The World Health Organization (WHO) established that the impact on the healthcare system due to the additional clinical and operational demands was substantial during the COVID-19 pandemic, which could lead to failure to prevent and protect Health Workers(HW) 1, 5 .
The facial protector is one of the essential PPE for HW in the management of COVID-19 patients 6, 7 . The Health Care Infection Control Practices Advisory Committee(HICPAC) recommend the face/eye protection used as an adjunct to other facial protection for preventing transmission of infectious agents in health care settings 8 .
The restricted access to PPE supplies such as medical masks, respirators, goggles, face shields, aprons and gloves are leaving frontline HW at risk to develop COVID-19 during the pandemic 1, 4 . Under the circumstances, to provide HW with sufficient PPE to increase facial protection, face shields could be 3D printed 9 . Regardless of not featuring high productivity as injection molding processes, 3D-printing allows fast-response, ondemand manufacturing of face shields by a broad spectrum of producers, including 3Dprinter equipped laboratories in universities, schools, companies and even at home.
For this reason, the aim of this study was to evaluate the face shields obtained by 3D-Printing technology, test chemical disinfectants and autoclaving to disinfecting the models and to assess the comfort, visibility and feasibility on real life.
The present study was conducted at the Hospital das Clínicas da Faculdade de Medicina   da Universidade de São Paulo(HC-FMUSP), a public, tertiary and teaching hospital,   affiliated to the Unified Health System with 2,000 beds, of which a building with 900 beds, including 250 intensive care beds dedicated to COVID-19. About 6,000 HW dedicated to taking care of COVID-19 as well. Use this video link:
https://youtu.be/yksZT9TvKFg and https://youtu.be/zeku1WRbl_s. Face shield was recommended for all HW as an additional protection; HW were instructed to use N95 respirators or surgical masks plus face shield according to the type of contact with patients. HW who provided direct patient care wore N95 masks and scrubs during their entire shifts. When examining or touching patients they added disposable gloves, a gown and a face shield. The face shields were communal and reused after 70% alcohol disinfection. Health workers wore the same face shield during duty, and disinfection was done after each patient contact.
Questionnaire. An online SurveyMonkey questionnaire comprised questions regarding comfort, visibility and feasibility of the 3D face shields was applied by WhatsApp for physicians were working at the Intensive Care Units, Emerging Department and Infectious Diseases wards.
At the moment, 3,343 COVID-19 patients were hospitalized; a total of 2,778 HW were personally trained and 30,000 face shields were used during the COVID-19 pandemic in our hospital.
We assessed the potential reduction in the visual quality of the shield after cleaning in a subset of interventions.
None of the face shields materials and layer thickness presented damages after up to 40 disinfection with ethanol 70%, H 2 O 2 -quaternary ammonium salt mixture or 0.1% sodium hypochlorite ( Figure 1A ). To reduce potential vapor damage, we recommend waiting 3-5 minutes after each disinfection, as 1min after 70% alcohol disinfection vapors can caused eye redness.
We The questionnaire about 3D-printing face shield. The first column described the variables assessed. The answers were classified using four categories: very good, good, regular or bad. Most of the evaluations showed very good answers about mobility, visibility, mask removal and disinfection (Table 1) . All designs were considered suitable, and there was no important difference between them. Nevertheless, two of the designs (GRU and INSPER) received higher user assessment grades. InovaUSP design was significantly lighter, demanding less material to be produced.
The present study evaluated different 3D-printed face shield designs using an online questionnaire as well. We observed excellent stability, comfort, visibility and feasibility after disinfection. The design usual made up three elements: a visor made from optically clear material, an interlocking headband, and a head strap that ties the two together 9 . The National Institute for Occupational Safety and Health (NIOSH) guidelines detail that face/eye protection must allow for appropriate peripheral vision, comfortable and adjustable to ensure a secure fit 10 .
Studies that used cough simulation demonstrated that face shields reduce the risk of inhalation exposure up to 95% immediately following aerosol production 11 . However, it protection decreased with smaller aerosol particles and 30min after cough simulation, due to persistence of airborne particles and particle flow around the sides of the mask 11 .
Therefore, the face shields should not be used as primary protection for preventing respiratory disease transmission, but they can be used as an adjunct to other facial protection such as surgical mask or N95 respirators. In addition, the face shield can be useful in a scenario of N95 respirators shortage and need for reuse, as a supplementary protection to avoid respirators contamination during patient care.
Although, the number of survey participants was a limitation of our study. The HW pointed out that face shields were preferred by them than glasses because they were more comfortable and fogged less easily, and the perceived protection was higher 5 .
Currently, reuse and disinfection of these face protectors are highly needed due to an imminent shortage of supply.
Disinfection of face shields is needed for reuse of them with safety, but improper decontamination could damage the blocking structure of this PPE. We evaluated the appearance of the 3D-printed face shields pre and post disinfection, but there was no 