Parametric nasopharyngeal swab for sampling COVID-19 and other respiratory viruses: Open source design, SLA 3-D printing and UV curing system

Abstract

Access to nasopharyngeal swabs for sampling remain a bottleneck in some regions for COVID-19 testing. This study develops a distributed manufacturing solution using only an open source manufacturing tool chain consisting of two types of open source 3-D printing and batch UV curing, and provides a parametric fully free design of a nasopharyngeal swab. The swab was designed using parametric OpenSCAD in two components (a head with engineered break point and various handles), which has several advantages: i) minimizing print time on relatively slow SLA printers, ii) enabling the use of smaller print volume open source SLA printers, iii) reducing the amount of relatively expensive UV resin, and iv) enabling production of handle on more accessible material extrusion 3-D printers. A modular open source UV LED box was designed, fabricated for $45 and tested for batch curing. Swabs can be fabricated for $0.06-$0.12/swab. The results of the mechanical validation tests showed that the swabs could withstand greater forces than would be expected in normal clinical use. The swabs were also able to absorb a significant amounts of synthetic mucus materials and passed abrasion and handling tests. The results show the open source swab are promising candidates for clinical trials.

Keywords: 3-D printing; Additive manufacturing; COVID-19; Medical hardware; Nasal swab; Nasopharyngeal swab; Open hardware; RepRap; SLA; UV curing.

Graphical abstract

Fig. 1

Top view of rounded top of nasal swab in yellow with hemisphere tip of adjustable radius, protuberance, and roundness with purple nobs surrounding in offset sequence.

Fig. 2

Side view of head of tip of open source swab with top in yellow, tip and nobs (arms) in purple, tapered sections in red, and neck in blue.

Fig. 3

OpenSCAD rendering of A) full side view of swab; B) press-fit handle with customizable text; and C) swab and handle assembled.

Fig. 4

OpenSCAD rendering of A) top (lengthwise) view of clamping section of tong handle; B) tong handle showing swab placement in relaxed state for easy removal (side view); and C) swab and handle assembled in front view profile with customizable writing.

Fig. 5

Detail of breakaway hole with neck of swab in blue, base in green, and handle in orange.

Fig. 6

Assembled parametric swab and handle.

Fig. 7

The UV curing box is first laid out in order to determine terminal block placement.

Fig. 8

Wires directly soldered to transfer power from one board to the next.

Fig. 9

Clipped LED leads placed into screw terminals. The other ends will get clamped in adjacent connector.

Fig. 10

Wires connecting two terminal blocks on a corner. The wires are made longer than necessary as they double as the hinge for the lid.

Fig. 11

Two cables tapped into a terminal set for power flow from the supply.

Fig. 12

The exterior of the completed open source UV curing box.

Fig. 13

Inside of the powered-on curing box. Note the wires being used as hinges and the corner and edge brackets are fully extended so the top can correctly align when it is placed.

Fig. 14

Inserting swabs into UV curing box.

Fig. 15

Recalibration Screen.

Fig. 16

Prusa Print Bed.

Fig. 17

Ready to Print.

Fig. 18

Final Prints.

Fig. 19

Closeup of swab tip.

Fig. 20

(A) Screen grab of Lulzbot Cura version 3.6.8 of the handle in layer view mode with coloration set to line-type. (B) batches of 45 handles are shown for the tong and (C) press-fit design, respectively.

Fig. 21

As printed version of handle on a Lulzbot Taz 6 print bed.

Fig. 22

Swab inserted in tong handle.

Fig. 23

Assembling swab with gloved hands.

Fig. 24

Using the open source nasopharyngeal swab and press-fit handle.

Fig. 25

Mechanical testing of swabs with an Instron 4206.

Fig. 26

Maximum tensile load at break for open source swabs as a function of UV curing time.

Fig. 27

Representative results of break point evaluation.

Fig. 28

Neck bending test.

Fig. 29

Open source 3-D printed nasal swab tip being tested for robustness to repeated insertions into and removal from a tortuous canal.