Particle image velocimetry (PIV) is an optical and contactless measurement method for analyzing fluid blood dynamics in cardiovascular research. The main challenge to visualization investigated in the current research was matching the channel material’s index of refraction (IOR) to that of the fluid. Silicone is typically used as a channel material for these applications, so optical matching cannot be proven. This review considers hydrogel as a new PIV channel material for IOR matching. The advantages of hydrogels are their optical and mechanical properties. Hydrogels swell more than 90 vol% when hydrated in an aqueous solution and have an elastic behavior. This paper aimed to review single, double, and triple networks and nanocomposite hydrogels with suitable optical and mechanical properties to be used as PIV channel material, with a focus on cardiovascular applications. The properties are summarized in seven hydrogel groups: PAMPS, PAA, PVA, PAAm, PEG and PEO, PSA, and PNIPA. The reliability of the optical properties is related to low IORs, which allow higher light transmission. On the other hand, elastic modulus, tensile/compressive stress, and nominal tensile/compressive strain are higher for multiple-cross-linked and nanocomposite hydrogels than single mono-cross-linked gels. This review describes methods for measuring optical and mechanical properties, e.g., refractometry and mechanical testing.

Understanding the tribological behavior of blood-lubricated interfaces is considered relevant for the design of heart pumps, heart valves or for the understanding of the blood flow in very narrow blood vessels. Tribological studies with real biological materials are challenging, e.g., due to their limited stability or potential risk of infections. To overcome these challenges, artificial materials are used in this study to mimic real blood and the biological interfaces. As for the lubricant, a hydrogel-based artificial blood with a glycerol-water solution, as a continuous phase, is used. Various compositions of artificial blood are investigated and compared with real plasma as well as platelet-rich plasma as lubricants. Soft biological interfaces are represented by a glass-ball-on-three-elastomeric pins setup. Results from tribological model system measurements on the different lubricants are shown in the form of Stribeck curves and possible lubricating mechanisms are discussed. Results from complementary shear rheological measurements of the blood fluids are shown and discussed.