P16104: Microfluidic Spectroscopy for Proteins within CubeSats
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

Goals for this Phase

  1. Create Prototypes of Microfluidic wells using PDMS
    • Is this material feasible?
    • Becoming familiar with the process
  2. Testing the feasibility of PEG on PDMS
    • Work on reducing the hydrophobic properties of PDMS
    • Test using water droplets vs. a control sample
  3. Test vibration as a vortexing replacement
    • Think of a vibration source
    • Feasibility of vibration in space
  4. Develop electronic schematics
  5. Test UV sensor and Teensy microcontroller
    • Connecting UV sensor with microcontroller
    • Test sensor using ultra-violet light sources
  6. Perform analysis of structures
    • Thermal analysis in a vacuum
    • Develop a plan of where components will be placed

Accomplishments

  1. Several PDMS wells used for testing
    • Identified additional risks
      1. Trapped air impedes fluid flow
      2. Any trapped air would explode well in the vacuum of space
    • Concluded that PDMS is a viable material for a well
  2. Tested functions of UV sensor using Teensy
    • Detected UV rays from the sun and laser
    • Corrected issues with pin location
  3. Tested and analyzed the feasibility of a small vibration motor
    • Determined that it would not provide a sufficient amount of vibration need to re suspend proteins.
    • A vibration motor in a micro gravity will not vibrate, it will rotate the entire cubesat
  4. Generated responsivity curves for sensors based on tryptophan emission
    • Have specific values of intensity and sensitivity for certain wavelengths and the sensor.

Prototyping, Engineering Analysis, Simulation

Electrical Detailed Design

Electrical Responsivity Curve

When modeling the responsivity curve of the sensor, the two sources modeled was the UV LED emitter, and the emission spectrum of Tryptophan. When modeling, the factors considered include the responsivity of the sensor, the efficiency of Tryptophan conversion, and the relative wavelength intensities emitted by both the UV LED emitter and the Tryptophan. The data above shows the responsivity of the LED and Tryptophan given an excitation to emission efficiency of 20%. The excitation and emission data can be found here and here. The data was obtained and posted on http://omlc.org/spectra/PhotochemCAD/html/091.html. The numbers in the last plot show the relative magnitudes contributed by the LED and tryptophan.

Below shows the responsivity curve of the same data given that the output is first passed through an optical filter with the characteristics shown in the first plot.

This data shows us that the relative magnitude of tryptophan relative to the LED is magnitudes of order greater.

UV Photodiode Testing and Feasibility

Initial Component Testing - Photo, Power, Temperature
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Adafruit breakout boards allowed for quick initial testing. Multiple subsystems were tested, providing a foundation for the final revisions.

Schematic:
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Structural Detailed Design

Protein Mixing:

Lyophilized proteins will be launched into space to prevent denaturing.To undergo spectroscopy the proteins need to be resuspended, which normally requires vortexing. Vibration motor considered to vibrate cubesat to replace vortexing and “mix” protein with reagent.

VibrationMotor

VibrationMotor

Vibration motors work by creating vibration through a spinning counter weight. An offset counterweight is fitted to the end of a motor shaft. When the shaft turns it creates an imbalance causing the handset to vibrate.

MotorSchematic

MotorSchematic

Lack of gravity in space will result in the Cubesat to spin to conserve angular momentum, L

AngularConservation

AngularConservation

Not feasible. Looking into other options.

Volume:

1U Cubesat must fit into 10cm X 10cm X 10cm space,000cm^3 Volume. Chassis walls result in a working volume of 953.15cm^3;Walls - 1.27mm thick, Bases - 1.5mm thick, 97.46mm X 97mm X 97.46mm interior.

Chassis

Chassis

Volume constraints results in strict monitoring of working volume remaining. Circuit board reduces working volume to 97.46mm X 80.1mm X 97.46mm interior, 759.8cm^3 total.

Chassis_CUT

Chassis_CUT

Thermal Analysis: Four sources of heat:Direct Solar radiation,Albedo (Radiation from sun bounces off earth), Earth Infrared, and Internal heat generation. Experimenting with different ways to incorporate all sources into model.
Thermal

Thermal

For this phase, a thermal model was created focusing on radiation. 5052-H32 Aluminum material properties were used. Heat Flux of 1W/m^2 was assumed. Initial temperature of CubeSat assumed to be 22°C.

Radiation Modeling Results

Radiation Modeling Results

Computer not able to run simulations past 8 hours. Minimum temperature as a function of time appears very linear. According to literature temperature should stabilize at about -40°C. Using best fit line -40°C will occur around 10.5 hours into orbit.

Minimum Temperature vs. Time

Minimum Temperature vs. Time

Microfluidic Detailed Design

Polyethylene Glycol Channel Coating

Procedure adapted from: ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5442393

Polyethylene Glycol (PEG) Channel Coating - Preliminary Qualitative Testing

Record of Activities: November 3, 3015

Two squares of polydimethylsiloxane (PDMS) were obtained and placed on glass coverslips. A drop of PEG was applied to one PDMS square. The coverslips were transferred to a Petri dish and then placed in a 150 degrees C oven for 25 minutes. The coverslips were then removed from the oven and allowed to cool. The excess PEG was siphoned off the PDMS square using a micropipette, leaving a cured layer of PEG on the PDMS square. A drop of water was placed on both the PEG square and the plain PDMS square and the contact angles of the water droplets were qualitatively compared.

Results:

PDMS without PEG coating

PDMS without PEG coating

PDMS with PEG coating

PDMS with PEG coating

Water droplet on PDMS

Water droplet on PDMS

Water droplet on PEG coating

Water droplet on PEG coating

Discussion: The PEG was easily applied to the PDMS, but there was not a significantly noticeable difference in the contact angle of the water droplet between the PEG surface and the PDMS surface. This could indicate that the PEG protocol needs to be adjusted to create a more hydrophilic surface. However, this testing was put on hold until actual experimentation with hemoglobin could start.

PDMS Layering Process

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The following animation demonstrates how the multiple layers of PDMS were assembled for the first Iteration 1. Each layer is sealed together using a corona wand and heat treatment. This same layering process was used to complete all of the other microchannel iterations.

PDMS layering process

PDMS layering process

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Solenoid Benchmarking

Experimentation with the PDMS led us to the conclusion that a valve type solenoid positioned between the wells would not be a feasible solution for moving reagent. We determined that a push type solenoid positioned above the reagent well (like a piston in a cylinder) to push reagent into the lyophilized protein well. Below is a table that summarizes a market benchmarking of push/pull type solenoids.
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Bill of Material (BOM)

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Test Plans

Electrical

Focus on confirming hardware works on PCB’s

MCU
UV Photodiode
Power/Temperature monitoring

Structural

Next Steps:

Begin incorporating other heat sources into model. All of the temperature data from radiation does not take into account the heat generation from the CubeSat itself. Begin investigating the changes on the thermal model when the CubeSat goes in and out of eclipse.

Microfluidics

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Project Design and Functional Changes

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Risk Assessment

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Link to Live Risks Document: Risks - Detailed Design.

Design Review Materials

The following presentation was given on November 19, 2015: Preliminary Detailed Design Review

Plans for next phase

Fifth Phase Gantt

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Anna Jensen's Three Week Plan: Anna's Goals.

Mallory Rauch's Three Week Plan: Mallory's Goals.

Darin Berrigan's Three Week Plan: Darin's Goals.

August Allen's Three Week Plan: August's Goals.

Andrea Mazzocchi's Three Week Plan: Andrea's Goals.

James Lewis's Three Week Plan: James's Goals.


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