Microinjection is the use of a glass micropipette to inject liquid at a microscopic or borderline macroscopic level. Usually, the target is a living cell. Often, microinjection is combined with imaging to precisely locate the target cell and deliver the injected substance into it. This allows for readouts such as immunofluorescence, bioluminescence, western blot and/or PCR. However, because of its physical nature, the injection technique can also impact cell viability and cytoplasmic protein expression.
Unlike electroporation, which is typically used to deliver charged molecules into cells, microinjection can be used to deliver uncharged molecule such as DNA, RNA and small proteins. It is especially useful for the delivery of a large pool of RNAs and for CRISPR/Cas9-mediated disruption of gene expression. It is also the most powerful technique to deliver nuclear and cytosolic proteins. However, it cannot deliver membrane proteins such as ion channels and neurotransmitter receptors.
While microinjection is a powerful single-cell manipulation technique, it is not as easy as it sounds. Using a manual pipette, even a proficient experimenter has difficulty performing microinjections at high efficiency, and the results can vary dramatically from experiment to experiment. This variability is primarily due to the complex fluid dynamics that are present during the injection process.
The Autoinjector is a new tool that facilitates accurate, high-throughput, automated microinjection in both live cells and fixed tissue. Powered by a computer algorithm, the Autoinjector can be trained to recognize and correctly align with the cell target of interest in the microscope image. The software then drives the robotic arm to a precise location within the microscope field of view (FOV) and then delivers the injected solution into the targeted cell. This automatic, high-throughput approach to microinjection allows for a significant increase in the number of successfully injected cells as compared to novice experimenters. It also enables researchers to study cell fate decisions that would be difficult or impossible to achieve with other manipulation techniques such as manual microinjection or a robotic system.
To test the performance of the Autoinjector, we designed a system to synchronize multiple flows in a microfluidic chip. The diagram below shows the inlet flows u1, u2, u3 and u5 during one cycle of microinjection. The pulsating flow patterns are generated by the interaction of the water (Droplet phase) and mineral oil (Current phase) in the microchannel.
During the injection phase, u3 pulsates with a frequency of 2 Hz and a duration of 4 ms. This pulsation allows for the generation of an accurate double-emulsion to be injected into the microneedle. The pulsating flow pattern also limits the collision of the double-emulsion with the corners of the T-junction.
The pulsations are powered by the two pumps 3 and 4, which have different amplitudes. The resulting forces act on the double-emulsion to drive it gently downstream preventing it from colliding with the corner of the T-junction. Once the injection is completed, the pump u5 stops and the flow becomes laminar. micro injection