CFD based analysis of 3D printed nasopharyngeal swabs for COVID-19 diagnostics.

Additive manufacturing of nasopharyngeal (NP) swabs using 3D printing technology presents a viable alternative to address the immediate shortage problem of standard flock-headed swabs for rapid COVID-19 testing. Recently, several geometrical designs have been proposed for 3D printed NP swabs and their clinical trials are already underway. During clinical testing of the NP swabs, one of the key criteria to compare the efficacy of 3D printed swabs with traditional swabs is the collection efficiency. In this study, we report a numerical framework to investigate the collection efficiency of swabs utilizing the computational fluid dynamics (CFD) approach. Three-dimensional computational domain comprising of NP swab dipped in the liquid has been considered in this study to mimic the dip test procedure. The volume of fluid (VOF) method has been employed to track the liquid-air interface as the NP swab is pulled out of the liquid. The governing equations of the multiphase model have been solved utilizing finite-volume-based ANSYS Fluent software by imposing appropriate boundary conditions. Taguchi's based design of experiment analysis has also been conducted to evaluate the influence of geometric design parameters on the collection efficiency of NP swabs. The developed model has been validated by comparing the numerically predicted collection efficiency of different 3D printed NP swabs with the experimental findings. Numerical predictions of the CFD model are in good agreement with the experimental results. It has been found that there prevails huge variability in the collection efficiency of the 3D printed designs of NP swabs available in the literature, ranging from 2 µl to 120 µl. Furthermore, even the smallest alteration in the geometric design parameter of the 3D printed NP swab results in significant changes in the amount of fluid captured. The proposed framework would assist in quantifying the collection efficiency of the 3D printed designs of NP swabs, rapidly and at a low cost. Moreover, we demonstrate that the developed framework can be extended to optimize the designs of 3D printed swabs to drastically improve the performances of the existing designs and achieve comparable efficacy to that of conventionally manufactured swabs.

使用3D打印技术增材制造鼻咽（NP）拭子为解决用于快速新冠病毒检测的标准植绒头拭子的即时短缺问题提供了一种可行的替代方案。最近，已经提出了几种用于3D打印NP拭子的几何设计，并且它们的临床试验已经在进行中。在NP拭子的临床试验期间，比较3D打印拭子与传统拭子功效的关键标准之一是采集效率。在这项研究中，我们报告了一个利用计算流体动力学（CFD）方法研究拭子采集效率的数值框架。 本研究考虑了一个由浸入液体中的NP拭子组成的三维计算域，以模拟浸渍测试过程。当NP拭子从液体中拔出时，采用流体体积（VOF）方法来追踪液 - 气界面。通过施加适当的边界条件，利用基于有限体积的ANSYS Fluent软件求解了多相模型的控制方程。还进行了基于田口方法的实验设计分析，以评估几何设计参数对NP拭子采集效率的影响。通过将不同3D打印NP拭子的数值预测采集效率与实验结果进行比较，对所开发的模型进行了验证。 CFD模型的数值预测与实验结果吻合良好。研究发现，文献中现有的3D打印NP拭子设计的采集效率存在巨大差异，范围从2微升至120微升。此外，即使3D打印NP拭子的几何设计参数有最微小的改变，也会导致所采集的液体量发生显著变化。 所提出的框架将有助于快速且低成本地量化3D打印NP拭子设计的采集效率。此外，我们证明所开发的框架可以扩展以优化3D打印拭子的设计，从而大幅提高现有设计的性能，并实现与传统制造拭子相当的功效。