Design of Hardware
Beginning with the above specification, we drafted up some initial designs that used press-together studs as their connection/conduction mechanism. This idea was inspired by the John Adams 'Hot Wires' Plug & Play Electronics set and other such ‘easy-build’ systems. We also reached out to John Adams to discuss features that make their products so successful within their target demographic.
As advertised on the John Adams website, these products are designed to reinforce ideas already taught as part of the United Kingdom national curriculum. However, with our project, we hope to explore entirely ‘new ground’ for end users. Currently, synthetic biology receives little to no mention before the final year of A levels in the UK, at age 17/18. Due to this, it was decided we would need attractive packaging and targeted advertising on pre-watershed TV to raise awareness and generate pester power. Above all, it was stressed that, due to the growing array of toy safety requirements, science-based products are becoming more expensive to develop. Potentially, the lack of domain-specific products prevents people from having the opportunity to explore (and become interested in) particular areas of science. These issues were given great thought, not least due to the public’s largely negative connotations associated with genetically modified (GM) organisms. It was deemed, we had to ensure, and advertised as so, that our system was as safe as possible.
We then gave a presentation about the iGEM competition and our project to groups of sixth form students across two open days. During the event, we presented our ideas as well as the Hot Wires kits along with two other variants and asked them for feedback on the products. We wanted to establish what they liked and features that could be improved, recording this information and feeding into our design rationale. Use of bright colours and clear labelling received unanimous praise, while snap-together studs were rejected as too fiddly. It was this observation that made us decide to pursue a magnetised system, using coloured perspex to ensure the kit was visually stimulating.
We wanted to produce a series of interchangeable parts that could house the hardwire required to activate the heat shock response within our bacteria contained in the microfluidic chambers. While also maintaining user-friendly functionality and an aesthetically pleasing product. This would allow for easy experiment preparation and consistency in any observations, as we would include all laser cut and 3D model designs for free.
In keeping with our previous stud-based design, we opted to use a series of nodes attached to bases, which were magnetised. This meant that depending on the circuits they wished to build; the bases could be rearranged in space, with strong connections between segments to ensure stability. All connector pieces and components used the same form factor based on these small-but-powerful round magnets, which guarantee stable conduction. Copper tape was soldered to each magnet and used to conduct across plastic connector pieces.
In testing, it transpired that although the magnetic nodes were visually appealing, they also contained small manufacturing inconsistencies. These inconsistencies meant we could not always get the stable connection we needed to deliver the electricity for heat shock. From this finding, the final iteration of the design was born.
Now we are using 8 mm neodymium disc magnets for our design, which are powerful but most importantly completely smooth, with the copper-magnet join taking place away from the connection surface. Finally, we had achieved the perfect current delivery method, and adapted all our pre-existing models and diagrams to incorporate the magnets.
During our experiments we had been using a Bio-Rad PowerPac Basic to supply electricity. Given the short time available to us we would have liked to develop our own variable PSU design and would love to see a team solve this problem in the future!
The parts for the kit can be produced using common equipment available at your local fabrication laboratory - we recommend finding your nearest FabLab initiative! Once cut, all the structures can be joined together using two-part resin. Tip: If ordering all the parts yourself, try using less powerful magnets (we used N35 neodymium magnets with 1.47kg of pull force) as they had a nasty habit of ripping other components apart during our testing!
Microfluidic Microbial Fuel Cell
Designing our new fuel cell was a challenging experience, but one that we feel yielded strong results. From our experiments using the University of Reading's microbial fuel cell kit, we wondered if the entire system could be made smaller and integrated into our breadboard but still provide measurable voltage output. To deconstruct the kit, it consists at a basic level of two separate chambers, separated by a cation exchange membrane and an electrode running into each chamber.
Having already used PDMS gel moulding to construct our basic genetic construct chambers, we wanted to make use of the existing protocols and expertise afforded to us by Dr Lucy Eland. With this in mind, we designed a new model to pour the gel around and had this 3D printed. While unfortunately due to some calculation errors the first prints were far too small, the second run was correctly sized and we were successful in creating a miniaturised fuel cell, sealed by bonding to a glass slide as per our other PDMS devices.
It was fantastic to see this particular device come to life over the course of the summer, as were able to design both the physical form and the genetic insert for the bacteria by improving on the past work of the 2013 Bielefeld iGEM team. For more details on how our microbial fuel cell performed, please click this link to see our results.