Capillary Flow Characterization and Application in Saliva Sampling

Abstract

The use of microfluidic channels is becoming increasingly prevalent in the biomedical field. Assuch, the characterization of capillary flow is vital to facilitate functional adaptations. The impact of progressive converging and diverging channels on open-channeled capillary flow is an area that lacks precise characterization. In this work, a theoretical model has been developed that predicts that convergent channels cause an increase and divergent channels cause a decrease in capillary flow velocity. Experimental validation of the model is presented in this work using an open-fluidic poly(methyl methacrylate) device with several liquids of varying viscosities and properties. Future work on this characterization will look at the behavior of immiscible plugs in dynamic open-microfluidic channels. Such manipulations in velocity have great potential in the application of capillary systems in biology and medicine. The implementation of open-microfluidic channels has been applied in our novel lollipop-based saliva collection tool, the CandyCollect. The CandyCollect is a device designed to function as an alternative method of sampling for streptococcal pharyngitis diagnosis. Streptococcal pharyngitis, commonly known as strep throat, is a disease prevalent in children that is caused by Streptococcus pyogenes. Left untreated, strep throat can spread throughout the body and cause permanent damage to vital organs (e.g., rheumatic heart disease and post-streptococcal glomerulonephritis). Current methods of diagnosis—rapid test, bacterial culture, and polymerase chain reaction (PCR)— require a pharyngeal swab, which can be an invasive and uncomfortable procedure that can discourage the pursuit of a diagnosis. The CandyCollect, modeled to function like a lollipop for the user, can overcome the deterrents in diagnosis. Featuring an open-microfluidic channel as the bacterial capture region, the device can concentrate the bacteria during the collection period and prevent bacteria loss from the device during sampling. The device also uses isomalt candy, which functions as a built-in timer to ensure the sampling timeframe is sufficient for sample collection. Following sample collection, the device is sent to a laboratory for quantitative PCR (qPCR) analysis, wherein the detection of S. pyogenes is indicative of strep throat. In this work, we demonstrate functionality of the device through in vitro experimentation. We show that bacteria accumulate on the plasma-treated device over time, isomalt and pooled saliva do not impact the capture of bacteria on the device, and the device has a shelf-life of at least two months. A protocol for the elution of the bacteria from the CandyCollect was optimized, using 5% ethanol in eSwab buffer. Thus far, the CandyCollect has been used in two human subject research studies. The first study (IRB-exempt protocol STUDY00012318) demonstrated that the candy-based timer mechanism can be used to set a minimum time frame for sampling based on the mass of isomalt applied to the device. The user feedback was favorable, with the majority of participants ranking the handling, appearance, taste and consumption positively. In second human research study (IRB-approved protocol STUDY00013842), the CandyCollect was consistently ranked higher than current saliva sampling methods—swab-based collection and spitting-based collection—in categories including best sampling, least invasive and most sanitary method for saliva collection. Samples from this study will be analyzed using qPCR to detect the commensal bacteria (bacteria that exists naturally in the microbiome), Streptococcus mutans and Staphylococcus aureus, to compare the efficacy of the CandyCollect to spitting-based collection and swab-based collection in healthy participants.