Final Year Project

Improving the Design of a Testing Rig for Stretching Polydimethylsiloxane in Wet Conditions

A Year Long Project

The aim of the project is to improve the design of an existing plastic stretching rig for stretching the polymer Polydimethylsiloxane (PDMS) with cornea cells attached to its surface. The rig will be used to analyse the effect cyclic stretching has on living rabbit cornea cells in an environment similar to the eye. By stretching the cornea cells under strain/stress, it is hoped that the results will demonstrate how cells move to repair damage from eye related diseases/injuries. This could potentially lead to new ways of treating patients with eye damage.

Specifically the rig must:

Stretch the sample by 5% of its length
Utilise a real-time imaging system
Heat the PDMS polymer to 37 degrees
Surround the cells with cell-medium during stretching
Create a customisable control mechanism which accommodates different sizes of samples
Distribute the load evenly across the sample

The final product is the result of an iterative design process, aimed to create a modular system that can be adjusted for future use. As part of the solution to the challenge of liquid containment, a mould was manufactured for casting PDMS samples. The sample design holds cell medium, removing the need for external liquid containers which erode metal components. The final design is adjustable in the X and Z axes and a custom temperature can be set. Furthermore the design operates under a CKX41 microscope meaning that the cells can be viewed in real-time.

The fully working prototype can stretch samples between 2mm to 8mm with an accuracy of 0.071mm. A custom sample design and corresponding mould was manufactured to plastic cast samples for testing. The custom sample has a well in its center which stores cell medium preventing corrosion on other parts of the rig. These samples are stretched at temperatures up to 37 degrees.

Final Testing 2 The final rig running on the CKX41 microscope. The rig heated to 34 degrees and stretched samples from 2mm to 8mm.	Final Testing 1 The final rig running on the CKX41 microscope. The rig heated to 34 degrees and stretched samples from 2mm to 8mm.	Arduino Programming The stretch testing rig used the microprocessor 'Arduino Uno' as the control method. The program was custom made in Arduino's open source software
Linear Actuator The linear actuator used to stretch the sample has a built in potentiometer which tracks the position of the moving arm. This information is relayed to the control centre and displayed for the user	FEA Analysis One of the stretch goals for this project is to use Finite Element Analysis (FEA) to analyse the stresses on the PDMS sample	NX 10 CAD Image of the Design For manufacturing and presentation purposes all parts of the design needed to be created in CAD prior to manufacture. This image shows the whole rig with one of the heating chamber walls removed (so the internals can be seen)
Programming This is a sample of the program used to run the stretch testing rig	Previous Design The original design of the stretch testing rig. This design had several flaws which were addressed int he re-design

As part of my final year, I completed a final year project set by a member of University staff. My supervisor is Yang Liu, a Senior lecturer of Healthcare Engineering, who tasked me with improving the design of a stretch testing rig manufactured by a previous student. The final prototype of the design was presented at the student's design exhibition in Loughborough University in 2017.

Final Year Project

A Year Long Project

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Final Testing 2

The final rig running on the CKX41 microscope. The rig heated to 34 degrees and stretched samples from 2mm to 8mm.

Final Testing 1

The final rig running on the CKX41 microscope. The rig heated to 34 degrees and stretched samples from 2mm to 8mm.

Arduino Programming

The stretch testing rig used the microprocessor 'Arduino Uno' as the control method. The program was custom made in Arduino's open source software

Linear Actuator

The linear actuator used to stretch the sample has a built in potentiometer which tracks the position of the moving arm. This information is relayed to the control centre and displayed for the user

FEA Analysis

One of the stretch goals for this project is to use Finite Element Analysis (FEA) to analyse the stresses on the PDMS sample

NX 10 CAD Image of the Design

For manufacturing and presentation purposes all parts of the design needed to be created in CAD prior to manufacture. This image shows the whole rig with one of the heating chamber walls removed (so the internals can be seen)

Programming

This is a sample of the program used to run the stretch testing rig

Previous Design

The original design of the stretch testing rig. This design had several flaws which were addressed int he re-design

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