Toward organ printing: Design characteristics, virtual modelling and physical prototyping vascular segments of kidney arterial tree This paper highlights the main issues regarding design characteristics, virtual modeling and physical prototyping of vascular kidney arterial segments

Organ printing is defined as the layer by layer additive biofabrication of three-dimensional (3D) tissue and organ constructs using tissue spheroids as building blocks. Ultimately, successful bioprinting of human organ constructs is dependent on a 'built in' vascular tree to perfuse and maintain the viability of the organ constructs. Thus, the design of the vascular tree is a critically important step in practical implementation of organ printing technology. Bioprinting a vascular tree requires detailed knowledge of the morphometrical, morphological and biomechanical characteristics of the sequentially branched segments of the natural vascular tree as well as insight on post-printing tissue compaction and remodelling. Toward accomplishing this goal, we characterised the morphometrical, morphological and biomechanical characteristics of the initial segments of the natural kidney arterial vascular tree of the porcine kidney. Computer simulation was used to model compaction of tissue engineered tubular vascular segments with different wall thicknesses virtually biofabricated from closely packed and fused uniformly sized vascular tissue spheroids. The number of concentric layers of tissue spheroids required to bioprint tubular vascular segments with desirable wall thickness and diameter was theoretically estimated. Our results demonstrate that vascular segment compaction correlates well with reported experimental data. Finally, physical prototyping of linear and branched tubular constructs using silicon droplets as physical analogues of tissue spheroids was performed. Thus, virtual and physical prototyping provide important insights into the design parameters and demonstrate the principal feasibility of bioprinting a branched vascular tree using vascular tissue spheroids.