Development of endothelialised small diameter tissue-engineered grafts for cardiovascular surgery

在冠状动脉旁路移植术（CABG）和周围血管手术中，需要小直径的血管来绕过因动脉粥样硬化过程而狭窄的动脉。由于易于形成血栓，目前可用的合成移植物不适合用于小直径血管的置换。此外，尽管实验工作的范围和强度，到目前为止，组织工程小直径血管结构的临床影响可以忽略不计。在最初的项目中，为了选择合适的生物材料用于心血管治疗和再生，研究了不同组织工程支架的适用性以及新的细胞播种方法。这些概念验证研究代表了基于天然水凝胶制备生物相容性、支持细胞生长的血管结构的重要一步。在更新建议中，我们打算采用3D技术来确定成人和儿童血管手术中可用于小直径动脉置换的血管大小。为了满足临床需要，我们的目标是生产由海藻酸盐/蛋白质水凝胶组成的中空圆柱体，管腔直径为0.5、1和2毫米。基于迄今为止获得的结果，我们相信3D打印代表了一种合适的方法来开发含细胞的生物制造血管支架。然而，打印具有高度分层结构的血管壁是一个具有挑战性的目标。在这种情况下，仍有待解决的关键问题是材料（水凝胶）的选择和组成以及制造过程的控制，以提供足够的机械稳定性和细胞存活率，在相对较大的管腔直径和壁厚下，不超过氧气的扩散极限。我们建议将重点放在生物打印结构的改进上，包括优化生物链接成分以提高细胞存活率，进一步开发挤出喷嘴装置以制造不同管腔直径的管状结构，以及通过逐层径向磁性细胞播种在生物打印支架上改善管腔定植和血管壁分层结构。我们相信，通过将细胞型支撑材料与先进的生物打印技术相结合，有可能克服目前可用移植物的局限性，从而制造出具有改进结构和功能的血管替代品。

In coronary artery bypass grafting (CABG) and peripheral vascular surgery, small diameter vessels are needed to bypass the arteries narrowed by the atherosclerotic process. Being prone to thrombogenicity, currently available synthetic grafts are unsuitable for small-diameter vessel replacement. Furthermore, despite the scope and intensity of experimental work, the clinical impact of tissue-engineered small-diameter vascular constructs has been negligible so far.Within the original project, the suitability of different tissue-engineered scaffolds along with novel cell-seeding methods was investigated in order to select adequate biomaterials for cardiovascular therapy and regeneration. These proof-of-concept studies represented an important step towards fabrication of biocompatible, cell-growth-supporting vascular constructs based on natural hydrogels. In the renewal proposal, we intend to employ 3D technique to the vessel sizes that can be used for small diameter artery replacement in adult and paediatric vascular surgery. Addressing the clinical need, we aim to produce hollow cylinders composed of alginate/protein hydrogels with lumen diameters of 0.5, 1, and 2 mm. Based on the results obtained to date, we are convinced that 3D printing represents a suitable approach to the development of cell-containing biofabricated vascular scaffolds. However, printing the vascular wall, with its highly hierarchical structure, represents a challenging aim. Among the key issues that remain to be resolved in this context are the selection and composition of materials (hydrogels) and control of fabrication process to provide sufficient mechanical stability and cell survival, at relatively large lumen diameters and wall thicknesses that do not exceed the diffusion limit of oxygen. We propose to focus on the improvement of the bioprinted constructs, including optimizing bioink composition in order to enhance the cell survival and further development of the extrusion nozzle setup to fabricate tubular constructs of different lumen diameters, as well as on the improvement of lumen colonization and vascular wall hierarchical structure by layer-by-layer radial magnetic cell seeding on bioprinted scaffolds.We are convinced that by applying the cell-type supporting materials in combination with advanced bioprinting techniques, it is possible to overcome the limitations of the currently available grafts in order to fabricate vessel substitutes with improved structure and functionality.