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.

This study evaluates hydrogel microparticle-based suspensions as blood-mimicking fluids for future in vitro applications. The impact of three artificial plasma phases on particle size, shape, rheological and mechanical properties was investigated.

Optical Coherence Tomography (OCT) is a standard imaging procedure in ophthalmology. OCT Angiography is a promising extension, allowing for fast and non-invasive imaging of the retinal vasculature analyzing multiple OCT scans at the same place. Local variance is examined and highlighted. Despite its introduction in the clinic, unanswered questions remain when it comes to signal generation. Multiphase fluids like intralipid, milk-water solutions and human blood cells were applied in phantom studies shedding light on some of the mechanisms. The use of hydrogel beads allows for the generation of alternative blood models for OCT and OCT Angiography. Beads were produced in Hannover, their size was measured and their long term stability was assessed. Then, beads were shipped to Karlsruhe, where OCT imaging resulted in first insights. The hydrogel acts as a diffusion barrier, which enables a clear distinction of bead and fluid when scattering particles were added. Further on, the scattering medium below the bead showed increased signal intensity. We conclude that the inside of the bead structure shows enhanced transmission compared to the plasma substitute with dissolved TiO2 surrounding it. Beads were found clumped and deformed after shipping, an issue to be addressed in further investigations. Nevertheless, hydrogel beads are promising as a blood model for OCT Angiography investigations, offering tunable optical parameters within the blood substitute solution.

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.

Blood exhibits complex flow behavior governed by red blood cell (RBC) deformation, aggregation, and confinement effects, which are difficult to reproduce in-vitro at single-cell level under confinement. Existing blood mimicking...

Graphical Rheological understanding of blood is relevant for the design of cardiovascular medical devices and implants. Erythrocytes are represented by hydrogel beads dispersed in a continuous glycerol phase. The model system is characterized by aims of optical and rheological characterization. The erythrocyte schematic has been taken from 1. The deformable nature of the hydrogel particles can be seen from the pictures taken during the squeezing experiment (see Fig. 4).