Critical Considerations for Regeneration of Vascularized Composite Tissues

Abstract

Effective vascularization is vital for survival and functionality of complex tissue-engineered organs. The formation of the microvasculature, composed of endothelial cells (ECs) alone, has been mostly used to restore the vascular networks in organs. However, recent heterocellular studies demonstrate that co-culturing is a more effective approach in revascularization of engineered organs. This review presents key considerations for manufacturing of artificial vascularized composite tissues. We summarize the importance of co-cultures and the multicellular interactions with ECs, as well as design and use of bioreactors, as critical considerations for tissue vascularization. In addition, as an emerging scaffolding technique, this review also highlights the current caveats and hurdles associated with three-dimensional bioprinting and discusses recent developments in bioprinting strategies such as four-dimensional bioprinting and its future outlook for manufacturing of vascularized tissue constructs. Finally, the review concludes with addressing the critical challenges in the regulatory pathway and clinical translation of artificial composite tissue grafts.

Recellularization of Bioengineered Scaffolds for Vascular Composite Allotransplantation

“…Blood supply is of critical importance to recellularization of VCAs. The vascular system provides important oxygen and nutrient delivery via blood perfusion to support tissue viability and survival in vivo ( 12 , 13 ). Specific to the integrity of the vascular system is the innermost lining composed of a monolayer of endothelial cells (ECs).…”

“…Mechanical testing is critical in considering the close relationship of mechanotransduction in influencing cell fate and differentiation, particularly for stem cells that differentiate based on matrix stiffness and elasticity ( 26 , 61 ). Further, tissues’ distinct anatomic locations and function as part of a composite tissue dictate the biomechanical forces required in the design of bioreactor systems to mimic physiological conditions of respective tissues, and the types of mechanical tests used for evaluation of the scaffolds ( 12 ). Thus far, mechanical testing has only been conducted in decellularized human and porcine ear, rat forelimb, and porcine fasciocutaneous flap scaffolds ( 7 , 48 , 50 , 51 ).…”

“…Many of these studies achieved cell engraftment and function after cell seeding but did not pursue recellularization strategies to promote tissue function regeneration which would otherwise require long-term culturing, implementation of biophysical stimuli during recellularization, and considerations for tissue-specific mechanical properties. For example, measurements for shear stress may be considered for blood vessels post-recellularization given that endothelial cells change phenotypes when shear stress is induced ( 12 ). The importance of analyzing mechanical properties post-recellularization cannot be understated as the seeded cells sense and rely on the surrounding mechanical environment and thus, heavily impact composite tissue recellularization outcomes.…”

“…Recellularization is heavily reliant on culture conditions to support cell survival and growth within scaffolds with considerations required for different cell types, cell medium composition, respective growth factors and supplements, and cell seeding densities ( 12 ). Tailoring recellularization strategies to control the stages of proliferation, differentiation, and subsequently, maturation of cells is also advantageous in regenerating tissues.…”

Bioengineering the Cardiac Conduction System: Advances in Cellular, Gene, and Tissue Engineering for Heart Rhythm Regeneration

“…Inability to stably integrate, poor cell viability, and core necrosis phenomena might be a consequence of the lack of effective oxygen and nutrient supply, which is particularly problematic when transplanting thick tissues, as observed in the first trials with native SANs (Ernst and Paulson, 1962 ; Starzl et al, 1963 ; Morishita et al, 1981 ) and expected for tissue-engineered conduction constructs. Vascularization must be promptly established to prevent ischemic conditions and necrosis, also envisaging the in vitro creation of vessel networks in tissue engineering approaches (Zhang et al, 2017 ; Shah Mohammadi et al, 2020 ).…”