Jacky Ko

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Wound Stabilization Bar

A research group at Novartis required an imaging stage that could clearly image mice skin wounds throughout the healing process. Breathing artifacts interfered with any time based imaging. Saline immersion with the previous bed was lacking, as the water would often leak off of the wound area over time. Imaging had to be stopped to reapply the saline solution. An existing bed was already in place, so I designed an attachment bar that was compatible with the existing bed to provide the image stabilization necessary for imaging while keeping saline water immersion of the wound area. All of the designs follow a similar principle. The skin on a mouse's back is very loose. By pulling the skin away from the body, breathing artifacts are eliminated. For this a two part system is necessary: an attachment to the wound area and a bar to pull this attachment up.

Design Goals

  • Reduce the vibrations from breathing on the imaging area.
  • Design a system where saline water stays on the wound.
  • Adapt the design to the current mouse bed to eliminate the need of creating another bed.
  • Allow for the device to be used for extended studies, with easy removal and attachment.
  • Design the device to be lightweight and without any sharp edges for mouse comfort.
  • Provide unobstructed access to the imaging area.

Magnet Design

Often times in design, the first idea that you have will not work perfectly. Designing is an iterative process which requires an open mind to changes. My first design was to have a circular array of neodymium magnets pull a shim washer (attached to the mouse) upwards. This would have led to a very easy snap on attachment and removal system. Unfortunately, the shim washers rusted in the saline solution. To combat this, I tried changing the material of the shim washer, but with higher water resistance comes with less magnetism. I also tried coating the surface of the shim washer, but rust still occurred under thin acrylic coats as shown by the picture to the right. Larger coats of acrylic increased the imaging distance a couple of mm, rendering the imaging region out of focus for depth imaging.

Rhino model of imaging bed with magnetic bar. Rusted shim washers shown on bottom right.

Screw Design

The second design that I came up with introduced a two part system. The attachment piece was made with a conical inset to fit the optical imaging lens. The piece would be attached to the mouse using surgical glue. The screws got in the way for deep imaging, and the bar was too large. This led to mice scratching them off in discomfort when they were returned back to their housing after imaging.

Disassembled and assembled screw stabilization bar.

Final Design

The final design consisted of a circular attachment piece with threads on the outer surface. These threads would twist into the bar mechanism to lock in place. During the design of the bar, various threading were tested by creating small test fixtures to determine the least amount of turns for a secure lock. After experimentation, a 5/8 11 thread was chosen.

The small tab on the edge of the attachment piece allowed for precise unscrewing of the locking mechanism with forceps if necessary. For this tab, a variety of material compositions consiting of acrylic and rubber were tested that allowed for easy turning of the screw, but also comfort for the mice when the device was not in use.

Final assembled stabilization bar with attachment piece.

Results

For the examples shown below, an area of the wound area was optically sectioned. The lines appearing in the "Before" image are caused by the breathing artifacts. There is a complete removal of those breathing artifacts with the use of the new holding bar with its attachment. In addition to the removal of breathing artifacts, there is a much clearer image, which can be seen by examining the epithelial cells. The new holding bar held the saline water immersion for the whole imaging session during testing (≈45 min).