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Due to the current COVID-19 pandemic, the world is experiencing a severe shortage of clinical supplies, as manufacturers struggle to meet demands.1 2 A decrease in the supply chain for diagnostic tests has led to increased interest in nasopharyngeal swabs produced by additive manufacturing methods, such as 3-dimensional (3-D) printing.3
To encourage innovation in this area, the Food and Drug Administration (FDA), USA, recently held a virtual town hall meeting regarding 3D printed nasopharyngeal swabs and has called for open sourcing of design blueprints through the National Institute of Health’s 3D Print Exchange (https://3dprint.nih.gov/).4 Callahan et al 5 recently published the design and clinical results for their 3D printed nasopharyngeal swabs. Although their results are excellent, a downside is that the stereolithography (SLA) printers and materials required to print their swab’s intricate tips are expensive (around US$3500 for SLA printer and US$250/kg for surgical grade resin)6 and difficult to source. Also, due to the complexity of the design, these swabs can be slower to print, requiring several printers for mass production. For countries with less manufacturing prowess and resources, this might not be possible.
How can 3-D printers be used to produce cost-effective nasopharyngeal swabs?
Fused deposition modelling (FDM) printers are the cheaper, more widely available 3-D printers, owned by most hobbyists. They can easily be purchased from an online vendor, such as Amazon.com, for less than US$500. In addition, polylactic acid (PLA) plastic filament is an FDA approved biocompatible, cheap (around US$25/kg) material, made from renewable resources such as sugarcane or tapioca roots.6 We sought to produce 3D printed swabs using PLA filaments, with the same biomaterial properties as a commercial swab. Due to the properties of FDM printing, reproducing the intricate lattice design used to create the tip on the resin swabs produced by the SLA printers is not possible. The Centers for Disease Control and Prevention (CDC) recommend that synthetic materials, such as polyester and nylon, are used on nasopharyngeal swabs’ tips,7 which is what is currently used on the widely distributed flocked nasopharyngeal swabs. Flocking is a manufacturing process, in which small fibres of a synthetic material are electrostatically deposited onto an adhesive-coated surface. To create a polyester tipped nasopharyngeal swabs, without the need for adhesives or a flocking machine, mini blunt-ended hooks were printed at the swabs’ tips to secure polyester threads. Initially, the polyester tips were wrapped manually around the PLA swabs’ tips. This was both time consuming and inconsistent, as the swab’s diameter and length varied, depending on the person performing the polyester wrapping. To ensure ease of application and consistency in the polyester tip diameter and length, 3D printed polyester tip applicators were created, allowing the swab to be assembled in under 10 s. The polyester tip applicator functions as both a gauge for the tip diameter (3.5 mm) and an assembly tool. Thin pieces of polyester filaments are placed in the applicator and the PLA swab’s tip is inserted and rotated, as you would use a pencil sharpener (figure 1). With assistance from a few volunteers, we were able to produce 2000 swabs a day using these simple tools, packaging them with viral transport media produced using the CDC protocol,8 after sterilising them using low-temperature plasma.
What are the benefits?
Three-dimensional printing offers several advantages, including rapid development and customisation, that is just not possible with subtractive traditional manufacturing methods.3 For example, a need arose at our hospital for paediatric swabs, with smaller diameters and shorter lengths (figure 2). We were able to instantaneously produce these, with minimal changes to our current manufacturing system. In addition, we were also able to reduce wastage by adapting our production rate according to clinical demands. Comfort with this technology at our hospital enabled us to adapt this technology to meet all other production needs, including using 3D printers to produce racks for the viral transport media tubes.
What are the possible harms?
There are several limitations to this technology. The production time for a single item can be long, depending on its complexity and size. The finish on 3D printers is also rougher than the finish on products produced by subtractive methods, such as laser cutting and milling. For large-scale production, traditional manufacturing methods, once established, are also more cost effective.9
What is the evidence so far?
Preliminary testing at our hospital, on 44 patients with COVID-19, demonstrated 91% positive agreement (0.81 Cohen’s kappa coefficient) with the commercially available swab. We provide a blueprint of our design for the swab, and polyester tip applicator at https://www.thingiverse.com/thing:4373981. During testing, no technical issues were encountered, such as unexpected breakage of the swabs’ shafts. Most patients described the swabs as more uncomfortable compared with the flocked swab but tolerable and none of the patients suffered significant nasopharyngeal trauma due to the swab. Similarly, Ryan et al 10 reported favourable testing with their rayon tipped swabs. Although Callahan et al’s5 study did not use synthetic fibres on their tips, their results demonstrated that 3D printed swabs were non-inferior to commercial swabs.
What can we expect in the future?
Historically, turbulent periods, such as the current COVID-19 pandemic, are often associated with advances in science, technology and medicine. Although 3D printing technologies are not new to medicine,9 they have become more widely adopted by clinicians recently to produce supplies that have been encountered shortages, such as personal protective equipment and ventilator splitters. We expect this trend to continue after the pandemic, as more clinicians are becoming comfortable with this technology and its applications.
The authors would like to acknowledge the assistance of Jaber Al-Ahmad Hospital team of volunteers, including the team working in the 3D printing lab, the wards, the Viral Transport Media team and the logistics team.
Contributors All the authors have contributed substantially to the planning, conducting and reporting of the submitted work.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval Ethical approval has been obtained for all clinical studies reported in this manuscript.
Provenance and peer review Not commissioned; externally peer reviewed.
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