Microfluidics and inkjet for biomedical engineering materials

喷墨打印是一种添加剂制造(AM)技术，广泛应用于从办公室打印机到基因组研究中的单细胞分配。与其他AM技术相比，这项核心技术具有许多优势，包括液滴大小可调(低至100Pl)、高分配速率以及以非接触方式将材料分配到各种基材上的能力。例如，这与基于拉伸的3D打印不同，后者是一种速度较慢的接触方法。因此，喷墨广泛用于对有机聚合物、导电油墨和生物材料(如蛋白质或细胞)进行成型。然而，粘度在~20 mPa.S以上的流体不能与喷墨兼容，因为它们不能在喷嘴出口处实现液滴夹脱。此外，具有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，导致可靠性较差(即有时液滴可能不会夹断)，并会无意中产生卫星液滴，从而导致打印质量较差。该研究计划的长期目标是通过设计能够可靠地打印粘度更高或表面张力更低的材料的新喷嘴，来扩大与喷墨打印兼容的材料的范围。为了将印刷性能与基本了解联系起来，流体和点胶过程将根据描述喷墨行为的相关无量纲基团进行表征，以便可以绘制出在改装后的喷墨喷嘴内为各种材料分配这些流体的操作空间。短期目标(1)是在喷墨喷嘴表面开发可控纳米拓扑学，目标是增加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，减阻有可能允许分配粘度更高的流体。这种纳米拓扑学还将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)是研究粘弹性和其他复杂聚合物溶液作为喷墨打印中的细胞包裹液的使用，旨在缩小细胞(或颗粒类似物)在分配液滴中的分布(即每个液滴一个细胞)。考察了离子浓度对聚合物溶液流变性、生物相容性和印刷效果的影响。研究结果将适用于一系列喷墨分配器和材料，包括粘合剂、聚合物和凝胶，并将减少调节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开发高精度、超高速单细胞配药的系统成为可能。

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.