Can glucose be monitored accurately at the site of subcutaneous insulin delivery?

Combining Glucose Monitoring and Insulin Infusion in an Integrated Device: A Narrative Review of Challenges and Proposed Solutions

The introduction of automated insulin delivery (AID) systems has enabled increasing numbers of individuals with type 1 diabetes (T1D) to improve their glycemic control largely. However, use of AID systems is limited due to their complexity and costs associated. The user must wear both a continuously monitoring glucose system and an insulin infusion pump. The glucose sensor and the insulin catheter must be inserted at two different body sites using different insertion devices. In addition, the user must pair and manage the different systems. These communicate with the AID software implemented on the pump or on a third device such as a dedicated display device or smart phone application. These components might be developed and commercialized by different manufacturers, which in turn can cause difficulties for patients seeking technical support. A possible solution to these challenges would be to integrate the glucose sensor and insulin catheter into a single device. This would allow the glucose sensor and insulin catheter to be inserted simultaneously, eliminating the need for pairing, and simplifying system management. In recent years, different technologies have been developed and evaluated in clinical investigations that combine the glucose sensor and the insulin catheter in one platform. The consistent finding of all these studies is that integration has no adverse effect on insulin infusion and glucose measurements provided that certain conditions are met. In this review, we discuss the perceived challenges of such an approach and discuss possible solutions that have been proposed.

Glucose Sensor Accuracy After Subcutaneous Glucagon Injections Near to Sensor Site

Background: Integrated hormone delivery and glucose sensing is warranted, but system performance could be challenged by glucose sensor susceptibility to pharmacological interferences. The aim of this study was to compare sensor accuracy (Medtronic Enlite 2^®) after subcutaneous (s.c.) administration of low-dose glucagon near to versus remote from sensor site. Methods: Twelve adults with insulin-pump-treated type 1 diabetes wore two continuous glucose monitors (CGM_glucagon and CGM_control) placed on each side of the abdomen before, during, and after two overnight 14-h in-clinic visits. During each visit, a s.c. 100 μg glucagon injection was administered 2 cm next to the CGM_glucagon followed by another injection of 100 μg glucagon 2 h later at the same site. CGM performance was evaluated using 4-h in-clinic Yellow Spring Instrument (YSI) measurements and 3-day self-monitoring of blood glucose (SMBG) in free-living conditions. Results: Using YSI as comparator, no difference in the median absolute relative difference (MARD) for CGM_glucagon (15.7%) and CGM_control (13.4%) was found (P = 0.195). Similarly, no difference in MARD was found between CGM_glucagon (11.0%) and CGM_control (6.2%) using SMBG as comparator (P = 0.148). Values in zone A + B of Clarke error grid analysis did not differ between CGM_glucagon and CGM_control using YSI (93.9% vs. 91.1%, P = 0.250) and SMBG (97.3% vs. 95.0%, P = 0.375) as reference measurement. The precision absolute relative deviation between sensors was 13.7%. Conclusions: Sensor accuracy was not significantly affected by administration of s.c. glucagon near to sensor site.

Emerging Technologies for Diabetes Care

New therapies, monitoring, and revolutionary enabling technologies applied to healthcare represent an historic opportunity to improve the lives of people with diabetes. These advances enable more meaningful monitoring of blood glucose values with the facilitation of more optimal insulin dosing and delivery. Newer insulins and delivery systems are in development that seek to mitigate both hyperglycemia and hypoglycemia and increase time in range. Information systems now exist that may be leveraged to merge data from previously discrete systems into new models of connected care. This review highlights important developments that serve to increase effectiveness while reducing the burden of diabetes care in the near future.

An Amperometric Glucose Sensor Integrated into an Insulin Delivery Cannula: In Vitro and In Vivo Evaluation

BACKGROUND

Labeling prohibits delivery of insulin at the site of subcutaneous continuous glucose monitoring (CGM). Integration of the sensing and insulin delivery functions into a single device would likely increase the usage of CGM in persons with type 1 diabetes.

METHODS

To understand the nature of such interference, we measured glucose at the site of bolus insulin delivery in swine using a flexible electrode strip that was laminated to the outer wall of an insulin delivery cannula. In terms of sensing design, we compared H₂O₂-measuring sensors biased at 600 mV with redox mediator-type sensors biased at 175 mV.

RESULTS

In H₂O₂-measuring sensors, but not in sensors with redox-mediated chemistry, a spurious rise in current was seen after insulin lis-pro boluses. This prolonged artifact was accompanied by electrode poisoning. In redox-mediated sensors, the patterns of sensor signals acquired during delivery of saline and without any liquid delivery were similar to those acquired during insulin delivery.

CONCLUSION

Considering in vitro and in vivo findings together, it became clear that the mechanism of interference is the oxidation, at high bias potentials, of phenolic preservatives present in insulin formulations. This effect can be avoided by the use of redox mediator chemistry using a low bias potential.

A field effect glucose sensor with a nanostructured amorphous In-Ga-Zn-O network

Amorphous indium gallium zinc oxide (IGZO) field effect transistors (FETs) are a promising technology for a wide range of electronic applications. Herein, we fabricated and characterized FETs with a nanostructured IGZO network as a sensing transducer. The IGZO was patterned using colloidal lithography and electrohydrodynamic printing, where an 8 μm wide nanostructured close-packed hexagonal IGZO network was obtained. Electrical characterization of the nanostructured IGZO network FET demonstrated a drain-source current on-off ratio of 6.1 × 10³ and effective electron mobilities of 3.6 cm² V^-1 s^-1. The nanostructured IGZO network was functionalized by aminosilane groups with cross-linked glucose oxidase. The devices demonstrated a decrease in drain-source conductance and a more positive V_ON with increasing glucose concentration. These changes are ascribed to the acceptor-like surface states associated with positively charged aminosilane groups attached to the nanostructured IGZO surface. Continuous monitoring of the drain-source current indicates a stepwise and fully reversible response to glucose concentrations with a short response time. The specific catalytic reaction between the GOx enzyme and glucose eliminates interference from acetaminophen/ascorbic acid. We demonstrate that nanostructured IGZO FETs have improved sensitivity compared to non-nanostructured IGZO for sensing glucose and can be potentially extended to other biosensor technologies.

Glucose Sensing Using Functionalized Amorphous In-Ga-Zn-O Field-Effect Transistors

Recent advances in glucose sensing have focused on the integration of sensors into contact lenses to allow noninvasive continuous glucose monitoring. Current technologies focus primarily on enzyme-based electrochemical sensing which requires multiple nontransparent electrodes to be integrated. Herein, we leverage amorphous indium gallium zinc oxide (IGZO) field-effect transistors (FETs), which have found use in a wide range of display applications and can be made fully transparent. Bottom-gated IGZO-FETs can have significant changes in electrical characteristics when the back-channel is exposed to different environments. We have functionalized the back-channel of IGZO-FETs with aminosilane groups that are cross-linked to glucose oxidase and have demonstrated that these devices have high sensitivity to changes in glucose concentrations. Glucose sensing occurs through the decrease in pH during glucose oxidation, which modulates the positive charge of the aminosilane groups attached to the IGZO surface. The change in charge affects the number of acceptor-like surface states which can deplete electron density in the n-type IGZO semiconductor. Increasing glucose concentrations leads to an increase in acceptor states and a decrease in drain-source conductance due to a positive shift in the turn-on voltage. The functionalized IGZO-FET devices are effective in minimizing detection of interfering compounds including acetaminophen and ascorbic acid. These studies suggest that IGZO FETs can be effective for monitoring glucose concentrations in a variety of environments, including those where fully transparent sensing elements may be of interest.

Fabrication of a Flexible Amperometric Glucose Sensor Using Additive Processes

This study details the use of printing and other additive processes to fabricate a novel amperometric glucose sensor. The sensor was fabricated using a Au coated 12.7 μm thick polyimide substrate as a starting material, where micro-contact printing, electrochemical plating, chloridization, electrohydrodynamic jet (e-jet) printing, and spin coating were used to pattern, deposit, chloridize, print, and coat functional materials, respectively. We have found that e-jet printing was effective for the deposition and patterning of glucose oxidase inks with lateral feature sizes between ~5 to 1000 μm in width, and that the glucose oxidase was still active after printing. The thickness of the permselective layer was optimized to obtain a linear response for glucose concentrations up to 32 mM and no response to acetaminophen, a common interfering compound, was observed. The use of such thin polyimide substrates allow wrapping of the sensors around catheters with high radius of curvature ~250 μm, where additive and microfabrication methods may allow significant cost reductions.