(445f) Droplet Generation in 3D Printed Microfluidics Using a Hydrophobic Resin

Droplet microfluidics devices have proven useful as nanoliter-sized reactors, and in the area of bioengineering they serve as single-cell reactors for a variety of research applications. We are using nL-sized aqueous droplets suspended in oil as growth chambers for individual bacteria that are exposed to various antibiotics to assess the antibiotic susceptibility of the bacteria. We are also using novel 3D printing to create truly 3D fluidic channels for these nanodroplets, not simply a 2D-layout of channels in PDMS covered with a glass slide. Printing 3D microfluidic droplet devices allows for fluid channel flexibility and for rapid design iteration of devices using truly 3D geometries. However, many of the monomers used in this type of 3D printing are too hydrophilic to provide stability of the aqueous droplets, in that they often stick to the sides of the channel. Combined oil-water flows in these hydrophilic resins tend to form co-flowing streams where both phases wet the sides of the channel. For example, converging channels and pinch points that usually form distinct droplets in PDMS microchannels simply force both fluids against the walls without forming droplets. This study presents the development of a 3D printing resin monomer that when polymerized is sufficiently hydrophobic to produce stable water-in-oil droplet formation in our 3D printed microfluidic devices. We present the surface energies and mechanical properties of several resins investigated during this development. Examples of droplet generation will be shown as well as the integration of 3D geometry in the manipulation of aqueous droplet suspensions in 3D printed microfluidic devices.