Hardware

Since our first idea was to have a mixture with all the different phages and a wide spectrum of colors, we designed a test with a simple system: One pit, in which the phage mixture can be stored. The sample can be added via another well that is connected via a channel to the big one.

1. The big pit containing our phage mixture. Covered with glass so the user can easily see the color of the mixture after mixing it with the sample.
2. Small pit for inserting the sample into the test.
3. The channel that connects that allows the sample to mix with the phage mixture.

Handling

Issues

1. First of all, we noticed that there is a problem with the amount of colors we would have to implement to our system to ensure every combination of bacteria and resistance is covered. It is really hard to find that many reporters that can be seen with the naked eye. In addition to that, it would be most likely that those reporters would need different lengths of time to be expressed, which makes it harder to standardize the test.
2. With the planned amount of colors there would also be an issue with differentiation. We can not expect every user to have the same understanding on where red begins and orange. And in terms of inclusivity we would put people with color blindness at a disadvantage, which is not in our interest.
3. Since we wanted to cover the big well to prevent the phage mixture from leaking, it is hard to get access to the big well. This on one hand makes it harder to throw away the liquid in a proper way. On the other hand it is harder to use the test again, because it is easier to just take a new test. In terms of ecological aspects, we wanted to prevent this.

The biggest issues with our first design were concerning the spectrum of colors. All of these concerns could be dispelled by changing our way of handling the phages: Instead of making one big phage-mixture, we are now thriving on making separate phage-solutions - each solution only containing one combination of phage and SPEAR-system. For the design of our hardware we therefore split the big pit into several smaller wells. The idea is now to fill one type of SPEAR-solution into one well per time. After adding the sample to each of the wells, only those wells will give a colored signal that is containing the detection system for the resistances the bacteria have. There are two upsides to that: First of all we can always use the same reporter. This makes us able to standardize the test in terms of time the user has to wait for a possible result. In addition we avert misunderstanding if there really is a change of color or not.
The second upside is that we can deliver the test itself and the phage-solutions separate from each other. This gives the user the possibility to decide on which resistances they want to test by pipetting the phages in the wells depending on the need. With that it is easy to just test on resistances against an antibiotic that they suggest to use.
The separate storage is also more sustainable because not every phage solution is used every time which will save a lot of resources.

1. 28 wells, which can be filled up individually with the SPEAR-solution.
2. Lowering of the surface to provide the possibility to seal the test to store it.

Handling

Issues

1. In our interview with Hamprecht he told us that an important factor is the hands-on-time. If a test takes too long to be done or is too complicated to set up some users might tend to use an alternative.

For an automatic system for distributing the sample evenly on all wells, we had many ideas. We thought a lot about using tubes that have junctions leading to all wells. We decided not to go with that draft, because we assumed it would cost too much to have complex systems like that produced. Since we want to provide an easily accessible test, we needed to find another solution. We decided to try the following system:

1. 28 wells that can be filled ip individually with the SPEAR-mixtures.
2. Slider that can be pulled out after the top wells have been filled up.
3. 28 top wells that can be filld up with the sample.
4. Channels that connect the upper wells with each other to provide an even distribution of the sample.

Handling

Issues

1. The channels may be too high. If there is not enough volume of the sample, the level of the liquid will fall under the line of the channels before distributing evenly to all wells. Therefore not every well will be filled and it will not be possible to test every resistance as wished.
2. We do not know how viscous the sample liquid will be. There might be a problem of the sample flowing easily through the channels before getting blocked.
3. There might be a problem with the surface tension of the sample as well. This could have an effect on two aspects. When the tension is too high, the sample might not flow through the channels. In addition, when the volume is small, there is a risk of the sample remaining on the upper wells after pulling out the slide.

When it comes to the material of our testing device it is really important to consider under which circumstances it will be used. We decided on looking for a plastic material because it is the cheapest and lightest one. Since there are many different plastic variants we looked for one that meets all the requirements:

1. First of all, the test has to be resistant against chemicals, especially solvents, and other liquids. When working in a lab and different solutions the material has to withstand them without dissolving or changing the structure.
2. We aim to make our test as reusable as possible. Therefore, the material must also be resistant to high temperatures. Since there is a high need of sterilizing it through autoclaving it.
3. For easy handling it would be nice to find a light material.