Department of Mechanical Engineering, Catholic University of America, Washington, DC, 20064, United States of America.
Biofabrication. 2017 Jun 30;9(3):034101. doi: 10.1088/1758-5090/aa786e.
Biopolymer membrane assembly in microfluidics offers precise spatial and temporal resolution for biomolecular and cellular interactions during and after assembly. Control over molecular transport across the biofabricated membranes requires microstructural characterization. This study investigates, for the first time, the birefringence of chitosan membranes assembled with flow in a microfluidic environment, and the effects of pH and flow rate on the membrane's micro-alignment. The optical anisotropy of the formed membranes was quantified using a de Sénarmont compensator for transmitted quantitative polarized light microscopy. The chitosan membranes were biofabricated within a small aperture in a microfluidic network with various flow and pH conditions of chitosan and alginate solutions. The measured optical retardance and parallelism index clearly indicate that the microstructure of the flow-assembled membrane was well organized and aligned along the direction of chitosan flow. Optical retardance increased significantly with the pH of the alginate solution, but was less sensitive to the variation of the flow rates of the polymer solutions during the biofabrication process. It was also determined that the birefringence signal dropped significantly across the membrane growth direction regardless of the molecular density in the membrane. The mechanism of the micro-alignment was discussed, which was presumably due to the molecular un-wrapping by shear flow. We envision that the current study paves a path to further understand and actively manipulate the microstructure of flow-assembled membranes for broad lab-on-a-chip applications.
在微流控中组装生物聚合物膜为生物分子和细胞相互作用提供了在组装过程中和组装后的精确时空分辨率。对生物制造膜中分子传输的控制需要进行微观结构特征描述。本研究首次研究了在微流环境中流动组装的壳聚糖膜的双折射，以及 pH 值和流速对膜微观排列的影响。通过用于透射定量偏振光显微镜的 de Sénarmont 补偿器来量化形成的膜的光学各向异性。壳聚糖膜是在微流网络中的小开口内生物制造的，壳聚糖和藻酸盐溶液具有各种流速和 pH 值条件。测量的光学延迟和并行指数清楚地表明，流动组装膜的微观结构沿着壳聚糖流动的方向很好地组织和排列。光学延迟随藻酸盐溶液的 pH 值显著增加，但对生物制造过程中聚合物溶液流速的变化不太敏感。还确定无论膜中的分子密度如何，双折射信号在膜的生长方向上都明显下降。讨论了微排列的机制，这可能是由于剪切流引起的分子解缠。我们设想，目前的研究为进一步理解和主动控制流动组装膜的微观结构铺平了道路，以实现更广泛的片上实验室应用。
