One of the primary focuses in recent years in tissue engineering has been the fabrication and integration of vascular structures into artificial tissue constructs. However, most available methodologies lack the ability to create multi-layered concentric conduits inside natural extracellular matrices (ECMs) and gels that replicate more accurately the hierarchical architecture of biological blood vessels. In this work, we present a new microfluidic nozzle design capable of multi-axial extrusion in order to 3D print and pattern bi- and tri-layered hollow channel structures. This nozzle allows, for the first time, for these structures to be embedded within layers of gels and ECMs in a fast, simple and low-cost manner. By varying flow rates (1-6 ml min-1), printspeeds (1-16 m min-1), and material concentration (25-175 mM and 1.5%-2.5% for calcium chloride and alginate, respectively) we are able to accurately determine the operational printing range as well as achieve a wide range of conduit dimensions (0.69-2.31 mm) that can be printed within a few seconds. Our scalable design allows for multi-axial extrusion and versatility in material incorporation in order to create heterogeneous structures. We demonstrate the ability to print distinct concentric layers of different cell types, namely endothelial cells and fibroblasts. By incorporating various layers of different cell-friendly materials (such as collagen and fibrin) alongside materials with high mechanical strength (i.e. alginate), we were able to increase long-term cell viability and growth without compromising the structural integrity. In this way, we can improve cellular adhesion in our biocompatible constructs as well as allow them to remain structurally sound. We are able to realize complex heterogeneous, hierarchical architectures that have strong potential for use not only in vascular tissue applications, but also in other artificially fabricated tubular or fiber-like structures such as skeletal muscle or nerve conduits.

中文翻译：

---

使用可扩展的多轴微流控挤出喷嘴，在凝胶支架内的异质双层和三层空心通道进行3D生物打印。

近年来，在组织工程中的主要焦点之一是将血管结构制造和整合到人造组织构造中。但是，大多数可用的方法都缺乏在天然细胞外基质（ECM）和凝胶内创建多层同心导管的能力，这些导管可以更准确地复制生物血管的层次结构。在这项工作中，我们提出了一种新的微流体喷嘴设计，该喷嘴设计能够进行多轴挤压，以便对3层打印双层和三层空心通道结构进行打印和图案化。该喷嘴首次允许将这些结构以快速，简单和低成本的方式嵌入到凝胶和ECM层中。通过改变流速（1-6 ml min-1），打印速度（1-16 m min-1）和材料浓度（25-175 mM和1.5％-2）。对于氯化钙和藻酸盐，分别为5％），我们能够准确确定操作打印范围，并实现可在几秒钟内完成打印的各种尺寸的导管（0.69-2.31 mm）。我们可扩展的设计允许多轴挤压和材料掺入的多功能性，以创建异质结构。我们展示了打印不同细胞类型（即内皮细胞和成纤维细胞）的不同同心层的能力。通过将不同细胞友好型材料（例如胶原蛋白和纤维蛋白）的不同层与具有高机械强度的材料（例如藻酸盐）结合在一起，我们能够在不损害结构完整性的情况下增加长期细胞活力和生长。通过这种方式，我们可以改善生物相容性构建物中的细胞粘附性，并使它们保持良好的结构。我们能够实现复杂的异构层次结构，这些结构不仅在血管组织应用中，而且在其他人工制造的管状或纤维状结构（例如骨骼肌或神经导管）中也具有强大的潜力。