Researchers at the CLF OCTOPUS Facility, Royal Holloway University of London and University of Birmingham have studied in “slow-motion" how micro-droplets react in air and the ways they can merge into structures whilst airborne. The experiment mimics how droplets from an ink-jet printer may behave. The long-term aim is to use 3D inkjet printing to create scaffolds that can assist regenerative medicine and tissue engineering applications.
3D inkjet printing is a technique that works very similarly to the inkjet printing that has been utilised in office printers to generate text and images on paper. Individual liquid “ink" droplets are “jetted" onto a surface from a nozzle to create the desired 3D structure very precisely, layer by layer. The ink used must have very specific properties – above all else, it needs to be liquid when leaving the printing nozzle and harden once it reaches its target destination.
The studies were performed by Dr. Gowsihan Poologasundarampillai (University of Birmingham), Dr. Andy Ward (CLF), Connor Barker (Royal Holloway University of London) and Francesca Lewns (University of Birmingham). The team used lasers to both suspend the ink droplets in air and to perform spectroscopy measurements. The droplet technique is of particular interest because it is has potential to be used with bio-compatible materials meaning it could be used for medical applications. Once in air and under specific conditions the droplet undergoes a chemical reaction to change from a solution (liquid) to a gel (solid-like). The droplets are collided together by steering the laser beams and the structures formed are lowered onto a solid surface. The resulting micro-structures can then be imaged at high resolution using a Focussed Ion Beam Scanning Electron Microscope which can slice the samples to examine the inner structure.
Dr Andy Ward said “This was an ambitious use of the Facility. We've levitated and juggled micro-droplets in air with lasers, made them turn from liquids into solids, deliberately collided them, lowered them onto a tiny landing area so they can be found using electron microscopy and then cut them in half to see what's inside!"
Figure 3 b) c) e), and f) from In Situ Sol-Gel Synthesis of Unique Silica Structures Using Airborne Assembly: Implications for In-Air Reactive Manufacturing. Connor R. Barker, Francesca K. Lewns, Gowsihan Poologasundarampillai, and Andrew D. Ward. ACS Applied Nano Materials Article ASAP. DOI: 10.102/acsanm.2c02683
The figures above show the droplets once they have merged and solidified. The top right image is a droplet cut into thin slices with a focussed ion-beam.