Microfluidic Devices With One-opening Chambers And Hydrophobic Valves For Sweat Collection And Analysis

Being noninvasive,sweat that contains various biomarkers starts to gain popularity for physiological health monitoring and disease diagnostics.However,the process of early sweat analysis in requires expensive equipment and trained professionals to collect and analyze the data.As an alternative,wearable microfluidic devices open opportunities to collect and analyze sweat in situ.Soft,skin-interface microfluidic platforms are capable of capturing,storing,and assessing sweat chemistry.However,for commonly used microfluidic channels that are hydrophobic,the sweat needs to overcome the positive capillary pressure to enter the microchannel for capture and collection.The sweat loss from the outlet of the microfluidic devices would often lead to the deviation of the measured concentration of the biomarker or electrolyte from the actual value.Here,we introduce the hydrophobic valves at the junction of the chamber and the microfluidic channel as a new chamber design to reduce sweat evaporation.The main work and results in this thesis include:1. The design of soft hydrophilic microfluidic device with hydrophobic valves for sweat collection.The hydrophilic microfluidic devices by exposed air plasma treatment with a negative capillary pressure to spontaneously wick the sweat into the channel.The hydrophobic valves at the junction of the chamber and the microfluidic channel as a new chamber design to reduce the unnecessary evaporation and contamination of the sweat in the collection chambers is vital for accurate sweat analysis.The small thickness of devices and low effective modulus of poly（dimethylsiloxane）（PDMS）avoids the delamination from the skin and damage upon mechanical deformations such as bending and twisting.2. Hydrophobic valves in hydrophilic microfluidic channels and working principle.The PDMS intrinsic hydrophobicity gradually recovers after the air plasma treatment.To address this challenge,subsequent low-energy polyvinylpyrrolidone（PVP）surface modification on the air plasma treatment PDMS was exploited.Because the advancing front of liquid in the hydrophilic microchannel is blocked by the hydrophobic valve,the fluid flows into the chambers,forms the initial meniscus,and completely fills the chambers along the initial meniscus.Fluid dynamic modeling and numerical simulations provide critical insights into the sweat sampling mechanism into the chambers.3. Chrono-Sampling and chemical analysis of the sweat.Human testing involved the evaluation of the skin-interfaced microfluidic device mounted on the forehead of the young adult volunteer during running exercises.Notably,the peak sweat rate from the measurement of the 1^st chamber corresponded to the initial stage of the exercise with the largest sweat rate.The average sweat rate per sweat gland during the entire period of the exercise was estimated to be 0.04μL/min.While the sweat p H from the lower back sequentially decreased,no substantial differences were observed in the sweat p H from the forehead and neck,providing critical insights into the underlying physiological variations.