Chapman Lloyd A C, Whiteley Jonathan P, Byrne Helen M, Waters Sarah L, Shipley Rebecca J
Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG, UK; Department of Computer Science, University of Oxford, Wolfson Building, Parks Road, Oxford OX1 3QD, UK.
Department of Computer Science, University of Oxford, Wolfson Building, Parks Road, Oxford OX1 3QD, UK.
J Theor Biol. 2017 Apr 7;418:36-56. doi: 10.1016/j.jtbi.2017.01.016. Epub 2017 Jan 12.
Generating autologous tissue grafts of a clinically useful volume requires efficient and controlled expansion of cell populations harvested from patients. Hollow fibre bioreactors show promise as cell expansion devices, owing to their potential for scale-up. However, further research is required to establish how to specify appropriate hollow fibre bioreactor operating conditions for expanding different cell types. In this study we develop a simple model for the growth of a cell layer seeded on the outer surface of a single fibre in a perfused hollow fibre bioreactor. Nutrient-rich culture medium is pumped through the fibre lumen and leaves the bioreactor via the lumen outlet or passes through the porous fibre walls and cell layer, and out via ports on the outer wall of the extra-capillary space. Stokes and Darcy equations for fluid flow in the fibre lumen, fibre wall, cell layer and extra-capillary space are coupled to reaction-advection-diffusion equations for oxygen and lactate transport through the bioreactor, and to a simple growth law for the evolution of the free boundary of the cell layer. Cells at the free boundary are assumed to proliferate at a rate that increases with the local oxygen concentration, and to die and detach from the layer if the local fluid shear stress or lactate concentration exceed critical thresholds. We use the model to predict operating conditions that maximise the cell layer growth for different cell types. In particular, we predict the optimal flow rate of culture medium into the fibre lumen and fluid pressure imposed at the lumen outlet for cell types with different oxygen demands and fluid shear stress tolerances, and compare the growth of the cell layer when the exit ports on the outside of the bioreactor are open with that when they are closed. Model simulations reveal that increasing the inlet flow rate and outlet fluid pressure increases oxygen delivery to the cell layer and, therefore, the growth rate of cells that are tolerant to high shear stresses, but may be detrimental for shear-sensitive cells. The cell layer growth rate is predicted to increase, and be less sensitive to the lactate tolerance of the cells, when the exit ports are opened, as the radial flow through the bioreactor is enhanced and the lactate produced by the cells cleared more rapidly from the cell layer.
生成具有临床实用体积的自体组织移植物需要对从患者采集的细胞群体进行高效且可控的扩增。中空纤维生物反应器因其具有扩大规模的潜力，有望成为细胞扩增装置。然而，需要进一步研究来确定如何为扩增不同细胞类型指定合适的中空纤维生物反应器操作条件。在本研究中，我们建立了一个简单模型，用于描述灌注中空纤维生物反应器中单个纤维外表面接种的细胞层的生长情况。富含营养的培养基通过纤维内腔泵送，然后通过内腔出口离开生物反应器，或者穿过多孔纤维壁和细胞层，再通过毛细血管外空间外壁上的端口流出。纤维内腔、纤维壁、细胞层和毛细血管外空间中流体流动的斯托克斯方程和达西方程，与通过生物反应器的氧气和乳酸传输的反应 - 平流 - 扩散方程以及细胞层自由边界演化的简单生长规律相耦合。假设自由边界处的细胞以随局部氧气浓度增加的速率增殖，如果局部流体剪切应力或乳酸浓度超过临界阈值，则细胞会死亡并从细胞层脱离。我们使用该模型预测不同细胞类型使细胞层生长最大化的操作条件。特别是，我们预测了对于具有不同氧气需求和流体剪切应力耐受性的细胞类型，流入纤维内腔的培养基的最佳流速和施加在内腔出口的流体压力，并比较了生物反应器外部出口端口打开和关闭时细胞层的生长情况。模型模拟表明，增加入口流速和出口流体压力会增加向细胞层的氧气输送，因此，对于耐受高剪切应力的细胞，其生长速率会增加，但对于剪切敏感细胞可能有害。当出口端口打开时，预计细胞层生长速率会增加，并且对细胞的乳酸耐受性的敏感性会降低，因为通过生物反应器的径向流增强，细胞产生的乳酸从细胞层清除得更快。
