A closed-loop insulin delivery system, sometimes called an artificial pancreas, is an advanced method for managing type 1 diabetes that automates the delivery of insulin. It is designed to mimic the function of a healthy pancreas by continuously monitoring glucose levels and adjusting insulin doses with minimal user intervention. The system’s primary goal is to maintain blood sugar levels within a healthy range, thereby lowering the risk of both high and low glucose events.
Core Components and Mechanism
A closed-loop system is comprised of three pieces of technology that work together. The first component is a continuous glucose monitor (CGM), a small sensor inserted under the skin. This sensor measures glucose levels in the interstitial fluid—the fluid between cells—every few minutes, providing a nearly continuous stream of data. This data offers a dynamic view of glucose fluctuations and captures trends missed with traditional finger-prick tests.
The second component is an insulin pump, a small, wearable device that delivers insulin into the body. The pump is connected to the body via a thin tube called a cannula, which is inserted under the skin. Unlike traditional pumps that deliver a pre-set background rate of insulin, a pump in a closed-loop system can adjust its delivery on the fly. It holds a reservoir of rapid-acting insulin and can administer it in precise increments.
The third component is the control algorithm, which connects the CGM and the insulin pump. This algorithm is housed in a smartphone app or the pump and acts as the system’s brain. It receives glucose data from the CGM and uses predictive models to forecast where glucose levels will be. Based on these predictions, it instructs the pump to deliver the appropriate amount of insulin or to suspend delivery if it predicts a low glucose event. This process of sensing, predicting, and delivering creates the “closed-loop” that automatically adjusts background insulin.
Evolution from Traditional Insulin Therapies
Closed-loop systems evolved from earlier diabetes management methods that required constant manual input. For decades, the standard was multiple daily injections (MDI), a regimen where individuals had to interpret frequent fingerstick glucose readings and calculate all insulin doses. This approach placed the entire burden of decision-making on the person with diabetes.
Traditional insulin pumps, or “open-loop” systems, were a step toward automation. These devices deliver a pre-programmed background (basal) rate of insulin, but the user was still responsible for manually delivering doses (boluses) for food and to correct high blood sugar. Closed-loop technology bridges this gap by automating basal insulin adjustments, which helps smooth out glucose fluctuations and reduces the constant calculations of older therapies.
Types of Closed-Loop Systems
Individuals can access closed-loop technology through two pathways: commercial and open-source systems. Commercial systems are developed, tested, and approved for use by regulatory bodies like the FDA. These integrated systems are manufactured by medical device companies and are available to patients by prescription. The components—pump, CGM, and algorithm—are designed to work together as a single, cohesive unit.
The patient community created an alternative through open-source, or “Do-It-Yourself” (DIY), systems. These systems are not developed by a single company or approved by regulators. They use open-source software algorithms, often developed by technically skilled individuals with diabetes, that can be installed on a smartphone or small computer. This software enables certain older, and sometimes newer, insulin pumps to communicate with a CGM to create a user-built system.
These DIY solutions arose from a desire within the community to access automated insulin delivery technology more quickly than commercial development cycles would allow. Users of these systems take on the responsibility for building, maintaining, and troubleshooting their own setup. This requires technical knowledge to ensure the system is configured correctly and functions safely. Commercial options offer an integrated, supported experience, while open-source systems provide more customization for users who can manage the technical aspects.
User Interaction and System Automation
While closed-loop systems automate many aspects of insulin delivery, they are not fully autonomous and are more accurately described as “hybrid” systems. They excel at managing background insulin but still rely on the user for several key functions.
A primary responsibility for the user is announcing meals. The system’s algorithm cannot know when a person is about to eat, so the user must calculate the carbohydrates in their meal and enter this information. This action prompts the pump to deliver a pre-meal bolus of insulin to cover the anticipated rise in blood glucose. Without this manual entry, the system would only react to the glucose rise after it has started, leading to post-meal hyperglycemia.
Managing physical activity also requires user interaction, as exercise can increase insulin sensitivity and cause blood glucose levels to drop. Many systems include features that allow the user to notify the algorithm of upcoming activity. This notification sets a temporary, higher glucose target or reduces insulin delivery to help prevent exercise-induced hypoglycemia.
The user must also perform routine maintenance. This includes changing the pump’s infusion set and the CGM sensor every few days and ensuring all components are charged and functioning correctly.