Bubble Chaser: Insulin Reservoir Filling Device for People with Visual Impairments

Developers:  Edward Liang and Sharon Sangermano

Advisors: Nancy Lelle-Michel, RN

Supervising Professor:  Kevin Caves


Our client has type I diabetes and must fill her insulin reservoir every two to three days. However, her retinopathy has made it difficult for her to locate and purge air bubbles in the reservoir. When introduced to her catheter line, these air bubbles interrupt insulin delivery, which could lead to dangerous spikes in blood sugar. As a result, our client currently relies on outside assistance to help safely fill her insulin reservoir. With our client’s visual needs in mind, we created a device suited to our client’s insulin pump paradigm that would allow her to independently fill her reservoir and eliminate air bubbles introduced during the filling process.

Introduction and Background
Our client is an adult with type I diabetes which has led to retinopathy and mild neuropathy. Diabetic retinopathy is associated with continuously diminishing vision and can eventually lead to blindness[1]. Currently, the client is able to read large bold fonts that utilize strong color contrasts between text and background. She wears a magnifying glass around her neck that she uses to complete most of her daily activities. Diabetic neuropathy is a form of nerve damage that causes pain and numbness in extremities[2]. Our client is able to do most daily activities, but has difficulty completing tasks that require fine motor skills of the fingers such as buttoning a button or threading a needle.

The client uses an insulin pump that clips onto her pants and delivers insulin through an injection point on her lower stomach. The pump has a 1.8mL insulin reservoir that the client refills every two to three days. The current refill process includes pulling air into the reservoir, pushing the air into the insulin vial, flipping the set-up, extracting insulin from the vial, and then disconnecting the reservoir and connecting it to tubing for injection[3]. During the transfer, it is common for air bubbles to form in the insulin which must be removed before it is inserted into the pump for use. When an air bubble is present in the tubing, insulin is not pushed to the client and the possibility of a spike in the client’s blood sugar level increases. The client is unable to visually detect air bubbles during the filling process, in the insulin, on her own and therefore needs assistance during the process.

Current devices available for patients with diabetes, such as the Prodigy Count-A-Dose and the Load-Matic, allow for the automated filling of syringes and utilize auditory alert systems to interact with users[4, 5]. However, these products are not for use with the client’s current syringe brand, and it would be cost-restrictive to switch to a different pump paradigm compatible with these filling devices. In addition, neither of these current products specifically ensure that air bubbles are not in the reservoir.

Project Goals
The goal of the project is to create a device that will allow the client to independently fill her insulin reservoir while minimizing the introduction of air bubbles in the reservoir or connected tubing. The device will automate the reservoir filling process and eliminate the need for visual checking of air bubbles. Additionally, operation of the device will require minimum user input and will follow simple steps. Device setup and use will be completed through large buttons and levers to ensure the device can be used as the client’s neuropathy continues to progress. All labels and instructions will be in large, easy to read print. Any feedback provided by the device to the user will utilize color changes or auditory signaling.

Design and Development
We designed a device that will assist the client in refilling the reservoir for her insulin pump. The device will minimize the introduction of air bubbles to the insulin during the filling process and will eliminate the need for visual checking of air bubbles. This will allow the client to independently fill reservoirs despite her continuously diminishing vision and fine motor skills. The design’s main features include the ability to secure the reservoir, vial, and connector, hold the reservoir in the vertical position, pull the reservoir plunger, flick the reservoir, and house all electronics. The reservoir, vial, and connector can be seen assembled in Figure 1.

Device Operation Overview
The current refill process encouraged by the insulin pump’s manufacturer includes pulling air into the reservoir, pushing the air into the insulin vial, flipping the set-up, extracting insulin from the vial, and then disconnecting the reservoir and connecting it to tubing for injection[3].
The device will utilize a similar filling technique. The client primes the vial with a volume of air equal to the amount she wishes to draw out. Then, with the plunger depressed, the reservoir/vial assembly is secured in a horizontal position. The front panel of the device then flips up such that the reservoir is in the upright position, allowing insulin to be drawn into the reservoir. After the user presses a button, the device begins to draw insulin into the reservoir at a slow and constant rate. While this is happening, the client uses a spring-loaded lever arm to flick the vial and dislodge air bubbles stuck to the reservoir walls. The user then presses the button again, which causes the dislodged air to be purged from the top of the reservoir back into the vial.

Securing the Reservoir, Vial, and Connector
A set of 3D printed parts will be used to securely hold the reservoir, vial, and connector in place as seen in Figure 2. The bottom piece of this set serves as a mold for the three components to sit in. The top piece of the set is shaped to fit the exposed portion of the reservoir and vial and is connected to front panel of the device via a hinge. Once the reservoir and vial are in place, this piece is lowered to the panel and locked into place using the third and final piece of the 3D printed set. The lock has an upside-down “T” shape and can easily be rotated to sit on and secure the top piece of the set. A tab has been added to the top piece to ensure that the lock does not slip off during use. An x-shaped handle has also been added to this top piece to allow the client to easily grip the piece while setting up the device.

Holding the Reservoir in Vertical Position
For ease of use, the device has been designed to so that the front panel will sit at 20⁰ above the horizontal while the client loads and locks the reservoir, vial, and connector in place as shown in Figure 3a. While filling the reservoir, the set-up must be held in the vertical position with the vial on top. To allow for this, the device is connected to its base via a hinge that allows it to rotate to the vertical position. The front panel is locked in the upright position using a latch and post as seen in Figure 3b.

Filling the Reservoir
To fill the reservoir with a precise amount of insulin, the device will need to be able to pull the plunger a set distance at a certain speed. A linear actuator has been added to the device that automates the pushing and pulling of the plunger and is activated by a push button. A 3D printed piece is used to attach the actuator to the plunger as shown in Figure 4. A guiding wall on this attachment piece assists the user in inserting the plunger into the device. In addition to filling the reservoir, the actuator will be able to push a small amount of insulin back into the vial after filling to ensure that any air bubbles that may have formed, have been removed. As a safety component, a limit switch has been added to the device. The switch is positioned so that if the actuator pulls the plunger further than the maximum volume the reservoir can hold, the switch will be triggered, the actuator will stop pulling, and will push the plunger forward a small amount. The device also contains a speaker which is used to play a melody to signal when the linear actuator has completed each task.

Flicking the Reservoir
While the filling technique used minimizes the chance of air bubbles in the reservoir, there is still a possibility of air bubbles forming. To protect against this, we have added a flicking mechanism to the device which consists of a spring loaded flicking arm attached to a post. As the insulin is being transferred to the reservoir, the client will use this feature to flick the reservoir. This will send any air bubbles to the top of the reservoir. The client will then flick the reservoir a few more times before pressing the button to signal for the linear actuator to push a small amount of insulin, and the air bubbles, back into the vial before the reservoir is disconnected form the set-up and inserted into the pump for use.

All electronic components of the device are properly secured inside a 3D printed box that connects to the front panel of the device. These electronics include an Arduino, a speaker (and associated wires), and a push button (and associated wires). The push button that is used to control the linear actuator is attached to the top of the housing unit, when in the vertical position, as seen in Figure 6b. The speaker is attached to the side of the housing unit as seen in Figure 6c. The power and USB ports on the Arduino are accessible through the exterior of the device to ease device set up and maintenance.

The client plans on using the device on her kitchen counter. The device is portable allowing the client to store it elsewhere and avoid occupying counterspace when not in use. The client will plug the device into a wall outlet when using the device and unplug it upon completion of the filling process.

The goal of the device was to allow the client to independently refill her insulin reservoir and eliminate the need to visually check for air bubbles. With the client’s retinopathy and neuropathy in mind, a number of design requirements were set so that she could confidently use the device with minimal external assistance. The device underwent a verification and validation process in which physical measurements, as well as subjective survey evaluations by the client and healthcare professionals, were taken and compared to these requirements.

The device was verified through a number of physical measurements and test runs in a controlled lab setting. A number of trials were run using both saline and insulin to test the consistency of the device and its ability to eliminate air bubbles and fill the reservoir with a precise volume of insulin. The device was validated through client testing, as well as trials with a healthcare professional. Through survey evaluations of the device, both the client and a diabetes nurse specialist expressed their confidence in the device’s operation and usefulness.

Overall, the device was successfully designed and constructed to meet our user’s needs. Each user interface component, including the operating button and audio notifications, was designed with our client’s retinopathy and neuropathy in mind. Quantitative verification testing showed that our device could consistently fill a reservoir with an accurate volume of insulin while eliminating dangerously sized air bubbles. Meanwhile, subjective validation by the client and a diabetes nurse specialist demonstrated that the device is safe and consistent enough for regular use. The total manufacturing cost was approximately $150, which is comparable in price to other insulin reservoir loading devices[4, 5]. Our device is custom made to be compatible with our client’s current pump and reservoir type, and has a built in flicking mechanism which other devices on the market lack.

If a client using a different pump were interested in our device, the features that hold the reservoir in place and the distances that the actuator pulls the plunger could be altered to meet these new specifications. Without this class or this device, insulin pump manufacturers would likely be responsible for creating devices that allow people with visual impairments to complete their daily health care steps. While Medtronic, the MiniMed 522 manufacturer, currently recommends that reservoirs be used immediately after filling them, it would be interesting to see if they could find a way to produce prefilled, bubble free, insulin reservoirs [3].

We would like to thank our professor Kevin Caves, our teaching assistant Paul Thompson, our clinical advisor Nancy Lelle-Michel. We would also like to thank the Duke Department of Biomedical Engineering, as well as the National Science Foundation for their generous grant.

1. Diseases and Conditions: Diabetic retinopathy. Mayo Clinic. March 2015. Retrieved September 18, 2017, from http://www.mayoclinic.org/diseases-conditions/diabetic-retinopathy/basics/definition/con-20023311.
2. Disease and Conditions: Diabetic neuropathy. Mayo Clinic. February 2015. Retrieved September 18, 2017, from http://www.mayoclinic.org/diseases-conditions/diabetic-neuropathy/basics/definition/con-20033336.
3. Filling Your Reservoir. Medtronic. May 2015. Retrieved October 1, 2017, from https://www.medtronicdiabetes.com/customer-support/device-settings-and-features/sd512-712/filling-your-reservoir
4. Prodigy Count-A-Dose. AbleData. 2012. Retrieved September 18, 2017, from http://abledata.com/product/prodigy-count-dose.
5. Load-Matic. AbleData. 2010. Retrieved September 18, 2017, from http://abledata.com/product/load-matic.

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