GOALI: Printing of Heterogeneous Tissue Constructs from Reactive Biomaterials using Intersecting Jets

喷墨生物打印是一种使用细胞悬浮液和水凝胶作为生物墨水创建3D组织结构的添加剂制造方法。许多水凝胶和细胞悬浮液可以混合，以制备用于传统混合然后打印应用的细胞生物墨水。然而，一些水凝胶在混合时会与细胞悬浮液发生化学反应。将这些水凝胶和细胞悬浮液混合制成的生物墨水严重恶化了可印刷性，甚至根本不能印刷。这项GOALI奖支持打印活性水凝胶和细胞悬浮液的边混合边打印方法的基础研究。这项研究的结果将扩大3D喷墨生物打印与活性生物材料的通用性。打印的异质组织结构可用作各种生物医学应用的器官模型，如药物筛选，并可能用于未来的器官移植。采用边混合边打印的方法，将反应性水凝胶和细胞悬浮液打印为两个单独的喷嘴；由于液滴的碰撞和合并，喷嘴破裂、相交和相互混合，从而形成凝胶的异质构建块。研究目标有两个：(1)了解打印条件对交叉射流时液滴形成、撞击、碰撞和聚结过程的影响；(2)阐明在打印时混合生物制造过程中液滴撞击、碰撞和聚结对材料混合性能的影响。为了实现第一个目标，将使用基于流体的体积计算方法来模拟细胞负载液滴的形成过程，以预测不同喷嘴直径和激励电压下的液滴形态、尺寸和速度。在不同相交角度和相隔距离下，液滴撞击、碰撞和聚结过程将使用无网格光滑粒子流体动力学方法进行模拟。一些模型的预测结果将与实验结果进行比较，并将使用高速成像技术测量射流相交前后的液滴形态、尺寸和速度。为了实现第二个目标，将根据活细胞在印刷结构中的分布情况来评估材料混合性能。基于对控制守恒方程和界面条件的尺度分析，将使用一组与材料特性和印刷条件相关的无量纲数字来模拟混合性能。预测的混合性能将与分别使用粒子图像测速仪和光学成像在不同液滴撞击、碰撞和合并场景下沉积的液滴和制造的组织结构的细胞分布进行比较。

Inkjet bioprinting is an additive manufacturing approach for creating 3D tissue constructs using cell suspensions and hydrogels as bioinks. Many hydrogels and cell suspensions can be mixed to prepare cell-laden bioinks for traditional mixing-then-printing applications. However, some hydrogels are chemically reactive with cell suspensions upon mixing. Bioinks prepared by mixing these hydrogels and cell suspensions have significantly deteriorated printability and even are not printable at all. This GOALI award supports fundamental research on a mixing-while-printing approach to print reactive hydrogels and cell suspensions. Results from this research will expand the versatility of 3D inkjet bioprinting with reactive biomaterials. Printed heterogeneous tissue constructs can be used as organ models for various biomedical applications such as drug screening, and might be used for organ transplantation in the future.With the mixing-while-printing approach, reactive hydrogels and cell suspensions are printed as two individual jets; the jets break up, intersect, and mix with each other due to droplet collision and coalescence, resulting in a gelled heterogeneous building block. The research objectives are two-fold: (1) to understand the effects of printing conditions on droplet formation, impingement, collision, and coalescence processes when using intersecting jets; and (2) to elucidate the influences of droplet impingement, collision, and coalescence on the material mixing performance during mixing-while-printing biofabrication. To achieve the first objective, cell-laden droplet formation process will be modeled using a volume of fluid-based computational approach to predict the droplet morphology, size, and velocity under different nozzle diameters and exciting voltages. Droplet impingement, collision, and coalescence processes will be modeled using a meshfree smooth particle hydrodynamic method under different intersecting angles and standoff distances. Some model predictions will be compared with experimental results, and the droplet morphology, size, and velocity before and after jet intersecting will be measured using high speed imaging. To achieve the second objective, material mixing performance will be evaluated in terms of how living cells are distributed in a printed structure. The mixing performance will be modeled using a set of material property and printing condition-related dimensionless numbers based on a scale analysis of governing conservation equations and interfacial conditions. Predicted mixing performance will be compared with the measured cell distribution of deposited droplets and fabricated tissue constructs using particle image velocimetry and optical imaging, respectively, under different droplet impingement, collision, and coalescence scenarios.