Concept and Implementation of a Novel Patch Pump for Insulin Delivery

Abstract

With the motivation to provide a small and discreet patch pump that complies with several customer needs, the recently CE-marked Accu-Chek® Solo micropump system was designed. The system consists of a tubeless insulin pump wirelessly controlled by the so-called diabetes manager. Via diabetes manager, basal rates and boluses are programmed; an integrated blood glucose meter and bolus calculator supports users in bolusing and offers several diary functions. The micropump features a quick bolus button for bolus initiation directly on the pump and is complemented by a disposable reservoir holding up to 200 U of rapid-acting insulin. The assembled pump is attached to the body via a pump holder containing soft cannula. The modular principle enables independent replacement of the single components if necessary.

Among people with type 1 diabetes, continuous subcutaneous insulin infusion (CSII) is a widespread option for insulin therapy. Currently, several different insulin pumps are available for CSII, varying in handling, material, design, and functions. Besides conventional durable insulin pumps, smaller and more discreet patch pumps are available on the market.^1,2

Recently, the tubeless Accu-Chek® Solo micropump system (Roche Diabetes Care GmbH) was CE-marked and is currently marketed in selected European countries.

Based on current user preferences and safety aspects the pump was designed with the motivation to meet and merge the current requests users have regarding their insulin pump. Its technical features, based on the initial motivation and background for the design of the system, are presented in the following.

Development of a Convenient Design

Previous surveys have shown that many patients with type 1 diabetes prefer insulin pumps without visible infusion set.^3-5 Furthermore, patients’ adherence to an insulin pump may be improved by a discreet insulin delivery.⁶ Compared to conventional insulin pumps, smaller and tubeless patch pumps fulfill these criteria. But often the simple patch pump devices, more likely intended for patients with type 2 diabetes, cannot fulfill the more sophisticated requirements of patients with type 1 diabetes, who need devices encompassing different basal rate profiles and bolus settings.⁷

Thus, a main requirement for the system development was to design a small and discreet but full-featured patch pump with variable basal rates and individually settable bolus amounts. Consequently, a patch pump consisting of a tubeless micropump with a remote control, the diabetes manager, was created (Figure 1). To keep the pump as small as possible, the configuration of the pump is outsourced and implemented wirelessly by the diabetes manager.

Figure 1.

Diabetes manager and micropump.

Design of the Controller

Via the rechargeable diabetes manager, bolus commands and basal rate settings can be delivered to the micropump, and data from the micropump, like status information and additional information regarding warning or reservoir level, can be received. Due to its typical smartphone-like design, the diabetes manager offers a discreet and intuitive pump operation also in public. If used in a typical usage pattern, the controller battery lasts for several days. The bolus and basal rate characteristics are given in Table 1.

Table 1.

Pump Characteristics.

Dimensions	63 × 39 × 14 mm
Weight	<29 g (with filled reservoir)
Insulin	Humalog, NovoLog, NovoRapid, Fiasp, Apidra, Insuman Infusat
Pump drive technology	Step motor
Basal rate
Number of profiles	5
Number of time blocks	24
Basal rate (U/h)	0.1-<5.0 (increments: 0.01) 5.0-<25.0 (increments: 0.1)
Basal insulin pulse	Every three minutes the pump checks whether a new delivery (of at least 0.042 U) is necessary or not
Temporal basal rate (manual programmable or predefined for special reoccurring situations)	0%-250% Increments: 10% Duration: 15-min increments for up to 24 h
Basal rate delivery accuracy	±16% at 0.1 U ±5% at 1.0 U
Bolus
Diabetes manager	Standard bolus Extended bolus (duration settable between 15 min and 24 h) Multiwave bolus (duration settable between 15 min and 24 h)
Micropump	Standard bolus
Bolus amounts (U)	0.2-50
Bolus increments (U)	Via diabetes manager: 0.05 (0.2-2.0), 0.1 (2.0-5.0), 0.2 (5.0-10.0), 0.5 (10.0-20.0), 1.0 (20.0-50.0) Via micropump (quick bolus buttons): 0.2/0.5/1.0/2.0
Start delivery time lag	0-60 min; 15-min increments
Delivery speed (U/min)	1.0-2.5
Bolus delivery accuracy	±30% at 0.2 U ±5% at 50.0 U

Reference: User’s Manual Accu-Chek Solo Micropump System.⁸

Upon activation, the status screen of the diabetes manager shows the most important current therapy information, such as blood glucose (BG) value, basal rate, ongoing boluses, and reservoir level at one glance. Via the separate main menu, all other features and settings can be accessed. While the status screen is always accessible, access to control features can be restricted via a PIN.

The diabetes manager features a built-in BG meter using Accu-Chek Aviva/Performa test strips and the Accu-Chek bolus advisor, whose concept has already been clinically proven in previous devices, eg, the Accu-Chek Combo and Accu-Chek Insight systems.⁹ BG measurements can directly be started when a test strip is inserted into the slot of the built-in BG meter; a LED at the slot lights enables measurements in dark environments. BG results are color-coded relating to the user’s target range and the last measured results can be used directly in the bolus advisor. Apart from standard formulas to calculate meal and correction insulin doses, the system offers the option to apply customizable factors to reflect, eg, activity or health conditions.

The current pump system version does not offer continuous glucose monitoring connectivity, but this feature could be part of future system versions. By connecting the diabetes manager and a PC, data can be displayed and evaluated via the Accu-Chek Smart Pix software.

Design of a Modular System

Another aim during system development was the everyday suitability of the system. The micropump consists of three main components, offering high flexibility and modularity. It is assembled from the reusable pump base and the disposable insulin reservoir. Via pump holder the micropump is attached to the body. The pump holder features an adhesive patch and, apart from carrying the micropump, it also fixes the soft cannula in place (Figure 2(a)-(d)). It allows the user to easily connect and disconnect the micropump. The pump base contains all electronics of the pump, including the drive, a buzzer, and the quick bolus buttons.

Figure 2.

Components of the micropump: (a) pump base, (b) reservoir, (c) pump holder, (d) cannula with casing and the insertion device (e).

Along with its modularity, allowing high flexibility, the system offers the user multiple possibilities to administer insulin: Bolus deliveries can be initiated on the diabetes manager or by the quick bolus buttons on the pump itself, in case the diabetes manager is not available or not desired by the user.

Difficult handling and painful insertion can impair the users’ compliance and thereby impair an effective insulin pump therapy.^10,11 Thus, the insertion device (Figure 2(e)) of this system is designed to be useable by one hand, offering the user an independent insertion. Due to the size of the micropump and the handy inserter, the pump can be worn on different parts of the body: in the abdominal region, on the upper arm, the outer thighs, and the hips.

For the system two lengths (6 mm or 9 mm) of the flexible Teflon cannula, offering an insertion angle of 90°, are available.

In clinical practice, the infusion assembly has to be changed occasionally after a short time, eg, due to inflammation or discomfort,^12,13 which means premature dumping of the pump delivery components and still applicable insulin in nonmodular pumps. In the current system, all single components can be exchanged independently, preventing premature waste generation in nonmodular systems.

In patch pumps, appropriate batteries for pumping the insulin in the small pumps are an increasing problem.¹ For the current system a zinc-air battery, powering the micropump for the complete use time of the reservoir and not containing mercury or other metals with negative environmental impact, is used. Due to its high energy density, only one button cell is necessary for the micropump; thereby the small size of the micropump can be maintained. However, to provide the battery with air, a small hole in the casing is required, thus the pump is splash- but not waterproof. But because of its modular design, the pump can be removed for taking a shower or bath, diving, or swimming and can be reattached afterwards.

To cover a broad spectrum of patients that can use the system, the reservoir was designed to be suitable for different amounts of insulin. It is filled manually with compatible rapid-acting U100 insulin of the user’s choice (Table 1). It has a maximum holding capacity of 200 U, which covers the insulin need most patients will have during the reservoir’s maximum use time of four days.

The reservoir can also be filled with as few as 80 U for patients requiring only smaller amounts of insulin per day. This may be relevant, for example in children, as the pump is intended for people with diabetes who are at least two years of age.

The individual fill level can easily be read from the transparent reservoir and be entered in the diabetes manager. Furthermore, the transparent design helps to detect potential bubble formation.

Design of Safety Features

For ensuring a safe handling, several safety aspects were integrated into the system. Insulin pumps with wireless features lead to additional security challenges. An interference with pump communication by an unauthorized third party undermining patient safety is a particular concern.¹⁴ In the current system, one micropump can be controlled only by a single diabetes manager: After an initial pairing process between the diabetes manager and the pump has been completed, the pump will not accept commands from any other device. For providing not only a highly secure communication but also convenient pairing, a unique identifier code is printed on each pump that can be scanned with the camera integrated in the diabetes manager.

To minimize the risk of accidental insulin delivery, any programming of insulin delivery, for boluses, activation of basal rate profiles, and temporary basal rates, that is started via the diabetes manager has a common endpoint: Confirmation via the “Insulin Button.” This hardware button is used for the single purpose of confirming insulin doses and starting insulin delivery and adds an extra amount of safety to the system.

Finally, the reusable inserter that is used to attach the infusion assembly and insert the cannula (Figure 2(e)) features a mechanism to prevent accidental activation prior to placing the pump holder device.

Beside bolus deliveries by the diabetes manager, deliveries directly on the pump can be initiated by quick bolus buttons, as mentioned before. The quick bolus buttons, placed on both sides of the micropump, only react when both buttons are pressed at the same time, thus preventing accidental bolus doses. The pump provides acoustic feedback on the number of button presses and requires the users to confirm before delivery to the bolus, further increasing safety. To maintain the small pump design, a vibration feedback was renounced.

Possible shocks against the system, occurring during daily life, will be attenuated by a metal sheet on the reservoir.

Summary

In conclusion, the recently marketed pump system comprises a small but full-featured patch pump for a broad range of patients with type 1 diabetes. With reusable and disposable components, a remote control, and bolus delivery options directly on the pump, the system combines advantages of durable insulin pumps and patch pumps.