Fully Biological Bioprinted Blood Vessel Substitutes

Abstract

Cardiovascular disease is a leading cause of death and often requires vascular reconstruction. There is considerable clinical need for alternatives to the autologous vein and artery tissues used for vascular reconstructive surgeries, lower limb bypass, arteriovenous shunts and repair of congenital defects to the pulmonary outflow tract. Engineering new tissues, ideally from the patient's own body cells to prevent rejection by the immune system, is a rapidly growing field that rests on three pillars: cells, supporting structures (or scaffold) and stimulating biological environment. However the use of scaffolds has often been associated with chronic inflammation and impaired tissue-remodeling and maturation. In this respect understanding the physical principles of biological self-assembly is essential for developing efficient strategies to build living tissues and organs. Here we exploit well-established developmental processes (such as tissue fusion, spreading or sorting phenomena) to engineer small-diameter blood vessels. We introduce a novel automated rapid prototyping method (bioprinting) that allows the building of three-dimensional custom-shaped tissue and organ modules without the use of any scaffold, thus making the final construct fully biological, as well as structurally and functionally closer to native tissues. Conveniently prepared bio-ink units (multicellular spheroids or cylinders composed of single or several cell types) are delivered into the bio-paper (a hydrogel support material) to build linear and branching tubular structures of small diameter (down to 0.9 mm OD). Structure formation takes place by the post-printing fusion of the discrete units. Upon removal of the support material, the fused construct is matured in perfusion bioreactor under pulsatile flow until desirable biomechanical (burst pressure, compliance) and biochemical (e.g. ECM) properties develop. Such constructs could fulfill the crucial need for small diameter vascular grafts and provide new strategies for vascularization of tissues for transplantation.