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The Components of an Artificial Pancreas
For an artificial pancreas to become a reality, three components must work together in harmony:
By working in tandem, this would be the long-awaited closed-loop system which many researchers and people with diabetes have dreamed of. Closed-loop feedback refers to the automatic interaction between a sensor and an insulin pump. With a closed-loop system, a glucose sensor relays information to the pump, which will in turn deliver just the right amount of insulin. An open-loop system is one where the patient must decide the correct amount of insulin to deliver, based on the glucose information obtained, usually by a finger stick blood-glucose measurement. This is how current external insulin pumps work.
A semi-closed-loop control system, however, will probably be the first available technology for clinical use. With this system, the patient will turn on the appropriate closed-loop control system just prior to meals, exercise and sleep.
Jeffrey Joseph, DO, director of the Artificial Pancreas Center, says computer-controlled insulin pumps can either be external to the body requiring a subcutaneous catheter, or totally implanted in the body. The implantable pump developed by MiniMed, and recently licensed to and optimized by Medical Research Group, has been approved in Europe for controlled insulin delivery (basal/bolus infusions). The pump is surgically placed under the skin and filled every few months by a physician. The insulin delivery catheter is placed into the lining of the abdominal cavity, providing portal vein insulin absorption.
"Clinical experience in Europe has been positive," says Joseph. "The technology has been safe and there have been no serious adverse events from over-delivery of insulin. Problems with the insulin formulation and the clogging of catheters have been significantly reduced."
Joseph says Medical Research Group is currently performing clinical trials using the pump to obtain FDA approval for insulin delivery in the United States. He expects commercialization to occur within the next two years. In the meantime, MiniMed, Disetronic and Animas Corporation manufacture miniature external pumps that deliver a precise dose of short-acting insulin (basal/bolus) to the subcutaneous tissue. Both implantable and external pumps are capable of providing controlled insulin delivery for an artificial pancreas.
What Will Control the Pump?
A computer-controlled algorithm is a key component of a closed-loop system for insulin delivery. Frequent glucose measurements that provide real-time information are required so the computer "knows" whether the blood glucose levels are increasing or decreasing and at what rate. Joseph says computer algorithms using a continuous glucose sensor have successfully and safely controlled blood glucose levels in the clinical setting.
Joseph adds a "semi-closed, computer-control algorithm" may be available for public use within three to four years.
Wanted: A Reliable Glucose Sensor
Joseph says that although sensors have improved greatly, they are still the limiting technology of the closed-loop system. However, he feels that an accurate sensor, specific for glucose and "robust in the clinical setting," is getting closer to reality.
"More than a dozen companies and academic medical centers are developing glucose sensors capable of controlling insulin pumps," says Joseph. "Most, however, require frequent calibration and placement of a new sensor every few days."
Joseph says Medical Research Group's long-term implantable sensor will be connected to its implantable insulin pump. Joseph says this could be "the first fully implantable artificial pancreas."
Joseph says in preliminary animal and human studies, Animas Corporation's optical implantable glucose sensor demonstrated the ability to accurately measure glucose in blood using infrared optics.
"The miniature sensor head will be placed around a blood vessel, with the light shining through the blood to a detector," says Joseph. "The absorption of light at specific infrared wavelengths will determine the glucose concentration."
How Close are We to an Artificial Pancreas?
There has been significant progress since 1977, when Anthony Michael Albisser, PhD, demonstrated that glucose could be controlled in the clinical setting using an artificial mechanical pancreas called the Biostator. The device consisted of two intravenous catheters for blood sampling and insulin delivery, a flow-through enzyme-based glucose sensor and a computer-controlled insulin pump. The Biostator could effectively regulate blood glucose in patients requiring intensive or surgical care. The large size of the device and need for large amounts of blood have limited this technology to diabetes research only.
Artificial pancreas systems have since been developed using miniature sensors that measure glucose in interstitial fluid, combined with a small computer and a miniature external insulin pump. Today, says Joseph, sensors, computers and displays are "small enough to be worn on a person's belt." In addition, the present sensors being developed are much smaller and more accurate than the earlier prototypes of the '80s and '90s.
Marc C. Torjman, PhD, associate director of the Artificial Pancreas Center at Jefferson Medical College, Thomas Jefferson University in Philadelphia, Pennsylvania, says there is nothing on the immediate horizon that looks like an ideal closed-loop system. Although optimistic about the technology, Torjman says that faster progress could be made if adequate funding were available. He adds that because there are many variables that affect glucose and insulin regulation, it will be necessary to test the product under various conditions (i.e. activity, age, food intake) which affect energy metabolism. Another challenge in the development of an artificial pancreas is finding a long-term insulin delivery catheter that may be implanted and permit free passage of insulin over years of use.
"There is no doubt that several academic institutions and biotechnology companies have devoted significant resources to achieve [control with a semi-closed and closed-loop system], but we are still looking at several years, perhaps 3 to 5 at the earliest," says Torjman.
Today, according to Joseph and Torjman, telemetry provides the advantages of wireless communications between the insulin pumps, computers and sensors, and they can be easily worn on a person's belt or wrist. They add that closed- or semi-closed-looped feedback control will automate the system, improving glucose control further and improving patient lifestyle.
"Demonstrating the efficiency of an artificial pancreas in diabetic patients is the goal for the next five years," says Joseph.