Project Overview

Solutions Overview

The chamber is a polycarbonate cylinder with a hinged lid. Tissue samples will be placed in 4 raised polycarbonate wells that will be attached to the chamber floor with LED back-lighting for better visual acuity. The lid of the chamber will have a sealable opening over each tissue well, and artificial cerebrospinal fluid (CSF) will be pumped through nylon tubing by a peristaltic pump into the high opening of the well, and will drain back to the reservoir using the low opening In the well.

An environment containing living brain tissue should be maintained at 37°C and 95% humidity (Lo, 2008; Spaethling et al., 2017). We have used an AC flexible heating element that has been attached to the ceiling of the chamber and controlled using a solid state relay in unison with a PID control. To control the humidity, saturated solutions of potassium sulfate (K₂SO₄) and potassium nitrate (KNO₃) will be used (Greenspan, 1976; International union, 2007). To control aspects of the chamber an Arduino Uno will be used and housed in the base of the design located in the twist off bottom of the chamber which will be wired to the heating elements and the temperature/humidity sensor for controlled heating.

We have 4 salt solution vats that are attached to the floor of the chamber, with a maximum capacity of 30 mL each. To achieve 95% humidity at 37°C, we plan to fill 3 wells with potassium sulfate (K₂SO₄) solution and 1 well with potassium nitrate (KNO₃) solution. Each sulfate solution should contain at least 0.1426 grams K₂SO₄ per mL of water, and each nitrate solution should contain at least 0.5847 grams KNO₃ per mL of water.

Updated Designs

Feedback Loop:

In order to improve the chamber one of the first issues to resolve was maintaining a constant temperature. To do this we used ¼ in diameter flexible heating element that allowed us to bend it for attachment to the chamber lid. The heating element is capable of putting out 450 watts to maintain temperatures in a cold room and is controlled using a solid state relay in unison with an Arduino Uno. This allows for a PID controlled heating element to maintain temperatures at 37±0.4°C. In case there is an emergency or non-heated environment needed, a switch has been placed within the electronics to ensure the heating element is able to be turned off at any point.

Electronic Storage:

We have designed a housing unit under the actual chamber that will hold the microcontroller, CSF reservoir, lights, and wiring. Wires will come out of the back of the chamber to plug into the wall and other wires will run inside a polycarbonate backbone to reach the top of the lid. This keeps everything compact and provides a neater and aesthetically pleasing design. In the front of this chamber will be toggle switches to manually turn on an off the system, thermoelectric heating blankets, lights, and CSF pump.

Inlet & Outlet for Wells:

The outlet hole was changed to be slightly below the inlet hole to reduce the change of stagnation of CSF in the well. The CSF needs to be constantly cycled over the tissue to refresh the nutrients.

Illumination:

The next issue was to illuminate the chamber so each well could be lit while attempting to run experiments. To do this the chamber is equipped with four 5VDC LED’s that rest under each well providing backlighting.

Cerebrospinal Fluid Delivery:

Also equipped in the base of the chamber is a peristaltic pump for transporting cerebrospinal fluid to the tissue wells. Since excised brain tissue requires nutrients, the proper voltage travels to the pump and sends CSF to the well in a dripping manner to reduce splashing. Since this is a peristaltic pump, the fluid never comes in contact with the pump and when combined with autoclaved tubing lowers the risk of contamination.

Displayed Values:

To improve ease of use, the chamber was also equipped with an LCD display that updates the user of the internal temperature and humidity conditions. Since these experiments are crucial to internal conditions the display is updated every ¼ second to update allowing for live updates during experiments.