22 Sep Novel density- and viscosity-matched blood analog for use with PDMS Sylgard
Silicone Sylgard 184 (PDMS) is commonly used when manufacturing geometries for bioflow studies due to its optical transparency and compliant nature. However, for use with particle image velocimetry (PIV), a suitable blood analog working fluid is needed which both matches the physical properties of blood and maintains the same index of refraction (RI) as PDMS. The often used 60/40 mixture (by volume) of water-glycerol yields the properties of blood, but the RI is too low for PIV studies. To increase the RI, most often sodium iodide (NaI) is added to the water-glycerol solution. Unfortunately, NaI is challenging to work with. It is expensive, corrosive, can cause discoloration of almost all materials it comes in contact with, and is difficult to store long term. Further, NaI increases the density of the solution significantly such that a water-glycerol-NaI solution can match the viscosity of blood and RI of PDMS, but cannot simultaneously match the density of blood.
In this work we propose a novel blood analog working fluid additive, urea, which when combined with water-glycerol solutions is able to simultaneously match the density and viscosity of blood as well as the RI of PDMS. Compared to NaI, urea is 5-15x cheaper, safer, easier to handle and use, and does not cause discoloration of material. We also demonstrate using water-xylitol-urea as an additional possible blood analog. We tested the novel additive, urea, using both Newtonian and non-Newtonian fluids, where Xanthan-Gum was added to the working fluid.
Overall, the results demonstrate urea is a useful and cheaper alternative to NaI as a blood analog additive. This novel blood analog is particularly important in cases where sensitive test environments exist, such as when flow loops need to be tested in a magnetic resonance imaging (MRI) machine.