In Vitro Nasal Tissue Model for the Validation of Nasopharyngeal and Midturbinate Swabs for SARS-CoV-2 Testing

Abstract

Large-scale population testing is a key tool to mitigate the spread of respiratory pathogens, such as the current COVID-19 pandemic, where swabs are used to collect samples in the upper airways (e.g., nasopharyngeal and midturbinate nasal cavities) for diagnostics. However, the high volume of supplies required to achieve large-scale population testing has posed unprecedented challenges for swab manufacturing and distribution, resulting in a global shortage that has heavily impacted testing capacity worldwide and prompted the development of new swabs suitable for large-scale production. Newly designed swabs require rigorous preclinical and clinical validation studies that are costly and time-consuming (i.e., months to years long); reducing the risks associated with swab validation is therefore paramount for their rapid deployment. To address these shortages, we developed a 3D-printed tissue model that mimics the nasopharyngeal and midturbinate nasal cavities, and we validated its use as a new tool to rapidly test swab performance. In addition to the nasal architecture, the tissue model mimics the soft nasal tissue with a silk-based sponge lining, and the physiological nasal fluid with asymptomatic and symptomatic viscosities of synthetic mucus. We performed several assays comparing standard flocked and injection-molded swabs. We quantified the swab pickup and release and determined the effect of viral load and mucus viscosity on swab efficacy by spiking the synthetic mucus with heat-inactivated SARS-CoV-2 virus. By molecular assay, we found that injected molded swabs performed similarly or superiorly in comparison to standard flocked swabs, and we underscored a viscosity-dependent difference in cycle threshold values between the asymptomatic and symptomatic mucuses for both swabs. To conclude, we developed an in vitro nasal tissue model that corroborated previous swab performance data from clinical studies; this model will provide to researchers a clinically relevant, reproducible, safe, and cost-effective validation tool for the rapid development of newly designed swabs.

Underscoring the effect of swab type, workflow, and positive sample order on swab pooling for COVID-19 surveillance testing

“…Swab release was quantified indirectly by using FITC labeled microparticles, as surrogate for cellular material, as previously reported 6 . The soft tissue portion of the model was saturated with the fluorescently labeled microparticles and was swabbed according to the procedure described above.…”

“…Previous studies have investigated uptake by dipping swabs into a vial of water or saline, which is not an accurate representation of clinical sample collection 9 – 11 . In our previous report, we demonstrated the relevancy and functionality of an in vitro nasal tissue model 6 , 7 that allows replication of the clinical swabbing workflow with high fidelity, while being accessible to researchers, safe, reproducible, and time- and cost-effective. The precursor to the silk-glycerol sponge was a cellulose sponge that required large amounts of PEO to fully saturate it.…”

“…Based on our previously developed 3D nasal cavity tissue model 6 , 7 , we utilized a bench top validation system to study different pooling workflows (Fig. 5 ) and relative swab performance (Fig.…”

“…We begin by describing two distinct workflows: dip and discard (DDW) and combine and cap (CCW). All studies were conducted using a previously developed 6 , 7 bench top in vitro experimental model of the nasal cavity comprised of silicone tubing lined with a silk-glycerol sponge. The sponge mimics the soft tissue of the nasal cavity, and the geometry of this model enables clinically relevant swabbing in a preclinical setting.…”

Recent Options and Techniques to Assess Improved Bioavailability: In Vitro and Ex Vivo Methods

“…To mimic the soft human tissue of the nasal cavity, they used aqueous silk sponges; thus, it does not require any cellular material, and the physiological nasal fluid was replaced with synthetic mucus. This model may provide a reproducible, safe, and cost-effective tool for the development of newly designed devices [85]. In order to obtain further information about biological aspects such as permeation, mucoadhesion, and ciliary clearance, in vitro anatomical models can be used in combination with both primary and immortalized cell cultures as well [86].…”