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Additive Manufacture of Emulsion Inks to Produce Respiratory Protective Filters
contaminants, such as virus-laden aerosol particles, while approaches to prevent the transmission. It is widely
letting air pass through. accepted that mask wearing could reduce COVID-19
This review presents the feasibility of a polymerized transmission as it provides continuous protection from the
high internal phase emulsion (polyHIPE)-based filter, and contamination from the respiratory droplets and acts as a
whether current emulsion-based AM techniques can be barrier to stop direct contacts of hands to mouth, nose, or
used to produce RPE against COVID-19. The motivation eyes . There is high certainty that the inhalation of the
[10]
behind AM to make a porous foam is that it can virus-containing aerosols is one of the infection modes,
produce complex geometries. The advantages include a as determined by computer modeling of speech and
multimaterial filter, localized and functionalized surface, cough generated droplets from infected individuals .
[11]
or tunable porosity gradients to control the airflow within Nevertheless, this is largely dependent on the respiratory
the filter itself. This approach could facilitate new filter droplets that suspend in the air for a certain period of time.
designs that capitalize on new material processing and The health care workers are at a great risk of
manufacturing techniques that may overcome some infection when using aerosol-generating procedures on
limitations of fibrous filters. Furthermore, the new COVID-19 patients as these airway-based procedures
[6]
filter designs may potentially filter the most penetrating can create fine particles of <5 µm which can remain
particle size of 0.3 µm, which is the most difficult to suspended in the air. For example, procedures such as
filter because this size is at the transition point between tracheal intubation and non-invasive ventilation can
particles that predominantly move by Brownian motion produce virus-laden particles of smaller than 10 µm,
and larger particles that move by straight trajectory. which are very likely to bypass the respiratory mucosa
This review provides an overview of the current filter- in the upper airways and penetrate deep into the lung,
based applications of emulsion templating, including the thereby increasing the infection risk . The World Health
[12]
current state of emulsion ink-based AM and the European Organization recommends having adequate supply of
Standard (EN) guidelines regarding the requirements of PPE, such as N95 respirators, filtering facepieces (FFP3
a RPE filter. or FFP2), or their equivalents, as part of the RPE .
[9]
In this review, the following considerations are Several ways the airborne particles can deposit onto
covered: the fibers include impaction, interception, and electrostatic
• RPE requirements including ISO standards and forces. To improve breathability, the respirators must be
regulations that a new filter material will need to permeable to air while maintaining their particle filtering
comply with; function. To achieve this, the fibers have electrostatic
• An overview of the polyHIPE material, current filter, charge to attract and trap airborne particles that attach
and separation-based applications; onto the fiber . Sterilizing these filters using ethanol
[14]
[13]
• AM of polyHIPE foams, their advantages, or isopropanol removes the electric charge from the
[15]
limitations, and the current progress in the literature fibers which reduces their effectiveness.
to 3D printing using emulsions. According to the US National Institute for
Occupational Safety and Health, N95 masks that can
2. Respiratory filter requirements for filter at least 95% of the airborne particles use an
COVID-19 prevention electrostatically charged non-woven polypropylene (PP)
RPE is a broad term covering respirators or breathing fiber to filter out airborne particles. The protective feature
apparatus that filter or remove harmful substances from of these masks is comparable to that of the European FFP2
the air we breathe. For health care workers, different RPE filters. In future, the masks should be designed in a way
types are recommended depending on the exposure risk to include a seal around the face to prevent the bypass of
from the COVID-19 patients . Furthermore, government submicron particles through the filter mechanism, which
[6]
[16]
guidelines are in place for infection prevention . The can occur during head movements . 3D printing is a
[7]
size of severe acute respiratory syndrome coronavirus-2 potential solution as it can be combined with detailed face
that causes COVID-19 is between 50 and 200 nm wide . scans to produce a customized face seal for improved
[8]
[17]
COVID-19 is thought to transmit through close contact wearer comfort and fit . A customized 3D-printed
and contaminated droplets over short distances . When reusable facemask with a replaceable filter membrane has
[9]
[18]
an infected patient coughs or sneezes, large airborne been proposed . FFP2/3 filter membranes can be used as
respiratory droplets laden with the virus are produced, a replaceable part of the mask.
contaminating surfaces and potentially transmitting the 3. RPE regulations
virus to others nearby. Hence, wearing a face mask is
able to protect the surrounding people from respiratory There are three classes of respiratory filters: FFP1,
droplets. Two-meter social distancing, frequent hand FFP2, and FFP3. A higher grade indicates a better filter
washing, and usage of mouth coverings/face mask are efficiency; FFP3 can filter out at least 99% of airborne
48 International Journal of Bioprinting (2021)–Volume 7, Issue 1