Engineering Cycle Summaries

Our engineering process included several iterations. Below some of the most significant iterations are pictured. Some of these iterations happened concurrently as our engineering, biology and human practices teams began specializing and focusing on individual sub-projects.

A summary of how we followed this engineering process approximately chronologically is found below:

Firefighters

Design

Aptamer: We designed a fluorometric assay to discover the concentration from literature of PFOA in a solution.
Housing: The housing for the PFOA sensor was designed by preliminary sketches. From the sketches, we designed a CAD model in SolidWorks. The housing includes a chimney to run wires out of it. The plan for future designs was to remove the chimney; the chimney allowed for quicker and easier prototyping. The housing provided locations for the LEDs and photodiode to slide into.
Electronics: We borrowed the bulk of the electronic design from last year’s IGEM team. We changed the LED for one that puts out the range of light that we needed and added an extra LED.

Build

Aptamer: We ordered a PFOA aptamer and got PFOA from the Roger Harrison Lab on BYU Campus.
Housing: We then printed the housing unit, using a relatively low infill.
Electronics: Using a bread board, we wired everything up with jumper cables.

Test

Aptamer: We tested if the assay would show the concentration of PFOA from the aptamer.
Housing: When we tested the entire system. We found that we could see the LEDs shining through the housing; the light showed the infill pattern.
Electronics: We tested the LEDs, the photodiode, and the button separately. Once we had everything working individually, we tested the entire electronics system. Once that worked, we wired it all into the housing and tested it. We were having trouble getting the button to work. We found that the button was not connected to the ground like we had thought.

Learn

Aptamer: We learned that we could successfully measure concentration using aptamers. We also from market research that we needed to pivot and find another use for aptamers.
Housing: We realized that the low infill was causing the light to escape; if the light was able to shine out of the housing, the light could shine into the housing. This would add noise to the system. We learned that for future iterations we need to increase the infill of the 3D print. We also saw the difference between theory and reality when building the housing.
Electronics: We learned that we need to test the connection points of the circuits. With electronics, it is hard to see what is going on. Checking power and individual components allows us to narrow the focus to find the problems.

Firefighters → Progesterone Pivot

Pivot demographic after additional market research
Pivot to a more sophisticated sensing method

Progesterone Iteration 1

Design

Aptamer: We found an electrochemical aptamer for progesterone that could have the modifications of a 6-thiol linker on the 3’ end of the aptamer sequence and a methylene blue on the 5’ end of the aptamer sequence.
Applicator: Thorough design criteria for the applicator were selected and developed (see applicator design criteria section for specifics).
User Manual: We created a user manual for the applicator. This was made by first laying out what we wanted in the user manual; we organized the layout and wrote the text in the spots.

Build

Aptamer: We bought the aptamer sequence.
Applicator: The individual parts for the applicator were 3D printed with PLA.
User Manual: We used a mixture of hand drawn images and CAD renders.

Test

Aptamer: We tested the kD and the binding affinity of the aptamer to progesterone using Isothermal Calorimetry and Circular Dichroism.
Applicator:
- We first tested the components interactions one on one. On their own, each interfaced with each other component properly.
- When all the components were combined together, we learned that some of the pressures were much higher than anticipated and others much lower. This caused things that weren’t supposed to bend, to bend, and things that were supposed to bend, didn’t bend.
User Manual: We tested this user manual with others.

Learn

Aptamer: We learned that the aptamer could bind to progesterone and learned the binding affinity of the aptamer to progesterone. These results helped us learn that the aptamer had a sufficient binding affinity to make a sensor that could be used to detect progesterone.
Applicator: To resolve this problem, we are going to vary the thickness of the compliant mechanisms to get the desired result. We learned that when everything is combined together, there can be unforeseen interactions within the system. When planning timelines for design, we need to include time to troubleshoot errors from interfacing everything together.
User Manual: The main feedback we got was to use all hand drawn images instead of the renders. We are currently working on making a new version of the user manual without CAD renders.

Progesterone Aptamer Iteration 2

Design

We found a supplier that would make the electrochemical modifications of the aptamer for progesterone that could have the modifications of a 6-thiol linker on the 3’ end of the aptamer sequence and a methylene blue on the 5’ end of the aptamer sequence. We also designed how the aptamer would be attached to a gold electrode to measure electrical impedance with the help of literature.

Build

We attached the aptamer to the gold electrode filling in the gaps with 6-mercaptahexanol. We also made attached an aptamer with a gold electrode with 2-mercaptaethanol filling in the gaps.

Test

We tested the voltage changes using alternating current voltammetry between when progesterone is bound to the aptamer and is unbound of both of the sensors created.

Learn

We learned that the 6-mercaptahexanol is essential to keep the stability of the device. The electrode with the 2-mercaptaethanol had the aptamers washed off the moment that we add more buffer to cause the aptamer to unbind from progesterone.

Future Cycles

Next Cycle

Design: Design integrated prototype for aptasensor
Build: Integrate circuit and aptamer together in physical prototype
Test: Test in biological material like blood / human samples after getting IRB approval
Learn: Assess performance and determine whether we can continue with the current approach

Possible Future Changes

Think about new aptamers that are more sensitive
Think about adding aptamers for other hormones
More robust
Realistic size (current circuit board is very big)
More Ready for Deployment: Future integration with mechanical housing and injection into arm, and with the app

Applicator Design Process Details

After evaluating our options for a continuous progesterone monitor (CPM), a monitor similar to a CGM (continuous glucose monitor) was chosen as the design. The engineering team was tasked with designing a mechanism for the user to safely and easily apply the monitor.

We started by gathering the high-level requirements for the applicator we were to design. - Easy to use - Safe - The sensor and monitor need to be functional

These requirements were broken down into their engineering requirements: - Easy to use - Minimize the steps that need to be taken to use the applicator - Have the applicator work with one motion
- Clear markings - It can be held in a single hand - Safe - User does not directly handle the needle - The user can not access the needle after the monitor has been applied - Include a safety mechanism to prevent accidental applications - Needle gauge should be as large as possible to reduce risk of bodily harm - Doesn’t go deeper into the skin than needs to be - It will be applied to the back of the arm to minimize risk of striking a vein - The sensor and monitor need to be functional - The sensor needs to be in at least the dermis to have access to progesterone - The sensor should not be damaged while being injected - The applicator secures the monitor so that it does not fall off

From these sub requirements, the following design limiting factors were made: - The sensor will be placed in the dermis - The needle will be just larger than the sensor but small as to not damage the user - 25-gauge hypodermic needle was selected - Designed to penetrate the skin - Sensor can freely rest in the needle - Fairly large gauge to minimize damage to the user - A single motion towards the back of the arm will apply the device - Needle is unaccusable after the monitor is applied - The applicator would be no bigger than 3” dia. x 6” tall and no smaller than 2” dia. X 3” tall.

From these requirements, sketch one models how the applicator will work.

(include sketch 1)

The exact details were not explored in this model. This model proved the general idea of the motions that the applicator would have to perform. Four ideas were pulled from mechatronics to help break the applicator into subsections, actuators, power, sensors, and controls. The actuators would facilitate the motion of the applicator, the power would provide the energy for the applicator to move, sensors would detect where the internal mechanisms of the applicator are located, and the controls would tell the applicator when to move.

CGMs were then researched to see how their users use their applicators work.

Once the general motion of the applicator was decided upon, the ideation process started for how these motions would be achieved.

(include sketch 2)

Sketch two shows many of the ideas for how the motion could be achieved.Each idea was then judged on feasibility, robustness, and simplicity. Using two springs was determined to be the most feasible, robust, and simple.

After the means for which the motion would be achieved was chosen, a simple test was run and determined that the springs would work. The springs provided the power for motion, and the external housing and springs would provide the actuation.

The next step was the ideation was on how the applicator would know when to do what it should. This would be done mechanically, to simplify the applicator. Pressure would act as sensors. The pressure would cause leavers to move, acting as the controls, to trigger motion.