Qualifying Insulin Delivery Pumps for Human Spaceflight

Project Overview:

Commercially available insulin pumps for treatment of insulin dependent diabetes (type 1 and 2) are currently not qualified to operate in the space environment. The purpose of this project is to assess the performance of COTS insulin pumps in simulated microgravity and hypergravity environments, and make recommendations for patient use in future spaceflight missions.

Dated Entries:

11/3/2023

The past two weeks of effort towards the project involved the detailed preparation for PDR. Design changes were implemented due to a lack of availability for nanoliter volumetric flow measurement devices, resulting in a new approach for insulin dosage measurement: capillary meniscus progression. This technique offers flow rates to be calculated by assessing the progression of fluid through a fine capillary over a set period of time, and a prototype demonstration was constructed for PDR.

A video capturing the meniscus progression through the insulin tubing from the prototype is presented below:

These outcomes were among the most significant for the preliminary design review that happened on October 31st. Additionally, updates to the CAD model were made based on the feedback from the MIT Microfluidics & Nanofluidics Laboratory, and those can be seen below. The updated bill of materials is presented alongside the CAD model.

Finally, developments on the electrical diagram were made to show the connections needed for the 3-axis accelerometer (left) to the Arduino (center) and the barometer senor (right). if time and resources permit, a custom PCB will be developed and manufactured to reduce likelihood of electrical disconnections during flight.

Moving forward, the schedule for this project was outlined for the concluding remarks in the PDR presentation. The schedule is shown below.

10/20/2023

This week a series of CAD files were drafted to visualize the conceptual design for the experimental setup. The first revision of the experimental setup CAD model is shown below.

For increased clarity of component positioning, the front three struts and connecting joint have been removed from the picture. The resulting illustration is below.

The rails in the middle of the box will be used for anchoring hardware to the floor, walls, and ceiling of the unit. 3D printed brackets will be secured to the rails to prevent movement of the insulin pump, flow sensor, fluid sink, environmental sensors, logic board, and potentially a camera should the need arise later in the design process. The brackets and housings for the fluid sink (shown in clear acrylic) and insulin pump have already been designed. As decisions are made for specific COTS components, more bracketing will be developed and added to the model.

10/13/2023:

This week the experimental design of the flight test began. A rough idea for the bolus profile is shown and the success criteria was identified for the experiment.

Success Criteria:

This experiment will be considered successful if the following conditions are met:

1. Fluid measurements from the insulin delivery system are gathered during the entire duration of the delivery profile for both the flight and ground experiments

2. Barometer and accelerometer data are gathered during the entire duration of parabolic flight

3. Experimental procedures are run with no anomalies

4. No measured safety or operating limits are exceeded

Experimental Design Overview:

Two experiments will be performed – one ground control test and one flight test. Both experiments will utilize a Tandem t:slim X2 insulin pump filled with a saline solution. The ground control test will ensure an accurate baseline is gathered to compare the flight test data to. The delivery profile used  will consist of two parts: the first part will be a zero-delivery command to assess whether the pump is able to prevent unwanted delivery during a time it is not actively dosing medication. The second part will be an extended bolus command to assess whether the pump accurately delivers the proper bolus quantity and achieves the proper rate of delivery during a time it is actively dosing medication. The bolus will be 60 units delivered over the span of 60 minutes. For the extended bolus delivery options, 0% of the bolus will be delivered up front such that 100% of the bolus is dispersed over the 60-minute delivery window. This bolus profile should yield approximately 10 microliters of fluid flow measured per minute. The delivery profile is shown below.

10/6/2023:

Building on the brainstorming from last week, a more refined system block diagram was developed. The diagram, shown below, features all major components of the experimental design. The connections and connection types are shown and defined in the legend at the bottom of the figure, and the system boundary is identified to illustrate which components exist within the physical housing of the setup and which are outside.

Currently, the laptop is the only major component that requires human input during the experimental procedures, and the power supply block is a representation for a physical/electrical connection to the plane itself. Further connections to the plane are also shown for the system boundary (representing an attachment to the plane for the box the experiment resides in), and the laptop, which will likely be attached to either the top of the experimental housing or the plane via Velcro straps.

Note the inclusion of sensors in this design as compared to the previous brainstorm. An accelerometer and barometer have been added to gather real-time data of the environment the insulin pump is in. These inclusions ensure accurate correlation for pump performance to both imposed and changing g-load, as well as any biases that might arise with the pressure-driven delivery system in the pump when the plane changes cabin pressure during the parabolic trajectory.

9/29/2023:

Early design considerations are identified as a result of a system-level brainstorming effort. The figure below identifies major physical components in the experimental setup and a rough layout of the testing apparatus. Other system-level considerations are show to ensure future design work acknowledges component-component interactions that could occur.

9/19/2023:

As it stands, NASA expressly prohibits anyone with type 1 diabetes, an autoimmune condition where the patient’s pancreas no longer produces insulin, from being genuinely considered during the astronaut selection process [1]. Diabetes treatment technology has advanced considerably in the last half century, with widespread access to insulin delivery pumps emerging in the last two decades [2]. These devices have drastically improved blood glucose control for patients, and is widely considered the state-of-the-art for diabetes treatment technology [3].

Certifying insulin pumps with the FDA is a lengthy and intensive process, and as such the manufacturer’s list of warnings when using the pump cautions patients from continuing pump therapy while in rapidly changing gravity environments, such as on roller coasters and in aerobatic planes [4]. Because of this, diabetics, like myself, face two major barriers of access for human spaceflight: the regulatory barriers which can only be solved through bureaucratic proceedings and social advocacy, and the uncertainty of pump safety while in space.

The proposed project will fly a state-of-the-art COTS insulin pump, the Tandem t:slim X2, and assess its delivery performance across the entire spectrum of the Zero-G flight experience through saline bolus measurements. The measured delivery will be compared to the expected delivery, shown both from control measurements in 1G environments in addition to the commanded delivery amount. Testing over the entire spectrum of gravity environments is critical to allow for accurate conclusions to be drawn about launch, in-space operations both in orbit and on the moon/mars, and entry/descent characteristics.

The proposed work is both outreach and research. The data gathered will be published to provide insight as to how currently available insulin delivery pumps perform in the space environment and over a complete mission life. The data gathered will be novel and groundbreaking for the advancement of human spaceflight accessibility. The combination of data and written work resulting from the Zero-G flight will inform future experiments to be sent into sub-orbital and orbital flights, eventually incorporate human trials, and provide a strong foundation to challenge the inherently ableist exclusion of type 1 diabetics, and the disabled community at large, from currently pursuing human spaceflight as a profession. My platform as a type 1 diabetic, a disabled person, is to challenge what is conventionally thought of as possible while living with diabetes. I have already sourced a second-hand t:slim X2 insulin pump for use in this testing, and will reach out to Tandem Diabetes Care for professional advice on the experimental design of the flight test. This is my community’s first step towards an inclusive space future: vetting our most trusted technology in the simulated gravitational environments of a Zero-G flight.