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Investigation of thermoplastic melt flow and dimensionless groups in 3D bioplotting
Rheologica Acta ( IF 2.3 ) Pub Date : 2020-01-16 , DOI: 10.1007/s00397-019-01186-4
Salim Gopi , Marianna Kontopoulou

We investigate the key 3D bioplotting processing parameters, including needle diameter and dispensing pressure, on the shear rates, shear stresses, pressure drops, and swell ratios of extruded miscible polycaprolactone (PCL) blends having a range of viscosities. Assuming simple capillary flow, we construct flow curves and we estimate that the shear stresses inside the needle of the bioplotter range from 2500 to 20,000 Pa and the corresponding shear rates from 2 to 25 s −1 , depending upon the viscosity of the blend. We further identify relevant dimensionless numbers that reflect the material rheological properties and processing conditions; these include the capillary number ( Ca ), Bond number ( Bo ), Weissenberg number ( Wi ), and elasticity number ( El ). At most processing conditions Ca > 1, whereas Bo < 1, suggesting that viscous forces dominated surface forces, except for needle diameters below 0.2 mm, where the flow approached micro-fluidic conditions. While Wi was below 1 at all conditions, El increased significantly with decreasing needle diameter. High El numbers at a needle internal diameter of 0.2 mm were associated with extrudate swell ratios above 2. Based on these results, we define ranges of operation in 3D bioplotting, which can serve as guidelines for process design. Even though this work is specific on the particular bioplotting equipment, the methodology described herein can be applied on any type of micro-extrusion equipment.

中文翻译:

3D 生物绘图中热塑性熔体流动和无量纲组的研究

我们研究了关键的 3D 生物绘图处理参数,包括针头直径和分配压力,以及具有一系列粘度的挤出混溶聚己内酯 (PCL) 混合物的剪切速率、剪切应力、压降和溶胀比。假设简单的毛细管流动,我们构建了流动曲线,我们估计生物绘图仪针头内的剪切应力范围为 2500 至 20,000 Pa,相应的剪切速率为 2 至 25 s -1 ,具体取决于混合物的粘度。我们进一步确定了反映材料流变特性和加工条件的相关无量纲数字;这些包括毛细管数 (Ca)、邦德数 (Bo)、魏森伯格数 (Wi) 和弹性数 (El)。在大多数加工条件下 Ca > 1,而 Bo < 1,表明粘性力主导表面力,除了针直径低于 0.2 毫米,其中流动接近微流体条件。虽然 Wi 在所有条件下都低于 1,但 El 随着针直径的减小而显着增加。针内径为 0.2 mm 时的高 El 数与高于 2 的挤出物膨胀率相关。基于这些结果,我们定义了 3D 生物绘图中的操作范围,可作为工艺设计的指南。尽管这项工作特定于特定的生物绘图设备,但本文所述的方法可以应用于任何类型的微挤压设备。El 随针直径的减小而显着增加。针内径为 0.2 mm 时的高 El 数与高于 2 的挤出物膨胀率相关。基于这些结果,我们定义了 3D 生物绘图中的操作范围,可作为工艺设计的指南。尽管这项工作特定于特定的生物绘图设备,但本文所述的方法可以应用于任何类型的微挤压设备。El 随着针直径的减小而显着增加。针内径为 0.2 mm 时的高 El 数与高于 2 的挤出物膨胀率相关。基于这些结果,我们定义了 3D 生物绘图中的操作范围,可作为工艺设计的指南。尽管这项工作特定于特定的生物绘图设备,但本文所述的方法可以应用于任何类型的微挤压设备。
更新日期:2020-01-16
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