Enhancing detection accuracy via controlled release of 3D-printed microlattice nasopharyngeal swabs

Nasopharyngeal (NP) swabs are essential tools for collecting clinical specimens, particularly evident during the COVID-19 pandemic for SARS-CoV-2 virus and antibody detection. Current commercial NP swabs, however, often employ a diluted release (DR) method using elution buffers, which significantly lowers analyte concentration and impacts the accuracy of point-of-care tests (POCTs). Low analyte concentration leads to decreased sensitivity, resulting in inaccurate results such as false negatives and delayed positives. While improving detection methods can enhance sensitivity, this approach is often resource-intensive and yields limited improvements. This research focuses on addressing the sample release process to overcome the concentration limitations inherent in current methods. 3D printing technology offers a solution to potential supply shortages, as previously demonstrated with the creation of 3D-printed NP swabs with solid structures and micro-convex arrays, showing comparable sampling effectiveness to commercial swabs. These 3D-printed swabs offered the advantage of customizable size and shape. Further advancements incorporated microlattice structures to enhance sampling, providing benefits such as increased surface area, improved flexibility, and enhanced capillary action. However, these advantages alone do not definitively make 3D-printed swabs superior to commercial ones, especially as the supply chain for commercial swabs has improved. This research utilizes truss-based mechanical metamaterial concepts to design 3D-printed microlattice NP swabs that offer distinct advantages over current options.

The existing literature highlights the challenges associated with current nasopharyngeal swab technology. Studies such as Quesada-González and Merkoçi (2018) and Panpradist et al. (2014) discuss the limitations of current point-of-care diagnostic tools and the effect of sample transfer methods on test accuracy. Bruijns et al. (2018) showed that significant amounts of DNA remain in various swab types after sample collection. The limitations of POCTs and the need for improved sensitivity are also discussed in Okuda et al. (2013). Previous work on 3D-printed swabs (Williams et al., 2020; Arnold et al., 2020; Starosolski et al., 2020; Tay et al., 2020; Pettit et al., 2021; Grandjean Lapierre et al., 2021; Hartigan et al., 2022; Martinez et al., 2021; Singh et al., 2020; Ford et al., 2020) demonstrates the potential of 3D printing in addressing swab supply issues and enabling customization. Research exploring microlattice structures for improved sampling (Bennett et al., 2020; Oland et al., 2021; Tooker et al., 2021; Arjunan et al., 2021) indicates the potential benefits of this design approach. However, the current work focuses on a novel controlled release mechanism to address the issue of analyte dilution, a challenge not fully addressed in prior studies.

The study involved the design and fabrication of three types of 3D-printed open-cell microlattice NP swabs: Auxetic (A), Dodecahedron (D), and BCC (X). These were modeled using Rhinoceros software and printed using a high-resolution LCD 3D printer with a transparent tough ABS-like photosensitive resin. The printing parameters, including exposure time and layer thickness, were optimized to ensure high-quality prints. After printing, the samples were cleaned and dried. Mechanical characterization involved bending, tensile, and compression tests using a micro testing system to evaluate flexibility, tensile strength, and compressive strength. Sample release was characterized using two methods: diluted release (DR), involving manual agitation in an elution buffer, and controlled release (CR), which utilized centrifugal force to separate liquid from the swab. Food dye and honey solutions (mimicking mucus viscosities) were used as model samples to assess the release efficiency. UV-Vis spectroscopy was employed to measure the concentration of the released samples. Antibody detection experiments were performed using anti-SARS-CoV-2 antibody (IgG/IgM) rapid test kits and a SARS-CoV-2 IgG ELISA kit to evaluate the impact of the CR method on detection accuracy. The ELISA method involved standard procedures for capturing and detecting anti-SARS-CoV-2 IgG antibodies, followed by absorbance measurement to quantify the concentration. Statistical analysis was performed to ensure the reliability and robustness of the results.

The 3D-printed microlattice NP swabs demonstrated significantly improved performance compared to commercial flocked swabs. The microlattice swabs exhibited up to 11 times greater flexibility, enabling better nasal cavity conformity and potentially reducing patient discomfort. The controlled release (CR) method resulted in a significantly higher concentration of the released analyte, at least dozens to thousands of times greater than with diluted release (DR). The CR method achieved a recovery efficiency of approximately 100%, effectively maintaining the original analyte concentration. Release volume was customizable, reaching up to 2.3 times greater than that of commercial swabs. Using food dye and honey solutions as models, the microlattice swabs consistently showed superior release performance, particularly for higher-viscosity samples. The antibody detection experiments using rapid test kits and ELISA confirmed that the CR method significantly enhanced the detection sensitivity and accuracy. The microlattice swabs enabled the detection of antibodies even at low concentrations, where traditional swabs using DR failed to detect them.

The findings demonstrate the significant advantages of 3D-printed microlattice NP swabs with the controlled release method for clinical specimen detection. The increased flexibility, enhanced sample release, high recovery efficiency, and ability to quantify analyte levels directly address the limitations of current commercial swabs. The superior performance in detecting antibodies, even at low concentrations, highlights the potential for improving diagnostic accuracy and sensitivity. This technology has significant implications for point-of-care diagnostics, potentially reducing false negatives and enabling earlier diagnosis. The customizable design allows for tailoring the swabs to specific needs, including the ability to accommodate different sample volumes and viscosities. The quantitative aspect of analyte release is crucial for obtaining accurate information about analyte levels in patients.

This study presents a novel 3D-printed microlattice nasopharyngeal swab with a controlled release mechanism, offering superior performance over traditional swabs. The enhanced flexibility, high recovery efficiency, and ability to maintain high analyte concentration significantly improve the accuracy and sensitivity of clinical specimen detection. Future research can focus on optimizing the microlattice structures to further enhance performance and exploring applications beyond nasopharyngeal sampling. The potential for customization and the quantitative nature of the release method makes this technology a significant advancement in the field of biomedical diagnostics.

The study used food dye, honey, and IgG as model samples. Real-world clinical samples are more diverse and complex, so the results might not fully generalize to all specimen types. Further research is needed to validate the technology with a wider range of clinical samples and to evaluate its performance in diverse clinical settings. The study focused on a specific 3D printing technology and resin; other methods and materials could affect the results.