Is there a trick to getting very, very sharp microinjection needles when pulling from glass capillaries with a 2-step needle puller?
I have achieved a tip width of about 15 µm using 2-step pulling and breaking the tip on the side of a microscopy slide (attached pic). Are there any tricks in breaking the tip or drawing it to make it even sharper, so that it penetrates cells easier?
Make sure the filament has a nice shape so you get a sharp, symmetric point, then adjust the heat at the filament and strength of the pull. Most pullers have adjustments for these. Higher heat and harder pull = smaller tip.
we use a Narishige puller which has adjustments for setting the current (to generate heat) and the magnetic force (for adjusting the pulling force). For us increasing the heat and putting the force lower makes the capillaries with linger tips.
Thanks for the input. I have been experimenting with both the heat and the force and gotten to the same conclusion as Asmita. To get the tip sharp I actually found this reference: doi:10.1038/nprot.2015.096 (linked below).
http://www.nature.com/nprot/journal/v10/n10/fig_tab/nprot.2015.096_F2.html
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