Sedimentation study of bioink containing living cells

Abstract

3D bioprinting utilizes a cell-laden bioink to fabricate 3D cellular constructs for a variety of biomedical applications. The printing process typically takes hours to fabricate heterogeneous artificial tissues with multiple types of cells, different types of extracellular matrices, and interconnected vascular networks. During the printing process, the suspended cells sediment within the bioink with time, resulting in inhomogeneous cell concentration, which significantly affects the printing reliability and accuracy. This paper is the first study to quantify the cell sedimentation process in the bioink containing living cells. In this study, the effects of polymer concentration and standing time on the cell sedimentation velocity and cell concentration have been systematically investigated. The main conclusions are (1) the cell sedimentation velocity is almost constant at different standing times, because the cell gravitational force is balanced by the cell buoyant force and the drag force; (2) with the increase of the polymer concentration, the cell sedimentation velocity decreases, while the cell mass density increases due to less water absorbed; (3) with the increase of the standing time, the cell concentration near the bottom of the bioink reservoir increases linearly. With the increase of the polymer concentration, this linear increase of the cell concentration with the standing time significantly slows down due to a significant decrease of the cell sedimentation velocity; and (4) for the bioink with a low sodium alginate concentration, cell concentration near the bottom of the bioink reservoir is not uniform, and cell aggregates are observed.

Homogeneous and Reproducible Mixing of Highly Viscous Biomaterial Inks and Cell Suspensions to Create Bioinks

“…In the last few years, many groups developed bioinks of the second category which show good biological response despite their high viscosity (in non-flowing state), mainly for bone and cartilage regeneration, but also in soft tissue applications or as wound filler for deep skin burns [ 13 , 14 , 15 ]. Highly viscous bioinks possess a potentially high polymer content, preventing the crucial problem of sedimentation of cells or particles due to a closer polymer net compared to low viscous bioinks which are impaired by cell sedimentation [ 16 ]. While for low viscosity bioinks, the timeframe of cell sedimentation lies within a range of a few minutes, being relevant for bioprinting; these times are significantly higher for highly viscous bioinks [ 16 ].…”

“…Highly viscous bioinks possess a potentially high polymer content, preventing the crucial problem of sedimentation of cells or particles due to a closer polymer net compared to low viscous bioinks which are impaired by cell sedimentation [ 16 ]. While for low viscosity bioinks, the timeframe of cell sedimentation lies within a range of a few minutes, being relevant for bioprinting; these times are significantly higher for highly viscous bioinks [ 16 ]. While there are demanding technical solutions addressing the sedimentation in low viscosity bioinks, highly viscous bioinks offer a clear advantage in this regard [ 17 ].…”

Investigation of Cell Concentration Change and Cell Aggregation Due to Cell Sedimentation during Inkjet-Based Bioprinting of Cell-Laden Bioink

“…Recently, there have been several studies focusing on the characterization of the cellular sedimentation behaviors. For instance, Xu et al have recently presented a comprehensive study on cell sedimentation behaviors during inkjet-based bioprinting of cell-laden droplets [24]. Cell sedimentation velocity was found to be inversely correlated with polymer concentration, the local cell concentration at the bottom of the bioink reservoir was consistently increased due to the accumulation of cells, and the cell aggregation phenomenon was observed after long-time printing.…”

“…More detailed information can be found in our previous paper [35]. Since cell sedimentation velocity is reported to be inversely correlated with polymer concentration, 0.5%, 1.5%, and 3% (w/v) sodium alginate were specifically selected in this study to represent high, medium, and low cell sedimentation velocity, respectively [24], while 1, 1.5, and 2 × 10 6 cells/mL cell concentration were selected to represent low, medium, and high chance of cell aggregation, respectively.…”

Multicomponent polysaccharide alginate-based bioinks

“…Further research on the influence of alginate concentration on cell behaviour, was carried out by the group of Xu, who studied the effect on cell sedimentation and local concentration. 45 During the printing process the cells embedded in a bioink may sediment or aggregate over time, leading to inhomogeneous cell distribution through the 3D scaffold. The researchers, therefore, tested the effect of different alginate concentrations (0.5-4.0% wt/vol) and different standing times (0-120 min) on the homogeneity of 3D scaffolds of fibroblasts.…”