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Hemodynamic experiments are crucial for the understanding of how chronic cardiovascular diseases develop, such as aneurysms—a silent often deadly condition [1]. Particle image velocimetry (PIV) is the most common technique used in in vitro studies to obtain hemodynamic. However, this technique is heavily limited by the materials used for the creation of anatomical “phantoms” that needs to be optically transparent and for the formulation of blood-mimicking fluids (BMF’s). For laser-PIV the main challenge is to match the refractive index of the phantom with that of the BMF. The most common approach for producing flow phantoms is the negative casting in transparent silicone elastomers [2]. It has been determined already that the refractive index of silicone-based materials (~1.41) can be matched with water-glycerol BMF formulations that can be considered as synthetic blood with similar properties to human blood like viscosity and density [3]. Nonetheless, the casting with silicone is a laborious time-consuming process that is not capable of reproducing fine patient-specific anatomical features [4]. Therefore, simplified average-anatomy models and approximate geometries have been mostly used. In contrast, 3D printing enables the fabrication of patient-specific models in a relatively broad range of materials [4]. However, the inherently inhomogeneous surface finish of 3D-printed parts makes it difficult to match the refractive index of the phantom (~1.47–1.51 at 532 nm [5]) with common BMF’s [6]. In this study, we investigated the BMF formulations that can match the refractive index of commercial SLA 3d-printable materials [4]–[6]. We selected resins yielding elastomeric 3D printed models that are as close as possible to the silicone-based standards. There are few studies in the literature to measure the refractive index of 3D printing materials and they are focused on hard resins which cannot mimic the realistic behavior of vascular tissue. The interaction of the flexible 3D-printed models with water/glycerol as a base solution, third-component solutions like water/glycerol/sodium iodide and water/glycerol/Urea and water/glycerol/Ammonium thiocyanate was studied. We also designed four-component solutions to achieve higher refractive index by more stable solutions. We develop the first comprehensive calibration to the effect of each component on the refractive index. The 3D printed rectangular strips were immersed in solutions and the transmission were measured via U-Vis spectroscopy quantitatively and with photography to show the potential of the solution qualitatively. The transparency improved with three and four-component solution by 90%. The optical and mechanical properties of each one of the 3D-printed materials was assessed. Viscosity, density, and refractive index were measured for each solution. We report the discovery of what seems to be the best BMFs based on matching the properties to human blood and being capable to match the refractive index of soft SLA 3D printing materials to enable their used in laser-PIV studies for hemodynamic studies. A flow phantom based on this study have been made to study the blood hemodynamics in popliteal aneurysms. The patient-specific 3D-printed phantom was printed in flexible SLA 3D printing materials which has enough optical and mechanical properties for PIV study.

References:

[1] K. M. Saqr et al., “What does computational fluid dynamics tell us about intracranial aneurysms? A meta-analysis and critical review,” J. Cereb. Blood Flow Metab., vol. 40, no. 5, pp. 1021–1039, 2020, doi: 10.1177/0271678X19854640.

[2] S. G. Yazdi, P. H. Geoghegan, P. D. Docherty, M. Jermy, and A. Khanafer, “A Review of Arterial Phantom Fabrication Methods for Flow Measurement Using PIV Techniques,” Ann. Biomed. Eng., vol. 46, no. 11, pp. 1697–1721, 2018, doi: 10.1007/s10439-018-2085-8.

[3] M. Y. Yousif, D. W. Holdsworth, and T. L. Poepping, “A blood-mimicking fluid for particle image velocimetry with silicone vascular models,” Exp. Fluids, vol. 50, no. 3, pp. 769–774, 2011, doi: 10.1007/s00348-010-0958-1.

[4] K. I. Aycock, P. Hariharan, and B. A. Craven, “Particle image velocimetry measurements in an anatomical vascular model fabricated using inkjet 3D printing,” Exp. Fluids, vol. 58, no. 11, pp. 1–8, 2017, doi: 10.1007/s00348-017-2403-1.

[5] M. S. Song, H. Y. Choi, J. H. Seong, and E. S. Kim, “Matching-index-of-refraction of transparent 3D printing models for flow visualization,” Nucl. Eng. Des., vol. 284, pp. 185–191, 2015, doi: 10.1016/j.nucengdes.2014.12.019.

[6] W. H. Ho, I. J. Tshimanga, M. N. Ngoepe, M. C. Jermy, and P. H. Geoghegan, “Evaluation of a Desktop 3D Printed Rigid Refractive-Indexed-Matched Flow Phantom for PIV Measurements on Cerebral Aneurysms,” Cardiovasc. Eng. Technol., vol. 11, no. 1, pp. 14–23, 2020, doi: 10.1007/s13239-019-00444-z.