FixTheMask offers designs for surgical mask sealers and braces that can be produced on 3D printers to improve the performance of surgical and other masks by preventing leakage around the sides.
What is particularly impressive here is that fixthemask apparently tested face masks (augmented by their mask sealers or mask braces) with TSI’s PortaCount Pro, which is normally used for respirators.[1] Not only was it possible to perform the fit test with face masks under these circumstances, the face masks (except apparently for a cloth one) passed the fit test required for N95 respirators. “The rating system goes from 0 to 200+, anything over 100 is a passing score for an N95 mask according to OSHA.” This suggests that a mask brace or mask sealer can get an ASTM Level 2 surgical mask to perform at close to the level of an N95 respirator for individual protection, or workplace protection where an actual respirator is not mandatory.
Also https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7179060/
[1] https://medium.com/@fixthemask/latest-testing-data-8a59dbb926a3