We’ve been cautious and cautious about selling 3D-printed COVID security tools right here at 3DPrint.com. We talked a few common precept of first doing no hurt and likewise mentioned security suggestions for 3D-printed medical gadgets. Particularly, we addressed security considerations associated to 3D printing masks and offered some suggestions.
It was notable that, on this present disaster, the U.S. Meals and Drug Administration (FDA) and different authorities relaxed their current requirements for face shields however didn’t accomplish that for respirators. A respirator is a close-to-the-skin machine that’s worn over one’s mouth for hours per day and might impede respiratory or might result in overseas particles within the wearer’s lungs. Even at their most creative and artistic, well being authorities wouldn’t budge from preserving it a Class II medical machine that must be made in an excellent manufacturing apply surroundings and topic to strict FDA regulation.
Preliminary findings level to the regulator’s findings being borne out by analysis. A paper by a workforce at Virginia Polytechnic Institute and State College (Virginia Tech) factors to a determined lack of effectiveness on the a part of 3D-printed respirators. We should level out that the paper itself is within the preprint stage. Preprint signifies that it has not but been peer reviewed. Which means that we at the moment are forming our opinion a few hasty engineering effort to make life-saving gadgets by way of a paper that itself has been offered to us earlier (and one would anticipate extra error-prone) than regular.
Simply to be clear, we have fun everybody’s engineering and maker efforts to make COVID gadgets of all types. We predict that is actually one of many brightest and greatest moments in our business’s historical past. We’ve an vital function to play in making spare components, new options, and unavailable gadgets on this present disaster. Moreover, it’s changing into clear to us and lots of extra folks that 3D printing has an actual function to play in lots of provide chains and in future crises, no matter they might be. We at the moment are way more related than at first of the yr to any additional breakdown of the very cloth of the worldwide provide chain or as some type of magical duck tape answer to a scarcity.
This expectation and curiosity is, in fact, a double-edged sword and we might squander it by over-claiming and underdelivering. Or we might meet the challenges of the longer term with forthrightness and honesty. Sure, we’re an attention-grabbing shape-making know-how. This doesn’t imply that every one of our shapes are practical for the entire purposes now, in all supplies.
The paper is by Bezek, L.B.; Pan, J.; Harb, C.; Zawaski, C.E.; Molla, B.; Kubalak, J.R.; Marr, L.C.; Williams, C.B. and is titled “Particle Transmission by way of Respirators Fabricated with Fused Filament Fabrication and Powder Mattress Fusion Additive Manufacturing“. The abstract is as follows (the textual content is quoted however formatted by me for readability):
“Outcomes from this examine present that respirators printed utilizing desktop/industrial-scale fused filament fabrication [FFF] processes and industrial-scale powder mattress fusion [PBF] processes have inadequate filtration effectivity on the dimension of the SARS-CoV-2 virus, even whereas assuming an ideal seal between the respirator and the person’s face.
Virtually all printed respirators offered <60% filtration effectivity on the 100-300 nm particle vary.
Just one respirator, printed on an industrial-scale fused filament fabrication system offered >90% effectivity as-printed.
Publish-processing procedures together with cleansing, sealing surfaces, and reinforcing the filter cap seal usually improved efficiency, however no respirator sustained the filtration effectivity of an N95 respirator, which filters 95% of SARS-CoV-2 virus particles.
As a substitute, the printed respirators confirmed comparable efficiency to numerous material masks.
Whereas continued optimization of printing course of parameters and design tolerances might be carried out to instantly print respirators that present the requisite 95% filtration effectivity, AM processes aren’t sufficiently dependable for widespread distribution and native manufacturing of N95-type respiratory safety with out commensurate high quality assurance processes in place.
Sure design/printer/materials combos might present enough safety for particular customers, however the respirators shouldn’t be trusted with out quantitative filtration effectivity testing. It’s at present not suggested to anticipate printed respirators originating from distributed designs to copy efficiency throughout totally different printers and supplies.”
Usually, plenty of the conclusions that the paper has made are what we’ve got beforehand identified and what many within the business had been saying, as properly. It appears that evidently, as soon as once more, we’re shadowboxing overinflated claims that the media (and a few of us) have made.
The paper factors out that
“One concern concerning the efficacy of utilizing AM to supply direct replacements for N95 respirators is the intrinsic porosity in FFF and PBF-produced components, which may have an effect on filtration effectivity, accuracy, and reliability of the printed respirators. In FFF processes, porosity may result from adjoining layers not absolutely fusing, gaps left from altering route and stopping/beginning soften extrusion, and/or gaps left from adjoining extruded paths failing to fuse collectively”
“Such inherent, process-induced defects have been proven to trigger as much as 32% porosity in FFF components, with 200-800 Mu diameter pores , which might render them ineffective in defending in opposition to zero.three mu virus particles.”
“Equally, components produced through PBF may be as much as 30% porous  as a result of inadequate supply of power, recoating defects, and/or the usage of closely recycled powder.”
One answer to mitigate porosity in printed polymer components is to seal them in a post-processing step.
“One other anticipated problem in the usage of AM to instantly fabricate PPE by way of shared digital designs is the inherent variability between AM machines, supplies, and construct parameters, which may have an effect on the mechanical properties of the printed supplies and the accuracy of the printed geometries.”
That remaining challenge can be a possible limitation to testing how efficient these masks are, since particular person machine settings, supplies, materials dealing with, toolpaths and native variables might have interfered with the check components themselves. The paper goes on to have a look at the components the place the masks might fail by way of insufficiently overlaying the face or by way of gaps.
The masks chosen had been the Montana masks by Make the Masks, the Factoria masks, and the Stopgap Surgical Face Masks. They printed these masks on a Sinterstation (polymer powder mattress fusion), Fortus 400mc (industrial FFF) and an Afinia (desktop FDM). We’ve made some progress for the reason that venerable Sinterstation and porosity has been decreased in present technology sintering machines with higher software program and processing in order that we might anticipate much less porosity than with a machine that was launched in 1998. On the one hand, it’s wonderful that these machines final so lengthy, however it’s maybe barely unfair to make use of a 22-year-old 3D printer as the commercial sintering system for this vital check.
The paper states that, “the PBF fashions had been de-powdered and bead blasted to take away adhered powder and enhance floor end,” however, crucially, it’s unclear if “rinse components with water to take away remaining media and dry components utilizing compressed air” was accomplished as per the overall instruction hooked up to the file. Additionally, they state that the powder used was “Nylon-12 (Factoria: 100% recycled; Montana/Stopgap: 50% recycled / 50% virgin).” It’s unclear whose powder it was. Now, its not obvious why they might use totally different mixes between virgin and recycled powder for various masks however a 100 % recycled materials will not be actually one thing I’d advocate. I feel it’s additionally unfair to match a 100 % recycled masks to something.
I even have considerations concerning the filament supplies printed. I additionally thought that ULTEM 9085 printed at 350°C? I’m confused concerning the ABS print that has 15-20% infill. To me, for a day-to-day use half, I’d use a a lot larger infill proportion of 30 % at the least. I additionally don’t perceive why the PLA half has 15 % infill both. I couldn’t discover the machine settings or the title of the filament provider both. There might be plenty of variability of their nozzle temperature as per indicated and precise additionally. Everyone knows that we are able to get plenty of layer adhesion variations in prints from pace, materials, temperature. So that is one caveat. I’d actually like for the Cura profile and the machine settings to be included in this sort of analysis. If we’re going to be testing components then we must always know the way they had been made.
This isn’t a gripe particular to this paper nonetheless; no papers have this. I personally can’t actually get ABS to work in any respect under a 100°C mattress temperature and most advocate 110°C, in order that appears low, whereas 260°C sounds prefer it might be fairly too fume-y. I’d by no means advocate that you simply print ABS above 250°C and, more often than not, I’d anticipate the precise temperature to be far decrease than that, a lot decrease than 260°C anyway. Additionally, every check half was solely printed as soon as (aside from the stopgap that they tried in two orientations). That to me is placing fairly plenty of inventory within the five-year-old Afinia’s accuracy and I’d have a lot fairly seen a variety of components printed and examined.
The workforce then reveals us that that they had seen defects within the prints.
“(a) The Stopgap respirator in ABS oriented with the filter cap face down on the construct aircraft has a number of mislaid layers; (b) The Stopgap respirator in ABS in an alternate orientation additionally suffers from periodic sparsity; (c) The Stopgap respirator in PLA is visibly skinny throughout most surfaces; (d) The Stopgap respirator in ULTEM reveals porosity on the floor parallel to the filter.”
“Determine 4c reveals the Stopgap respirator fabricated with PLA held as much as a light-weight to allow statement of a number of areas of skinny materials alongside the shell (as in Determine 4a and b), alongside the seal to the face, and on the floor flush with the filter cap. Determine 4d shows the Stopgap respirator fabricated with ULTEM held as much as a light-weight. Macroscale pores throughout your complete floor flush on the construct aircraft are noticed regardless of this half being printed in 100% infill on an industrial-scale FFF system,” the authors write. The workforce does say that the Stopgap respirator was made for powder mattress fusion ,in order that it was not meant to be printed with FFF/FDM. They go on to check the Stopgap FFF/FDM prints and I feel that that is fairly unfair.
I’ve an actual challenge with the authors altering the roll of filament for construct orientation prints “a” and “b” and never mentioning that it is a totally different materials. Even when it was from the identical vendor and the dealing with was the identical, then the totally different colorants imply that there’s a totally different optimum print temperature there. It’s unusual to me to each change print orientation and materials after which evaluate these prints. Additionally, the authors say that that is an adhesion challenge, however is it? Is it digging by the nozzle? The “c” half is a superb instance why you shouldn’t have letters in your half. The hatched sample on the “d” print comprised of ULTEM may be very unusual. Is that the Sparse Double Density infill sample? Did it not print as a result of they didn’t assist the half properly?
The workforce went on to check the outcomes of the totally different filter designs:
“The particle analyzer merely counts the frequency of detected nanoparticles; it doesn’t distinguish between nanoparticles ensuing from the generated aerosol and residual nanoparticles ensuing from stray particulates shed from the shell,” was a problem that they recognized.
They go on to deal with the masks, saying that the “FFF respirators had been rinsed totally with faucet water and dried with compressed air. Since water might trigger aggregation amongst dry powder, the cleansing step for PBF respirators concerned further compressed air adopted by the appliance of two coats of acrylic paint to type a sealant.”
I’m confused about this since I do know that water can have an affect on porous sintered components long-term, however am undecided why the researchers didn’t simply wash them in water, which might be superb short-term. Additionally, portray it adjustments the half and makes it much less versatile. I don’t perceive the “aggregation amongst dry powder” half in any respect actually and am undecided why they’d want to color the mannequin. I particularly fear that the coats of paint will impact how the totally different components of the masks match collectively. I could have learn it improper however why then within the desk above do they are saying that they rinse and dry the PBF components? Additionally I’m fairly certain that the PLA fashions had been made extra brittle by the water, however maybe that’s a limitation of the masks that’s good to incorporate.
The paper goes on to indicate that, “not one of the printed respirators offered the requisite 95% filtration effectivity.”
“Montana respirator outcomes (Determine 5a) present filtration effectivity constantly underneath 60% for the ABS, PLA, and nylon supplies, which is much from the baseline efficiency of the ULPA filter medium. The ULTEM variant of the Montana respirator couldn’t be examined as printed as a result of the filter cap was too unfastened to adequately safe the filter.”
The workforce makes the next dedication:
“The Factoria respirator outcomes are offered in Determine 5b. The PLA and ABS respirators filter out extra particles than within the Montana respirator design, however each nonetheless solely shield in opposition to ~75% of particles. The ULTEM Factoria respirator offers the very best noticed efficiency, with a filtration effectivity between 90-95%, relying on particle diameter; nonetheless, it falls barely lower than the examined ULPA filter (99% effectivity). Much like the Montana respirator outcomes, the PBF-printed respirator presents the bottom filtration effectivity (~45%).”
“Montana and Factoria respirators are practically equivalent in shell design, it’s anticipated that the distinction in filter cap design is the trigger for the constantly worse efficiency of the Montana respirator in comparison with the Factoria respirator. The press-fit cap of the Montana respirator might have allowed particles across the filter (which correlates to the loose-fitting filter cap printed in ULTEM), whereas the bigger cap of the Factoria respirator utterly encloses the filter.”
One other factor that I don’t get is that this: “It’s noticed in Determine 6a that cleansing the ABS Montana respirator will increase the filtration effectivity measurement by ~20%, however the ABS Factoria measurement decreases in effectivity by ~10%. The ABS Stopgap effectivity measurements considerably enhance, with each print orientations providing comparable efficiency as soon as cleaned. In Determine 6b, it’s seen that the ULTEM Factoria respirator decreases by ~15% effectivity following cleansing.”
I’m fairly stunned that there could be such an enormous distinction in filtration effectivity simply from cleansing the components? To me, this factors to the truth that the testing equipment is selecting up unfastened powder and particles on the masks themselves from earlier than, or that they’re created or launched by way of cleansing. However, I don’t know sufficient concerning the filtration aspect of issues to know.
The workforce concedes, “These outcomes spotlight the inherent variability in outcomes because of the testing technique and testing situations, which is why it was vital to make use of the identical respirators for repeat exams. The testing surroundings was saved as near the identical situations every time, but the Factoria respirators by some means declined in filtration effectivity. It’s believed coupling of the failure modes recognized in Part 1.2 might be contributing to the erratic developments.”
They go on to look deeper, “Utility of the epoxy sealant to the shell will increase effectivity to peak at ~75%. This means that the porosity of the PLA materials drops filtration effectivity by ~20%.” And “Residual powders from printing, post-process, or dealing with are prone to blame for the poor efficiency of the respirators as-printed. This additionally corroborates the explanation why the as-printed nylon Montana and Factoria respirators had such low filtration effectivity. Whereas testing some intermediate modifications had been forgone, it’s evident that the dominant failure mode is the filter cap/shell interface.”
Their conclusions are the next:
“As printed, a lot of the respirators carried out poorly, with virtually all offering lower than 60% filtration effectivity (considerably under the requisite 95% effectivity of a N95 respirator). This result’s particularly discouraging when contemplating that the testing was accomplished with the approximation of an ideal seal between the respirator and person’s face (a standard failure mode for normal N95 textile respirators, and certain a major failure mode for the inflexible printed polymers). When printed in ULTEM on an industrial-scale FFF system, the Factoria respirator offered the very best filtration effectivity of these evaluated, constantly exceeding 90% effectivity for all particle sizes.”
Additionally they say that, “For instance, whereas the Factoria respirator in ULTEM reached >90% filtration effectivity within the as-printed state, its measured effectivity was decreased to ~80% following cleansing. No examined design with modifications was in a position to constantly attain 95% filtration effectivity, though the nylon Stopgap respirator with modifications was in a position to filter ~85% of particles on the dimension of 300 nm.”
“The outcomes from this examine don’t utterly low cost AM from being acceptable for making an efficient N95 respirator,” the authors write. “The ULTEM Factoria’s efficiency means that (i) top quality, repeatable printing know-how with (ii) correct course of settings, and (iii) tolerancing of the filter cap/shell interface that’s aligned with a selected machine/materials mixture might present an efficient answer.”
Additional on they, say, “Within the case of the Montana and Stopgap respirators, the as-printed efficiency falls under that of many easy textile supplies. The as-printed Factoria respirators and post-process modified Stopgap respirators present equal safety to those textile supplies and surgical masks, with the ULTEM Factoria and modified PBF Stopgap respirators offering barely enhanced efficiency to those supplies.” This was a consequence that many people would even have been pleased with, I consider.
Additionally, “The modified PBF Stopgap respirators can carry out higher than the surgical masks, high-threaded cotton, and N95 respirator from the examine by Konda . This examine reveals AM respirators are able to attaining competitively excessive filtration effectivity on par with non-medical use masks solely when assuming an ideal seal to the face.” It is a superb consequence nonetheless and one which we’d be very pleased with. However, because the paper rightfully states, this good seal is illusory and might be not the case for these comparatively inflexible components. The shortcoming to make an excellent seal, particularly when in comparison with a home-sewn masks has all the time to me been the Achilles heel of 3D-printed respirators.
On the entire, it is rather good that this sort of analysis is being accomplished. I’m a little bit confused by among the printing and parameters concerned. I’d have favored to have seen extra consistency there. However meeting and print-related points in experiments solely trigger me to contemplate how such variability precludes us from making respirators. On the entire, we are able to conclude that it will likely be troublesome to make a respirator that works properly with 3D printing. This doesn’t imply that we ought to be dissuaded from attempting to enhance these designs however fairly that we must always welcome scientific rigor and evaluation to our endeavors.
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