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

在冠状动脉旁路移植术（CABG）和外周血管手术中，需要小直径血管来绕过由动脉粥样硬化过程变窄的动脉。由于容易形成血栓，目前可用的合成移植物不适合于小直径血管置换。此外，尽管实验工作的范围和强度，组织工程化的小直径的血管结构的临床影响已经可以忽略不计，到目前为止，在原来的项目中，不同的组织工程支架的适用性沿着新的细胞接种方法进行了研究，以选择适当的生物材料用于心血管治疗和再生。这些概念验证研究代表了基于天然水凝胶的生物相容性、细胞生长支持血管构建物的制造的重要一步。在更新提案中，我们打算将3D技术用于成人和儿科血管手术中可用于小直径动脉置换的血管尺寸。为了满足临床需求，我们的目标是生产由藻酸盐/蛋白质水凝胶组成的中空圆柱体，其管腔直径为0.5，1和2 mm。根据迄今为止获得的结果，我们相信3D打印是开发含细胞生物制造血管支架的合适方法。然而，打印具有高度层次结构的血管壁是一个具有挑战性的目标。在此背景下仍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，以在不超过氧的扩散极限的相对大的管腔直径和壁厚下提供足够的机械稳定性和细胞存活。我们建议重点改进生物打印结构，包括优化生物墨水组成以提高细胞存活率，以及进一步开发挤出喷嘴装置以制造不同内腔直径的管状结构，以及通过逐层-在生物打印支架上的层径向磁性细胞接种。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，为了制造具有改进的结构和功能的血管替代物，可以克服目前可用的移植物的局限性。

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.