Development and Evaluation of PVA-H 3D Printed Blood Vessel Biomodels With Several Stiffness

       Biomodels of blood vessel are in high demand for the use of surgical trainings and assessment of medical devices. As a material for vascular models, poly (vinyl alcohol) hydrogel (PVA-H) is increasing attention since it has similar viscoelasticity to that of blood vessels, and its stiffness can be controlled by changing the concentration. Recently, as a new method for fabricating PVA-H blood vessel biomodels, we have developed a PVA-H 3D printer that can relatively control wall thickness of models. The current PVA-H 3D printer consists of a dispenser for injecting PVA solutions and a system for fabricating molds. Models are fabricated by repeating making the mold and injecting the solution, and gelation is performed in a freezer afterward. The PVA-H 3D printer has been fabricating models with homogeneous stiffness. However, since the stiffness of blood vessels varies from one part to another, reproducing this nonuniformity in biomodels may contribute to giving better realism to trainings and simulations. In this regard, the PVA-H 3D printer may be applied to reproduce such nonuniformity by applying its fabrication process. In order to make models with various stiffness, PVA solutions of various concentrations are necessary to be injected, and these hydrogels should be connected. Thus, the purpose of this study is to assess the performance of the PVA-H 3D printer when fabricating models composed of parts exhibiting different stiffness (multi-parts), layer-dependency and the mechanical characteristics of these models.

       In this study, multi-parts 3D printed PVA-H specimens were fabricated, and tensile tests and swelling observations were performed. Multi-parts specimens were fabricated by injecting 10 wt% PVA, which is expected to have lower longitudinal elastic modulus, before and after injecting conventional PVA solutions. For the use of reference, several specimens were also fabricated by injecting a single solution for each (single-part).

       Firstly, tensile tests were performed by using a tensile testing machine in order to assess the longitudinal elastic modulus and the layer-dependency. The specimens were shaped following the Japanese Industrial Standards (JIS) dumbbell No.8. The tests were performed in two directions, parallel and perpendicular to the layering direction, at 20 mm/min until the engineering strain reached 0.5. Secondly, swelling observations were performed in order to assess the compliance. Specimens were fabricated into tubular shape (length: 50 mm), and their inner and outer diameter were 4 mm and 8 mm, respectively. The Specimens were set to a system that captures the deformation with a video camera and the pressure with a pressure sensor during swelling and deformed by air. Based on the diameter and the pressure, the local compliance was calculated at several points in each specimen.

       The overall stiffness of PVA-H multi-parts specimens changed compared to single-part specimens, and their longitudinal elastic modulus followed the theoretical equation for obtaining longitudinal elastic modulus of composite materials. The layer-dependency was not observed. By comparing the compliance between multi-parts specimens and single-part specimens, the compliance became higher only in areas where the PVA-H concentration was 10 wt%.

       It is revealed that PVA-H multi-parts models can be fabricated while maintaining the mechanical properties of each part. These results indicate that the PVA-H 3D printer is capable of fabricating vascular PVA-H multi-parts models. Fabricating such biomodels has a possibility to give better realism to surgical trainings or assessments by reproducing nonuniformity of actual blood vessels.