(a) Zebrafish embryo immobilized by suction capillary. (b) Needle inserted into yolk sack. (c) Electroosmotic pumping of methylene blue solution into the embryo by the application of 25 V for 10 s. (d) Needle retracted from the embryo. Credit: McMaster Engineering
“This device is to drug discovery what the assembly line was to the automobile or the silicon chip to information technology,” explains Ravi Selvaganapathy, assistant professor of mechanical engineering at McMaster and lead author of the research. “It turns what was a complex, resource-intensive process available to a few into an automated, predictable, reliable, and low-cost system accessible to almost anyone.”
Notably absent is the need for a microscope or optical magnification to conduct the process, which is required for manual injection and to monitor transfection methods. The microfluidic device also allows easy integration of post-processing operations including cell sorting and the testing of cell viability on the same chip.
“The micro-injectors can easily be run in parallel and allow for scientists to test far greater combinations of materials in a much shorter time than current processes. It also makes it more feasible to pursue drug discovery for many so-called neglected diseases.”
The micro-injector also holds great promise for in-vitro fertilization as it provides far greater accuracy and control than current manual injections procedures, which have high rates of failure, require trained expertise and can be time intensive.
We present a novel PDMS-based microinjection system in a microfluidic format with precise electroosmotic dosage control. The device architecture is fully scalable and enables high-throughput microinjections with integrated pre- and post-processing operations. The injection mechanism greatly simplifies current methods as only a single degree of freedom is required for injections. The injections are performed inside a fully enclosed channel by an integrated microneedle. Actuation of the needle is achieved by the compliant deformation of the channel structure by an external actuator. Reagent transport is achieved using electroosmotic flow (EOF) which provides non-pulsating flow and precise electrical dosage control. The potentials used for injections were between 5 V–25 V. The electrical properties and flow rates for the device were characterized for Zebrafish embryos and Rhodamine B and Methylene blue in pH 10 buffer solution. We also propose a method to enable precise individual dosing of embryos using direct electrical feedback. Additionally, we show that electrical feedback can be used to verify the location of the needle inside the injection target. A preliminary viability study of our device was conducted using Zebrafish (Danio rerio) embryos. The study involved the injection of ultrapure water into the embryos in an E3 buffer, and resulted in embryos that showed normal development at 48 hours.