A 3D-Printed Nasopharyngeal Swab Prototype with a Helical Tip Design: A Feasibility Study with Numerical/Experimental Correlation

The clinical reliability of swabs is affected by their ability to collect and elute biological samples for further detection. Since elution is particularly critical for swab functionality, the goal of this work was to develop a nasopharyngeal swab prototype that could potentially facilitate the release of biological specimens through controlled elastic deformation. To this end, a helical swab-head geometry was designed and 3D-printed by means of stereolithography (SLA). A dual post-curing process combining UV and thermal treatment was employed to maximize the mechanical stiffness of the resin—up to about 750 MPa. Microtomography of the 3D-printed prototypes demonstrated the accuracy of SLA printing, with only 0.12% closed porosity due to printing defects. The mechanical deformation of the prototype under compression was then investigated through numerical modeling and experimental analysis. The results of Finite Element (FE) simulations revealed stress localization in the upper coils, with global mechanical integrity. Experimental compression tests validated the predicted deformation behavior, as supported by video tracking and displacement analysis at multiple nodes, showing good agreement between numerical and experimental displacement. Furthermore, preliminary functional tests with P. aeruginosa and S. aureus, both in saline solution and artificial mucus, demonstrated that the swab-tip prototype per se, without any coating or any applied compression, could perform comparably to commercial cotton and flocked swabs. About a 2-log reduction in bacterial load was detected for all swabs compared to the inoculum when used in saline solution, while a bacterial load roughly matching the inoculum was found when the swabs were used in artificial mucus. Overall, these findings demonstrate the feasibility and the potential of the designed swab prototypes.