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，需要小直径的血管绕过动脉粥样硬化过程中狭窄的动脉。由于人工血管易致血栓，目前已有的人工血管不适合小直径血管置换。此外，尽管实验工作的范围和强度很大，但到目前为止，组织工程化小直径血管构建物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，我们研究了不同的组织工程支架和新型细胞种植方法的适用性。这些概念验证研究代表了基于天然水凝胶制造生物兼容、支持细胞生长的血管结构的重要一步。在更新方案中，我们打算将3D技术应用于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，管腔直径分别为0.5、1和2 mm。根据到目前为止所获得的结果，我们确信3D打印是开发含有细胞的生物软化血管支架的合适方法。然而，打印具有高度层次化结构的血管壁代表着一个具有挑战性的目标。在这方面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，在不超过氧气扩散限制的相对较大的管腔直径和壁厚下。我们建议将重点放在生物打印结构的改进上，包括优化生物墨水组成以提高细胞存活率，进一步开发挤出喷嘴装置来制备不同管腔直径的管状结构，以及通过在生物打印支架上逐层径向种植磁性细胞来改善管腔定植和血管壁分级结构。我们相信，通过将细胞类型的支持材料与先进的生物打印技术相结合，有可能克服现有移植物的局限性，从而构建结构和功能都得到改善的血管替代物。

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.