Hardware, in synthetic biology, can be used as a way of implementing experimental results to tackle real-life needs or problems---and this is, indeed, the ultimte goal of our project and our hardware. The solution to invasive snails, GAStroPurifier, would become highly systematized if a hardware is produced as a carrier of functional results that are proofed in our wet lab sessions. Currently, there are no such devices that perfectly suit the requirements of using synthetic biology to solve invasive snails such as Giant African Snails(GAS). We aim to provide a practical, effective and straightforward hardware that solves this issue and meets the needs of not only the situation in Shenzhen, but also the situations of scientists and other people attempting to solve similar issues in different places across the globe. By producing such hardware, we will be able to culture synbio products, trap GAS and eliminate A. cantonensis inside the snails--- these are all happening in a single hardware placed in areas where the eradication program is strongly required. The structure of our hardware, alongside kill-switch and autosomal selection in our engineered products, ensures that its harm would be minimal to the surrounding environment.
GAStroPurifier, as its name suggests, is a device that 'purifies' GAS from A. cantonensis through the implemented ALERTS procedure. At first, our team intended to build GAStroPurifier into a complex machine containing a lot of parts that ensures the specificity in eliminating A. cantonensis. However, we were advised, in the consultations with engineering experts, Shenzhen Wildlife Protection & Control Bureau and other potential consumers of GAStroPurifier, to make the hardware more cost-effective and less complicated. Therefore, after taking advices from the consultations and making some other adjustments, we had a total of three versions of the GAStroPurifier.
The ultimate goal of our hardware is to provide our local community with a templated approach for the integrated control of invasive species. We aim to create a hardware design that is both time and cost-efficient at exterminating A. cantonensis while also being simple enough for others to replicate and use for the benefits of the indigenous ecosystem.
With this we present to you, the GAStroPurifier!
Fig1. first version of the outer overall structure of our hardware design
A spiral structure that emulates the curvature of a snail's shell. The hardware is bifurcated into two levels, a foundational layer and an upper layer, in the middle lies a box with numerous holes that allows the smell of the attractive odor of the dough to spread. The base of the hardware is a circular plate that can be rotate clockwise and anticlockwaise transporting snails to different chambers.
Upon entry, the Giant African Snail is promptly deposited onto the plate, which rotates and compels the snail to start its journy in the GAStroPurifier:
1) 1st chamber - extermination room. Within this space, the snail will consume the extermination dough, thereby exterminating the A. cantonensis within.
2) 2nd chamber - detection room. In here the mucus will be extracted from the brush. The back of the brush is connected to the test paper, which will indicate whether the snail still harbors A. cantonensis. The data displayed by the test paper will be collected by a color sensor within the room which determines whether the snail can proceed to the next chamber or should return to the 1st chamber.
3) 3rd chamber- sorting room. Within this chamber, a net is present that only permits small snails to exit through the bottom section, while the GAS are detained and collected in the room above.
Fig 2. Meeting with Mr. Henry
Version 1 of GAStroPurifier was produced after brainstorming with our team members and advisors. Before making the actual model, however, we decided to meet with Mr. Henry from Links Spider Co. Mr. Henry specializes in engineering and proposed two main rooms of changes.
1) The selective mechanisms of our hardware did not appear to possess the ability to distinguish between Giant African Snails and other animals. To address this issue, we proposed using specific sensors and built-in mechanisms to increase the selectivity of animals, allowing only those that are similar in weight and size to Giant African Snails to be brought inside the GAStroPurifier.
2) The overall structure of our hardware was deemed overly complicated, resulting in unecessarily high production costs. To tackle this issue, we decided to simplify the design by deleting any unnecessary structures and recreating the outer structure of our hardware to reduce unnecessary expenditure while still achieving equal or even better outcomes.
Fig3. 3D second version of the overall outer structure of our hardware design
Fig4. Flow diagram of the second version of our hardware
Following a thorough discussion of version 1, we have made significant changes to our hardware design.
1) Instead of a circular shape, we have opted for a box structure measuring (500*540*540mm).
2) Holes were drilled on one side of our hardware to facilitate the spread of 𝛼-pinene and Isoamyl acetate from fermented dough. In addition, a middle platform contains a centrifugal blower that blows on the dough to maximize the spread of the scent and attract more snails.
3) An infrared sensor is added to detect GAS's presence, triggering the motor to rotate and turn the wheel, which will then rotate the gate for 270°. The snail will then be pushed into our GAStroPurifier. Once the motor has rotated to the point where the front door touches the micromotion sensor, it will immediately stop rotating. After a few minutes, the motor will turn 270° in the opposite direction, opening the one-way entrance block once again.
Fig.5 Conducting user testing with workers in Shenzhen Wildlife Protection & Control Bureau
We stayed in touch with workers in Shenzhen Wildlife Protection & Control Bureau(SWPCB) after one of our Human Practices activities as they are very interested in the progress of our hardware. Workers in SWPCB are familiar with current eradication methods for GAS and can also sent official approvals of using the hardware to Shenzhen goverment. Therefore, we sought authentic and authoritative user feedbacks from SWPCB.
After our second meeting with SWPCB, we were met with a slew of critical feedback regarding our modeling design. In our inital and second version, we could not significantly lower the cost of our hardware. Following the meeting, we quickly realized that our previous approach was far too complicated in the case of GAS in Shenzhen. The bureau highlighted several flaws in our design, each of which we worked hard to address.
1) There was no conclusive evidence to support the use of centrifugal blowers, which would only increase energy expenditure. Our solution was to increase natural ventilation in order to spread the attractive scent more effectively.
2) The battery cell would not last for very long and our design was quite expensive. Our solution was to eliminate all of the sensors and motors in our original design and replace them with alternative methods, with the exception of the dough compressor.
3) Our metal plated structure would rust when exposed to humid environments. Our solution was to switch to acrylic plates, which would reduce both corrosion and hardware costs.
4) The number of entrances in our design was insufficient. Our solution was to create additional one-way entrances that would allow snails to crawl in more easily.
Fig6. 3D Final version of the inner overall structure of our hardware design, simulated by Autodesk Fusion360.
Fig7. 3D Final version of the outer overall structure of our hardware design, simulated by Autodesk Fusion360.
Fig8. Cycle of hardware. 1) Snail has been attracted by the odor of 𝛼-pinene and Isoamyl acetate inside dough with engineered yeasts 2) Follwing the aroma the snail arrives at the entrance of GAStroPurifier 3) Through the selective on-way-gate the snail enters into the ground floor of GastroPurifier; From time to time the syringe pushes out some dough 4) The snails consumes the Cry protein containg dough 5) A. cantonensis is exterminated
Fig9. Actual pictures of our hardware
After our second meeting with Shenzhen Wildlife Protection & Control Bureau(SWPCB), we modified previous drafts of our hardware according to their feedback. The main compartamization is similar to version 1, as the top half is used for dough placement and the bottom for trapping Giant African Snails(GAS). According to the SWPCB, minimizing the complexity of the design is more suitable for situations in Shenzhen. This significantly lowers the cost of making the hardware and allows easy production and assembling for users and manufacturers.
1) The turning gate and sensors are deleted for version 3 as they increases the complexity for workers without engineering experience to assemble the hardware. Workers from SWPCB also emphasized that smaller indigenous snails are usually not present in areas where large-scale eradications of GAS are required. Therefore, we decided to simplify the gateway into only one-way blocks after fencing.
2) Ventilation is improved as three sides of the outer covering are all ventilated in comparison with version 1. The centrifugal blower is therefore removed to furtherly reduce the cost. Window screens are sticked onto the openings to ensure the biosafety of the hardware: larger animals such as insects cannot enter the dough placement compartment, but odors released by the dough will be blown out of the hardware by natural winds and sensed by the GAS.
Ventilation is also connected with the lower level so that odor from the aroma box can eventually spread out through openings below one-way doors. This guides the GAS towards the entrances.
3) Another small box is fixed onto the main lid of the box and contains battery supply and the dough compression set. It is more convenient for users to regularly replace dough in the syringe, therefore dough containing Cry-protein is continuously released into the snail cage.
The simplicity and low-cost of GAStroPurifier ver.3 meets the needs and situation of GAS eradication in Shenzhen and therefore we chose to assemble and use it for field testing.
Firstly, fencing is located in front of the entrance to block any larger animals. Each of the three movable one-way doors are located behind fencings surrounding three sides of our hardware. The doors, made of plastic foam pads, are restricted by the fencing---snails can only push them inwards to enter the trap instead of getting out.
Fig10. 3D modeling of fencing, simulated by Autodesk Fusion360.
Fig11. actual picture including one-way doors
The structure of dough compressor contains 4 main parts. 1. Micro thumb putter2. Actuator3. Battery box 4. Plastic syringe. The Micro thumb putter will be connected to the syringe's plunger piston, thus pushing it downwards and squishing out the extermination dough onto the ground floor of the GAStroPurifier.
Fig12. Structure diagram of the Micro thumb putter [3]
Fig13. Actual picture of Dough Compressor
Fig14. Actual picture of Dough Compressor
Two rectangular blocks are joined above the bottom of the box to form a simple drawer that may be used for Reassuring presence of A. Cantonensis. Associated workers can simply open the drawer by handles and collect slight amount of snail mucus for carrying out SHERLOCK detection.
Fig15. 3D design of the Muscus collecting drawer
Fig15. 3D design of the Muscus collecting drawer
Fig16. Actual Picture of the Muscus collecting drawer
| Name | Description | Quantity | Individual Cost (USD) | Total Cost (USD) |
| Acrylic plate | Transparent plate for stuctural support and at the sametime providing minimum weight | 23.00 | customized | 32.20 |
| Plastic foam mat | White foam boards | 3 | 1.33 | 4.00 |
| Battery box 12v 14000mAh | Power cell for the hardware | 1 | 21.89 | 21.89 |
| Micro thumb putter(distance150mm; 15mm/s-12V-150N) | A device or mechanism to connect to the syringe and push out the dough | 1 | 15.00 | 15.00 |
| Plastic syringe | Container for nematode extermination dough | 1 | 0.53 | 0.53 |
| Actuator (15mm/s-12V-150N) | Push the dough | 1 | 5.00 | 5.00 |
| Aluminium triangle(15*15*M4) | Hold acrylic plate to gether | 22 | 0.26 | 5.72 |
| Stainless steel handle( pitch-row110mm; diameter 8mm) | Gripper on the box | 1 | 0.66 | 0.66 |
| Stainless steel window screen (220mm x 220mm, thickness 0.8mm) | Allow for the spread of attractive sent | 4 | 0.68 | 2.72 |
| Stainless steel bracket | Connect and support plates | 8 | 0.11 | 0.88 |
| Hinge, 50mm x 75mm | Allow movement of one-way doors and lids | 4(packages of 2) | 0.85 | 3.40 |
| *M4 10mmscrew+nut | Connecting plates | 100 | packaged | 1.40 |
| *M5 12mmscrew+nut | Connecting plates | 100 | packaged | 1.60 |
| Hexagonal copper pillars (M5) | Fixing dough compressor into the box | 2 | 0.05 | 0.10 |
| 95.10 |
Fig.17 Putting our hardware into real-life testing.
After we built up the 1st prototype of GAStroPurifier version 3, we contacted a local community administration centre so that we were allowed to carry out a functionality test of the hardware: this is for testing its durability during moderate rainfall and determining the safe sites of using the GAStroPurifier. No bio-engineered organisms, parts of bio-engineered organisms or GAS attractants such as dough or fruits were placed in this hardware during the test. Products of synbio were never in contact with our hardware during the entire dry lab session.
The results were positive: there was no excessively stagnant water inside the hardware. Besides, screws remained attached to the connective parts and the window screens were still glued onto the acrylic boards.
Fig.18 Results sent from the residental community administrative centre.
We reported the results of our hardware durability test to the community administration centre, and workers from there enthusiastically invited us to hand in the GAStroPurifier ver. 3 to them for conducting user testing with natural attractants.
Since administrators and sanitation workers from the community centre have dealt with GAS eradication programs before, they are more experienced in safely conducting the user testing than us. We also assured that they will only use natural, unfermented dough containing fruits to attract GAS to the bait: this furtherly ensures the biosafety of such functionality tests. The results were proved to be positive and workers in the community centre sent us photos during their test: GAS were able to be guided and enter the doorways, all the way into the trap. They did not witness any other animals when checking the hardware.
During the user testing from the community centre, we received some feedbacks that could be used for modifying the GAStroPurifier ver.3 in the future.
1) The box is too big and is not easy to be transported in long distances. It is possible to shorten the height of the box, as surface area of the hardware's bottom is more important for retaining more GAS.
2) We may try to remove the top box and place the dough compressor inside the second level. This is more difficult but can significantly reduce the extra space occupied by the box.
3) Sanitation workers suggested that we should reduce the spacing of fencing so that smaller rats will not be able to enter the trap. This can also be linked with reducing the size of the box.
In our pursuit of implementing our experimental results to address real-life needs and problems, we sought opinions from a diverse range of perspectives to ensure our hardware design aligns with reality. Throughout the entire hardware development process, we have engaged with our potential users on three occasions, receiving constructive feedback. In response to each and every one of these valuable inputs, we have made appropriate changes and adjustments.
During the user testing, we realized that our device was impractically large. To address this, we plan to reduce its overall size in the next iteration. Additionally, we discovered that using acrylic plates could pose challenges, leading us to explore alternative materials. For our one-way gates, originally, we considered using straw mattresses, but they proved to be fragile and ineffective. Eventually, we found that plastic foam boards were lightweight, cost-effective, and sustainable, making them an ideal choice.
When presenting our second iteration to the Shenzhen Wildlife Protection & Control Bureau, we learned that more evidence was needed to prove the efficacy of the centrifugal blower to make it a possible candidate. While we initially solely considered GAStroPurifier's efficiency, we realized it did not align with the bureau's values of affordability. However, in areas with lower humidity, we may explore incorporating the centrifugal blower in future versions. Due to time constraints, making significant changes to our design based on the feedback was challenging. However, after successful verification of our Cry protein, we will be able to modify our kill switch and embed it properly in the hardware.
During a formal meeting with our parents, an intriguing query was raised: "Could we establish connections with alternative entities?" This significant statement has unveiled a realm of limitless possibilities for the potential applications of our hardware. Our original intention was to act as a mediator between GASs and our potential users, with the objective of capturing them and eradicating the A. cantonensis parasites they harbor. As previously mentioned, if our users belong to the local community, they may express a desire to preserve the captured GASs and relocate them elsewhere. Conversely, if our users are affiliated with a snail extermination committee, they could seamlessly integrate our hardware with their preferred methodologies for snail eradication. This expansive perspective unlocks a myriad of possibilities and facilitates the exploration of the vast potential embedded within our hardware design.
We also realized that version 3 of the GAStroPurifier may not be universally applicable to different situations across the globe. Situations can be more complicated than Shenzhen as different regions hold different purchasing powers, contains different ecosystems and more specific selection of GAS may be necessary at the gateways of the hardware. This is complementary to the functions of GAStroPurifier ver.2 as the design actively enrolls GAS and blocks other indigenous species.
To expand the reach and impact of our hardware, we have devised a comprehensive event strategy. Firstly, we plan to introduce our product to real estate management companies within our local communities, as they will be our primary target users. By showcasing our hardware to these key stakeholders, we aim to generate interest and establish partnerships that can facilitate widespread adoption. Secondly, we intend to participate in research sharing sessions and conferences. This platform not only allows us to present our designs and innovative approaches in addressing invasive species within our local community, but also provides an opportunity to showcase our project on a global scale. By sharing our experiences and insights, we can not only contribute to the broader scientific community but also attract attention and potential collaborations from individuals and organizations worldwide. These events serve as crucial avenues for networking, knowledge exchange, and promoting our hardware to a wider audience. By strategically targeting local real estate management and engaging in research sharing sessions, we aim to maximize the exposure and impact of our product, ultimately driving its adoption and fostering positive change in the fight against invasive species.
We have also worked on the production of a software for citizens to report sites where GAS is present in Shenzhen city. This greatly aids in choosing sites for placing our hardware onto places where the GAS eradication can be effective, and we may furtherly refine our hardware for forming a stronger connection with this app program.
We aspire for our hardware to not only play a significant role within our iGEM project but also transcend its boundaries and serve as a template for the wider community of synbio scientists, community workers, ecologists and more. We envision that in the future, when confronted with invasive species akin to GASs, our design, thoughtful considerations, and experiences can ignite inspiration among others, providing them with valuable insights.
We furtherly modified version 3 of our hardware for demonstrations at iGEM jamboree. The overall size of the hardware is significantly smaller and inner constructions have been improved.
Fig.19 GastroPurifier version4 at iGEM 2023 Grand Jamboree.
Fig.20 An ultrasound mouse repeller
