Cell-laden bioink circulation-assisted inkjet-based bioprinting to mitigate cell sedimentation and aggregation

Three-dimensional (3D) bioprinting precisely deposits picolitre bioink to fabricate functional tissues and organs in a layer-by-layer manner. The bioink used for 3D bioprinting incorporates living cells. During printing, cells suspended in the bioink sediment to form cell aggregates through cell-cell interaction. The formation of cell aggregates due to cell sedimentation have been widely recognized as a significant challenge to affect the printing reliability and quality. This study has incorporated the active circulation into the bioink reservoir to mitigate cell sedimentation and aggregation. Force and velocity analysis were performed, and a circulation model has been proposed based on iteration algorithm with the time step for each divided region. It has been found that (a) the comparison of the cell sedimentation and aggregation with and without the active bioink circulation has demonstrated high effectiveness of active circulation to mitigate cell sedimentation and aggregation for the bioink with both a low cell concentration of 1 × 10⁶cells ml^-1and a high cell concentration of 5 × 10⁶cells ml^-1; and (b) the effect of circulation flow rate on cell sedimentation and aggregation has been investigated, showing that large flow rate results in slow increments in effectiveness. Besides, the predicted mitigation effectiveness percentages on cell sedimentation by the circulation model generally agrees well with the experimental results. In addition, the cell viability assessment at the recommended maximum flow rate of 0.5 ml min^-1has demonstrated negligible cell damage due to the circulation. The proposed active circulation approach is an effective and efficient approach with superior performance in mitigating cell sedimentation and aggregation, and the resulting knowledge is easily applicable to other 3D bioprinting techniques significantly improving printing reliability and quality in 3D bioprinting.