Xia Bingzhao, Jiang Zhongliang, Debroy Daniel, Li Dongmei, Oakey John
Department of Chemical Engineering, University of Wyoming, Laramie, Wyoming 82071, USA.
Biomicrofluidics. 2017 Jul 12;11(4):044102. doi: 10.1063/1.4993122. eCollection 2017 Jul.
Encapsulating cells within biocompatible materials is a widely pursued and promising element of tissue engineering and cell-based therapies. Recently, extensive interest in microfluidic-enabled cell encapsulation has emerged as a strategy to structure hydrogels and establish custom cellular microenvironments. In particular, it has been shown that the microfluidic-enabled photoencapsulation of cells within PEG diacrylate (PEGDA)-based microparticles can be performed cytocompatibly within gas-permeable, nitrogen-jacketed polydimethylsiloxane microfluidic devices, which mitigate the oxygen inhibition of radical chain growth photopolymerization. Compared to bulk polymerization, in which cells are suspended in a static hydrogel-forming solution during gelation, encapsulating cells via microfluidic processing exposes cells to a host of potentially deleterious stresses such as fluidic shear rate, transient oxygen depletion, elevated pressures, and UV exposure. In this work, we systematically examine the effects of these factors on the viability of cells that have been microfluidically photoencapsulated in PEGDA. It was found that the fluidic shear rate during microdroplet formation did not have a direct effect on cell viability, but the flow rate ratio of oil to aqueous solution would impart harmful effects to cells when a critical threshold was exceeded. The effects of UV exposure time and intensity on cells, however, are more complex, as they contribute unequally to the cumulative rate of peroxy radical generation, which is strongly correlated with cell viability. A reaction-diffusion model has been developed to calculate the cumulative peroxy radical concentration over a range of UV light intensity and radiation times, which was used to gain further quantitative understanding of experimental results. Conclusions drawn from this work provide a comprehensive guide to mitigate the physical and biochemical damage imparted to cells during microfluidic photoencapsulation and expands the potential for this technique.
将细胞封装在生物相容性材料中是组织工程和基于细胞的疗法中广泛探索且颇具前景的一个方面。最近，对基于微流控技术的细胞封装产生了广泛兴趣，这是一种构建水凝胶和建立定制细胞微环境的策略。特别值得一提的是，已证明在基于聚乙二醇二丙烯酸酯（PEGDA）的微粒中对细胞进行微流控光封装可在透气的、充氮的聚二甲基硅氧烷微流控装置内以细胞相容的方式进行，该装置可减轻自由基链增长光聚合反应的氧抑制作用。与本体聚合相比，在本体聚合中细胞在凝胶化过程中悬浮于静态水凝胶形成溶液中，而通过微流控工艺封装细胞会使细胞暴露于一系列潜在有害应力下，如流体剪切速率、短暂的氧耗竭、压力升高和紫外线照射。在这项工作中，我们系统地研究了这些因素对通过微流控光封装在PEGDA中的细胞活力的影响。研究发现，微滴形成过程中的流体剪切速率对细胞活力没有直接影响，但当超过临界阈值时，油相和水相溶液的流速比会对细胞产生有害影响。然而，紫外线照射时间和强度对细胞的影响更为复杂，因为它们对过氧自由基生成的累积速率贡献不均等，而过氧自由基生成的累积速率与细胞活力密切相关。已开发出一个反应扩散模型来计算在一系列紫外线强度和辐射时间范围内的过氧自由基累积浓度，该模型用于进一步定量理解实验结果。这项工作得出的结论为减轻微流控光封装过程中对细胞造成的物理和生化损伤提供了全面指导，并拓展了该技术的应用潜力。
