), calculated using one point in vivo calibration matched quite closely the concomittantly measured plasma glycaemia. 

The major problem that has plagued these kinds of implantable biosensors is the gradual decrease in sensitivity and in some cases a complete loss of function within just hours of implantation. Biofouling, oxygen limitation, electrochemical interference and GOD inactivation have been considered as explanations of this behaviour. For instance, a tissue reaction to the sensor implantation may result in a limitation in the blood supply to the tissue surrounding the probe and thus in a lower availability of glucose and oxygen. 

Kessler et al. (1984) developed a glucose sensor with an extremely low oxygen demand and a stability of 3 months, which appears to be suitable for implantation. Another sensor that might be implantable is based on the use of ferrocene as an electron acceptor for GOD (Cass et al., 1984 David et al., 1985), which eliminates the need for oxygen. The sensor exhibits an advantageous linear range of 1-30 mmol/l. However, experiments with the sensor implanted subcutaneously in animals revealed a rapid sensitivity decrease (Pickup, 1987). 

Biomimetic/cell/ tissue-based sensors, instrumented cells (nanocanary), e.g., B-cell sensors implantable sensor devices with presymp-tomatic sensitivity to biomarkers... 

The described optical effects could also be used for implanted biosensors which combine the aspects of biocompatibility and biodegradability with the optical effects which are retained upon implantation. Monitoring of a sensor implanted underneath the skin can be accomplished by merely... 

Prichard HL, Schroeder T, Reichert WM, Klitzman B. Bioluminescence imaging of glucose in tissne snrrounding polynrethane and glncose sensor implants. Journal of Diabetes... 

Edagawa K, Fuchiwaki Y, Yasuzawa M. In vivo evaluation of fine needle amperometric glucose sensors implanted in rabbit s blood vessel. Journal of the Electrochemical Society 2014 161(2). B3111-B5. 

Pickup, J. C., Claremont, D. J., Shaw, G. W. (1993). Responses and cahbration of amper-ometric glucose sensors implanted in the subcutaneous tissue of man (Translated from Enghsh). Acta Diabetologica, 30(3), 143-148 (in English). 

Implantable devices Assessment and treatment devices Implantable sensors Implantable medical devices Sensory aids Retina implants Cochlear implants... 

Kondo T, Ito K, Ohkura K, Ito K, Bceda S (1982) A miniature glucose sensor, implantable in the blood stream. Diabetes Care 5(3) 218-221... 

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