Design Solution

Possible Design Solutions:
- Decision Matrix
- Project Management Strategy
Design Solution
- Final Design
Evaluation and Testing
Final Result

Possible Design Solutions:

Originally, there were three alternative solutions for this project that were broken down into three solution areas for prototyping. Three designs were considered to develop and validate a proof-of-concept design. All the choices were chosen based on their viability to address the utility of blue-light for catheter tubing sterilization.

1. Light-emitting Diode: Blue light LEDs are one of the strongest proposed solutions to have antimicrobial effect. LEDs have a precise value of the wavelength which is really important for this project. The wavelength that has been proven to have antimicrobial effect is from 400nm- 405nm which is a small range. The other important parameter for a light source to be effective is its intensity.

It is proven for a light source to be effective in eradicating the bacteria, it has to reach a certain intensity which is the minimum of 60mW/cm^2. Using high power LED lights, it is possible to generate such intensity, and since the variety of these lights’ wavelengths are different, they will be logical designs to test. The only downside of using LEDs with such high power is they are not as small as other LEDs (They are 3.4 x 3.4mm) which might be problematic to test in urinary bladder catheters later on.

2. Electroluminescent or Fiber Optics light source: Using fiber optics and electroluminescence as sources of light are the second and third alternatives for this project.These wires are flexible and they only need a high electric field to be working. These wires are also much smaller in diameter so they can be easily implemented into a catheter later once it is proven that it is an effective antimicrobial technology. These electroluminescent wires are available in many colors, which correlate to different wavelengths, so different wavelengths of blue light can be easily tested. Electroluminescent wire is also fairly inexpensive so the cost of the design and testing different wavelengths and powers can be possible. One important aspect that these wires misses is that they are not made to produce high intensity lights.

Decision Matrix

For the purpose of which design to go forward with, decision matrix was extremely helpful to show us which design is more logical. As shown in the table, we decided to approach and tackle this medical problem using the first design which is to use of LED as the blue light source. The goal is to eradicate the free-floating bacteria using blue light; in order to achieve this high intensity blue light LEDs would be employed, and corresponding testing procedures will take place.

Project Management Strategy (Gantt Chart)

Modified version of Gantt Chart for Winer Quarter 2019

Design Solution

Circuit design construction:

This involved the construction of two series circuit and two parallel circuit

`2. Intensity modification of power source generator:

In order to maintain a high intensity power for LEDs to be effective in eradicating bacteria, power source generator needs to reach high voltage values.

3. Antimicrobial effect test:

This will take place in laboratory under supervision of a microbiologist to test for efficacy of blue light LEDs.

Final Design (Series design only)

The design solution for this project is to construct two sets of circuits, and test each circuit with two different LED wavelengths. The LEDs being used for both designs are high power, single color high forward voltage capacity LEDs that are small enough to fit into the catheter tubes for future testing. Two major components mentioned in papers about the effectiveness of blue light LED lights were the wavelength and intensity. The design was modified by substituting high power LEDs instead of regular low power ones as well as introducing a parallel circuit to avoid overheating and killing bacteria by heat which can manipulate the result. The variable power source, which is the same one used for previous group’s design, will allow us to adjust the forward voltage value suited for each circuit design.

Evaluation and Testing

Bacterial (E.Coli) Growth Behavior

Due to time constraints, the only prototype that was able to be tested out of the four prototypes was the Violet Series Circuit Prototype that has a wavelength of 393 nm. Data for this prototype was recorded for the bacterial content in the synthetic urine sample vials before and after exposure to the design prototypes for 24 hours at a time. The positive control was the synthetic urine vial with no catheter. The Blue Light 18 V was the device inside of the synthetic urine and powered on. Lastly, the catheter control was the catheter put in the synthetic urine vial but powered off. The graph below indicates that there was no significant change observed from all three controls. A significant change by FDA clinical regulations is a 10^4 magnitude of change. Figure 3 shows the result of this experiment in which there was no significant changes in the level of bacteria after the prototype was removed from the synthetic urine sample.

Final Result

Due to time constraints, only one of the four prototypes was able to be tested. The only prototype tested was the 393 nm Violet Series Circuit prototype. As seen from the figure, there was no significant magnitude of change (10^4) to indicate that the device has worked in eradicating E. coli in synthetic urine. These standards are based off the FDA’s protocols for clinical devices. Therefore, we concluded that Violet light cannot be used to eradicate E. coli in synthetic urine. Though blue and violet light does work in eradicating E. coli on agar plates. The reason our hypothesis might’ve failed could be due to many reasons such as E. coli having a different expression system in liquid vs solid forms. Another reason could be that the device itself could be faulty. The device should’ve been tested on E. coli agar plates first, since blue light has been proven to eradicate E. coli on agar plates. If the device works on E. coli agar plates, we can conclude that the device itself works, however, it cannot function as an antimicrobial device to eradicate free floating bacteria in urine sample.

Figure. Planktonic concentration in synthetic urine sample over 24 hours after being exposed to 393nm violet series circuit prototype. Positive control is synthetic urine by itself, with no device. Blue Light 18 V is the prototype powered on with the synthetic urine. The catheter control is the device in the synthetic urine, but powered off.

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