has anyone try to inject drug to nude mouse vein for 30 days continuously

I am trying pronuclear injection using Eppendorf Femtotip IIs. I am having a real problem getting penetration of the plasma membrane--for each injection I have to go almost all the way through the zygote, and even this doesn't work most of the time. So I am doing the manipulations explained in "Manipulating the Mouse embryo", but it doesn't work nearly as well as I was accustomed to. I used to use injection needles I pulled myself, but have since changed institutions where I don't yet have my own puller. I didn't have such a big problem with this in the past. Does anyone have experience using Femtotip IIs for this purpose? Any advice? I thought these would be better and more reproducible.
I am killing way too many embryos, as it seems the tips aren't sharp enough are somehow deficient in breaking that membrane. And when it does break it is often too violent.

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