Custom-made 3D-printed Face Masks

In the case of life-threatening pandemic situations with a lack of professional FFP2/3 face masks for healthcare workers inside and outside hospitals, a potential alternative solution should be easily accessible, at low cost, and with global availability. With the introduction of new-generation smartphones with at least two cameras and dedicated applications, modern imaging techniques like 3D facial scanning have become available worldwide. In the PoC presented here, 3D individualized facial scanning and export of the OBJ format data file by secure e-mail took less than 2 min 30 s. The 3D facial scanning procedure applied was safe. No self-scanning was performed and the scanned person had no physical contact with the smartphone, ruling out potential cross-contamination. The person who performs the 3D face scan and handles the smartphone needs to wear protection glasses, clothing, and a face mask, since interpersonal contact would be reduced to a critical distance of less than 1 m.

There is clear evidence in the literature on the high accuracy of 3D facial scanning with stereophotogrammetry.4 Integrated workflows with 3D facial scanning have been implemented in the daily clinical routine of maxillofacial surgery, facial plastic surgery, and craniofacial surgery.5 However, it appears that there is no report available in the literature on the accuracy of the surface geometry of 3D face scans performed with the Bellus3D FaceApp that was used in the PoC workflow presented here. One might assume that it is less precise than professional 3D cameras, but the study by Piedra-Cascón et al. indicates a high precision. In their study, published in 2020, a mean precision value of 0.32 mm and a high intra-class correlation of 0.99 was found for 10 3D facial reconstructions when using a dual-structured light facial scanner (Face Camera Pro Bellus; Bellus3D, Campbell, CA, USA) that was mounted on a smartphone.6 This hardware component makes the presented PoC workflow more broadly applicable since it is no longer limited to iPhone smartphones, but basically can be adapted to every type of smartphone or tablet with the facial scanner mentioned above.

Additive manufacturing with 3D SLS printing has proven its value in routine clinical surgical facial reconstruction because of its high accuracy.7 Secure downloading of the OBJ file and adaptation of the virtual 3D face mask to the individual facial mask by the CAD designer took less than 10 min. Although professional CAD software was used in this PoC, 3D modelling can also be done with free download software. 3D printing of the two reusable components for four clinical prototypes took 11 h, with an additional post-processing time of 12 h (breakout, cool-down, and sandblasting of the 3D-printed face mask). More powerful commercially available 3D printers could increase the volume up to 60 individual 3D-printed face masks per 3D printer within 24 h, including post-processing.

The head fixation bands (Velcro or elastic bands) are believed to be easily available worldwide. The disposable filter membrane can be acquired globally from non-medical vendors selling non-woven melt-blown FFP2/3 industrial fabrics. In addition, the CAD design of the 3D face mask can be adjusted to the specific disposable filter membrane and head fixation components available in different regional parts of the pandemic.

The authors emphasize that additional clinical testing of this prototype is essential prior to widespread use in real-life situations, for several reasons. First, the performance of a protective face mask depends not only on the efficiency of the filter membrane, but also on its individual fit to prevent leakage around the perimeter. Clinical pictures in frontal and two-thirds right facial profile view (Fig. 2) show the clinical adaptation of a commercially available disposable surgical face mask and disposable FFP2 and FFP3 face masks on the same face. Although a mathematical Boolean calculation implements an accurate virtual adaptation of the individual 3D face mask to the corresponding static 3D facial mask (Fig. 2), further clinical testing is ideally required both in static and dynamic situations. This also applies to commercially available disposable protective face masks.

Secondly, the polyamide composite material used in the PoC has been used for over 3 years in daily clinical surgical routine for CAD-designed ‘cutting’ and ‘resection’ guides in maxillofacial procedures at AZ Sint-Jan Hospital. Although for the latter standardized sterilization procedures are performed (15 min at 135 °C), in this case a disinfection procedure is proposed instead, to avoid logistical sterilization issues (less time-consuming). The recommended COVID-19 disinfection protocol at AZ Sint-Jan Hospital for the cleaning and disinfection of facial shields needs official local hygiene and virological verification and approval prior to use in this specific case. A list of disinfectants for use against the novel coronavirus COVID-19 has been published online.8

Third, there are some dermatological considerations. Allergic and decubitus lesions due to specific contacts, especially at the nasal bridge, might occur after prolonged application of the individual 3D face mask in humid and warm infected virological units. Additional skin unguents applied to the outside contour of the 3D individualized face mask may be required. Last but not least, virological testing for leakage between the two reusable components and contamination of the components themselves after one or multiple disinfection cycles is essential before application in real-life situations.

This PoC illustrates that 3D printing of individualized 3D face masks in combination with FFP2/3 filter membranes is feasible and may prove a valid alternative resource. However, there are no data on virological validation, of either the individual fitting or the disinfection process and the number of times the face mask can safely be reused with new filter membranes and headbands.