Optical imaging is commonly used to investigate biological flows and cardiovascular disease using compliant silicone polydimethysiloxane (PDMS) Sylgard 184 geometries. However, selecting the working fluid with blood density and viscosity, and PDMS index of refraction (RI) for such experiments is challenging. Currently, water–glycerol is commonly used and sodium iodide (NaI) is often added to increase the index of refraction without changing fluid viscosity. But the resulting fluid density is well above blood. Moreover, NaI is expensive, has safety and material discoloration concerns, and has been reported to affect non-Newtonian fluid behavior. Here, we present a new blood-analog alternative based on urea. Urea is approximately 5–15 times less expensive than NaI, safe and easy to handle, optically clear, and causes no discoloration. Water–glycerol–urea solutions, unlike those with NaI, simultaneously matched the density and viscosity of blood and RI of PDMS. Water–xylitol and water–xylitol–urea solutions are also possible blood-analog solutions. 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. The results showed that the XG weight percent affected viscoelastic properties more than the weight percent of urea or NaI tested in this study. 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.Graphical abstract

中文翻译：

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具有 PDMS 折射率的密度和粘度匹配的牛顿和非牛顿血液模拟溶液

光学成像通常使用合规的有机硅聚二甲基硅氧烷 (PDMS) Sylgard 184 几何形状来研究生物流和心血管疾病。然而，为此类实验选择具有血液密度和粘度以及 PDMS 折射率 (RI) 的工作流体具有挑战性。目前，常用的是水-甘油，并且经常添加碘化钠（NaI）以增加折射率而不改变流体粘度。但由此产生的液体密度远高于血液。此外，NaI 价格昂贵，存在安全性和材料变色问题，并且据报道会影响非牛顿流体行为。在这里，我们提出了一种基于尿素的新型血液模拟替代品。尿素比 NaI 便宜大约 5-15 倍，安全且易于处理，光学透明，并且不会引起变色。与 NaI 溶液不同，水-甘油-尿素溶液同时匹配血液的密度和粘度以及 PDMS 的 RI。水-木糖醇和水-木糖醇-尿素溶液也是可能的血液模拟溶液。黄原胶 (XG)-水-甘油非牛顿溶液在此处使用的尿素和 NaI 的重量百分比（约 15-25%）范围内保持相似的粘弹性。结果表明，XG 重量百分比对粘弹性的影响大于本研究中测试的尿素或 NaI 的重量百分比。总的来说，我们证明尿素对于 PDMS 血液模拟实验很有用，也应该被视为一种廉价的添加剂，以及 NaI 的替代品。图形摘要