All-aqueous printing of viscoelastic droplets in yield-stress fluids
All-aqueous printing of viscoelastic droplets in yield-stress fluids
复制标题
屈服应力流体中粘弹性液滴的全水打印
DOI：
10.1016/j.actbio.2022.09.031
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发表时间：
2022
影响因子：
9.7
通讯作者：
Cai, Li-Heng
中科院分区：
文献类型：
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作者：
Zhu, Jinchang;Cai, Li-Heng
屈服应力流体中粘弹性液滴(AaPVD)的全水打印是一种新兴的体素生物打印技术的核心，该技术使球形生物墨水颗粒(DASP)能够进行数字组装，以创建功能组织模拟物。然而，aaPVD的发病机制在很大程度上还不清楚。在这里，通过实时量化整个打印过程的动力学，我们确定了对aPVD至关重要的两个参数：(1)打印喷嘴的加速度，(2)液滴/喷嘴直径比。此外，我们区分了与aaPVD相关的三个阶段：液滴产生、脱离和松弛。为了产生圆度好的液滴，油墨应该是高度粘滞的剪切稀释液。利用粒子图像测速仪和标度理论，建立了不同印刷条件下液滴位移的通用描述。沿喷嘴运动方向，液滴位移由脱离数确定，该无因次参数定义为来自喷嘴的拖拉力与来自支撑基质的约束力之间的比率。与喷嘴运动方向垂直，液滴位移由Oldroyd数确定，这是一个无量纲参数，描述了打印喷嘴附近支撑基质的屈服面积。对于松弛的液滴，液滴尾长与液滴/喷嘴直径比无关，而由喷嘴加速度决定。我们得出的结论是，良好的保真度打印液滴需要相对较大的液滴/喷嘴直径比和中等喷嘴加速度。这些确保了液滴更像固体，不会与喷嘴一起流动，形成蝌蚪样的形态，并且屈服应力流体的约束力足够大，以防止液滴的大位移。我们的结果为在3D空间的指定位置生成和沉积具有良好圆度的高粘弹性液滴提供了知识和工具，这有助于建立体素相关生物打印的基础科学。意义陈述从像素到二维(2D)图像的类似物，以小立方体或球体的形式的体素是三维(3D)对象的基本单位。粘弹性液滴的全水打印(AaPVD)是体素相关生物打印的核心，体素相关生物打印是一项新兴技术，它使用球形生物墨水体素作为构建块来创建3D组织模拟。与现有技术依赖经典的瑞利-高原不稳定性来产生液滴不同，aaPVD利用以前未被探索的复杂流体的非线性流体动力学来精确操纵3D空间中的粘弹性液滴。发展起来的知识和工具不仅有助于推进生物制造，而且还鼓励在软质和复杂流体方面的新的研究方向。
All-aqueous printing of viscoelastic droplets (aaPVD) in yield-stress fluids is the core of an emerging voxelated bioprinting technology that enables the digital assembly of spherical bio-ink particles (DASP) to create functional tissue mimics. However, the mechanism of aaPVD is largely unknown. Here, by quantifying the dynamics of the whole printing process in real-time, we identify two parameters critical to aaPVD: (1) acceleration of print nozzle, and (2) droplet/nozzle diameter ratio. Moreover, we distinguish three stages associated with aaPVD: droplet generation, detachment, and relaxation. To generate a droplet of good roundness, the ink should be a highly viscous shear-thinning fluid. Using particle image velocimetry and scaling theory, we establish a universal description for the droplet displacements at various printing conditions. Along the direction of nozzle movement, the droplet displacement is determined by the detachment number, a dimensionless parameter defined as the ratio between the dragging force from the nozzle and the confinement force from the supporting matrix. Perpendicular to the direction of nozzle movement, the droplet displacement is determined by the Oldroyd number, a dimensionless parameter that describes the yielded area of the supporting matrix near the print nozzle. For a relaxed droplet, the droplet tail length is independent of droplet/nozzle diameter ratio but determined by the nozzle acceleration. We conclude that printing droplets of good fidelity requires a relatively large droplet/nozzle diameter ratio and intermediate nozzle accelerations. These ensure that the droplet is more solid-like to not flow with the nozzle to form a tadpole-like morphology and that the confinement force from the yield-stress fluid is large enough to prevent large droplet displacement. Our results provide the knowledge and tools forin situgenerating and depositing highly viscoelastic droplets of good roundness at prescribed locations in 3D space, which help establish the foundational science for voxelated bioprinting.Statement of significanceAnalogues of pixels to two-dimensional (2D) pictures, voxels – in the form of small cubes or spheres – are the basic units of three-dimensional (3D) objects. All-aqueous printing of viscoelastic droplets (aaPVD) is the core of voxelated bioprinting, an emerging technology that uses spherical bio-ink voxels as building blocks to create 3D tissue mimics. Unlike existing technologies relying on the classic Rayleigh-Plateau instability to generate droplets, aaPVD exploits previously unexplored nonlinear fluid dynamics of complex fluids to precisely manipulate viscoelastic droplets in 3D space. The developed knowledge and tools not only help advance biomanufacturing but also stimulate new research directions in soft matter and complex fluids.