On the Dynamic Contact Angle of Capillary-Driven Microflows in Open Channels.

The true value of the contact angle between a liquid and a solid is a thorny problem in capillary microfluidics. The Lucas-Washburn-Rideal (LWR) law assumes a constant contact angle during fluid penetration. However, recent experimental studies have shown lower liquid velocities than those predicted by the LWR equation, which are attributed to a velocity-dependent dynamic contact angle that is larger than its static value. Inspection of fluid penetration in closed channels has confirmed that a dynamic angle is needed in the LWR equation. In this work, the dynamic contact angle in an open-channel configuration is investigated using experimental data obtained with a range of liquids, aqueous and organic, and a PMMA substrate. We demonstrate that a dynamic contact angle must be used to explain the early stages of fluid penetration, i.e., at the start of the viscous regime, when flow velocities are sufficiently high. Moreover, the open-channel configuration, with its free surface, enhances the effect of the dynamic contact angle, making its inclusion even more important. We found that for the liquids in our study, the molecular-kinetic theory is the most accurate in predicting the effect of the dynamic contact angle on liquid penetration in open channels.

Capture of Group A Streptococcus by Open-Microfluidic CandyCollect Device in Pediatric Patients.

Importance: Obtaining high-quality samples to diagnose streptococcal pharyngitis in pediatric patients is challenging due to discomfort associated with traditional pharyngeal swabs. This may cause reluctance to go to the clinic, inaccurate diagnosis, or inappropriate treatment for children with sore throat. Objective: Determine the efficacy of using CandyCollect, a lollipop-inspired open-microfluidic pathogen collection device, to capture Group A Streptococcus (GAS) and compare user preference for CandyCollect, conventional pharyngeal swabs, or mouth swabs among children with pharyngitis and their caregivers. Design: Participants of this cohort study were recruited over a 7-month period in 2022 - 2023. Setting: This study was conducted at an ambulatory care clinic that serves pediatric patients in the Madison, Wisconsin, metropolitan area. Participants: Study participants were diagnosed with GAS pharyngitis using a traditional pharyngeal swab via rapid antigen detection test (RADT); those testing positive were approached or reached out to about participation in the study. A total of 74 caregiver/children dyads were contacted about the study: 23 declined to participate; 21 were not eligible; and 30 willing and eligible participants were admitted into the study. A caregiver provided verbal consent and parental permission, and all children provided verbal assent. Immediately after the standard of care visit in which the throat swab was obtained, a research nurse guided participants through collecting oral samples: CandyCollect device and mouth swab (ESwab TM ). CandyCollect and mouth swab samples were analyzed for GAS by quantitative polymerase chain reaction (qPCR) at the University of Washington. Exposure: Detection of salivary GAS using qPCR analysis of samples obtained from CandyCollect devices and mouth swabs. Main Outcomes and Measures: The proportion of pediatric patients with GAS pharyngitis, as determined by a positive pharyngeal swab tested via a RADT, who were also positive using a CandyCollect and mouth swab analyzed by qPCR. Results: All child participants (30/30) were positive for GAS by qPCR on both the mouth swab and CandyCollect. Caregivers ranked CandyCollect as a good sampling method overall (27/30), and all caregivers (30/30) would recommend the CandyCollect for children 5 years and older. Twenty-three of 30 children "really like" the taste and 24/30 would prefer to use the CandyCollect if a future test was needed. All caregivers (30/30) and most children (28/30) would be willing to use the CandyCollect device at home. Conclusion and relevance: All participants tested positive for GAS on all three collection methods (pharyngeal swab, mouth swab, and CandyCollect). While both caregivers and children like the CandyCollect device, some caregivers would prefer a shorter collection time. Future work includes additional studies with larger cohorts presenting with pharyngitis of unknown etiology and shortening collection time, while maintaining the attractive form of the device. Trial Registration: Registry name: ClinicalTrials.gov ClinicalTrials.gov Identifier: NCT05175196 Weblink: https://classic.clinicaltrials.gov/ct2/show/NCT05175196. Key Points: Question: In pediatric patients with Group A Streptococcus pharyngitis, how do test results and user experience compare across three sampling methods-CandyCollect devices, mouth swabs, and pharyngeal swabs?Findings: In this cohort study of 30 children, aged 5-14 years, saliva samples were collected with CandyCollect devices and mouth swabs and analyzed via qPCR. The results show CandyCollect, a pathogen collection tool preferred by children, had 100% concordance with the results from pharyngeal swabs positive with a rapid antigen detection test performed as part of their clinical care.Meaning: With further development and testing, the CandyCollect device may potentially become an alternative sampling tool for the diagnosis of streptococcal pharyngitis.

On the dynamic contact angle of capillary-driven microflows in open channels.

The true value of the contact angle between a liquid and a solid is a thorny problem in capillary microfluidics. The Lucas-Washburn-Rideal (LWR) law assumes a constant contact angle during fluid penetration. However, recent experimental studies have shown lower liquid velocities than predicted by the LWR equation, which are attributed to a velocity-dependent dynamic contact angle that is larger than its static value. Inspection of fluid penetration in closed channels has confirmed that a dynamic angle is needed in the LWR equation. In this work, the dynamic contact angle in an open channel configuration is investigated using experimental data obtained with a range of liquids, aqueous and organic, and a PMMA substrate. We demonstrate that a dynamic contact angle must be used to explain the early stages of fluid penetration, i.e., at the start of the viscous regime, when flow velocities are sufficiently high. Moreover, the open channel configuration, with its free surface, enhances the effect of the dynamic contact angle, making its inclusion even more important. We found that for the liquids in our study, the molecular-kinetic theory (MKT) is the most accurate in predicting the effect of the dynamic contact angle on liquid penetration in open channels.

At-Home Saliva Sampling in Healthy Adults Using CandyCollect, a Lollipop-Inspired Device.

Respiratory infections are common in children, and there is a need for user-friendly collection methods. Here, we performed the first human subjects study using the CandyCollect device, a lollipop-inspired saliva collection device .We showed that the CandyCollect device can be used to collect salivary bacteria from healthy adults using Streptococcus mutans and Staphylococcus aureus as proof-of-concept commensal bacteria. We enrolled healthy adults in a nationwide (USA) remote study in which participants were sent study packages containing CandyCollect devices and traditional commercially available oral swabs and spit tubes. Participants sampled themselves at home, completed usability and user preference surveys, and mailed the samples back to our laboratory for analysis by qPCR. Our results showed that for participants in which a given bacterium (S. mutans or S. aureus) was detected in one or both of the commercially available methods (oral swab and/or spit tubes), CandyCollect devices had a 100% concordance with the positive result (n = 14 participants). Furthermore, the CandyCollect device was ranked the highest preference sampling method among the three sampling methods by 26 participants surveyed (combining survey results across two enrollment groups). We also showed that the CandyCollect device has a shelf life of up to 1 year at room temperature, a storage period that is convenient for clinics or patients to keep the CandyCollect device and use it any time. Taken together, we have demonstrated that the CandyCollect is a user-friendly saliva collection tool that has the potential to be incorporated into diagnostic assays in clinic visits and telemedicine.

At-home saliva sampling in healthy adults using CandyCollect, a lollipop-inspired device.

Respiratory infections are common in children, and there is a need for user-friendly collection methods. Here, we performed the first human subjects study using the CandyCollect device, a lollipop inspired saliva collection device. 1 We showed the CandyCollect device can be used to collect salivary bacteria from healthy adults using Streptococcus mutans and Staphylococcus aureus as proof-of-concept commensal bacteria. We enrolled healthy adults in a nationwide (USA) remote study in which participants were sent study packages containing CandyCollect devices and traditional commercially available oral swabs and spit tubes. Participants sampled themselves at home, completed usability and user preference surveys, and mailed the samples back to our laboratory for analysis by qPCR. Our results showed that for participants in which a given bacterium ( S. mutans or S. aureus ) was detected in one or both of the commercially available methods (oral swab and/or spit tubes), CandyCollect devices had a 100% concordance with the positive result (n=14 participants). Furthermore, the CandyCollect device was ranked the highest preference sampling method among the three sampling methods by 26 participants surveyed (combining survey results across two enrollment groups). We also showed that the CandyCollect device has a shelf life of up to 1 year at room temperature, a storage period that is convenient for clinics or patients to keep the CandyCollect device and use it any time. Taken together, we have demonstrated that the CandyCollect is a user-friendly saliva collection tool that has the potential to be incorporated into diagnostic assays in clinic visits and telemedicine.

CandyCollect: at-home saliva sampling for capture of respiratory pathogens.

Streptococcus pyogenes is a major human-specific bacterial pathogen and a common cause of a wide range of symptoms from mild infection such as pharyngitis (commonly called strep throat) to life-threatening invasive infection and post-infectious sequelae. Traditional methods for diagnosis include collecting a sample using a pharyngeal swab, which can cause discomfort and even discourage adults and children from seeking proper testing and treatment in the clinic. Saliva samples are an alternative to pharyngeal swabs. To improve the testing experience for strep throat, we developed a novel lollipop-inspired sampling platform (called CandyCollect) to capture bacteria in saliva. The device can be used in clinics or in the home and shipped back to a lab for analysis, integrating with telemedicine. CandyCollect is designed to capture bacteria on an oxygen plasma treated polystyrene surface embedded with flavoring substances to enhance the experience for children and inform the required time to complete the sampling process. In addition, the open channel structure prevents the tongue from scraping and removing the captured bacteria. The flavoring substances did not affect bacterial capture and the device has a shelf life of at least 2 months (with experiments ongoing to extend the shelf life). We performed a usability study with 17 participants who provided feedback on the device design and the dissolving time of the candy. This technology and advanced processing techniques, including polymerase chain reaction (PCR), will enable user-friendly and effective diagnosis of streptococcal pharyngitis.