An in vitro analysis of the effect of geometry-induced flows on endothelial cell behavior in 3D printed small-diameter blood vessels.

Clinical recovery from vascular diseases has increasingly become reliant upon the successful fabrication of artificial blood vessels (BVs) or vascular prostheses due to the shortage of autologous vessels and the high incidence of vessel graft diseases. Even though many attempts at the clinical implementation of large artificial BVs have been reported to be successful, the development of small-diameter BVs remains one of the significant challenges due to the limitation of micro-manufacturing capacity in complexity and reproducibility, as well as the development of thrombosis. The present study aims to develop 3D printed small-diameter artificial BVs that recapitulate the longitudinal geometric elements in the native BVs using biocompatible polylactic acid (PLA). As their intrinsic physical properties are crystallinity dependent, we used two PLA filaments with different crystallinity to investigate the suitability of their physical properties in the micro-manufacturing of BVs. To explore the mechanism of venous thrombosis, our study provided a preliminarily comparative analysis of the effect of geometry-induced flows on the behavior of human endothelial cells (ECs). Our results showed that the adhered healthy ECs in the 3D printed BV exhibited regulated patterns, such as elongated and aligned parallel to the flow direction, as well as geometry-induced EC response mechanisms that are associated with hemodynamic shear stresses. Furthermore, the computational fluid dynamics simulation results provided insightful information to predict velocity profile and wall shear stress distribution in the geometries of BVs in accordance with their spatiotemporally-dependent cell behaviors. Our study demonstrated that 3D printed small-diameter BVs could serve as suitable candidates for fundamental BV studies and hold great potential for clinical applications.

4D Printed Cardiac Construct with Aligned Myofibers and Adjustable Curvature for Myocardial Regeneration.

As an innovative additive manufacturing process, 4D printing can be utilized to generate predesigned, self-assembly structures which can actuate time-dependent, and dynamic shape-changes. Compared to other manufacturing techniques used for tissue engineering purposes, 4D printing has the advantage of being able to fabricate reprogrammable dynamic tissue constructs that can promote uniform cellular growth and distribution. For this study, a digital light processing (DLP)-based printing technique was developed to fabricate 4D near-infrared (NIR) light-sensitive cardiac constructs with highly aligned microstructure and adjustable curvature. As the curvature of the heart is varied across its surface, the 4D cardiac constructs can change their shape on-demand to mimic and recreate the curved topology of myocardial tissue for seamless integration. To mimic the aligned structure of the human myocardium and to achieve the 4D shape change, a NIR light-sensitive 4D ink material, consisting of a shape memory polymer and graphene, was created to fabricate microgroove arrays with different widths. The results of our study illustrate that our innovative NIR-responsive 4D constructs exhibit the capacity to actuate a dynamic and remotely controllable spatiotemporal transformation. Furthermore, the optimal microgroove width was discovered via culturing human induced pluripotent stem cell-derived cardiomyocytes and mesenchymal stem cells onto the constructs' surface and analyzing both their cellular morphology and alignment. The cell proliferation profiles and differentiation of tricultured human-induced pluripotent stem cell-derived cardiomyocytes, mesenchymal stem cells, and endothelial cells, on the printed constructs, were also studied using a Cell Counting Kit-8 and immunostaining. Our results demonstrate a uniform distribution of aligned cells and excellent myocardial maturation on our 4D curved cardiac constructs. This study not only provides an efficient method for manufacturing curved tissue architectures with uniform cell distributions, but also extends the potential applications of 4D printing for tissue regeneration.