Intraocular lens glucose sensor

A visually distinguishable light interfering bioresponsive silica nanoparticle hydrogel sensor fabricated through the molecular imprinting technique

Methods of the early detection of diseases are based on recognition of the smallest change in the levels of a disease-specific biomarker in body fluids.

Continuous glucose monitoring: 40 years, what we've learned and what's next

After 40 years of research and development, today continuous glucose monitoring (CGM) is demonstrating the benefit it provides for millions with diabetes. To provide in vivo accuracy, new permselective membranes and mediated systems have been developed to prevent enzyme saturation and to minimize interference signals. Early in vivo implanted sensor research clearly showed that the foreign body response was a more difficult issue to overcome. Understanding the biological interface and circumventing the inflammatory response continue to drive development of a CGM sensor with accuracy and reliability performance suitable in a closed-loop artificial pancreas. Along with biocompatible polymer development, other complimentary algorithm and data analysis techniques have improved the performance of commercial systems significantly. For example, the mean average relative difference of Dexcom's CGM system improved from 26 to 14% and its use-life was extended from 3 to 7 d. Significant gains in usability, including size, flexibility, insertion, calibration, and data interface, have been incorporated into new generations of commercial CGM systems. Besides Medtronic, Dexcom, and Abbott, other major players are also investing in CGM. Becton Dickinson is conducting clinical trials with an optical galactose glucose binding system. Development of fully implanted sensor systems fulfills the desire for a discreet, reliable CGM system. Research continues to find innovative ways to help make living with diabetes easier and more normal, and new segments are being pursued (intensive care unit, surgery, behavior modification) in which CGM is being utilized.

First clinical evaluation of a new long-term subconjunctival glucose sensor

BACKGROUND

To evaluate the feasibility of an implantable subconjunctival glucose monitoring system (SGMS) for glucose monitoring in humans, we investigated the in vivo performance of the sensor in a clinical trial with five patients.

METHODS

The new SGMS consists of an implantable ocular mini implant (OMI) and a hand-held fluorescence photometer. The implantable subconjunctival glucose sensor is composed of a fluorescence resonance energy transfer system based on Concanavalin A chemistry, embedded in a nelfilcon polymer hydrogel disk. Blood glucose changes in humans were induced by oral glucose intake and insulin injections.

RESULTS

The in vivo response of the new SGMS was tested in a first human clinical study with five diabetes patients. The OMI was well tolerated in the eyes of the patients. The SGMS exhibited high correlation coefficients (>0.88) with blood glucose changes and a good stability of the sensor response to glucose for the study period of 2 weeks. Lag times were in the range of 5-10 min. A total of 98% of all data pairs was in the clinical acceptable ranges A and B of the consensus error grid.

CONCLUSIONS

For the first time, the possibility to measure glucose in vivo in the subconjunctival interstitial fluid for a period of 2 weeks was demonstrated in a human clinical trial.

Diabetes and contact lens wear

The literature suggests that diabetic patients may have altered tear chemistry and tear secretion as well as structural and functional changes to the corneal epithelium, endothelium and nerves. These factors, together with a reported increased incidence of corneal infection, suggest that diabetic patients may be particularly susceptible to developing ocular complications during contact lens wear. Reports of contact lens-induced complications in diabetic patients do exist, although a number of these reports concern patients with advanced diabetic eye disease using lenses on an extended wear basis. Over the past decade or so, there have been published studies documenting the response of the diabetic eye to more modern contact lens modalities. The results of these studies suggest that contact lenses can be a viable mode of refractive correction for diabetic patients. Furthermore, new research suggests that the measurement of tear glucose concentration could, in future, be used to monitor metabolic control non-invasively in diabetic patients. This could be carried out using contact lenses manufactured from hydrogel polymers embedded with glucose-sensing agents or nanoscale digital electronic technology. The purpose of this paper is to review the literature on the anterior ocular manifestations of diabetes, particularly that pertaining to contact lens wear.

Preclinical in vivo study of a fluorescence affinity sensor for short-term continuous glucose monitoring in a small and large animal model

BACKGROUND

The performance of a fiber-coupled fluorescence affinity sensor (FAS) was studied in vivo in small and large animal models, in order to assess its feasibility and safety for short-term glucose monitoring in humans.

METHODS

Determination of interstitial glucose concentrations in skin tissue of hairless rats and small pigs was facilitated by measuring the fluorescence response of the implanted FAS over several hours and multiple days. Blood sugar changes in animals were induced by injections of insulin and dextrose. The Medtronic Minimed CGMS (Medtronic Diabetes, Northridge, CA) was used for comparison.

RESULTS

The acute in vivo performance study of the fiber-coupled FAS showed that more than 96% of the paired FAS/venous blood glucose readings were in the clinically acceptable A and B regions of the Clarke Error Grid. Mean absolute relative difference (MARD) and root mean squared error (RMSE) values for small and large animal models were 18.5% and 19.8 mg/dL and 15.9% and 16.3 mg/dL, respectively. In comparison, MARD and RMSE for the Medtronic Minimed CGMS in small and large animal models were similar (in rats, 25.4% and 19.8 mg/dL, respectively; in pigs, 18.4% and 16.2 mg/dL, respectively). No instance of irritation or infection was observed at any implantation site. The in vivo performance of FAS over a 3-day period was successfully demonstrated in both animal models.

CONCLUSIONS

Overall, the fiber-coupled FAS was safe, and its performance during 4-h and 3-day testing compared favorably to the commercially available Medtronic Minimed CGMS, indicating its potential value for diabetes management.

Fiber-coupled fluorescence affinity sensor for 3-day in vivo glucose sensing

BACKGROUND

To evaluate the feasibility of an implantable fiber-coupled fluorescence affinity sensor (FAS) for glucose monitoring in humans, we studied the acute and chronic in vivo performance in hairless rats and pigs.

METHODS

The implantable fiber-coupled FAS was constructed by filling a dialysis chamber made of a regenerated cellulose membrane mounted to the distal tip of an optical fiber with fluorescent chemistry based on concanavalin A. Blood sugar changes in animals were induced by injections of insulin and dextrose. Determination of interstitial glucose concentrations in skin tissue was facilitated by measuring the fluorescence response of the FAS.

RESULTS

The acute in vivo response of the fiber-coupled FAS exhibited good correlation coefficients (>0.77) with blood sugar changes and minimal lag times (2-10 min) after 2 hours of sensor implantation. Equilibrium of the sensor signal with interstitial fluid was required less than 60 min after implantation. For both rats and pigs, chronic response of the FAS to blood sugar modulations measured during the third day of implantation successfully demonstrated proof-of-concept for short-term glucose monitoring. A slight decrease in sensitivity after 3 days in the small animal model was assumed to be caused by excessive mechanical forces on the implanted device because of high animal motility.

CONCLUSIONS

Overall, the chronic in vivo performance of the FAS in two different animal models over 3 days was clinically acceptable and comparable to other continuous glucose monitoring platforms. The major benefit of the FAS is the absence of "autodestructive" side products and any device-related warm-up time after sensor reconnection.

Fluorescent measurement in the non-invasive contact lens glucose sensor

BACKGROUND

The purpose of the present study was to determine the effectiveness of software in the hand-held photofluorometer permitting the monitoring of a second fluorescent signal to improve a contact lens glucose sensor for the non-invasive monitoring of glucose.

METHODS

One fasting normal patient was given an oral challenge consisting of 75 mL of Sustacol (Thomson Micromedex, Greenwood, CO). The two contact lens fluorescent signals and fingerstick blood glucose were measured over a 3-h period.

RESULTS

Subtracting the second fluorescent signal from the main signal produced a product that appeared to track blood glucose well. The contact lens was comfortable and well tolerated.

CONCLUSION

The biwavelength contact lens glucose sensor shows promise as a non-invasive home glucose monitor.

Concanavalin A for in vivo glucose sensing: a biotoxicity review

Over the last two decades there as has been surging scientific interest in employing the glucose- and mannose-specific lectin Concanavalin A (ConA) in affinity biosensors for in vivo glucose monitoring in diabetics. Numerous research groups have successfully shown in in vitro and in vivo studies that ConA-based affinity sensors can monitor glucose very accurately and reproducibly over many months, making ConA-based sensors an extremely interesting prospect for long-term implantation in humans. Despite this progress, there remains concern over the safety of ConA, which has widely been reported as a toxin in the literature. In this article, we review in vitro and in vivo studies related to ConA toxicity in order to assess the health risks posed by ConA in the context of an implantable biosensor. Based on the wealth of information available and on data from our own studies, we can conclude that the site of implantation (subcutaneous skin tissue) and the small amount of ConA (<10 microg/microl) being used in implantable glucose-sensitive detector devices like those proposed by various research groups would pose little or no health risk to its bearer even in the event of unexpected sensor rupture.

Initial clinical testing of a holographic non-invasive contact lens glucose sensor

INTRODUCTION

The purpose of the present study was to determine the effectiveness of a new holographic contact lens glucose sensor for the non-invasive monitoring of blood glucose.

METHODS

One fasting normal subject was given an oral challenge consisting of 44 g of glucose. The contact lens hologram signal and fingerstick blood glucose were measured over a 26- min period.

RESULTS

The contact lens hologram signal appeared to track blood glucose well. The contact lens was comfortable and well tolerated.

CONCLUSION

The holographic contact lens glucose sensor shows promise as a non-invasive home glucose monitor.

Clinical trial of a noninvasive contact lens glucose sensor

OBJECTIVE

The purpose of the present study was to determine the effectiveness of a fluorescent contact lens glucose sensor in monitoring glucose in patients with diabetes.

METHODS

Under an institutional review board-approved protocol, five fasting patients with type II diabetes were given a challenge consisting of 75 mL of Sustacal (Thomson Micromedex, Greenwood, CO) by mouth. Contact lens fluorescence and venous blood glucose were measured over a 3-h period.

RESULTS

Contact lens fluorescence appeared to track blood glucose well. The fluorescent daily-wear disposable contact lenses were comfortable and were tolerated well, even in patients who had not previously worn contact lenses.

CONCLUSION

The contact lens glucose sensor shows promise as a home glucose monitor.

Non-invasive glucose measurement technologies: an update from 1999 to the dawn of the new millennium

There are three main issues in non-invasive (NI) glucose measurements: namely, specificity, compartmentalization of glucose values, and calibration. There has been progress in the use of near-infrared and mid-infrared spectroscopy. Recently new glucose measurement methods have been developed, exploiting the effect of glucose on erythrocyte scattering, new photoacoustic phenomenon, optical coherence tomography, thermo-optical studies on human skin, Raman spectroscopy studies, fluorescence measurements, and use of photonic crystals. In addition to optical methods, in vivo electrical impedance results have been reported. Some of these methods measure intrinsic properties of glucose; others deal with its effect on tissue or blood properties. Recent studies on skin from individuals with diabetes and its response to stimuli, skin thermo-optical response, peripheral blood flow, and red blood cell rheology in diabetes shed new light on physical and physiological changes resulting from the disease that can affect NI glucose measurements. There have been advances in understanding compartmentalization of glucose values by targeting certain regions of human tissue. Calibration of NI measurements and devices is still an open question. More studies are needed to understand the specific glucose signals and signals that are due to the effect of glucose on blood and tissue properties. These studies should be performed under normal physiological conditions and in the presence of other co-morbidities.