Microstructure analysis and image-based modelling of face masks for COVID-19 virus protection

Wenjia Du, Francesco Iacoviello, Tacson Fernandez, Rui Loureiro, Daniel J. L. Brett & Paul R. Shearing - The Electrochemical Innovation Lab, Department of Chemical Engineering, University College London, London, UK; Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex, UK

Until March 2021, around 120 million coronavirus disease (COVID-19) infected cases and over 2.6 million deaths have been reported worldwide. […] Recent investigations have implied that face masks help to reduce the disease transmission and therefore slow down the growth of the epidemic curve. However, there are still ongoing debates on the efficacy of wearing masks […] since there is a general lack of information relating to the material structure of commonly used face masks.

In this paper, we have studied three common types of face masks by correlative application of X-ray computed tomography (CT) and infrared (IR) thermal imaging techniques. We have used high-resolution (350 nm) microscale X-ray tomography to observe the 3D microstructures of fibres and related pore networks. Microstructural parameters have been comparatively quantified via skeletonization and pore network modelling (PNM). […] We found that a reusable mask has the best breathability and comfort whereas the N95 mask provides the best aerosol filtration. We have made the data freely available to the scientific community and to the general public in order to help develop better filtration devices and face masks and to aid wider public understanding.

How Amira-Avizo Software is used

The reconstructed micro-CT datasets were imported into Avizo 2019.4 software (Thermo Fisher Scientific, USA) for further segmentation and quantification

>> Watch 3D Microstructure video

The advanced PNM (Pore Network Model) module in Avizo was applied to the three masks after binarization of filtered datasets.

>> Watch Pore Network video

Advanced skeletonization modules (cylinder correlation and trace correlation line) in Avizo (XFiber Extension) were interactively used to detect and track the curved fibrous structures.

>> Watch Fiber Analysis video

The absolute permeability (χ) along the Z-axis direction (perpendicular to mask plane) was calculated in Avizo XLab Hydro (an image-based model based on the Stokes’ equations).

>> Watch Air Permeability video