Authors: Eguiluz, A., Sanchez-Herencia, A.J.
Tailoring Through Colloidal Processing Group
Instituto de Cerámica y Vidrio(CSIC), Madrid, Spain
Manufacture of breathing machines and face protecting shields by 3D printing is appearing in media press as a method to relief the stress that healthcare resources are suffering by the high number of contagions of COVID-19. Here it is presented the technology behind the Fused Filament Fabrication to understand why it is used in fighting the pandemic.
The pandemic COVID-19 has managed to keep the entire world on the edge of its medical capabilities. Most countries are implementing safety measures like mobility restrictions or totally lockouts for the whole nation. The point in this is an attempt to break the fast increase of infected people. In many countries, included Spain, this situation has caught unaware to the healthcare systems, who have suffered the lack of the necessary equipment to combat the critical situation that we are living.
In some cases COVID-19 patients require respirator machines, which are not available. In other cases, the healthcare workers do not have the individual protection equipment necessary to lower the risk of contracting the virus when attending to patients. Parts to assembly these equipments are usually fabricated by the technique of injection moulding, where a melted plastic is injected into a mould and cooled until the plastic solidifies and hardens, so the piece keeps the shape of the mould. This is the most extended shaping method for quick fabrication of pieces of plastic. But adaptation of the production lines, specially the fabrication of moulds, is a process that delays and takes a time which now is not available. It is under this emergency where the 3D printing community is developing the potential of the most disseminated Additive Manufacturing technique, the Fused Filament Fabrication or FFF. But, what is 3D printing and how it can tackle the necessities of parts for breathing machines or protection equipments?
Firstly, it is necessary to clarify that most of the news citing 3D printing, are referring to the technique known as Fused Filament Fabrication (FFF) or Fused Deposition Modelling (FDM). As any other Additive Manufacturing technique, the FFF creates a physical object from a digital model (usually a CAD representation) which is sliced in layers at consecutive height levels. A computerized interface drives a machine to lay down the successive slices of material, following the profiles defined by CAD model. There are many different types of additive manufacturing (or 3D Printing) techniques which are classified by the technology and material used in the process of fabrication.
Figure 1. A) Controlling software of the FFF Printer; B) Experimental printer of laboratory; C) Scheme of the FFF printing device
The Fused Filament Fabrication (FFF) is based in the deposition of fused material extruded through a heated nozzle. The process requires of a thermoplastic material like polylactic acid (PLA), polycaprolactone (PCL), polyethylene terephthalate-glycol modified (PTEG) or acrylonitrile butadiene styrene (ABS) that, in form of filament, feed a mobile head with the heated nozzle that lay out the viscous plastic melt onto a bed (usually warmed) and create the shape of the piece. The computer interface controls the bed position and temperature, the head position and height as well as the nozzle temperature, which depends on the type of filament used (PETG 220-250 °C; ABS 210-250 °C; PLA 180-230 °C; PCL 50-60°C). This technology does not require of high energetic sources nor heavy machinery, nor toxic materials, which makes FFF a very versatile technique and a perfect process to novel users, reasons why is the most disseminated technology (Figure 1) in our society. 3D scanners, design tools software and internet apps allow the creation of CAD files (with extensions STL, OBJ, 3DS, etc.) with the digital information of the pieces to be fabricated by non-expert users.
The extensive use of the FFF equipment in houses, laboratories and crafts, the economic access to filament and the easy distribution of the files with the shape information (extensions STL, OBJ, 3DS, etc…) have been the weapons used by the 3D printing community to help during the pandemic crisis of COVID-19. Several Spanish consortia composed of medical doctors, engineers and scientists have fabricated innovative breathing machines with parts and connections designed by CAD to be fabricated by FFF. For these parts with complex shapes and under cyclic stresses, the materials have to be tough (ABS or PC), the equipment of high performance and the operator expert. Although this is not the more extended case of equipment, the adaptability of the technique has been critical to address the quick fabrication of the designed parts.
Other goal of the community has been the fast response to the lack of individual protection for the healthcare workers. In this case, from novel users to big companies have printed face shields to help to dodge this problem. In this case the large number of pieces demanded and the lower of the mechanical requirements have enabled the participation of many anonymous individuals as well as private and public institutions (like CSIC), universities (URJC, UC3M, UPM, etc…) or 3D printing platforms (FAB3D, Aditimat-CM, etc…). In this case the most employed material has been PLA, which has a lower melting temperature and provides a certain plasticity to the frames, making possible a better adjustment to the head (figure 2).
Figure 2. A) First layer of shield frame support; B and C) Frames finished by FFF (Courtesy of Guillermo Frías); D) Assembled in use by healthcare personnel at Hospital La Paz, Madrid.