Design, manufacture, and testing of customized sterilizable respirator

Abstract

The respirator as one of the personal protective equipment is essential for industrial activities (e.g., mining, painting, woodcutting, manufacturing) for protection from contaminants in the air and during the Covid-19 pandemic to protect the wearer from infection. The respirators nowadays are commonly made of rigid plastic. They are expensive, cumbersome, and not comfortable to wear. The many components with complex structures prevent it from cleaning and reusing. We develop a practical and scalable strategy to create customized respirators with durability using computational modeling and 3D printing. It is shown that by morphing the shape according to the user's photo, the respirator is designed to fit a user's face without air leaks. Using a printing-mold-casting method, this respirator can be manufactured by silicone rubber with accuracy, which is highly durable, with its mechanics primarily not affected by sterilization. These features provide the current respirator adaptivity and convenience in carrying and storing, as well as more comfort for long-time wearing.

Keywords: 3D printing; Computation modeling; Environmentally friendly; Morphing; Sterilizable respirator.

Fig. 1

3D modeling and printing of an arbitrary respirator connecting to respiratory devices and test airtight with a CO₂sensor. a. schematic diagram for the design procedure of the respirator. b. the computational model of the respirator, the multi-material 3D printer, and the 3D printed respirator connecting to a respiratory device. c. The test of CO₂ of the printed mask at different positions along its edge against the face during normal breathing, d. schematics of how the sensor is connected to the analog input of an Arduino board and a computer, as well as the main reason for the air leak at the top of the mask. e. The CO₂ test results of i) at the right side, ii) at the bottom, and iii) at the top of the mask, as illustrated in panel b.

Fig. 2

Using simple photos to customize the face profile 3D model for accurate mask design. a. Different featuring points are selected from the photo to recognize their 3D coordinates for face morphing. b. illustrate of how the model profile is edited from the original model after receiving information from different photos.

Fig. 3

Stress-strain curve of different polymer materials in comparison to natural material. (a-d) for 4 different kinds of silicone rubbers (Polytek, n.d.) and (e) for a polyurethane material (Solutions, n.d.). We tested different materials a few times to reduce the error from preparing the sample. f. the stress-strain curve of pigskin in a tensile test. It is shown that the overall strain stiffening behavior of the silicone rubbers agrees with that of natural skin and is thus more mechanically compatible than other strain softening polymers. Different line colors in each panel simply mean different repeats of the mechanical test with the same testing parameters. The statistical results of the mechanical properties of the materials are summarized in Table 2. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Design and production of the customized respirator. a. 3D model of the respirator modified according to the customized face profile (orange) for large fitness. b. the 4-pieces mold (grey) used to cast and make the silicone respirator (orange). c. The silicone respirators are made from mold. d. simple devices (vacuum chamber, pump, mold, silicone gels) are used to make the mask. e. testing of the mask for airtight by blocking the front with a piece of paper towel (upper) and surgery respirator (lower). This is to qualitatively mimic the effect of the filter of the respirator in blocking the airflow, in order to test the breathability and air tightness of the respirator against the face. f. the CO₂ was recorded during normal breathing at different positions. The low CO₂ magnitude suggests airtight at any place around the mask edge. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Stress-strain curve and SEM images of Silicone 1 Material in different sanitizing treatment times. a. Sanitizing in boiling water for 1, 2, 3, 4, and 8 h, respectively. b. Sanitizing in Alcohol for 5 and 8 h, respectively. We tested different materials a few times to reduce the error from preparing the sample and the statistical results of the mechanical properties of the materials are summarized in Table 3 c. the stress-strain curve of Silicone 1 sample under 100 loading-unloading cycles with a constant speed of 100 mm/min and the upper strain of 2.0. The inserted plot gives the stress history as a function of the time and shows how the peak stress decay as the number of loading cycles. SEM images of d. original Silicone 1 dogbone sample (without treatment, scale bar: 100 μm) e. with treatment in boil water for 4 h (scale bar: 50 μm) and f. with treatment in Alcohol for 8 h (scale bar: 50 μm). By comparing the SEM images (d, e, f, and many others not shown), we do not find any significant difference in the microstructure of the silicone surface after the treatment.