Abstract: The 2019 novel coronavirus outbreak has had an accelerated growth rate throughout the world. In the same rapid manner, the maker community has been working extremely hard in trying to create masks, face-shields, ventilator attachments, and many other 3-D printable equipment parts as fast as possible. The challenges that are a result of this are the lack of protocols for different materials, and the ineffective design of said equipment without the help or guidance from a trained medical professional. In this report, there is a compendium on what the disease/virus is, what the boundary conditions for its life are-i.e., what it takes to eradicate it, and how to properly handle 3-D printed masks depending on their materials.
First off, the 2019 novel coronavirus is a virus . The exact name of the virus is Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The disease it causes is the coronavirus disease (COVID-19). The virus replicates itself by attacking healthy cells on the body and makes its way to the respiratory system which leads to lung inflammation and in more severe cases pneumonia or death. There are many ways currently, and more to come, to combat the virus. The following forms may prove beneficial when disinfecting equipment: Heat-thermal inactivation-disinfection , ultraviolet ray inactivation-disinfection , alcohol-based sanitizers , and soluble antiseptic-disinfecting agents. However, material deformation, degradation, and other forms of structural/compositional decay may result from an incorrect coupling of cleaning treatment regarding material properties. Another important note is the logarithmic reduction that is resultant from the different forms of cleansing. Logarithmic reduction, in simple terms, is how much smaller the amount of a substance is found. It follows that the number (2log, 3log… etc.) is a multiple of ten in reduction.
The current research [5-8] as of April 2020 shows that heat treatment can be used to deactivate strains of the viruses (Murine Coronavirus, SARS-CoV) as well as other viruses with similar properties. The research shows that while the virus is suspended in a test tube, high temperatures for extended periods of time are capable of deactivating the virus. This form of treatment may result in the deformation of the materials that it is applied to such as low temperature polymers or filters. Along with deformations to tubing that needs to be properly fitted in order to mitigate air leakage into a patient’s breathing system. The following temperatures can be used with their relevant exposure time; Provided by Kampf, et al.
Ultraviolet Irradiation Treatment
Sterilization through ultraviolet irradiation shows promise in being able to deactivate the virus without an aggressive approach to the material properties of the equipment needing to be sanitized [9-10]. Polymers still degrade under high energy irradiation from ultraviolet light but this form of degradation is focused more on the elasticity, maximum tensile strengths, and overall toughness of the polymers. The deformations might not be significant enough to render the equipment useless and offers a relatively rapid form of decontamination at 1.7 minute exposure times. The experiments done by Hamzavi, et al result in a 3log reduction in SARS-CoV leading to a 99.9% decontamination with decreased strength to elastic bands that hold up the masks. The breaking strength of the elastic bands were lowered by 20-51%. Further experimentation must be done in order to determine the use of this method with 3-D printed structural parts of ventilators and other such devices that have any form of loading applied. The main concern with using ultraviolet irradiation for sterilization is the manufacturing of low-cost yet highly efficient UV bulbs and its respective equipment for operation during the pandemic. In order for hospitals and other medical institutions to get a quick return of investment on the UV cleaning equipment, it must be altered to fit a system that requires hundreds of masks to be cleaned daily per machine. More masks being cleaned means less need to keep overdemanding the short supply of masks that there are currently in the market.
Prototype in development by Daavlin
The method that may not be as effective as heat or ultraviolet irradiation is using an alcohol-based sanitizer for sterilizing medical equipment. The main concern for this method is that the use of sanitizer is a limited option due to the low supply of sanitizers. The equipment afterward would need to dry or be wiped down in order to return to its intended function. Another shortfall of this method is that the possibility of contraction for medical workers is increased since the infected equipment needs to be handled more in order to be wiped down. Even with all of the setbacks for this method, using alcohol-based agents does have high rates of inactivation for SARS-CoV. The following agents can be used with their relevant exposure time to inactivate SARS-CoV; Provided by H. Fathizadeh, et al. It can be seen in the case of ethanol and propanol the reduction of viral infectivity decreases as their purity percentage increases.
A similar method to alcohol-based sanitizers is a soap anti-septic/disinfecting agent. By dissolving the lipid layer of the virus, soap accomplishes two functions. It deactivates the virus so that it can no longer be harmful on the equipment or surface it’s located and it allows for the simple removal of the virus from the porous surface that it is occupying. Anti-septic agents differ from disinfecting agents in that they can be harmful to human contact, therefore it is impediment to take proper precautions in order to not come in contact with the infected equipment or the cleaning agents used, as they can lead to cracking of the skin’s surface where the virus would have an easier way of infiltrating the human body. In a test by Delanno et al , The MHV virus was reduced considerably to the point where all of the following chemicals at a 30 second exposure time can be said to be effective.
The Medical Industry
The medical industry can stand to benefit from further testing of COVID-19 and its specific boundary conditions, instead of using the similarities between SARS-CoV-2 and other viruses to deduce what can be used to combat it. The medical industry has been benefiting greatly from the maker’s movement in the 3-D printing of masks, face-shields, and other medical equipment from individuals or companies who are focused on being of assistance as much as possible. There are however many individuals who do not have the proper guidance from medical personnel to create or design the equipment that they have been uploading for others to make. Several factors to take into account when 3-D printing or fabricating masks are properties of their effective material, the possibility for air leakage, the correct protocol for disposal/reuse of the equipment, and whether or not the design is approved for medical use by the FDA or certified medical professionals.
FDA approved mask: https://3dprint.nih.gov/discover/3dpx-013429
The most common materials found for 3-D printing is Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS), Nylon, and Thermoplastic Polyurethane (TPU). They each vary in significant material properties and because of that, must each be handled in a different manner according to their structure or function. Heat has the potential to deform PLA, ABS, TPU considerably, but not Nylon for instance. This is due to Nylon’s higher crystallization and melting temperatures. TPU has the option flex and mold to a face's surface shape in order to negate air leakage but PLA and ABS are too stiff to do so. Nylon has the option to flex if the internal structure (infill) is correct; Concentric infill or Cross infill allows for flexibility within 3-D prints while maintaining strength and durability. The following tables are the commonly found material properties, along with a correlation of effective ways to combat the disease based on assumptions made about the material properties. The criteria for the utility of the different methods are the following: glass transition temperatures must stay over heat treatment temperatures, Ultraviolet Irradiation must not render the material unusable due to material strength degradation, alcohol sanitizer must not cause crazing or stiffening, water molecules in soap must not degrade polymer bonds.
Experiments must still be conducted to accurately determine the best material and method of decontamination for the specific equipment used. However, through a careful analysis, the best material for 3-D printing facemasks appears to be TPU due to its high elasticity and viability of being cleaned with the different methods available. PLA should be used on a disposable basis and due to its deterioration from biodegradability must not be washed. ABS and Nylon present the next best options to TPU but further testing should be done for ABS to determine its viability after ultraviolet irradiation.
FDA approved files can be found at this link:
FDA frequently asked questions about 3-D printing for coronavirus purposes:
CDC on facemasks
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 Hamzavi Iltefat H., et al. “Ultraviolet germicidal irradiation: possible method for respirator disinfection to facilitate reuse during COVID-19 pandemic”. Journal of the American Academy of Dermatology, Elsevier, 1 April 2020, https://www.sciencedirect.com/science/article/pii/S0190962220305089
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