A new in vitro pre-clinical method for testing SARS-CoV-2 nasopharyngeal swabs

The SARS-CoV-2 pandemic underscored the critical role of nasopharyngeal swabbing in virus detection and containment. The urgency for mass production of swabs highlighted the necessity to evaluate their efficiency against the global shortage of medical supplies. Traditional pre-clinical swab testing methods often overlook the complexities of the nasopharyngeal anatomy and mucus properties. This study introduces an innovative in vitro pre-clinical model using a 3D-printed nasopharyngeal cavity lined with a mucus-mimicking SISMA hydrogel, to generate a novel assessment protocol for nasopharyngeal swab efficiency. Reconstructing nasopharyngeal anatomy from CT images, the model used flexible and rigid resins to simulate soft tissue and bone properties. Our evaluation compared the sample collection and release performance of experimental Heicon-type injection-molded swabs and conventional nylon flocked swabs. The Heicon swabs exhibited superior SISMA release efficiency, compared to the standard tubular model. Both swab types demonstrated lower cycle threshold (Ct) values in the tubular model, indicative of higher viral load retrievals. RT-qPCR results confirmed these differences and validated the hydrogel's suitability as a mucosa equivalent. The findings support using our nasopharyngeal model, which better simulates clinical conditions, potentially improving swab design and the reliability of viral detection assays.