Microfluidics and inkjet for biomedical engineering materials

喷墨打印是一种增材制造（AM）技术，用于广泛的应用，从办公室打印机到基因组学研究中的单细胞点胶。与其他AM技术相比，该核心技术具有许多优势，包括其可调液滴尺寸（低至100 pL），高点胶速率以及以非接触方式将材料点胶到各种基板上的能力。例如，这不同于基于挤出的3D打印，这是一种较慢的接触方法。因此，喷墨被广泛用于图案化有机聚合物、导电油墨和生物材料，例如蛋白质或细胞。然而，粘度高于约20 mPa·s的流体与喷墨不兼容，因为它们不能在喷嘴出口处实现成功的液滴夹断。另外，具有低表面张力的流体存在问题，因为它们的液滴可润湿喷墨喷嘴的外表面并导致差的可靠性（即，有时液滴可能不会夹断）以及无意中产生的卫星液滴导致较差的打印质量。该研究计划的长期目标是通过设计能够可靠地打印具有更高粘度或更低表面张力的材料的新喷嘴来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，流体和分配过程将根据描述喷墨行为的相关无量纲组来表征，以便可以映射操作空间，用于在修改的喷墨喷嘴内分配这些流体，用于各种材料。短期目标（1）是开发喷墨喷嘴表面的受控纳米形貌，目的是增加按需喷墨对高粘度和低表面张力流体的适用性。通过在流体/喷嘴界面处产生滑移，减阻具有允许分配具有更高粘度的流体的潜力。这种纳米形貌还将减少喷嘴面上的污垢，从而允许对低表面张力流体进行更可靠的液滴打印。短期目标（2）是研究粘弹性和其他复杂聚合物溶液在喷墨打印中作为细胞包封流体的用途，旨在缩小分配液滴中细胞（或颗粒类似物）的分布（即，目标是每个液滴一个细胞）。离子浓度对聚合物溶液流变性、所得生物相容性和印刷结果的影响将被研究。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，并将使能够开发用于组织工程和测序的高精度，超高速单细胞分配系统。

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.