Artificial endocrine pancreas and optimal blood glucose regulation in diabetic patients--from bedside-type to wearable-type

Stimuli sensitive polymers and self regulated drug delivery systems: a very partial review

Since the early days of the Journal of Controlled Release, there has been considerable interest in materials that can release drug on an "on-demand" basis. So called "stimuli-responsive" and "intelligent" systems have been designed to deliver drug at various times or at various sites in the body, according to a stimulus that is either endogenous or externally applied. In the past three decades, research along these lines has taken numerous directions, and each new generation of investigators has discovered new physicochemical principles and chemical schemes by which the release properties of materials can be altered. No single review could possibly do justice to all of these approaches. In this article, some general observations are made, and a partial history of the field is presented. Both open loop and closed loop systems are discussed. Special emphasis is placed on stimuli-responsive hydrogels, and on systems that can respond repeatedly. It is argued that the most success at present and in the foreseeable future is with systems in which biosensing and actuation (i.e. drug delivery) are separated, with a human and/or cybernetic operator linking the two.

Development of an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer

The instability of enzymatic glucose sensors has prevented the development of a practical artificial pancreas for diabetic patients. We therefore developed an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer (MIP). This sensor has the advantages of improved stability and a simplified manufacturing procedure. An adduct of glucose and 4-vinylphenylboronic acid (VPBA) was synthesized by esterification and was then purified. The copolymer of the glucose/VPBA adduct and methylene bisacrylamide was grafted onto an indium tin oxide electrode surface. Glucose was washed out from the copolymer to obtain an MIP layer. Cyclic voltammetry of ferrocyanide in aqueous solution was performed using an MIP-grafted electrode, and the effect of glucose on the anodic current intensity was evaluated. The anodic current intensity was sensitive to the glucose concentration, and the dynamic range (0-900 mg/dl) covered the typical range of diabetic blood glucose levels. The response time of the MIP-grafted electrode to a stepwise change in the glucose concentration was approximately 3-5 min. Thus, we can conclude that, by taking advantage of its gate effect, it is feasible to use an MIP-grafted electrode as a glucose sensor for monitoring blood sugar in diabetic patients.

Current status and future prospects of parenteral insulin regimens, strategies and delivery systems for diabetes treatment

A strong relationship between long term metabolic control and low frequency of chronic diabetes complications was shown in the Diabetes Control Complication Trial (DCCT). However, the subcutaneous intensive insulin therapy required to achieve the glycemic goals defined by the DCCT led to an unacceptable frequency of severe hypoglycemia and a significant weight gain. This limits the benefits of this therapy and excludes groups of patients such as young children, the elderly or hypoglycemia prone patients. The intensive therapy and self blood glucose monitoring (SMBG) necessary to limit hypoglycemia represent a heavy burden for the patients and their family. Improvements in parenteral insulin therapy are possible by either modifying subcutaneous insulin characteristics (analogs, adjunction of peptides such as amylin, GLP1, IGF1), or by developing better routes of administration and making SMBG easier, which is a key to intensive insulin therapy success. The ultimate goal remains the development of an automated, glucose controlled device.