Hardware

Overview

To facilitate the delivery of the fluid produced by our wet lab team as a potential therapeutic for alleviating hay fever symptoms, we designed a nasal spray device. Conventional commercial sprays typically incorporate a metal spring mechanism, which complicates recycling and often results in disposal as landfill waste. In contrast, our prototype is fully 3D-printed using recyclable plastics, eliminating the need for metal components. To replace the spring, we implemented a manual pull-back piston mechanism, which allows the user to prime the device before spraying. This design maintains functionality while simplifying both manufacturing and recyclability. Additionally, the device features modular, replaceable parts, ensuring that individual components can be substituted in the event of damage or fluid depletion. This approach extends the device's lifespan and reduces both cost and environmental impact compared to purchasing an entirely new spray unit.

The final prototype consists of six major components: the cover, case, upper receiver, lower receiver, lower receiver cap, and cartridge.Though this final prototype has a straight nozzle, in the design phase, we also considered a version where the nozzle would be placed at an angle. This would theoretically pre-aim the spray in such a way that the user can just insert the nozzle straight and it would point to the desired location. However, we ultimately abandoned this approach, because;

• It could ironically make it more difficult to use the nasal spray, because it would have to be eased in to have the nozzle pointing at the desired location.
• The nozzle would have to be pointing in the correct direction before being inserted, and speedy application would be hindered.
• A tilted nozzle would make it more difficult to atomise the liquid more consistently, as the angle would mean either less length for atomisation, or uneven atomisation.
• A tilted nozzle is also more difficult to make a nozzle cover for, as just the tip does not offer enough friction to keep the cap in place, while a cap covering the bent part and straight part of the nozzle would be very difficult to replace.
• For those reasons, it was a more logical choice to implement a straight nozzle.

Fig.1: The completed nasal spray.

Equipment

• Creality FDM printer Ender 3 V3 KE
• Creality CR-PETG Arctic White
• Sunlu TPU 95A Grey
• Autodesk Fusion 360
• Creality Print 6

Structure

The nasal spray is composed of three primary components: the cartridge, the lower receiver (housing for the pumping mechanism), and the upper receiver (housing for the nozzle and cartridge interface). Multiple variants of each part were designed to enhance modularity and adaptability. In addition, we incorporated a replaceable hygienic nozzle cover, which improves sanitation during repeated use and reduces the risk of cross-contamination when the device is shared.

Lower Receiver

The lower receiver contains several critical components, including the dip tube, check valve, and piston cylinder. If reprinting is required and the check valve ball needs to be recovered, it can be removed by carefully cutting away the surrounding plastic. A hot knife or soldering iron can be used to remove the outer wall, followed by opening the internal cage with a small knife to release the ball. Caution should be taken when using a hot knife for the entire process, as molten plastic can adhere to the ball surface and affect its smoothness.

Regarding the threaded regions, it is important that the thread be modeled and printed as a continuous feature along its full length. Starting a thread mid-surface often results in bridging errors and failed prints (see Figure 2.1 and 2.2 for a comparison of correct and incorrect thread geometries). To avoid excessive support material, we recommend printing the lower receiver in an inverted orientation, which eliminates the need for supporting the bottom rim (see Figure 3).

Fig. 2.1 (Bad Threading)

Fig. 2.2 (Good Threading)

Fig. 3 (The lower is oriented upside down to minimise support volume)

Upper Receiver

The upper receiver primarily consists of the piston head and nozzle, with the addition of a removable protective cap to maintain hygiene during use.

When printing the piston head, it is advisable to prepare multiple size variations to ensure a proper fit. Because TPU tends to compress slightly during extrusion, printed parts often result in dimensions that are larger than expected. This effect also complicates the precise sizing of the liquid guide tubing leading to the nozzle tip. To address this, we designed the piston head to accommodate both larger and smaller tubing diameters. By default, the design is modeled for a thicker guide tube; if a thinner tube is required, the wall thickness can be adjusted accordingly (see Figure 4.1 and 4.2).

Fig. 4.1

Fig. 4.2

The nozzle itself incorporates an internal mixing feature. While fine geometries such as a swirl chamber composed of multiple micro-channels are impractical to fabricate with FDM printing, we implemented a screw-shaped insert to induce a vortex. This modular design allows additional inserts to be stacked, enabling adjustment of the vortex strength as needed (see Figure 5.1 and 5.2).

Fig. 5.1

Fig. 5.2

Limitations and Future Improvements

While our prototype successfully demonstrated the feasibility of a fully 3D-printed, springless nasal spray, several limitations remain.

First, the use of FDM printing introduced dimensional inaccuracies, particularly in fine features such as threading and internal channels. These inaccuracies occasionally caused leakage or poor component fit. Resin-based printing would allow for far greater precision in these areas. However, conventional resins are toxic in their uncured state, require careful post-processing with solvents such as isopropyl alcohol, and often produce brittle parts. If resin printing is pursued in the future, it will be necessary to employ certified biocompatible resins (such as those used in medical or dental applications) to ensure safety and stability when in contact with biological fluids. Although these materials are more expensive and demanding to process, they would allow higher accuracy while maintaining safety standards.

Second, while our modular design enabled flexibility, our evaluation of ergonomics was limited. More targeted surveys—for example, on preferred handle shapes, grip styles, or nozzle ergonomics—could provide valuable insights to guide future design iterations. Incorporating user feedback at this level would improve both comfort and accessibility of the device.

Third, we underestimated the development time required to design and refine a nasal spray device. While the basic concept appears simple, the precision needed for components such as check valves, pistons, and nozzles made the engineering process more challenging than anticipated. Allocating additional time for prototyping and testing would have allowed us to optimize performance further and evaluate a wider range of design variants.

Conclusion

Through this project, we demonstrated that it is possible to design and fabricate a fully 3D-printed, springless nasal spray device that is modular, recyclable, and customizable. By optimizing print parameters and adapting the design for FDM limitations, we created a functional prototype that balances usability, durability, and environmental considerations.

For additional information about our hardware design or implementation, please contact our team's hardware specialist via the contact information provided on our iGEM team page.