The high demand for PPE during the COVID-19 pandemic left millions of healthcare workers unprotected, endangering the functioning of the entire healthcare system. Most of Brazil’s public healthcare institutions did not have enough PPE, and few of them had face shields, which were used only in high-risk areas. The Higia project was created on 20 March 2020 when the period of community transmission of the new coronavirus had started over the entire Brazilian territory, when the number of confirmed cases of COVID-19 had reached 904 with 11 deaths. Ten days later, the Higia project was distributing their first volunteers-produced 3D-printed face shields to hospitals, while Brazil’s updated numbers were showing 4,309 confirmed cases with 139 deaths. After 13 days of production, 24x7, more than 10,000 face shields had already been delivered. Such data showed the great potential for rapid device production using 3D printing in an emergency. Many 3D printer owners, small business owners, startups, and university students took their 3D printers home to have around 1,000 face shields printed daily in production hubs in different cities. Due to the application of a design for the face shield frame as simple as possible the 3D printing of the frame was carried by volunteers without difficulties. The greatest challenge was the materials acquisition for production, as since the stores and shops were closed and the volunteers were under lockdown or social distancing measures, sometimes unable to leave their houses.
The logistics for production and delivery of face shields mass production during the confinement period in a country with continental dimensions like Brazil was a big challenge. An important factor was the possibility of delivery of 3D-printed face shields for hospitals rapidly and continuously despite the lower number produced. This problem was solved with simple delivery logistics trying to access the volunteer closer to the requesting hospital. The IM face shields production allowed an increase in the number of manufactured frames by 100 times, each day. However, this high production volume was accumulated in a single location, and the logistics of delivery from a single spot became a challenge.
4.1 Design and usability
Many countries around the world have used the FDM process to produce cost-effective medical face shields [35-36, 41-46]. However, due to process’ heterogeneity, some devices have been produced with no standardized procedure or medical approval. Face shields were adapted for oral and maxillofacial surgeons  and the radiology sector  with a design that makes cleaning a difficult activity. Face shields with very thin frames are more fragile, they can break during transportation or use, and are less comfortable and reliable. However, some 3D-printed face shield are as good as commercial standard-models . It is possible to define the practicality, and clinical suitability of 3D-printed face shields related to weight, printing time, and if it required assembling tools to find an ideal dataset to be used for printing, scalability, and economic efficiency .
The Higia face shield designed in this study meets general requirements and specific ANVISA standards to reduce the potential for autoinoculation by preventing the user from touching their face . The main features of the face shield are space for safe air ventilation and comfortable and low weight head fixation that does not limit the user's movements. Despite the recommendation that the face shield should avoid an open area between the first and second arc of the frame (Fig. 3), a consensus was established to reduce this distance and leave the area open, reducing the 3D printing time from 5 to 1.5 hours. This design ensures adequate space for the use of additional equipment such as surgical masks, respirators, eyewear, among other.
In this study, the level of protection offered by the use of the face shield it was not accessed, but it is known that this device protects to reduce transmissibility below a critical threshold . The acetate and PETg used in the visors are transparent with high optical clarity, providing a good physical barrier to respiratory droplets. Acetate provides the best clarity and is more scratch-resistant against chemical splash protection, and PETg offers chemical splash protection at a lower cost. The Higia face shield is reusable, a replacement transparent sheet can be found in office supply stores. For disinfection, cleaning the face shield with soap and water or another type of disinfectant approved by the hospital infection control service is sufficient. Sterilization using high temperatures or abrasive materials is not possible.
4.2 Qualitative comparison of FDM and IM processes to produce face shields
The main advantage of additive manufacturing is the design freedom that may be applied at any point in the process. The FDM is the most commonly used 3D printing method using thermoplastics materials, with ease of handling, rapid processing, simplicity, and cost-efficiency . The final cost is reduced due to machine and material low cost, but the process shows some limitations , as filaments such as PLA and ABS vary in material composition, porosity, and environmental stability. Although no mechanical tests were performed with the 3D printed face shields in this study, it is known that mechanical properties such as tensile strength, Young’s modulus, elongation at break, and impact strength are lower in an object that is manufactured under FDM process compared with the ones under the IM process . However, the mechanical stress that a face shield receives is extremely low, and although the facial protector produced by IM has better quality, both have a comparable functionality level.
Even though some authors claim that the FDM is a slow process and not suitable for mass production of face shields [35,43,46], the IM process, in contrast, requires skilled operators and relatively costly materials and equipment to be carried out. None of the additive manufacturing technologies is yet able to practically replace IM for medium- and high production volumes . However, this study showed that low-volume production of a network on volunteers using the FDM process may offer an alternative for short lead times and a decreased overall production cost. While IM allows producing a large number of parts in a short period time, the distribution through a continental country like Brazil takes a long time, making it difficult to fulfill large orders in a quick fashion, regardless of production method. Despite not being as fast as IM processes, the FDM method allows the at-home, on-demand manufacture of face shields by a broad spectrum of users . It is also possible also to have multiple frames printed at the same time to decrease production time using stacked frames. In this study, it was not possible to calculate the effective cost of FDM process production, as different 3D printers and filaments were used. A comparative analysis should be based on cost regarding the purchase of the manufacturing equipment, material, labor, and other costs.
This study showed the viability of using the FDM process in low cost 3D printers for rapid modeling and the production of small batches of face shields by volunteers with a simple process that can be organized for larger-scale production. Due to the support provided by 3D printing, the delivery of face shields started first, whereas the IM mold was still being produced, which the allowed for large-scale production. The FDM process allowed daily deliveries while the IM process allowed the production of large quantities in a short period time and it may be the best option for the production of a large quantity for remote areas that do not have access to 3D printers. This project shows how the FDM process allows small scale decentralized production of consumer goods at a pandemic situation as a response from civil society, allowing assistance to hospitals in need . The results highlight the role of the ‘‘maker’’ or ‘‘citizen supply chain’’ community across the world, with collaborators from industrial and academic institutions, in a network, in a short period, to donate face shields to healthcare professionals . This mobilization happens mainly due to the commotion and the sense of unity that is ongoing during the pandemic. Since the STL file of the Higia face shield was made available on the internet, many people in other countries such as Israel, Portugal, Jordan, Poland, Germany, the USA, and China have also produced face shields. It comes to show the accessibility and possibilities of integration and collaboration that 3D printing can promote.