![]() ![]() NaCl has also been used to increase the index of refraction of water-glycerol, but this increases the solution viscosity above that of blood ( Shuib et al. However, NaI is expensive, corrosive to equipment, and can cause discoloration of material upon direct contact ( Yousif et al. To increase the RI of a 60/40 water glycerol solution, sodium iodide (NaI) is often added because it increases index but does not change the kinematic viscosity of the fluid ( Long et al. A water-glycerol mixture with the same RI of PDMS has a viscosity about 2–3 times higher than blood. However, a 60/40 water-glycerol mixture yields an index of refraction of approximately 1.39, well below that of PDMS at 1.414 ( Yousif et al. A 60/40 (by volume) water-glycerol mixture is one of the most widely used blood analogue solutions for use with PDMS. While dynamic scaling may be used in cases where the working fluid does not match that of blood, this is not always possible and can add complexity to the experiment and the calculation of properly scaled spatiotemporal gradients. The working fluid must also simultaneously match the fluid properties of blood (ρ = 1060 kg/m 3, μ = 2.9–4.37 mPa-s) ( Mayer 1964 Yazdi et al. For complex geometries, even small differences in RI can result in significant optical distortion ( Patil and Liburdy 2012). Imaging requires the fluid to be optically clear and have the same index of refraction (RI) as the material of the geometry section. (2018).įor optical experiments using PDMS models, selecting the proper working fluid is critical, but difficult even for Newtonian fluids ( Yazdi et al. Detailed evaluation and review of in vitro experimental techniques, including test section manufacturing, are presented by Wright et al. Although 3D printing and plastic materials are also used, they are limited to rigid test sections. For such experiments, the test geometries are often made of silicone polydimethysiloxane (PDMS) Sylgard 184 because the versatility in the curing process allows for specific shapes and compliances to be represented ( Wright et al. Optical in vitro imaging measurement techniques, such as particle image velocimetry (PIV), are used because they provide well-controlled flow fields with high spatiotemporal resolution. In vitro flow experiments are used to evaluate a range of vascular diseases. Overall, we demonstrate urea is useful for PDMS blood analog experiments and should also be considered as an inexpensive additive, and an alternative to NaI. The results showed that the XG weight percent affected viscoelastic properties more than the weight percent of urea or NaI tested in this study. Xanthan gum (XG)-water-glycerol non-Newtonian solutions maintained similar viscoelastic properties throughout the range of weight percent (about 15–25%) of urea and NaI used here. Water-xylitol and water-xylitol-urea solutions are also possible blood analog solutions. Water-glycerol-urea solutions, unlike those with NaI, simultaneously matched the density and viscosity of blood and RI of PDMS. Urea is approximately five to fifteen times less expensive than NaI, safe and easy to handle, optically clear, and causes no discoloration. Here, we present a new blood analog alternative based on urea. Moreover, NaI is expensive, has safety and material discoloration concerns, and has been reported to affect non-Newtonian fluid behavior. But the resulting fluid density is well above blood. Currently, water-glycerol is commonly used and sodium iodide (NaI) often added to increase the index of refraction without changing fluid viscosity. However, selecting the working fluid with blood density and viscosity, and PDMS index of refraction (RI) for such experiments is challenging. Optical imaging is commonly used to investigate biological flows and cardiovascular disease using compliant silicone polydimethysiloxane (PDMS) Sylgard 184 geometries. ![]()
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