Finding the perfect fit
The performance of any insulin pump is clearly the major concern, and the importance of the size of the pump should not be understated.

“When we surveyed patients and endocrinologists, we found that size was a major issue with insulin infusion pumps,” said Clint Vilks, senior program manager at Deltec, a manufacturer and distributor of medical devices, including a wide range of infusion therapy products. “People with diabetes are going to be wearing their pumps 365 days a year. If the pump is even the slightest bit too big, it can present a number of problems, from clothes not fitting over the pump properly to simple comfort issues. That’s why everyone we talked to wanted something that would be effective, but also small and stylish, almost like it wasn’t even there.”

Design challenge: big results from small parts
Deltec faced some unique challenges, most notably designing and manufacturing parts small enough to fit, yet capable of delivering big performance. The company enlisted the help of a manufacturer of nonball lead screws, Kerk Motion Products, to produce a critical part in what would prove to be the solution, the Deltec Cozmo Pump.

“Kerk listened to our requirements and took them seriously,” Vilks said. “Yet, where changes were required to accept the reality of manufacturing, they came up with some innovative suggestions that would accomplish our objective without sacrificing quality. They always presented viable options. Ultimately, there was a true exchange on both sides to achieve the goal rather than to chase some theoretical specifications.”

Design solution: a high-precision lead screw and nut
The design resulted in a lead screw and nut—what Deltec describes as a “drive rod”—that compresses the syringe to inject the insulin. Essentially, Kerk helped Deltec replace the human element—the finger that would push down on the syringe’s plunger—with a lead screw and nut. The lead screw pushes down on the drive rod, which is actually a machined plastic plunger. The nut incorporates threads working with the screw to set in motion the pump’s inner lock mechanism, which uses a quarter-turn thread to engage the disposable insulin syringes. The entire mechanism is driven by a small motor that rotates the lead screw that’s positioned parallel to the motor.

The nut is made from self-lubricating acetal plastic, and the screw incorporates Kerk’s proprietary TFE coating, which increases lubricity and typically extends the normal nut life by more than 300 percent.

The precision is more critical than it might be in other applications, given the ramifications of a faulty mechanism. If there is any unwanted flow, or if the overall fit of the plunger in the mechanism is loose, the accuracy of the insulin dose could be affected. The precision fit of the lead screw and nut ensures the proper performance of the pump and creates sealing features that help maintain a strict separation between the medication and the pump parts, mandatory in any medical device.

A safe treatment option
The partnership resulted in a product that is safe and performs effectively. The pump is lightweight, the size of a cell phone and delivers insulin at regularly scheduled intervals—day and night—through a short, flexible plastic tube inserted just under the skin. Operation is very simple, and the interface is similar to a cell phone keypad. The cartridge holds 300 units of insulin and uses one AAA battery.

The new pump offers significant advantages over previously available insulin pumps, most notably its size, ease of use and flexible programming. It allows people with diabetes to personalize their treatment to meet their lifestyle demands.

“We were looking for a safety factor of five,” said Vilks. “With Kerk’s help we were able to achieve a factor of 10.” The product was awarded a Medical Design Excellence Award.

The pump brings effective treatment to people with diabetes, allowing them to maintain active lifestyles. A creative design approach and manufacturing expertise contributed to the production of an instrument that will positively affect millions of lives.