Micro injection is a simple yet effective method for injecting cell-specific molecules into living cells. The technique can be used to deliver DNA, RNA or proteins into cells, and is especially useful for studying the function of specific genes in a cell type or layer. In addition, it can be used to study gap-junctional communication between neurons and can help identify molecular mechanisms governing synapse formation and development.
To achieve a high level of precision and accuracy, micro injections are performed with an automated system, known as the Autoinjector. The Autoinjector is a highly accurate, microfluidic device that enables the user to precisely control the volume of an injection. It also allows multiple injections to be carried out at the same time, and the volume of the injection can be measured using an external scale.
The Autoinjector can be operated by both experienced and novice users. It is able to deliver a higher injection rate and success rate than manual microinjection. It has a lower startup cost than other injection systems and can be used by researchers of any background.
Before performing the injection, it is important to prepare the injection site. Make sure that the skin is clean and dry. If you are using a tourniquet, make sure to tie it loosely and that it is not too tight. Leaving a tourniquet on for too long can cause the blood vessel to collapse and you will not be able to inject into the vein.
Next, carefully prepare the injection needle. Use a razor blade (VWR scientific 55411-050) to open the tip of the needle. Be careful not to cut too far into the needle, as this can cause it to pierce an artery and lead to significant bleeding. Ensure that the tip of the needle is open to a diameter of about 10-20 mm. Lastly, insert the needle into the microinjection apparatus (World Precision Instruments Inc PV820 pneumatic picopump).
Once the equipment is set up and ready to be injected, carefully insert the needle into the vein. Once the needle is inserted, you should see a little bit of dark red blood come out of the hole of the needle. If you see a lot of blood coming out, you have pierced an artery and should immediately remove the needle. Apply pressure to the injection site until the bleeding stops.
The pulsating flow of the passive microinjection is governed by four key coefficients. Choosing the appropriate value of each of these coefficients guarantees that the passive microinjection will work as intended. Specifically, the ratio of the velocity at the main channel (Current) to the dripping instability at the T-junction is chosen to manage the period during which the Droplets are marching downstream with a defined size and distance from each other9. The density and dynamic viscosity of each fluid phase are carefully selected as well to achieve these conditions10.