Use of the site of subcutaneous insulin administration for the measurement of glucose in patients with type 1 diabetes

A Glucose-Responsive Cannula for Automated and Electronics-Free Insulin Delivery

Automated delivery of insulin based on continuous glucose monitoring is revolutionizing the way insulin-dependent diabetes is treated. However, challenges remain for the widespread adoption of these systems, including the requirement of a separate glucose sensor, sophisticated electronics and algorithms, and the need for significant user input to operate these costly therapies. Herein, a user-centric glucose-responsive cannula is reported for electronics-free insulin delivery. The cannula-made from a tough, elastomer-hydrogel hybrid membrane formed through a one-pot solvent exchange method-changes permeability to release insulin rapidly upon physiologically relevant varying glucose levels, providing simple and automated insulin delivery with no additional hardware or software. Two prototypes of the cannula are evaluated in insulin-deficient diabetic mice. The first cannula-an ends-sealed, subcutaneously inserted prototype-normalizes blood glucose levels for 3 d and controls postprandial glucose levels. The second, more translational version-a cannula with the distal end sealed and the proximal end connected to a transcutaneous injection port-likewise demonstrates tight, 3-d regulation of blood glucose levels when refilled twice daily. This proof-of-concept study may aid in the development of "smart" cannulas and next-generation insulin therapies at a reduced burden-of-care toll and cost to end-users.

Combining an Electrochemical Continuous Glucose Sensor With an Insulin Delivery Cannula: A Feasibility Study

BACKGROUND

Combining a continuous glucose monitor with an insulin delivery cannula (CGM-IS) could benefit clinical outcomes. We evaluated the feasibility of a single-needle insertion electrochemical investigational CGM-IS (Pacific Diabetes Technologies, Portland, Oregon) in type 1 diabetes adults.

METHODS

Following 48 hours run-in using a Medtronic 780G in manual mode with a commercial insulin set, 12 participants commenced insulin delivery using the CGM-IS. A standardized test meal was eaten on the mornings of days 1 and 4. Venous samples were collected every 10 minutes one hour prior to and 15 minutes post-meal for four hours. CGM-IS glucose measurements were post-processed with a single capillary blood calibration during warm-up and benchmarked against YSI. A Dexcom G6 sensor was worn post-consent to study end.

RESULTS

Mean absolute relative difference (MARD) for the CGM-IS glucose measurements was 9.2% (484 paired data points). Consensus error grid revealed 88.6% within zone A and 100% in A + B. Mean (SD) % bias was -3.5 (11.7) %. There were 35 paired YSI readings <100 mg/dL cutoff and 449 ≥100 mg/dL with 81.4% within ±15 mg/dL or ±15%, and 89.9% within ±20 mg/dL or ±20%. Two cannula occlusions required discontinuation of insulin delivery: one at 70 hours post insertion and another during the day 4 meal test. Mean (SD) Dexcom glucose measurements during run-in and between meal tests was respectively 161.3 ± 27.3 mg/dL versus 158.0 ± 25.6 mg/dL; P = .39 and corresponding mean total daily insulin delivered by the pump was 58.0 ± 25.4 Units versus 57.1 ± 28.8 Units; P = .47.

CONCLUSIONS

Insulin delivery and glucose sensing with the investigational CGM-IS was feasible. Longer duration studies are needed.

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.

Digital Diabetes Management: A Literature Review of Smart Insulin Pens

Digital health management is increasingly pivotal in the care of patients with diabetes. The aim of this review was to evaluate the clinical benefits of using smart insulin pens with connectivity for diabetes management. The search was performed using PubMed and PubMed Central on May 15, 2019, to identify publications investigating the use of insulin pens. Studies evaluating insulin pens with connectivity via Bluetooth/Near Field Communication, with an associated electronic device enabling connectivity, or with a memory function were included in the review. Nine studies were identified in the search. Overall, these studies lacked data on smart insulin pens with a connectivity function, with eight of the available studies investigating only pens with a memory function. The studies focused primarily on assessing patient preference, usability, and technical accuracy. The number of studies assessing clinical outcomes was small (n = 3). However, the majority of studies (n = 8) reported that patients preferred smart insulin pens because they increased confidence with regard to diabetes self-management. These results suggest a lack of published data regarding smart insulin pens with connectivity for the management of diabetes. However, the available published data on usability and patient preference suggest that the use of smart insulin pens holds promise for improving and simplifying diabetes self-management.

Measuring glucose at the site of insulin delivery with a redox-mediated sensor

Automated insulin delivery systems for people with type 1 diabetes rely on an accurate subcutaneous glucose sensor and an infusion cannula that delivers insulin in response to measured glucose. Integrating the sensor with the infusion cannula would provide substantial benefit by reducing the number of devices inserted into subcutaneous tissue. We describe the sensor chemistry and a calibration algorithm to minimize impact of insulin delivery artifacts in a new glucose sensing cannula. Seven people with type 1 diabetes undergoing automated insulin delivery used two sensing cannulae whereby one delivered a rapidly-acting insulin analog and the other delivered a control phosphate buffered saline (PBS) solution with no insulin. While there was a small artifact in both conditions that increased for larger volumes, there was no difference between the artifacts in the sensing cannula delivering insulin compared with the sensing cannula delivering PBS as determined by integrating the area-under-the-curve of the sensor values following delivery of larger amounts of fluid (P = 0.7). The time for the sensor to recover from the artifact was found to be longer for larger fluid amounts compared with smaller fluid amounts (10.3 ± 8.5 min vs. 41.2 ± 78.3 s, P < 0.05). Using a smart-sampling Kalman filtering smoothing algorithm improved sensor accuracy. When using an all-point calibration on all sensors, the smart-sampling Kalman filter reduced the mean absolute relative difference from 10.9% to 9.5% and resulted in 96.7% of the data points falling within the A and B regions of the Clarke error grid. Despite a small artifact, which is likely due to dilution by fluid delivery, it is possible to continuously measure glucose in a cannula that simultaneously delivers insulin.

Novel Single-Site Device for Conjoined Glucose Sensing and Insulin Infusion: Performance Evaluation in Diabetes Patients During Home-Use

OBJECTIVE

This study evaluated a novel diabetes treatment device that combines commercially available continuous glucose monitoring and insulin infusion technology in such a way as to perform insulin delivery and glucose sensing through a single skin insertion site (single-port device).

METHODS

Ten type 1 diabetes patients used the device for up to six days in their home/work environment for open-loop insulin delivery and glucose sensing. On an additional day, the device was used in combination with an algorithm to perform automated closed-loop glucose control under hospital settings. To assess the performance of the device, capillary blood glucose concentrations were frequently determined and a continuous glucose sensor was additionally worn by the patients.

RESULTS

The average mean absolute relative deviation from blood glucose concentrations obtained for the sensor of the device was low (median, 13.0%; interquartile range, 10.5-16.7%; n = 10) and did not differ from that of the additionally worn glucose sensor (versus 13.9%; 11.9-15.3%; P = 0.922). Furthermore, insulin delivery with the single-port device was reliable and safe during home use and, when performed in combination with the control algorithm, was adequate to achieve and maintain near normoglycemia.

CONCLUSION

Our data show the feasibility of open- and closed-loop glucose control in diabetes patients using a device that combines insulin delivery and glucose sensing at a single tissue site.

SIGNIFICANCE

The reduction in device size and invasiveness achieved by this design may largely increase patient convenience and enhance acceptance of diabetes treatment with continuous glucose monitoring and insulin delivery technology.

Development of a Single-Site Device for Conjoined Glucose Sensing and Insulin Delivery in Type-1 Diabetes Patients

OBJECTIVE

Diabetes patients are increasingly using a continuous glucose sensor to monitor blood glucose and an insulin pump connected to an infusion cannula to administer insulin. Applying these devices requires two separate insertion sites, one for the sensor and one for the cannula. Integrating sensor with cannula to perform glucose sensing and insulin infusion through a single insertion site would significantly simplify and improve diabetes treatment by reducing the overall system size and the number of necessary needle pricks. Presently, several research groups are pursuing the development of combined glucose sensing and insulin infusion devices, termed single-port devices, by integrating sensing and infusion technologies created from scratch.

METHODS

Instead of creating the device from scratch, we utilized already existing technologies and introduced three design concepts of integrating commercial glucose sensors and infusion cannulas. We prototyped and evaluated each concept according to design simplicity, ease of insertion, and sensing accuracy.

RESULTS

We found that the best single-port device is the one in which a Dexcom sensor is housed inside a Medtronic cannula so that its glucose sensitive part protrudes from the cannula tip. The low degree of component modification required to arrive at this configuration allowed us to test the efficiency and safety of the device in humans.

CONCLUSION

Results from these studies indicate the feasibility of combining commercial glucose sensing and insulin delivery technologies to realize a functional single-port device.

SIGNIFICANCE

Our development approach may be generally useful to provide patients with innovative medical devices faster and at reduced costs.

Technology in the management of type 1 diabetes mellitus - current status and future prospects

Type 1 diabetes mellitus (T1DM) represents 5-10% of diabetes cases worldwide. The incidence of T1DM is increasing, and there is no immediate prospect of a cure. As such, lifelong management is required, the burden of which is being eased by novel treatment modalities, particularly from the field of diabetes technologies. Continuous glucose monitoring has become the standard of care and includes factory-calibrated subcutaneous glucose monitoring and long-term implantable glucose sensing. In addition, considerable progress has been made in technology-enabled glucose-responsive insulin delivery. The first hybrid insulin-only closed-loop system has been commercialized, and other closed-loop systems are under development, including dual-hormone glucose control systems. This Review focuses on well-established diabetes technologies, including glucose sensing, pen-based insulin delivery, data management and data analytics. We also cover insulin pump therapy, threshold-based suspend, predictive low-glucose suspend and single-hormone and dual-hormone closed-loop systems. Clinical practice recommendations for insulin pump therapy and continuous glucose monitoring are presented, and ongoing research and future prospects are highlighted. We conclude that the management of T1DM is improved by diabetes technology for the benefit of the majority of people with T1DM, their caregivers and guardians and health-care professionals treating patients with T1DM.

Duration of Catheter Use in Patients with Diabetes Using Continuous Subcutaneous Insulin Infusion: A Review

Increasing proportions of patients with diabetes use continuous subcutaneous insulin infusion (CSII) therapy mostly due to its clinical efficacy and flexibility for insulin dosing and adjustments. Some challenges are nevertheless associated with this technology. A key and underlooked component of CSII technical difficulties is the subcutaneous catheter used to infuse insulin. Several adverse events (AEs) have been experienced by patients in relation to catheters, such as blockage, kinking, and insertion site reactions, including irritation, infections, lipohypertrophies etc., all of which could compromise the metabolic control. With the objective of minimizing these AEs, recommendations for changing catheters every 2-3 days have historically been provided by manufacturers based on reports derived from small studies and anecdotal data. The aim of this review was to provide an updated analysis of current recommendations and patients' practices in relation to frequency of catheter change. Our main findings are: (1) adequately designed and powered studies investigating optimal catheter wearing time are still lacking; (2) increasing catheter wearing time is generally associated with increased frequency of catheter AEs; (3) however, interpatient variability is large, with some individuals needing to change their catheters every 2-3 days, whereas others probably being able to keep them in place for longer periods without problems. Further research is thus warranted to provide more solid and evidence-based recommendations while exploring personalized approaches at the same time. Increasing catheter wear life without significant side effects is an important goal to simplify CSII therapy and reduce its associated costs and burdens.

Systematic in vivo evaluation of the time-dependent inflammatory response to steel and Teflon insulin infusion catheters

Continuous subcutaneous insulin infusion (CSII) catheters are considered the weak link of insulin pump therapy. Wear-time considerably varies between patients and the choice of catheter material is based on personal preferences rather than scientific facts. Therefore, we systematically assessed and quantified the inflammatory tissue response to steel versus Teflon CSII catheters over a maximum wear-time of 7 days in swine. Tissue surrounding catheters was analysed using histopathology and quantitative real-time PCR. The area of inflammation increased significantly over time independent of material which was confirmed by an increase in CD68 expression and an increase in mononuclear and neutrophil cell infiltrate around the catheters. We observed substantially higher fibrin deposition (p < 0.05) around steel on day 4 of wear-time. IL-6 gene expression increased within 24 hours after insertion, returned to normal levels around Teflon (p < 0.05) but remained high around steel (p < 0.05). IL-10 and TGF-β levels did not resolve over time, indicating impaired wound healing. In conclusion, there was a major temporal effect in the acute inflammatory response to CSII catheters but we found little difference between materials. This study setup presents a robust tool for the systematic analysis of the tissue response to CSII catheters.

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.

Moving Toward a Unified Platform for Insulin Delivery and Sensing of Inputs Relevant to an Artificial Pancreas

Advances in insulin pump and continuous glucose monitoring technology have primarily focused on optimizing glycemic control for people with type 1 diabetes. There remains a need to identify ways to minimize the physical burden of this technology. A unified platform with closely positioned or colocalized interstitial fluid glucose sensing and hormone delivery components is a potential solution. Present challenges to combining these components are interference of glucose sensing from proximate insulin delivery and the large discrepancy between the life span of current insulin infusion sets and glucose sensors. Addressing these concerns is of importance given that the future physical burden of this technology is likely to be even greater with the ongoing development of the artificial pancreas, potentially incorporating multiple hormone delivery, glucose sensing redundancy, and sensing of other clinically relevant nonglucose biochemical inputs.

First application of a transcutaneous optical single-port glucose monitoring device in patients with type 1 diabetes mellitus

The combination of continuous glucose monitoring (CGM) and continuous subcutaneous insulin infusion can be used to improve the treatment of patients with diabetes. The aim of this study was to advance an existing preclinical single-port system for clinical application by integrating the sensors of a phosphorescence based CGM system into a standard insulin infusion set. The extracorporeal optical phase fluorimeter was miniaturised and is now comparable with commercial CGM systems regarding size, weight and wear comfort. Sensor chemistry was adapted to improve the adhesion of the sensor elements on the insulin infusion set. In-vitro tests showed a linear correlation of R²=0.998 between sensor values and reference glucose values in the range of 0-300mg/dl. Electrical and cytotoxicity tests showed no negative impact on human health. Two single-port devices were tested in each of 12 patients with type 1 diabetes mellitus in a clinical set-up for 12h. Without additional data processing, the overall median absolute relative difference (median ARD) was 22.5%. For some of the used devices the median ARD was even well below 10%. The present results show that individual glucose sensors performance of the single-port system is comparable with commercial CGM systems but further improvements are needed. The new system offers a high extent of safety and usability by combining insulin infusion and continuous glucose measurement in a single-port system which could become a central element in an artificial pancreas for an improved treatment of patients with type 1 diabetes mellitus.

AP@home: The Artificial Pancreas Is Now at Home

In the past years the development of an artificial pancreas (AP) has made great progress and many activities are ongoing in this area of research. The major step forward made in the last years was moving the evaluation of AP systems from highly controlled experimental conditions to daily life conditions at the home of patients with diabetes; this was also the aim of the European Union-funded AP@home project. Over a time period of 5 years a series of clinical studies were performed that culminated in 2 "final studies" during which an AP system was used by patients in their home environment for 2 or 3 months without supervision by a physician, living their normal lives. Two different versions of the AP system developed within this project were evaluated. A significant improvement in glycated hemoglobin was observed during closed-loop conditions despite the fact that during the control period the patients used the best currently available therapeutic option. In addition, a "single-port AP system" was developed within the project that combines continuous glucose monitoring and insulin infusion at a single tissue site. By using such a combined device the patients not only have to carry one less device around, the number of access points through the skin is also reduced from 2 to 1. In summary, close cooperation of 12 European partners, both academic centers and industry, enabled the development and evaluation of AP systems under daily life conditions. The next step is to develop these into products in cooperation with commercial partners.

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

Because insulin promotes glucose uptake into adipocytes, it has been assumed that during measurement of glucose at the site of insulin delivery, the local glucose level would be much lower than systemic glucose. However, recent investigations challenge this notion. What explanations could account for a reduced local effect of insulin in the subcutaneous space? One explanation is that, in humans, the effect of insulin on adipocytes appears to be small. Another is that insulin monomers and dimers (from hexamer disassociation) might be absorbed into the circulation before they can increase glucose uptake locally. In addition, negative cooperativity of insulin action (a lower than expected effect of very high insulin concentrations)may play a contributing role. Other factors to be considered include dilution of interstitial fluid by the insulin vehicle and the possibility that some of the local decline in glucose might be due to the systemic effect of insulin. With regard to future research, redundant sensing units might be able to quantify the effects of proximity, leading to a compensatory algorithm. In summary, when measured at the site of insulin delivery, the decline in subcutaneous glucose level appears to be minimal, though the literature base is not large. Findings thus far support (1) the development of integrated devices that monitor glucose and deliver insulin and (2) the use of such devices to investigate the relationship between subcutaneous delivery of insulin and its local effects on glucose. A reduction in the number of percutaneous devices needed to manage diabetes would be welcome.

What Are the Next Steps in Continuous Glucose Monitoring?

The development of glucose sensors for continuous glucose monitoring (CGM) is likely still in its early days. A number of novel approaches-along with many attempts to improve current CGM systems-are in development. The next generation of glucose sensors (NGGS) will also enable, for example, reliable glucose measurement in the low glycemic range. NGGS systems represent an important step forward for closed-loop systems. This commentary discusses a number of aspects that are relevant in this context.

Patch pump versus conventional pump: postprandial glycemic excursions and the influence of wear time

BACKGROUND AND AIMS

The aim of this study was to compare blood glucose and plasma insulin profiles after bolus insulin infusion by a patch pump (PP) versus a conventional pump (CP), directly after placement and after Day 3 of use.

PATIENTS AND METHODS

Twenty patients with type 1 diabetes came in for two blocks of visits: one block of two visits while wearing the OmniPod® (Insulet Corp., Bedford, MA) insulin pump (PP) and one block of two visits while wearing the Medtronic Diabetes (Northridge, CA) Paradigm® pump (CP). Patients administered an identical mealtime insulin bolus of at least 6 IU.

RESULTS

For PP, maximum glucose levels were 28.7% lower on Day 3 (P=0.020), when maximum insulin levels were 30.3% higher (P=0.002). For CP, maximum glucose levels were 26.5% lower on Day 3 (P=0.015), when maximum insulin levels were 46.4% higher (P=0.003). Glucose levels (mean [interquartile range]) were significantly lower on Day 3 for PP (168.2 [145.8] mg/dL vs. 139.4 [77.8] mg/dL; P=0.013), but not significantly so for CP (159.0 [66.1] mg/dL vs. 139.5 [57.9] mg/dL; P=0.084). Mean insulin levels were significantly higher on Day 3 for CP (195 [120] pmol/L vs. 230 [90] pmol/L; P=0.01), but not significantly so for PP (178 [106] pmol/L vs. 194 [120] pmol/L; P=0.099). There were no significant differences between the two catheter lengths.

CONCLUSIONS

Postprandial glycemic excursions were lower on Day 3 of catheter wear time, but there were no differences between PPs and CPs. These findings support the proposal that catheter wear time plays an important role in insulin absorption.

Feasibility of adjacent insulin infusion and continuous glucose monitoring via the Medtronic Combo-Set

BACKGROUND

Subcutaneously infused insulin may interfere with the function of nearby glucose-sensing electrodes and vice versa. The prototype of the Combo-Set device (Medtronic) incorporates a subcutaneous insulin delivery catheter and continuous glucose monitoring (CGM) sensor assembled on the same platform and separated by 11 mm. We aim to evaluate Combo-Set's insulin delivery and glucose-sensing functions.

METHODS

Ten subjects with type 1 diabetes wore a Combo-Set and a Sof-Sensor inserted subcutaneously in contralateral abdominal areas connected to iPro recorders (Medtronic) for 53.25 ± 0.75 h (mean ± standard deviation). The Combo-Set delivered insulin diluent except during meal tests on days 1 and 3 when insulin lispro was delivered as a meal bolus and postmeal basal. Venous plasma samples were collected at the following time points from meal start: 0, 30, 60, 120, and 180 min for insulin measurements. The accuracy of the Combo-Set sensors was evaluated and compared with that of the Sof-Sensor, with each referenced against capillary glucose values (Contour Link Meter, Bayer).

RESULTS

Accuracy of the Combo-Set sensor was comparable to that of the Sof-Sensor. Clarke error grid analysis showed that 97% of Combo-Set and 93% of Sof-Sensor values were in the A+B regions (p = .20, not significant). The Combo-Set showed the expected postbolus peak insulin time (67 ± 9 min, mean ± standard error). One "no delivery" alarm occurred during the 21 patient days of use.

CONCLUSION

A device providing for simultaneous adjacent placement of an insulin infusion catheter and a CGM sensor is feasible and functions within acceptable limits. The low "no delivery" alarm rate was similar to that of other infusion sets.

Periodic extraction of interstitial fluid from the site of subcutaneous insulin infusion for the measurement of glucose: a novel single-port technique for the treatment of type 1 diabetes patients

BACKGROUND

Treatment of type 1 diabetes patients could be simplified if the site of subcutaneous insulin infusion could also be used for the measurement of glucose. This study aimed to assess the agreement between blood glucose concentrations and glucose levels in the interstitial fluid (ISF) that is extracted from the insulin infusion site during periodic short-term interruptions of continuous subcutaneous insulin infusion (CSII).

SUBJECTS AND METHODS

A perforated cannula (24 gauge) was inserted into subcutaneous adipose tissue of C-peptide-negative type 1 diabetes subjects (n=13) and used alternately to infuse rapid-acting insulin (100 U/mL) and to extract ISF glucose during a fasting period and after ingestion of a standard oral glucose load (75 g).

RESULTS

Although periodically interrupted for extracting glucose (every hour for approximately 10 min), insulin infusion with the cannula was adequate to achieve euglycemia during fasting and to restore euglycemia after glucose ingestion. Furthermore, the ISF-derived estimates of plasma glucose levels agreed well with plasma glucose concentrations. Correlation coefficient and median absolute relative difference values were found to be 0.95 and 8.0%, respectively. Error grid analysis showed 99.0% of all ISF glucose values within clinically acceptable Zones A and B (83.5% Zone A, 15.5% Zone B).

CONCLUSIONS

Results show that ISF glucose concentrations measured at the insulin infusion site during periodic short-term interruptions of CSII closely reflect blood glucose levels, thus suggesting that glucose monitoring and insulin delivery may be performed alternately at the same tissue site. A single-port device of this type could be used to simplify and improve glucose management in diabetes.

Analysis of insulin in human breast milk in mothers with type 1 and type 2 diabetes mellitus

Despite the important role that insulin plays in the human body, very little is known about its presence in human milk. Levels rapidly decrease during the first few days of lactation and then, unlike other serum proteins of similar size, achieve comparable levels to those in serum. Despite this, current guides for medical treatment suggest that insulin does not pass into milk, raising the question of where the insulin in milk originates. Five mothers without diabetes, 4 mothers with type 1, and 5 mothers with type 2 diabetes collected milk samples over a 24-hour period. Samples were analysed for total and endogenous insulin content and for c-peptide content. All of the insulin present in the milk of type 1 mothers was artificial, and c-peptide levels were 100x lower than in serum. This demonstrates that insulin is transported into human milk at comparable concentration to serum, suggesting an active transport mechanism. The role of insulin in milk is yet to be determined; however, there are a number of potential implications for the infant of the presence of artificial insulins in milk.

AP@home: a novel European approach to bring the artificial pancreas home

The development of an artificial pancreas (AP) made huge strides from 2006 to 2008 and a large number of activities are going on in this area of research. Until now, most AP systems under development were tested only under highly controlled conditions. The aim of our project, funded by the European Union, is to develop an AP system to such a level that it can be studied under daily life conditions at the home of patients with diabetes (hence AP@home). Based on a subcutaneous-subcutaneous closed-loop strategy (i.e., glucose sensing and insulin infusion in the subcutaneous tissue), two different approaches will be taken to achieve this aim: a two-port AP system and a single-port AP system. The two-port AP system will use off-the-shelf-components for the glucose sensor and insulin pump in combination with closed-loop algorithms generated in Europe. As to the single-port AP system, two different innovative single-port systems will be developed; in this case, continuous glucose monitoring and insulin infusion will take place via a single catheter. The first clinical trials with the two-port AP system under controlled clinical conditions have started and good progress has been made in the development of the single-port AP systems. We believe that our consortium of 12 European partners, which builds on existing achievements and close cooperation between academic centers and industry, can contribute substantially to the development of an AP system that can be used by patients in daily life.

Effect of the sensor site-insulin injection site distance on the dynamics of local glycemia in the minipig model

BACKGROUND

Previous studies have shown that at the near steady state attained by slow insulin infusion, the local glycemia of subcutaneous fluid tracks the venous glucose concentration (i.e., it is not perturbed by the infusion of insulin). Here we test whether the subcutaneous glycemia near the site of injection of a bolus of insulin is perturbed by the injection in the minipig model without diabetes.

METHODS

A bolus of short-acting diluted insulin was administered in the animal's flank while three to five continuous glucose monitoring systems measured the subcutaneous glucose concentrations at 0.5, 1, 2, and 3 cm ("near sensors") and at 10-15 cm ("far sensors") from the injection site.

RESULTS

We found no statistically significant (P < 0.05) evidence that near and far sensors differ in response time, that is, the elapsed time to onset of signal drop or the elapsed time to minimum signal following insulin injection. We found mixed evidence that near and far sensors differ in the percentage drops at the glycemic minimum. The near versus far difference for near sensors at 0.5 and 3 cm from the injection site was statistically significant (P < 0.05): the average percentage drops for these near sensors were 3% and 11%, respectively, below those for far sensors. We did not find evidence of a difference for near sensors at 1 and 2 cm.

CONCLUSIONS

Because there is some evidence that insulin injection can cause a minor perturbation (about ≤10%) in the local glycemia, caution is warranted when co-locating glucose sensing and insulin injection sites.

Closed-loop insulin delivery: from bench to clinical practice

Automated closed-loop insulin delivery, also referred to as the 'artificial pancreas', has been an important but elusive goal of diabetes treatment for many decades. Research milestones include the conception of continuous glucose monitoring in the early 1960s, followed by the production of the first commercial hospital-based artificial pancreas in the late 1970s that combined intravenous glucose sensing and insulin delivery. In the past 10 years, research into the artificial pancreas has gained substantial momentum and focused on the subcutaneous route for glucose measurement and insulin delivery, which reflects technological advances in interstitial glucose monitoring and the increasing use of the continuous subcutaneous insulin infusion. This Review discusses the design of an artificial pancreas, its components and clinical results, as well as the advantages and disadvantages of different types of automated closed-loop systems and potential future advances. The introduction of the artificial pancreas into clinical practice will probably occur gradually, starting with simpler approaches, such as overnight control of blood glucose concentration and temporary pump shut-off, that are adapted to more complex situations, such as glycemic control during meals and exercise.