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Sherborne and Claeyssens
particulates. During classification, the respirators are requirements of the European Directive on PPE Regulation
tested to certify whether they conform to the British (EU) 2016/425. This covers the legal obligations to ensure
or European standard (BS) EN 149:2001+A1:2009 . that the manufacture of PPE meets the required standards
[19]
The “Conformité Européen” (CE) marking affixed to relating to the design, manufacture, and marketing of
the PPE is an evidence of compliance to this legislation PPE. Furthermore, commission recommendation (EU)
and an indication of the effectiveness of the respirator. 2020/403 was introduced recently during the COVID-19
A selection of these requirements is summarized in crisis to speed up the delivery of PPE to the market,
Table 1. In the United Kingdom, the HSG53 (2013) is specifically for the medical professionals.
a guideline recommending the best industry practice for
the usage of RPE and its standard requirement. FFP3 4. Overview of the polyHIPE
is recommended in clinical use for protection against PolyHIPE is a porous polymer that is created by
biological agents, including pandemic flu. Comparison polymerizing the continuous phase of an emulsion where
tests between FFP3, FFP2, FFP1, and surgical masks the droplet phase exceeds over 74% of the total liquid
show that there is a gradual decrease in the protection volume; this type of emulsion is called a high internal
level with surgical masks offering the lowest level as phase emulsion (HIPE). The two liquids have to be
they do not seal around the face . Performance testing immiscible with each other; therefore, when they are
[20]
showed that the FFP2 and FFP3 masks achieved <1% mixed together with either a surfactant or a small pickering
and <0.03% for the penetration of polydisperse sodium particle, one of the liquids is broken into droplets (droplet
chloride (NaCl) aerosols with a MMD (mass median phase) that disperses within the other (continuous phase).
diameter) of 238 nm, respectively . Surgical masks offer A polymeric material known as a polyHIPE is created
[15]
some protection against the large droplets and contact when the emulsion’s continuous phase is set into a solid.
transmission so symptomatic patients should wear it to This can be done using either a light , heat , or a redox-
[23]
[22]
minimize the spread of respiratory secretions that could based polymerization reaction . During the crosslinking,
[24]
transmit the infection to the surrounding. Respirators the 3D architecture of the emulsion’s continuous phase is
with a tight face seal are recommended over masks for fixed as a solid polymer, and subsequently, the draining of
enhanced protection. In regard to 3D-printed PPE-related the droplet phase leaves behind a porous polymer. A unique
devices from the 3D printing community, care should be property of the polyHIPE is that the porosity parameters
taken when using them, as the devices are not approved can be independently tuned through the initial emulsion
by the relevant regulatory bodies for clinical use and their mixing conditions and ingredients. These include physical
effectiveness is not guaranteed. Therefore, these devices parameters, such as temperature , speed of mixing [25-27] ,
[23]
should be used at the user’s discretion. and the rate the droplet phase is added . The emulsion
[28]
The assigned protection factor indicates the level constituents can be varied from different aspects, such as
of protection that could be provided by the respirator water volume ratio , monomer type [30,31] , solvent used
[29]
(Table 1). A protection factor of 10 means that the user in the emulsion [32,33] , amount of surfactant , surfactant-
[34]
particle exposure level is reduced by a factor of 10, so free pickering emulsion , solubility of the initiator ,
[36]
[35]
one-tenth of the air contaminants will be breathed in. and addition of electrolytes to the droplet phase . These
[31]
FFP3 is considered to be twice as effective as FFP2. variables affect the stability of emulsion, the droplet
All respirators require a tight-fitting face seal otherwise size, and the way the monomer polymerizes around the
particles can bypass the filter through the open gaps. The droplets. A representative scanning electron microscope
total permitted inward leakage accounts for all potential image of the polyHIPE structure is shown in Figure 1.
leakage paths around the filter when the face seal leaks . During the polymerization, the monomers cross-
[21]
Furthermore, any PPE or RPE for the European link to form a polymer chain. This process coincides
market has to meet the required health and safety with a significant volume reduction or contraction.

Table 1. Classification requirements of FFP1, FFP2, and FFP3 respirators
Classification Protection factor Max. penetration of test aerosol: Max. permitted Total permitted
95 l/min max % resistance (mbar) inward leakage
(%)
Sodium chloride Paraffin oil Inhalation Exhalation
30/l min 160 l/min
FFP1 4 20 20 0.6 3 25
FFP2 10 6 6 0.7 3 11
FFP3 20 1 1 1 3 5
Information adapted from the British standard: BS EN 149:2001+A1:2009 . FFP, filtering facepieces.
[19]
International Journal of Bioprinting (2021)–Volume 7, Issue 1 49