Feb/March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 2 1 2 3 MATERIALS SCIENCE AND CORONAVIRUS SERIES OPTIMIZING 3D-PRINTED, REUSABLE METAL N95 FILTERS BY 3D CHARACTERIZATION AND MODELING As N95 masks are in short supply and high demand, reusable, sterilizable metal filters for masks built using 3D microstructural characterization and simulation methods are a promising alternative. Aaron Acierno,* Erica Stevens,* Teddi Sedlar, Katerina Kimes,* and Markus Chmielus,* Department of Mechanical and Materials Science Engineering, University of Pittsburgh Kurt Svihla and Steve Pilz, Ansys Inc., Canonsburg, Pennsylvania Patrick Dougherty, The ExOne Company, North Huntingdon, Pennsylvania Thomas Spirka, Synopsys Inc., Mountain View, California B y the end of 2020, the novel coro- navirus disease (COVID-19) had infected over 60 million individu- als worldwide and caused over 1.5 mil- lion deaths [1] . As wide distribution of vaccines rolls out, research on disease transmission rates [2,3] and mitigation ef- forts [4] have concluded that mask wear- ing is an effective measure for reducing transmission, and public health recom- mendations follow accordingly [5] . With all sectors of the population advised to wear masks, highly effective N95 masks are in short supply and high demand. Breathable, accessible, reusable, high- ly effective respiratory protection from outside the current supply chain is de- sirable to meet demand and protect the populace. Additionally, beyond this cur- rent pandemic, reusable masks would not only stabilize stocks at healthcare centers, ensuring that staff are imme- diately and sufficiently protected in the event of a future airborne virus pub- lic health emergency, but also reduce the environmental impact of billions of single-use masks. Aiming to leverage the potential for effective and reusable metal filters produced outside of the current sup- ply chain, a collaboration of research- ers from the University of Pittsburgh, ExOne, Synopsys, and Ansys fabricated, characterized, and modeled binder jet 3D-printed copper and stainless-steel metal mask filters. This article de- scribes the 3D microstructural charac- terization, simulation, and modeling of final binder jetted parts, develop- ing an iterative process framework for the streamlined development and as- sessment of 3D-printed, porous, metal N95-filters (Fig. 1). Using feedstock powder from three separate suppliers per compo- sition, 316L stainless steel and copper samples were binder jet 3D printed and sintered by ExOne using an ExOne In- novent. Various amounts of connected porosity were generated through par- tial sintering at specific temperatures: 800, 850, and 900°C for copper; and 900, 1000, and 1100°C for stainless steel. 3D porosity analysis by micro computed *Member of ASM International One materials class alternative for producing reusable, sterilizable N95-quality filters is metals: copper or stainless steel. Copper has been shown to exhibit antimicrobial properties [6] , and stainless steel has established cleaning procedures within hospitals and clinics. Thus, metal reusable filters for masks could be sterilized and reused while also meeting N95 filtration re- quirements after optimizing geometry and permeability to balance breathabil- ity and efficacy. Design freedom for geometry and permeability can be found in the addi- tivemanufacturingmethod of binder jet 3D printing, a technique that selective- ly deposits a liquid binding agent onto each successive layer in a powder bed and presents unique advantages for fil- ter fabrication: (1) material compatibil- ity includes both copper and stainless steel [7] , (2) high printing speed [8] , (3) fab- rication at room temperature prevents ready oxidation [9] , and (4) customized post-processing can be used to tailor porosity levels [10] .