Final Year Project
Developing a Rig for Stretch Testing PDMS in Wet Conditions
2016-2017
The completed test rig placed onto the microscope. The rig is being tested for accuracy and if the cornea cells can be seen by the user.
The rig was extensively developed in the CAD environment. The finished rig is shown above completely assembled.
Sample of the code used to control the testing rig.
The completed test rig placed onto the microscope. The rig is being tested for accuracy and if the cornea cells can be seen by the user.
Project Brief
I was given one year to complete a final project which would use a range of different skills I learned as a Product Design Engineer. I wrote a dissertation and created two posters on my project which were displayed for visitors to the University.
I chose to re-design a test rig constructed by a previous student. The rig's is used to stretch test cornea cells. Researchers used this data to determine how strain affects the eye's healing process (usually after laser eye surgery). Cornea cells were placed on a polymer called Polydimethylsiloxane (PDMS) which had similar properties to a living eye. The cells were submerged in a fluid which kept them alive. The PDMS was then stretched under a microscope in conditions mimicking the eye.
The Old Design
The previous rig stretched two samples simultaneously using a linear actuator. It was housed in a plastic container which heated to body temperature. The design had several flaws including:
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The actuator was programmed to only move in one direction and could not be reset
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The arm was submerged in fluid which corroded the components
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The design could not be adjusted for different sized samples
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The case obscured the microscope's view
Key Challenges
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Providing heating to the system in a non-intrusive way
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Ensuring the microscope had a clear view of the cells
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Programming the actuator to be accurate and move in both directions
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Making the system modular and adjustable
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How to provide the cells with fluid to sustain them, while also not damaging or corroding the components
Achievements
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I learned C and C++ to program an Arduino Uno (my chosen controller for the rig)
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Build a custom plastic mold to produce PDMS samples for stretching. These hold the liquid for sustaining the cells, overcoming a major design challenge
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Used CAD and CAM to design and make components
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Manufactured components on hand operated lathes and milling machines
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Learned about the biology of the human eye to meet my project goals
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Developed a modular and adjustable design for the rig
Result
I received a high 1st for my dissertation and physical project hand in. My tutor and I were extremely happy with the result. My project is now used by PhD students to research the human eye. The rig can stretch a sample to within 0.5 mm. This exceptional accuracy was achieved after extensive testing and re-calibration efforts.
I would like to thank my tutor Dr Yang Liu for all of her assistance. Without her this project would not have been possible.
