Developing an insulin-delivery technology that comes in a discreet package and suits the needs of diabetics can offer an array of design challenges. In this article, a company shares its experiences and obstacles to success while in the midst of the device’s evolution. They are presented so that other drug delivery device OEMs may hopefully avoid them.

SFC Fluidics is developing a wearable drug delivery device targeted for more convenient and low-cost delivery of insulin for patients who inject multiple times per day. The current management of diabetes can be viewed as bothersome as it requires the patient to keep a source of supplies with them at all times. Further, at certain times during the day, patients must repeat the process of placing insulin into a syringe and then inject themselves.

This process is both inconvenient and limits the patient’s ability to be discreet. SFC Fluidics has been working on technology that automates as much of the process as possible while keeping the patient’s lifestyle in mind. The current challenges include making a pump small enough to wear under an individual’s clothing while also being a reliable medical device that delivers insulin.

Development Challenges
The first challenge that SFC overcame was developing a non-mechanical pump. SFC Fluidics’ ePump technology is a patented electro-chemiosmotic means for precisely moving fluid without any mechanical parts. Application of a low voltage (≤1.5V) drives a pumping fluid across a selective membrane. This, in turn, causes an elastic diaphragm to expand and push a controlled amount of fluid, insulin in this case, to the patient. Reversing the direction of the voltage reverses the direction of fluid flow. The result is very precise flow from a reciprocating pump that can be tailored to fit any application by allowing virtually unlimited freedom in size and shape design. This pump mechanism has demonstrated that it provides reliable, accurate dosing.

The subsequent challenges were to miniaturize the pump engine – including pump, valves, and control system – to fit within the discreet insulin delivery pod, and to design the parts in such a way that they can reliably and inexpensively be manufactured and assembled in large quantities.

Figure 1: The pump engine housing contains the pump and valves and fits in a footprint that is 25 × 50mm.The primary challenge for miniaturization of the pump engine was to balance the size of the pump with the requirement to deliver insulin into the patient in a clinically useful timeframe. While the ePump technology allows unlimited design freedom in the pump geometry, the maximum pumping rate scales with the active area of the selective membrane and, to some extent, the overall volume of the pump. At the same time, the pump must be designed with enough support to deliver insulin reliably against the pressures encountered during subcutaneous injection. The ePump technology has been shown to be able to generate up to 300psi of pressure, but care must be taken in a miniature pump with microfluidic pumping requirements that deformation of the pump walls does not result in insulin delivery errors. The pump shown in Figure 1 is able to pump U100 insulin against typical subcutaneous backpressures fast enough to fill the needs of the vast majority of diabetic patients. For diabetics with very high insulin requirements, the pump is precise enough to be able to deliver more concentrated forms of insulin, up to and including U500, in a safe and reliable manner. This pump has a footprint of approximately 18 × 18mm.

Another challenge is that the reciprocating nature of this miniature pump requires external valves to deliver fluid directionally. The pump draws in a small amount of insulin from the reservoir and then delivers that insulin to the patient. The valves in the fluidic circuit therefore also act as an additional safety barrier between the insulin reservoir and the patient. Minimizing the overall size of the insulin delivery pod requires miniaturization of all components, which includes not only the valves, but also the battery. The SFC Fluidics team designed a proprietary valve that controls the flow of insulin in the fluidic circuit, using a minimal amount of power. These valves were integrated into a C-shaped housing that surrounds the pump and also contains the fluidic manifold joining the two. This manifold, including the pump, has a footprint of about 50 × 25mm (Figure 1). The pump engine for the patch insulin delivery device will consist of the single fluidic manifold piece created around these valves and the pump, along with the control system.

The pump and valves are operated using an electronic control system that allows for programmable basal and bolus delivery with real-time modification. The pump will come with a wireless controller, smaller than a smartphone, which will be able to control the insulin delivery operation at the touch of the screen. This pumping technology allows for complex basal-bolus pumping algorithms to be programmed into the patch pump, as well as the ability for the patient to change the pumping parameters in real time. For example, the pump can have a single basal rate, or a basal rate that could be higher during the day than at night or even temporarily suspended if blood glucose levels dropped below a programmed threshold level. In the same respect, the mealtime bolus doses can be preprogrammed, delivered on-demand, or a combination thereof, all without ever removing the device. The control system has been designed to be small enough to fit within the footprint of the valve manifold housing, creating an entire controllable pump engine that fits within a 50 × 25mm footprint.

Figure 2: The wearable insulin delivery pod with wireless controllerThe pump engine together with the control system will be able to deliver 3.0mL of insulin over a three-day period using a disposable battery. The final device – consisting of the pump engine, power supply, 3.0mL reservoir, and cannula – will be able to fit within a pod with the dimensions of 55 × 58 × 10mm (Figure 2).

SFC Fluidics has secured manufacturing partners to bring the ePump technology to market as an insulin delivery device. The absence of mechanical parts means that the pumps can be fabricated almost entirely out of injection-molded plastic parts, and the few metal parts are very thin and can easily be stamped. This amounts to a precise insulin delivery device that can be constructed out of very inexpensive parts, but there are many parts required for the pump to work properly. These parts must be designed so that they can be assembled inexpensively and reliably. Currently, SFC Fluidics is working with the manufacturing partner to identify low cost materials and to design the pump so that it can be rapidly and reliably assembled. Along with the development of quality control and quality assurance processes, this will ensure precise, controllable insulin pumping at the lowest cost for the patient.

The technological hurdles that lie ahead are integrating the pump with an infuser, controller, and reservoir while maintaining the customer’s need for discretion and convenience. Once the final step of FDA clearance is achieved, a more discreet, convenient insulin delivery option will be available to diabetic patients.