Table 2.

Published studies on new face mask design, functionality and sustainability factors to help address supply chain shortage and improvements in waste managements presented by ongoing COVID-19 pandemic.

Innovations	Main development(s)	Citing reference(s)
Computational fluid dynamics for face mask filter efficacy	Face mask filters – textile, surgical or respiratory – understanding of droplet dynamics through and around a face mask filters resembling cough many – new criterion for calculating mask efficiency to consider penetration dynamics proposed – masks do not provide complete protection	Dbouk and Drikakis, 2020a, Dbouk and Drikakis, 2020b
Air dispersion distances through patient simulator	Normal cough induces turbulent flow that spreads about 70 cm from the subject – N95 mask prevented air leakage than surgical mask during coughing. But there remains sideway leakage.	Hui et al., 2012
Forward jet of droplets and leakage around mask – droplet transmission	Using the Schlieren optical method, it was shown that wearing a standard surgical mask blocks the forward jet of droplets, but allows leakage around the top, bottom and sides. N95 reduces the droplet leakage around mask edges during coughing – none of the masks entirely prevented penetrating or escaping the mask – i.e., droplet transmission.	Tang et al., 2009
Self-designed triple-layer cotton masks to suppress respiratory droplet levels	Self-designed triple-layer cotton masks worn by respiratory infected person (influenza and COVID-19 participants) were shown to be similar to medical masks for suppressing droplet levels in regular bedroom and a car with air conditioning where cough/sneeze counts were measured	Ho et al. (2020)
Face masks with respiratory valve had lower exchange rate of breathing assistance	Studies to evaluate and characterize the comfort sensation and performance of 12 types of face masks (related to shape, respiratory valve, brand, main materials and protection level) related to breathing assistance for healthcare in fog and haze weather [non-COVID-19] – dynamic changes in airflow rate and breathing resistance were acquired by virtual instrument system- cotton mask had lower rate of breathing assistance than nonwoven fabric masks.	Yao et al., 2019
Mask face detection based on a hybrid AI, deep transfer learning and classic machine learning model	Use of Artificial Intelligence (AI), deep transfer learning and classic machine learning to evaluate mass usage of face masks to potentially inform protection and compliance during COVID-19. Researchers used three data sets: Real-World Masked Face (RMFD) consisting of images of 5000 masked faces and 90,000 unmasked faces; Simulated Masked Face Dataset (SMFD) with 785 for simulated masked faces and 785 for unmasked faces; Labelled Faces in the Wild (LFW) containing 13,000 masked faces of celebrities. Focus was in training for accuracy of face mask detection.	Loey et al., 2021
Use of spray-simulation method (mimicking a sneeze) along with germ-free mice	Development and validation of spray-simulation method (mimicking a sneeze) for determining efficacy of combed-cotton textiles used as two-layer barriers for protecting germ-free mice from bacteria carrying droplets. Authors used aqueous suspension of 12 probiotic-cultured dairy bacteria – authors advocated use of bacteria as they exist in association with respiratory viruses in respiratory fluids – they also used bacteria to quantify number of droplets that escape textile barrier	Rodriguez-Palacios et al., 2020
Surgical and homemade masks, even without fitting, reduces particles emitted via breathing, talking, and coughing	Wearing of surgical masks, or N95 respirators, even without fit-testing, reduces number of emitted expiratory particles from breathing, talking, and coughing from experimental studies. But, efficacy of wearing homemade cloth or paper masks is less clear, and confounded by shedding of masks fibres, with some reductions observed, particularly for larger particles (>0.5 μm). Authors did not measure virus-laden aerosols and droplets, but observations consistent that wearing mask can help with mitigating pandemic-associated with respiratory disease.	Asadi et al., 2020a
Bio-based facemasks – use of electrospinning gluten and carbonization	Suggested sustainable future-use of wheat gluten biopolymer, a by-product of cereal industries, as alternative to using petrochemicals for reusable facemask. Fine mesh nanofilter membrane structure to be achieved via electrospinning and subsequent carbonization at over 700 °C.	Das et al., 2020
Design, velocity and fitness innovation for sustainable face masks including home made	Understanding performance of commercial masks and Advantages of wearing commercial and home-made face coverings during pandemic. Review of masks made from household materials. Limited studies that used randomised control trials for investigating efficacy of cloth masks showing that they are not suitable for HCWs.	Davies et al., 2013; Chughtai et al. (2013); Chua et al., 2020
Cloth masks loose filtration efficacy after frequent washing and drying cycles.	Studies on the effect of washing and drying on cloth mask highlighted a drop in filtration performance that was correlated to pore size and shape of the masks. It was found that the PM10 filtration efficiency dropped by 20% after 4th washing and drying cycle, that was attributed to continuous stretching of the masks, enlarging the pore size, thus impairing mask performance.	Neupane et al., 2019
Engineering multifunctional face masks	Increasing trend for published information that highlights innovation to improve filtering capacity (such as pore size) of mask materials and improving additional functions in terms of design (such as antimicrobial properties, coatings) to enhance user comfort, and convenience (such as introduction of self-cleansing and sensing properties. However, these are laboratory studies.	Chua et al., 2020
Increased super hydrophobicity and transparent qualities of masks materials	Graphene-coated masks shown to exhibit significant superhydrophobic and photothermal performance that can repel incoming aqueous droplets masks exposed up to 80 °C under sunlight illumination can achieve self-sterilisation. Transparent properties included on face masks to improve quality for the hearing impaired such as digital face recognition, human-facing industry.	Son et al., 2020; Zhong et al., 2020; Chua et al., 2020
Differences in FFE for head tie, ear-loop face masks	29 different face masks alternative including expired N95 respirators with intact elastic straps and respirators subjected to ethylene oxide or VH2O22 sterilisation – procedural face masks with elastic ear loops showed lowest fitted filtration efficacy at 38.1%. Thus, highlighting increased risk.	Sickbert-Bennett et al., 2020