Experimental Assessment of Microfluidic Device Performance: Exploring Hydraulic Resistance Across Materials and Geometries for Hemorheology Research

Abstract

This project aimed to develop an experimental setup for evaluating the hydraulic resistance and compliance of various microfluidic devices, constructed from different materials (polydimethylsiloxane (PDMS) and Norland Optical Adhesive (NOA)), featuring diverse geometries (tapered-parallel network, hexagonal networks, and retina network), and handling different fluids (water, glycerol, and blood) to optimize microfluidic chip designs for facilitating hemorheology research. The research comprises three main objectives: (1) characterizing the mechanical properties of PDMS and NOA, (2) quantifying compliance under flow rate conditions in microfluidic networks, and (3) analyzing the pressure-flow rate relationship to estimate hydraulic resistance in different geometries. To achieve these objectives, three experimental projects have been performed. The first project investigates the mechanical and hydraulic properties of tapered-parallel networks fabricated with PDMS and NOA. Results revealed that NOA exhibited a rougher surface, less deformation under pressure, increased hydrophobicity post-plasma treatment, and has a tensile strength 800 times higher compared to PDMS. These mechanical insights offer valuable guidance for material selection to enhance device performance tailored to specific applications. Compliance was computed by measuring the characteristic time of tapered-parallel networks in both NOA and PDMS devices. The analysis demonstrated that NOA microfluidic devices exhibited lower compliance compared to PDMS devices, suggesting potential for improved consistency in microfluidic research. Lastly, the pressure-controlled setup was employed to quantify experimental hydraulic resistance. For tapered-parallel networks, PDMS devices showed higher percentage error in hydraulic resistance due to increased channel deformation and compliance. iv The second project evaluates the hydraulic resistance in hexagonal networks under variable red blood cell (RBC) rigidity. An increase of RBC rigidity is associated with an increase in RBC circularity and decrease in deformation. Therefore, the hydraulic resistance will also increase. The results highlight the nuanced interplay between cellular properties and microfluidic resistance, providing a deeper understanding crucial for optimizing microfluidic device performance in hemorheology research. The third project is collaborative research on the retina network to observe the effect of different fluid viscosities (glycerol and blood) on the hydraulic resistance. In the retina network, resistance increased linearly with glycerol concentration which is typical for Newtonian fluids. In contrast, for blood, the experimental resistance is higher than theoretical values, likely due to uneven distribution of the cells and cell deformability, further highlighting the complex nature of blood flow rate. Overall, the outcomes enhance understanding of microvascular behavior and facilitate the development of efficient microfluidic devices with applications in biomedical engineering and healthcare.