Advances in Manufacturing A Novel Combinatorial Shield Design for Eye and Face Protection in COVID-19

The World Health Organization (WHO) has emphasized the importance of goggles and face shields in medical personnel protection as early as the outbreak of the COVID-19 pandemic. However, but not surprisingly, there was a rather long period that almost all countries suffered from a critical supply shortage of goggles and face shields, as for many other Personal Protective Equipments (PPEs), due to the lack of key medical material supplies on the one hand and the poor efficiency of existing fabrication methods caused by the need to avoid crowds during the outbreak of the COVID-19, on the other hand. In this context, we have proposed a novel combinatorial shield design for face and eye protection based on the rapid preparation method of 3D printing technology. The designed prototype, being in forms of eye-face shields, are made available and accessible to the general public, thus offering more possibilities for yield improvement in PPEs during emergent infectious disease events such as COVID-19. Corresponding Author: Zi-kai Hua Shanghai University School of Mechatronic Engineering and Automation CHINA Corresponding Author Secondary Information: Corresponding Author's Institution: Shanghai University School of Mechatronic Engineering and Automation Corresponding Author's Secondary Institution: First Author: Xiu-ling Huang First Author Secondary Information: Order of Authors: Xiu-ling Huang

Thank you for your letter and for the reviewers' comments concerning our manuscript entitled "A Novel Combinatorial Shield Design for Eye and Face Protection in COVID-19" (ID: MANU-D-20-00460). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer's comments are as flowing: Responds to the reviewer's comments: Reviewer #2: 1. Comment: Anti-fogging performance usually has considerable influences on systematic protection effectiveness, thus affecting the potential users in making their proper choices. Although some anti-fogging methods were briefly recalled in the discussion part of the present paper, can the authors explain why none of them has indeed been implemented in the proposed models? Response: We totally agree with the reviewer's comment and have full awareness of the importance of anti-fogging treatments when designing our goggles. However, the overall methodologies in the present work should be understood in a rather specific global context, say, upon some emergent infectious disease events such as COVID-19, for instance. Bearing in mind that almost every emergent health event is usually accompanied with a critical supply shortage, we must keep the design of any PPE from being structure-complicated and material-demanded. Therefore, our present design makes a good trade-off between protective effectiveness and supply restrictions considering the fact that ordinary glasses are always among the most easy-to-get materials during such an event. On the other hand, our design has sufficient flexibility in the implementation of anti-fogging lens since the latter does not change the structure nor the parameters but only local materials of our models. Response: Thank you very much to the reviewer for pointing out our incomplete consideration. Based on the Comment of the reviewer, we checked all the pictures in this paper and revised Figure 2, which was added with the size indicator. 4. Comment: The authors have applied Chinese GB 14866-2006 standard for the conception of the goggles integrated in the all-in-one face shield. Does it mean that the proposed models merely fit in size to Asian users or more narrowly spoken, to Chinese users? Considering the significant variance in facial morphology among potential users from all over the world, what changes should be employed to make the product applicable as well to those from other countries? Response: Many thanks to the reviewer for his/her comment. Actually, our products are appropriate in size for users from all over the world without any further adjustment. The reason for that is threefold: Firstly, we noticed that the American designed 3M 1621AF goggles have exactly the same lens width (150mm) with the Chinese designed CKY-136FW goggles, regardless of the difference in facial morphologies between American and Chinese costumers, thus giving rise to faithful evidence that this variance plays no dominant role in the conception process of the product. That's why we set the lens width of our middle-size goggles to be 150mm. Secondly, large-size goggles with lens width of 164mm are also provided to offer more optional possibilities for different users. We believe that these two sizes can indeed cover the vast majority of actual requirements in clinical applications all over the world. Thirdly, the mechanical structure of the goggles is sufficiently compliant when TPU is used as the printing material, allowing the joint profile to accommodate itself as conformal as possible to the user's face. Special thanks to you for your good comments. Other changes: (1). In the Introduction part, the word of "neijhoft" were corrected as "Neijhoft". (2). In the 2 Design of Eye-face shield part, "which mainly refers to ISO 4849:1981" was added (3). In the 3.2 Assembly Process of Eye-face shield part, the word of "shied" were corrected as "shield" We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And we have marked the changes in red in revised paper. We appreciate for Editors and Reviewers' warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.

Introduction*
Since March 2020, the coronavirus disease (COVID-19) has become a worldwide pandemic. COVID-19 is transmitted via droplets and fomites during close unprotected contact, and transmission through the ocular surface should not be ignored [1,2]. According to China's anti-epidemic experience, personal protective equipment (PPE) for doctors includes masks (N95/disposable medical masks being the most effective), protective clothing, disposable gloves, goggles, and face shields [3,4]. The protection of the eyes and face is very important. When a face shield is used in conjunction with a mask and goggles, the former immediately keeps the vast majority of the potentially infectious droplets at a reasonable physical distance, while the latter offers locally enhanced protection in a further step. However, it is both inconvenient and uncomfortable for medical staff to wear traditional face shields and goggles simultaneously (particularly for long periods), owing to the extra weight of the frame of the face shield. Therefore, we propose a combined design of goggles and shields based on the three-dimensional (3D) rapid manufacturing mode. We designed a special structure to quickly and easily assemble the goggles and face shields while removing the frame required by traditional face shields. 3D printing facilitates the production of PPEs with a shortage of materials during the COVID-19 pandemic.
Any company or individual with 3D printing equipment can freely obtain our eye-face shield model files through the link provided at the end of the article for production. Similarly, Tino [5] and Neijhoft [6] used a 3D-printing method to make protective equipment such as masks and face shields and provided an open-access model that can be downloaded. Our design has been used in hospitals in China since February 5 2020. To our knowledge, no medical staff who used our eyeface shields were reported to be infected with COVID-19. Therefore, the clinical effectiveness of the eye-face shield has been preliminarily confirmed. The main objective of this study was to Novel Combined Shield Design for Eye and Face Protection from COVID-19 provide a novel design and fabrication method for the rapid production of all-in-one eye-face shields. Our design can serve as either an alternative or a complement to traditional fabrication methods of goggles and face shields, according to the practical requirements.

Design of eye-face shield
The eye-face shield is composed of four parts: goggles, lenses, face shields, and elastic bands. The goggles protect the eyes and support the face shield with a special connection structure. The requirements for goggles used in clinical settings are presented in Table 1. We designed goggles with three different sizes (dimensions are shown in Table 2). The size was based on the Chinese GB 14866-2006 standard, which mainly refers to ISO 4849:1981, as well as the goggles on the market. According to the requirements and dimensions of the aforementioned goggles, we created a 3D model of the goggles using SolidWorks, NX, 3Dmax, and other 3D modeling software programs. We found defects through sample try-on and repeatedly modified the model to improve the airtightness, comfort, and aesthetics.
For satisfying requirement A in Table 1, the goggles do not have any holes except for the lens holes (see Fig. 1) and the elastic-band holes (see "3" in Fig. 1). We adjusted the arc of the goggles to fit the face and improve the airtightness. We designed an inverted "V" shape at the nose wings (see Fig. 1) to fit the slope of the nose bridge.
For satisfying requirement B in Table 1, the edges that fit the face are designed with flanging. The outward flanging (see "4" in Fig. 1) is 12 mm wide and approximately 90° from the horizontal plane. The inward flanging at the nose (see "5" in Fig. 1) has a width of 5 mm. The flanging improves the airtightness, increases the stress area, and reduces the number of pressure sores.
For satisfying requirement C in Table 1, we designed anchors on both sides of the goggles (see "7" in Fig. 1) to connect the face shield. There are four anchors: two on the left and two on the right.
For satisfying requirement D in Table 1, we designed two types of lenses: a single-lens and a double-lens (see Fig. 2). The single-lens has a wider field of vision, but the cutting process is more complex. The double-lens shape is square, which can simplify the lens cutting process. Four slots on the interior of the front panel (see "2" in Fig. 1) were added to reinforce the lenses.

Preparation of eye-face shield (3DP-S-M considered for example)
This section describes the preparation process for the eye-face shield, including the production of the 3D-printed goggles, lens, and shield and the assembly process of the eye-face shield. For users to quickly understand the manufacturing method of the eye-face shield, the manufacturing details are disclosed in detail here. We are willing to mobilize all possible social resources to help front-line medical personnel fight against the epidemic.

3D-printed goggles
After printing the goggle samples, we tried them on and modified them repeatedly, and the final material and printing method were determined. This article recommends the use of the SLA printing method. The material should be selected from medical, safe photosensitive resin, or thermoplastic polyurethane elastomer. After the goggle model is complete, the user should save it as STL files, which are then imported into the printing software for parameter setting before printing. Firstly, supports should be established for the model. The support setting style is shown in Fig. 3. The printing parameters are important, as they determine the quality of the sample. After many printing cycles, we obtained the optimal printing parameters, and the success rate was 100%. When setting the printing parameters, one can refer to the main printing parameters presented in Table 3. After completing the printing-parameter setting, a print preview should be performed. Figure 4 shows the correct print preview of some layers. In the checking of the print preview, a different posture of the model and different parameter settings will make the preview image different. If one sets the parameters to be consistent with the parameters that we provided and is unsure whether the print preview is correct, one can refer to Fig. 4. Alternatively, he/she should consult a 3D-printing professional.

Assembly process of eye-face shield
The eye-face shield includes four parts: the face shield, lenses, goggles, and elastic band (see Fig.  5). The assembly of the eye-face shield can be divided into three steps. The first step is to apply glue to the lens and attach it to the goggles, during which the users should pay attention to the slots. The second step is to pass the end of the elastic band through the elastic-band holes and then fix it by stitching, gluing, knotting, and other methods. The third step is to press the cross hole on the face shield into the four anchors. The corresponding relationship is shown in Fig. 6. The assembled eye-face shield is shown in Fig. 7.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 Novel Combined Shield Design for Eye and Face Protection from COVID-19

Fig. 6 Correspondence between cross holes and anchors
For face shield section, there are three sizes of the eye-face shield. For users to understand the preparation of the eye-face shield more accurately, pertinent documents are presented at the end of the article. Considering the different bending stiffnesses of transparent plastic sheets with different thicknesses, we recommend using a 0.5-1.0 mm transparent PVC plastic sheet after trial production. In lens section, in designing the eye-face shield, a single-lens and a double-lens were considered, for allowing individuals or small groups to fabricate the eye-face shield without limitations on the cutting process. The double-lens cutting process is easier, and the users simply need to cut a square transparent plastic sheet. In the single-lens eye-face shield, the middle baffle is removed, and the field of vision is larger. When the cutting process is not limited, it is recommended to use a single-lens eye-face shield. The lens files can be accessed via the link presented at the end of this article. The gaps of the lens slots are 1.5 mm wide, and the users must reserve the installation space. For the eye-face shield lenses, a transparent plastic sheet with a thickness of 0.5-1.0 mm is recommended.

Discussion
Regarding effectiveness, the eye-face shield has been used in many hospitals in Shanghai, China since February 5 2020. To date, >300 medical personnel have used the eye-face shield, none of whom were reported to be infected by COVID-19. This result preliminarily confirms the effectiveness of the eye-face shield for protection. Regarding the issue of fogging, commercially available anti-fogging liquid, anti-fogging paste, or anti-fogging agents for swimming goggles can be considered. In the case of a shortage of the foregoing materials, antibacterial hand sanitizer, soap detergent, iodophor, or other substances can be smeared on the lens and surface to prevent fogging [7]. Regarding the manufacturing method, the applicability of 3D printing was discussed and validated in the design of the model, confirming that the best manufacturing method is 3D printing. At present, the daily output of face-eye shields with 3D printing in China can reach 2000 pieces [8]. Additionally, in China, companies have used 3D printing to produce samples for making molds. After the mold was obtained, face-eye shields were prepared using traditional manufacturing methods such as injection molding and compression molding. This not only provided more possibilities for the production of face-eye shields but also saved time and reduced costs. Of course, users are encouraged to try other production methods.