Capillary Networks for Bio-Artificial Three-Dimensional Tissues Fabricated Using Cell Sheet Based Tissue Engineering

Abstract

One of the most important challenges facing researchers in the field of regenerative medicine is to develop methods to introduce vascular networks into bioengineered tissues. Although cell scaffolds that slowly release angiogenic factors can promote post-transplantation angiogenesis, they cannot be used to construct thick tissues because of the time required for sufficient vascular network formation. Recently, the co-culture of graft tissue with vascular cells before transplantation has attracted attention as a way of promoting capillary angiogenesis. Although the co-cultured vascular cells can directly contribute to blood vessel formation within the tissue, a key objective that needs to be met is the construction of a continuous circulatory structure. Previously described strategies to reconstruct blood vessels include the culture of endothelial cells in a scaffold that contains microchannels or within the original vascular framework after decellularization of an entire organ. The technique, as developed by authors, involves the progressive stacking of three-layered cell sheets onto a vascular bed to induce the formation of a capillary network within the cell sheets. This approach enables the construction of thick, functional tissue of high cell density that can be transplanted by anastomosing its artery and vein (provided by the vascular bed) with host blood vessels.

Vascularization in Bioartificial Parenchymal Tissue: Bioink and Bioprinting Strategies

“…Droplet ejection is controlled via thermal or acoustic (piezoelectric) forces [ 25 ] ( Figure 1 b). Thus, bioink formulations for inkjet bioprinting must possess very low viscosities (<10 mPa s [ 21 ]) and require immediate, extensive layer-by-layer crosslinking to form 3D structures [ 15 ]. This requirement generally limits the spectrum of materials eligible for this technology [ 13 ].…”

“…Furthermore, integration of living cells into the bioink has been found to influence vascularization properties [ 4 ]. Besides effector cells for respective functions of the manufactured tissue, additional cell types have been studied with regard to the possible promotion of vascularization [ 15 , 50 , 81 ]. The inner lining of vessels is built by ECs.…”

“…The small number of authorized TEPs includes products such as keratinocyte-containing scaffold sheets for traumatic burns, chondrocyte spheroids for cartilage defect regeneration, and autologous stem cells for corneal defect regeneration [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. In contrast to such bioengineered bradytrophic and almost completely avascular bioartificial tissues, the scaled generation of solid parenchymal tissue with long-term viability and function still represents a major challenge in tissue engineering [ 4 , 13 , 14 , 15 , 16 , 17 ]. Based on existing study evidence, it is considered that constructs with dimensions of more than 100–200 µm need an endogenous vascular perfusion system to provide oxygen and nutrient supply and discard metabolic byproducts [ 18 , 19 , 20 , 21 ].…”

“…Based on existing study evidence, it is considered that constructs with dimensions of more than 100–200 µm need an endogenous vascular perfusion system to provide oxygen and nutrient supply and discard metabolic byproducts [ 18 , 19 , 20 , 21 ]. In parenchymal organ replacement therapy, all constructs need to be scaled to dimensions that need endogenous perfusion systems to achieve the necessary number of cells [ 15 , 18 , 21 , 22 ]. Thus, a major limitation central to any cell therapy approach is the establishment of perfusing vascularization in a TEP that supports cell survival, integration, and function [ 4 , 7 , 13 , 15 , 22 , 23 ].…”

“…In parenchymal organ replacement therapy, all constructs need to be scaled to dimensions that need endogenous perfusion systems to achieve the necessary number of cells [ 15 , 18 , 21 , 22 ]. Thus, a major limitation central to any cell therapy approach is the establishment of perfusing vascularization in a TEP that supports cell survival, integration, and function [ 4 , 7 , 13 , 15 , 22 , 23 ]. At this moment, the objective is twofold: (i) acceleration of the process towards an anastomosis between bioartificial graft and host vasculature and (ii) the establishment of sufficient intragraft vascular density.…”