Microfluidics and inkjet for biomedical engineering materials

喷墨打印是一种广泛应用的增材制造（AM）技术，从办公室打印机到基因组学研究中的单细胞点胶。与其他增材制造技术相比，该核心技术具有许多优势，包括可调液滴尺寸（低至100 pL），高点胶速率，以及以非接触方式将材料分配到各种基板上的能力。例如，这与基于挤压的3D打印不同，这是一种较慢的接触方法。因此，喷墨被广泛用于有机聚合物、导电油墨和生物材料，如蛋白质或细胞的图案。然而，粘度大于~ 20 mPa·s的流体不能与喷墨兼容，因为它们不能在喷嘴出口成功地吸出液滴。此外，低表面张力的流体也存在问题，因为它们的液滴会弄湿喷墨喷嘴的外表面，导致可靠性差（即，有时液滴可能不会被夹断），并且无意中产生卫星液滴，导致打印质量差。这项研究计划的长期目标是通过设计能够可靠地打印高粘度或低表面张力材料的新型喷嘴，扩大与喷墨打印兼容的材料范围。为了将打印性能与基本理解联系起来，将根据描述喷墨行为的相关无量纲群来描述流体和点胶过程，以便可以绘制操作空间，以便在改进的喷墨喷嘴内为各种材料分配这些流体。短期目标(1)是在喷墨喷嘴表面开发可控纳米拓扑，以提高按需滴墨喷墨对高粘度和低表面张力流体的适用性。通过在流体/喷嘴界面产生滑移，减少阻力有可能分配更高粘度的流体。这种纳米拓扑结构还可以减少喷嘴表面的污垢，使低表面张力流体的液滴打印更加可靠。短期目标(2)是研究在喷墨打印中使用粘弹性和其他复杂聚合物溶液作为细胞封装流体，旨在缩小细胞（或颗粒类似物）在分配液滴中的分布（即每个液滴瞄准一个细胞）。研究离子浓度对聚合物溶液流变学、生物相容性和打印效果的影响。研究结果将适用于各种喷墨点胶机和材料，包括粘合剂、聚合物和凝胶，并将减少调整流体粘度和表面张力的需要。这将对印刷电子领域产生重大影响，并将使能够为组织工程和测序提供高精度，超高速单细胞分配的系统的开发成为可能。

Inkjet printing is an additive manufacturing (AM) technique used for a wide range of applications, from office printers to single cell dispensing in genomics research. This core technology has many advantages over other AM techniques, including its tunable droplet size (as low as 100 pL), high dispensing rate, and the ability to dispense material onto a wide range of substrates in a non-contact manner. For example, this differs from extrusion-based 3D printing, a slower contact method. As such, inkjet is widely used to pattern organic polymers, conductive inks and biological materials such as proteins or cells. However, fluids with a viscosity above ~ 20 mPa·s are not compatible with inkjet because they cannot achieve successful droplet pinch-off at the nozzle exit. Additionally, fluids with low surface tension present issues because their droplets can wet the outside surface of the inkjet nozzle and cause poor reliability (i.e., sometimes the droplet may not pinch-off) and the unintentional generation of satellite droplets leading to poor print quality. The long-term objective of this research program is to expand the range of materials that are compatible with inkjet printing by designing new nozzles that can reliably print materials with higher viscosity or lower surface tension. To connect printing performance with fundamental understanding, the fluids and dispensing process will be characterized in terms of the relevant dimensionless groups that describe inkjet behaviour, so that an operating space can be mapped for dispensing these fluids within the modified inkjet nozzles for a wide range of materials. Short-term objective (1) is to develop controlled nanotopology at the surface of inkjet nozzles, with the goal to increase the applicability of drop-on-demand inkjet to high viscosity and low surface tension fluids. By creating slip at the fluid/nozzle interface, drag reduction has the potential to permit the dispensing of fluids with higher viscosity. This nanotopology would also reduce fouling on the nozzle face, permitting more reliable droplet printing for low surface tension fluids. Short-term objective (2) is to investigate the use of viscoelastic and other complex polymer solutions as cell-encapsulating fluids in inkjet printing, aiming to narrow the distribution of cells (or particulate analogues) in dispensed droplets (i.e., aiming at one cell per droplet). The effects of ion concentration on the polymer solution rheology, the resultant biocompatibility and the printing results will be investigated. The results of the research will be applicable across a range of inkjet dispensers and materials, including adhesives, polymers and gels, and will reduce the need to tune fluid viscosity and surface tension. This will have significant impact on the field of printed electronics and will enable the development of systems capable of highly accurate, ultra-high speed single cell dispensing for tissue engineering and sequencing.