E.K. Marecki, C. Bowman, D. Gutierrez, M. Ketcham, R. Rayhan, B. Davidson, P. Knight, K.W. Oh
SUNY University at Buffalo,
United States
Keywords: microfluidic, nanoparticle, 3D-hydrodynamic flow focused
Summary:
Abstract Control of nanoparticle fabrication efficiency and nanoparticle size remains an ongoing issue. A 3D-hydrodynamic flow focused microfluidic design using easy-to-fabricate hillock structures and a droplet generation part showed efficient and size-controlled microcapsule and microbead synthesis while also preventing channel blockage after synthesis due to the microcapsules and microbeads being surrounded by sheath flow has been previously shown [1]. Nanoparticle synthesis in microfluidic designs occurs by self-assembly when rapid mixing is induced. [2,3]. Applying the easy-to-fabricate hillock structure to the controlled synthesis of self-assembling nanoparticles is herein proposed. Methods A simplified fabrication process is shown in Figure 1. Microfluidic channels were created with a hillock structure above and below the main flow to focus the nanoparticle self-assembly to within the shear flow. Two photomasks were used to transfer the two-layered design onto a silicon wafer by photolithography. Figure 2 shows a fabricated wafer as well as an alignment feature which confirms good alignment. HMDS was evaporated onto the multi-layered design on the wafer surface. Then, PDMS was poured on the wafer to create the molds. One mold per pair was hole punched and then each pair was aligned and bonded together after exposing to oxygen plasma, creating the finished device with hillock structures above and below the main central channel. These channels are shown in Figure 3 along with the locations of the hillock structures in the channels that direct the sheath flow around the central flow where the nanoparticles are self-assembling. Simulations conducted using COMSOL Multiphysics. Nanoparticle testing will consist of syringe pumps for the two inlets to control the optimized flow rates as well as the use of a microscope for observation. Final solution will contain nanoparticles in a buffer solution and will be characterized by efficiency of formation, nanoparticle size, and nanoparticle surface charge. Experimentation/Results Simulations showing optimized flow conditions are shown in Figure 4. These conditions were optimized for oil as main flow and water as sheath flow. After optimizing the flow rates at the inlets, a 3D-hydrodynamic flow focused stream can be seen credited to the addition of the hillock structure. Nanoparticle formation will occur in this stream and experience less collisions with other nanoparticles and the walls thus generating less undesired larger nanoparticles and reducing the chances of the nanoparticles clogging the channel. Flow rates for the nanoparticle and buffer solutions will need to be optimized just as has been shown here to generate the 3D-hydrodynamic flow focused stream that is needed. The nanoparticles made from this device should exhibit higher efficiency of formation, smaller and more controlled nanoparticle size, and an appropriate surface charge allowing entry into a cell. Nanoparticles generated using this device have many applications including drug delivery. References [1] https://pubs.rsc.org/en/content/articlelanding/2011/LC/C0LC00036A [2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6191180/#R64 [3] https://www.sciencedirect.com/science/article/pii/S0142961221001824